Blocks are mechanical contrivances, possessing the properties and powers of pulleys. They are generally made by machinery, of ash, and are, what are called, made or mortised.
The made block, Fig. 220, Plate 30, consists of four principal parts, as follows:-The shell or outside, consisting of two or more pieces pinned together; the sheave or wheel. (b), over which the rope passes; the pin or axle (a), on which the sheave turns, and the strap, either rope or iron, which encircles the whole, and by which it is confined to its particular place.
The sheave may be of metal or of lignum-vitae; if the latter, it is bouched (c), in all blocks except those used for the gun tackles. In the patent blocks the bouching contains friction rollers. Fig. 221.
In the common block the bouching is counter-sunk, and made of a composition of 100 parts of copper and 16 of tin. The sheaves of blocks used for gun tackles are not allowed to be bouched, and the pins are made of hardened copper. The pin of the common block is made of iron.
Mortised blocks, Fig. 222, Plate 30, are made from a single piece of wood, mortised out to receive the sheave.
Blocks are single, double, treble or threefold, and fourfold, according to the number of sheaves contained within the shell; are either single or double scored, and are measured by their length-that is, the length of the shell.
The scores are the notches cut at the ends of the shell to admit the strap.
The sizes of blocks used in the navy range from 4 inches to 22 inches inclusive, as follows:-4-inch, 5-inch, 6, 7, 8, 9, 10, 11, 12, 14, 16, 18, 20, and 22, single and double of each size, and treble blocks for the largest purchases.
Not included in the above are viol blocks, large blocks used for warping, &c.
Blocks take their name from the purposes to which they are applied, or from some peculiarity of form, the following being the principal ones in common use:-
Bee-Blocks, or simply BEES, are thick pieces of oak bolted to the sides of the bowsprit, having heavy metal sheaves in them for the fore-topmast and fore-topmast spring stays to reeve through.
|Cat-Block, a large, double or three-fold block, iron-strapped and composition sheaves. It has a large hook connected with the strap by a link, to admit play. It is used to raise the anchor to the cathead. Fig. 225.Cheek-Blocks are made of a half-shell, and bolt against a mast or spar, which acts as the othercheek or half of shell. The chief bolt serves as a pin for the sheave to turn on. Used on gaffs for brails, &c.Clew-garnet Blocks are single, iron-bound, and hook or shackle to the iron bands on the quarters of the fore and main yard. They hang under the yard and receive the clew-garnets, by which the courses are hauled up. The name also applies to the blocks which hook in the clews of the sail.
Clew-line Blocks are those which are attached to the clews of the topsails for the clew-lines. Formerly, the name applied only to the block on the yard, now called QUARTER-BLOCK.
Clump-Block. Strongly made blocks with a thick metal sheave, having a large swallow or opening in proportion to the length. Used for the topsail and topgallant lifts in the top; also on collar of main stay for fore-topsail brace, &c.
The same name is applied to any short thick block, such as fore and main tack blocks, &c.
Dasher-Block is the small block sometimes strapped to the extremity of the spanker-gaff, for reeving the ensign halliards.
Euphroe. A long piece of wood having a number of holes in it, through which the crow foot for the awnings is rove. It has a score around it for a strap, and is strapped with a thimble for bending the crow-foot halliards.
Fish-Block. For fishing the anchor; a large double or treble block, iron strapped, fitted with several links of chain and a hook to hook on the arm of the anchor.
Fiddle-Blocks, Fig. 223, Plate 30, are made with a long shell so as to have one sheave over the other, the lower being smaller. Used for top-burtons and as hanging blocks. When used for fore or main buntlines the two parts are connected by a swivel.
Fly-Block is the upper block of the topsail halliards. It is double, has sister hooks and thimble for hooking to the topsail tye. Friction rollers.
Gin-Blocks, Fig. 224, Plate 30, are large composition sheaves which turn in a metal framework. Used principally for topsail tyes, and hook to iron bands, made to fit snugly over the topmast tressle-trees. The name is also applied to the small metal blocks used aloft for various purposes, such as for topgallant and royal braces, topgallant buntlines, etc.
|Girt-line Blocks are single, through which girt-lines, or single whips reeve, as the mast-head girtlines, in rigging ship, etc. Sometimes called gantlines.Hanging-Blocks. Any block depending at a mast-head, as a lead for running rigging; such as the fiddle-blocks at fore-topmast head for head halliards and topsail buntlines, etc.Jack-Blocks are large single blocks, used for sending up and down topgallant and royal yards.
Jeer-Blocks are large double or treble blocks for reeving the purchases for sending up and down the lower yards.
Jewel-Blocks are single blocks at the extremities of the topsail, topgallant, and sometimes, though rarely, royal yards, through which the studding-sail halliards reeve. The head of the studding-sail, when set, is hoisted to them.
Main-sheet Block is a double or treble block, strapped to the main-boom of a schooner or sloop, for the main-sheet, or a single block for main-sheet of square riggers.
Quarter-Blocks, on the topsail or topgallant yards, are double, and are iron-strapped to the quarters of the yards, to give lead to the sheet of the sail above and clewline of the sail below. On the lower yard they are single, for the topsail sheet alone, and on the royal yard they are single, for the royal clewline alone. Those for the topgallant and royal yards go with sister hooks, that they may be readily detached.
