NAUI Master Scuba Diver 264 Boating, Diving, and Seamanship conditions. The following overview and definitions of these forces will help you become a more competent ship handler: • Propeller Thrust: Your boat moves forward through the water because the pitch of the propeller creates a low pressure area in front of the propeller and a high pressure area behind it. The boat will move forward toward the low pressure area. • Rudder Force: When you turn the rudder to one side, a high pressure area is created on the leading edge side of the rudder, and a low pressure area develops on the trailing edge side. The stern of the vessel will swing (or turn) toward the low pressure side. This is why the stern will swing to the opposite side toward which you turn the rudder. • Side Force: Side force is the direction your boat moves in relation to the direction of the spin (or rotation) of your propeller. If you have a right-handed propeller (facing from the stern to the bow) your propeller turns clockwise and the stern of the boat will swing to the right when idling forward and to port upon backing. Visualize, as the propeller turns, that the tips of the blades of the propeller “walk” along the bottom. Side force is much more pronounced at slower speeds. • Pivot Point: The pivot point (where it turns) of your boat varies with the speed and its load. On most boats, the pivot point is one-third the distance back from the bow when the boat is moving forward. • Bank Cushion: When passing close or near another boat or seawall, the bow of your vessel will be pushed away. When moving ahead, water is funneled back along a narrow channel which causes the bow to be pushed out or away. The opposite happens in reverse, where the stern is pushed away. • Bank or Bottom Suction: As your vessel moves forward, water is pulled (or sucked) from ahead of the propeller and discharged astern. Moving into shallow water (a harbor or reef) causes a bottom suction effect, and the stern of the boat will sink lower into the water. INTRODUCTION TO RULES OF THE ROAD The three worst emergencies that might occur while at sea are: 1. Collision with another vessel 2. Sinking (usually caused by #1) 3. Fire (which usually causes #2) This section examines ways to prevent collision with another boat. As with our freeway systems, there are specific waterway rules governing when and where boats are allowed to maneuver (figure 12-8). The international collision prevention regulations (abbreviated COLREGS) apply to offshore waters and the high seas. Rules for inland waters are also modeled on these regulations. These rules were designed to reduce “risk of collision.” You will find it extremely difficult to convince the Coast Guard or a judge that “risk of collision” did not exist when two vessels have collided. Ironic as it may seem, most collisions occur during daylight hours, in open seas with unlimited visibility. You should have a proper lookout, use a safe speed, warn a vessel that may not see you, and avoid hindering another vessel. Before we discuss the basic rules of the road, you need to understand the buoy system, to ensure that you enter and exit harbors safely and correctly (figure 12-7). When coming in from sea to the harbor, the red channel buoys are kept to your right (starboard) side. The three “r’s” will help you remember: red, right, returning. Who has right of way? It is generally assumed that sailboats have right of way over power-driven vessels. For the most part, this is true. However, there are power-driven boats, due to the nature of their work or other circumstances, that have right-of-way over sailing vessels. Simple Collision Avoidance 1. Head-on Boats: When meeting another boat head on (bow to bow) both boats should alter course to starboard (right), if possible. 2. Crossing: The vessel ahead of you and on your starboard has right of way. You are the “give way” vessel and must slow or turn to starboard and pass behind. The other “stand on” vessel should maintain course and speed.
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