![]() Raising the vessel’s centre of gravity ( G) causes a decrease in the metacentric height ( GM) and thereby smaller values of the rightin levers ( GZ). ![]() In this regard, the freeboard and the ratio between the vessel’s breadth and depth are very important. The shape of the righting lever curves, the metacentric height ( GM) and value of the righting lever ( GZ) are dependent on the form of the vessel and its loading. (b) the maximum value of the righting lever ( GZmax), GZ curves are used to evaluate the vessel’s stability, but these following factors, among other things, should be observed: Stability curves ( GZ curves) are used to show graphically how the stability lever ( GZ) changes when the vessel is heeled. ![]() Therefore, the moment of statical stability to return the vessel to the upright position will be considerably less than that of the previous illustration. Should the vessel’s centre of gravity ( G) be near the metacentre ( M) the vessel will have only a small metacentric height ( GM) and the righting lever ( GZ) will also be a small value. The lower the centre of gravity ( G), the bigger is the righting lever ( GZ). The vessel’s centre of gravity ( G) has a distinct effect on the righting lever ( GZ) and consequently the ability of a vessel to return to the upright position. This is referred to as the moment of statical stability. Therefore, the force involved in returning the vessel to the upright position is the weight of the vessel acting down through the centre of gravity ( G) multiplied by the righting lever ( GZ). The horizontal distance from the centre of gravity ( G) to the vertical line from B1 is measured in metres and is referred to as the righting lever ( GZ). The force of buoyancy, which is equal to the force of gravity, acts vertically up through the new centre of buoyancy ( B1). The centre of buoyancy ( B), being the geometric centre of the underwater section, has moved to a new position B1. The force of gravity acts vertically downward through the centre of gravity ( G). When heeled by an external force, the vessel’s centre of gravity ( G) does not change.
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