A Tackle is an assemblage of ropes and blocks, and is known in mechanics as a system of pulleys.
The simplest contrivance of this kind is the single whip, or girtline, which consists of a rope rove through a single stationary block. By this arrangement, a better lead is given the rope, but no power is gained by it.
But this arrangement is extremely convenient and often absolutely necessary, as in hoisting articles from the holds to the upper decks, or from the decks to the masts and yards.
It is quite different, however, when the single block is movable, or attached to the weight to be moved, and generally these two principles obtain in all tackles, namely, that stationary blocks give no gain, but only serve as a lead to the rope, and all increase of power is derived from movable blocks.
The block having the greatest number of parts of the fall should be attached to the weight to be moved, in order to gain the greatest mechanical advantage. The power gained is equal to the number of parts at the movable block.
As, in all purchases, a considerable proportion of power is expended in overcoming friction alone, and as stationary blocks, while they serve to augment friction, yield no mechanical advantage, there should be as many movable blocks as possible.
To Determine the Relation of Power to Weight in any system of pulleys, we have to remember that the tension on a rope is the same throughout, from the point hauled on to that at which it is made fast, friction not considered. If we then make a figure of a system of pulleys, tracing up the tension on each part, marking the hauling part as 1, we find the purchase by adding the values thus assigned to each part of rope at the weight, or reeving through the block at the weight. When the rope itself starts with a doubled power as at A, Fig. 253, each part of such a rope must be marked 2; if it starts with a quadrupled power as at B, Fig. 255, each part must be marked 4, &c.
Plate 32 shows the manner of estimating the power in this way, with the forms of purchase in ordinary use.
|Fig. 244, Single whip; power gained, none.
Fig. 245, The same with block at the weight; power gained, 2.
Fig. 246, Gun tackle, purchase, power gained, 2.
Fig. 247, The same inverted, power gained, 3.
Fig. 248, A luff tackle, power gained, 3.
Fig. 249, The same inverted, power gained, 4.
Fig. 250, Double purchase, power gained, 4.
Fig. 251, The same inverted, power gained, 5.
Fig. 252, Single Spanish burton, power gained, 3.
Fig. 253, Double Spanish burton, power gained, 5.
Fig. 254, Bell purchase, for topsail halliards, power gained, 7.
Fig. 255, Luff upon luff, power gained, 16.In the above estimate for Bell purchase, the angle between the two parts, C, D, should be considered.
The general rule for ascertaining the power necessary to raise a given weight with a tackle, is todivide the weight to be raised by the number of parts of rope at the movable block or blocks, the quotient being the power required to produce an equilibrium, friction not considered.
To ascertain the amount of purchase required to raise a given weight with a given power, divide the weight by the power, and the quotient will be the number of parts of rope which must be attached to the lower block.
To ascertain what weight given tackling will raise, the weight a single rope will bear is multiplied by the number of parts at the moving block.
When one tackle is put upon another, multiply the two powers together to get the total amount of purchase gained. Thus with a luff tackle, with four parts at the movable block, the gain is four. A luff upon luff would give an increase of 16 times, another luff clapped on to the fall of the second, 16 x 4, or 64 times, &c.
These rules require considerable modification for friction.
Power can only be increased at the expense of time, hence there are many cases on board ship where a great deal of purchase would be a positive disadvantage. Were treble-blocks used for the side tackles of a broadside gun, the gun could be run out more easily than with a double and a single block, but then it would be longer in running out, and there would be an inconvenient accumulation of fall.
The tackles of a broadside gun furnish a good illustration of the relative advantages of the stationary and movable blocks. The train tackle, as ordinarily hooked, yields the greatest advantage for running the gun in. If, through inadvertence, the blocks were reversed, the effort would be applied to rouse the train bolt out of the deck, rather than to run the gun in. The side tackle is necessarily hooked so
|as to afford the least mechanical advantage, in order to give a proper lead to the fall.Friction. Perhaps we shall not be far wrong if we estimate one sixth of the original force to be consumed by friction each time the rope passes round a sheave. Thus, supposing the tension or strain on the hauling part be 6, that on the next will be 5, the next 4, the next 3, and so on. So that if the strain on the fall of a two-fold tackle be 6, the strains on the parts of the rope will be represented by the figures 6, 5, 4, 3, and their sum, 18, will nearly represent the power of the tackle, instead of 24, which it would have been had there been no friction; or about one fourth of the force would have been consumed by it.
If the rope which passes round the sheave of the block be small, it will be more flexible; a less force will be necessary to “nip” it round the sheave, and there will be less resistance by friction against the inside of the shell of the block.
From these considerations, we gather that work is lightened by using large blocks and small ropes; the boatswain’s rule, that the hauling part of a fall bears double the strain of the standing part, is not far wrong; that as the pin of a block is more worn on one of its sides, it should be frequently turned; and that as sheaves nearest the standing part do least duty, they should be shifted occasionally with the others.
