Naval architecture

Naval architects design safe, useful or beautiful ships and boats for their clients. For details of construction techniques see shipbuilding and boat building.

Efficiency

Broadly, a commercial vessel is efficient if the ship's owner can make a profit against the mortgage. A pleasure vessel's efficiency is harder to measure, but some boats, such as racing yachts, are every bit as tightly designed as any commercial vessel.

Related Topics:
Commercial vessel - Mortgage - Racing yacht

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Generally, the speed of a vessel is critical to its efficiency. The basic speed of a vessel is its hull speed. For hull speed of displacement (non-planing) vessels, adding more energy to the propulsion has little effect on the speed. For this type of vessel the maximum efficient speed increases as the square root of the mean waterline length divided by the width of the waterline.

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There are tricks to exceed hull-speed, such as hydroplaning and hydrofoils. All these tricks depend on either removing the hull from the water, or increasing the effective waterline-length.

Related Topics:
Hydroplaning - Hydrofoil

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The basic trick to making a fast hull is to maximize the buoyancy while minimizing the wetted area. This goal directly interferes with instantaneous stability, which prefers a wide, flat hull. Most hulls are clever compromises between stability, buoyancy, and wetted-area.

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If ultimate stability isn't important, as on inland lakes, a catamaran is an extremely clever compromise. A catamaran is a boat built on two widely-spaced narrow hulls. It has good instantaneous stability because the hulls are widely spaced. It has a good hull speed because the hulls are narrow, and very long for their width. It is usually comfortable, because it is wide, and can have a wider cabin or cargo area. The trade-off is loss of ultimate stability; most catamarans will capsize at less than 90 degrees of roll. Once capsized a catamaran will tend to invert, from which it may be very difficult to right the vessel. Some catamarans employ a float near the top of the mast to prevent inversion after a capsize.

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