Abstract:
A boat lift supported completely from land adjacent to water in which a boat is to be operated for movement between storage and launching positions by the use of parallelogram linkage powered by pairs of hydraulic actuators arranged at opposite sides of the boat lift. A walk and handrails are formed between the hydraulic actuators for use by passengers boarding the boat in the boat launch position.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to boat lifts and more particularly to a boat lift that is mounted on land adjacent to the water for lowering a boat from a storage position on land to a launching position in the water.  
       BACKGROUND OF THE INVENTION  
       [0002]     Boat lifts of various kinds have been developed but most are limited in one way or another because they rely on supporting underwater structures for installation and require special permits because they occupy submerged land owned by other than the riparian owner.  
         [0003]     One structure which avoids many of these problems is disclosed in the patent to Voegeli U.S. Pat. No. 6,598,549 issued Jul. 29, 2003. In that patent the boat lift is supported from land adjacent to the water such as a bulkhead or seawall without relying on any underwater support. The Voegeli boat lift has many advantages but is limited to smaller boats because of the maximum weight of the boats that can be handled. This limitation is believed to result from the arrangement of hydraulic actuators which are disposed so that one actuator expands and the other simultaneously contracts between adjacent points on a parallelogram linkage and more widely spaced points on the land supported base structure.  
       SUMMARY OF THE INVENTION  
       [0004]     It is an object of the invention to provide a boat lift which can be supported on dry land adjacent to the water and which moves a boat through a parallelogram linkage between a boat storage position on dry land and a boat launching position in which a boat is delivered to the water adjacent to the boat lift.  
         [0005]     It is another object of the invention to provide a hydraulic system for such boat lifts in which the forces needed to move the boat are transmitted efficiently.  
         [0006]     It is still another object of the invention to provide a boat lift having a hydraulic system in which the cylinders at each side of the boat lift are operated from a fully extended boat launching position to a collapsed or retracted boat storage position.  
         [0007]     It is a further object of the invention to provide a boat lift having a hydraulic system in which pairs of cylinders are operated at the same time without any particular effort to make them operate in sequence or in a timed relationship to each other.  
         [0008]     Yet another object of the invention is to provide a boat lift in which cylinders can be arranged at opposite sides of the boat lift to provide for the passage of users to the launched boat.  
         [0009]     The objects of the invention are attained by a boat lift having a base member secured on land and a boat supporting structure connected to the base member by a lift frame having opposite ends pivotally connected to the base member and to the boat supporting frame at a pair of first pivot axes and a pair of tie bars having a length equal to the lift frame are connected at their opposite ends to the base member and supporting frame of a pair of second pivot axes. The first and second pivot axes are equally spaced to form a pair of parallelogram linkages with one at each side of the base member for guided movement of the boat supporting structure between a boat launching position and a boat storage position. Movement of these parallelogram linkages are attained simultaneously by a pair of support arms pivotally connected and extending upwardly at opposite sides of the base member with a first pair of fluid pressure actuators with one disposed at each side of the base member and acting between the support arm and base member and a second pair of fluid pressure actuators with one disposed at each side of the base member and operative to act between said support arm and the parallelogram linkage. The first and second pairs of fluid pressure actuators are operative to move the boat supporting platform between a boat launching position in which all of said actuators are fully extended and a boat storage position in which all of said actuators are fully retracted. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a side elevation of the boat lift embodying the invention illustrating a boat storage position in full line and a launch position in phantom line;  
         [0011]      FIG. 2  is a perspective view of the boat lift apparatus in its boat launching position in which the boat supporting platform would be submerged in water; and  
         [0012]      FIG. 3  is an end elevation taken on line  3 - 3   FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0013]     The boat lift embodying the invention is designated generally at  10  with its major components comprising a base  12  which is supported on land and a main frame  14  which supports a boat during the lifting operation and a lift frame  16  between the main frame and the base  12 . The base  12  has a pair of rails  17  to be fixed to a foundation or pad  18  adjacent to the shore or seawall  20  (as seen in  FIG. 1 ) separating the land from the water at the shore of a body of water.  
         [0014]     The main frame  14  is fabricated of steel I-beams and has a pair of side members  22 , each which has a horizontal portion  23 , a vertical portion  24  and an angled upper arm  25 . The main frame side members  22  are spaced apart the same as the side rails  17  of base  12 . The horizontal portions  23  of main frame  14  can be fitted with wooden stringers  26  to engage opposite sides of a bottom of a boat  27  to support it during lifting operations. Such stringers  26  are custom made to fit the boat bottom to be handled.  
