Fan disturbing sand at the bottom of a body of water so that it may be pumped up efficiently

A fan for hydraulically disturbing sand at the bottom of a body of water, said fan comprising a central supporting member having a frusto-conical outer surface which is larger at its upper than its lower end and a plurality of vanes attached along their inner edges to said surface, said vanes being circumferentially distributed about said supporting member and extending for a substantially uniform distance from said frustoconical surface throughout their lengths, the lower part of each vane being substantially straight while its upper part is curved toward the direction of rotation of the fan.