For many years the problem of obtaining a satisfactory compass for naval vessels, especially for use as battle compass, has been one beset with all manner of difficulties. In order to avoid errors caused by masses of iron and steel about the compass, chart houses, bridge rails, fittings and instruments on the bridge or in the vicinity of the compass have been made of brass or other nonmagnetic material. If the compass is to be below in some protected position, it is naturally surrounded by various masses of metal. With all precautions that seem to appear feasible, it has been impossible to secure a satisfactory magnetic compass that can be used in the conning tower or central station of a battleship, or below in a submarine. Even those compasses which are above decks, on the bridges and steering stations, are very erratic under battle conditions. Electric alarms, distant control, search-light appliances, telephones, etc., when near the compass, affect it in various ways; while the shock of firing guns and the training of the turrets throw the compasses off to a very material extent.
To conduct accurate battle maneuvers with a fleet, an accurate and reliable compass is essential, in order that courses may be steered exactly and that each change of course may be exact. Likewise, in taking bearings for tracking or plotting the position of the enemy, accuracy of compass is a prime necessity. Applying corrections for compass error is always a disconcerting operation, and opportunities for applying corrections in the wrong direction are always present. Especially is it necessary to have an accurate compass at conning tower or other ship-control station; but with the magnetic compass it seems hardly to be possible.
The development of the gyroscopic-compass so that it has reached the stage of commercial practicability gives us promise of a remarkable step in advance in securing an accurate and reliable compass, that will enable courses to be steered with precision and bearings taken accurately while ship is swinging, as well 2when she is on her course, and will permit these bearings to be immediately plotted, without loss of time or opportunity for misapplying corrections.
The principle of the gyroscopic compass is in brief general terms as follows: A gyroscope set rotating and freely suspended will eventually take a steady position of equilibrium with it; axis parallel to the axis of the earth, and its direction of rotation the same as that of the earth. This can be shown by taking a small toy gyroscope and, while it is spinning, moving it in a circular path. The axis of the gyro will take a position in the meridian with reference to the circular path in which the gyro is moved, and if the motion is reversed the gyro will immediately tumble and thus make its direction of rotation that of the movement to which it is subjected. A gyroscope once in the meridian will resist any force tending to move it out of this position, the resistance increasing with the size of the gyro and the speed of the revolution. Thus any gyroscope of sufficient size and speed of revolution might be used as a compass. The larger the gyroscope and the greater its speed of revolution, the more directive force will such a gyroscope possess.
In order to secure good directive force the gyroscope must have a high speed of revolution and be of fair size; but sufficient directive force can be obtained with practical running speeds, and without
making the apparatus cumbersome.
The Sperry gyroscopic compass uses the principle of the gyroscope, but the practicability of its use lies largely in the mechanism for showing the headings without bringing any appreciable force upon the gyro. This apparatus has been the result of years of study and experiment.
The following is a brief description of the apparatus, the description being assisted by several views of the compass and its accessories.
The apparatus consists of a master compass, repeating compasses, the motor generator and switchboard. The master compass, with attachments, is shown in Figs. 1 and 2. The gyroscope is driven by an alternating motor and is included in the gyroscope case. This gyroscope is well protected by its case and is suspended by a piece of pianoforte wire. The gyroscope is operated at a speed of 8000 revolutions per minute. The gyro carries a pointer and contact maker which moves over a contact circle: and as the heading changes, the contact circle moves over this pointer contact maker and this brings into operation the azimuth motor (shown at top of apparatus), which brings the compass circle around to correspond to the position of the gyroscope. It is really only an electric follow-up gear.
The contact circle, compass circle, motor, etc., are carried in gimbel rings, and the apparatus is suspended by springs from some part of the ship's structure. This can be seen from the photograph. The only force exerted by the gyro is to move the contact maker, and this force is practically nil, and there is thus no tendency for the compass to lag and the compass is sensitive to even very small changes in heading. There is a correction made for the speed of the vessel. This correction is very small and only amounts to about two degrees for a difference of thirty knots. The speed correction is made by means of a cam which slightly changes the position of the compass circle. The adjustment is made by moving a pointer over a dial.
The heading by master compass is communicated to the repeating compasses by an electric step-up apparatus; the connection being made at the edge of the compass circle, and it is put into operation as the heading changes. The exact heading of the master compass is by this apparatus given to the compass card of the repeater compass. Repeating compasses are connected by means of a two-wire cable, and as many repeating compasses as may be deemed desirable can be connected, and they can be located anywhere. The repeating compass consists of a small bowl containing the step-up motor, which operates a compass card similar to the card used on magnetic compasses. This card can be seer in Fig. 3. The mechanism of the repeating compass is small and simple, and it is easily portable, the cable being the only attachment required.