         [0015]     The lift frame  16  is generally rectilinear with a pair of side members  28  of steel I-beams and a pair of transverse tubular pivot members  29  and  30  at opposite ends of the side members  28 . The pivot members project outwardly from opposite sides of the side members  28  to form bearing support for other components of the lift  10  such as the base member  12  and main frame  14 . As seen in  FIG. 1 , the outer ends of the tube  29  are journaled in bearing members  31  fixed near the juncture of vertical member  24  and upper arm  25  in each of the side members  22 . The outer ends of lower tube  30  are journaled in bearing members  32  fixed in a similar manner at opposite sides of base member  12 .  
         [0016]     A pair of tie bars  36  are disposed parallel to side members  28  of lift frame  16 . One end of each of the two tie bars  36  are connected at pivot elements  38  to the outer ends of upper arms  25  of lift frame  16  and the other ends of tie bars  36  are each connected at pivot elements  40  to the upper ends of vertical members  42  extending upwardly from the side rails  17  of base  16 . A pair of braces  43  extend from side rails  17  of base  12  to vertical members  42  and the bearing members  32  are supported in the braces  43 .  
         [0017]     The various components form four corners of a parallelogram linkage. A first pivot axis A is formed at the axis of tube  30  between base  12  and lift frame  16  and a second pivot axis B is formed at the axis B tube  29  between main frame  14  and lift frame  16 . Similarly, the pivot connections  38  at one end of tie bar  36  at main frame  14  forms a third pivot axis at C and the pivot connection  40  at base  12  forms a fourth pivot axis at D. The distance between pivot axes A and B are equal to the distance between pivot axes C and D to form the long side of the parallelogram linkage. Similarly, the pivot axes A and D and pivot action B and C are equal spaced to form the short sides of a rectangular parallelogram linkage.  
         [0018]     The parallelogram linkage serves to move the base supporting horizontal member  23  of the main frame  14  and to maintain it in its horizontal position during all of its movement between a boat storage position as seen in full lines in  FIG. 1  and a boat launching position as seen in  FIG. 3 . From an examination of  FIG. 1  it will be seen that the parallelogram linkage is tilted from the horizontal so that the upper arm  25  of main frame  14  between pivot axis A and B moves in an arc between a boat storage and launch positions with the horizontal portion  23  of the main frame  14  moving away from the base member  12  and downwardly toward the water.  
         [0019]     The hydraulically powered means for moving the parallelogram includes a pair of upwardly extending load transfer arms  46  having their lower end pivoted to tube  30  at a point between braces  43  of base  12  and the lift frame  16 . The upper ends of transfer arms  46  are provided with a connector  47  forming the mounting for pivotal connection to a pair of double acting hydraulic actuator cylinders  48  and  49  each having a cylinder end  50  and a rod end  51 . As seen in  FIG. 1 , the cylinder end  50  of each of the hydraulic cylinders  48  and  49  is connected to the connector  47 . The rod end  51  of hydraulic cylinder  49  is connected to a mounting member on the base frame  12  and the rod end  51  of cylinder  48  is connected to a pivot member fastened to tube  31  at the pivot axis B. The arm  46  and cylinders  48  and  49  are duplicated at opposite sides of the lift structure  10 .  
         [0020]     Upon transmission of hydraulic fluid simultaneously to all four cylinders when the main frame  14  is in its boat storage position as seen in  FIG. 1  and with all of the cylinders initially collapsed, the extension of rods  50 ,  51  of the hydraulic actuators  48  and  49  causes the parallelogram to move the main frame  14  until the horizontal member  23  is submerged in the water in its boat launching position as seen in phantom line in  FIG. 1  and in  FIG. 2 .  
         [0021]     To move the lift in a return direction to a boat storage position the hydraulic actuators are operated to retract from their fully extended position to a fully collapsed or retracted condition as seen in full line in  FIG. 1 . In that position the angled portion of the lift frame  16  between the horizontal portion  23  and vertical portion comes into abutting relation with a complementary top surface of the base  12  as seen in  FIG. 1  so that the lifting mechanism and the boat on the platform  23  are relieved of the loads experienced during movement to and from the boat launch position seen in  FIG. 3 .  
         [0022]     The boatlift  10  is provided with a gang plank or walk which is disposed between hand rails  62  at opposite sides and is disposed centrally of the boatlift  10  between the mechanism at opposite sides. The walk and hand rails  62  are mounted on the transverse mounting tubes  29  and  30  at opposite ends of the lift frame  16  and moves therewith so that it is accessible for use when the boatlift  10  is in its boat launching position as seen in  FIG. 3 . In the boat storage position seen in  FIG. 1  the walk and hand rails  62  are disposed vertically.  
         [0023]     The hydraulic controls and the various hydraulic lines are not shown but can be mounted in selected locations, for example, to one side of the lift  10  where operation of a single lever controlled valve gives the operator the control and good visibility of the boat launching and boat storage operations.