The rope being well stretched, the falls are to be cut of sufficient length to allow the full recoil, leaving end enough to hitch round the straps of their inner blocks, when hooked to the middle bolts.
212. Blocks for gun-tackles should have pins of hardened copper, turned smooth, and sheaves of lignum-vitæ without bouching. Those to reeve 3-inch falls to be 10 inches, those for 2 1/2 inch falls 9 inches, and those for 2 1/4 inch falls 8 inches long. The hooks of gun-tackle blocks are not to be less than one and a half inch diameter at the bend for heavy, and one and a quarter for light, broadside-guns.
Metallic blocks with nibs, which keep the blocks fair with the falls, and thus prevent the falls from fouling in the recoil, are to be supplied to all Marsilly and heavy pivot carriages.
GRIOLET.
213. The Griolet-Purchase 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 larger 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 cascabel-block of iron is made either with a shackle or to fit between the jaws of the cascabel, where it is secured by the cascabel-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 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 cascabel-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; it is to be stopped afterwards with a plug of wood coated with white-lead.