1. The disposition of the weights of a ship determines the position of its centre of gravity, which, ciuteris paribus, increases or diminishes the sta bility according to its being lower or higher in the ship. This is as well known in practice as clearly demonstrable by science. The distribution of the ballast as low as possible, is therefore always neces sary when the stability is required to be increased. The nearer the middle of the ship, in the full parts of the body, the ballast is stowed, the lower it will be, and consequently, the greater the stability. This, in almost all cases, is good stowage, in relation to the stability of a ship, as the case is rare when the lading of the ship is of such great specific gravity as to ren der it necessary to raise the weights, by putting arti cles of less specific gravity under.
2. estimating the influence of the stow age on the rolling of a ship, it must he considered in dependently of the stability. The permanent inclina tion caused by the force of the wind, depends entire ly on the stability; but the vibratory action of rolling depends on other causes, some of which are uncon nected with the stability. Two ships of equal stability are frequently known to possess very different quali ties in this respect; the one may roll slowly and easi l•, the other quickly and uneasily.
The rolling of a ship is caused by waves striking a ship's side; it is generally deepest either when a sud den change of wind takes place, and the ship sailing free, is struck en the side by the waves, which con tinue to run in the direction of the wind before the change; or in a calm, when the swell of the sea gives the body of the ship a constant disposition to incline, without any inclining force to keep the ship steady.
The rolling of a ship is sometimes (as has been be fore remarked,) considered analogous to the vibra tions of a pendulum. Supposing some point below the ship to be the point of suspension, the length of the pendulum is measured by each particle into the square of its distance from the centre of suspension, divided by the whole body into the distance of the centre of suspension from the centre of gravity. The length of the pendulum would, therefore, be increas ed by removing the weight as far as possible from the centre of suspension. The disposition of the movea ble weights in a ship, according to this consideration, therefore, to increase the length of' the isochronal pendulum, would he to place them as far as possible from the vertical and longitudinal plane passing through the centre of gravity. By the increase of the length of the pendulum, the time of the oscillation is increased, so that the ship's rolling would be propor tionally slower.
The analogy, however, between the oscillations of a pendulum and the rolling of a ship cannot be consid ered strictly correct.
An easier method of considering the effect of the weights on the rolling of a ship, is, simply, by esti mating their resistance to rotatory motion by their inertia. As the inertia of any weight is measured by each particle into the square of its distance from the cen tre of suspension, the placing these weights furthest from the centre of suspension, would most increase their resistance to motion, In a ship, the centre of suspension must be considered to coincide with the centre of gravity, so that the further the weights are removed from the centre of gravity, the greater would be the resistance to quick and uneasy rolling.
The practice of " winging the weight," as it is technically called, suggested by these principles, is found to be fully justified by experience. Care should, however, be taken that the centre of gravity of the weights may not be raised by this disposition, that the stability may not be diminished by it.
Quick and violent rolling is frequently found to be very injurious to the hull and masts of a ship. Many modes of security of the beam ends and ship's sides have been adopted, which have been of great advan tage in sustaining the strain caused by this action. Due consideration to form and good stowage are, however always found greatly to reduce the violence of a ship's rolling.
3. a ship is so far passed over a wave, that the fore part is unsupported by the water, the mean vertical direction of the water acting abaft the centre of gravity, causes the bows to pitch for ward into the hollow of the wave. This motion, as far as it is influenced by the distribution of the weights, is subject to the same laws as the rolling. The far ther the weights are from a vertical transverse plane passing through the centre of gravity, the greater will be their inertia, and consequently, the slower and deeper the pitching. These two motions are, how ever, to be considered very differently, as to their ef fect on the ship. The advantage of increasing the time and depth of the rolling has been considered in diminishing the strain of the hull and masts; but the effect of deep pitching must, on the contrary, be con sidered as disadvantageous, by retarding the velocity of the ship's motion, and rendering it uncomfortable to the men, by the waves breaking over it.