DISTRIBUTION OF ARMOR IN SHIPS OF WAR.
THE SUBSTANCE OF TWO LECTURES DELIVERED AT THE ROYAL NAVAL COLLEGE, GREENWICH, ENGLAND, 1885,
By Assistant Naval Constructor W. E. Smith, R. N.
(Reprinted from the Admiralty Report.)
LECTURE I.
The subject chosen for our consideration is one of the utmost importance to all of us, to Naval Officers and to Naval Architects alike. The professional reputation of the Naval Architect, and the ability of the Naval Officer to effectually safeguard his country, are intimately associated in this one question of armor distribution.
Ever since the introduction of shell guns capable of sending with a fair amount of accuracy powerful incendiary shell, protection of some kind has become a necessity for every ship called upon to face a well-sustained fire from an enterprising enemy. This protection at first consisted of iron armor, and was looked upon mainly as a means of shielding the men and guns in the batteries against serious casualties, and of protecting certain parts of the ship against the incendiary power of common shell. It was neither considered necessary to armor-plate the water-line throughout its entire length, nor to protect the lower parts of the ends of the vessel by strong armored under-water decks, and such protection therefore was not given.
As examples embodying these ideas we have the Warrior and Black Prince, each having a central citadel of armor 4 ½ inches thick, protecting a battery of about 213 feet in length. The total length of ship on the water-line is 380 feet, and the only protection afforded to the lower compartments in the hold at the ends of the vessel is given by a very thin water-tight platform, which can in no sense be considered an armored deck. Two other examples having about the same proportion of armored middle part to total length, are afforded by the Resistance and Defence, which in respect of armor distribution may be looked upon as small Warriors, just as Ajax and Agamemnon may be looked upon, so far as distribution of armor is concerned, as small Inflexibles.
The introduction of armor and the protection it afforded to the men and guns in the batteries, very naturally soon directed attention to the unarmored ends of the above vessels, and to the want of power possessed by these ships of maintaining their buoyancy and stability, in a way altogether foreign to the way of looking at the question when we were dealing with the old wood ships. In their case no question of buoyancy or stability was ever raised or even thought of, it was simply recognized that their destruction was a mere matter of time, and that their real safety lay in silencing their enemy's fire by their own guns, or capturing his ship by boarding, and not in any resistance the wooden sides might be capable of offering.
Attention having been drawn to this side of the question, the vessels next succeeding were made large enough to be armored on their water-lines throughout their entire length. These comprised the Agincourt, Minotaur, and Northumberland, each of 400 feet in length, and of a displacement of about 10,700 tons. The Achilles, originally designed like the Warrior, was altered in the early stages of construction, and was provided with a water-line belt extending from stem to stern. The length of armor protection in these vessels is as under:
| Length of Water-line. Feet. | Length of Armored Battery. Feet. | Length of Belt. Feet. |
Achilles | 380 | 213 | 380 |
Agincourt | 400 | All but 24 feet at bow | 400 |
Minotaur | 400 | All but 24 feet at bow | 400 |
Northumberland | 400 | 185 | 400 |
In two other vessels a contrary development took place, and in these, the Hector and Valiant, instead of having an unarmored battery of less length than the ship associated with a belt at the water-line extending throughout the entire length, we have an armored battery extending from stem to stern, and a waterline protection stopping about 30 feet short of each end.
During the above early development of the armor question, two other developments were going on which enabled constructors for some time to keep their water-line and battery armor up to and even slightly ahead of the power of the gun. These were, first, the reduction in the number of guns carried in the ship, which admitted a reduction in the size of the battery, and a corresponding thickening of the armor; and secondly, greatly improved methods of constructing the hull, which enabled weight to be taken from the hull and put into armor.
For these reasons it was possible to build all British ships, of the sizes considered suitable for the Navy, with water-lines completely armored from stem to stern, and the guns and gunners protected by vertical armor also, which was about equal to the power of the gun at moderate ranges.
These vessels comprised among others:
| Maximum Thickness of Water-line Armor. Inches. |
Bellerophon, single-screw | 6 |
Hercules, single-screw | 9 |
Sultan, single-screw | 9 |
Penelope, twin-screw | 6 |
Audacious, class twin-screw | 8 |
Swiftsure and Triumph, single-screw | 8 |
Alexandra, twin-screw | 12 |
Monarch, single-screw | 7 |
In these vessels an attempt was made to protect the rudder head, which was entirely exposed in the Warrior and contemporary vessels, by dipping the stern down into the water and covering the rudder head. Many of these ships, however, were single-screw vessels, and the protection could not be very good, as on that account the steering gear had of necessity to pass over the top of the blades of the screw.
In 1875 the Shannon was launched, having a belt extending right aft to protect the steering gear, the vessel being a single-screw vessel, but the belt stopped 60 feet short of the bow, and the lower part of the fore end of the vessel was protected by an under-water armored deck which ran right forward to thoroughly support the ram. The Nelson and Northampton immediately followed, but being twin-screw ships, the rudder and steering gear could be much better protected by an under-water deck than by side armor, and in these two vessels we have the first examples of the type of water-line protection adopted in the Admiral class now building, viz. a central belt amidships and strong underwater decks at the ends.
[The difference is very great between the protection afforded to the steering gear by an under-water deck in a twin-screw vessel, and a belt with a single screw. The steering gear in one case is well under a strong protective deck, which is itself a long distance under water. The whole of the gear is supported from the platform next below the protective deck, and has no attachment whatever to the protective deck itself, so that even if this deck were struck it could be driven down to a considerable extent without damaging any of the gear beneath it. Projectiles coming into the ship above the protective deck can do no harm to the steering gear at all.
In the other case the weakness of the thin belt, as compared with a deck some distance under water, is still further intensified by the necessity of carrying the tiller, &c., above the top of her single screw. The tiller is secured to the protective deck, immediately over it, and a blow on this deck might disable the steering gear. The steering gear can also be easily reached through the thin side armor. Projectiles striking in the same region in the central citadel ship cannot reach the steering gear.
In the case of a belted ship not being a single-screw ship the gear can, of course, be placed lower, but even then can be much more readily reached through the thin side armor or the above-water deck than through an underwater deck.]
As time went on the penetrating power of the gun continually increased, and although the absolute weight of armor at the disposal of the Naval Architect increased also, the armor rapidly became more and more inadequate for protection under the conditions of close range and a square hit, notwithstanding the thickening made possible by the reduction of its area; and now at the present moment there are guns afloat capable of sending projectiles not only through the thickest armor actually afloat, but through the thickest armor being arranged for in ships building.
It is possible, of course, to design ships armor-proof against all existing guns, and even to leave a margin against future gun development, provided we accept the consequent size of ship. It has, however, been decided everywhere by those persons controlling national expenditures and the sizes of ships, to build even the largest vessels with armor not proof under the above conditions of close range and squareness of hit to guns those ships may have to face.
The problem of the Naval Architect, then, instead of being the very easy one of making a ship proof against all guns actually existing or imagined as being in existence at a future time, and having no restriction placed on the size of his ship, has become the much more difficult one of arranging the imperfections necessarily imposed on his ship by limiting her size in such a manner as to allow no kind of imperfection to be so great as to admit of her speedy destruction by any possible mode of attack she is liable to be subjected to, and to produce as well balanced a set of defences against all the various risks his ship has to run as the size placed at his disposal will admit of. He has to produce the best result on a given size and cost, and he wants to know what the best result is.
If all persons were perfectly agreed as to the relative values of the various risks to be run by any one ship, we should have advanced a long way towards the best balancing of imperfections. The case, however, is not so easy. As we all well know, the relative importance of the various risks a ship has to run is estimated by each person in a way peculiar to himself, and the suitability of a given set of defences against those risks will also, of course, be judged by each person in the light of what he considers their relative values.
My duty to-day is to explain to you the modes in which the armor defences have been arranged in the principal types of ships, and not simply to express any opinion of my own as to the respective merits and demerits as a whole of any one plan. All the plans have good points, and all have bad points. Each particular plan has its own special advantages, and for certain kinds of risk is superior to other plans. For different risks the advantage may change sides, and what was the superior defence may become the inferior defence.
After having explained the various special advantages and disadvantages attached to each plan, I must leave each one of you to draw his own conclusion as to the best plan for general all-round work, and in doing so you must bear in mind that the ship is of necessity imperfect in every single respect. No one feature gives us complete and perfect satisfaction. Every quality of the ship admits of enhancement, and we are not entirely satisfied with any one. A pillar to a roof supports the roof perfectly. We could not replace the pillar by one doing its work better. Every ship could be replaced by another having any one or more of its qualities enhanced, and for this reason we may truly say that a given ship is much too slow, that she does not turn rapidly enough, nor in a small enough space. She does not carry sufficient coal, her guns are too feeble and too few, and take too long to load, and notwithstanding this, she rolls and pitches so much that the few and feeble shots she is able to fire are nearly all wasted, due to this cause alone; and sometimes she cannot open fire at all on account of the heavy seas to which she is exposed. Her armor is too thin—much too thin, even where it is thickest, and is altogether absent from places where we should like to have at least a little. She is very vulnerable against the ram and torpedo, and her propellers are so much exposed to fouling as to render her incapable of steaming with impunity at a high rate of speed among the floating wreckage incidental to an action, and in spite of all her imperfect defensive powers, her means of saving life as a last resource, viz. her boats, are all so much exposed to machine-gun fire as to be quite useless after a well-contested fight.
I must insist on the above being duly appreciated before going onto describe the armor defences in our battle ships. In a floating body every increase of defence in one direction means either decrease of power in some other direction or else increase of size. I say increase of size, because largeness of size in a ship is looked upon as a defect in itself. The question of cost is, of course, important also, but only involves difficulties which are in our own hands. As soon as the taxpayer and his Naval Advisers agree that it is necessary to spend a large sum of money on a single ship, that money will be forthcoming and the ship built. No agreement between the taxpayer and his Naval Advisers enables a single ship of limited size to have more than a certain limit of defensive and offensive power. The size of a ship to fulfill certain requirements depends partly upon the properties of the materials we find in the market, properties over which we have only a very limited control, and partly upon what might be called the general level of engineering knowledge and professional skill existing at any given moment. At any given instant there are always certain things as impossible to obtain in combination as it is to obtain the moon, and the case of a single ship of limited size having all the qualities that various critics require is of this nature. All this must be clearly realized and willingly conceded before criticizing the armor defences in any one vessel, as we must bear in mind that the ship is sadly deficient in other respects—in respects in the opinion of many critics as important or more important than that of armor protection.
One man for instance says: I am willing to take my chance of being sunk just as the individual soldier is willing to take his chance of being shot; but you must give me great speed, plenty of guns, and guns as big as you can make them. I recognize fully that war involves serious risks, but I accept them all, provided you give me ample power of destroying my enemy. If my ship sinks, the other ships carry on my work just as in a land battle the survivors carry on the fight after the loss of their comrades. In my opinion it is as unwise to attempt to make ships invulnerable, or nearly so, as it is to attempt to make soldiers bullet-proof. You must depend upon numbers, and not upon individual invincibility.
Another says: In my opinion the torpedo is my deadliest foe, and, therefore, you must give me an armored inner bottom to protect me against torpedoes. I cannot get away from torpedo boats because they outrun me. I go 15 knots, they go 20. I cannot hope to sink them all by machine guns, or by my own torpedo boats even in daylight, and I cannot keep my torpedo nets down at a high speed. At night and in fogs I am still worse off, as I may not see the torpedo boats at all. You must therefore protect me against torpedoes by a proper construction of the hull, or else my ship, costing three-quarters of a million, may be destroyed by the enemy at a cost to him of only a few hundreds.
A third says: I must have a belt of armor at least all round my water-line to protect me against the gun. The gun is not like the torpedo or ram; it cannot be avoided by any skill on my part. My buoyancy and stability must therefore be protected by armor against the gun. The gun must be defeated by resistance, as it cannot be by avoidance. The primary duty of the ship is to float and to keep afloat; if she cannot do this she can do nothing, her power is gone. Everything must therefore give way and be subordinated to the necessity of perfect and complete protection to the water-line.
A fourth says: You must protect all my gunners, torpedo-men, and men serving the ammunition against heavy machine-gun fire. The big guns I am willing to risk; they cannot fire very fast, and the practice is sure to be indifferent. My men, however, are only very few, the men who can shoot well are still fewer, and are necessarily among those most exposed. If casualties happen to them, I cannot efficiently replace them. The machine-gun bullets will come in a perfect hail, and only a few of them will be sufficient to kill all my men. You must therefore give me good protection against machine guns.
Such a critic does not always remember that machine guns are possible which would perforate the thickest armor of the Warrior.
A fifth person says: I am fairly satisfied with the offensive and defensive powers of my ship as a whole, but I want many more men under my command than you have given me. I am entirely powerless out of my ship. If I destroy batteries and forts I must still keep to my ship. I cannot land any men; and if I beat my enemy at sea and capture his ship, I cannot take her as a prize into port, because I cannot put enough men on board her to prevent her again falling into the hands of the enemy and at the same time keep my own vessel efficient. I have no choice but to destroy what may be worth nearly a million of money. You must certainly give me many more men.
These examples might be carried much further, but we must let the above suffice.
Now, although all the above things are obtainable in a single ship, provided we make no restriction as regards size, it is a fact that there is no war ship at present in the world even nearly large enough to embrace them all.
If we wanted a belt of armor 24 inches thick amidships and 18 inches thick at the ends, a belt by no means completely gun-proof, four 150-ton guns, twelve 6-inch guns with a 3-inch side in front of them, a 4-inch inner bottom protection against torpedoes, ten feet in from outer bottom, and twenty knots speed, we should have a vessel of 20,000 to 25,000 tons displacement, and a cost for completed ship not much short of £2,000,000. The ship, large and costly as she is, is still imperfect; her armor will roll out of the water and under the water. There is no protection against ground mines, and the belt, especially at the ends, is still vulnerable. The length of the vessel must be from 500 to 550 feet (i.e. nearly half as long again as the Warrior), the beam about 75 feet, the mean draught about 28 feet, and the indicated horse power about 30,000. Now, leaving out of consideration all question as regards cost, the size of this vessel, still imperfect, strikes one as being too great for a single officer to command. As regards size, she is already almost a fleet. If it were attempted to remedy the deficiencies indicated above, she would be still larger; and she is already so long as to neutralize to a considerable extent the advantage of her speed in ramming her enemy, as she cannot hope to turn so rapidly as a shorter ship.