Sister-Blocks, Fig. 226, Plate 30, are formed of one solid piece and two sheaves, one above the other; between the sheaves is a score for a middle seizing, and on the sides a score for the shrouds to fit in. They are seized between the two forward shrouds of topmast rigging, and give lead to the topsail lift and topsail reef tackle, Fig. 270, Plate 38. Frequently, of late, the reef tackle is given a different lead, in which case but one sheave is seized in.
Secret-Blocks, Fig. 227, Plate 30, are so made that the sheave is entirely screened, the rope leading through an orifice in the shell just large enough to admit its free passage, the object being to prevent its fouling by small gear catching in the swallow and choking it. Used for clewlines, which are frequently fouled by reef-points, and for clew-jiggers. The shell of the block, Fig. 227 (a and b), is made of lignum-vitae, and has an iron half-strap. The hooks fitted to this block are known as cliphooks. Similar hooks are shown in Fig. 228, but opening perpendicular to the sheave instead of opening in line with it. Hooks fitted as in Fig. 228 are known as sister hooks.
Snatch-Blocks, Fig. 229, are always single and iron-bound, with swivel hooks. The shell at the breech is
|left open, and the strap at that part fitted with a clamp, so that the bight of a rope may be “snatched.”Telegraph-Blocks are pyramidal shaped blocks, with a number of small brass sheaves, used for making telegraphic signals.Top-Blocks, Fig. 233, Plate 31, are large, single, iron-bound blocks, used for sending up and down topmasts. They hook to an eye-bolt in the lower cap, hooking from in, out, so that the bill of the hook points outward, and the top pendants reeve through them. Sometimes shackled.
Topgallant-top Block is similar to the above, but smaller. It is used for the topgallant-mast rope, and hooks from in, out, to an eyebolt in the topmast cap.
Tye-Blocks are large, single, iron-bound blocks, which bolt or shackle to iron bands on the topsail yard, for the topsail tyes to reeve through.
Viol-Blocks are large single blocks, with a swallow large enough to take a small hawser.
In the navy-yards there are fourfold blocks of 30 inches and over, for heavy purchases.
Block-and-Bock, or “two blocks,” is the term applied to a tackle when its two blocks are drawn so close together that they cease to operate. The act of drawing the blocks apart is called fleeting the purchase, or overhauling it.
Blocks should frequently be examined, not only as to strapping, but also by knocking the pin out and inspecting the bouching. The loss of power, and strain on rope, occasioned by a worn bouch, is considerable. The working blocks of tackles (for instance, the fly block of topsail halliards) are always more worn than the lower ones, and, therefore, without waiting until the sheaves shriek and become dumb, the blocks should be shifted and the sheaves transposed. This remark applies also to quarter-davit blocks.
The sheave, on which the hauling part of the rope works, does most duty; and this calls for greater strength, and frequent alterations in upper blocks.
All blocks which stand horizontally must be placed with the square end of the pin upwards: as, when the shell shrinks, it is liable to fall out if placed otherwise.
Hanging, Tye, and Quarter-Blocks, undergo great strains when bracing sharp up; if the former aretwo blocks, the weather halliards should be eased up sufficiently.
Hooks. There is no proportion for hooks, so that while handling heavy weights, unless the hooks be evidently very strong, it is safer to use a shackle or a good mousing. More accidents happen from open hooks than from chain or cordage. Great support may be given a hook by slipping a link or a shackle over the point, Fig. 234, Plate 31.
Thimbles are made both perfectly round, and also,
|with the ends nearly joined. Two are sometimes united for the purpose of giving easy play to the adjoining straps or block, as well as a different stand. These are called LOCK-THIMBLES.
The majority of the largest blocks supplied to men-of-war are iron-strapped; quarter-blocks, brace-blocks, clew-garnet-blocks, top-blocks, cat-blocks, blocks for boat falls, and many others are of this class. All the above, except the cat-blocks and top-blocks, are also provided with friction rollers, and the same may be said of nearly all iron-strapped blocks which are not subjected to very heavy strains. Some blocks are made entirely of iron, such as the jeer-blocks for small vessels, secured permanently in the chain sling. See also Fig. 231, for a treble iron block.
Figs. 229 and 233 show one method of strapping blocks with iron. Another plan is to use inside iron straps, as in Figs. 230 and 232, which are probably the strongest straps yet devised.
When not iron-strapped, blocks are fitted with straps of hemp or wire-rope.
A wire-rope strap differs from a hemp one in being wormed, parcelled and served, and in being usually made of rope one half the size of the corresponding hemp strap. In wire straps for ordinary single blocks, the splice comes on the side instead of the breech, to avoid a nip near the splice.
Hemp-rope for block-straps should be well-stretched, or until it begins to look “long-jawed,” that is, the angle of the lay diminished.
The common but rather rough rule for the size is, that the rope for the strap should be in circumference one third the length of the block, increasing the size for the straps of heavy purchase blocks; and the old rule requiring the block to be in length three times the size of the rope it reeves, brings the rope reeving and the strap about the same size.
