Low profile lift for watercraft

[0002] This application claims priority from U.S. provisional application No. 60/086,428, filed May 22, 1998, entitled LOW PROFILE LIFT FOR WATERCRAFT.

[0003] The invention relates to lifting devices, and in particular to devices for lifting watercraft, for example, boats and sea planes.

[0004] Known is U.S. Pat. No. 5,184,914 issued to the inventor of the present invention which is incorporated herein by reference and discloses a watercraft lifting device having a rectangular stationary base formed of two longitudinal parallel beams and two transverse beams, generally described as front and rear transverse beams. The rectangular base is submersible under water. Pivoting booms connect each of the four corners of the rectangular base to swingable mounting arms positioned parallel to and coplanar with each of the longitudinal beams to form two pairs of pivoting booms, generally described as front and rear pivoting booms. The two pair of pivoting booms form with the mounting arms collapsing parallelograms on which watercraft supports extended a predetermined distance above the mounting arms hold the craft during lifting. A double-acting hydraulic cylinder is pivotally connected to the rear transverse beam and its piston rod is pivotally connected to the two front pivoting booms such that expansive energization of the double-acting hydraulic cylinder extends the piston rod and swings front pair of pivoting booms upward from a collapsed attitude. The parallelogram linkage forces the mounting arms and rear pair of pivoting booms to follow the front pair of pivoting booms. Thus, expansive energization of the double-acting hydraulic cylinder raises the front pair of pivoting booms and lifts the rear pair of pivoting booms, the mounting arms and the watercraft supports attached to the mounting arms upward to lift a watercraft out of the water. Upward movement continues until the pivoting booms pass through a vertical orientation into an overcenter orientation whereby the watercraft is supported above the surface of the water.

[0005] Retractive energization of the double-acting hydraulic cylinder retracts the piston rod into the piston jacket of the double-acting hydraulic cylinder and reverses the motion of the pivoting booms. Thus, retractive energization of the double-acting hydraulic cylinder first raises the pivoting booms and lifts the mounting arms and watercraft supports attached to the mounting arms upward. Upward movement causes the pivoting booms to pass back through vertical orientation. Continued retraction of the piston rod into the double-acting hydraulic cylinder combined with the weight of the latching apparatus and the watercraft collapses the parallelograms whereby the watercraft is lowered into the water. The piston rod continues to retract into the double-acting hydraulic cylinder collapsing the parallelograms, including the mounting arms and watercraft supports attached to the mounting arms, until contact between the watercraft supports and the watercraft is broken and the watercraft can float free.

[0006] Although the apparatus of the prior art operates effectively in many practical applications, a need exists for a watercraft lifting apparatus which operates effectively in shallow water applications where the typical water depth is minimal and the apparatus of the prior art cannot collapse sufficiently to break contact between the watercraft supports and the watercraft and release the watercraft to float free.

[0007] The present invention resolves limitations of the prior art by providing a low profile watercraft lifting apparatus. The present invention is a watercraft lifting apparatus which includes a generally rectangular base adapted to be submerged under water. The base is formed of two longitudinal beams joined by two transverse beams generally described as front and rear transverse beams. Pivoting booms connect each of the four corners of the rectangular base to swingable mounting arms positioned generally parallel with the longitudinal beams to form two pairs of pivoting booms, generally described as a front pair of pivoting booms and a rear pair of pivoting booms. The pivoting booms form with the mounting arms collapsing mock parallelograms on which watercraft supports hold the craft during lifting.

[0008] According to one aspect of the present invention, the low profile lifting apparatus of the present invention provides a self-guiding watercraft entry attitude by providing the pivot points for the rear pair of pivoting booms at a position above the pivot points for the front pair of pivoting booms. Positioning the rear boom pivot points above the pivot points for the front pair of pivoting booms provides a mock parallelogram shape in a side elevation view wherein the rear pair of pivoting booms and thus the rear ends of the mounting arms are positioned at a lower attitude than the front ends of the mounting arms and are angled downwardly from the higher elevation of the front ends of the mounting arms when the lifting apparatus is in a collapsed attitude. In one preferred embodiment, the pivot points for the rear pair of pivoting booms at a position above the centerline of the longitudinal beams of the base.

