Abstract:
A boatlift including two floatation chambers operably engaged to a boat hull engaging means by a lifting means connected therebetween. The lifting means is adapted to raise and lower the boat hull engaging means with respect to the floatation chambers, which, in turn, is adapted to buoyantly support both the boat hull engaging means and the lifting means. The boat lift may be either connectable to a stationary object such as a dock, pier or seawall, or may be adapted to be trailerable by land vehicle.

Description:
This is a continuation-in-part of application Ser. No. 07/229,928 filed Aug. 8, 1988, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to docking and trailering means for boats, and more particularly to a floatable boatlift for raising a boat from the water during storage and servicing. 
     As an alternative to mooring and storing a boat in the water tied to a pier or bulkhead, in addition to dry storage, two well-known devices are available to a boat owner. The first is in the form of a conventional boat trailer wherin the boat may be hoisted atop the trailer and removed from the water by a towing vehicle. 
     The second option generally available is in the form of a floating dock. This system includes a pair of spaced apart parallel, elongated floatation chambers which may be filled with water as required. Structures connected between these floatation chambers are adapted to engage the hull of the boat and to support same thereatop. In order to utilize this well-known system, the floatation chambers are filled with water to submerge the entire system, whereupon the boat may be driven or pulled in position directly over the center hull engaging member. Thereafter, the water is pumped from the floatation chambers, whereupon the entire system and the boat thereatop are raised above the surface of the water. 
     Significant limitations are associated with such floatable docks. One such limitation resides in conjunction with the potential imbalance during filling of the floatation chambers whereupon the entire system may roll or pitch within the water-carrying with it the potential of the boat sliding from its resting position into the water. An additional limitation resides in the deeper water required in order to completely submerge this assembly beneath the waterline so that the boat may be driven or pulled thereover. 
     With regard to towable boat trailers, applicant is unaware of any significant floatation means in conjunction therewith which would render these devices floatable. 
     The present invention provides a boatlift which may be provided in a form which is tieable to a stationary object such as a pier or seawall or may be made towable behind a land vehicle. The floatation chamber is moveable upwardly and downwardly in relation to the boat hull engaging member so that the boat placed thereatop may be conveniently raised and lowered without any of the undue limitationhs heretofore described. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention is directed to a boatlift including two floatation chambers operably engaged to a boat hull engaging member by a lifting member connected therebetween. The lifting member is adapted to raise and lower the boat hull engaging member with respect to the floatation chambers, which, in turn, are adapted to buoyantly support both the boat hull engaging member and the lifting member. The boat lift may be either connectable to a stationary object such as a dock, pier or seawall, or may be trailerable by land vehicle. 
     It is therefore an object of this invention to provide a boatlift which is connectable to a stationary object such as a pier or bulkhead and which will supportively receive a boat placed thereatop to be raised above the water by this invention. 
     It is another object of the above invention which minimizes the depth of water required for full functioning thereof. 
     It is another object of the above invention to provide a boatlift which may be towable by a land vehicle and which provides upward and downwardly moveable floatation chambers to facilitate raising a boat placed thereatop from the water both at a boat ramp and in open water, if required. 
     In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with reference to the accompanying drawings in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a three dimentional view of the invention. 
     FIG. 2a is an end view of one half of the system showing the tanks empty and lift beams up. 
     FIG. 2b is an end view of one half of the system showing the tanks flooded and lift beams down. 
     FIG. 3 is a top view of the system adapted to a boat trailer. 
     FIG. 4 is an end view of the system that is adaptable to a boat trailer. 
     FIGS. 5a and 5b are sideviews of the feedscrew ends showing threadless stops. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention relates generally to docking a boat above the water and more specifically to a shallowdraft floating boatlift for raising a boat above the water for servicing and storage; This concept being adaptable to an existing boat trailer. 
     This system is comprised of two floatation tanks (FIGS. 1--1a and 1b) equipped with bilge pumps for raising and lowering (not submerging) the tanks. 
     The tanks will be connected with two fixed beams (FIGS. 1--3a and 3b) at the bottom of the tanks for the purpose of separating and stabilizing the tanks at the width of the boat to be lifted creating essentially a binary (or catamaran) system. In addition there will be two movable lifting beams (FIGS. 1--2a and 2b) one fore and one aft of the fixed beams, upon which the boat will be cradled. Each extreme end of the lifting beams will be affixed to a feed screw (FIGS. 2--8) for the purpose of raising and lowering said beams. This could be accomplished in other ways; but for the purpose of this invention, the inventor intends to utilize threaded rod (worm gears). 