I have been obliged to treat lightly of the ship as a whole, because otherwise it is quite impossible to intelligently devote consideration to any one feature. Our task is to view the armor defences of our ships under the above limitation of making a well-balanced set of offensive and defensive powers in a ship of limited size. It is very easy to say that the ship carries too little coal, has too little armor, and too little speed; that her guns are too small and too few. It is also easy to show that any given ship could be much strengthened as regards certain specified risks if one feature were developed and the others correspondingly diminished. On the other hand, it is very difficult to show that a given combination represents the best combination for general all-round work. This, however, is the task the designer of a ship has before him when his design is challenged, and in consequence of the variety of the risks to be run by his ship, and the various values put upon those risks by his critics, he can satisfy nobody. Each critic calls the ship defective, because he sees that the particular risk he attaches most importance to could be more safely run by diminishing the power of the ship to meet other risks he thinks more lightly of, and applying the saving in the direction he desires. The result of such criticism can only be that a given ship which perhaps best satisfies as a whole the criticism so freely bestowed upon her has nobody but her designer to defend her. All other persons see only the faults they desire to have removed.
Coming to the actual distribution of armor in the latest types of English battle ships, we may say that they are all central citadel ships, the turret ships having a comparatively high and short central citadel, and the barbette ships a shallower but longer belt. The armored length of water-line is given below:
Name of Ship | Whether Barbette or Turret | Length of Citadel (Feet) | Length of Ship (Feet) | Percentage of Area of Water-line covered by Armor |
Inflexible | Turret | 110 | 310 | 42 |
Ajax | Turret | 104 | 280 | 45.4 |
Colossus | Turret | 123 | 325 | 42.75 |
Camperdown class | Barbette | 150 | 330 | 56.35 |
The turret ships are compelled to carry their side armor high enough to protect the turning gear actuating the turrets, and as a consequence, a less length of water-line, and a correspondingly less percentage of its area can be protected by armor than is the case in the barbette ships. In the barbette ships the turning gear is in the barbette itself, and requires no armor on the side of the ship to protect it.
The arrangement of the armor in the turret central citadel ships is clearly shown in Figs, 1 to 1d, which represent the Agamemnon. A central citadel of armor 104 feet in length reaches from 6 feet under water to the upper deck. This extends longitudinally throughout the length of the engine and boiler rooms, and encloses the two turrets. The maximum thickness of armor is 18 inches, and the top of the side armor is joined by an iron deck 3 inches thick. The ends of the citadel are formed of bulkheads, of nearly the same thickness as the side armor, as shown in Fig. 1b. The midship section of the ship is shown in Fig. 1c, from which we see that the armor is worked "sandwich fashion," that having been considered the best method of working the iron armor in use at that time. The armor in the ships now building is faced with steel, and is made in one thickness.
At the ends of the vessel we have no side armor at all, but a 3-inch underwater deck running from the ends of the central citadel forward to the stem, and most thoroughly supporting the ram, and aft to the stern of the ship to protect the compartments below it. The steering gear and the compartments below the protective deck are as completely protected against the big gun as we can well imagine. It is very difficult for a big gun projectile to get either through or below this deck on account of its being so far under water. Such projectiles striking the vessel near the water line simply go through the ship above the deck, and the inflow of water cannot extend below the deck. A big gun projectile striking a belted ship in the water-line region, where the belt is thin, would get through the thin side armor and be under the protective deck, which is on the top of the belt; there is nothing to prevent the projectile reaching the magazine in the belted ship and blowing up the vessel. This risk the under-water deck of the central citadel ships entirely obviates. Even if the magazine of the belted ship were not blown up, a very large and perhaps fatal quantity of water would find its way into the compartments below the protective deck, which in her is above water.
Returning to Agamemnon, all the magazines, shell rooms, &c., are under the protective deck, itself under water, and the ammunition is conveyed under cover of the protective deck till it gets within the limits of the central citadel, and is then taken up to the guns; the magazine arrangements are alike in the two ends of the vessel to ensure a prompt supply to the guns, and to enable the action to continue should one end be flooded. The top of the protective deck is covered by coals and other stores, which serve to exclude water when the thin ends are damaged. When the stores are consumed or partially so, and the thin ends riddled, the vessel does not sink so far beyond her load draught of water as when all the stores are in place, as the following table shows:
Name of ship | Sinkage from Load-draught with all Stores and Coals on Under-water Deck in place and Ends riddled. (Inches) | Ditto, but with Half Coal and Stores in Ends, the other Half being consumed. (Inches) | Ditto, but with All Coal and Stores in Ends consumed. (Inches) |
Inflexible | 23 | 19 | 15 |
Agamemnon | 22 | 20 | 18 |
Colossus | 18 | 16 | 14 |
Collingwood | 17 ½ | 15 | 13 |
Camperdown | 14 | 12 | 10 |
At the sides of the vessel on the under-water deck there are two belts of cork clearly shown on Figs, 1b and 1d. These are separated by a "coffer dam," into which packing may be put for limiting the inflow of water when the sides are penetrated.
The stores in the ends on the protective deck are separated into several water-tight compartments, all of which must be destroyed before the sinkages given in the above table can be realized.
In the barbette Admiral type of ship we have an arrangement of armor differing from the above somewhat in detail, although the general plan is the same. The barbettes are placed much farther apart than the turrets are in the turret ship, and this necessitates an increased length of citadel to secure a protected communication between the barbettes and the magazines. The additional area protected by the longer belt allows the cork to be dispensed with.
In these vessels, see Figs. 2 to 2d, we have a central belt 150 feet in length and covering 56.35 per cent, of the total area of the water-line. This protects the engines and boilers. The belt is 18 inches thick, is of steel-faced armor, extends to five feet under water, and rises two feet six inches out of water, The top of the belt is joined by a 3-inch steel deck, and the ends of the side armor are joined by bulkheads nearly as thick as the sides of the belt. There is a strong under-water deck at each end as in the turret ship. This deck thoroughly supports the ram and protects the compartments beneath it. The deck is covered with stores in the manner described for the turret ship, and shown clearly at the ends of Fig. 2b.
The deck is subdivided by water-tight bulkheads, and spaces are appropriated for a "water chamber" at each end. This water chamber is an empty space into which water can be voluntarily admitted, and when partially filled it is found as a matter of practical experience at sea—one having been in use in the Inflexible in her recent commission—that the behavior of the vessel is much improved as regards rolling. (For further particulars respecting this water chamber, see page 793.)
The barbettes are connected to the top of the armored belt by a circular tube covered with thick armor. All the ammunition to the barbette guns goes through these tubes and remains completely under protection during its whole passage from the magazine to the gun. The loading gear in the barbette is well protected against the big gun, as it is all behind thick inclined steel-faced armor. The men in the barbettes are protected against the big gun by the thick side armor, and against the machine guns in the enemy's tops by a machine gun-proof plate covering the top of barbette. The barbette is protected from shell bursting immediately beneath it by a 3-inch floor shown in Fig. 2. There is a battery of six 6-inch guns and 6-pounder quick-firing guns under a light spar deck, and this is protected from raking fire by armored screens 6 inches thick, reaching from the barbette walls to the sides of the ship. The side in front of these guns is one inch thick. Along the top of the deck covering in the belt there is a coal bunker at the side of the ship as shown in the midship section at Figs. 2b and 2c. The section at the end of the ship is shown in Fig. 2d. All the hatches on top of the deck over the belt that are necessarily open when fighting the ship are protected by armored glacis plates and coffer dams, which rise to a height of more than five feet above water.
It is easy to see what the strong points of the above central citadel system are.
- The guns and gunners are exceedingly well protected for the size of ship.
- The ventilating tubes communicating with the boilers and engine rooms, and the tubes for bringing the ammunition through, are also equally well protected.
- The engines and boilers are better protected against projectiles than if the same weight were carried along in the shape of a complete belt.
- The magazines and shell-rooms in the ends of the vessel and the steering gear are much better protected by the under-water deck than if the sides were armored with armor not projectile proof, and the under-water deck removed from where it is underneath the coal and water to the top of a belt above water. The vitals of the ship—her machinery, her powder, or her rudder and steering gear—can only be reached, and the ship disabled by a single blow, provided that blow is much heavier than would suffice if the same weight of armor were more diffused in the shape of a complete belt.
- For a length of about one-half of that of the entire length of the ship, viz. the unarmored ends, it is a matter of non-vital importance whether a big gun projectile strikes at the water line or not. In a belted ship such a projectile striking at this point might either blow up the ship or completely flood one end and render the magazine useless. The amount of water admitted would, in the belted ship under the above circumstances, be so great as to render her quite unmanageable and an easy prey to her enemy, even if it did not at once sink her outright. In the central citadel ship the amount of water admitted under these circumstances would be so moderate in amount as to leave the ship, as I shall show further on (see pp. 786-7), with her sea-going qualities and fighting qualities practically unimpaired.
An incidental advantage of the central citadel system is that the ram is very much better supported by a riveted deck than by side armor attached to the ship only by a comparatively small number of bolts.
It is also easy to see in what respects the above system is defective.
The ends of the vessel being formed only of thin plate, are readily penetrable not only by the lightest ship guns proper, but also by machine guns, and this penetrability renders a diminution of speed and stability both possible and probable.
If, however, we wished to carry the belt to the ends of the vessel and retain unimpaired all her existing qualities, we should want considerably more than 1000 tons additional displacement, and if we did carry the belt to the ends we should be less safe against certain risks than we now are. The steering gear would be more exposed, the magazines and shell rooms could be more easily reached, and it would be much more likely that the big gun would completely flood one or both ends of the ship, than when the strong deck was well under water. In attempting to obviate the risk of having a moderate quantity of water almost certainly admitted to the ends, we have largely increased the risk of having fatal quantities of water admitted, increased the probability of blowing the ship up, or rendering her unmanageable by disabling the steering gear, and have largely increased the size of ship. It is also certain that we have not obviated the particular risk we attempted to, for the belted ship is exposed to precisely the same defect of getting water«in on her armor deck, notwithstanding that it is commonly spoken of as being above water, as the central citadel ship is of getting water in oh her deck, that is under water. This defect is a defect common to both types of vessel, and not peculiar to the central citadel ship, as I now proceed to show.
If all the light projectiles reaching the two types of ship were to strike them only in the region marked by the belt in the belted ship, the belted ship would not suffer at all, and the central citadel ship would have a certain quantity of water admitted into her interior. For light projectiles striking the two types in any other parts there is nothing to choose between them, both are exactly on the same footing.
Fig. 2e represents the Camperdown constructed with a complete belt from stem to stern. The wave shown on it is that raised by Collingwood on her recent steam trials. Any projectiles striking the bow under the wave as shown, admits water to the vessel just as freely as in the under-water deck central citadel ship; if the projectile strike amidships just above the belt, the hole, in any seaway, is under water a great deal on account of the rolling of the vessel and the passage of waves along her sides. Large quantities of water may therefore find an entrance into the vessel, and it must be clearly realized that the alternation of the belt going under water and coming out of the water offers no impediment whatever to the accumulation of a fatal quantity of water. Unless the hole can be stopped or the inflow of water be prevented from obtaining a free access to the interior of the vessel upon the armored deck by water-tight subdivisions still remaining intact and undamaged, it is incontestable that the water must come in faster than it can go out, the water will accumulate and capsize the vessel—a defect which is said by some to be peculiar to the central citadel ship. The rate at which water enters and leaves the holes is determined by the difference of level between the external and internal water, and this may he considerable, and depends on the extent to which the vessel is rolling and the kind of waves that pass her. The rate at which the water leaves the hole depends upon its height above the hole. As soon as the hole gets fairly out of the water the internal water, under the assumed circumstances of having no available water-tight subdivision left, lurches over to the other side. It cannot escape through the hole above water, because it leaves it for the other side; it cannot escape through the hole it finds there, because the external water is higher than the internal water. The vessel, therefore, very soon capsizes. Any consideration, therefore, of the effect of water on the decks of a central citadel ship must be given with a full recognition of the fact that water is as injurious in the belted ship, and that the belted ship has only the same unarmored defence against fatal quantities of water being admitted as the central citadel ship has. The practical question for consideration is not, therefore, "Could we not escape all danger of this kind by making our ships a little larger, and giving them a belt all along the water line?" but, "Is there sufficient speed, stability and buoyancy in the central citadel ship to ensure a reasonable probability of survival in action?" The answer to the first question we have just seen, as demonstrated by the model, is no; the answer to the second question I will endeavor to show you is yes. I am, of course, compelled to say a reasonable probability, because from the nature of the case, certainty of survival is unattainable. After everything has been done the ship will have to run some risk she can ill afford to run. Absolute safety she cannot have; she must be satisfied with less. That probability of survival could of course be increased by enhancing her present defensive powers, either by increased size or by diminution of some other quality in the ship.
Let us, then, consider the behavior of the central citadel ship a little more closely. To understand the principles regulating the sinkage of these ships when their unarmored ends are perforated and the whole of the internal watertight subdivision completely destroyed, let us consider a simple case.
It is a well-demonstrated truth that the weight of all floating bodies is equal to the weight of the fluid displaced by them. All bodies of the same weight must, therefore, have the same volume of displacement, no matter what their shapes may be, and if a body of given weight loses displacement in one place it must be made up in another. Corresponding to a given fixed weight we must have a given fixed volume of displacement.
The amount of water that comes in is quite independent of the nature of the stores and other articles, but only depends on the volume unoccupied by the stores themselves. So long as this volume remains unchanged the stores may be as heavy as lead, or as light as feathers, without making any difference to the amount of water that comes in. The loss of volume of displacement occasioned by the entry of water we may call v.
The vessel will sink in the water till the additional volume of displacement between the original and her new water line is equal to v. The necessary amount of sinkage to ensure this depends on the area of water line still capable of displacing water as the vessel sinks into it. This area is the area of the armored central belt + a certain fraction of the unarmored ends depending on the proportion of space in these ends occupied by solid water-excluding stores. If the space is half filled we must take half the area, if three-fourths we must take three-fourths, and so on. If, then, A be the area of the central belt, a the area of that portion of the unarmored ends still available for displacing water as the water sinks lower into it, the additional volume of displacement due to a given sinkage, s, must of necessity be = (A + a)s. The sinkage due to the riddling of the unarmored ends is therefore = v/(A + a) = the volume of the interstices between the under-water deck and the original water line, divided by what we may call the effective area of the water line after allowing for the ends being damaged. The new water line is at a height s above the original water line.
