Obviously the Hoverskid is only able to operate when it can detect solid ground beneath it and the range of it's sensors is only up to 2 meters. Therefore it works in shallow water and dry ground but it doesn't work in deep water.
Or in space.
(whew...continuity of the Worldspanner universe still intact)
Or something like...the hover effect only works over land but the skid auto-adjusts to stay above water, as long as land beneath it is within operating range.