[0009] According to another aspect of the present invention, the self-guiding watercraft entry attitude provided by the positioning of the rear boom pivot points above the front boom pivot points is accentuated by providing the pivot points for the front pair of pivoting booms at a position below the centerline of the longitudinal beams of the base. Positioning the front boom pivot points below the longitudinal beam centerline provides an accentuated mock parallelogram shape in a side elevation view by accentuating the downward angle of the mounting arms when the lifting apparatus is collapsed. Furthermore, varying the lengths of the front and rear pivoting booms by the amount of the off-set between the front and rear boom pivoting points reduces the downward angle of the mounting arms when the booms are fully extended such that mounting arms are essentially parallel with the longitudinal beams of the base when the lifting apparatus is in an upright or extended orientation.

[0010] According to yet another aspect of the invention, each pair of pivoting booms are positioned either inward or outward of the two longitudinal beams of the base rather than coplanar with the longitudinal beams. Thus, the booms collapse into a side-by-side orientation with the longitudinal beams of the base providing a lower profile lifting apparatus as compared with the prior art apparatus by providing more complete collapsing of the mock parallelogram.

[0011] According to another aspect of the invention, a low profile lifting apparatus is provided by providing one or more convex-shaped cross supports or cross braces joining the pair of rear pivoting booms. The shaped cross supports or cross braces provide a low profile lifting apparatus by reducing the dimension by which the watercraft supports must be extended above the mounting arms to provide a hull-clearing channel portion for shaped boat hulls. At least one cross brace joining the pair of rear pivoting booms is positioned adjacent the pivot points on the longitudinal beams and provides a boom extension projecting downward beneath the level of the pivot points. A double-acting hydraulic cylinder or other suitable actuator is pivotally connected between the downward projecting boom extension on the rear pair of pivoting booms and the front pair of pivoting booms such that expansive energization of the double-acting hydraulic cylinder extends the piston rod and swings both pairs of pivoting booms upward from a collapsed attitude. Thus, expansive energization of the double-acting hydraulic cylinder causes the hydraulic cylinder to exert a first rotational force against the front pair of pivoting booms which rotates the front pair of pivoting booms upward and a second equal and opposite rotational force on the downward projecting boom extension of the cross braces on the rear pair of pivoting booms which acts over a lever arm distance and causes the rear pair of pivoting booms to rotate upward.

[0012] According to another aspect of the present invention, pivotally connecting the double-acting hydraulic cylinder to a boom extension projecting downward beneath the rear pivoting booms' pivot point on the longitudinal beams of the base compounds the rotational action exerted by the double-acting hydraulic cylinder providing increased rate of rotation of the pivoting booms relative to the base. Thus, the unique mounting of the double-acting hydraulic cylinder provided by the invention provides increased actuation speeds without an increase in hydraulic pressure. Thus, expansive energization of the double-acting hydraulic cylinder raises both the front and rear pairs of pivoting booms and lifts the mounting arms and the watercraft supports upward to lift a watercraft out of the water. Continued expansive energization of the hydraulic cylinder causes upward movement to continue until the piston rod is fully extended providing a locked upright attitude. Alternatively, upward movement continues until the pivoting booms pass through a vertical orientation into an over-center orientation whereby the watercraft is supported above the surface of the water. According to yet another alternative, upward movement continues to some intermediate orientation between the collapsed and fully extended orientations and which orientation is maintained by a force exerted against both front and rear pivoting booms by the pressure in the hydraulic cylinder.

[0013] According to yet another aspect of the present invention, retractive energization of the double-acting hydraulic cylinder retracts the piston rod into the piston jacket of the double-acting hydraulic cylinder and reverses the motion of the pivoting booms. Thus, when the watercraft lifting apparatus is locked in an over-center attitude, positive retractive energization of the double-acting hydraulic cylinder first raises the pivoting booms and lifts the mounting arms and watercraft supports attached to the mounting arms upward. Upward movement continues until the pivoting booms again pass through a vertical orientation. Continued retraction of the piston rod into the piston jacket of the double-acting hydraulic cylinder combined with the weight of the lifting apparatus and the watercraft collapses the mock parallelograms whereby the watercraft is lowered into the water. Positioning the downward projecting boom extension of the rear pair of pivoting booms beneath the level of the pivot points on the longitudinal beams provides a low profile lifting apparatus by providing more complete collapsing of the mock parallelogram formed by the two pair of pivoting booms and the mounting arms on which the watercraft supports are mounted. Thus, continued retraction of the piston rod into the piston jacket of the double-acting hydraulic cylinder collapses the mock parallelograms, including the mounting arms and watercraft supports attached to the mounting arms into a low profile mock parallelogram at which point contact between the watercraft supports and the watercraft is broken and the watercraft can float free even in relatively shallow water.

