a long round piece of timber, elevated perpendicularly upon the keel of a ship, to which are attached the yards, the sails, and the rigging. A mast, with regard to its length, is either formed of one single piece, which is called a pole-mast, or composed of several pieces joined together, each of which retains the name of mast separately. The lowest of these is accordingly named the lower-mast, fig. 1. The next in height is the top-mast, b, which is erected at CCLXXX the head of the former; and the highest is the top-gallant mast, c, which is prolonged from the upper end of the top-mast. Thus the two last are no other than a continuation of the first upwards.
The lower-mast is fixed in the ship by an apparatus, described in the articles HULK and SHEERS: the foot, or heel of it, rests in a block of timber called the step, which is fixed upon the kelson: and the top-mast is attached to the head of it by the cap and the treble-trees. The latter of these are two strong bars of timber, supported by two prominences, which are as shoulders on the opposite sides of the mast, a little under its upper end: athwart these bars are fixed the crofs-trees, upon which the frame of the top is supported. Between the lower-mast-head and the foremost of the crofs-trees, a square space remains vacant, the sides of which are bounded by the two treble-trees. Perpendicularly above this is the foremost hole in the cap, whose after-hole is solidly fixed on the head of the lower-mast. The top-mast is erected by a tackle, whose effort is communicated from the head of the lower-mast to the foot of the top-mast; and the upper end of the latter is accordingly guided into and conveyed up through the holes between the treble-trees and the cap, as above-mentioned. The machinery by which it is elevated, or, according to the sea-phrase, swayed up, is fixed in the following manner: the top rope, fig. 3, passing through a block e, which is hooked on one side of the cap, and afterwards through a hole, furnished with a sheave or pulley f, on the lower end of the top-mast, is again brought upwards on the other side of the mast, where it is at length fastened to an eye bolt in the cap g, which is always on the side opposite to the top-block e. To the lower end of the top-rope is fixed the top-tackle h, the effort of which being transmitted to the top-rope d, and thence to the heel of the top-mast, necessarily lifts the latter upwards, parallel to the lower-mast. When the top-mast is raised to its proper height, fig. 4, the lower end of it becomes firmly wedged in the square hole above described, between the treble-trees. A bar of wood or iron called the fid, is then thrust through a hole i in the heel of it, it across the treble-trees, by which the whole weight of the top-mast is supported.
In the same manner as the top-mast is retained at the head of the lower-mast, the top-gallant-mast is erected, and fixed at the head of the top-mast.
Besides the parts already mentioned in the construction of masts, with respect to their length, the lower-masts of the largest ships are composed of several pieces united into one body. As these are generally the most substantial parts of various trees, a mast, formed by this assemblage, is judg'd to be much stronger than one consisting of any single trunk, whose internal solidity may be very uncertain. The several pieces are formed and joined together, as represented in the section of a lower-mast of this sort, fig. 5, where a is the shaft, or principal piece into which the rest are fixed, with their sides or faces close to each other. The whole is secured by several strong hoops of iron, driven on the outside of the mast, where they remain at proper distances.
The principal articles to be considered in equipping a ship with masts are, 1st, the number; 2d, their situation in the vessel; and, 3d, their height above the water.
The masts being used to extend the sails by means of their yards, it is evident, that if their number were multiplied beyond what is necessary, the yards must be extremely short, that they may not entangle each other in working the ship, and by consequence their sails will be very narrow, and receive a small portion of wind. If, on the contrary, there is not a sufficient number of masts in the vessel, the yards will be too large and heavy, so as not to be managed without difficulty. There is a mean between these extremes, which experience and the general practice of the sea have determined; by which it appears, that in large ships every advantage of sailing is retained by three masts and a bowsprit.
The most advantageous position of the masts is undoubtedly that from whence there results an equilibrium between the resistance of the water on the body of the ship on one part, and of the direction of their effort on the other. By every other position this equilibrium is destroyed, and the greatest effort of the masts will operate to turn the ship horizontally about its direction; a circumstance which retards her velocity. It is counterbalanced indeed by the helm; but the same inconvenience still continues, for the force of the wind, having the resistance of the helm to overcome, is not entirely employed to push the vessel forward. The axis of the resistance of the water should then be previously determined, to discover the place of the mainmast, in order to suspend the efforts of the water equally, and place the other masts so as that their particular direction will coincide with that of the mainmast. The whole of this would be capable of a solution if the figure of the vessel were regular, because the point, about which the resistance of the water could be in equilibrium, might be discovered by calculation.
But when the real figure of the ship is considered, these flattering ideas will instantly vanish. This observation induced M. Saverien to employ a mechanical method to discover the axis of resistance of the water, which he apprehended might be used with success in the manner following:
When the vessel is launched, before the places of the masts are determined, extend a rope AB, fig. 6, from the head to the stern. To the extremities A and B attach two other ropes, AD, BC, and apply to the other ends of these ropes two mechanical powers, to draw the ship according to the direction BC, parallel to itself. The whole being thus disposed, let a moveable tube Z, fixed upon the rope AB, have another rope ZR attached to it, whose other end communicates with a mechanical power R, equal to the two powers D and C. This last being applied to the same vessel, in such manner as to take off the effects of the two others by sliding upon the rope AB, so as to discover some point Z, by the parallelism of the ropes AD, BC feebly extended with the rope ZR; the line ZR will be the axis of the equilibrium of the water's resistance, and by consequence the mainmast should be planted in the point Z.
The figures E, E, E, are three windlasses on the shore, by which this experiment is applied.
With regard to the situation of the other masts, it is necessary, in the same manner, to discover two points, so that the direction of the two mechanical powers operating, will be parallel to the axis of resistance RZ already found.
The exact height of the masts, in proportion to the form and size of the ship, remains yet a problem to be determined. The more the masts are elevated above the centre of gravity, the greater will be the surface of sail which they are enabled to present to the wind; so far an additional height seems to have been advantageous. But this advantage is diminished by the circular movement of the mast, which operates to make the vessel stoop to its effort; and this inclination is increased in proportion to the additional height of the mast, an inconvenience which it is necessary to guard against. Thus what is gained upon one hand is lost upon the other. To reconcile these differences, it is certain, that the height of the mast ought to be determined by the inclination of the vessel, and that the point of her greatest inclination should be the term of this height above the centre of gravity. See the article Trim.
With regard to the general practice of determining the height of the masts, according to the different rates of the ships in the royal navy, the reader is referred to the article Sail.
In order to secure the masts, and counterbalance the strain they receive from the effort of the sails impressed by the wind, and the agitation of the ship at sea, they are sustained by several strong ropes, extended from their upper ends to the outside of the vessel, called foreyards, as represented in fig. 4. They are further supported by other ropes, stretched from their heads towards the fore-part of the vessel.
The mast, which is placed at the middle of the ship's length, is called the mainmast; that which is placed in the forepart, the foremast; and that which is towards the stern, is termed the mizenmast.
N.B. Mizen is applied to this mast by all the nations of Europe, except the French, who alone call the foremast mizzenmast.