Boom

Boom, in a ship, is a general name for the long spars which jut out from certain supports or uprights, to stretch or extend the bottom edge of sails. According to their connections, they receive the names of jib-boom, flying jib-boom, main boom, square-sail boom, &c. In the old 110-gun ships of Nelson's days, these booms varied from 57 to 32 feet in length. Modern ironclads are provided with a number of booms to be fitted at intervals along their sides, from which may be suspended a huge net encircling the ship at a sufficient distance from the side to render an explosion from an enemy's torpedo harmless. The term boom is also applied to a strong iron chain, or a combination of spars, &c., lashed together with chains and cables, and employed in barring the navigable passage of the mouth of a harbour or river. The wooden boom across the harbour was an important feature in the famous defence of Londonderry in 1689.