Patent Publication Number: US-6709197-B1

Title: Large capacity boat lift

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/299,642 filed Jun. 20, 2001. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a large capacity boat lift and, more particularly, to a lift capable of raising and lowering vessels having weights of 75,000 pounds and greater. 
     BACKGROUND OF THE INVENTION 
     Conventional boat lifts for heavy vessels normally employ a plurality of winder driven cables located on respective sides of a boat supporting platform. Pulleys are occasionally utilized to improve the mechanical advantage exhibited by the lift. However, such systems tend to exhibit a number of disadvantages. For one thing, the lift cable when being wound experiences an effect known as reeving wherein stress is exerted unevenly on individual segments of the cable between, for example, the winder, the respective pulleys and the tie-off point of the cable. An especially large force may be exerted on the cable segment that drops from the winder. This may result in premature cable wear and expensive cable replacement. Undesirable wear on the cable is also frequently caused because the cable rubs against the grooves of the winder and/or on the sides of the pulleys. This occurs due to the fleet angle formed between the plane of the winder groove or the pulley groove and the center line of the cable. This too may unduly stress the cable and necessitate premature repairs. 
     Conventional cable driven boat lifts also tend to permit undesirable longitudinal motion of the boat supporting platform during the raising and lowering operations. This results because the supporting cables effectively shift position longitudinally on the helix of their respective winder grooves as the winders are operated and the cables are wound and unwound. Preferably, the supported vessel should remain as longitudinally stationary as possible during the lifting operation. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an improved large capacity boat lift that is capable of efficiently and effectively raising and lowering virtually all sizes of vessels and which is particularly suited for lifting boats having a weight of 75,000 pounds or more. 
     It is a further object of this invention to provide a cable operated boat lift that experiences much less cable wear than conventional lifts and which requires less frequent cable repair and replacement. 
     It is a further object of this invention to provide a cable oriented boat lift that substantially equalizes the tensile stresses on the individual segments of each cable. 
     It is a further object of this invention to provide a cable operated boat lift that reduces the reeving effect upon the cables. 
     It is a further object of this invention to provide a cable operated boat lift that permits minimal longitudinal movement of the boat supporting platform during the lifting operation. 
     This invention results from a realization that a highly efficient large capacity boat lift which exhibits equalized weight distribution on the cables and reduced longitudinal sway may be achieved by operably interconnecting both ends of each lifting cable to opposing grooves on a respective winder such that the cable is raised and lowered at each end. 
     This invention features a boat lift that includes a pair of axially rotatable winders mounted above the water on respective longitudinal sides of the boat to be lifted. Each of the winders is supported on a respective support structure. A boat supporting platform is disposed between the supporting structures and is operably interconnected to each winder by a respective lifting cable. The cable is attached proximate one of its ends to a first section of the winder and proximate an opposite second end to a spaced apart second section of the winder. Each cable is movably interengaged with an associated set of lower pulleys carried by the platform. An intermediate segment of the cable is also interengaged with the support structure by an upper pulley or otherwise. The winders are axially rotated, typically by respective drive mechanisms to longitudinally drive the respective cables and thereby selectively raise and lower the boat supporting platform. More particularly, when the winder is operated in a first direction to wind its respective cable thereon, the cable is raised to lift the platform. Conversely, when the winder is operated in an opposite direction, the cable is unwound from the winder and extended to lower the platform. 
     In a preferred embodiment, the cable may be interengaged with its associated lower support structure by means of one or more upper pulleys. The platform may carry at least one set of three axially rotatable lower pulleys on each side of the platform. In such versions, the cable is typically interengaged with a pair of upper pulleys carried by the support structure. The upper and lower pulleys are preferably in the same plane thus eliminating any fleet angle between them. Each upper pulley is located intermediate a respective pair of the lower pulleys carried by the platform. The cable extends alternately ran between the lower and upper pulleys. Typically, the number of lower pulleys exceeds the number of upper pulleys by one. When an even number of lower pulleys and an odd number of upper pulleys are utilized, a centrally located upper pulley remains rotationally stationary during the raising and lowering operations. The cable is one piece. Thus, when the lift is stationary each vertical segment of the cable carries the same load. Equalizing weight distribution prolongs cable life. All of the remaining pulleys rotate as the cable is longitudinally driven and interengages each pulley. Alternatively, when an even number of upper pulleys and an odd lower pulleys are utilized, a centrally located lower pulley (i.e. a lower pulley located between two upper pulleys) remains rotationally stationary during raising and lowering of the platform. All of the remaining pulleys again rotate in interengagement with the longitudinally driven cable. In each version, the stress differential on the individual cable segments is minimized and longitudinal movement of the platform is virtually eliminated. 
