GENERAL INFORMATION
Page 1C-4 90-857138R1 MAY 2000
1. Hook: Exists when bottom is concave in fore-and-aft direction when viewed from the
side. When boat is planing, “hook” causes more lift on bottom near transom and allows
bow to drop, thus greatly increasing wetted surface and reducing boat speed. “Hook”
frequently is caused by supporting boat too far ahead of transom while hauling on a
trailer or during storage.
2. Rocker: The reverse of hook and much less common. “Rocker” exists if bottom is con-
vex in fore-and-aft direction when viewed from the side, and boat has strong tendency
to porpoise.
3. Surface Roughness: Moss, barnacles, etc., on boat or corrosion of outboard’s gear
housing increase skin friction and cause speed loss. Clean surfaces when necessary.
WATER ABSORPTION
It is imperative that all through hull fasteners be coated with a quality marine sealer at time
of installation. Water intrusion into the transom core and/or inner hull will result in additional
boat weight (reduced boat performance), hull decay and eventual structural failure.
CAVITATION
Cavitation is caused by water vapor bubbles forming either from a sharp edge or angle on
the gear case, from an irregularity in the propeller blade itself or from improper engine instal-
lation (too high). These vapor bubbles flow back and collapse when striking the surface of
the propeller blade resulting in the erosion of the propeller blade surface. If allowed to contin-
ue, eventual blade failure (breakage) will occur.
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