=BLUE PETER.=--A square blue flag with a square white centre, hoisted to denote that a vessel is about to sail and that all persons concerned must repair on board immediately (the letter “P” in the international flag signal code.) =BOOM.=--A boom is a pole extending outboard--i.e., away from the sides of a vessel. =Lower and Quarter Booms.=--Booms, conveniently placed, to which boats can make fast. =BORE.=--The interior diameter of a gun at the muzzle; also the name given to the interior of a gun. Also a word used to express a sudden rise of the tide in certain estuaries as in the Severn. =To bore.=--When down by the head a ship is said to “bore.” =BOTTOMRY.=--The hull of a ship pledged as security for a loan. =BOWS.=--A term indicating those portions of a vessel immediately on either side of her stem (q.v.). Differentiated in association with the terms “Port” or “Starboard.” =BOWSPRIT.=--A pole of “sprit” projecting forward from the stem of the ship. =BOX THE COMPASS.=--To name the points of the compass in regular order, i.e., in the direction taken by the hands of the clock. =BREAKWATER.=--An artificial wall or bank, set up either outside a harbour or along the coast, to break the violence of the sea and so create a smooth shelter. =BREECH.=--The end of the gun into which the projectile and cartridge are inserted when loading. =BREECH-BLOCK.=--A heavy steel block which seals the breech when the gun is loaded. =BREECH-LOADER= (=B.L.=)--Formerly a gun which was loaded at the breech end as opposed to a muzzle-loader. Now used to denote a gun the cartridge of which is not contained in a metal cylinder. =BROADSIDE.=--The number of guns which can be brought to bear on one side of, or the total weight of metal which can be fired at once from either side of a ship. =BULKHEAD.=--A structure, transverse or longitudinal, dividing the interior of a ship into compartments. =BURDEN.=--The capacity of a vessel, as 100 tons burden, etc. =BURGEE.=--Properly a flag ending in a swallow-tail. Yacht clubs’ burgees are frequently “pennants” which are flags ending in a point. =CADET, NAVAL.=--A youth who is under training to become a commissioned officer in the Navy. =CAISSON.=--A hollow, watertight vessel which can be raised or sunk by compressed air or water, and which is used when building foundations under water; or, specifically a lock gate used for closing the entrance to dry docks. =CAISSON DISEASE.=--A disease to which divers are subject. =CALIBRE.=--The calibre of a gun is the diameter of the bore (q.v.). This diameter is used as a unit of measurement. Thus, a 50-calibre 12-in. gun is a 12-in. gun which is 50 ft. long, etc. =CAMEL.=--A hollow tank or vessel filled with water and placed under the hull of a stranded ship. When well secured, the water it contains is pumped out, and the buoyancy thus created helps to lift the ship to which it is attached.