STABILITY AND METACENTRIC HEIGHT

A Stable ship

A stable ship is one that can right itself if it is heeled. When it is upright the ship's centre of gravity, G, and buoyancy, B, are acting on the centre line. When the vessel is heeled, B moves in the direction of the heel so that its upward force combines with the downward force, G, to right the ship. This stability is measured by the position of the metacentre, M, a theoretical point where the upward force B meets the ships vertical midline.

An Unstable ship

An unstable ship cannot return to a normal position when heeled. Since the vessel is narrower and top heavy B and G are located further apart. When the ship heels, the force G shifts towards the direction of the heel and together the two opposing forces act to heel the ship even further until it capsizes. The metacentre, M, instead of being above G is below it.

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