     The winders may be mounted on respective cable beams. Each cable beam may extend between a pair of support posts or pilings. Certain versions of this invention may incorporate at least a pair of winders and associated cables and pulleys on each side of the platform. Each winder may be driven by an associated motor and drive mechanism. Alternatively, a single motor drive mechanism may operate a pair of winders on each side of the lift platform. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Other objects, features and advantages will occur from the following description of a preferred embodiment and the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a preferred large capacity lift wherein a pair of lift assemblies according to this invention are provided on each side of the lift apparatus; 
     FIG. 2A is an elevational side view of the upper portion of a representative one of the lift assemblies; 
     FIG. 2B is an elevational side view of a portion of one of the lift assemblies including the lower pulleys that are mounted to one side of the lift platform; 
     FIG. 3 is a top plan view of the lift assembly of FIGS. 2A and 2B; 
     FIG. 4A is an elevational side view of a preferred winder; 
     FIG. 4B is a cross sectional view taken along line  4 B— 4 B of FIG. 4A; 
     FIG. 4C is an enlarged view of the grooves employed in the winder; 
     FIG. 5 is an elevational view of the left-hand side of a representative lift assembly illustrating how the lift assembly may be mounted on a support piling; 
     FIG. 6 is a cross sectional view taken along line  6 — 6  of FIG. 5; and 
     FIG. 7 is a cross sectional view taken along line  7 — 7  of FIG.  2 B. 
    
    
     There is a shown in FIG. 1 a large capacity boat lift  10  that is particularly suitable for lifting yachts and other large vessels having weights of 75,000 pounds and greater. It should be understood that the particular lifting capacity of the apparatus is not a limitation of this invention and the lift may be utilized to raise and lower vessels having weights less than 75,000 pounds. Nonetheless, the construction of lift  10  is especially effective for raising and lowering heavier vessels. Lift apparatus  10  comprises four distinct lift assemblies  11 , which are designed to selectively raise and lower a boat supporting platform  30 . As will be described more fully below, each lift assembly  11  is situated adjacent, and is operably interengaged with a respective corner of the lift platform. It should be understood, however, that in alternative embodiments of this invention other numbers of lift assemblies similar to those shown may be employed. 
     Each lift assembly  11  includes a pair of pilings  12  or other type of support structure. Typically, pilings  12  are mounted adjacent to one another in a known manner in the bottom or floor of a body of water W. In the version show herein four pairs of pilings  12  are employed. Two pairs (i.e. two lift assemblies  11 ) are arranged on each side of the slip or other space that accommodates the vessel to be lifted. The four pilings on each side of the slip are arranged side-by-side in a generally linear fashion along each side of the vessel. It should be understood that in alternative embodiments, various other numbers and arrangements of pilings or other types of support means may be utilized on each side of the vessel. 
     Each pair of pilings  12  supports an elongate cable beam  13  that extends between the upper end of the respective pilings. Each cable beam  13  is secured to its supporting pilings  12  by appropriate means such as brackets  15 , which are described in detail below. Each beam  13  supports a respective winder mechanism  14  above water W. More particularly, each winder mechanism includes a winder drum, hidden in FIG. 1, that is accommodated in an elongate housing or enclosure  16 . The housing and enclosed winder drum are mounted on beam  13  such that the drum is axially rotatable in a manner that is described more fully below. A drive mechanism  18  is also attached to the upper surface of each beam  13 . The drive mechanism is operably interconnected to the winder drum so that the drum may be driven selectively in opposing first and second directions. Once again, the details of the drive mechanism and its interengagement with the winder drum are described more fully below. A stop assembly  20  is mounted at the opposite end of beam  13  in interengagement with the winder drum. The construction and operation of this component are likewise described and illustrated more fully below. 