[0014] FIG. 1 is an isometric view of the low profile watercraft lifting apparatus according to one embodiment of the present invention shown in an extended attitude;

[0015] FIG. 2 is an isometric view of the low profile watercraft lifting apparatus according to one embodiment of the present invention shown in a collapsed attitude;

[0016] FIG. 3 is a detail view of the double-acting hydraulic cylinder pivotal connection to the rear pivoting booms according to one embodiment of the present invention; and

[0017] FIG. 4 is an operational side elevation view of the watercraft apparatus according to one embodiment of the present invention;

[0018] FIG. 5 is an isometric projection of another embodiment of a low profile lift for watercraft in accordance with the invention;

[0019] FIG. 6 is a side plan view of the lift of FIG. 5 in an extended configuration;

[0020] FIG. 7 is a side plan view of the lift of FIG. 5 in a retracted configuration;

[0021] FIG. 8 is an isometric projection of the lift of FIG. 5 showing optional attachments;

[0022] FIG. 9 is an isometric projection of a first attachment bracket in accordance with the invention;

[0023] FIG. 10 is an isometric projection of a second attachment bracket in accordance with the invention;

[0024] FIG. 11 is a partial top plan view of the accessories of FIG. 8 mounted on the lift with the brackets of FIGS. 9 and 10; and

[0025] FIG. 12 is a partial front plan view of the accessory mounting of FIG. 11.

[0026] FIGS. 1 and 2 show isometric views of the low profile watercraft lifting apparatus according to one embodiment of the present invention in an upright or extended attitude and a collapsed attitude, respectively. In FIGS. 1 and 2 the watercraft lifting apparatus 10 includes an essentially rectangular base 12 including a front transverse beam 14 and a rear transverse beam 16 connected to opposite ends of spaced-apart longitudinal beams 18a, 18b. In one embodiment, longitudinal beams 18a, 18bare essentially equal in length and parallel with one another and transverse beams 14, 16 extend beyond the connection points with longitudinal beams 18a, 18bto form “I”-shaped base 12. In a preferred embodiment, base 12 further includes four sleeves 20. One sleeve 20 is connected to each end of transverse beams 14, 16. Each sleeve 20 receives a support post 22 which is independently adjustable for positioning and leveling base 12 at a desired depth submerged under water. Support posts 22 include shoes 24 which rest on the river or lake bed.

[0027] Four pivoting booms 26a, 26b, 26c, 26dare attached to rectangular base 12, one pivoting boom 26 adjacent each of the four corners of rectangular base 12, with the lower ends of each front boom 26a, 26bpivotally joined to base 12 adjacent front ends of each longitudinal beam 18a, 18band the lower ends of each rear boom 26c, 26dpivotally joined to base 12 adjacent rear ends of each longitudinal beam 18a, 18b. In a preferred embodiment, longitudinal beams 18a, 18bare fitted with brackets 28 which include a pivot point 30 extended an off-set distance 32 above the centerline 34 of longitudinal beams 18a, 18b. Brackets 28 pivotally join rear booms 26c, 26dto longitudinal beams 18a, 18bsuch that rear booms 26c, 26dpivot about pivot point 30 relative to longitudinal beams 18a, 18b. In one preferred embodiment, pivot point 30 is several inches above centerline 34. Brackets 28 position rear booms 26c, 26deither between longitudinal beams 18a, 18b(shown) or astride longitudinal beams 18a, 18b(not shown) such that in a fully collapsed attitude, rear pivoting booms 26c, 26dare positioned in a side-by-side orientation with longitudinal beams 18a, 18b.

[0028] One or more cross supports or cross braces 36 provide structural integrity to front pair of pivoting booms 26a, 26b. Those of skill in the art will recognize that alternative cross support configurations may provide structural integrity to front pair of pivoting booms 26a, 26b. The cross supports or cross braces 38a, 38b, 38c, 38dprovide structural integrity to rear pivoting booms 26c, 26d. The cross braces 38 may be formed in a hull-clearing convex or channel shape. In one preferred embodiment, the cross support 38ais a “V”-shaped member extending between rear pivoting booms 26c, 26dwhich points generally rearward when watercraft lifting apparatus 10 is in an extended attitude as shown in FIG. 1 and point generally downward when watercraft lifting apparatus 10 is in a collapsed attitude as shown in FIG. 2. The hull-clearing “V” shape of cross support 38aprovides increased clearance for watercraft having generally “V”-shaped hulls as compared with the lifting apparatus of the prior art. Lower cross support 38bis a “V”-shaped member which extends between rear pivoting booms 26c, 26dadjacent pivot point 30. In one embodiment, cross supports 38c, 38dextend between the outer ends of intermediate cross support 38aand the approximate center of lower cross support 38b. Those of skill in the art will recognize that other configurations of cross supports may be employed, for example, intermediate and lower cross supports 38a, 38bmay be formed as a straight beam or in a “U” shape or a “C” shape, and the cross supports 38c, 38dextending between cross supports 38a, 38bmay be positioned parallel with the rear booms 26c, 26dor at any other suitable orientation whereby the cross supports 38a, 38bprovide a shape suitable for clearing the bottoms of boats having shaped hulls.