The above principle has been applied to the following typical vessels, with the results stated against each. The sinkage of these same vessels due to coaling has been added for information and comparison:
| Sinkage due to Riddling the Unarmored Ends, estimated as above. Inches. | Sinking due to Coaling. Inches. |
Warrior | 32 | 16 |
Resistance | 42 | 16 |
Inflexible | 23 | 27 |
Agamemnon | 22 | 20 |
Colossus | 18 | 22 |
Collingwood | 18 | 22 |
Camperdown | 14 | 22 |
Beginning with the Inflexible in the above table, we see that the sinkage due to the riddling of the ends and the complete destruction of the numerous water-tight subdivisions is less than that she experiences every time she coals. In Agamemnon the sinkage is slightly greater, in the Colossus and Collingwood the sinkage is again less, and in Camperdown the sinkage due to coaling is 50 per cent, greater than that due to riddling. In Warrior and Resistance it will be noticed that the sinkage due to riddling is twice that due to coaling.
If both ends of the ship be freely riddled and the whole of the sub-divisional bulkheads on the under-water deck completely destroyed, the sinkage is less, and in some cases much less than that due to coaling. The amount of sinkage due to riddling is not great in itself, and unless it involves the loss of sea-going and fighting qualities in the ship, cannot in itself be objected to. This feature of the case I now proceed to deal with.
If only one end be riddled, the ship will change trim unless water be voluntarily admitted to the other end, and for which provision has been made. This change of trim can easily be calculated by the Naval Architect, or can be experimentally ascertained by means of a model. Both methods have been resorted to in the case of Inflexible with concurrent results. The change of trim is in no case sufficient to cause even much inconvenience on board and does not imperil the ship in the slightest degree. In Agamemnon the water line with the fore end only riddled is shown by c. d. in Fig. 1. It will be noticed that the fore end has not gone down much, and that the stern has not lifted to such an extent as to imperil the rudder or the propeller blades.
Allowing the water to come in at one end only, she tips only slightly; allowing it to come at both, she sinks bodily, but leaves her armor still above water. We may therefore feel perfectly certain that so far as increase of immersion is concerned the central citadel ship is quite safe with either or both ends completely riddled.
The same two courses may be followed with respect to her stability. The Naval Architect may either calculate the stability of his vessel in any assumed condition of damage, or he may ascertain the same thing experimentally by the aid of an accurate model. Both these methods have been resorted to in the case of Inflexible with perfectly harmonious results.
The stability of a vessel is usually represented by what is called "a curve of stability," the construction of which will be readily understood from Fig. 3. When inclined over at a given angle of inclination, the weight of the vessel acts vertically downwards through G the centre of gravity of the ship, and the support of the water acts along the line marked "line of buoyancy." These two lines have a perpendicular distance, GZ, between them, the length of which is an exact measure of the amount of stability the vessel has in the condition assumed. When GZ is great the stability is great also, and when small the stability is small. The weight of the vessel always acts through G, the centre of gravity of the vessel, at all angles of inclination. The determination of the amount of stability a vessel has in a given condition and at a given angle of inclination depends simply upon an arithmetical calculation of the position of the line marked "line of buoyancy." The length of GZ is calculated for various angles, and the results set off graphically as shown in the shape of a curve, which is appropriately called a curve of stability.
The curves of stability of Inflexible for various conditions of ship are given in Fig. 4. The soundness of the principles on which these curves were calculated was examined by the members of the Inflexible Committee, consisting of Admiral Sir J. Hope, President, Dr. Woolley, G. W. Rendel, Esq., W. Froude, Esq.
This committee considered the soundness of these principles unassailable, and further considered that the amount of stability the vessel had was sufficient. In their report they said "e or f might fairly be assumed to represent the greatest amount of damage the ship would be likely to suffer in action. This represents the unprotected ends completely riddled and waterlogged, but the materials and cork remaining and adding buoyancy. In e the whole of the coal is assumed in place, in f it is assumed to be removed. If reduced to this condition the ship would possess both buoyancy and stability enough to face all contingencies of weather. The united movement of all her guns from the loading to the firing position would not heel her more than 2 ¼°…It cannot be said that the armored citadel is invulnerable, or that the unarmored ends are indestructible, although the character of the risks they run is different. But, in our opinion, the unprotected ends are as well able as the armored citadel to bear the part assigned to them in encountering the risks of naval warfare, and therefore we think that a just balance has been maintained in the design, so that out of a given set of conditions a good result has been obtained."
This Report was signed December 4th, 1877.
A previous committee, presided over by Lord Dufferin, reported in 1871 that the "only method of bringing about a well-considered armor- plated ship was to have a central belt and raft ends with an under-water deck." Two naval members of the committee, Admiral Ryder and Admiral Elliot, went much further in this direction, and advocated the entire abolition of side armor for the protection of buoyancy and stability, and to employ armor-plating only for the protection of guns and gunners. The water-line was to be protected by a cellular structure only. The members of this committee were: Lord Dufferin, President; Sir W. Thomson, Admiral Elliot, Admiral Ryder (these two members recommended the entire abandonment of side armor from stem to stern in all classes of ships); Admiral Hornby. Admiral Stewart, Dr. Woolley, Professor Kankine, W. Froude, Esq., Captain Hood, Captain Goodenough, G. W. Rendel, Esq., Peter Denny, Esq., C. P. Bidder, Esq., T. Lloyd, Esq.
We therefore have it on record that the above committee deliberately formed the opinion that the central citadel ship, with under-water decks at the ends, was the best ship that could be devised for encountering the varied risks of naval warfare. This opinion was arrived at after hearing all that could be said on the subject by any person who had anything to say. The above two committees had seven naval members, all of flag rank, except two. Two flag officers dissented from the above only to the extent of giving up even the central armored belt amidships. So far from objecting to the unarmored ends, they were willing that the water line should have no armor at all.
I do not, however, wish you to be guided in this important matter merely by the weight of authority, however great that authority may be. You may say, too, that the conditions have changed since the above reports. Let us assume, then, that on account of the development of the machine gun, the quick-firing 6-pounder, and the introduction of the smaller breech-loading guns, that we must have adequate protection against these weapons. Such protection, of course, is much to be desired, if we can afford it. Other increases of defence are also desirable. It is not so easy to give protection against the above guns as some suppose. It is quite certain that the addition of a complete belt along the whole length of water line does not give us this protection.
If an enemy can destroy the unarmored upper works of a ship, as some say is almost certain to be the case, the only conclusion we can come to is, that the belted ship, although less safe in other respects than the central citadel ship, is no safer in this one respect of being capsizable by light guns only.
Let us take a completely belted ship, such as that in Fig. 5. It is easy to see at once, that apart from her unarmored upper works, she is a low freeboard vessel and has no useful range of stability.
All foreign vessels of this type, like their English rivals, depend for their stability in a well-contested action on the improbability of their unarmored upper works being completely destroyed. If their unarmored upper works are opened up freely to the sea they will capsize quite easily, in spite of their belt, as I have previously shown. The floating models before you show very clearly that these vessels depend for their stability on their unarmored upper works. I do not want to leave an impression on your minds, from having witnessed these experiments, that the belted ship is less safe against the machine-gun and small-gun risk, than the central citadel ship is, or that you would easily capsize the belted ship if she were your enemy in an action by accomplishing the complete destruction of her upper works, as supposed in the model. I am only showing that it is altogether wrong to suppose, as some do, that the possession of a completely armored water line takes away all anxiety as regards light-gun fire. It is perfectly true that the Admiral type of ship is destructible by light guns if they have time enough. It is perfectly true, also, that the belted ship is destructible by the same weapons, and has more chance of being destroyed by the big gun. So much for the complete destruction of the upper works in both types of ship.
When the damage stops short of completeness it is purely arbitrary to say we should provide that a certain amount of stability should be left when specified parts are penetrated. All assumptions that may be made as to the probable damage a ship may experience are open to objection. All such assumptions are mere guess-work, and probably no two persons would agree in making them. The best method is to look at the matter generally, and not in any specified precise way. Adopting this plan, we may say that in our English Admiral type a very large proportion of the unarmored upper works must be destroyed to reduce the range of stability to 30°, and even when this has been done the vessels will, in the words of the Inflexible Committee, be able to face all contingencies of weather.
The stability of our battle ships depending so much on their unarmored parts, it is important to make these unarmored parts as efficient as possible for the purpose. In the English battle ship this unarmored defence has been made as great as possible by the suitable disposition of water-excluding stores,—the coal, cables, provisions, and in some cases of cork,—most of which are well protected by being under water.
I do not know the exact nature of the unarmored defences in the belted ships of the world, but the model experiments you have seen show that it is quite certain that they are as much needed in their case as in the case of the central citadel ship.
LECTURE II.
We have seen for ourselves how the stability of the central citadel ship and of the belted ship stands in smooth water, and we have also seen what the Inflexible Committee thought of the sufficiency of the stability of that ship to provide safety against stress of weather and sea. Let us now look a little into the matter ourselves and ascertain the grounds of safety at sea.
It must be a perfectly well-known thing to everybody here that if we take a pendulum or a man in a swing and carefully time our impulses we shall certainly get the pendulum over its point of suspension, no matter how feeble our impulses may be, always provided they are kept up long enough and that there is no resistance. If the resistance is very great, due to the pivot being jammed or to the pendulum having to vibrate in a fluid, it may not be possible to capsize the pendulum even with the most sustained and most carefully timed impulses. The resistance might be too great for the applied force to overcome even if it could be kept up without flagging. If the applied force were too small in relation to the stability or resistance or could not be kept up long enough, the pendulum might be perfectly safe against capsizing.
In the case of a ship 1500 miles from port we cannot depend upon the capsizing forces not being kept up long enough, the sea is untiring, and therefore our only safety lies in having a sufficient amount of stability and resistance to rolling. The stability and resistance to rolling are in our own hands, and we may make them, within certain limits, what we please. The motion of the sea is beyond our control; this we have to contend with as best we may.
I must ask you to bear in mind what is so frequently lost sight of, viz. that both resistance to rolling and stability are necessary to safeguard a ship against capsizing at sea. No amount of stability, apart from resistance, could give a well-founded assurance of safety, and no amount of resistance to rolling apart from stability is sufficient to safeguard the ship. We must have a combination of both.
The stability of a vessel, apart from resistance to rolling, is a thing that effectually safeguards the ship from capsizing only in still water under steady inclining forces, such as having a deck load on one side of the vessel or a wing compartment filled with coal or water. In a seaway the stability depends for its value on the extent to which it is associated with resistance to rolling. The more and more the resistance to rolling is increased, the more and more does a given amount of stability assure the safety of the vessel. The more the resistance increases, the less is the needful amount of stability to ensure safety against capsizing by the heave of the sea. With an increased resistance to rolling a small amount of stability may leave just as large a margin of safety as a larger amount of stability and a decreased amount of resistance. With no resistance to rolling all vessels would be unsafe under circumstances to which they might at any time be exposed.
Coming back to our pendulum; we could baffle the efforts of a man to capsize it, either by loading it more heavily and increasing its stability, or by leaving its stability alone, or even decreasing it, provided we jam the pivots harder, and increase its resistance to oscillation.
Now the increase of resistance to rolling is precisely that which happens when we perforate the ends of the central citadel vessel and reduce her stability. As the ship rolls, the water in her ends dashes about from side to side, and increases her resistance to rolling to such an extent that under these circumstances the vessel will roll much less than when intact and undamaged, and be in no more danger of capsizing than before her ends were wounded.
This power of the water to reduce rolling has, I know, been looked upon with a very scanty amount of belief by many persons, as being contrary to a practical seaman's judgment, but here is an experiment to show you that the statement is beyond question.
[At this point of the lecture models were used representing the midship sections of the Admiral class, and were both of the same weight and size. Each model was mounted on trunnions, at about the level of the water line, and both oscillated freely on these trunnions in exactly the same time. The models were placed one behind the other, so that the parallelism of the masts was evident to the audience. One model was provided with a glass tube into which varying quantities of water could be put. An amount of water representing 1/100th of the total weight of the model, i.e. 100 tons in a 10,000-ton ship, was now placed in the tube, the models were started from the same angle as before, and the model with the loose water, instead of keeping up exactly with the other, or rolling more violently, came almost instantaneously to rest.]
Notwithstanding the result of the above experiment, there may be some persons in the room who are still dissatisfied as to the power of the water to moderate the rolling of a ship at sea. Such persons may say I cannot disprove the accuracy of your experiment, but I am satisfied there is some error in your inference, because your inference does not accord with my practical experience at sea. My experience at sea teaches me that if one of my guns, for instance, takes charge, the ship at once rolls more violently in consequence, and if there is any truth in your theory, the reverse ought to take place; the ship ought to be steadied by the motion of the gun.
I have no hesitation at all in saying that the motion of the ship is steadied by the motion of the gun, and here is an experiment to prove it.
[One of the models described above was provided with a grooved traverse in which a marble could freely run from side to side, the marble being stopped at each end of its roll by the sides. The weight of the marble was on the scale of 100 tons for a 10,000-ton ship. The tube in the second model was emptied of water; the marble put in the first model, and the two started from the same angle as before. The model with the marble freely traversing the deck came almost at once to rest.]
As regards the shot or gun at sea, its effect is baneful as regards the ship's structure and men's legs, but beneficial as regards the violence of rolling.
There may also be some persons in the room who will say, I admit all that you say you have done, but that does not cover my point. You have taken 100 tons of water or 100 tons of gun and shown that that quantity effectually moderates the rolling. I have never doubted that it would. You may, however, have 600 tons of water on deck, and if you do, what will happen then? I may take one grain of arsenic with perfect safety or even with advantage, but what will happen if I take six? As regards the arsenic I am not competent to answer that question; but I can tell you what will happen if you increase the amount of water. The action of the water in moderating the rolling depends entirely on the possibility of its moving; if the space is full and the water in consequence cannot move, you get no more effect than if the water were so many tons of pig ballast, and here is an experiment to prove it.
[The tube in the model was here filled with varying quantities of water, and the effect was always to stop the model much sooner than the model with no weights free to move. The two models were always started from the same angle, so that their relative behavior could be easily seen. When the tube was quite full there was practically no effect. The two models rolled almost together.]
In the actual ship we may have a small quantity of water with plenty of space to move about in, or a larger quantity with less space to move about in. As the empty space gets more and more filled with water the space available for the motion of the water becomes less and less, and ultimately with the ends quite filled with water only a small portion of the upper part of the water can be considered as free to move. The lower part is locked on account of filling the space it occupies.
