Capstan.— The capstan is a machine smilar in principle to the windlass, and like it used for raising great weights. In large vessels it is used for raising the anchor, in place of the windlass, but is more frequently employed in hoisting out the cargoes in merchant-vessels, or such like purposes, these having a windlass also. There is also another machine used on board ship, called a Crab, for the same purpose, and differing from the capstan only in this respect, that the latter is stationary in one place of the deck, while the crab is made so as to be shifted to any required place. Both these are in principle a vertical windlass, the bars or levers by which they are hove round being placed horizontally in the upper part or head of the capstan. The rope to be worked is taken two or three times round the lower half of the body of the capstan, and at this part the pieces called the whelps are made with a certain projection, to prevent the rope from rising too high, and thereby straining the spindle, which is fixed in a strong beam or chock in the deck, and around which the capstan revolves. See Plate XI. Figs 6, 7, 8, & 9, the last of which represents the capstan in a finished state. Fig. 6 is a ground-plan of the barrel, whelps, spindle, and pawls; and as the capstan is commonly placed a little abaft the after hatchway in ships and brigs, suppose M to be the after part of the coamings of the hatch, N a piece of wood fitted against the coamings, and bolted down to the deck for take 1-3d of the whole diameter in the compasses, place the one point in j, bring the other to intersect the line ef, as in the point k; then will the distance ki be the breadth of the panes of your ten squares. Set this distance equal on each side of the point e, on the side ab of the piece — you will then have the points l and m; turn the distance lm all round the circle on the end of the piece; draw from point to point, which will give the ten sides of the barrel marked off, the other end being divided in the same manner; after the barrel is thus lined on the ends, it may be sawn exactly to the size.
The pieces for the head should be provided as early as possible. They should be sound, well seasoned pieces of timber or plank cut near to the proper size, and left in some dry place where they will be fully exposed to the drought, until such time as they are to be put together; for when the capstan is finished, the head part is most exposed to the weather, and from the manner in which it is cut for the bars, it is very liable to split and cling. When the head-pieces are thus prepared, next proceed with the whelps. These must also be solid pieces of timber, quite free from rents and sapwood. Having procured pieces for this purpose, side them up to the thickness, and dress them all out to the mould; square and cut them to the next length; place them alongside of each other, with their lower ends quite fair to a square across them; set off the exact height of the coags from the lower end on the outside ones; then with a straight edge scrive them across, and you will have the size and position of the coags. Draw in the outside edge of all the whelps; apply a square from the inside edge of the whelps to the scrive on the outer edge; square this across their sides, and proceed to cut out the dovetail chack for receiving the ends of the coags; and it is better to do this before the whelps are bolted on the barrel. But before bolting on the whelps, get on the hoop on the lower end of the barrel. Be very particular in drawing the centre-lines for the whelps on the sides and ends of the barrel; a centre-line must also be drawn on the ends of the whelps, so that when they are laid on the respective panes of the barrel, they may come exactly fair to the centre of the pane. The barrel must be bored up through to the size of the diameter of the spindle, or rather a small thing wider, so as to allow the capstan to run freely. When the whelps are all placed on their respective panes of the barrel, put a chain round the whole; set it tight with wedges, to hold the whelps firmly to the barrel. Observe that they are standing exactly to their proper places, and fix them with a couple of nails at their upper ends, and with a small bolt, about three inches from the lower end; also put three small threenails in the middle, two between the lower and the middle coag, and one a little above the latter one (see Plate XI. Figs. 7 and 9.) When the whelps are all fastened to the barrel in this manner, fit in all the coags, and fasten them with a small bolt and nail at each end. Care must be taken that the bolts through the coags and whelps into the barrel, are short of the hole for the spindle, which is bored when the barrel is begun with. After the barrel is thus far ready, begin and dress the pieces for the drumhead to their exact thickness and shape, and joint [sic] them together, beginning with the lower pieces first. Lay the two pieces together; mark the size of the square mortise for the head of the barrel; also draw the situation for the bar-holes. These are generally from 3-5ths to 2-3ds of their depth taken out of the lower half of the drum-head, <-- p 313 --> and the remaining part out of the upper half. The handspike-holes are commonly from 4½ to 6 inches inwards to the centre of the drum-head — about 3 inches square at the outer part, and 2 5/8 inches square at their inner end. The mortise in the under side of the drum-head for receiving the head of the barrel, is about 1-3d of the diameter of the drum-head the one way, and 1 or 1½ inches less the other. The size of this mortise, however, and also the depth of the bar-holes, should, if possible, be contrived so that two small bolts can be put through the edges of the two lower pieces of the top (to hold them together), clear of the mortise, for the barrel, and the holes for the bars or handspikes. This may be easily obtained, if you consider it at first, when drawing out the sketch plan of the capstan. When the two lower pieces