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Powerboating Glossary

A B C D E F H
N O P R S T U V W

afterplane: The surface bottom behind the break; or the section of the main hull behind the sponsons.
air dam: A device in the tunnel beneath the bow or the leading edge of a three-point hydroplane that creates turbulence under the boat, reducing lift.
air rudder: See tail fin.
air trap: A tunnel created by the inner vertical walls of the sponsons, which channels high-pressure air that's forced underneath by the boat's forward motion.
angle of attack: The angle between the sponson's planing surface and the surface of the water.

break: The section on a three-point hyrdroplane where the afterplane meets the forward part of the hull bottom.
bustle: A hydrodynamic shape attached to the chine that increases the area available for buoyancy.

cab-over: A boat in which the driver sits in front of the engine. Such a boat usually has a pickle-fork bow.
canard: A small wing, usually mounted between the sponsons.
canoe: A portion of a three-point hydroplane, comprising the sponson, chines, and air trap, molded as a single piece.
chine: The line where the side and bottom of a v-bottomed boat meet; in a three-point hydroplane, the inclined side of a sponson or the hull.

deck: The platform or surface covering the hull.
deck fence: An upward extension of the sponson wall that rises above the deck.
deck trap: Same as deck fence.
displacement: Descriptive of a powerboat design in which a large section of the hull is always underwater.

elevator: A movable surface on the trailing edge of a canard or ram wing that can be adjusted to direct the airflow.

horizontal stabilizer: An airfoil-shaped surface that's mounted above the rear of the hull.
hydrofoil: A wing-like structure that raises part or all of a powerboat's hull out of the water.
hydroplane: A powerboat designed so that the prow and much of the hull lift out of the water at high speeds, decreasing drag and therefore increasing speed. As a verb, to skim along the surface of the water.

inboard: Descriptive of anything located entirely within the hull; often shorthand for an inboard motor or a boat powered by an inboard motor.
inboard motor: A motor that's mounted entirely inside a boat's hull.

non-trip chine: A chine (on the sponson) that's angled so it won't "trip" on the water during a turn.
nose cowl: A streamlined covering over the front of the superstructure.

outboard: Descriptive of anything positioned outside the hull; also shorthand for an outboard motor or a boat powered by an outboard motor.
outboard motor: A detachable motor that can be mounted outside the hullt.

pickle-fork: Descriptive of the hull of a three-point hydroplane in which the two sponsons extend beyond the center hull section; because of the shape.
plane: Shorthand for hydroplane, as a verb.
planing: Descriptive of a hull that is designed to rise farther out of the water as boat speed increases. Such a hull is typically shaped like a V, as seen in cross-section from the front or rear.
prop: Short for propeller.
propeller: The bladed device, powered by the engine, that rotates in the water to develop thrust.
propeller shaft: A rotating shaft that transmits power from the engine to the propeller.

ram wing: The center hull section of a three-point hydroplane, which is shaped like an airfoil to generate lift.
runner: The planing surface on the bottom of a sponson.

semi-displacement: A type of powerboat design in which the stern is lower than the rest of the hull and is designed to be in the water, while the front portion of the hull is designed to hydroplane.
semi-planing: Same as semi-displacement.
shaft log: A fitting in the hull bottom that contains the propeller shaft.
skid fin: A blade attached vertically to the hull that extends below the waterline to keep the boat from skidding during a turn.
slat: An aerodynamic device mounted on or just forward of the ram wing to create a slot effect.
slot: The gap between a slat and the ram wing's leading edge.
slot effect: A lessening of turbulence over an airfoil caused by airflow through a small opening.
spar: A structural member that attaches the sponsons or canoe to the main hull, or a brace between the sponsons.
speed brake: An aerodynamic device that decreases speed by interfering with airflow.
spoiler: An aerodynamic device that reduces lift. On a hydroplane, it may be an air dam beneath the bow or a speed brake mounted above the hull.
sponson: A pontoon-like hull, or portion of a hull, that provides lift. A three-point hydroplane has two sponsons, one each side of the main hull.
strut: Any brace or support, but most commonly the support for the propeller shaft's rear bearing.
stuffing box: See shaft log.

tail fin: An aerodynamic surface mounted vertically on the superstructure, near the transom, to improve directional stability; sometimes called the air rudder.
three-point hydroplane: A hydroplane that has two sponsons, one at each side of the hull. The sponsons lift the hull so that, at high speeds, only they and the propeller are in contact with the water, hence three points.
transom: A vertical structure that marks the end of the main hull or sponson.
tunnel: The channel formed by the bottom of the main hull and the inner walls of a sponson.