     Each lift assembly  11  also includes a multiple part lifting cable  22 , which is operably attached at each end to the winder drum so that it may be selectively wound about that drum. Each cable  22  depends from the drum and operably interengages a plurality of a upper and lower pulleys mounted on beam  13  and platform  30 , respectively. An upper series of pulleys, not shown in FIG. 1, are located in the cable beam  13  associated with the particular winder drum on which cable  22  is wound. A respective set of lower pulleys  24 ,  26  and  28  are axially rotatably mounted to one corner of boat supporting platform  30 . More particularly, the platform includes a plurality of transversely extending cradle beams  32  that extend generally between a pair of opposing lift assemblies  11 . In FIG. 1, a first group of three cradle beams  32  extends between a forward pair of opposing lift assemblies  11  and a second group of three cradle beams  32  extends between a second, rearward pair of lift assemblies. Each group of three cradle beams is interconnected by mounting plates  34  secured at respective transverse ends of the cradle beams. The cradle beams may be composed of wood, plastic or a corrosion resistant metal or metal alloy. The end plate  34  is likewise typically composed of a material that is resistant to corrosion. The end plates may be secured to the cradle beam by bolts or other suitable means of attachment. In the version shown in FIG. 1, two separate end plates  34  are formed along each side of platform  30 . As a result, platform  30  is effectively formed in two discrete sections. In alternative embodiments, a single continuous end plate or other numbers of end plates may extend along each side of the platform and be secured to various numbers of cradle beams. In this way, the platform may be formed in a single or multiple sections. Each section may be associated with one pair or multiple pairs of lift assemblies. 
     Appropriate bunk boards  40  and  42  of the type known in the boating industry are secured to and extend across the cradle beams. At least one bunk board  42  interconnects the discrete sections of the platform. A boat, not shown, is maneuvered into the space between the opposing pairs of lift assemblies  11  and is supported on the bunk boards  40  and  42  of platform  30  in a known manner. It should be understood that the bunk boards and cradle beams may have various alternative configurations and constructions, which will be understood to persons skilled in the art. The manner of securing the bunk boards to the transverse cradles may be altered within the scope of this invention. Assorted types of brackets and fasteners may be utilized. 
     Each cable  22  is secured at each of its opposite ends to a respective winder drum and is operably interengaged with respective sets of upper pulleys (hidden in FIG. 1) and lower pulleys  24 ,  26  and  28 . Operating the winder, in a manner described below, causes the cable to selectively raise and lower an associated corner of platform  30 , and more particularly, one end of a group of adjoining, interconnected cradle beams  32 . It should be understood that the cable may comprise a multiple or single filament component and may be composed of metal, plastic, rope or other material suitable for use in a boat lift. The term “cable” should be construed broadly and may comprise virtually any type of flexible, strong element that is capable of being wound on a winder drum and interengaged with pulleys. 
     A representative one of the lift assemblies  11  is depicted in FIGS. 2A,  2 B and  3 . In FIGS. 2A and 3 the front and upper walls, respectively, of housing  14  are removed for WA clarity. The longitudinal ends of housing  14  are mounted by respective support plates  51  and  52  to cable beam  13 . More particularly, housing  14  is attached to plate  51  by an angle bracket  54  and associated bolts. The opposite end of the housing is likewise attached to plate  52  by a pair of angle brackets  56  and associated bolts. 
     A winder drum  60  is supported for axial rotation within housing  14  and, more particularly, includes a distal axle  62  that is received in a bearing  64  attached to the distal (left-hand) end of housing  14 . Winder drum  60 , which is shown alone in FIG. 4, includes a pair of circumferentially grooved sections  66  and  68  that are formed proximate respective ends of the drum. Each grooved section comprises a threaded or spiral groove that is cut into the circumference of the drum by an appropriate cutting tool. Each groove extends inwardly along drum  60  from a respective end of the drum. Section  66  comprises a righthand spiral and section  68  is a mirrored left-hand spiral. A cable receiving hole  70  is formed in each grooved section proximate a respective end of the winder drum. This hole receives a respective end of cable  22 , which is secured in place by set screws received in holes  72 . In this manner, cable  22  is secured at each end of the cable proximate respective ends of winder drum  60 . The diameter and number of turns exhibited by each grooved section may be varied within the scope of this invention. However, in certain preferred embodiments, approximately thirty turns or winds are formed in each grooved section and the groove has a dimension capable of accommodating a cable with a diameter of approximately {fraction (7/16)}″. FIG. 4C depicts an enlarged portion of one of the grooved sections with cable  22  accommodated in the groove. 
     Referring again to FIGS. 2A,  2 B and  3 , winder drum  60  is connected through a reducer  80  to drive mechanism  18 . The drive mechanism is secured by bolts  81  that interconnect the drive to support plate  52  and the upper surface of beam  13 . The drive mechanism includes a motor  82 , which may exhibit various speeds and horsepowers. The motor is connected through a reduction mechanism  84  to reducer  80  that is in turn secured and transmits rotation to winder  60 . The reduction mechanism may include a cycloidial reducer or other form of reduction means (e.g. gears, belts and pulleys or chains and sprockets) known to persons skilled in the art. When the motor and reduction mechanism are actuated, they drive winder drum  60  to axially rotate. The motor is operable in two directions such that the winder drum may be rotated to either raise or lower the attached cable as needed. 
