centerboard

[sen-ter-bawrd, -bohrd]
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noun Nautical.

a pivoted fin keel that can be swung upward and aft within a watertight trunk when not in use.

Compare daggerboard.

Origin of centerboard

An Americanism dating back to 1840–50; center + board
Also called drop keel.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for centerboard

Historical Examples of centerboard