shapes of sail to accommodate different wind strengths and points of sail. A suite of sails on a racing yachts would include several weights of jib and spinnaker, plus a specialized storm jib and trysail (in place of the mainsail). Performance yachts are likely to have full-battened kevlar or carbon-fiber mainsails. Underwater foils can become more specialized, starting with a higher-aspect ratio fin keel with hydrodynamically efficient bulbs for ballast. On some racing yachts, a canting keel shifts angle from side to side to promote sailing with less heeling angle (sideway tilt), while other underwater foils take care of leeway (sideways motion). Motor yachts Motor yachts range in length from before they are considered super-yachts or mega-yachts, which are and longer. They also vary by use, by style, and by hull type. As of April 2020 a yacht, REV Ocean, was under construction, which when launched would replace the Azzam as the longest superyacht. As superyachts have grown size, the distinction between a yacht and a ship (perhaps converted for personal use) has become unclear. A proposed definition for calling a vessel a yacht rather than a ship would if it was constructed solely for personal use and has a combined occupancy of less than 100, including crew. Classification The United States Coast Guard classifies motorboats—any vessel less than , propelled by machinery—in four classes by length: Class A: motorboats less than Class 1: motorboats Class 2: motorboats Class 3: motorboats Style A motor yacht's style can both be functional and evoke an aesthetic—trending towards the modern or the traditional. Among the styles, mentioned in the literature, are: Cruiser – A cruiser has a displacement hull for economical, long-distance passage-making. Sports cruiser – A sports cruiser has a semi-displacement or planing hull for fast trips. Sports fisherman – A sports fisherman has a semi-displacement or planing hull for fast trips and carries gear for recreational catching of large fish. Expedition –An expedition yacht has a displacement hull for economical, long-distance passage-making to remote destinations. These are also called yachts. Lobster – A lobster yacht is styled like a Maine lobster boat and has a semi-displacement or planing hull for fast trips. Trawler– A trawler has conservative, traditional styling and has a displacement hull for economical, medium-distance passage-making. Hulls There are three basic types of motor yacht hull: , , and , which have progressively higher cruise speeds and hourly fuel