Abstract: A wheelmotor direct-drives the bucketwheel for wet underwater service in dredging. This eliminates the combination of an intervening gear box and a watertight chamber to house the rotating shaft hydraulic motor of conventional dry underwater service practice. In a preferred embodiment, a compression seal is provided which is adapted to create a chamber within the seal thereby providing a first line of defense against the intrusion of water into the junction of the stationary shaft and the rotating case. By injecting underwater lubricating grease into this chamber, displacing all of the air therein, the sliding contact surfaces are lubricated and a second line of defense against the intrusion of water is provided.

Abstract: The electrostatic recovery of gold in the drywasher is improved by providing means to scavenge the waste heat from the internal combustion engine that powers the air blower. This preheats the intake air to the air blower, whereby the equilibrium temperature of the compressed air delivered to the partially fluidized bed of ore particles on the riffle table is raised about 50.degree. F. above ambient temperature. The layer of fabric underlying the bed of particles is maintained at bone dryness, the ore particles are dried, and the electrostatic forces operate under most favorable conditions at low relative humidity.