The variation of stability with draught of water in ships

Of all the properties possessed by a ship none is more vital to her safety and efficiency than that of stability. At the same time none is dependent for its existence and amount upon so many, or such diverse and variable, circumstances as it. The stability of a ship is regulated and determined by her outward size and shape, and also by the separate amounts and positions of all the weights that go to make up her structure, equipment, and loading. No change of any kind can be made in dimensions or form, or in the quantities or distribution of the various items of equipment, stores, or cargo without affecting stability. It is, of course, essential to the safety of every vessel that her stability should not become reduced during all the changing conditions of her employment and career below a certain definite amount. The result of neglect in this respect may be a dangerous inclination or complete capsize when unlooked for, or exceptionally trying, emergencies occur. Deficient stability, whether caused by faulty design or stowage, may admit of a vessel being suddenly capsized by the action of the wind and waves, or of her being forcibly heeled to a dangerous angle of inclination by the shifting of some of her internal weights, such as coals or cargo. Although in every vessel there is a minimum limit below which it is not prudent or safe to diminish the stability, it does not follow that this limit is the same or similar in character in all sizes and types of ships. It is not only necessary to guard against the stability of a ship becoming reduced below a safe minimum amount, but there is also a maximum limit which it should not be allowed to exceed. Excessive stability Has its own peculiar objections and dangers. It causes heavy and uneasy rolling which may not only be uncomfortable and trying to passengers and crew, but at times sufficient to strain and even fracture portions of the structure, and displace or damage some of the fittings. The masts and rigging generally suffer most on account of their distance from the axis of rotation, and the change of motion in them at the end of each roll, being greater than that of any other part of the vessel; and also because their attachment to the hull is less direct and secure. The straining effect of too great stability often shows itself early, and in a marked manner, upon the masts and rigging of a vessel. Seamen frequently say of a ship that is laden with heavy cargo placed low down in the hold, that unless some of the weights are raised,i. e ., unless the stability is reduced, she will roll her masts out. The violent and deep rolling caused by excessive stability also tends to move over towards one side of the ship such cargoes as grain or coals which are free, to some extent, to shift as a whole; or such portions of other classes of cargo as admit of being displaced. Speaking generally, it may be said that, whereas large stability helps to prevent inclination to a great angle in the event of cargo shifting, the very possession of such large stability often increases the chances of shifting.