Once and a half the round of the block gives a good measure for the common strap, in which the two ends are joined by a short splice; first reeving the ends through the eye of the hook; a seizing of marline, houseline, spun-yarn, hambroline, or larger stuff, according to the size of the block, is then clapped on between the thimble and the block.
The splice should be placed at the breech of the block. After getting a good strain on the strap, the splicing ends may be trimmed off.
Covering block-straps at all is objectionable, particularly
|if they are much exposed, as they decay more rapidly, and break without warning.To preserve straps from chafe, however, as in the case of purchase-blocks, they are either served or covered with canvas or leather.All blocks below twelve inches should be measured for straps with a piece of spun-yarn, around the block, in the score; and those above twelve inches, with a piece of small stuff, such as 6, 9, 12, or 15-thread ratline, in the same manner, as the size of the strap increases.
A Threefold Block Strap. Large blocks for heavy work, such as the main purchase of masting sheers, &c., are strapped with eyes for toggling, as in Fig. 235, Plate 31.
These blocks, being so unwieldly, require a purchase to heave the strap out, and a wedge, or large fid, to fix it in. When this block is strapped on board merchant ships, it is generally done in a vertical direction; reeving a rope through one of the sheave-holes, and making it fast to a ring-bolt, &c.; then hooking a stay tackle (c), Fig. 236, to the two bights of the strap, and setting it taut. A frapping, or temporary seizing, is next put on above the block, and hove well taut by a heaver. A large fid (e) is driven in betwixt the head and the frapping, and a stop of spun-yarn (d-which is too low down in the plate) is clapped on; being rove through the upper part of the sheave-hole on each side, and nippered round the strap with a heaver, which keeps it in its place. The fid is then knocked out, the frapping taken off, and the seizing clapped on as before. In men-of-war, when these blocks are strapped, they use a chock, instead of a fid, and a wedge is driven in between the chock and the block. The nipper (d) is taken round both the strap and block, and hove taut with a heaver.
A Grommet-strap. Measure with a rope-yarn the neat round of the block, and the thimble, the latter placed at the proper distance from the end of the block. With this measure of rope-yarn, lay off on the rope intended for the strap (having previously got it on a stretch) three lengths from the end, marking each one distinctly, with chalk, and cut a little beyond the last mark, to allow for sticking the ends. Unlay the strand, bring the first and second chalk marks together, lay up the grommet and stick the ends. If well made, the grommet will lie flat on the deck. Before forming the grommet, the end must be rove through the eye of the hook. Get it on a stretch; worm, parcel and serve-cover with canvas, leather or point, as required; pass the seizing of marline, spunyarn, or small stuff, according to the size. These seizings are always crossed. This makes a neater strap than one which is spliced.
A Common Strap, Fig. 237, Plate 31. First,
|cut the rope once and a half the round of the block, get it on a stretch; worm, parcel and serve as near the end as possible, not to interfere with splicing; then splice the ends together with a short splice, and finish serving snug up to the splice. Stretch it and cut the ends off, or you may serve over the ends. If there are a number of these straps required, it would be best to get the rope on a stretch, and serve off the required number before cutting.The Single Strap, with Lashing Eyes. Besides being fitted with hook and thimble, the single strap may be fitted with lashing eyes, as in the case of jewel-blocks, &c. when they are made as in Fig. 238, Plate 31.The Double Strap, Figs. 239 and 240, a and b, Plate 31. When strapping large blocks, requiring considerable strength, as in heavy purchases, or when a certain lead is required, the double strap is used, which is simply a single strap of twice the usual length, doubled.
The double strap may be fitted with the thimble only, Fig. 240, with the hook and thimble, or with lashing eyes, Fig. 239.
The leading blocks at the fife-rail are strapped, as in Fig. 240, the thimble playing on a thwartship-rod of iron, otherwise they would not give the fore-and-aft lead.
The Two Single Straps, Fig. 241. It may happen that the double strap will not give the block the desired lead, in which case two single straps are used.
When not iron-strapped, the tye-blocks on the topsail-yards are fitted as in Fig. 241 (a), Plate 31, with lashing eyes.
The same strap is required for jeer blocks when rope strapped, to give a fore-and-aft lead.
Strap and Pendant. When a single block is strapped with a pendant, an eye is spliced in the latter much larger than the circumference of the block, and a good seizing, is then hove on as in Fig. 242.
Tail-blocks, Fig. 243, Plate 31, are used for single whips, and, generally, whenever a single block is used temporarily. A piece of rope may be spliced around a block, leaving a long tail with the end whipped, or may be unlaid and plaited, as in the figure. Such a block is used in the main rigging for the fore topmast studding-sail tack, and a double one when the boom-brace is used. Sometimes the yarns of the tail are merely opened out and marled down, selvagee fashion.
The double block of a jigger is often strapped with two such tails, and called by sailors a handy billy. This is very convenient for clapping on anywhere, as when getting the topsail sheets close home. &c. Fig. 264, Plate 35.
Rules for Cutting and Fitting all the usual kinds of hemp straps will be found in Appendix B.