The motive force being the wind, sailing is more economical and environmentally friendly than any other means of propulsion. A hybrid type of vessel is a motor sailing yacht that can use either sail or propulsion (or both) as conditions dictate.Many "pure" sailing yachts are also equipped with a low-power internal-combustion engine for use in conditions of calm and when entering or leaving difficult anchorages. Vessels less than 7 metres (23 ft) in length generally carry a petrol outboard-motor of between 3.5 kilowatts (5 hp) and 30 kilowatts (40 hp). Larger vessels have in-board diesel engines of between 15 kilowatts (20 hp) and 75 kilowatts (101 hp) depending on size. In the common 7 metres (23 ft)-14 metres (46 ft) class, engines of 20 to 40 horsepower are the most common. Modern sailing yachts can be equipped with electric inboard motors in order to reduce consumption of fossil fuel. The latest technology are outboard electric pod drives that can also regenerate electricity (motogens). These Motogens can be made retractable to increase the efficiency of the yacht. Some of these yachts are extremely efficient and do not need additional diesel generators. This technology is called Green Motion.
