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| Semi-Displacement |
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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.
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| Shaft Log |
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A fitting in the hull bottom that contains the propeller shaft.
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| Skid Fin |
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A blade attached vertically to the hull that extends below the waterline to keep the boat from skidding during a turn.
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| Slat |
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An aerodynamic device mounted on or just forward of the ram wing to create a slot effect.
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| Slot |
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The gap between a slat and the ram wing's leading edge.
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| Slot Effect |
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A lessening of turbulence over an airfoil caused by airflow through a small opening.
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| Spar |
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A structural member that attaches the sponsons or canoe to the main hull, or a brace between the sponsons.
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| Speed Brake |
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An aerodynamic device that decreases speed by interfering with airflow.
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| Spoiler |
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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.
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| Sponson |
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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.
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| Strut |
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Any brace or support, but most commonly the support for the propeller shaft's rear bearing.
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