     A pair of keeper roller assemblies  86  and  88  are mounted within housing  14  for engaging the segments of cable  22  wound about grooved winder sections  66  and  68  respectively. Each roller assembly includes a mounting bracket  90  that supports an elongate roller  92  in rotatable interengagement with the cable  22  wound about drum  60 . The roller  92  of assembly  86  bears against the cable wound about groove  66 . Likewise, the roller of assembly  88  bears against the cable received by grooved section  68 . Each of the mounting brackets  90  is secured by appropriate bolts to the upper surface of beam  13 . As the winder is rotated and cable  22  is wound onto or off of the winder, the keeper rollers  92  bear against the cable and help to prevent the cable from slipping out of the grooves and thereby disrupting operation of the lift assembly. 
     An automatic stop mechanism  100  is also mounted on the upper surface of beam  13  proximate the distal end of the winder housing  14 . More particularly, automatic stop  100  is supported at the upper end of a transverse plate  102  that is in turn secured to a support plate  104  on beam  13  by an angle bracket  106  and associated bolts  108 . Automatic stop mechanism  100  is disclosed more fully in co-pending application Ser. No. 09/531,984 filed Mar. 20, 2000. The description contained in that application is incorporated herein by reference. More particularly, the automatic stop mechanism includes a shaft  110  that is interconnected with winder drum  60 . A constrained nut mounted within the enclosure  112  of mechanism  100 , and not shown herein, is driven along shaft  110  as the winder drum rotates. The constrained nut eventually engages one of a pair of limit switches (hidden) within  112 . Actuation of one of the switches stops rotation of the winder drum in a first direction and actuation of the other switch halts operation of the winder drum in the other direction. As a result, the automatic stop limits raising and lowering of the lift assembly. 
     Cable beam  13  comprises a generally rectangular beam that is composed of aluminum, plastic or similar durable, rugged and corrosion resistant material employed in the boat lift industry. As shown in FIGS. 2A,  2 B and  5 - 7 , a plurality of upper sheave assemblies or pulleys  114  and  116  are axially rotatably mounted to beam  13 . More particularly, as best shown in FIGS. 5-7, beam  13  comprises a pair of C-channel components  120  and  122  that are arranged longitudinally side-by-side in an opposing fashion. Each of the C-channel elements  120  and  122  is interconnected along its lower flange to plates  115  that are engaged with the upper surfaces of respective pilings  12 . The upper flange of each channel element is likewise secured to the previously described plates  104 ,  51  and  52 . Such attachment is typically accomplished by bolts (shown in the accompanying drawings) or other suitable means of attachment. 
     Pulleys  114  and  116  are mounted between elements  120  and  122  on respective shafts  124 . A third elongate C-channel component  128 , FIGS. 6 and 7, is mounted a proximate one end between a lower angle bracket  119  attached to piling  12  and plate  51 . The opposite end of channel  128  is similarly mounted between a like angle bracket attached to the other piling and plate  52 , FIG.  2 A. The inwardly facing longitudinal surface of beam  13  (i.e. the side facing opposite element  128 ) is open to facilitate access to the upper pulley shaft  124 . See FIGS. 6 and 7. 
     Cable beam assembly  13  is secured to the upper end of each of the associated pilings  12  by bracket  15  shown in FIGS. 5 and 6. In particular, a pair of forward and rearward straps  130  and  140  are secured to each piling  12  by bolts or similar fasteners. Forward and rearward piling attachments  142  and  144  are secured to plate  115  and element  128  respectively by bolts or like fasteners. Attachments  142  and  144  interengage the elements  122  and  128  of beam  13  and help to hold those elements securely on each piling  12 . 
     The three lower pulleys  24 ,  26  and  28  are best depicted in FIG.  2 B. As previously described, each of these pulleys is axially rotatably mounted to a plate  34  defining a side of platform  30 . In the version shown herein, the upper and lower sets of pulleys are arranged in an axially parallel manner and are oriented generally within the same plane. However, in alternative embodiments, the individual pulleys may be arranged at differing orientations. For example, the upper pulleys may be arranged such that they are axially perpendicular to the lower pulleys. It is not required that all of the pulleys be arranged in the same plane or be axially parallel to one another. 
