DOUBLE-ACTING ENGINE. One in which the steam acts upon the piston against a vacuum, both in the upward and downward movement. DOUBLE-BANK A ROPE, TO. To clap men on both sides. DOUBLE-BANKED. When two opposite oars are pulled by rowers seated on the same thwart; or when there are two men labouring upon each oar. Also, 60-gun frigates which carry guns along the gangway, as was the custom with Indiamen, are usually styled _double-bankers_. DOUBLE-BITTED. Two turns of the cable round the bitts instead of one. DOUBLE-BLOCK. One fitted with a couple of sheaves, in holes side by side. DOUBLE-BREECHING. Additional breeching on the non-recoil system, or security for guns in heavy weather. DOUBLE-CAPSTAN. One shaft so constructed as to be worked both on an upper and lower deck, as in ships of the line, or in Phillips' patent capstan. DOUBLE-CROWN. A name given to a plait made with the strands of a rope, which forms part of several useful and ornamental knots. DOUBLE DECK-NAILS. _See_ DECK-NAILS. DOUBLE DUTCH COILED AGAINST THE SUN. Gibberish, or any unintelligible or difficult language. DOUBLE EAGLE. A gold coin of the United States, of 10 dollars; value £2, 1_s._ 8_d._, at the average rate of exchange. DOUBLE-FUTTOCKS. Timbers in the cant-bodies, extending from the dead-wood to the run of the second futtock-head. DOUBLE-HEADED MAUL. One with double faces; top-mauls in contradistinction to pin-mauls. DOUBLE-HEADED SHOT. Differing from bar-shot by being similar to dumb-bells, only the shot are hemispherical. DOUBLE-IMAGE MICROMETER. Has one of its lenses divided, and separable to a certain distance by a screw, which at the same time moves an index upon a graduated scale. When fitted to a telescope for sea use, as in chase, it is called a _coming-up glass_. DOUBLE INSURANCE. Where the insured makes two insurances on the same risks and the same interest. DOUBLE-IRONED. Both legs shackled to the bilboe-bolts. DOUBLE-JACK. _See_ JACK-SCREW. DOUBLE-LAND. That appearance of a coast when the sea-line is bounded by parallel ranges of hills, rising inland one above the other. DOUBLE-SIDED. A line-of-battle ship painted so as to show the ports of both decks; or a vessel painted to resemble one, as used to be frequent in the Indian marine. DOUBLE-STAR. Two stars so close together as to be separable only with a telescope. They are either optically so owing to their accidental situation in the heavens, or physically near each other in space, and one of them revolving round the other. DOUBLE-TIDE. Working double-tides is doing extra duty. (_See_ WORK DOUBLE-TIDES.) DOUBLE UPON, TO. _See_ DOUBLING UPON. DOUBLE WALL-KNOT. With or without a crown, or a double crown, is made by intertwisting the unlaid ends of a rope in a peculiar manner. DOUBLE-WHIP. A whip is simply a rope rove through a single block; a double whip is when it passes through a lower tail or hook-block, and the standing end is secured to the upper block, or where it is attached.