[0029] Two mounting arms 40a, 40bare pivotally mounted adjacent the upper ends of pivoting booms 26 to rotate about pivot points 42a, 42band swing with pivoting booms 26 as a mock parallelogram. The invention provides an essentially parallel relationship between mounting arms 40 and longitudinal beams 18 when lifting apparatus 10 is in a fully extended or upright orientation. The essentially parallel relationships between mounting arms 40a, 40band longitudinal beams 18a, 18b, respectively, are provided by varying the lengths of front pair of pivoting booms 26a, 26brelative to the lengths of rear pair of pivoting booms 26c, 26d. When front pivoting booms 26a, 26bare adapted to pivot about a pivot axis passing through centerlines 34 of both longitudinal beams 18a, 18b, the lengths “A” of front pivoting booms 26a, 26bare essentially equal to the lengths “B” of rear pivoting booms 26c, 26dplus dimension “C” defined as an off-set distance 32 between rear boom pivot point 30 and centerline 34 of longitudinal beams 18a, 18b. Thus, the relationship between the lengths of front pivoting booms 26a, 26band rear pivoting booms 26c, 26dis given by:

[0030] A=B+C  (Eq. 1)

[0031] A=lengths of rear pivoting booms 26a, 26bdefined as the distance between pivot point 42aand a pivot axis passing through centerlines 34 of both longitudinal beams 18a, 18b,

[0032] B=lengths of rear pivoting booms 26c, 26ddefined as the distance between pivot point 42band pivot point 30, and

[0033] C=off-set distance 32 as defined by the vertical distance between rear pivot point 30 and centerline 34.

[0034] When lifting apparatus 10 is retracted to a collapsed orientation as shown in FIG. 2, mounting arms 40a, 40bare oriented at an angle relative to longitudinal beams 18a, 18b. Mounting arms 40a, 40bangle downward toward the rear portion of lifting apparatus 10 to provide a self-guiding aspect whereby the bow of a boat is guided into the center of lift apparatus 10 midway between mounting arms 40 by the rising angle of mounting arms 40 leading toward FRONT of lifting apparatus 10. The downward and backward sloping angle of mounting arms 40 is provided in part by the position of pivot point 30 relative to the pivot points of front booms 26a, 26babout an axis passing through centerline 34 and in part by the shorter lengths of rear pivoting booms 26c, 26drelative to the lengths of front pivoting booms 26a, 26b. In one preferred embodiment, watercraft supports (not shown) attached to mounting arms 40 brace the watercraft during lifting.

[0035] In one embodiment of the present invention, a suitable actuator, for example a double-acting hydraulic cylinder 44, extends diagonally across the mock parallelogram. Double-acting hydraulic cylinder 44 comprises a piston rod 46 extending from and retracting into a piston jacket 48. In a preferred embodiment, upper end 50 of piston rod 46 is connected to cross rod 52 and cross rod 52 is rotatably fitted in flanges 54 which are attached to front pivoting booms 26a, 26badjacent the upper ends of booms 26a, 26b. Alliteratively, upper end 50 of piston rod 46 is connected to a collar (not shown) rotatable on cross rod 52 as disclosed in prior U.S. Pat. No. 5,184,914. Lowering and raising of mounting arms 40 and watercraft supports (not shown) is achieved by extension and retraction of piston rod 46 of double-acting hydraulic cylinder 44. Those of skill in the art will recognize that the present invention may be practiced using alternative raising and lowering means or actuator, for example, pneumatic cylinders, opposing single-acting hydraulic cylinders, electrically driven push/pull rods, or other suitable actuator including chain, cable, or rope pulley drives.

