A new series of diesel outboard motors has been developed and settled on the market since 1987 in Japan and since 1988 outside Japan. The diesel engines for these units ware specially developed for outboard use and incorporate several innovative design features and new concepts. They achieve 4500 rpm operation for the first tine ever with this land of small direct injection diesel, and are also the lightest diesels in this horsepower range with a weight power ratio of 1.55 kg/HP.In the early stage of the development, basic research was conducted on the engine structure and injection / combustion system in order to overcome the weight barrier of the diesel and even so to maintain its durability and reliability for marine use. The result is a unique structure, incorporating an integrated aluminium cylinder head-block with cast iron cylinder liners casted in, a high speed direct injection combostion system using a mini unit injector, a timing belt drive OHC, direct sea water cooling, a vertical crankshaft, etc.The YDOM (Yanmar Diesel Outboard Motor) features: Certain starting and reliable operation. Extremely low fuel consumption. (1/2∼l/4 of gasoline consumption) Higher torque and safer cruising. Same maneuverability as GOM (gasoline outboard motor). Low vibration and noise. Less inflamable fuel.With these features, around 3000 units have already been marketed and are performing well, not only on work and fishing boats but on pleasure boats as well.