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NAUI Scuba Diver closer to shore, the ripple marks get closer together. This fact gives you one useful reference. The positions of the sun and shadows at the start of your dive are another useful reference. The back-and-forth movement of water close to shore is known as surge. The movement is usually toward and away from shore, so this gives you another clue to your location. The water gets deeper as you go further away from shore and shallower as you return to shore or approach reefs. You will see underwater landmarks, such as rock formations, large and unique plants, crevices, and wrecks (figure 3-64). You and your buddy can keep track of your position under water and be able to return to your starting point without surfacing by paying attention to all of these natural aids. Compass Navigation When you dive at night or in water with limited visibility, natural aids are not as helpful to you. You must rely more on a compass and your depth gauge. Using a compass allows you to navigate by dead reckoning, which can be very accurate. The compass shows you directions and your depth gauge tells you your vertical position in the water. A diving compass must be filled with liquid to withstand pressure underwater, have a reference line called a lubber line and have a means, such as a rotating bezel, to show that you are on a selected bearing or direction (figure 3-65). Because a compass is magnetic, ferrous metal (iron or steel) objects close to it will affect it. When you use a compass, you keep the lubber line aligned with the centerline of your body. You can wear your compass on your wrist or mount it on your console with the rest of your diving instruments (figure 3-66). Where you carry the compass is not critical; having it aligned with your body is. When you reference your compass, always be sure that you are lined up with the lubber line and that the compass is level. The compass needle always points to magnetic north. If you point the lubber line towards shore, the compass needle points to one point. Rotate the index 88 Diving Skills FIGURE 3-64. REEF FORMATIONS ARE EXCELLENT NATURAL AIDS FOR NAVIGATION. FIGURE 3-65. THE UNDERWATER COMPASS MAKES NAVIGATION ACCURATE DURING A DIVE. FIGURE 3-66. YOU MUST ALWAYS ALIGN THE COMPASS WITH THE CENTER OF YOUR BODY.


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