There are about five different purchases in common use, viz.:
A Single Whip, Fig. 256, Plate 33, which consists of a single stationary block and fall. By it the power can be more convenient y applied to the weight, but no power is gained. It is therefore, in reality, no purchase at all. The term whip is sometimes applied to tackles, as the water-whips.
A Runner, Fig. 257, Plate 33, a single movable block and fall. In this case, the fall is called the runner, and has a thimble spliced in the end, for hooking a purchase to. By it the power is doubled. The main bowline and topsail tyes are instances of runners. Runners, as in the figure, are used for setting up backstays, and generally wherever they can be applied to advantage.
A Gun Tackle Purchase, Fig. 258, Plate 33, is composed of two single blocks, strapped with hook and thimble, the standing part of the fall bent to the becket, or spliced into the strap of the block from which the fall leads. The advantage derived from this purchase has been given already. Its gain is as 1 to 3.
A Luff Tackle, Fig. 259, Plate 33, consists of a double and single block, each strapped with a hook and thimble, the standing part of fall bent to the becket, or spliced into the strap of the single block. If the double
|block is hooked to the weight, the power is multiplied four times; if the single block, then but three times, &c.A Twofold Purchase, Fig. 260, Plate 33, consists of two double blocks, the standing and hauling part leading from the same block, and on opposite sides, so that the block will not cant. The power gained is four or five times, as it may be applied.
A Threefold Purchase consists of two treble blocks, having the fall and standing part leading from the same block, and from opposite sides. Its power is six or seven times.
The foregoing are the principal kinds of purchase in use on board ship; all others are combinations or modifications of these, and take their names from the purpose for which or place where used, the following being those in most general use.
Boom Tackle, or boom-jiggers, used in large ships for rigging in and out the studding-sail booms. In schooners, the tackle which guys the main boom forward, when going large.
Burtons are light tackles. The term burton by itself, is generally understood to apply to those which are nearly always kept hooked to the pendants, at the topmast heads, ready for use, and called top burtons. They are the same purchase as a luff, but instead of the common double block like a luff, it has a fiddle block, both for neatness and convenience, there being but little room close up under the eyes of the topmast rigging. The falls of these burtons are long enough to permit both the lower block and hauling end to reach the deck, with plenty to spare, while the upper block is hooked to the topmast pendant.
Spanish Burtons are of various styles.
A single Spanish burton, Fig. 261, Plate 33, consists of two single blocks, the standing part spliced in to the strap of the movable block and the bight seized or bent to the hook. This increases the power three times.
The double Spanish burton, Fig. 253, Plate 32, has one double and two single blocks the standing part spliced in the strap of one single block, then rove through the double or fixed block, and the bight seized to the strap of the lower block, to which the weight to be lifted is hooked. The end is then rove up through the double block, through the lower and lastly through the single block to which the standing part is secured. This purchase gives an increase of five times the power applied. Figure 254, Bell’s purchase, increases the power seven times.*
A Deck Tackle is a heavy purchase, of a double and single, or two double blocks. It is used for rousing in chains, and for heavy work generally.
* See also Bell’s purchase, and Plate, Chapter IX., HALLIARDS.
|Fish Tackle is a heavy purchase of double or treble blocks, used for fishing the anchor; that is, for raising the crown to get the inner fluke up to the bill-board after catting.A Fore-and-aft Tackle is one used to get the awnings on a fore-and-aft stretch. The term is also of general application to any tackle whose use, for the time being, may be in the direction of the length of the ship. In the same way we have thwartship-tackles.
The Griolet Purchase, Fig. 263, Plate 34, for dismounting guns on covered decks, is composed of-
A toggle block, made of elm or oak, the outer end or head of which is made rather greater in diameter than the inner one, which exactly fits the bore of the gun. The head has two sheaves in it, so as to form the lower block of the muzzle purchase, and is bound at the outer end with an iron band.
A double cascable block of iron is made usually with a shackle, to fit between the jaws of the cascable, where it is secured by the cascable pin. The iron pins on which the sheaves revolve are formed with eyes, for the convenience of hitching the standing part of the purchase.
Two iron treble blocks, one for the upper muzzle and the other for the breech purchase.
The muzzle purchase block is so fitted as to be either shackled or toggled to the housing bolt above the port, and the breech purchase block has an iron strap terminating above, with an eye by which it is shackled to a bolt passing through the deck above the gun. This bolt has an eye in one end and a screw or key-slit at the other, and when in place, is secured above the deck with a nut or key, between which and the deck a washer of hard wood or iron, of suitable breadth and thickness, is placed.
The hole through which this bolt is put, should be directly above the cascable block when the muzzle of the gun is under the housing bolt, and may be bored at the time the gun is to be dismounted; and bouched with a composition screw-tap.
