A stationary rectangular base frame is mounted underwater and supports generally upwardly extending, swingable, parallel links or arms. A lift platform or lift pads are supported at the upper end portions of the arms and, in combination with the base frame and arms, form one or more upright parallelograms....http://www.google.es/patents/US4895479?utm_source=gb-gplus-sharePatente US4895479 - Lift for watercraft
