During the last fifteen years, the marine industry has seen results of a technological revolution in the form of diagnostic tool development. With application of computers and oscilloscopes, certified service technicians can tell just about any characteristic of an engine…whether it be wear rates from the internal frictional surfaces of the engine components or performance characteristics of the total propulsion system. Extensive research and development work has been done in the area of marine performance analysis. A system has been developed that utilizes all of the diagnostic tools developed over the years in a systematic approach to make a definitive measurement of the entire propulsion system. This program evaluates the fuel system, cooling system, propeller, transmission and the air/intake and exhaust system. In marine vessel operation, it is vitally important to have a properly matched propulsion system. It is a major consideration for a naval architect when designing the vessel and the propulsion system. But the complexity of that system makes if difficult to predict how all components will match up while the vessel is under way and loaded. It requires precise calculations of complex data; and with the aid of a computer, the job can be done quickly and accurately.