Stable trim implies that the centre of buoyancy is directly above the centre of gravity.
2.
For stability, the centre of gravity should be " below " the centre of buoyancy.
3.
A stable horizontal trim requires that diver's centre of gravity is directly below the centre of buoyancy ( the centroid ).
4.
For example, when a perfectly cylindrical hull rolls, the centre of buoyancy stays on the axis of the cylinder at the same depth.
5.
These are gravity acting downwards at the centre of mass and the same magnitude force acting upwards through the centre of buoyancy, and through the metacentre above it.
6.
As the hull rights, work is done either by its centre of mass falling, or by water falling to accommodate a rising centre of buoyancy, or both.
7.
This situation is typically valid for a range of heel angles, beyond which the centre of buoyancy does not move enough to provide a positive righting moment, and the object becomes unstable.
8.
Similarly, much of the diver's buoyancy is determined by the equipment in use, particularly the buoyancy compensator, which can significantly influence centre of buoyancy shifts as it is inflated and deflated.
9.
The reason why a ship may be crank cannot be summarized into one precise underlying cause, but rather anything that may affect the centre of buoyancy and the centre of gravity to each other essentially anything that affects the ships stability.
10.
Conversely if a hull having a perfectly rectangular cross section has its centre of mass at the water line, the centre of mass stays at the same height, but the centre of buoyancy goes down as the hull heels, again storing potential energy.
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