8 BASIC POWERBOATING. SAFETY & RESCUE FOR SAILING INSTRUCTORS 2. The Powerboat


KEY CONCEPTS E Types of Boats


E How a Propeller Works TYPES OF BOATS


If it had been possible to come up with the perfect powerboat design, all powerboats would look nearly alike. However, there is an infinite variety of types and sizes aimed at fulfilling different boating activities.


Displacement Boats


Displacement hulls create a bow wave as they push through the water. When the hull is trapped between a wave at the bow and another at the stern, it has reached its maximum speed.


Generally, boats with displacement hulls always move “through” the water at slow to moderate speeds, rather than riding on top of the water. As they increase in speed, they develop waves at their bow (front end), along the sides, and at the stern (back end). As they continue to increase speed, the waves become larger and the distance between them lengthens until the hull becomes trapped between the large wave at its bow and another large one at its stern. At this point, the displacement hull has reached what is called hull speed. This is the maximum speed for this hull. One of the most familiar examples of a displacement hull at hull speed is a tugboat moving at maximum speed with its hull sunk low in the water, with a large bow and stern wave. Characteristics of displacement hulls: E Good maneuverability E Speed limited by length (hull speed) E Good ability to hold a course steered (directional stability)


E Good load carrying capacity E Performance not greatly affected by load E Good rough water handling E May roll excessively when seas are coming sideways to the hull


Planing Boats A planing hull behaves like a


displacement hull at low speeds, forming waves at its bow (front end) and along the length of the hull. Upon reaching a certain speed, it goes through a transition stage (semi-displacement)


A planing hull is designed to ride on top of the water once it has reached sufficient speed.


where it climbs the face of its bow wave. At this point the boat may become unstable, fuel consumption is high, and the operator may not be able to see over the raised bow.


Table of Contents E Engine Controls


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