Abstract:
A watercraft lift for raising and lowering a watercraft in water, including a buoyant pontoon, a lifting cradle and at least one pivot arm. The lifting cradle includes at least one air tank and a support bunk configured to receive and support the watercraft. The air tank has an internal chamber configured to receive and release pressurized air. The internal chamber has sufficient internal volume that when sufficient pressurized air is received therein the air tank has sufficient buoyancy to lift the lifting cradle to a raised position with the watercraft out of the water when positioned on the support bunk and that when sufficient pressurized air is released from the internal chamber the air tank loses sufficient buoyancy to sink the lifting cradle to a lowered position sufficiently submerged to receive and deploy the watercraft. The pivot arm is pivotally connected to the pontoon and pivotally connected to the lifting cradle to guide movement of the lifting cradle between the lowered position and the raised position.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention generally relates to an apparatus and method for lifting watercraft out of the water.  
       DESCRIPTION OF THE RELATED ART  
       [0002]     The use of watercraft lifting devices is well known. Out-of-water storage prevents damage resulting from boat contact with docks, other craft or floating debris. It reduces the possibility of the boat breaking free from its moorage and floating adrift or running aground. Out-of-water storage also lessens boat damage associated with long-term exposure to water and water-based pollutants and the attachment of barnacles or other marine growth to the boat&#39;s hull. Once a boat is lifted it can be maintained in its position for extended periods of time, relieving the user of maintenance concerns. In certain situations where the water fluctuation is high, water depth is too deep, or permanent mounting is undesired, floating watercraft lifting devices are used. A number of floating lift designs are currently known that provide this basic function.  
         [0003]     U.S. Pat. No. 5,002,000 to Rutter uses air filled pontoons as a lifting device combined with a complicated array of air inlet and outlet valves to control lateral stability while lifting. With this device the rear portion of the pontoons are lowered more than the forward portion of the pontoons to allow ingress and egress of the boat. This device, however, is limited in that the watercraft will not be raised or lowered in a horizontal position which is undesirable to many users.  
         [0004]     U.S. Pat. No. 5,860,379 to Moody comprises of an inflatable fabric air chamber as the lifting device. While this device raises the boat out of the water, it has many disadvantages including a complicated rope tying configuration for stabilizing, non-horizontal lifting by raising the bow of the watercraft before the stern, and incompatibility with all boats by only fitting boats with outboard and inboard/outboard motors.  
         [0005]     U.S. Pat. No. 6,848,380 to Sainz is a floating watercraft lift that addresses the fore and aft stability issues and non-horizontal lifting with the boatlifts described in Moody and Rutter by using air chambers with an arcuate longitudinal top surface and a base side that is flat. While addressing these stability issues, the lift suffers from a number of disadvantages including the lack of a means for keeping the lift stable if air pressure is lost in one or all pontoon chambers, the ability to fit in a narrow boat slip, and the lack of reserve buoyancy to keep the device from sinking if all air pressure is lost.  
         [0006]     Two known devices, one from Hydrohoist International, Inc. and the other from Shoremaster, address the fore and aft stability and non-horizontal lifting described in Moody and Rutter in another fashion. Both devices are air displacement watercraft lifts using stabilizing brackets fixed to a dock or slip to maintain horizontal lifting of the watercraft. These fixed stabilizing brackets are undesirable for marina operations and limit the ease of portability for these lifts. A similar method for stabilizing a boat lift is described in U.S. Pat. No. 4,750,444 to Lemvig, wherein the lift is comprised of a platform with a deck and lifting skirt and link arms connecting the platform to a quay. Air is supplied to the lifting skirt to raise a watercraft while the link arms attached to the quay stabilize the platform. Similar to the Hydrohoist and Shoremaster devices, the device of Lemvig requires link arms fixed to a quay to stabilize the lift limiting the portability of the lift.  
         [0007]     Hydrohoist International, Inc. and Airberth address portability issues with free floating side tie lifts. These lifts use air tanks rigidly attached to side floatation to control lifting and stability. While allowing for portability and side tie capabilities, these lifts do not raise the watercraft in a horizontal position and have similar disadvantages to Rutter and Moody.  
         [0008]     In addition to the above stated short comings, the floating watercraft lifts of Rutter, Moody, Sainz, Hydrohoist, Shoremaster and Air Berth may inadvertently lower the watercraft into the water if air pressure is not maintained in one or all air chambers. In this case the watercraft will become susceptible to the damaging elements described above.  
         [0009]     Another difficulty facing floating watercraft lift manufacturers is the multitude of mounting scenarios. To meet the lift mounting requirements, the manufacturers offer different lifts for slip, side-tie and forward mounting applications. By offering three different lifts the manufacturer and dealer must increase inventory levels and warehouse storage space.  
         [0010]     Accordingly, there is a need in the art for a floating watercraft lift that addresses all of the following issues of horizontal lifting of the watercraft with a desirable stabilizing feature, compatibility with all boat drive configurations, stability if air pressure is lost in one or all air chambers, the ability to fit in narrow boat slips, portability for ease of installation and removal, damage tolerance to keep the watercraft out of the water if one or all of the air chambers lose air pressure, and convertibility to most floating watercraft lift mounting scenarios.  