We must now be quite satisfied that as regards the particular models before us, there is a very rapid reduction in the arc of oscillation due to the transverse motion either of free water or a moving solid weight. I want you to infer from what you have seen, that the same reduction must always occur in a rolling ship it we have a loose weight of any kind, whether the weight be water or a gun. If this reduction did not take place, we should have something to explain which would be quite inexplicable. For suppose we have two ships alike in all respects as regards size, shape, weight, time of oscillation, &c, and situated on precisely the same seas, but one having all her weights properly secured, and the other with a weight capable of traversing the deck every time the ship rolls. If the two vessels were to roll to exactly the same extent we should have the sea not only rolling the ship with the loose weight to the same extent as the ship with all her weights fixed, but the sea would, in addition, be doing all the work involved in the transversing of the heavy weight across the deck, which is quite impossible under the circumstances of perfect similarity we have supposed. The sea can only do the same work on both. In the one case that work consists entirely in rolling the vessel, in the other it consists partly of rolling the ship and partly in dashing the weight about. The rolling in the latter must therefore inevitably be less than in the former case.
Let us apply the same reasoning to our two models. If they were placed in vacuo, and mounted on frictionless pivots, the one without the moving weight would go on swinging forever. If the other with the moving weight went onswinging forever also, we should have a perpetual source of energy in the blows caused by the traversing of the weight,—a source which we all know is an impossibility. We should have all the work of hammering which we could apply to do any work we please. Stated in this way the reduction of roll follows as a necessity. The truth is that every time the blow occurs the marble or the water is made a little hotter than it was before, precisely in the same way that the stoppage of a bullet against a target generates enough heat to partially or entirely melt the bullet. All the additional energy in the water or marble due to its increased temperature has had to come from the energy stored up in the oscillating model, and coming from this source has, of course, reduced the extent of oscillation in the manner you have witnessed.
Considerations of the above sort led to the conclusion that although with the ends waterlogged, the ship would of necessity have less stability than when intact, yet the resistance to the rolling would be so much increased as to make that stability, degree for degree, much more valuable than when intact, and also make the ship much steadier and consequently render her big guns more formidable.
The power of loose water to reduce the rolling motions of ships having been ascertained experimentally, has been applied on a large scale in the Inflexible. In this ship a water-chamber has been in successful operation on actual service at sea, and the behavior of the ship, although very good without the water-chamber in operation, was considerably improved when water was admitted to it. In all the recent designs of English battle ships a space for a water-chamber has been appropriated. The Admiral class of vessels has less meta-centric height than the Inflexible has, and has the same advantage as the Inflexible as regards water-chamber. It is quite certain, therefore, that the excellence of behavior we have had reported from the Inflexible will be more than realized in the Admirals. It is important to bear this in mind, because one class of critic says the central citadel ship may be made perfectly safe against capsizing when the ends are riddled, provided you make your stability when intact so great as to admit of the necessary reduction of stability you incur when your ends are damaged. The stability necessary for this purpose will, however, certainly make your vessel roll much more than you need to make her roll, whereas in the belted system you need only provide as much stability as is necessary for the intact condition. This criticism, however, can have no weight in the face of the favorable reports received as to the behavior of Inflexible, the ship which we are quite certain will roll under ordinary circumstances more than any of the Admirals.
A series of very careful experiments has also been made at Spithead in smooth water on board the Edinburgh, to ascertain the effect of varying quantities of water in adding to the ship's rolling resistance, and also for ascertaining the best quantity of water to put in the water-chamber. It was found that 100 tons was the best quantity to be used in the water-chamber provided. The best quantity of course varies with the size of water-chamber and other features, such as size of ship, time of swing of ship, &c., and can only be found experimentally in each individual case. It was found that when rolling to 10° the rolling resistance was increased by 43 per cent.
Two feet addition to the bilge keels would add 67 per cent, to the rolling resistance at all angles of roll. The water-chamber is more effective at small angles of rolling than the bilge keel, and is consequently much more efficacious in bringing the ship to a dead stop than the bilge keel, whose power of stopping the ship gets less and less as the angle lessens. The relative effects of the water-chamber and two feet of additional bilge keel are compared below:
The water-chamber at 3° adds 6 times as much as 2 feet additional bilge keel.
The water-chamber at 5° adds 3 times as much as 2 feet additional bilge keel.
The water-chamber at 12° adds the same as much as 2 feet additional bilge keel.
The water-chamber at 18° adds one-half as much as 2 feet additional bilge keel.
For violent rolling at sea the bilge keel is the more efficient of the two, but for moderate angles of roll in good fighting weather the water-chamber is the more efficient of the two in steadying the guns.
As illustrating still further the effect of moving water in steadying the ship, let us consider the following table prepared by the Inflexible Committee:
| Range of Roll. Degrees. | Range of next Roll. Degrees. | Loss of Range. Degrees. |
Sultan | 10 | 9.6 | 0.4 |
Inconstant | 10 | 9.2 | 0.8 |
Devastation | 10 | 8.0 | 2.0 |
Inflexible, intact | 10 | 9.0 | 1.0 |
Inflexible, riddled and gutted | 10 | 2.6 | 7.4 |
Inflexible, in condition f | 10 | 2.2 | 7.8 |
In the first four examples in the above table we have no moving water and a small reduction of range of roll. In these four examples the figures are obtained from the actual ships. In the two last examples the figures have not been obtained from the actual ship, the ship never having been in the condition supposed. These results were obtained from a model of the vessel, most carefully constructed as to distribution of weight, &c., so as to accurately represent the ship. It was also estimated by the Inflexible Committee on principles that were thoroughly tested by actual trials at sea, Mr. Froude having previously gone to sea on purpose, that if the Inflexible were exposed to a series of waves as large as any on record, viz. about one-fourth of a mile in length and 40 feet in height, her maximum angle of rolling would be as under:
Condition of Ship. | Maximum Angle of Ship’s Deck with the Horizon. Degrees. | Maximum Angle of Ship’s Deck with Wave Surface. Degrees. |
Riddled and gutted | 2 | 7 ½ |
In condition f | 6 ½ | 10 |
The angle of vanishing stability in these two conditions is over 30°, and the committee reported in consequence that the ship “would possess both buoyancy and stability enough to enable her to face all contingencies of weather.” As regards buoyancy and stability, then, we may rest assured that the central citadel ship when well designed is perfectly safe, even when her unarmored ends are freely riddled.
I now proceed to deal with the question of speed. The Inflexible Committee reported that in the above extreme conditions of damage the speed may be seriously impaired, but in all other respects the vessel would be able to exercise all her powers…The heel due to her circling at the highest speed attainable would not be an element of danger.
Some persons suppose that the above feature of reduction of speed under extreme conditions of damage is in itself a fatal objection to the adoption of central citadel ships. If this feature were peculiar to central citadel ships it would of course be a very serious objection to them. This defect is, however, by no means peculiar to the central citadel type; it exists also in the belted ship, and to an equally fatal extent, as I shall show. If I were to tell you that when the three main compartments in the hold of a belted ship were bilged the vessel would go down, and that, therefore, the belted type was a bad type, you would say it may be useful to know that the ship would go down under these circumstances, but so would any other ship, and therefore the fact in itself says nothing as regards the badness of type. Your very natural answer is the one I am compelled to adopt. I am very sorry the central citadel ship is liable to the above reduction in speed. I am equally sorry the belted ship is also liable to the same reduction. The belted ship is liable, in addition, to other defects not existing in the central citadel ship, as I now proceed to show.
If we take the case of the two ships at rest in smooth water and open a smart fire on them of heavy machine guns and of 6-pr. guns, we should admit, if we completely destroyed the internal subdivision over the under-water deck, 600 tons of water into the central citadel ship, and the ship (Camperdown) would sink fourteen inches in consequence. If the destruction of the internal subdivision were less complete, less water would be admitted, and the sinkage would be less than fourteen inches. All the damage to the belted ship would be above the top of her belt, which is 2 ½ feet above water. In this vessel, therefore, there would be no entry of water (under the circumstances supposed of being motionless in smooth water) and no sinkage. Both ships are certain not to capsize. The central citadel ship has sunk fourteen inches, the belted has not gone down an inch.
If, now, we were to steam ahead with both ships, and suppose no more water admitted to the citadel ship and none to the other, the central citadel 10,000-ton Camperdown would lose one-fourth of a knot due to the fourteen inches increase of immersion, and the belted ship would lose nothing. The central citadel ship was able to start with an additional knot over the belted ship on account of being able to put more weight into machinery due to savings from the belt. All the time, therefore, no further water comes in, she is three-fourths of a knot better off than her belted antagonist, notwithstanding she has lost a quarter of a knot and the belted ship has lost nothing.
It is not reasonable, however, to suppose that no more water (under the above circumstances) will come into the central citadel ship; some of the holes will be scoop-shaped and tend to draw water into the ship, and the holes may also be very numerous. It must be admitted that more water may come in. It must also be recognized that the complete destruction implied by the admission of the 600 tons referred to above can only be a slow process, during which the belted ship cannot hope to remain undamaged, and whatever may be the amount of water contended as being certain to come into the central citadel ship over and above the preceding 600 tons must also come into the belted ship, because all the time she is steaming at a fighting speed her belt is not 2 ½ feet above water as it is in harbor, but is more than covered at the stern by the stern wave, and is from six to ten feet under the water at the bow, see Fig. 2e. The midship part is also half its time under water on account of the roll of the ship and the passage of waves along her sides, and the tendency of this is, as we have seen on page 9, to accumulate water. The truth is, that so far as the accumulation of water goes, the top of armor is in both cases under water; in the belted ship it is 6 to 10 feet under water at the bow, and in the central citadel ship it is about 4 feet more. It is just as easy to get water into the belted ship when she is steaming ahead at a fighting speed in a seaway or even in smooth water as it is in the central citadel ship, and both must deal with the incoming water in the same way, i.e. allow it to run overboard again through suitable relief scuttles as fast as it comes in, or deal with it if possible by the pumps. It is important, too, to bear in mind that during all this time the central ship is steadier than the belted ship, making her big guns more formidable, and as her rolling is reduced by the loose water in her ends, water cannot find its way in above the belt amidships so rapidly as in the ship belted during the whole length of her water-line.
If it be contended that the central citadel ship may have all her unarmored structure destroyed, and that she will then be unable to steam ahead without danger of capsizing, I say you must allow that the belted ship may have all her unarmored structure destroyed, and here is an experiment to show you that she also cannot steam ahead without certainty of capsizing. The only inference one can draw from seriously reflecting on the case is either that you must give up contending that these extreme conditions will certainly be realized, or else come to the conclusion that naval warfare is impracticable on account of the certainty of destruction of all those engaged in it. There is no choice in this respect between the belt and the central citadel; both alike will be certain to capsize.
The case, however, is not really as bad as the above. In both types of vessel we have to bear in mind that the holes made are what we might call chance holes. Some are made in one way and some in another. Some, on account of their shape and position, induce a rapid inflow of water, and some, owing to their shape and position, induce an equally rapid outflow. The aggregate tendency of the holes to run water into the ship may not, therefore, be very much, but whatever it is, it is the same in both types of vessel and must be dealt with in the same way, viz. the water must be allowed to run out again through holes provided for that purpose in the design of the vessel and opened when occasion requires. It is perfectly true that the limitation of speed pointed out by the Inflexible Committee exists in the central citadel type of ship, and must be borne in mind by her commanding officer. It is equally true that the same defect exists in the belted ship and must be borne in mind by her commanding officer.
Having considered the various points of difference between the central citadel ship and the belted ship item by item, I submit that I have established the following:
1. That all modern battle ships depend for their stability to a large extent on their unarmored parts. Their probability of survival in action, so far as stability goes, depends almost entirely on the improbability of the whole or the greater portion of the unarmored superstructure being completely opened to the sea. The possession of a complete belt along the water line cannot keep a vessel from capsizing if the unarmored superstructure is entirely opened to the sea. A belted ship is no safer in this respect, and is less safe in other respects.
2. In the under-water deck system some portion of the superstructure above armor is under water, and is not so easily destroyed as the above-water portions in the belted system.
3. Although in the under-water deck system it is practically certain that moderate quantities of water will be admitted to the ends of the vessel, it is quite certain that the admission of only moderate quantities will not prejudice the stability of the vessel to an important extent, and will so steady the vessel as to enable her to make good practice with her big guns. On the other hand, it is much more likely that very large or fatal quantities of water will be admitted to the ends of the belted vessel, and it is also much more likely that the powder and steering gear will be reached in the belted ship by the big gun than in the central citadel ship, because the thin vertical armor on the belt at the ends and the above-water deck over its top are more penetrable to the big gun than the under-water deck of the central citadel ship, well covered as it is by the sea and stores on its top.
4. As regards the loss of speed occasioned by the admission of water, what might be called the smooth-water sinkage of the central citadel ship causes a loss of only one-fourth of a knot in speed, out of an additional knot it was possible to arrange for in the design to start with.
5. As regards the loss of speed due to any supposed rushing in of the water through scoop-shaped holes, it is not a difficult thing to let the water out again by holes suitably shaped and properly positioned; and even if it were, this is a defect which is as great in the belted ship as in the under-water deck ship, because all the time the vessel is steaming at a fighting speed, each end of the belt is permanently under water on account of the waves raised by her progress (see Fig. 2e), and the midship part of the belt is half its time under water on account of the rolling of the ship, and the passage of sea waves along her side.
6. That the central citadel system with under-water decks at the ends protects the magazines in the ends of the ship, the steering gear, and supports the ram much better than the belted system does, and at the same time provides, on a given weight of armor, a very much thicker belt amidships than the belted system does, and as a consequence gives greater protection to the engines and boilers also.
7. That with the central citadel and under-water decks, the admission of water to one end alters the trim so little as to leave it a matter of option and not of necessity with the commanding officer whether he will voluntarily admit water to the other end or not. If water be voluntarily admitted to the ends before going into action there can be no further derangement of trim, the vessel will be quite safe, will be almost perfectly steady, and will have lost only one-fourth of a knot in speed out of an additional knot provided for in the original design.
In the preceding part of my lectures I have laid great stress on the limitation placed on the Naval Architect as regards the size of his ship, and showed that it was not possible to have a belt the whole length of the water line on the size adopted, and at the same time to have all the other qualities asked for.
