Hydraulic boat lift

A hydraulic boat lift assembly will raise and lower a boat cradle remotely, and will securely lock the cradle in an uppermost storage position. The lift as provided with a manual mechanism for unlocking the cradle from its uppermost storage position for operation when the hydraulic system is not available. The lift has a support frame that is mountable on the outside of the transom of a boat with hydraulic connections to a hydraulic system and controls within the boat. A lift mechanism connected to the support frame raises and lowers a cradle that supports a small boat or tender. The lift mechanism includes one or more hydraulic lift cylinders. In a retracted position of the lift cylinder, the cradle is elevated above the water in a storage position when the boat is under way. To ensure security of the tender, the lift mechanism employs a lock cylinder that prevents inadvertent motion of the lift cylinder from the retracted position by mechanical and hydraulic mechanisms. The lock cylinder must be deliberately unlocked by the hydraulic system before the lift cylinder will lower the cradle. A manual unlock mechanism is provided for use when the hydraulic system is unavailable and the tender must be launched.

FIELD OF THE INVENTION

This invention relates to hydraulic lifts for raising and lowering a boat into and out of the water, and more particularly to a hydraulic mechanism for locking the lift in the elevated position.

BACKGROUND

Small boats are often carried on larger vessels. They may be stored on a deck, and provided with a device that picks up the boat swings, it over the side or stern, and the lowers it into the water. Alternatively, the boat may be stored above the water in a cradle in a lift assembly mounted on the outside of the larger vessel's transom. The lift assembly may be powered by one or more hydraulic cylinders. Because the vessel may be subjected to vigorous motions, it is desirable to be able to lock the cradle securely in the uppermost storage position when underway. It would also be useful to be able to raise and lower the boat remotely with hydraulic controls.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a hydraulic boat lift assembly that will raise and lower a boat cradle remotely, and that will securely lock the cradle in an uppermost storage position. It is another object that the lift be provided with a manual mechanism for unlocking the cradle from its uppermost storage position for operation when the hydraulic system is not available. The lift has a support frame that is mountable on the outside of the transom of a boat with hydraulic connections to a hydraulic system and controls within the boat. The hydraulic passages through the transom and within the lift are devoid of flexible hydraulic hoses for maximum security and durability. A lift mechanism connected to the support frame raises and lowers a cradle that supports a small boat or tender. The lift mechanism includes one or more hydraulic lift cylinders. In a retracted position of the lift cylinder, the cradle is elevated above the water in a storage position when the boat is under way. To ensure security of the tender, the lift mechanism employs a lock cylinder that prevents inadvertent motion of the lift cylinder from the retracted position by mechanical and hydraulic mechanisms. The lock cylinder must be deliberately unlocked by the hydraulic system before the lift cylinder will lower the cradle. A manual unlock mechanism is provided for use when the hydraulic system is unavailable and the tender must be launched.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now first to the drawingFIGS. 1-9, vessel28has a transom27. Bolted onto the outside of the transom is a support frame25of a boat lift1of the invention. A boat cradle30is pivotally connected by lift mechanisms2with connecting links23to the support frame in a pantographic arrangement so that the cradle will remain horizontal as it is moved from an elevated position ofFIGS. 1 and 4above the water to a lower position ofFIGS. 2 and 3where a small boat, or tender,26resting on the cradle will be at or near the water surface for launching. Raising and lowering the cradle is accomplished by hydraulic lift mechanisms2. There may be one or more lift mechanisms.

Each lift mechanism2includes a hydraulic lift cylinder3pivotally connected at a first end7to the support frame25. A lift piston4is sealingly disposed for translatory motion under hydraulic fluid force within the lift cylinder. A first piston rod6affixed at a first end to the piston4extends through seal8from a second end of the cylinder3to pivotal connection24at a second end10to a connecting link23. Extension and retraction of rod6causes the cradle30to lower and to raise respectively. A second piston rod9extends from a second end of the lift piston and lies completely within the cylinder3during motion of the piston. A recess17at the free end of9will be used to lock the lift in the elevated position. Rods6and9lie in a common axis with the central axis of cylinder3.

A lock cylinder12is fixedly disposed adjacent the lift cylinder. A lock piston13is sealingly disposed within the lock cylinder12for reciprocating motion therein under hydraulic fluid force and spring bias between an extended lock position (FIGS. 9,12, and13), and a retracted unlock position (FIGS. 10,11,14, and15). A first lock piston rod15extends from a first end of lock piston13with a rod engagement member16at a free end thereof. This rod engagement member16passes into lift cylinder3and is received in the recess17of the free end of rod9when lock piston rod15is in extended position to prevent motion of the lift mechanism. A compression spring14forces the lock piston13and rod9to the extended and lock position when there is no hydraulic fluid force. The spring14may be a metal spring or a non-metal spring such as a polyurethane spring, as desired. A second lock piston rod18extends from a second end of lock piston13with a free end that extends out from a free end of lock cylinder12through a fluid seal19and terminates in pull fixture20to enable manual unlocking when hydraulic fluid force is unavailable. The lock piston serves an additional function of blocking the flow of hydraulic fluid through the lift cylinder when the lock piston is extended. That function will be detailed below.

As shown inFIGS. 7 through 10, the hydraulic fluid circuit5includes a hydraulic pump31, fluid reservoir32, and controls33of a type sufficiently well known in the art that details need not be given here. A first hydraulic passage35and a second hydraulic passage36through the transom27are removably connected to the hydraulic circuit5. The controls33enable one of the two passage35to receive hydraulic fluid under pressure while the other passage36passes return hydraulic fluid to the reservoir32to cause the lift cylinder to raise the cradle. To lower the cradle, the controls reverse the order of hydraulic fluid flow with passage36receiving hydraulic fluid pressure and passage35fluid returning to reservoir. As shown inFIG. 8, the passages35and36are in fluid communication with a rotary valve34that is affixed to the support frame25. The rotary valve34is of a type well known in the art for connecting two fixed passages containing fluid under pressure through an arc of rotation to two other passages without the use of flexible hoses. Not all the details are visible in the drawings. The rotary valve34incorporates the first end7of the lift cylinder to connect passage36to lift channel37that extends up into the lock cylinder12past right check valve38which only passes fluid left into a chamber formed by a reduced diameter portion40of the first lock piston rod15. Pressurized fluid path is indicated by a series of small circles. Fluid continues up to the reduced diameter portion41at the other end of the lock piston. Because the area of the piston exposed to the fluid pressure at40is greater than at41, the pressure difference will force the piston13upward to the fully retracted position shown inFIGS. 10 and 15. The rod engagement member16is withdrawn from the recess17in the piston rod9so that the lift piston is free to move. Spring14is compressed and annular passage42in piston13is now in position to allow pressure fluid in lift channel37access to channel43that is in fluid communication with the right side of lift piston4to extend rod6and lower the cradle. When the lift is at the lowered position shown inFIG. 11, pressurized fluid, as shown by closed circles, from passage35will be applied to the left side of lift piston4when the cradle is to be lifted. Fluid on the right side of piston4, as shown by open circles, will be forced up through channel43and then through left check valve39to force lock piston13up until passage42is open to enable flow of return hydraulic fluid to the reservoir of the hydraulic circuit5.