a float suitable for use as a buoy or as a component for a wave - powered vehicle . the float includes an upper member whose height can be changed and / or which remained substantially vertical even when the float is in wave - bearing water . a low drag cable suitable for use as a tether in a wave - powered vehicle has a streamlined cross - section and includes a tensile member near the front of the cross - section , at least one non - load - bearing member behind the tensile member , and a polymeric jacket . wave - powered vehicles having a float , a submerged swimmer and a tether connecting the float and the swimmer , include a means for determining whether the tether is twisted ; or a means for untwisting the tether ; or a pressure - sensitive connection which can disconnect the tether when the vehicle is dragged downwards by entanglement with a whale ; or a 2 - axis universal joint securing the tether to the float or to the swimmer ; or elastic elements which absorb snap loads created by the tether ; or two or more of these .