A steam generator, in the sense of an auxiliary boiler on a ship, is a form of boiler. It uses high-pressure superheated steam from the main steam supply used for propulsion, and uses this to generate low pressure saturated steam. This is then used to power auxiliary steam engines around the ship such as winches or pumps, or to supply any steam requirement on the ship that does not require high superheating, such as boiler feedwater and freshwater evaporators.
Low-pressure steam generators
A typical generator produces around 10,000 lb/hour at around 120 psi, using inlet steam supplied at 600 psi. They are constructed as a cylindrical steel pressure vessel, either horizontal or vertical, containing a series of heating coils. There is a strong resemblance to the design of evaporators, although steam generators can be rather simpler as they use treated feedwater, rather than scale-producing seawater.