[0036] FIG. 3 shows a detail view of the pivotal connection between double-acting hydraulic cylinder 44 and rear pivoting booms 26c, 26daccording to one embodiment of the present invention. A boom extension 56 projects from rear pivoting booms 26c, 26dopposite pivot point 30 whereby a lever is formed. The lever includes a first lever arm defined by rear pivoting booms 26c, 26d; a second lever arm defined by boom extension 56; and a fulcrum defined by pivot point 30 positioned between the first and second lever arms. In one preferred embodiment, boom extension 56 projects downward from the approximate center of lower cross support 38band provides a pivot point 58. The lower end 60 of hydraulic cylinder piston jacket 48 is adapted to pivotally connect to boom extension 56 at pivot point 58. According to one preferred embodiment, pivot point 58 is located at a distance 62 from rear boom pivot point 30. Distance 62 provides the lever arm over which the force exerted by hydraulic cylinder 44 acts to rotate rear pair of pivoting booms 26c, 26dabout pivot point 30. In one preferred embodiment of the present invention, pivot point 58 is located at a distance 62 from rear boom pivot point 30 selected to provide an adequate force movement.

[0037] FIG. 4 shows an operational side elevation view of the watercraft apparatus according to one embodiment of the present invention. To lift a watercraft from the water, watercraft lifting apparatus 10 is positioned in a first retracted or collapsed attitude (shown in solid) with the craft to be lifted (not shown) floating above mounting arms 40 and watercraft supports, if so equipped. Piston rod 46 of double-acting hydraulic cylinder 44 is extended by introduction of water under pressure into the lower end 60 of piston jacket 48 as disclosed in prior U.S. Pat. No. 5,184,914. A piston (not shown) inside piston jacket 48 extends piston rod 46, forcing cross rod 52 and hence front pivoting booms 26a, 26bto swing upwardly and forwardly from their collapsed attitudes to their raised attitude (shown in phantom). Simultaneously, lower end 60 of piston jacket 48 exerts an equal and opposite force on pivot point 58 of boom extension 56 acting over lever arm distance 62 forcing cross supports 38 and hence rear pivoting booms 26c, 26dto swing upwardly and forwardly about pivot point 30 from their collapsed attitude to their raised attitude above the water surface (shown in phantom). Pivotally attached mounting arms 40 follow as the mock parallelogram is deployed. Thus, a craft is lifted out of the water on mounting arms 40 or watercraft supports, if so equipped. In a preferred embodiment of the present invention, full extension of watercraft lifting apparatus 10 is achieved when the piston (not shown) inside piston jacket 48 extends piston rod 46 to its fully extended attitude.

[0038] Prior U.S. Pat. No. 5,184,914 discloses various alternative means of defining full extension of watercraft lifting apparatus 10 which are fully applicable to the present invention. For example, each longitudinal beam 18a, 18bmay be equipped with boom stops (not shown) located adjacent rear transverse beam 16 and/or adjacent front transverse beam 14 engaging sides of pivoting booms 26 adjacent their lower pivoting ends to brace pivoting booms 26 and mounting arms 40 in their fully extended attitude. Alternatively, full extension of hydraulic cylinder 44 may swing booms 26 from a collapsed or retracted attitude through a vertical attitude into an over-center attitude which locks watercraft lifting apparatus 10 in a fully extended attitude. Another alternative combines both boom stops and an over-center locking position.

[0039] According to one embodiment, the present invention provides an over-center locking position including booms stops. The present invention provides brackets 66 connected between the ends of each pivoting boom 26 and the ends of each mounting arm 40. Each bracket 66 provides pivot point 42 such that one mounting arm 40ais oriented in a plane defined by front pivoting boom 26aand rear pivoting boom 26cand the other mounting arm 40bis oriented in a plane defined by front pivoting boom 26band rear pivoting boom 26d. Brackets 66 are configured to position pivot points 42 such that a portion of mounting arm 40 contacts the end of each pivoting boom 26 when lifting apparatus 10 is in a fully extended upright and over-center attitude. Brackets 66 are further configured such that, when lifting apparatus 10 is oriented in any attitude other than a fully extended upright and over-center attitude, clearance is provided between the ends of each pivoting boom 26 and each mounting arm 40.

[0040] Retraction of watercraft lifting apparatus 10 is accomplished by positive retractive energization of double-acting hydraulic cylinder 44 which retracts piston rod 46 into piston jacket 48. Retraction of piston rod 46 causes upper piston rod end 50 to pull front pivoting booms 26a, 26bfrom their raised attitude back over-center if an over-center lock is used. Simultaneously, the force exerted by retraction of piston rod 46 acts over lever arm 62 causes lower piston jacket end 60 to pull boom extension 56 upwardly which rotates pivoting booms 26c, 26dabout pivot points 30 from their raised attitude back over-center. After booms 26 pass through their vertical over-center attitude, the weight of booms 26, mounting arms 40 and the supported craft lower watercraft lifting apparatus 10 into its collapsed or retracted attitude.

