COGAS stands for Combined Gas And Steam and refers to a type of combined cycle propulsion system for ships. In a COGAS system, a gas turbine is used to provide main propulsion motive force, but heat from the turbine is then used to drive a steam turbine which provides additional power. In essence, it is a means of recovering energy that would otherwise have been wasted. The lower power setting efficiency of a COGAS system is notably higher than that of a gas turbine alone, while still allowing for the high maximum power delivery of the gas turbine plant. COGAS is used to specifically refer to systems where both plants provide mechanical energy; if either turbine is used to drive a generator, the system is usually referred to as a COGES system (Combined Gas, Electric, Steam). See also: CODOG, COGAG, COGOG, COSAG, CODAD, COSAG.