Pair of keels on either side of the hull, usually slanted outwards. In yachts, they allow the use of a drying mooring, the boat standing upright on the keels (and often a skeg) when the tide is out.

Related Terms

ABSORBER

That part of the low side of an absorption system, used for absorbing vapor refrigerant.

CHINE

The intersection of the middle and sides of a boat

NAVAL TRAWLER

A converted trawler, or boat built in that style, used for naval purposes.

WEATHER SIDE

The side of a ship exposed to the wind.

HALF-TIDE BASIN

A lock of very large size and usually of irregular shape, the gates of which are kept open for several hours after high tide so that vessels may enter as long as there is sufficient depth over the sill. Vessels remain in the half-tide basin until the ensuing flood tide before they may pass through the gate to the inner harbor. If entry to the inner harbor is required before this time, water must be admitted to the half-tide basin from some external source.

HARMONIC FUNCTION

Any real function that satisfies a certain equation. In its simplest form, as used in tide and tidal current predictions, it is a quantity that varies as the cosine of an angle that increases uniformly with time

HARMONIC CONSTANTS

The amplitudes and epochs of the harmonic constituents of the tide or tidal current at any place

HIGH WATER

The maximum height reached by a rising tide. The height may be due solely to the periodic tidal forces or it may have super- imposed upon it the effects of prevailing meteorological condi- tions. Use of the synonymous term HIGH TIDE is discouraged.

HALF-TIDE LEVEL

A tidal datum midway between mean high water and mean low water. Mean sea level may coincide with half-tide level, but seldom does; the variation is generally about 3 centimeters and rarely exceeds 6 centimeters. Also called MEAN TIDE LEVEL.

SHELL PLATING

The plates forming the outer side and bottom skin of the hull

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