When the peak of a wave is amidships, causing the hull to bend so the ends of the keel are lower than the middle. The opposite of sagging. Also refers to a permanent distortion of the hull in the same manner caused, over time, by the bow and stern of a ship being less buoyant than the midships section. During the Age of Sail, shipwrights employed a number of different designs of braces to stiffen ships' hulls against this warping.

Related Terms


This describes the middle side area of a tanker's or other vessel's exterior hull which is flat and usually vertical. This is usually the area of the hull that is in contact with the pier when a vessel is docked. This area is measured from aft of the bow where the hull reaches maximum beam and then proceeds aft with little variance until the hull recesses again towards the centerline near the stern. This area is the same on both sides of a vessel and therefore runs in parallel down the middle of the ship.

The length of the mid-body is important to know when voyage planning to determine if a vessel will safely be able to moor at a particular facility. Also known as PBL, PMBL, or Mid-Body Length.


A through hull valve, a shut off on a plumbing or drain pipe between the vessel's interior and the sea.


A shut off valve through the hull for intake or discharge piping.


The center of the area of the underwater transverse or longitudinal section of a hull at a particular trim, hence the point at which the force of buoyancy is regarded to be acting vertically upwards.


The effect that due to the depth of water, the speed of the vessel and shape of the vessel's hull causes the vessel to sink deeper in the water especially in shallow water and at high speed. The vessel becomes sluggish in responding to the rudder.


The act or process of floating a ship after only hull construction is completed; in some cases ships are not launched until after all construction is completed.


The oscillatory vertical rise and fall, due to the entire hull being lifted by the force of the sea. Also called HEAVING


An opening for supplying seawater to condensers, pumps, etc. located in the hull below the waterline and having means for the attachment of the associated piping


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


A triple hulled vessel

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