Hog (Hogging)

The condition of a vessel caused by the unequal distribution of cargo. When a vessel loads too heavily at the ends it causes an arching, or bending upward, of the hull at the midships area. This can also be caused by the vessel working in heavy seas with a large wave under the amidships section.

A ship is said to hog when the middle part of her keel and bottom are so strained as to curve or arch upwards. This term is therefore opposed to sagging, which, applied in a similar manner, means by a different sort of strain, to curve downwards. In order to elucidate this subject, let us suppose a vessel to be acted upon by several forces as in the figure a b, [a simple “force” diagram] with the forces or weight, e, f, acting downwards [at either end], and c, d,
the pressure of the water, acting upwards [amidships; could be a single force; that there are two of them emphasizes the notion that the upwards force is applied to some extent over the length of the ship, but predominantly amidships]; the vessel may in this state be maintained in equilibrio, provided that it has a sufficient degree of strength; but, so soon as it begins to give way, we see that it must bend in a convex manner, since its middle would obey the forces c and d, acting upward, whilst its extremities would be actually forced downwards by the forces or weights e and f. Vessels deficient in strength are generally found in such a situation; and, since similar effects continually act whilst the vessel is immersed in the water, it has happened but
too often that the keel has experienced the bad effect of a strain. Hence it is evident, that hogging may arise either from want of strength in the component parts of a vessel, or from disarrangement in the stowage. Many long, deep, straight floored vessels, too slightly built, have been found to hog, owing to the great upward pressure of the water upon the broad part of the bottom; and it has been found that, the longer and larger ships are, the more easily have their bottoms bent or hogged, even when the stowage has been correct; and much more so when it has been unequally distributed towards the head and stern. Ships deeply laden, with very heavy cargoes or materials nearly amidships, have, on the contrary, been sometimes found to sag downwards, in proportion as the weight of the cargo has exceeded the upward pressure of the water.

But, according to the present practice of building in Great Britain, these disadvantages are little to be feared; although, in a less advanced state of the art, they were frequently found in British vessels, and are still as frequently found in vessels of foreign construction; many of the latter being of too small scantlings and too slightly constructed. Even sharp built vessels of this country, upon the present construction, are seldom found to hog; and we presume that no vessel constructed agreeably to the Table of Dimensions and Scantlings, given hereafter, will be found so to do. But it is to be particularly observed, that these dimensions, with respect to the strength of the body, will not admit of diminution. If, however, the relative dimensions be changed; and, if the length be increased, as recommended in some cases, in order to produce an increase in the velocity, or, if the ship is intended to be laden with very heavy materials, as lead, &c. the strength may be proportionably increased by enlarging the scantlings of the thickstuff at the joints of the timbers.