A modern sailing ship or sailship is any large wind-powered vessel. A "ship-rigged" sailing ship is a sailing vessel that carries three or more masts with square sails on each. Large sailing vessels that are not ship-rigged may be more precisely referred to by their sail rig, such as schooner, barque (also spelled "bark"), brig, barkentine, brigantine or sloop. In 1902 the sailing vessel Preussen was the first to assist handling of sails by making use of steam power without auxiliary engines for propulsion. The steam power was used to drive the winches, hoists and pumps. A similar ship Kruzenshtern, a very large sailing vessel without mechanical assists, had a crew of 257 men, compared to the Preussen, which required only 48 men. In 2006, automated control had been taken to the point where sails could be operated by one person using a central control unit, DynaRig. The DynaRig technology was first developed in the 1960s in Germany by W. Prolls as a propulsion alternative for commercial ships to prepare for a possible future energy crisis. The technology is a high-tech version of the same type of sail used by the Preussen, the "square-rigger". The main difference is that the yards do not swing around a fixed mast but are rigidly attached to a rotating mast. DynaRig along with extensive computerization was used in the proof-of-concept Maltese Falcon to enable it to be sailed with no crew aloft. As of 2013, with increasing restrictions on use of bunker fuel, attempts were underway to develop hybrid sailing ships using automated sail and alternative fuels.