Most motor yachts use twin fixed pitch propellers that are driven by diesel engines, with a great variety in the size and power of the systems dependent on the yacht. Sailing yachts are mainly fitted with one or two fixed pitch propellers. Under this umbrella there are many variables, including waterjet propulsion, pod propulsion and hybrid propulsion. Diesel electric and electric hybrid systems, which make use of combined power sources, are seeing increased advances, with more yachts being developed and built with “green” propulsion systems.