ROLLING

That motion by which a ship vibrates from side to side.

Rolling is therefore a sort of revolution about an imaginary axis passing through the centre of gravity of the ship: so that the nearer the centre of gravity is to the keel, the more violent will be the roll, because the centre, about which the vibrations are made, is placed so low in the bottom, that the resistance made by the keel to the volume of water which it displaces in rolling, bears very little proportion to the force of the vibration above the centre of gravity, the radius of which extends as high as the mast-heads.

But, if the centre of gravity is placed higher above the keel, the radius of the vibration will not only be diminished, but such and additional force to oppose the motion of rolling will be communicated to that part of the ship’s bottom as may contribute to diminish this movement considerably.

It may be observed that, with respect to the formation of a ship’s body, that shape which approaches nearest to a circle is the most liable to roll; as it is evident, that if this be agitated in the water, it will have nothing to restrain it; because the rolling or rotation about its centre displaces no more water than when it remains upright, and hence it becomes necessary to increase the depth of the keel, the rising of the floors, and the deadwood afore and abaft.