[0041] According to one embodiment of the present invention, longitudinal beams 18a, 18bare fitted with brackets 70 which include a pivot point 72 extended a distance “D” defined as off-set distance 74 below centerline 34 of longitudinal beams 18a, 18b. Brackets 70 pivotally join front booms 26a, 26bto longitudinal beams 18a, 18bsuch that front booms 26a, 26bpivot relative to longitudinal beams 18a, 18bat pivot point 72. Brackets 70 position front booms 26a, 26beither between longitudinal beams 18a, 18b(shown) or astride longitudinal beams 18a, 18b(not shown) such that in a fully collapsed attitude, front pivoting booms 26a, 26bare positioned in a side-by-side orientation with longitudinal beams 18a, 18b. Positioning of pivot points 72 at offset distance 74 below centerline 34 of longitudinal beams 18a, 18baccentuates the self-guiding watercraft entry attitude of the invention by accentuating the downwardly and rearwardly sloping angle of mounting arms 40 when lifting apparatus 10 is collapsed. Thus, front boom pivot points 72 are off-set a total vertical off-set distance “E” defined as vertical off-set distance 76 from rear boom pivot points 30 which accentuates the downwardly and rearwardly sloping angle of mounting arms 40 when lifting apparatus 10 is in a collapsed attitude. Off-set distances 32, 74 in combination with the differing lengths of front pivoting booms 26a, 26brelative to the lengths of rear pivoting booms 26c, 26dreduces the downwardly sloping angle of mounting arms 40 when booms 26 are fully extended such that mounting arms 40a, 40bare essentially parallel with longitudinal beams 18a, 18bwhen lifting apparatus 10 is in an upright or extended attitude.

[0042] According to this embodiment, the essentially parallel relationship between mounting arms 40a, 40band longitudinal beams 18a, 18bwhen lifting apparatus 10 is in an upright or extended attitude is provided by varying the lengths “A” of front pair of pivoting booms 26a, 26brelative to the lengths “B” of rear pair of pivoting booms 26c, 26d. The lengths “A” of front pivoting booms 26a, 26bminus off-set distance 74 are essentially equal to the lengths “B” of rear pivoting booms 26c, 26dplus off-set distance 32. Thus, the relationship between the lengths of front pivoting booms 26a, 26band rear pivoting booms 26c, 26dis given by:

[0043] A′−D≈B+C  (Eq. 2)

[0044] where:

[0045] A′=lengths of rear pivoting booms 26a, 26bdefined as the distance between pivot point 42aand pivot point 72,

[0046] B=lengths of rear pivoting booms 26c, 26ddefined as the distance between pivot point 42band pivot point 30,

[0047] C=off-set distance 32 as defined by the distance between pivot point 30 and centerline 34, and

[0048] D=off-set distance 74 as defined by the distance between centerline 34 and pivot point 72.

[0049] In one preferred embodiment, pivot point 72 is several inches below centerline 34.

[0050] Stated differently, the lengths “B” of rear pivoting booms 26c, 26dplus vertical off-set distance 76 between rear boom pivot points 30 and front boom pivot points 72 are essentially equal to the lengths “A” of front pivoting booms 26a, 26b. Thus, the relationship between the lengths of front pivoting booms 26a, 26band rear pivoting booms 26c, 26dis alternatively given by:

[0051] A′≈B+E  (Eq. 3)

[0052] where:

[0053] A′=lengths of rear pivoting booms 26a, 26bdefined as the distance between pivot point 42aand pivot point 72,

[0054] B=lengths of rear pivoting booms 26c, 26ddefined as the distance between pivot point 42band pivot point 30, and

[0055] E=off-set distance 76 as defined by the vertical distance between rear pivot point 30 and front pivot point 72.

[0056] Referring next to FIGS. 5-7, another embodiment of a lift 100 formed in accordance with the invention is shown. The lift 100 includes a rectangular base 112 formed from front and rear transverse beams 114, 116, respectively, that are each connected to parallel longitudinal beams 118a, 118b. A sleeve 120 is connected to each of the transverse beams 114, 116. Each sleeve 120 is sized and shaped to receive a support post 122. A plurality of openings 123 in each sleeve 120 and each support post 122 enables independent adjustment of the base 12 relative to support shoes 124, which can rest on a river bed or lake bed.

