Abstract: A self-propelled machine has an internal chamber having a conveyor mechanism extending through an opening in a wall. A buoyancy control allows admission of pressurized air into the chamber to allow adjustment of the buoyancy of the machine. A series of conveyors within the chamber convey material into the chamber which is washed to leave behind sediment and other materials. Washed nodules are conveyed to a transport machine and are stacked in the transport machine. The transport machine may be disconnected from the self-propelled machine to allow nodules to be brought to the surface. Sensors are provided in the self-propelled machine to control attitude, direction, and movement.