=astrolabe=—An instrument of the late Middle Ages with which mariners attempted to learn their latitude. The instrument was very imperfect in its workings. =astronomical ring=—An instrument that was meant to improve on the astrolabe, but which was just as inaccurate. =athwart=, =athwartships=—Across. Hence the rowers’ seats in an open boat are called thwarts because they lie _athwart_, or across the boat. To drop _athwart_ anything—To come across it; to find it. =auxiliary=—A sailing ship equipped with an engine for use in emergency or in crowded waters is said to be an auxiliary. Sometimes sails are carried on power-driven vessels for use in case it is desirable not to use the engine or in case of breakdown. In this case also the ship is an auxiliary. =avast=—The order to stop or pause in any exercise; as, “_Avast_ heaving.” =aweather=—Toward the weather side; _i. e._, the side upon which the wind blows. =aweigh=—Spoken of an anchor when it has been lifted from the bottom. =aye= (_adv._, perhaps from _ajo_, Lat. (defective verb), to say yes)—Yes; always used in lieu thereof at sea, with a repetition, “_Aye, aye_, sir,” meaning, “I understand; and will execute the order.” =back=—With sailing ships: To _back_ a square sail is to haul it over to windward so that the wind blows it against the mast. With steam vessels: _Back_ her is an order to reverse engines, so that the ship may be suddenly stopped or made to go astern. =back-stays=—Ropes stretched from a mast to the sides of a vessel, some way aft of the mast, to give extra support to the masts against falling forward. =balance lug=—See LUG. =bale=, =baler=—To _bale_ or _bale out_ is to remove water from a boat by means of a _baler_, which may be any small container capable of holding water. =ballast=—Weight deposited in a ship’s hold when she has no cargo, or too little to bring her sufficiently low in the water. It is used to counterbalance the effect of the wind upon the masts and give the ship a proper stability, that she may be enabled to carry sail without danger of upsetting, and is sometimes used in steam vessels to increase their stability or to correct their “trim”; that is, in order that neither bow nor stern will float too high. =balloon canvas=, or =press canvas=—The extra spread of canvas (_i. e._, sail) used by yachts in racing, generally, in a great sail often called a “ballooner.” =bank= (of oars)—A tier of oars all on one level. In ancient oar-driven ships there were often several banks. All the oarlocks that were at the same distance above the water level mounted oars said to be in the same bank. =barbette=—The heavy armoured foundation on which the turret of a modern battleship is mounted.