Due to short passages and fast turns, the high-speed marine diesel engines for high-speed vessels, passenger ships, and ferries operate under severe conditions of frequent starts, rapid acceleration, and hot shutdown. We consider that various failures of high-speed diesel engines are associated with such maneuvering patterns of high-speed vessels. In order to determine the load characteristics of high-speed engines during operation, full-scale measurements of a fast ferry with a water-jet were carried out. The shaft output and in-cylinder pressure of the engine were measured continuously from engine start to shutdown. The data acquisition method is described, and the transient performance of engine load, from harbor to cruise maneuvering, and characteristic relationship between power absorption and shaft speed of the water jet are presented. An engine performance analysis using in-cylinder pressure in various running conditions is also presented.