It can hardly be necessary for me to point out that there are two sides to the question of increasing the sizes of ships. The problem of the Naval Administrator must always reduce itself ultimately to that of obtaining the maximum of offensive and defensive power on a given sum of money. The amount of money may be large or small, but he, like everybody else, has to obtain the maximum value for it. Some people contend for having large ships of great powers, and fewer of them; others contend for greater numbers and less individual powers. It would be presumptuous for me to say anything on this point; but I presume you expect me to say something as to the policy of having a belted water line if the present sizes of ships were considerably increased. I therefore go a step further and say that even with the larger ship and greater amount of armor possible for her to carry, it follows from the above summary that, as the belted water line gives so little advantage as regards some kinds of risk, none at all against others, and involves greater risks in several vital respects than the central citadel system does; it would be much better to employ the additional weight of armor in thickening the decks, the central belt amidships, and particularly in increasing the height of the central citadel armor, than to employ it in making a belt along the whole length of water line. A short high belt amidships, where the vessel is broad, costs no more per foot of the ship's length than where the vessel is narrow, but has a much greater value in maintaining the buoyancy and stability than the same armored area, extending the whole length of the water line and reaching only 2 ½ feet above it.
The question of having 2-inch or 3-inch armor on certain parts as a protection against quick-firing guns does not properly come within the scope of the above comparison between the two types. For machine-gun risk both types would be better with such protection, but on a given size of ship would be more vulnerable to the big gun. The development of the machine gun has stopped at its present stage simply on account of the acceptance of thin sides. If a serious attempt were made to defeat the machine gun by thickening the sides of our vessels, the same fight between the machine gun and the armor opposed to it would certainly be gone through, as we have seen in the past evolved from the 68-pounder mounted on truck carriages, and the 4 ½-inch iron armor of Warrior. The result of such a fight you are all in as good a position to imagine as I am.
I have endeavored in the above to bring clearly before you the differences between the two systems of protection. We will now consider in another way the effect of having a complete belt as compared with a central citadel. The table below gives the percentages of the total ship appropriated to each particular item. It will be seen that the completely protected water line leads to a considerable increase of size, a diminished speed, a diminished weight of armament and of coals. The big guns are also protected to a much less extent than in the central citadel ship, and we have fewer ships in proportion to the total outlay.
| Typical Ship with Short Belt (Percentages) | Typical Ships with Belts from End to End | |
No. 1 (Percentages) | No. 2 (Percentages) | ||
General equipment | 3.5 | 4.5 | 2.0 |
Armament | 8.5 | 6.5 | 6.5 |
Machinery | 13.5 | 11.0 | 10.5 |
Coals | 9.0 | 6.0 | 7.0 |
Armor and backing | 30.0 | 36.5 | 38.5 |
Hull | 35.5 | 35.5 | 35.5 |
Total | 100.0 | 100.0 | 100.0 |
| |||
Displacement in tons | 10,000 | 10,900 | 11,200 |
Speed in knots | 16 | 15 | 15 |
Max. thickness of armor | 18 ins. | 21 ½ ins. | 21 ½ ins. |
Protection of powder passages to barbettes | 12 ins. | 4 ins. | 12 ½ ins. |
Barbette armor | 14 ins. Sloping | 15 ¾ ins. Vertical | 16 ½ ins. Vertical |
Principal armament | 4 63-ton guns | 4 48-ton guns | 3 75-ton guns |
Conning tower | About 90 tons | Machine-gun proof only | Machine-gun proof only |
Nature of protection to loading gear of big gun | Protected by thick armor | Protected only by machine-gun proof shields | Protected only by machine-gun proof shields |
I will say in conclusion that as a Naval Architect I have been compelled to carefully think over the above subjects for some years past. I have endeavored to place the various issues before you in a manner devoid of technicalities, and my principal points I have demonstrated experimentally. I thank you very much for the earnest attention you have paid me, but at the same time feel it my duty to warn you that many more than the two hours we have spent together on the subject must be devoted to it by any person before his opinion can be of much value.
PORTS IN THE WEST INDIES.
By Lieutenant Charles Belknap, U. S. N.
While navigator of a ship on the home station, I made the following notes in regard to various West Indian ports visited; and I have prepared them for the Naval Institute, in the hope that they may prove to be not without some little interest to those about to go over the same ground for the first time.
Of late years it has been the custom of the vessels in the home squadron to cruise in the West Indies during the winter months; and if, after leaving Hampton Roads, the fleet is to cruise at first in company, it will probably make its way to the neighborhood of 20° N. and 63° W. as a convenient rendezvous from which it can disperse, each vessel to pursue its allotted course. As the saving of time will naturally yield place to the saving of coal, probably the best course will be to make to the eastward, passing to the southward of the Bermudas, so that the trades may be encountered well to windward. This will easily be done during the winter season, on account of the prevailing northerly winds; in summer I think the same rule will hold good, though the opinion is held by some that the coast should be held outside the Gulf Stream well down to the 30th parallel, on account of the westerly winds then and there prevalent. If the destination be one of the Windward Islands, it will be well to keep farther to the eastward than if going to St. Thomas or Porto Rico, and to cross the 25th parallel in about 60° W. longitude, that the course may be laid to windward of the islands, where the trades will be steadier. In this case, if bound to Martinique or Santa Lucia, due allowance must be made for the westerly current which sets in very strongly, especially during fresh trades. If Barbados is to be visited, it is perhaps needless to say that it will be better to go there first, and thence to Santa Lucia or Martinique.
Santa Lucia.—Port Castries presents no difficulties that may not be avoided by a study of the chart and Sailing Directions. It is admirably situated for a coaling station; but at present, owing to the limited space, the facilities are poor. If the proposed harbor improvements are effected, it will, upon the completion of the Panama Canal, become an important port.
Trinidad.—Unless the trades happen to be well to the northward, the passage outside St. Vincent and Grenada is to be preferred, in order to avoid falling to leeward of the Dragon's Mouth. Port of Spain is easy of access; there are no pilots, and none is needed. After entering the gulf the vessels at anchor off the city will come into sight, and as the bottom shoals very gradually, a berth at single anchor can be taken at will. The coaling hulk Ripon is moored in fifteen feet water in about the centre of the anchorage, and may be approached as nearly as the draft of the ship will allow: the marks mentioned in the Sailing Directions are not easily recognized. There are two boat landings; one at the wharf in front of the lighthouse, the other on the pier at the southwest angle of the town. The former is the regular boat landing, but at low water it becomes impracticable for ship's boats; when intending to land at the latter, a small ladder becomes very convenient, on account of its height above the level at low water. Water for steam launches may be obtained at the last mentioned pier, and, when desired, a wrench should be carried, as the man in charge of the water is generally absent. While, on account of the distance of the anchorage from the shore, Port of Spain is not a convenient place for rating chronometers, the Gulf of Paria offers perhaps the best place in the West Indies for the determination of compass deviations.
If bound to Demerara, the Serpent's Mouth is not used, on account of the dangerous navigation, and the usual route is through the Dragon's Mouth around between Trinidad and Tobago. To the westward of the Gulf of Paria a strong westerly current is met along the coast, and if bound to Carupano, care must be taken to avoid falling to leeward and getting embayed in the bight between Margarita Island and the main. As the coast has not been carefully surveyed, shoal water may exist between the Testigos and the mainland, and on that account the route to La Guayra will be outside those islands, and between Margarita and the Hermanos.
La Guayra.—Sentinel Rock forms a good landmark for recognizing La Guayra, which is further distinctly marked by the Saddle of Caracas. At dawn the mountains back of La Guayra are generally visible, later in the day they become obscured by clouds and haze; but frequently when the coast line is invisible, the Saddle of Caracas may be seen showing above the clouds. To the eastward of La Guayra is a large cultivated valley, while to the westward the coast line is rugged and uninhabited. The differences in the soundings reported are due probably to changes in the bottom caused by fresh winds and strong currents; the roadstead is limited in size, and the way to a berth must be felt by the lead. The general custom is to stand to the westward, round to and to approach the anchorage from that direction; the cathedral clock-tower bearing southeast by east (true) will lead in. During the day vessels ride to the trades, but during the night it often falls calm, and then the current is apt to turn and to be from the westward; allowance must therefore be made for the change in heading. On account of the surf, native boatmen are generally employed to transfer passengers and stores from the ship's boats to the beach. The custom is to make a contract with a couple of boatmen, and to give them a small flag to carry to distinguish their boat.
While in general the current between Curasao and the main is to the westward, it sometimes near the land sets the other way, but feebly. Absolute reliance cannot therefore be placed upon it, and great caution is necessary in going between the ports of Curasao and Puerto Cabello.
Curasao.—The narrow entrance and the varying velocity of the current outside render access to this port difficult. While the current sometimes sets to the eastward when the trades are feeble, it generally flows to the westward with a force varying between one and three knots. As it sets directly upon the reef off the Rif Fort, care and judgment will be required to avoid touching that shoal in leaving as well as in entering. Even under the management of the authorized pilot, vessels have struck upon this dangerous obstruction, and if the port is to become of commercial importance, harbor improvements are of imperative necessity.
The name of Santa Ana Harbor is applied to the channel connecting the lagoon, or Schottegat, with the sea; at no place spacious, its width is lessened by the shipping moored alongside the bulkheads on each side. Men-of-war usually anchor in the lagoon, which, being exposed to the full force of the trades, is delightfully cool and free from mosquitoes, when compared with the anchorage in Santa Ana harbor. The bottom, however, is of soft mud with an underlying stratum of stiff clay, and if an extended stay is made, considerable difficulty may be experienced in weighing the anchor. The Dutch man-of war which remains at Curasao the greater part of the year lies, for the sake of convenience, in the cove on the western side of Santa Ana harbor just south of the lagoon, and it is customary for steamers before entering or leaving to blow the whistle as a warning to boats, and also if going to or from the lagoon to allow the man-of-war to come up with her bow fast, which reaches over to the eastern shore.
The Belvidere mentioned in the Sailing Directions is in ruins, and, as it is nearly hidden by other buildings, it no longer serves as a leading mark, nor is the crane or crab longer visible; it will not, however, be difficult to tell from seawards when the channel is fairly opened, as the banks or the shipping may be seen on each side. Without local knowledge a sailing vessel would require a pilot, but a steamer may enter without one, although pilotage is compulsory. The rule generally followed is to stand along the coast at a distance from one to two miles until the channel is fairly opened, which may be known as mentioned above; then at good speed to stand in, passing the white buoy off Fort Nassau close aboard to starboard. The head sails should be ready to hoist in case, as the bow enters the still water of the harbor, the current should sweep the ship over towards the reef off the Rif Fort against the helm. The channel here is about half a cable wide, and between the forts it is still narrower, but the eastern shore may be approached to within ten or twenty yards. When abreast the forts, being then beyond the influence of the current, the vessel may be slowed down. In leaving the port it is customary when abreast the forts to go ahead at full speed, passing the buoy close aboard, having after sail ready in case the current should catch the bow and render the ship unmanageable. While there is ample depth of water in the harbor and lagoon, the shoals that encumber the entrance are serious obstacles to vessels of large draft, and until they are removed Curasao will not attain much commercial importance, although it has an admirable situation in connection with the Panama Canal. Of late years the population has increased; phosphates have been discovered and are mined to a considerable extent, and there is considerable trade with the Venezuelan ports in the vicinity, carried on by means of small vessels of light draft. Cardiff coal may be obtained in limited quantities at about $10 a ton; rain-water is supplied at a cent a gallon, and well-water at half a cent, but neither is fit to drink.
In leaving Curasao for a port to the westward, the passage outside of Oruba is to be preferred, on account of the irregularity of the currents at the mouth of Maracaibo Gulf.
Santa Marta.—The reputation that this port has of being an unsafe anchorage, and the railway from Savanilla to Baranquilla, have combined to destroy any commercial importance it may have had. A railway to connect Santa Marta with the Magdalena river is now building, and as the depth of water is ample, wharves are to be built at the head of the bay, alongside of which vessels will be in a measure protected from the force of the furious gusts of wind which sweep down from the hills, and against which ordinary ground tackle seems to be of little avail. The land in the vicinity is incorrectly laid down upon the chart; Cuerno Point especially will be seen, when approaching from the eastward, to extend seawards much farther than might be expected from an examination of the chart. Though there is a lighthouse at Santa Marta, the light is of feeble intensity, being visible barely eight miles; and, moreover, it is not to be depended upon, as I saw it, during the short stay that the ship made, extinguished one night for over an hour.
Savanilla.—This is the port of Baranquilla, a town of some commercial importance upon the Magdalena river, with which it is connected by a railway. The mouth of the Magdalena is so obstructed by shifting shoals that its navigation is extremely perilous: in consequence, most of the produce of the region drained by the Magdalena finds it exit from Savanilla. The harbor is buoyed and lighted, yet the water is so shoal at such a distance from Salgar, the terminus of the railway, that it cannot be considered a convenient port. If the improvements projected at Santa Marta are completed, it is probable that that place will become commercially of greater importance than Savanilla.
Cartagena.—But little is known of the coast between Savanilla and Cartagena, and as the coast line is said to have been altered by an earthquake, a wide berth will be given it until it has been resurveyed. No dependence whatever can be placed upon finding the shoals in Cartagena harbor marked as indicated by the chart, which in other respects is accurate. Were the channels properly marked by buoys, there would be no necessity for taking a pilot, and it is perhaps on this account that the pilots fail to report the disappearance of the marks. But with any uncertainty in regard to the buoyage, as the Boca Chica is narrow and tortuous, and the current swift; and as the time occupied in passing through is too limited to allow of the taking and plotting of bearings, while not absolutely necessary, it would be advisable for any one unfamiliar with the locality to take a pilot, and by firing a gun when outside the Boca Chica, one will put out from the village just inside.
The general description of Cartagena in the Sailing Directions is correct, but time has effected many changes since the volume was published. The forts are fast falling into ruins; San Fernando is scarcely visible from seawards, being hidden by bushes and trees, and its flagstaff and signal-post have disappeared, as also have Angel Fort and the outwork to the eastward of Boca Chica village. As the shores are low and covered with mangrove bushes, and as there is a lack of prominent marks, the chart will fail to convey an accurate idea of the harbor to a stranger. There is a prominent clump of mangrove bushes to the northward and eastward of Boca Chica village, and a remarkable bare patch on the hillside back of Buena Vista. Mangrove Cay and Punta Arena also are valuable marks, but beyond these little will be recognized at a glance. In case a pilot is not taken the following directions may be of some value:—
Should Long Hill be obscured by the haze, bring Sandy Point bearing about east, and stand boldly for it, recollecting that it may be approached to within 100 feet with five fathoms water, and also that at this point the current is strongest. Some beacons may now come in sight, but without previous knowledge as to their position they are as likely to mislead as to direct, for it will be difficult to determine at sight upon which of the shoals they are placed, and there will be no time to identify them by bearings. When Fort San Fernando comes in sight, round to, to give it a berth of a cable's length, and stand along the shore with the clumps of mangrove bushes to the northward and eastward of Boca Chica village a point or so on the port bow; when nearly abreast the village and with Fort San Jose S. by W. ¼ W. (true), run off SE. by E. until the bearings show that Carreya Shoal has been passed, when haul up to pass between Brujas Island and Santa Cruz Bank, leaving the three fathom patch on either side at convenience. Santa Cruz Bank will be seen even if it is not marked, as a portion of it is now nearly dry, and no difficulty will be found in passing between it and the mainland, or in avoiding the remaining shoals to the anchorage so long as it is clear weather, as they are then plainly visible. Pilots take vessels over the Carreya Bank, but the water is apt to be too much discolored to allow of the guidance of the ship from aloft, and in consequence this route could hardly be taken without local knowledge. The outer lagoon is admirably adapted to the determination of compass deviations.
