Abstract: The invention concerns an hydraulic machine, typically a submerged surface cleaner which comprises a body having a liquid inlet and a liquid outlet and a conduit extending between the inlet and the outlet. A drive element is supported in or adjacent to the conduit, with a clearance between the drive element and the interior of the conduit, in a manner permitting eccentric location and rotation of the drive element relative to the conduit. The conduit can be connected in a liquid flow path so that liquid passing through the conduit past the drive element, when the drive element is positioned eccentrically relative to the conduit, applies differential forces to the drive element to cause it to rotate relative the conduit. The rotation of the drive element is used directly or indirectly to drive the cleaner over a submerged surface.