FLAT-ABACK. When all the sails are blown with their after-surface against the mast, so as to give stern-way.
FLAT-AFT. The sheets of fore-and-aft sails may be hauled flat-aft, as the jib-sheet to pay her head off, the driver or trysail sheets to bring her head to the wind; hence, "flatten in the head-sheets."
FLAT-BOTTOMED. When a vessel's lower frame has but little upward inclination.
FLAT CALM. When there is no perceptible wind at sea.
FLAT-FISH. The Pleuronectidæ, a family of fishes containing the soles, flounders, turbots, &c., remarkable for having the body greatly compressed laterally; they habitually lie on one side, which is white, the uppermost being coloured, and having both the eyes placed on it.
FLAT-NAILS. Small sharp-pointed nails with flat thin heads, longer than tacks, for nailing the scarphs of moulds and the like.
FLATS. All the floor-timbers that have no bevellings in midships, or pertaining to the [dead-flat] (which see). Also, lighters used in river navigation, and very flat-floored boats for landing troops.
FLAT SEAM. The two edges or selvedges of canvas laid over each other and sewed down.
FLAT SEIZING. This is passed on a rope, the same as a round seizing, but it has no riding turns.
FLATTEN IN, To. The action of hauling in the aftmost clue of a sail to give it greater power of turning the vessel; thus, if the mizen or after sails are flatted in, it is to carry the stern to leeward, and the head to windward; and if, on the contrary, the head-sails are flatted in, the intention is to make the ship fall off when, by design or accident, she has come so near as to make the sails shiver; hence flatten in forward is the order to haul in the jib and foretop-mast staysail-sheets towards the middle of the ship, and haul forward the fore-bowline; this operation is seldom necessary except when the helm has not sufficient government of the ship, as in variable winds or inattentive steerage.