MAINDECK
Main deck
The main deck of a ship is the uppermost complete deck extending from bow to stern. A steel ship's hull may be considered a structural beam with the main deck forming the upper flange of a box girder and the keel forming the lower strength member. The main deck may act as a tension member when the ship is supported by a single wave amidships, or as a compression member when the ship is supported between waves forward and aft.The above text is a snippet from Wikipedia: Main deck
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