Abnormal Refraction. Displacement of visible horizon and observed objects by an unusual amount. Objects that would, normally, be below horizon may be seen above it. Usual check is by 'Back Altitude'.
Aboard. On board. In, into or inside a vessel. Close alongside.
'Aboard Main Tack.' Order to haul main tack down to chess tree. Given when sailing close-hauled in a square-rigged ship.
Abordage.*The act of boarding and taking an enemy vessel.
About. Used, in conjunction with other word or words, with reference to changing from one tack to the other when under sail.
About Ship. To put a ship, under sail, on the opposite tack. 2. Order to crew to go to stations for tacking or wearing.
A-Box. Said of yards when those on one mast are braced in a direction opposite to that of yards on next mast.
'A' Bracket.Forging that carries after end of propeller shaft in twin-screw vessel. Upper arm is secured to shell plating or to a plate inside vessel, lower arm is secured to keel or to a steel casing on keel.
Abreast. Said of ships on parallel courses when abeam of each other. Objects inside a ship are abreast when they are in the same transverse line.
Abroad.* Said of a flag, or sail, when it is hoisted or extended.