Aspinwall.—Approaching from the eastward, a strong current setting to the southward and eastward may be experienced, and it will therefore be well to lay the course well clear of Manzanilla Point. The harbor is so crowded now-a-days that some difficulty may be experienced in selecting a berth that will afford convenient access to the shore.
From Aspinwall to Cape San Antonio, the route generally taken by steamers is to sight Old Providence Island, and passing to leeward of it and of Quita Sueno, to steer due north until abreast Thunder Knoll. If, however, it is deemed advisable to keep clear of Mosquito Bank, the course will be laid between Quita Sueno and Serrana Cay; but while in the former case, fore and aft sail may be set from the moment of leaving port, in the latter it will not probably draw before the 13th parallel is reached, when the trades begin to haul to the eastward. As the trades are apt to be fresh during the winter months, this is an important consideration. From Thunder Knoll to Cape San Antonio a current of a knot or more an hour will be met setting to the northward and westward, but the course should be laid in mid-channel, as under San Antonio the current becomes very feeble. After rounding San Antonio the remarks in the Sailing Directions in regard to the Gulf Stream, if heeded, are sufficient.
New Orleans.—While hardly within the title of this article, a word may be inserted in regard to the jetties at the mouth of the Mississippi. There is a shifting lump of mud outside the entrance of the jetties, and its exact position can be learned only from the pilots. Its approximate position may, however, be learned from the profile maps published each year by the commission in charge of the improvement of the Mississippi passes, which may be obtained upon application to the officer of the U. S. Engineers stationed at New Orleans. The lump is so soft, however, that but little danger may be apprehended from striking it. There is also a shoal patch on the eastern side of the inner entrance to the jetties which may be avoided by keeping over towards the Southwest Pass side.
Matanzas.—The Pan of Matanzas marks the position of this port most unmistakably. In approaching from the westward the shore line may be followed by the eye until Savanilla Point is rounded. Coming from the eastward, the Camarioca Paps will be found about five or six miles southeast of the place assigned them on the chart. But little difficulty will be experienced in entering the bay and in taking a berth, unless it be in the sugar season, when the anchorage may be crowded with vessels. The shoals in the harbor are supposed to be buoyed, but owing to the insecure method by which the buoys are moored, no reliance whatever should be placed upon finding them in position. Moreover, as the buoys are placed inside the shoals, allowance must be made, and they must not be rounded too closely. When a buoy goes adrift, some time may elapse before it is replaced, and then the chances are that a different kind of buoy will be substituted for the one formerly occupying the position.
Maya Point is low and sandy. Upon its extremity is a cluster of white houses with red roofs; these serve to mark the point, which could not otherwise be distinguished from the adjacent shores when abeam. The east shore of the bay is not high, and is covered with a dense growth of underbrush and trees; at the head of the bay the land is low, while the west side is high and almost destitute of trees.
Underneath the slight eminence called Peiias Altas are the celebrated caves of Bellamar, and just to the westward is the suburb of Playa Judia, in which are several summer residences and resorts, painted white, and quite prominent from seaward. In the new city, the railway station, a brick building with a French roof, and the dome of the exhibition building, white, with a cupola, will be noticeable, and the city ends at the San Juan river, in a long blank yellow wall, the rear of sugar warehouses. On the ridge to the northward of Matanzas is the church of Montserrat, overlooking the valley of the Yumuri, a noted spot in Cuban scenery. The church, surrounded as it is by trees, forms a conspicuous landmark from the harbor. Two bridges connect the new city with Matanzas, and adjacent to the upper in the latter city is the market, at a point easily reached by steam launches or other market boats. The suburb of Versalles is connected by a bridge to Matanzas; in it are two noticeable buildings, the church of Virgen del Carmen, a dilapidated yellow structure with towers, and the hospital of Santa Isabel, a large rectangular yellow building, making a landmark easily recognized. An alameda extends along the shore from Versalles, but it is a poor dusty road, lined with stunted trees; some little distance beyond its extremity is San Severino Castle, a small walled fortification of a dingy grey hue, by no means so prominent as might be inferred from the Sailing Directions.
The shoals in the harbor are as marked on the chart, and not as described in the Directions. In standing in, the Sugar Loaf may be steered for on a southwest by west bearing until Maya Point opens south of the Camarioca Paps bearing southeast by east; the reef off Maya Point will then have been passed, and the course may be laid to round Sabanilla Point at a distance of from one-quarter to one-half a mile. By keeping the houses on Playa Judia shut in by Sabanilla Point, Maya Reef will be avoided. After rounding Sabanilla Point the distance from the shore should be increased, but the fringing reef will be plainly visible, and there will be no difficulty in running to the shoals which form the inner harbor. Should this appear to be crowded, anchorage may be had in ten fathoms outside the reefs, to the northward of Bajo Nuevo, the berth generally taken by merchant steamers. It will be smoother, however, and more convenient to anchor inside Laja Bank, and as the latter is plainly visible through its whole extent at all times, no trouble will be experienced in passing around either end of it, even if it be not marked by buoys; the bottom is of stiff clay mud. In all probability more room will be found to the westward and southward of Laja Bank, as merchant vessels are anchored there only when all other berths are occupied, and in this case care must be taken to avoid the banks which extend nearly three-quarters of a mile off the southern shore. The banks here are rocky; the water shoals rapidly from ten to three fathoms, and as its color gives no sign, this part of the anchorage is very generally avoided.
The best landing for boats is on the left bank of the San Juan river just above the first bridge; but care must be taken to select a spot free from submerged piles, driven to protect the bank from the wash of passing tugboats. The stakes marking the channel into the San Juan should be left on the starboard hand, and the left (or Matanzas) bank should be closely hugged at the mouth, as a mud flat extends off the right bank nearly across. Pulling boats may land alongside the pier marked on the chart, but during the sea breeze there is generally some little sea at this point. Bearings true.
Matanzas is about three miles further east than the position given by the chart, or in approximately 81° 34' W. longitude. Before taking observations ashore, it will be necessary to obtain the written permission of the Governor, otherwise one is likely to be interrupted by a guard of soldiers and compelled to retire. Provisions are scarce and dear; coal may be procured in moderate quantities, at from $9 to $10 a ton; water may be had at one cent a gallon, but it is strongly impregnated with lime.
Cay Frances.—The land in the neighborhood of this port is difficult to recognize; but upon standing in, the cays of Santa Maria will open out and distinguish the locality. Cayman is moderately high, and between it and Cay Santa Maria is a small low cay not marked on the chart. The first noticeable mark upon Cay Frances will be several white houses with red roofs at the extreme western end; the spars of vessels at anchor may then be seen, and finally the frame for the light will be distinguished. This light is of feeble intensity, and can be discerned when eight or ten miles off with great difficulty by means of a glass. The distance it is clearly visible is too small to render it of much practical value. The lights at Bahia de Cadiz and Cruz del Padre, on the contrary, are very good ones, visible seventeen and ten miles each respectively.
Cay Sal.—This island is covered with bushes, and on the west side is bordered by white sand beaches, which render it visible in the night time from a distance of 2 to 3 miles. The east point of the cay terminates in a conspicuous bluff of white rock; it makes a valuable landmark, as it may be seen from a distance of ten to twelve miles through the haze from the eastward. The anchorage off the west side is in from 7 to 10 fms., hard sand bottom; in standing in for it, on no account allow the north end to be brought to bear to the southward of east, or the south end to the northward of NE. by N., as both terminate in shoals that extend off for some distance.
The anchorage on the bank to the westward of Anguila Island was, so far as observed, free from obstruction.
San Juan de Porto Rico.—Approaching from St. Thomas, the preferable route is to the northward of Culebra, where the wind is steadier and fresher. The port is rather difficult of access, and it must be borne in mind that the buoys on the western side of the channel are in fifteen feet water. While there is a fair amount of room in the inner harbor, the depth of water is but little over three fathoms, and the channel leading in is narrow, and it may therefore be preferable to remain in the outer harbor. Some swell may be felt there in fresh trades, but this disadvantage is counterbalanced by the foulness of the water and bottom in the inner harbor, caused by the sewerage of the town.
Samana Bay.—Clara Bay affords a good anchorage, though in deep water. A stream of water empties into the bay, from which the ship can be supplied. Santa Barbara is a town of no importance except as a port of call of the Clyde line of steamers from New York to San Domingo City. There is a railway in process of construction from Las Canitas at the head of the gulf, to Santiago, in the interior, eighty miles to the westward.
Porto Plata.—The limited space and the shallowness of the water render this a difficult, if not dangerous port to a vessel of any size. It will perhaps be better to lie off and communicate by means of a boat. If there is not much swell the ship may be brought up with a kedge in from twenty-five to thirty fathoms, hard mud bottom, with Owen Rock bearing west by south, and the lighthouse south by west (true) while communicating with the shore.
Turk's Island.—Approaching from the southward, Sand Cay should be made by daylight, when there will be no difficulty in avoiding Endymion Reef. The bank may be crossed between Sand and Salt Cays, with not less than ten fathoms; this is done regularly by the Clyde steamers, and so far as observed there were no hidden dangers. There is no good anchorage near the town on Grand Turk, but Riding Place perhaps affords more shelter, with better holding ground than any other part of the bank in the vicinity. Riding Place is south of the Commissioner's residence, a prominent house with a flagstaff and outbuildings on the beach south of English Point. Being the only house in the southern part of the island it is easily recognized. To reach this anchorage, run in for the beach about two cables south of the residence on an easterly course; bring Toney Rock in one with the south end of Grand Turk Island, and the flagstaff at the residence to bear N. by E., and drop anchor in five fathoms; this will ensure twenty fathoms of chain being upon the bank, enough to hold a vessel in ordinary weather. While anchored here the ship rode easily to fresh easterly squalls of wind for three days.
Cape Haytien.—A current of from one-half to one knot an hour setting to the westward and northward may be expected anywhere between Hayti and the banks to the northward, and allowance must be made in crossing. The ruins of the palace and citadel of Sans Souci, built by Christophe upon the summit of Mount Milot, some ten or twelve miles to the southward of Cape Haytien, form a good landmark for the port. No reliance can be placed upon finding the buoys in position, but the reefs in the harbor can always be seen when the water is smooth and the sun moderately high; if it be rough, the sea breaks continuously upon the weather side of all but La Trompeuse Most of the marks mentioned in the Directions have become indistinguishable.
Gonaives.—This town lies between two barren hills, Grammont to the south, Bienac to the north. On the southern slope of the latter is a remarkable vertical precipice, which, brought to bear between ENE. and NE. by E. (true), will lead into the bay clear of danger. The ruins of Fort Castries are upon the southern slope of a small hill called Mont Blanc, lying under Bienac; they are overgrown, and unrecognizable until close to, but if the clump of trees on the last mound to the southward, on Mont Blanc, be brought in one with the vertical precipice on Bienac, it will correspond to the mark mentioned in the Sailing Directions. The boat landing is alongside a wharf to the northward of the ruins of a small battery.
Navassa Island.—The settlement and landing place are on the southwestern side of the island, off which anchorage may be had.
English Bay.—Good anchorage, in fresh trades, may be found to leeward of Grosse Cay, in from five to seven fathoms.
Jacmel.—Between English Bay and Jacmel a current of one-half a knot an hour setting to the eastward was experienced close in to the shore. About eleven miles to the westward of Jacmel and just to the eastward of Cape Bayaneta is a town of considerable size; it lies underneath a notch in the mountain range, bearing N. by W., and is a good landmark for Jacmel, for which, owing to the general similarity of the coast as described in the Directions, it might be mistaken. Cape Bayaneta may be recognized by a line of white bluffs of even height; to the eastward of the town is another line of white bluffs, but of irregular height.
Cape Jacmel is a reddish-colored bluff, and the extremity seen from the southwest looks like a detached rock; just to the westward of it are several noticeable white chalk cliffs. Morne Rouge is the westernmost of a series of whitey cliffs; it is red, particularly at the top, and is square-shaped when seen from the eastward, terminating in a long chalky cliff. Patira Island is not easily distinguished.
San Domingo City.—If bound to this port, after leaving Jacmel, advantage may be taken in fresh trades of the current which sets to the eastward along the shore. Occasionally the trades blow a strong gale during the winter months (the season of rollers), and as under such circumstances the anchorage at San Domingo is unsafe, and communication with the shore impossible, it will be better to seek an anchorage under False Cape or Alta Vela, and to wait for the lull which follows. Off Alta Vela strong winds and a heavy sea may be met with, and hence with the ports of San Domingo and Hayti to visit, it might be better after leaving San Juan de Porto Rico to go to San Domingo City first and thence to Samana Bay, especially if the trades were light. The coast line between San Domingo City and Saona Island is imperfectly known, but if a survey disclose no off-lying dangers, the latter plan would no doubt prove the more advantageous.
The chart of the coast between Jacmel and San Domingo City (Hyd. Off. No. 36) is of little use after passing Alta Vela, as the trend of the coast only is given; the position of the ship must therefore be determined by observations. Ranges of hills extend from Alta Vela as far as San Domingo City; one to the northward of the Neiva River is noticeable, as it is to a certain extent isolated. To the westward of San Domingo City there is a high range culminating in a remarkable flat-topped peak; towards Ocoa Bay is a number of irregular conical peaks. As the land to the eastward of the city is low, it will not be seen when approaching from the westward until the city itself is recognized upon the extreme point visible to the northward and eastward. Near Nisao Point, inland, is a sugar mill with a tall, prominent yellow chimney; Torrecilla Point is marked only by the breakers off it. The church of San Carlos, a large yellow building, upon a hill to the westward of the city, is quite prominent; the fortifications are in ruins; the saw-mills marked upon the chart have disappeared, but a dye-factory has been built just to the northward of the sandspit upon the left bank. As remarked above, the anchorage at San Domingo is deemed unsafe owing to the rollers, apparently culminations of a series of waves, which sweep in with dangerous results. The trade is carried on in vessels of sufficiently light draught to cross the bar at the mouth and to enter the river, where they are protected. As the bar is continually shoaling, it is but a question of time when the products of this part of the country will find exit through some other port, probably in the vicinity of Ocoa Bay.
