place and the compass can be corrected for the magnetism in this iron. But what happens now if you come up to take the wheel with a jackknife or a bunch of iron keys in your pocket? This knife and any iron you have in your pockets will contain magnetism and will draw the compass away from the true magnetic north. Your compass will be in error and you may steer the ship onto the rocks. Therefore, never go near the compass with any iron or steel on your person. All our big ships and submarines and many of our destroyers now have gyrocompasses as well as magnetic compasses. The gyrocompass is a heavy wheel made to revolve about 8,000 revolutions per minute by means of an electric motor. By a combination of a weight attached to this gyro and the revolution of the earth the axis of this gyro points to the true north pole. This compass, then, does not depend on magnetism at all. It is usually placed in the safest part of the ship, far below the water line. Repeater compasses, which are simple compass cards with electrical connections to the gyrocompass, are placed near the wheel and in various parts of the ship. These repeater compasses are operated by and show the same readings as the gyrocompass. RELATIVE BEARINGS Lookouts always report anything they sight to the officer of the deck by relative bearings from the ship. There are 32 points to the circle or 16 points from ahead to astern. Figure 64 shows the relative bearings on the starboard side. They are the same for the port side, merely changing "starboard" to "port." CHAPTER 14 VISUAL SIGNALS 1. All men must know how to signal by means of semaphore. You will often be called upon to use the semaphore system, especially if you stay in the seaman branch. This is a rapid system of signaling and is used principally for fairly short distances, as the flags are small. 2. The alphabet is given on page 174. 3. Always spell out numbers. 4. The attention, answering, and front sign are shown in Figure 65. 5. Procedure signs ordinarily used are given below. Letters overscored are made as one word: 1 Followed by number spelled out. 2 Used only when call flags are not used. When flags are used, the hauling down of the call signifies "dispatch received." |