a low profile carriage is mounted on widely spread wheels to roll along the underwater surfaces of a swimming pool . the carriage is propelled by a high velocity stream of water projecting from a rearwardly directed thrust nozzle . there is a venturi restriction just forward of the thrust nozzle , creating a low pressure zone that induces flow of water through the bottom of the carriage , drawing in leaves and other debris . the water so drawn in passes through a screen , trapping the debris in a removable pod or bin depending from the carriage . the top of the carriage is relatively flat and the depending debris pod is curved downward to form an inverted air foil , whereby the pressure differential between the top and bottom of the carriage biases the carriage against the swimming pool surface traversed thereby .