Abstract: An hydraulic boat lift utilizing readily available city water as the pressure fluid comprises one or more lift cylinders buried vertically under a body of water with the upper ends of the cylinders protruding into the water. To increase the pressure of the water and the resultant lift of the hydraulic cylinder, a single booster cylinder and a transfer cylinder for each of the lift cylinders are provided with the piston in the booster cylinder having a larger area than any of said transfer pistons and being rigidly connected to one another so as to provide equal displacements of the booster and transfer pistons and to simultaneously operate all of the lift cylinders at equal rate of displacement. Means are provided for automatically operating the booster cylinder through a number of charge and discharge cycles to accomplish complete elevation of a cradle.

Abstract: An hydraulic boat lift utilizing readily available city water as the pressure fluid comprises one or more lift cylinders buried vertically under a body of water with the upper ends of the cylinders protruding into the water, a cradle supporting plate is connected to the top of each cylinder ram to support a cradle below the water surface until the cradle is elevated above the water surface, the cradle being stabilized in a horizontal plane by at least three poles vertically buried below the water and spaced equiangularly about each lift cylinder, each pole at its upper end being connected by a rigid radial member to the upper end of the lift cylinder and the cradle supporting plate being connected to the upper end of each pole by a chain having means to adjust its length to prevent the plate and cradle from being unbalanced out of horizontal position.