     As best shown in FIGS. 2A,  2 B and  5 , cable  22  depends or hangs from grooved sections  66  and  68  of winder drum  60 . In particular, as previously described, one end of cable  22  is fastened to winder section  66  proximate the distal (left-hand) end of the winder. The cable is wound about the grooves in section  66  and depends from the winder as cable segment  22   a . The opposite end of the cable is similarly attached to grooved section  68  of winder drum  60 . That end portion of the cable is likewise operably engaged with the grooves of section  68  and the cable depends from section  68  as illustrated by cable segment  22   b . Cable segments  22   a  and  22   b  hang downwardly from winder  60  through the gap between C-channel elements  120  and  122 , FIGS. 6 and 7. Segments  22   a  and  22   b  extend downwardly until they eventually engage lower pulleys  24  and  28  respectively. See FIGS. 1 and 2B. Pulleys  24  and  28  cause the multiple part cable to reverse direction. As best shown in FIG. 2B, cable segment  22   c  extends upwardly from pulley  24  and eventually engages upper pulley  114 . Likewise, cable segment  22   b  extends upwardly from pulley  28  until it engages upper pulley  116 . Once again, segments  22   c  and  22   d  extend through the gap between the elongate C-channel elements  120  and  122  of beam  13 . 
     Upper pulleys  114  and  116  again reverse the direction of the cable. A cable segment  22   e  drops from pulley  114  and engages central lower pulley  26 . Similarly, cable segment  22   f  drops from upper pulley  116  until it eventually engages central lower pulley  26 . Cable  22  therefore drops from grooved section  66  and sequentially interengages pulleys  24 ,  114 ,  26 ,  116  and  28 . The cable then returns to grooved section  68  of winder drum  60  wherein it is wound about and attached to the winder drum in the above described manner. 
     Each lift assembly  11  is constructed in the foregoing manner or in an analogous manner within the scope of this invention. Various alternative constructions are contemplated within the scope of the invention. For example, each lift assembly may include various other numbers of upper and lower pulleys. Typically, in each lift assembly, the platform will carry one more pulley than is mounted on the corresponding cable beam. In some versions, an odd number of upper pulleys and an even number of lower pulleys may be employed. It should be noted that, in either case, the central pulley of the set featuring an odd number (which is central lower pulley  26  in the version described herein) may comprise a fixed point of attachment rather than a sheave assembly or pulley. This is because the cable does not movably engage pulley  26  or such other central point of attachment. Movable engagement is exhibited between the cable and the remaining pulleys in the manner described below. 
     Lift apparatus  10  is raised and lowered by operating each of the lift assemblies  11  in a synchronous manner. This may be accomplished by wiring the motors  82  so that the respective lift assemblies are operated in unison. It should also be noted that a single motor may be mounted between adjoining pairs of winders on each side of the lift apparatus. If the motor is interconnected to a pair of adjoining winders, those winders are then be synchronously and efficiently driven in a selected direction by a single motor. In the embodiment shown herein, the lift apparatus may therefore be driven by two rather than four motors. 
     In operation, the motor  82  of each lift assembly is operated in a first direction to wind cable  22  onto the winder and therefore raise the platform. Alternatively, the motor may be operated in an opposite direction to unwind the cable from winder  60  and thereby lower platform  30 . When the motor is operated in the first direction, cable segments  22 a and  22   b  are wound onto grooved sections  66  and  68  respectively. This causes pulleys  24 ,  26  and  28  to be pulled upwardly in the direction of arrow  180 , FIG.  2 B. As cable  22  interengages and is drawn through pulleys  24  and  28 , pulley  24  rotates in the clockwise direction of arrow  181  and pulley  28  rotates in the counterclockwise direction indicated by arrow  182 . At the same time, the cable is drawn through pulleys  114  and  116  causing them to rotate in the opposing directions indicated by arrows  186  and  188 . This causes segments  22   e  and  22   f  of cable  22  to be pulled simultaneously upwardly in the direction of arrow  180 . Pulley  26  is drawn upwardly; but due to the equal but opposing forces exerted on segments  22   e  and  22   f , pulley  26  does not rotate. As pulleys  24 ,  26  and  28  are raised, they elevate the attached plate  32  of platform  30 . This lifting operation occurs simultaneously in each of the lift assemblies  11  so that platform  30  and the boat supported thereon are raised evenly and efficiently out of the water. Necessary maintenance and repairs may then be performed. 