[0057] Four pivoting booms 126a, 126b, 126c, 126d, are pivotally attached to the rectangular base 112 at each of the four corners 127. Ideally, brackets 128 are connected to the rear booms 126c, 126dand the longitudinal beams 118a-bsuch that the rear booms 126c, 126dpivot about a pivot point 130. The pivot point 130 is a distance 132 that several inches above a longitudinal axis 134 of the longitudinal beams 118a, 118b. In one embodiment the pivot point is in the range of five (5) to twelve (12) inches above the axis 134. In the embodiment shown, the brackets 128 position the rear booms 126c, 126dinside the longitudinal beams 118a-b, although the brackets 128 can be mounted astride the longitudinal beams 118a-bsuch that when in a fully collapsed attitude, the rear pivoting booms 126c, 126dare positioned in a side-by-side orientation with the longitudinal beams 118a-b. A first pair of cross braces 136 provides structural integrity to the front pair of pivoting booms 126a, 126b. A second pair of cross braces 138 provides structural integrity to the rear pivoting booms 126c, 126d. In the depicted embodiment, the cross braces 138 are formed to have a v-shape, with the vertex 139 pointing downward when the lift 100 is in a collapsed configuration, as shown in FIG. 7. This v-shape of the cross support 138 provides increased clearance for a watercraft having generally v-shaped hulls. Other configurations of the cross brace 138 may also be used as desired.

[0058] Mounted to the top of pivoting booms 126aand 126cis a support rail 140a; and similarly mounted to pivoting booms 126b, 126dis a support rail. Mounting brackets 142 are fixedly attached to pivoting booms 126a-dand provide a pivot attachment point 143 for attachment of the support rails 140a-b.

[0059] The length and function of the pivoting booms 126a-dis the same as described above with respect to the pivoting booms 26a-din FIG. 1, and will not be described in detail herein. As shown in FIG. 6, the support rails 140a-bare essentially parallel to the longitudinal beams 118a-bwhen the lift 100 is in the extended configuration.

[0060] An actuator 144, similar to the double-acting hydraulic cylinder 44 described above with respect to FIG. 1, is connected to the pivoting booms 126a-dby means of a front T-bar 152 connected to forward pivoting booms 126a, 126band a rear T-bar 154 connected to rear pivoting booms 126c, 126d. The front T-bar 152 is rotatably mounted to support brackets 156, each attached to a respective pivoting boom 126a, 126b. The rear T-bar 154 is similarly pivotally attached to support brackets 158 that are each attached to pivoting booms 126, 126d. The actuator 144 is attached to the rear T-bar 154 with a sleeve 160 and to the front T-bar 152 by a yolk 162. Ideally, the T-bars 152, 154 can be easily replaced to facilitate interchangeability of high-pressure and low-pressure activators.

[0061] In a preferred embodiment, a bunk 164a,bis pivotally mounted to each support rail 166a,b. The bunks 164a,bcan pivot about a longitudinal axis that is parallel to the axis 134 of the longitudinal beams 118a-b. The bunks 164a,bcan either freely pivot or be attached to a fixed orientation, thus accommodating hulls of a particular configuration.

[0062] Referring again to FIGS. 6 and 7, the relationship between the actuator 144 and the pivoting booms 126a-dis illustrated. In FIG. 6, the lift 100, working in a cantelever arm arrangement, is in an extended configuration wherein the actuator 144 is fully extended. In FIG. 7, the lift 100 is in a collapsed configuration wherein the actuator 144 is retracted.

[0063] In a preferred embodiment, the front pivoting booms 126a,bhave a pivot point 129 that is lower than the pivot point 130 of the rear pivoting booms 126c,d. The relative distance between the pivot points 129, 130 ranges from four inches to ten inches, and in the configuration shown in FIG. 6, is eight inches. In other words, the rear pivot point 130 is approximately 8 inches higher than the front pivot point 129. It is to be understood that these distances can vary according to the size of the lift 100.

[0064] The actuator 144 provides a linkage through the front and rear T-bars 152, 154 with the pivoting booms 126a-d. When mounted as shown, the actuator 144 provides a pushing force on the forward and rear booms 126a-d. The pushing action of the actuator 144, in combination with the moving mounting points of the actuator 144 on the pivoting booms 126a-d, enables lifting of loads with nearly uniform force throughout the travel of the pivoting booms 126a-d.

[0065] In addition, as shown in FIG. 7, when the lift 100 is in a retracted or collapsed configuration, the bunks 164a,bare angled downward towards the rear of the lift 100. This facilitates in loading of watercraft, especially in very shallow water.