[The Sailing Directions referred to are The Navigation of the Caribbean Sea and Gulf of Mexico, U. S. Hyd. Office 1877, and The West India Pilot, Vols. I and II.]
NOTES ON THE NICARAGUA SHIP CANAL,
As Relocated and Revised by the U. S. Surveying Expedition of 1885.
By Ensign W. I. Chambers, U. S.N.
The President's annual message of last year notified the Congress that a treaty had been concluded with Nicaragua which gave the United States the right to build a ship canal across the American Isthmus within the territory of that Republic, following the most available route from ocean to ocean. Because of his previous service and great interest in this canal and his thorough knowledge of the Nicaraguan country, Civil Engineer A. G. Menocal, U. S. N., was ordered to proceed to Nicaragua to perform certain preliminary labors connected with the surveys already made, to direct particular attention to certain changes in the route which had been suggested as available for shortening the canal and diminishing its cost, and to assist in making clear to the Nicaraguan government the advantages of the treaty to that country. Civil Engineer R. E. Peary, U. S. N., and Ensign W. I. Chambers, U. S. N., were ordered to assist him.
The report of this Expedition may be regarded as a supplement to that of Commander E. P. Lull, U. S. N., of the work done and the results obtained by the U. S. Surveying Expedition in 1872 and 1873, and therefore does not dwell on the full description of the country, the inhabitants and other salient features contained in the latter; but it is voluminous and clear in its narration of the work done and the success achieved by the small party during three months of constant and hard surveying work in that country. As considerable delay is anticipated in reproducing the drawings and photographs of Mr. Menocal's report, it is thought that an abstract of its salient features will be acceptable to the Institute in this number of the Proceedings.
FITTING OUT AND SAILING OF THE EXPEDITION,
The expedition sailed from New York December 20, 1884, arrived in Panama December 30, and while waiting for the U. S. S. Lackawana to prepare for sea, employed the time in examining the progress of work on the Panama Canal.
Arrived at Corinto on January 7, 1885, and in company with Captain A. P. Cooke, U. S. N., and other officers of that ship, paid an official call on the President of Nicaragua, at Managua, who extended a cordial welcome, and emphatically expressed the hope that the American Congress would ratify the pending canal treaty, and that he would be fortunate enough to see the work inaugurated during his administration. Arrived at Grenada January 13, where a force of natives was hired to complete the personnel of the expedition. On the 19th parted company with the officers of the Lackawana, and left Grenada by the regular lake steamer, having been joined by P. A. Surgeon John F. Bransford, U. S. N. Several delays were experienced on the river in making connections with the steamers, but the party arrived at the confluence of the Rio San Juan with the river Sarapiqui, the point of preliminary operations, January 22.
FIELD WORK.
Colonel O. W. Childs in 1850-51 and M. Blanchett in 1879 had proposed to convert the river San Juan, above its junction with the Sarapiqui, into an extension of the lake, by the construction of a dam 74 feet high at that place, thereby reducing the length of the canal excavation, from the dam to Greytown, to 21 miles. Three days of observation at this place established beyond a doubt that to raise the water of the San Juan by a dam at that point was impossible, and that any further exploration at that point would be useless.
The other proposed change consisted in locating a line from Greytown direct to the valley of the river San Francisco and through this valley to the river San Juan. Accordingly camp was moved to the mouth of the river San Francisco, and a transit and level line started up the valley of that stream and one of its principal tributaries coming from a northeasterly direction. This line was pushed with much labor over ground alternately swampy and hilly, and covered with a dense vegetation through which every foot of the trail had to be cut with the machete, and where travelling was fatiguing in the extreme, officers and men being compelled in many instances to go over long distances buried to the waist in mud and water with a very uncertain bottom to stand upon. Systematic reconnoisances were made at all main branches of the San Francisco contained in the basin, and the camp was again shifted up the principal branch coming from the east; from which base a thorough examination was made of the country about its head-waters, and the transit and level advanced across the lowest depression of a "divide" separating them from the waters flowing from a northeasterly direction towards the low lands and the lagoons about Greytown. The instrumental examination of these streams showed very favorable indications for the location of a canal, both on account of their direction and the features of their valleys.
The work of exploring the dividing ridge is referred to in detail in the report, so as to show that the selection of the pass and the location of the canal lines was not decided on in haste, but was the result of a thorough investigation, and mature consideration of all the facts connected therewith. The survey was continued in spite of many privations, hardships and copious rains, down the eastern slope. 12 miles of offsets to the main line were run on either side of the line and the topography of the country thoroughly delineated. The time fixed for the return of the expedition was nearly up, and the line was stopped at a point 29 feet above sea level and separated from the lagoons of Greytown by about 8 miles of low and level country, but this line was afterwards connected by Mr. Peary by running a line towards it from sea level at Greytown, while the work of connecting it from the site of the dam was in progress, and after telegraphic permission had been received to continue the work for another month. The country in the vicinity of the confluence of the rivers San Carlos and San Juan was next examined with a view to finding a suitable site for the dam across the latter, and after a week's exploration an excellent location was made near Ochoa, between two steep and rocky hills on opposite sides of the river, which is here 1133 feet wide, with an average depth of 6.6 feet hard bottom. After careful examination was made to be sure that these hills were spurs of ranges extending to the mountains in the interior, camp was again shifted to a point near this site, and the transit and level line started from the left bank of the river in a northeasterly direction to connect with the previous line in the valley of the river San Francisco. This work was continued with great labor through jungles over the spurs of hills and across extensive swamps for 4 miles into the valley of the west branch of the river San Francisco, when the base of supplies was again shifted to the mouth of that river, and the camp pushed up to within 5 miles of the end of the line. After this the survey was rapidly advanced and the whole instrumental connection completed between the site of the dam at Ochoa and Greytown, a distance of about 30 miles. Numerous observations of prominent ranges and peaks were taken by cross bearings from the tops of high trees in elevated positions on the line, which assisted materially in the delineations of the topography of the country.
The party started to return April 26, 1885, by way of Granada, Leon, Corinto and Panama, at which place while waiting six days for the sailing of the steamer for New York, thorough examination of the Panama Canal in detail was made.
Arrived in New York June 2, and on July 17 commenced the preparation of the extensive maps and plans, the result of their work.
THE PROPOSED ROUTE.
The proposed route extends from the harbor of Greytown on the Caribbean Sea to Brito on the Pacific. Its total length is 169.8 miles, of which 38.98 miles will be excavated canal and 130.82 miles navigation by Lake Nicaragua, the river San Juan, the basin of the river San Francisco, and seven locks.
The Lake (or inland sea) of Nicaragua is about 90 miles long and forty miles wide, and will be connected with the Pacific by a canal, and with the Atlantic by slack water navigation in the river San Juan, by a short section of canal from the river San Juan to the basin of the river San Francisco, navigation through this basin, and by a canal thence to the Caribbean Sea.
The route has been divided into three Divisions: the Western, the Middle, and the Eastern.
The Western Division extends from the western shore of the lake to the port of Brito on the Pacific, a distance of 17.27 miles. It leaves the lake at the mouth of the river Lajas, the channel of which it follows for about a mile and a half, and then crosses a plain three-fourths of a mile wide and enters the valley of the Guscoyol, a small tributary of the Lajas, proceeding from the summit, which it follows to the highest point, 4.7 miles from the lake and 41.4 feet above its surface, a valley about two miles wide. The line then descends at the rate of about nine feet per mile over a moderately undulating country, and in one and three-quarter miles meets the Rio Grande, a large mountain stream which drains an extensive area of the eastern slope of the Cordillera. This stream is to be diverted into the lake, through the river Lajas, which is also to be diverted, so as to have its channel free for the canal. The line of the canal then follows the valley of the tortuous Rio Grande by curves 4500 and 4000 feet radii, and in about one and a half miles it frees itself from the hills on either side and runs through a broad valley as it curves towards Las Serdas. This point is 8.94 miles from the lake, and is the junction of this route with that of the Rio del Medio, recommended by the expedition of 1872-73. Beyond Las Serdas the canal follows the valley of the Kio Grande with an average inclination of nine feet to the mile for a distance of 8.33 miles to Brito. Along this section the canal cuts projecting bends of the river at four different points, artificial channels being in those cases provided for the river.
It is proposed to pass the Tolo river and several small watercourses across and under the canal, as the bed of the river is at all points—between Las Serdas and Tolo—several feet below the water in the canal, and seven waste-weirs are proposed for the discharge of surplus water. Ditches are proposed along the lower portion of the canal to intercept the surface drainage and convey it to the sea. To descend from the level of the lake to that of the sea at Brito, four locks are proposed, the lower of which may be situated one and a quarter miles from the harbor, which distance is practically an extension of the harbor, where ships may lie or pass each other.
The other locks are located with advantage to foundations and economy in excavation, the lifts for all four being 26.4 feet, 29.7 feet, 29.7 feet, and 24.2 to 33.18 feet, respectively, the variable lift of the latter being due to variations in the state of the tide at Brito.
The Middle Division extends from the western shore of the lake to the western slope of "the divide" between the basin of the river San Francisco and that of the river Sanjuanillo. The total distance is 133.05 miles, and maybe divided as follows: Lake navigation 56.5 miles, navigation by the river San Juan 64.54 miles, navigation through the basin of the San Francisco (including three short sections of canal, amounting to three miles) 12.01 miles. The lake navigation extends from the mouth of the river Lajas to the head of the river San Juan at Fort San Carlos. At the mouth of the Lajas some rock excavation and dredging will be required for a distance of 2000 feet. From this point on the west side of the lake to within eight miles of its outlet it is deep and free to navigation. In those eight miles, dredging in soft mud to a depth of three and a half feet will be required to secure the proposed depth of 26 feet. Along that distance a channel 150 feet wide at bottom has been estimated for. It is proposed to obtain slack water navigation at the river San Juan by the construction of a dam 52 feet high at Ochoa, 64 miles from the lake, and with a fall of three-quarters of an inch to the mile for that distance; that portion of the stream will be practically an extension of the lake, where, with the exception of the first 28 miles, from the lake to Toro Rapids, the navigable channel will be at no point less than 1000 feet wide, with a depth varying from 28 to 130 feet. Between the lake and Toro Rapids, rock blasting under water and dredging to a mean depth of cut of four and a half feet will be required at several places, amounting in the aggregate to 24 miles. The average depth of water as raised by the dam over the shallow places where deepening has been estimated for is 26 feet deep by 125 feet wide at bottom.
The dam is located between two steep and rocky hills, and its effective length on the crest will be 1255 feet. The mean depth of water in the river at this site is but 6.6 feet and the maximum 17 feet close to the right abutment, and rock underlies the gravel and sandy bottom. The foundations have been estimated at 20 feet below the surface of the water throughout the whole distance and across the entire body of the dam, to be of cement concrete, with a wood lining on top and lower side. A strong apron is proposed to prevent undermining by the fall of the water.
On the left bank of the river immediately above the dam, a break in the hills forms the valley of the small river Machado, and just in the rear of the range, the last spur forms the right abutment of the dam. Another narrow valley extends easterly from that of the Machado. The first valley offers an excellent entrance to the canal, free from the influence of river current; and the latter has been taken advantage of for a distance of 3300 feet, as a portion of the canal itself. From the head of this valley the canal cuts across a broken country of moderate elevations confined by high hills, then soon falls into a deep narrow ravine discharging into the San Juan, where a short embankment is proposed, so as to preserve the summit level in the canal. In a distance of 1.82 miles from the beginning of the cut at the entrance valley, the canal enters the basin of the river San Francisco, which it follows to the foot of "the divide" and the end of the Middle Division. It is believed that this basin extends from the base of the divide to within one and three-quarter miles of the valley in rear of the dam at Ochoa, and that by making a short detour to the north of the line of survey, it will be freely navigable throughout that distance. It is proposed to retain the summit level as established above the dam, throughout this basin, by an embankment 6500 feet long on the crest and 51 feet maximum depth, connecting the ranges of hills which confine the waters of the San Francisco. This deep broad basin is regarded as a striking feature in this route, not only from economical considerations, but because it affords unrestricted navigation for 8.5 miles, and presents a favorable solution of the important problem of drainage. The water in this basin, which does not pass through the locks in the Eastern Division, will either back through the canal into the river San Juan and over the dam, or discharge over a waste-weir 1000 feet long cut through the hill at the southeast extremity of the embankment. There will also be cut through this same hill, for use in emergency, a tunnel controlled by gates, and large enough to discharge the whole flow of the San Francisco in floods, or even empty the basin if necessary.
The Eastern Division completes the line of canal to Greytown, a distance of 19.48 miles. Within this distance is comprised 63 per cent, of the total excavation, and 61 per cent, of the total cost of excavation for the entire canal, and being an entirely new location, with essentially new features, merits a full description.
Beginning at the eastern extremity of the proposed inland lake in the San Francisco valley, the canal runs nearly due east through a broad flat valley, a distance of about 1600 feet, the average elevation being 125.1 feet above sea level, or 19.13 feet above the level of the canal. Thence across projecting spurs, "the divide" is reached at an elevation of 280 feet in a distance of 4600 feet from the before-mentioned basin of the San Francisco. The line then curves with a radius of 10,733 feet for a distance of 2500 feet across the little plain at the summit, cuts a steep narrow spur, enters the valley of a stream flowing towards Greytown, called Deseado, the bed of which it follows a short distance, then across to the left bank of that stream, and reaches the site of Lock No. 3, in a rocky spur of the northern hills 14,200 feet distant from the canal level on the other side, the average cut for this distance being 119.5 feet above the water in the canal.
The summit level stretching from Lock No. 4 beyond the lake—a distance of 144.8 miles—ends at Lock No. 3, where the level of the canal drops 53 feet through the solid rock. Passing by easy curves of 4800 and 5280 feet down the winding valley of the Deseado, Lock No. 2 is reached 4600 feet from Lock No. 3. This lock drops the canal 27 feet, and at this lower level it passes along the still widening and gradually sloping valley of the Deseado in a northeasterly direction, a distance of 1500 feet, to Lock No. 1, which lowers it 26 feet to the sea level, and from which it crosses the flat basin of the San Juanillo, cutting that stream in several places, and passing through the swamps of the lagoon region to the harbor of Greytown, a distance of 6100 feet, the average height of surface above tide level from this latter distance being 10.5 feet.