The purchase falls should not be less than three and a half inches in size, and should be made of manilla rope of sufficient length to reeve full, the gun being supposed to be on deck and the upper blocks in place, allowing also sufficient end for splicing in the thimble and hitching the standing part of the purchase when rove.
An iron thimble large enough to hook the double block of a side, or train tackle, is spliced in to the end of each purchase fall.
Garnet Tackle is the purchase used in getting guns in on a covered deck. The garnet itself is a single piece of rope or a pendant passed through a hole, bored for the purpose in the spar deck, and has a hook and thimble
|spliced in one end, and a thimble in the other, or upper en 1, to which the pendant tackle hooks.Girtlines are, generally, single whips. The name applies particularly to those used at the mast-head in getting up tops, rigging, &c., when rigging ship. Hammock Girtlines are simply lines on which to stop scrubbed hammocks for drying. They are fitted in various ways, and formerly had permanent (nettle) stops attached; but now the “long” or harbor clothes-lines are used for the purpose.
Gun Tackle. A double and a single block, or two double blocks. Gun-tackle falls are made of manilla, or such other pliable rope as may be directed from time to time by the Bureau of Ordnance. It is prohibited to blacken them or to diminish their pliability. Three-inch rope will be found large enough for the heaviest, and from 2 1/4 to 2 1/2-inch for the lighter guns.
The rope being well stretched, the falls are cut of sufficient length to allow the full recoil, leaving end enough to hitch round the straps of their double blocks, when hooked to the middle or fighting bolts.
Gun Tackle Purchase. See ante. Two single blocks.
Hatch Tackles. These are common luff purchases, and are used generally in the hatches over the holds. When the upper block is required to be above the spar deck, it should not be permitted to hook to the lower stay, but to a long pendant, hooking to the lower cap and stopped out to the stay by a lizard.
Jeers, for sending up and down the lower yards, are variously rove. The plan now is, to have one or two double or treble purchases according to the size of the yard. For small vessels the blocks (iron) are fitted in one with the slings, Fig. 262, Plate 33.
Jiggers, Fig. 264, Plate 35, are small luffs, having the double block strapped with one or two tails, and are used for a great variety of purposes about decks.
Luff Tackle. Double and single block, as already described. But rigging luffs used in setting up rigging are either double or single. Double rigging luffs may be ordinary luff tackles or double purchases, used for setting up lower stays, and called stay luffs. Single rigging luffs have two single blocks, and are used in setting up shrouds.
We then have-
|In former days when ships’ batteries were light, the gun tackles had only two single blocks, hence the term, gun-tackle purchase; a heavier purchase is required with modern ordnance.Rigging luffs in former days were composed of double and single blocks, but in time were made up with two single blocks instead, as the double block was too large, much in the way, and liable to split in setting up shrouds.
Retaining the old names, and changing the tackles themselves, has caused a confusion of terms which the above table is intended to simplify.
Pendant Tackles are large tackles, composed of double blocks. They hook to the mast-head pendants, whence their name, and are used for setting up lower rigging, staying the mast, or steadying it under certain emergencies.
Propeller Purchase. A purchase used in tricing up the propeller. See Fig. 277, Plate 40.
Reef Tackles are for rousing the leeches of the top-sails and courses up to the yard arms for reefing. They are variously fitted, and may be either a luff or a gun-tackle purchase, as will be explained hereafter.
Relieving Tackles are for the purpose of hooking to the tiller, in order to steer the ship in the event of the wheel ropes being shot away in action, or to assist in steering in very heavy weather, when the motions of the rudder are sudden and violent. Double and single block.
Rolling Tackles hook to the quarters of the yards (lower and top-sail) and to the mast, for the purpose of steadying the yards in a heavy sea, when the ship rolls much, and to relieve the strain on the trusses, slings, or parrel.
Rudder Tackles hook to the rudder chains or pendants, to steer the ship in case of accident to the tiller or rudder head.
Runners have already been described.
A Runner and Tackle, Fig. 265, Plate 35, is simply composed of a tackle (double and single block) attached to a runner. They are for aiding in staying the lower masts. The power gained is eight times.
Stay Tackles are those which hook to the triatic stay, or a lower stay, and are called respectively,forestay tackle and mainstay tackle-used in getting the boats in and out. These are large double or treble purchases with a hook and several links of chain on the lower blocks. One link is round, and into it hooks the yard tackle.
Side Tackle for running out and training broadside guns. A double and a single or two double blocks.
A Sail Tackle, Fig. 266, Plate 35. The upper block is often double; the small single block below is to act as a fair leader, and the fall to act as a guy in keeping the
|sail clear of the yards and top when swaying aloft. The burtons are used as sail tackles.Stock and Bill Tackle is a small tackle used when securing the anchor.
