Large V12 engines are also common in ships. For example, Wärtsilä offers V12 engines with various cylinder bore diameters between 26 and 50 centimetres (10 and 20 in) with power output ranging from 4,080 to 14,400 kW (5,470 to 19,310 hp). These engines are commonly used especially in cruise ships, which may have up to six such main engines.[12] The largest medium-speed diesel engine, Wärtsilä 64, was also offered in V configuration, and a single 12V64 prototype with an output of 23,280 kW (31,220 hp) was produced for an experimental power plant in the late 1990s.[13]