The drainage area occupied by the canal of the southwestern side of "the divide" is very limited, and the waters by means of two short channels will be diverted into the basin of the San Francisco. On the northern and eastern sides of the divide to a point within 4000 feet of Lock No. 3, the natural drainage is away from the canal, the Deseado flowing nearly parallel to and from 500 to 1300 feet north of it. At this point the Deseado will be divided by a channel north of the canal, and from here to its last intersection with the canal, a distance of 43,000 feet, the latter will be protected on both sides by drainage channels formed partly by the present bed of the stream and partly by artificial ditches. The remainder of the canal, also about 43,000 feet, from the Deseado to the sea will be protected by embankments, an artificial channel being cut south of the canal to divert the river San Juanillo, and another north of the canal to give Laguna Bernard and its tributaries an independent outlet to the sea.
Through the "divide," rock underlying a few feet of earth may be counted upon the entire distance; from Lock No. 3 to Lock No. 1, loose earth, gravel, clay and rock in the deeper cuts; while from Lock No. 1 to Greytown, a distance of 12 miles, nearly if not all material will be dredgable. This latter portion (12 miles) of the canal, from the lowest lock to the sea (as at Brito), may be regarded as practically an extension of the harbor.
DIMENSIONS OF THE CANAL.
The apparent insufficiency of the Suez Canal to accommodate a traffic of more than 6,000,000 tons a year without serious delay to navigation, due to its reduced sectional area and an inadequate number of turnouts, shows that the dimensions proposed in previous reports for a canal across Nicaragua should be considerably enlarged. It is proposed now, not only to enlarge the water prism of the canal, by increasing its width and depth, but to provide also two large basins at the extremities of the locks where vessels can wait or pass without delay. These turnouts, together with the lake, the river, and the San Francisco basin, will greatly facilitate navigation by this route, and allow ships going in opposite directions to pass each other at almost all points. These modifications will necessarily involve an increase in the estimated cost of the canal, but it has been thought best to provide for the unrestricted passage of the largest vessels of commerce, and a traffic of not less than 12,000,000 tons per year.
The following are the respective dimensions and salient features of the canal proposed in 1872-73, and that herein estimated for:
FEATURES COMPARED.
| Location of 1872-73 | Location of 1885 |
Total distance (Greytown to Brito) | 180.76 miles | 169.8 miles |
Length of actual canal or cutting required | 61.7 miles | 40.3 miles |
Height of summit level above mean sea level | 107 feet | 110 feet |
Length of summit level | 102 feet | 144.8 feet |
Number of dams | 4 | 1 |
Number of locks | 21 | 7 |
Length of lock chamber | 400 feet | 650 feet |
Width of lock chamber | 60 feet | 65 feet |
Number of curves in actual canal | 26 | 14 |
Minimum radius of canal curves | 2200 feet | 4000 feet |
Length of canal in curves | 12.2 miles | 10.8 miles |
Depth of water in canal | 26 feet | 28 and 30 feet |
Width of bottom in that part of San Juan where dredging is required | 80 feet | 125 feet |
Do. Lake Nicaragua | 80 feet | 150 feet |
Do. rocky cuts | 72 feet | 80 feet |
Do. deep earth cuts | 50 feet | 80 feet |
Do. terminal cuts | 72 feet | 120 feet |
Time allowed to pass through locks alone, allowing for old design, 30 minutes; for new design, 45 minutes | 10.5 hours | 5.3 hours |
Turnouts at extremities of locks 650 feet by 150 feet at bottom | None | 12 |
Time required for ship to pass from Greytown to Brito | 37 hours | 30 hours |
Estimated cost (computed on same basis) | $52,577,718 | $39,040,134 |
Estimated cost according to new dimensions and increased prices |
| $51,234,958 |
Provision has also been made for illuminating the whole route sufficiently to insure safe navigation at night. Greater speed can be made in the canal both on account of its enlarged dimensions and the protection of the slopes by stone pitching wherever necessary. Several bends in the river have been cut off, and easier navigation thereby secured.
THE LOCKS.
The proposed locks have a uniform length of 650 feet between gates, and a least width of 65 feet between the gate abutments. Locks Nos. 1, 2 and 4, 5 and 6 have lifts of 26 feet, 27 feet, 26.4 feet, 29.7 feet and 29.7 feet respectively. No. 3 has a lift of 53 feet, and No. 7, being a combination of tide and lift lock, its lift will vary between 24.2 feet and 33.2 feet, depending on the state of the tide. No. 3 will be cut out of the solid trap rock and the rest made of concrete, and all locks will have a heavy timber lining from top of walls to 15 feet below low water level. Cribs or fender piles will be placed at the approaches, and provision has been made for making ships fast to floats in the lock walls, so that the lines may rise or fall with them, and thus preserve an equal tension on the fasts. Each lock will be filled or emptied by two conduits, each ten feet in diameter, extending along the sides of the locks from the upper to the lower reach of the canal, and 22 branch culverts, eleven on each side, connecting them with the lock chamber. Each main culvert will have an upper and a lower valve or gate to admit or to exhaust water. The time required to fill or empty Lock No. 3 will be 15 minutes, and the others an average of 11 minutes. Two styles of gates have been designed, one sliding and the other rolling, both capable of being worked quickly and safely, while providing economy of space and power and facility of removal or repairs, with strength, simplicity and economy of cost.
CAPACITY OF THE CANAL.
In order to estimate with a fair degree of precision, both the traffic-carrying capacity of the canal and the time of transit, the report compares the dimensions of the Suez Canal with those of the proposed canal. It shows that vessels of 4400 tons, 400 feet long, 52 feet beam, and drawing 22 feet of water, can go through the Suez Canal with an average speed of 6 statute miles per hour, and that the speed of smaller vessels varies between 6 and 8 miles per hour. A table is added showing the dimensions proposed for the Nicaragua Canal in the several sections into which the route has been subdivided, which is taken as a basis for computing the traffic-carrying capacity of the canal and the effective sailing time from ocean to ocean. An inspection of this table shows that in 22.37 miles, or 57 per cent, of the excavated canal, the prism is large enough for vessels in transit to pass each other, and of a sectional area in excess of the maximum in the Suez Canal. The remaining distance in which large vessels cannot conveniently pass each other is so divided that the longest is only 3.67 miles in length. That, with two exceptions, those short reaches of narrow canal are situated between the locks, and can be traversed by any vessel in less time than is estimated for the passage of a lock; consequently, unless a double system of locks be constructed, nothing will be gained by an enlargement of the prisms. The exceptions referred to are the rock cuts through the eastern and western divides, 2.58 miles and 3.67 miles respectively. Both the bottom width and the depth of the proposed canal are larger than those of the Suez Canal, even in these two short cuts.
In the lake and in the greater portion of the San Juan, vessels can travel as fast as at sea. In some portions of the river the speed may be somewhat checked by reason of the curves.
ESTIMATED TIME OF TRANSIT.
(Maximum.) | Hours. |
38.98 miles of canal (at 5 statute miles per hour) | 7.48 |
8.51 miles in basin of San Francisco (at 7 statute miles per hour) | 1.14 |
64.54 miles in San Juan River (at 8 statute miles per hour) | 8.04 |
56.50 miles in Lake (at 10 statute miles per hour) | 5.39 |
For passing 7 locks (45 minutes each) | 5.15 |
Allow for detention | 2.00 |
Total time | 30.00 |
The traffic of the canal is limited by the time required to pass a lock, and on the liberal basis of 45 minutes above estimated, and allowing but one vessel to each lockage, the number of vessels that can pass in one day will be 32, or in one year 11,680; which at the average net tonnage of vessels passing the Suez Canal, will give an annual traffic of 20,440,000 tons. This is on the basis that the navigation will not be stopped at night. With abundant water power at the several locks, at the dam, and through the "divides," there is no reason why the whole canal should not be sufficiently illuminated by electric lights, and with beacons and range lights in the river and lake, vessels can travel at all times with perfect safety.
MATERIALS OF CONSTRUCTION.
Considerable space is devoted to showing the abundance of fine timber for all purposes, the prevalence and quality of the rubble masonry and cement of the country, the excellent quality and great quantity of granite, trap rock and brick clay for construction purposes in the country throughout the line of the canal.
CLIMATE, RAINFALL AND HEALTH.
Numerous statistics and authoritative opinions are quoted, to show the average temperature and rainfall, and that the climate is comparatively healthy. Not one of the party was affected by sickness due to climatic influences, although its work was confined to what is generally regarded as the most unhealthy portion of the country.
WATER SUPPLY.
Some space is devoted to showing from careful observations, that the supply of water from the great inland equalizing reservoir, Lake Nicaragua, will be more than ten times enough at the lowest and driest state to supply the traffic of the canal at 32 lockages per day.
HARBORS.
No changes are proposed in the methods submitted in Captain Lull's report for the improvement of the harbors at the termini of the canal; but the change of location of the tide lock near Brito to a place 1.4 miles inland, will simplify the difficulties at that place and will render a large bay for the accommodation of vessels at anchor unnecessary.
THE ESTIMATES.
The estimate of the cost of the canal has been prepared after careful computations of all the works required for the completion of the canal and its accessories, from data obtained by an actual instrumental location of the line, after searching examinations and a full appreciation of the topography of the country. The surveys have been conducted with the utmost care, and sufficiently in detail to insure a close estimate of the cost of the work. The estimate is complete in its attention to all the details necessary to equip and complete the work. The prices adopted are believed to be sufficient to cover the work under any possible unfavorable circumstances, if controlled by an intelligent and business-like management. It is estimated that the canal can be completed in six years, and will cost, including a contingent of 25 per cent, added, $64,043,697.
Eleven sets of drawings, a report on the geological specimens collected by the party, and 56 photographs of interesting features in the country, accompany this report.
REPORT ON BAIRD'S STEAM STEERING GEAR.
U. S. Navy Yard, Washington, D. C,
December 29, 1884.
Sir:—In obedience to your order of December 2, 1884, the Board has carefully and thoroughly examined the plans and working model of the Steam Steering Apparatus designed by P. A. Engineer Geo. W. Baird, U. S. N., and submit the following report:
The device consists essentially of a hollow metallic drum as shown at A, Fig. I, on the accompanying cut, part in elevation and part in section, supported on suitable bearings B B, and fitted at one end with a hand-wheel C, and at the other with an ordinary cycloidal or friction gear-wheel D. The gear-wheel D works into a corresponding gear-wheel E, firmly secured to a shaft that receives its motion from a pair of engines with cranks set at right angles. On the prolongation of the axis of the drum a screw thread is cut and fitted into a nut F, to which is attached the end of a floating lever G, that operates the piston reversing valve H, for admitting steam to the engine. A nut is connected to the middle of the lever G, in which the screw K is turned by means of the gear-wheels L and M, which receive their motion through the shaft N, from the steam hand-wheel O. The reversing valve H is fitted with only sufficient lap to insure a complete closure of the steam and exhaust ports when it is in its middle position. When the device is properly adjusted for its work, the reversing valve H is in middle position, the nuts F and I are in the middle of the lengths of the threads on which they work, and the floating lever G is normal to the axis of the drum, while the tiller is amidships and the wheel ropes are wound tightly around the drum A in the usual manner.
The following is its mode of action:
The hand-wheel O being turned in any required direction, gives a corresponding motion to the reversing valve H, through the intervention of the shaft N, gear-wheels L and M, and the nut I on the screw K. When the valve H is opened the engines are set in motion, and through the gear or friction wheels D and E, revolve the drum A, upon which the tiller ropes are coiled. But when the drum A revolves, the nut F moves along its thread and carries with it the end of the floating lever G, in a direction to stop the engine.
The parts are so proportioned that whatever angle of motion is given to the hand-wheel O, it will immediately be followed by a corresponding motion of the drum, and the engines will automatically stop by the closure of the reversing valve when the same angle of motion has been reached; and in the case of a sea striking and carrying the rudder with it through any given angle, the drum will be caused to revolve through a corresponding angle by means of the wheel ropes, and thereby open the reversing valve and start the engine as soon as the excessive impact of the sea has expended itself, and will again stop automatically when the rudder is brought to the angle indicated by the hand-wheel.
The small working model, which was tested by steam, was fitted with ordinary cycloidal gear-wheel for communicating motion to the drum from the engine shaft, which received its motion from the two small oscillating cylinders.
The whole arrangement was neat, compact, and accessible in every part, and worked with rapidity and certainty. In case of derangement or accident to the steam mechanism, provision is made for disconnecting it by fitting the key P so that it can be readily withdrawn to allow the drum A to revolve freely within the gear-wheel D as a bearing; the device then becomes an ordinary steering gear with C for a hand-wheel. The design embraces some modifications of the detail which are not essential to the effective working of the device, but may be regarded rather as a matter of convenience or individual choice; such as the employment of a single wheel fitted with suitable clutches for both steam and hand steering, and either the use of the ordinary cycloidal gear-wheel or the noiseless friction wheel for transmitting the power to the drum.
When the latter is employed, provision is made for taking up the wear of the friction wheel by resting the bearings B and B on keys or wedges as shown on Fig. 2, that can readily be backed, and the friction between the faces can then be regulated to any desired amount by setting on the cap-bolt nut. In the opinion of the Board the device is simple and ingenious in design, consists of few parts, is not liable to get out of order, and acts with celerity and precision; again, as the parts of the steam-steerer are so proportioned that the movement of the steam hand-wheel is identical with that of the ordinary steering gear, any one who can steer a vessel with the ordinary wheel can have no difficulty in steering with the device, however unfamiliar he may be with the manipulation or use of machinery.
Although the Board is of the opinion that the Steam Steerer in question will be found upon trial to be a valuable and reliable device for the purpose for which it was designed, yet it cannot recommend its purchase for use in the Naval Service until it is proved so to be by a thorough practical trial in steering a vessel under different conditions of wind and sea, and to that end the Board recommends that a Steam Steerer, of the above design, be purchased and fitted on board some sea-going vessel of the Navy for trial. We are, sir, very respectfully, your obedient servants,
David Smith, U. S. N.,
Chief Engineer.
A. Kirby, U. S. N.,
F. A. Engineer.
Commodore A. A. Semmes, U. S. N.,
Commandant.