BACK. The outside or convex part of compass-timber. Also a wharf.
BACK, OF A SHIP. The keel and kelson are figuratively thus termed.
BACK, OF THE POST. An additional timber bolted to the after-part of the stern-post, and forming its after-face.
BACK-BOARD. A board across the stern sheets of a boat to support the back of passengers; and also to form the _box_ in which the coxswain sits.
BACK-CUTTING. When the water-level is such that the excavation of a canal, or other channel, does not furnish earth enough for its own banks, recourse is had to _back-cutting_, or the nearest earth behind the base of the banks.
BACK-FRAME. A vertical wheel for turning the three whirlers of a small rope-machine.
BACK-HER. The order, in steam-navigation, directing the engineer to reverse the movement of the cranks and urge the vessel astern.
BACKING. The timber behind the armour-plates of a ship.
BACK-O'-BEYOND. Said of an unknown distance.
BACK OFF ALL. The order when the harpooner has thrown his harpoon into the whale. Also, to back off a sudden danger.
BACK-ROPE. The rope-pendant, or small chain for staying the dolphin-striker. Also a piece long enough to reach from the cat-block to the stem, and up to the forecastle, to haul the cat-block forward to hook the ring of the anchor--similarly also for hooking the fish-tackle. (_See_ GAUB-LINE.)
BACKS. The outermost boards of a sawn tree.
BACK-STAFF. A name formerly given to a peculiar sea-quadrant, because the back of the observer was turned towards the sun at the time of observing its zenith distance. The inventor was Captain Davis, the Welsh navigator, about 1590. It consists of a graduated arc of 30° united to a centre by two radii, with a second arc of smaller radius, but measuring 6° on the side of it. To the first arc a vane is attached for sight,--to the second one for shade,--and at the vertex the horizontal vane has a slit in it.
BACKSTAY-PLATES. Used to support the backstays.
BACKSTAYS. Long ropes extending from all mast-heads above a lower-mast to both sides of the ship or chain-wales; they are extended and set up with dead eyes and laniards to the backstay-plates. Their use is to second the shrouds in supporting the mast when strained by a weight of sail in a fresh wind. They are usually distinguished into breast and after backstays; the first being intended to sustain the mast when the ship sails upon a wind; or, in other terms, when the wind acts upon a ship obliquely from forwards; the second is to enable her to carry sail when the wind is abaft the beam; a third, or shifting backstay, is temporary, and used where great strain is demanded when chasing, chased, or carrying on a heavy pressure of canvas: they are fitted either with lashing eyes, or hook and thimble with selvagee strop, so as to be instantly removed.