     The platform and vessel supported thereon are subsequently lowered by simply reversing the foregoing operation. Motor  82  is switched to run in an opposite direction. Winder drum  60  is thereby driven such that cable  22  is unwound from grooved sections  66  and  68 . Cable segments  22   a  and  22   b  are thereby lowered in the direction of arrow  190 . As the cable is deployed downwardly, pulley  24  is driven in the counterclockwise direction indicated by arrow  192  and pulley  28  is rotated clockwise as indicated by arrow  194 . Upper pulleys  114  and  116  likewise reverse the rotation described above, with pulley  116  rotating in a clockwise direction and pulley  116  turning in a counterclockwise direction. Cable segments  22   e  and  22   f  are extended downwardly in the direction of arrow  190  such that central pulley  26  is lowered in the same direction. Indeed, as cable  22  is unwound from winder drum  60 , all three of the pulleys  24 ,  26  and  28  are lowered with platform  30  in the direction of arrow  190 . When all of the lift assemblies are operated in this manner, the entire platform  30 , FIG. 1, is lowered in synchronized fashion. The vessel supported by the platform is thereby returned to the body of water W. 
     A number of advantages result from the use of the foregoing structure and make lift apparatus  10  especially suited for use with heavy vessels. Significantly, tensile force is exerted much more evenly or uniformly upon the respective cable drops or segments  22   a - 22   f . In conventional devices wherein one end of the cable is tied-off or anchored to either the platform or the support structure, stress is distributed very unevenly to the individual cable segments. This can cause premature cable wear, which may require expensive repairs and replacements. In the version described herein, the force differentials and reeving effect are significantly reduced because the winder lifts a single, one-piece cable from both ends of the cable. When the lift is stationary, each vertical segment or drop of the cable carries the same load. Weight is distributed much more evenly along the cable. Overall stress on the cable is reduced dramatically. As a result, premature cable failure and frequent, expensive repairs are largely avoided. The system employed by this invention does exhibit less mechanical advantage because both ends of the cable are simultaneously lifted by the winder; however, this loss in mechanical advantage may be overcome by employing more efficient reduction means in reducer  84 , FIGS. 2 and 3. 
     A further advantage exhibited by lift apparatus  10  is that each lift assembly virtually eliminates longitudinal movement of the lower pulleys, and therefore the boat supporting platform, relative to the winder. Because the platform is supported by two segments  22   a  and  22   b  of the same cable  22  attached to mirrored grooved sections  66  and  68  of the winder  60 , the lower pulleys and platform  30  remain virtually stationary relative to the longitudinal axis of the winder as the cable  22  is wound onto or deployed from the winder. This provides for a much more stable and safer lifting and lower operation. The platform and supported vessel remain longitudinally stationary and do not shift or sway in fore and aft directions they are being raised and lowered. 
     Winder  60  also minimizes the rubbing against the winder grooves that a cable normally experiences when it is wound onto or off of a grooved winder. As the cable segments  22   a  and  22   b  are unwound and extended, the position from which each segment depends from winder drum  60  moves longitudinally toward the respective end of the winder at which the cable is attached. Conversely, as the winder winds the cable, the position from which the cable segment drops from the winder moves inwardly toward the longitudinal center of the winder. As a result, each of the cable segments  22   a  and  22   b  drops from the winder at a virtually constant angle relative to the longitudinal axis of the winder at all times during the raising and lowering operations. This causes the cable to maintain a consistent profile within its respective grooved section. See FIG.  4 C. There is little, if any, fleet angle between the plane of each winder groove and the longitudinal axis of the cable. Rubbing between the cable and the edge of each groove is minimized. This further reduces cable wear and prolongs cable life. Moreover, the upper and lower pulleys are coplanar such that fleet angle between the pulleys is avoided. 
     Various alternative configurations of this invention may be employed. For example, two winders driven by a single motor may be mounted along each side of the platform. For exceptionally large vessels, three or even more lift assemblies, as previously described, may be employed along each side of the platform. Once again, in these versions, multiple winders may be operated by a respective motor. 
     From the foregoing it may be seen that the apparatus of this invention provides for a large capacity boat lift. While this detailed description has set forth particularly preferred embodiments of the apparatus of this invention, numerous modifications and variations of the structure of this invention, all within the scope of the invention, will readily occur to those skilled in the art. Accordingly, it is understood that this description is illustrative only of the principles of the invention and is not limitative thereof. 
     Although specific features of the invention are shown in some of the drawings and not others, this is for convenience only, as each feature may be combined with any and all of the other features in accordance with this invention. 
     Other embodiments will occur to those skilled in the art and are within the following claims.