     OPERATIONAL SUMMARY 
     The unique shallow draft operation of this boatlift is accomplished by combining two existing physical principles. The first principle is buoyancy. Lift and draft (height and depth), are accomplished by pumping water in or out of said tanks. The tanks reduce in height as water is pumped in and increase in height as water is pumped out. There is 57.14 pounds of lift per cubic foot of displacement (Oxford Companion to Ships and the Sea). The second principle is mechanical: the intended application being an inclined plane (feed screw). The height and draft of the lift beams are exchanged by screwing the lift beams up or down. 
     For the purpose of entering the lift with a boat, the floatation tanks will be flooded lowering their top surfaces to within six inches of the water and their bottom surfaces will be 21/2 feet below the water, (if the tanks are hypothetically 3 feet tall). The tanks will never be totally submerged since the drive winches will be located under the deck in individual compartments (FIGS. 1--5a,b,c,d and FIGS. 2-4). The lift beams will be concurrently screwed to their lowest position at the bottom surfaces of the tanks (if the beams are hypothetically 6 inches tall). There is at this point 2 feet to 21/2 feet (depending on capacity and assembly of said boatlift) of draft for boat entry (FIG. 2b). The average hull draft of a 20 foot--28 foot pleasure boat is approximately 14 inches-18 inches depending on type and manufacturer. The shalloow draft character of this invention becomes obvious since the boat needs only 6 inches of water beneath its keel to enter the boatlift. At this point the water is pumped out of the tanks creating lift beneath the hull of the boat and partially raising the boat out of the water. As the vessel&#39;s waterline starts raising above the water the feed screws (FIGS. 1--2a and 2b) will be engaged creating the finishing lift needed to raise the vessel to a point at which the keel exits the water (FIG. 2a). 
     Since there is no super structure on this lift, it is obviously low profile. This is more than aesthetic in nature because there are no beams and machinery to climb over or under allowing easy boat boarding and de-boarding. 
     In addition to the basic request for patent on the shallow draft, floating boatlift there are other claims being made. FIG. 1 shows fixed beams (FIGS. 1--3a and 3b) and lift beams (FIGS. 1--2a and 2b) sectioned with a beam in a sleeve in each instance. This option allows telescopic width adjustment making it possible to fit different width vessels. 
     Another design feature pertains to the feed screws having no threads at the top and bottom 6 inches (FIGS. 5a and 5b. This disallows overwinding which if done would be damaging and potentially dangerous. 
     Another feature has to do with the method for cradling the vessel on the lifting beams. The inventor proposes suspending straps (FIGS. 2--7) from the triangles (FIGS. 2--6) at the extreme ends of each lift beam (FIGS. 2--1). This accomplishes several things: straps take up very little space, they are non abrasive to said vessel, and they spread the load over a longer line. Mostimportantly, the vessel does not touch the beams&#39; centers, consequently; most of the downward load of the boat is at the extreme beam ends vastly reducing the tendency of the floats to envelope (fold up and in). Using lifting straps is not a unique idea, however; using them in conjunction with rigid lifting beams is. Lift straps normally extend above the gunnel (point at which boat side and boat deck meet) of the vessel being lifted, and ending at the lift super structure such as in a boathouse lift. This new method will maintain a low profile since the strapping extends only to the chine (point at which boat side and boat bottom meet) of the vessel being lifted. This system also allows a reduction in material cost for producing said boatlift. The normal cradle system presently utilized consists of wooden 4&#34;×4&#34;s perpindicular to or horizontal with the boat&#39;s keel (depending upon vessel size and type). In either application the downward loading is in the center one-third of the lift beams. 
     Another claim being made by this inventor is the same hydro-mechanical principle being applied as an add on system to an existing boat trailer. By attaching screw collars to the trailer frame, placing triangular shaped buoyancy tanks beneath and up between trailer members and feeding screws through the add on collars to the tanks, a floating lift trailer will be accomplished (FIG. 4). These tanks will have to be customized to the particular trailer allowing for the different designs. 
     Cradling systems will not be addressed since they are already incorporated in said trailers. The operation will be the same for the trailer lift system except the complete trailer will be screwed up or down in conjunction with or opposition to said buoyancy tank. These lifts are of special interest to boat racers. Racers will not have to wait for the crane to load and unload their vessels between heats with a trailer float lift. 
     The winches or power mechanisms will not be discussed since there are several currently produced that may be purchased and utilized, and the inventor makes no claim here. Mooring methods similarly will not be claimed since there are many and they have no bearing here.