In most areas with large waves, surf, and heavy surge, visibility will be poor. Different beach conditions require different entry-and-exit techniques, so always get an orientation to any new diving area from a NAUI Instructor or a NAUI Divemaster. Tides Tides cause water movement in many areas. Tides are caused by the gravitational attraction between the Earth, the Moon, and the Sun. In different areas of the world, the water level change between low tide and high tide can range from less than 0.3 meters (1 foot) to 12 meters (40 feet). Usually, the difference between low and high tide is only a few feet of water. The change in the water level at a dive site due to the tide can cause problems while you are on your dive if you do not plan for it. For example, when the tide is in, or high, the water extends further onto the beach, covering rocks that are just outside the waves. This makes it easy to enter the water, because you can swim over the rocks. When the tide is out, or low, the water recedes, uncovering any rocks. If this happens while you are in the water, you might be forced to climb back over the rocks to return to the beach. This can be much more difficult and dangerous than swimming over them. You avoid this by timing your dive properly. Chapter 8- Diving Environment Tides can also affect your diving if you are using a small boat that is docked or launched at a marina. As the tide goes out, floating dock and launch ramps can become quite steep. Launch ramps in particular can be extremely slippery, because the marine plants that grow on them are exposed at low tide. Water movement because of tides can also affect underwater visibility. The best diving visibility is usually during high tide. There are exceptions, and you will learn more about local tides from your instructor as part of your open water training. Currents A current is the movement of water in a particular direction. Currents are like rivers or streams within the ocean. Winds, tides, gravity, and the Earth’s rotation cause currents in the oceans. Rivers have a generally constant current flow due to gravity. You must consider currents when you plan a dive, because attempting to swim against a strong current can exhaust you very quickly. Usually, you begin a dive into the current, no matter how slight it is. If your entry and exit points are the same, you can use the current to help you return to your exit point at the end of your dive. If you are diving from an anchored boat, a trail line 30 meters (100 feet) long with a buoy at the end should be extended behind the boat (figure 8-14). This way, if you accidentally end your dive downcurrent from the boat, you will usually be able to grab the line and pull yourself back to the boat. In the NAUI Advanced Scuba Diver course, you can learn how to drift dive. When you drift dive, you use the current to move you along, planning your exit downcurrent of your entry point. Diving Environment 183 FIGURE 8-13. SURF FORMS WHEN WAVES BREAK CLOSE TO SHORE. Trail Line FIGURE 8-14. BE SURE TO USE A TRAIL LINE WHEN YOU DIVE FROM A BOAT IN AN AREA THAT MIGHT HAVE A CURRENT.
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