For furnishing the current for the motor and alternator, there is a motor generator set, mounted on a common base, and this with a small switchboard completes the apparatus. The electric power required is very small, only a few amperes. An attachment is also made for operating the gyro in a vacuum. Operating in vacuum materially reduces the power required for operation.
The master compass is located below decks in some well-protected position, and adjacent to it are placed the motor generator set and the compass switchboard. At installation the apparatus is adjusted, and the adjustment once being made, the compass can be stopped and started as desired.
In order to avoid a large number of vibrations past the meridian, and to hasten the settling of the compass in the meridian, a dampening device is fitted. This allows the compass to come to rest in the meridian with but a few vibrations across it. Means for lubricating the various bearings are provided. Spare azimuth motors, and motors and parts of repeating apparatus, can be fitted without disturbance of the gyro.
Starting Compass.—The compass is put in operation by starting the gyro motor. When all connected up and motor generator in operation, this is done by simply throwing a switch. If the compass is set so as to be approximately in the meridian, it will adjust itself so as to point true north in a few minutes. If started ninety degrees away from north, it will require about two hours to get settled down on true north. After having settled down in the meridian, it will remain there as long as kept going In port, whenever the compass is not wanted it can be shut down and started again before getting under way. The compass can be started from any heading it may be on, and will itself find the meridian. If it is started near the meridian, it will adjust itself much sooner than if started from a position away from the meridian.
The gyroscopic compass is subject to no magnetic influence whatever. It can be located anywhere, and any mass of magnetic material can be moved about it with impunity. Variation is eliminated, and there is no change due to change in longitude, temperature or heeling. The compass always points true north. The master compass can be mounted at or near the center of motion of the vessel, and, as it is suspended by springs, rolling and pitching have no appreciable effect upon it. There is no heeling error and the compass maintains its heading steady while rolling, and is sensitive only to actual changes in course. The repeating compass is not affected by either its position, motion, or surroundings; it can be placed or moved anywhere as long as it has its cable connected.
Points of Advantage in Use
The following points of advantage in using this compass readily appear.
(1) Steadiness.—As long as the course is not changed, the compass does not move. Rolling, pitching, or vibration do not cause the compass to move, and there is no vibration or swinging of the compass. The helmsman can thus keep right on his course to a degree of exactness never to be approached with the magnetic compass. For fast vessels the exact steering of courses is most important and may make a material difference in the actual space traversed by the vessel.
(2) Reliability.—As the compass points true north and is not subjected to any magnetic influences either in or outside of the vessel, and simply depends upon keeping the gyroscope in motion, there is practically nothing to throw the compass out.
(3) Adaptability and Flexibility of Location.—The master compass is placed below in some well-protected place, but the repeating compasses can be placed anywhere and in any position, and can be moved from one position to another at will. For plotting work the compass can be put right on the plotting board and any bearing plotted directly from it.
(4) Accuracy.—All courses can be steered accurately without having to look up the deviation or variation. All changes in course can be made exactly without running the risk of introducing errors in deviation or variation.
(5) Safety of Compass Installation.—The master compass being in a thoroughly protected position, there is no danger of having the compasses knocked out by shell fire or other damage to the vessel. Repeating compasses can be connected in anywhere, and can be shifted from one place to another, and all these compasses will read alike and are accurate.
(6) Recording Feature.—A continuous recording apparatus can be attached to the compass, and from such a record the course actually steered and any variations in course are recorded. Such a record will be of great value when running in a fog, in night attacks, etc.
One class of naval craft in which it has been especially difficult to obtain a satisfactory magnetic compass is the submarine. On these craft the compass must necessarily be close to many sources of magnetic disturbances, and hence the magnetic compass is unsatisfactory. The gyroscopic compass overcomes all such difficulties that have here been found. The master compass can be located below, and the commanding officer can carry a repeating compass around with him from whatever position he may be handling the vessel.
The Sperry gyroscopic compass has been exhaustively tested and experimented with ashore. It has been tested on the merchant steamer Princess Anne, and has also been tested on several naval vessels. These tests have shown it to be an entirely practical apparatus and an accurate compass. The compass is now being manufactured on a commercial basis, and the principal field for its use will no doubt be naval vessels and the large passenger and freight vessels.