Marine Boiler

Form of internally fired boiler for steamship use. It has to be self-contained, as no brick-setting is po ible. In large ve els, the boilers are on both sides of a central gangway from which the firing is done, the boilers in groups delivering their smoke and gases to a central stack. In the type now approved, the shell is cylindrical, with two fur naces in the lower part. The furnaces and the ash-pit are surrounded with water in water-legs, and the gases pa back through large flues. In a back-connection, also surrounded by water, the smoke and gases rise and come forward through tubes to the front connection, whence they pa off to the chimney: hence the water level stands high in such boilers. There is often no dome on each separate boiler, but a large pipe connects the boiler through a valve with a steam chimney (see DOME). The earlier or Martin boiler was not circular, but was shaped with flat areas, so as to conform to the profile of the hull athwart-ship: the flat surfaces were stayed together. Marine boilers are often of plate 14 inch thick, and carry from 120 to 160 lbs. pre ure per sq. in. Torpedo boats often use LOCOMOTIVE BOILERS (q.v.): see also BOILERS.