There is no new thing under the sun
The problem of anchoring in a designated spot usually involves only the placing of the bow of a ship over the required location and the dropping of the anchor when the bow is in Position. Normally this is a simple exercise in seamanship and navigation. The captain of one of the large battleships, or one of the plane carriers, in a ship of 33,000 tons with a draft of 32-34 feet has another factor to consider whenever he attempts to anchor in an assigned berth. Like every other ship captain, he must put the bow of his ship over the designated spot and let go the anchor when the bow is in the correct position, and, in addition, he must so regulate his approach to the anchorage that his ship will be practically "dead in the water" when the anchor is dropped. It is imperative that the commanding officer of one of these large ships know the exact distance and course at all times if he is to so regulate his approach as to reach his position in the desired manner. The problem, then, becomes one of plotting instantaneous bearings so that the position of the ship is definitely known at all times during the approach.
The four anchoring diagrams appearing on pages 69-72 were developed on board the U.S.S. Lexington for the use of that vessel. No new principle is involved but it is believed that this method gives the captain the required information more quickly than other methods in common use. This scheme was devised by E. H. Belknap, Chief Electrician, U. S. Navy, while W. J. Lafferty, Quartermaster 1c, U. S. Navy, did the drawing and suggested refinements in the method which have led to its usage in navigation in restricted waters as well as in anchoring problems.
The problem is the establishing of the position of the ship by three cross-bearings. This is effected by stretching “three strings from fixed objects at known measured angles” of corresponding arcs and observing where the intersection of strings on the anchorage chart takes place. This can be done as fast as the bearings are called out.
San Pedro chart C.S. 5143, berth X-4.—This chart or a section of it is secured to a drawing board. The bearings of the berth are San Pedro Breakwater Light 249.5° true, Long Beach Breakwater Light 310 true, Tower Villa Riviera Hotel 006° true. The berth is plotted. Around this spot anchoring circles are drawn as follows: At distances of 100 yards for the first 600 yards; at 750 yards; at 1,000 yards. From 1,000 to 4,000 yards circles are drawn at each 500 yards. One hundred yards is used as the distance from the bridge to the hawse pipe. The drop bearings are next established for the 100-yard anchoring circle. For the Lexington these are San Pedro Light 250° true, Long Beach Light 312° true, Tower Villa Riviera Hotel 006° true.
Compass arcs at different radiuses to avoid interference are drawn, with the navigation objects selected, as the center of each arc. Another compass arc is drawn with the plotted anchorage as the center. This arc provides the courses to the anchorage. A few radial bearing lines drawn through this arc will greatly assist in determining the course and any set or drift which may occur.
Two sets of small brass weights are constructed (see illustrations). One anchor is fixed and is centered accurately over each navigational object by a pin through its center. The other anchor is portable and it also has a small pin through its center. The two anchor pins are connected by a silk or linen thread. Each pair of anchors provides a line of bearing or a position line. The third line of bearing is provided by securing a rubber band or line to a thumb tack. This line may be stretched through its arc, or it may be led around the pin inserted in the center of berth and carried through the compass rose of the anchoring circles for a compass course. This line may be quickly released at any time convenient to the navigator and removed to avoid any possible congestion.
Sometimes, owing to frequent changes of courses and large variations in speed, especially when backing, the gyrocompasses suddenly jump, i.e., leave the meridian. It is then that errors of one or more degrees appear. The present method indicates definitely and accurately the amount of error and the direction.
When an error develops in compasses it is well known that instead of perfect intersection in a three-point fix, a triangle will be formed. The size of the triangle determines the amount of the error, and the location of the triangle relative to the initial bearing to the anchorage determines the direction of the error providing the course remains the same for about 2 or 3 plots. If the triangle remains to the right of the initial bearing, the error is easterly; if it is to the left, the error is westerly. This follows the old rule “True right East, True left West.” In other words, an easterly error plots the position to the right of the true position, while the westerly error plots to the left of the true position. Navigators can soon judge by the size of the triangle the amount of the compass error.
Restricted water diagrams.—The above method has been extended as shown on pages 70-71, by simply drawing additional arcs for any navigational objects required to obtain fixes. This operation requires some previous preparation. The pelorus operators are informed, before the approach of the passage, of the objects required for bearings as this avoids possible confusion. Three navigational marks should be sufficient for any position.
The advantages of this method over others are: (1) The simplicity and rapidity by which bearings may be plotted with accuracy; (2) the means of keeping a continuous position plotted on a chart as demonstrated by the transit of Rich Passage (see page 70); (3) the rapidity and accuracy of determining gyrocompass errors.
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Ships work for their own countries, just as railroads work for their terminal points. From every standpoint, it is unwise for the United Stales to rely upon the ships of competing nations for the distribution of our goods.—Theodore Roosevelt.