[0066] Referring next to FIGS. 8-12, shown therein is the lift 100 of FIG. 5 having optional accessories attached thereto. More particularly, four guide-ons 802 are attached near the free ends of the pivoting booms 126a-d. In addition, a stern stop 804 is connected to the upper ends of the pivoting booms 126c,d.

[0067] Each of the guide-ons 802 are formed from tubular members 806 having a 90° bend to create first and second legs 808, 810, respectively. The first leg 808 is attached to the lift 100 by an attachment bracket 812, which is shown more clearly in FIG. 10.

[0068] Referring to FIG. 10, the attachment bracket 812 comprises a mounting plate 814 having a pair of mounting holes 816 formed therein. Attached to the plate 814 adjacent the holes 816 is a sleeve 818 sized and shaped to slidably receive the first leg 808 of the guide-on 802. A pair of set screws 820 are threadably engaged with the sleeve 818 such that as the screws 820 are threaded into the sleeve 818, they project into the internal bore 822 of the sleeve 818 and will bear against the guide-on 802. Alternatively, holes may be formed in the guide-on 802 to accept the screws 820.

[0069] The stern stop 804 is of tubular construction having a U-shaped configuration with two legs 824 joined at a 90° bend by a cross member 826. The stern stop 804 is attached to the bunk support rails 166a,bwith attachment brackets 828, shown in greater detail in FIG. 9. As shown therein, each attachment bracket 828 includes a mounting plate 830 with openings 832 formed therein, that is attached to or integrally formed with a sleeve 834. The sleeve 834 has a longitudinal axial bore 836 with a circular cross-sectional configuration. The mounting plate 830 is attached at a right angle to the sleeve 834 and reinforced with a gusset 838. A pair of set screws 840 (only one shown in FIG. 9) are threadably received in the sleeve 834 such that when tightened, they project into the axial bore 836 and will bear against the stem stop 804 or be received in preformed holes in the stem stop 804, as shown in FIG. 11.

[0070] FIGS. 11 and 12 show the attachment of the guide-on 802 and stem stop 804 to the bunk support rail 166bon the pivoting boom 126d. To facilitate mounting of the brackets 812, 828 and the bunk 166bto the support rail 164b, a universal plate 842 is provided. As shown more clearly in FIG. 12, the universal plate 842 has a substantially rectangular configuration with one of its planar sides attached to the support rail 166b, preferably by welding, although other attachment means known in the art may be used. Mounting holes 844 centrally located on the universal plate 842 are used for attachment of the brackets 812, 828. Additional holes 846 are provided near the top of the universal plate 842 for attachment of the bunk 164b. As shown here, a bunk attachment plate 848 connects the bunk 164bto the universal plate 842.

[0071] As shown in FIG. 12, the bunk attachment plate 848 is connected to the universal plate 842 through one opening 846 (on the right side) to permit rotation of the bunk 164babout an axis that is parallel with the axis 134 of the longitudinal beam 118b. This permits orienting the bunk 164bto accommodate different hull shapes. The bunk 164bcan be attached to the bunk support rail 166bin a fixed orientation, or it can be freely rotatable, as desired.

[0072] To enable the bunk 164bto rotate without interference from the universal plate 842, the top corners 850 of the plate 842 are angled downward as shown. However, the top edge 852 between the corners 850 remains straight to provide a bearing surface for the bottom surface 854 of the bunk bracket 848. This prevents the bunk 164bfrom inadvertently rotating counterclockwise (from the orientation shown in FIG. 12) and causing damage to a boat hull.

[0073] As shown more clearly in FIG. 11, the guide-on 802 mounting bracket 812 is first attached to the universal plate 842 followed by the stern stop bracket 828 through the openings 844 with suitable fasteners (not shown). The guide-ons 802 and stem stop 804 are inserted into their respected sleeves 818, 834 where they are slidably received for adjustable positioning to accommodate the watercraft. The guide-ons 802 aid in centering the watercraft on the lift 100, while the stem stop 804 is contacted by the stern drive or outboard drive to position the boat longitudinally on the lift 100.

[0074] Suitable materials for use in a marine environments, as known to those skilled in the art, can be used to construct the components of the lift 100, including the accessories described above, i.e., the guide-ons 802, stem stop 804, and associated brackets 812, 828, and universal plate 842, and fasteners. The guide-ons 802, as well as the stern stop 804, can be formed from sturdy plastic that will help prevent damage to the exterior of the boat hull and the stern drive or outboard drive components. While a preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes may be made therein without departing from the spirit and scope of the invention. Consequently, the invention is to be limited by the scope of the claims that follow.