Train Tackle is composed of a double and a single or two double blocks for running in a broadside gun, or to prevent it from running out in a sea-way, while loading.
Tricing Lines are generally single whips. Sometimes, however, they are gun-tackle purchases, as the fore-topmast studding sail boom tricing lines.
Watch Tackle. A common luff purchase or jigger.
A Whip and Runner. Similar to a runner and tackle, but smaller. The main bowline of a large ship is a whip and runner.
Yard Tackles are large tackles used on the lower yards, in connection with the stay tackles, for getting the boom-boats in and out, purchasing anchors, &c. They are called fore and main yard tackles, respectively, and are fitted with large double or treble blocks, strapped with single hooks. Fig. 230 shows an inside iron-strapped treble block for yard tackle.
Water Whips are tackles for hoisting in water, when it is brought off in gang casks; or for medium weights generally.
Besides the yard and stay tackles described above, for hoisting in and out boats, lighter purchases, known as the yard and stay water whips, are used for getting in provisions, Fig. 267.
This purchase consists of two water-whips. The upper block of the stay whip has a pendant which hooks into the lower cap, and is fitted with a lizard hauling it out to the collar of the lower stay, where it is secured.
The upper block of the yard whip is fitted with a strap as in Fig. 267 to go around the yard arm. Both lower blocks may be fitted with chain pendants and hooks. Sometimes the lower stay block alone is fitted with chain, the lower yard block having a hook only.
Besides the foregoing, there are various jiggers and whips, all of which will be explained when used.
General Remarks. One great advantage of a tackle on board ship, which renders its application of constant occurrence when mere power is not wanting, must not be overlooked; as, for example, when hoisting, a jerking is to be avoided, and a steady, gradual strain required, as in staying a mast. Another advantage of a purchase, when fitted to any part of a ship’s rigging, is that on coming up, when some little must necessarily be given back, only a mere fractional part is lost on the rope itself, as in the laniard of a dead-eye, &c.
|The greater the amount of purchase used, the steadier will be the strain.The swallow of a block should be full large in proportion to the size of the fall; generally one-tenth of an inch swallow for every one-fourth of an inch in circumference of the rope.
The fall of a purchase should have as clear a lead as possible, and the hauling part be in a line parallel to the rest of the purchase.
A score is generally cut in the breech of a block to admit the standing part of the fall being passed under the strap, so as to splice the end into its own part. When this is done, the splice should be tapered and neatly served over with marline. But in jiggers, luffs, deck and pendant tackles, the standing part is bent to a becket, worked around the strap of the single block, with a sheet or becket bend, and the end stopped down. This is to allow the fall to be shifted, end for end, or to be unrove at pleasure.
By reason of friction, the becket in the breech of the standing block may be much less in size than the fall, as the fall there bears less strain than at the hauling part, and the greater the number of parts of a fall, the greater will this difference be. Notwithstanding this, in heavy purchases, where great weights are to be moved, the standing part is hitched around the neck of the strap, between the block and the thimble; and it is a good precaution, when using any tackle for a great strain, to cast off the standing part from the becket and hitch it around the strap. In large blocks, the standing part is made to go on the side opposite to that from which the fall leads, making it lead fairer, and preventing the tendency of the block to slew in the strap. Fig. 268, Plate 35.
When a racking is to be put on a purchase fall, the hauling part is racked to the part next to it.
Sometimes, as in the case of a boat’s fall, by the block capsizing, or through carelessness in overhauling, the fall gets a thoroughfoot in it-that is, the parts get crossed; before use the thoroughfoot must be taken out.
The following is the result of a carefully-executed experiment with tackles:
A tackle of 2 upper and 1 lower sheave requires on the fall 3/5 of the weight of the resistance in order to raise it, but only 1/4 to sustain it in its place. In hoisting, the standing part takes a strain of about 1/3 of the weight suspended, 1/4 in keeping it suspended, and 2/5 in lowering the weight. When composed of one upper and one lower sheave, the fall of the tackle requires the exertion of a power equal to about 5/9 of the weight to move it, and 4/9 to keep it in equilibrium, so that the strap should be 3 times the strength of the fall, or 1 1/2 times its size.
The Purchase gained by Swigging Off.
|What is called swigging off-that is, pulling at right angles to a rope, is, at first, a very great power; but it decreases as the rope is pulled out of the straight line. A purchase upon this principle may be conveniently applied to several purposes. By it a boat may be hauled up on the beach. At some distance up from the water, drive in a stake, and near the water, in a line with the boat, drive in another. To the upper stake secure the boat’s painter, passing it along against the lower one. Now, by swigging off upon the painter midway between the stakes, the boat’s crew will pull with an increased power, and if this be insufficient, it may be increased by moving the stakes farther apart.