A bolt then is generally a cylindrical pin of iron, of which there are various sorts, used for sundry occasions in ship-building.
The bolts are principally employed either to unite several members of a ship’s frame into one solid piece, or to fasten any moveable body on a particular occasion. Those which are calculated for the former purpose have commonly small round heads, somewhat flatted, as in fig. 1 & 2. plate [II]. On the contrary, the bolts which are intended for the latter use, have either a large round head, as those of the chains, fig. 4. or an eye, with or without a ring in the same place, fig. 5, 6, and 39, as those which are designed to secure the great guns, the jears of the main-sail and fore-sail, the stoppers of the cables, &c.
The bolts are short or long, according to the thickness of the timber wherein they are to be lodged: they penetrate either quite through the pieces into which they are driven, or to a certain determinate depth. The last of these, called a rag-bolt, is retained in its situation by means of several barbs, fig. 3. which, fastening into the timbers, prevent the bolt from loosening from its station by the working of the ship. The first, after being driven through the pieces it is intended to unite, is confined by a flat iron wedge, called the forelock, which is thrust through a narrow hole in the small end of the bolt, where it is hardened home by a hammer; and to prevent the forelock from cutting the wood-work in this position, a little iron ring is fixed over the end of the bolt, between the forelock and the timber.
Those bolts, which have the largest of the round-heads, are called fender-bolts, being driven into the wales, stem, or sides of some small vessels of burthen, as lighters, beancods, prames, &c. to defend their timber-work from the shock of any other vessels which may fall aboard by accident.
A boom-iron is composed of two iron rings, formed into one piece, so as nearly to resemble the figure of 8. It is employed to connect two cylindrical pieces of wood together, when the one is used as a continuation of the other; such is the jib-boom to the bowsprit; and such are the studding-sail booms to the respective yards from whose extremities they are prolonged. The rims, or circles of the boom-irons, are broad and flat; and one of them, which is firmly driven upon the main, or fore-yard-arm, is somewhat larger than the other, as exhibited in fig. 7. plate [II]. The studding-sail-boom usually rests in the small ring, through which it is occasionally thrust outwards from the yard-arm, when the studding-sail is to be set. Every boom of this kind has, or ought to have, two boom-irons, one of which is fixed on the extremity of the yard, and the other further inward. The former of these is frequently framed of one ring only, which projects from the end of the yard, where it is fastened by a strong iron bar, opening into a sort of fork or crotch that slides upon the yard lengthwise, where it is fastened by nails driven from above and below.
ISLAND of ICE, a name given by sailors to a great quantity of ice collected into one huge solid mass, and floating about upon the seas near or within the arctic circle.
Many of these fluctuating islands are met with on the coasts of Spitzbergen, to the great danger of the shipping employed in the Greenland fishery.
JUNK, bouts de cable, a name given to any remnants or pieces of old cable, which is usually cut into small portions for the purpose of making points, mats, gaskets, sennit, &c. See Points, &c.
JURY-MAST, a temporary or occasional mast, erected in a ship to supply the place of one which has been carried away by tempest, battle, or the labouring of a ship in a turbulent sea.