of the drum-head are bolted together, mark off the neat size of the bar-holes, and chack them out to the exact depth: but observe to leave the cutting out of the mortise for the head of the barrel until the two halfs of the head are completely fastened together, as it can then be done more perfectly, and with less risk of splitting. When the lower half of the head is thus got on with, proceed to the upper half; lay the pieces upon the lower half in the proper position; fasten them down to the lower pieces with two nails in each, driven in temporarily. so as to be easily drawn out; then scrive in all the bar-holes to correspond exactly with those in the lower half; take off the upper half-pieces, and having cut them out, put it on again, and proceed to fasten it down for a full due. The holes for the bars should be all exactly square, and as near as possible of the same size. For the better certainty of lining them out correctly, you should shape a piece of wood exactly square in the edges, and to the size of the intended bars, for a mould with which to draw by all the holes. When the bar-holes are cut out, the uppper and lower half of the head are to be fastened together with a few nails or small bolts, keeping them clear of the handspike or bar-holes, and the place of the ring, which is next to be sunk neatly into the head, one in the upper side and one in the lower side. In laying on the rings to draw them by, also attend that none of the through-bolts will come in the way of the bar-holes. When the rings are let into the head, drive and clench the bolts, and it is then ready for fitting down on the head of the barrel. The square on the top of the barrel, which fits into the mortise on the under side of the drum-head, stands three inches up above the ends of the whelps, but the mortise in the head is cut 4 inches deep; and when the head is fitted neatly down to the shoulders of the tenon on the barrel, take the compasses and scrive on the under side of the head, all round the outside of the barrel and ends of the whelps; take off the head and chack out all round by the inside of the scrive 7-8ths of an inch deep, flat through to the square, so that when the head is again put on, it may natch that much down, and have a complete hold of the whole barrel, resting on the outsides of the same and end of the whelps. Before the head is put on, the bush must be sunk into the top part of the barrel, and the plate for bearing the weight of the capstan on the end of the spindle properly fitted and secured down to the barrel. This method of hanging the weight of the capstan on the top of the spindle, is more frequently used than the following, which, however, is supposed to be the best, only a little more troublesome; i.e. In place of having the spindle so long as represented in the drawing (Plate XI.), kept 7 or 8 inches short of the top of the barrel; then opposite to the point of the spindle, allowing the lower end of the capstan to be a little clear of the deck, cut a flat mortise-hole through the barrel to take in a plate of iron about 2 inches broad and half an inch thick; then drive through this plate, so that the top of the spindle may rest against its under side. This makes a very secure job, as it cannot get started off or damaged by any weighty thing falling on the head of the capstan. In the other case, this would be apt to start the plate, and of course the capstan would settle down. But also, if it is desired to prevent the capstan from rising up from the spindle, you have only to turn a groove or a small natch round the spindle, a little below the bush, and put a small cutter through the barrel, bearing with one edge in the natch.
With respect to fixing the pawls, fit and bolt a solid piece of oak down to the deck, and against the coamings of the hatch. Before fastening it down, the deck under it should be served over with a coat of warm tar and flannel, or boat-builders' blair, to prevent it from rotting under the chock; then fit the fore-ends of the pawls into a circular joint, so that they may turn on the bolt, and at the same time bear the whole strain on the chock or piece, which is firmly bolted down to the beam for that purpose.
The principal construction of the common capstan being thus explained, an inspection of the drawings will be sufficient to assist the young shipwright in completing the machine. The power of the capstan may be estimated in the same manner as the windlass, as before noticed.
Messrs. J. Keenlyside and Company, whose increased power for the windlass has been noticed, also propose the application of the same principle to increase the power of the capstan, by fixing the drum-head to the spindle, so that the spindle is made to turn round with the head. On the lower part of the spindle, at the deck, is fixed a kind of crank, which works into the interior circumference of the lower end of the capstan, diminishing the velocity of the barrel to the head in the ratio of 4 to 1, so that the power is increased in the same proportion. The ingenuity of this invention deserves particular notice, and must be considered a very great improvement on the capstan.
Peter Hedderwick: A Treatise on Marine Architecture, containing the theory and practice of shipbuilding, with rules for the proportions of masts, rigging, weight of anchors, &c including Practical Geometry and the Principles of Mechanics; observations on the Strength of Materials, Hydrostatics, &c. with many valuable tables calculated for the use of shipwrights and seamen; also the proportions, scantlings, construction, and propelling power of steam-ships. Illustrated with twenty large plates, containing plans and draughts of merchant-vessels from fifty to five hundred tons, with mast and rigging plans; plans and sections of a steam-boat of eighty-horse power; and eight quarto plates of diagrams, &c., by Peter Hedderwick.
Printed for the Author, Edinburgh, 1830. pp 310-314.
Transcribed by Lars Bruzelius.
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