       SUMMARY OF THE INVENTION  
       [0011]     A watercraft lift for raising and lowering a watercraft in water. The watercraft lift includes a buoyant pontoon, a lifting cradle and at least one pivot arm. The lifting cradle includes at least one air tank and a support bunk configured to receive and support the watercraft. The air tank has an internal chamber configured to receive and release pressurized air. The internal chamber has sufficient internal volume that when sufficient pressurized air is received therein the air tank has sufficient buoyancy to lift the lifting cradle to a raised position with the watercraft out of the water when positioned on the support bunk and that when sufficient pressurized air is released from the internal chamber the air tank loses sufficient buoyancy to sink the lifting cradle to a lowered position sufficiently submerged to receive and deploy the watercraft. The pivot arm is pivotally connected to the pontoon and pivotally connected to the lifting cradle to guide movement of the lifting cradle between the lowered position and the raised position.  
         [0012]     In one embodiment the pontoon includes a buoyant port pontoon portion and a buoyant starboard pontoon portion. The port and starboard pontoon portions are spaced apart sufficient to receive the watercraft therebetween.  
         [0013]     The watercraft lift may further include ballast removably attached to the port pontoon portion and ballast removably attached to the starboard pontoon portion in amounts sufficient to prevent the watercraft lift from rolling when the watercraft is positioned on the support bunk with the watercraft lift in the raised position when all pressurized air is released from the internal chamber the air tank. The port and starboard pontoon portions are made of a first material and the ballast is made of a second material, the first material being different than the second material.  
         [0014]     The pontoon includes a buoyant port pontoon portion having an end portion and a buoyant starboard pontoon portion having an end portion. The port and starboard pontoon portions are spaced apart sufficient to receive the watercraft therebetween. The pontoon further includes a buoyant connection pontoon portion having the end portions of the port and starboard pontoon portions attached thereto. The combined buoyancy of the port pontoon portion, the starboard pontoon portion and the connection pontoon portion is sufficient hold the watercraft out of the water when the watercraft is positioned on the support bunk with the watercraft lift in the raised position when all pressurized air is released from the internal chamber the air tank.  
         [0015]     The port pontoon portion, the starboard pontoon portion and the connection pontoon portion have upper surfaces arranged to provide a floating dock surface for access to the watercraft from three sides thereof when positioned on the support bunk.  
         [0016]     The connection pontoon portion has buoyant port and starboard connection pontoon portions, with the end portion of the port pontoon portion attached to the port connection pontoon portion and the end portion of the starboard pontoon portion attached to the starboard connection pontoon portion. The port connection pontoon portion and the starboard connection pontoon portion are removably attached together.  
         [0017]     The watercraft lift may further include a lock operable to lock the pivot arm relative to the pontoon when the lifting cradle is in the raised position to prevent downward movement of the pivot arm and thereby movement of the lifting cradle to the lowered position. The lock includes a selectively rotatable upright member having an engagement member attached thereto, the rotatable member being rotatable between a locked position and an unlocked position. In the locked position the engagement member is positioned in locking engagement with the pivot arm to prevent downward movement of the pivot arm and thereby movement of the lifting cradle to the lowered position. In the unlocked position the engagement member is positioned out of locking engagement with the pivot arm to allow downward movement of the pivot arm and thereby movement of the lifting cradle to the lowered position. The lock may include a security member which when engaged prevents rotation of the rotatable member out of the locked position.  
         [0018]     Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)  
       [0019]     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, which are schematic, and not to scale, wherein:  
         [0020]      FIG. 1  is an isometric view of a watercraft lift according to the present invention in a lowered position.  
         [0021]      FIG. 2  is an isometric view of the watercraft lift of  FIG. 1  in a position between a raised position and the lowered position.  
         [0022]      FIG. 3  is an isometric view of the watercraft lift of  FIG. 1  in the raised position.  
         [0023]      FIG. 4  is an enlarged, isometric view of an air tank of the watercraft lift of  FIG. 1 .  
         [0024]      FIG. 5  is an enlarged, isometric view of a lifting cradle of the watercraft lift of  FIG. 1 .  
         [0025]      FIG. 6  is an isometric view of ballasted floating pontoons of the watercraft lift of  FIG. 1 .  
         [0026]      FIG. 7  is a side view of a swing arm of the watercraft lift of  FIG. 1 .  
         [0027]      FIG. 8  is an front view of the swing arm and torsion bar assembly of the watercraft lift of  FIG. 1 .  
         [0028]      FIG. 9  is a sectional side elevational view of the watercraft lift of  FIG. 1  showing a 4-bar linkage arrangement of the swing arms.  
         [0029]      FIG. 10  is an enlarged, isometric view of a lock mechanism of the watercraft lift of  FIG. 1 .  
         [0030]      FIG. 11  is a rear elevational view of the watercraft lift of  FIG. 1  in the lowered position with the watercraft in the load/unload position.  
         [0031]      FIG. 12  is a rear elevational view of the watercraft lift of  FIG. 1  in the raised position with the watercraft in the stored position.  
         [0032]      FIG. 13  is a top plan view of the watercraft lift of  FIG. 1  in a 4-point tie configuration in a slip.  
         [0033]      FIG. 14  is a top plan view of the watercraft lift of  FIG. 1  in a forward mounting tie configuration.  
         [0034]      FIG. 15  is a top plan view of the watercraft lift of  FIG. 1  in a side tie configuration.  
         [0035]      FIG. 16  is an isometric view of the watercraft lift of  FIG. 1  with a canopy mounted to the floating pontoons.  
         [0036]      FIG. 17  is an isometric view of the watercraft lift of  FIG. 1  with a hydrodynamic element to control the acceleration and velocity of raising and lowering the lifting cradle.  
         [0037]      FIG. 18  is an isometric view of multiple watercraft lifts of the type shown in  FIG. 1  mounted side by side.  
         [0038]      FIG. 19  is an isometric view of the watercraft lift of  FIG. 1  with air hoses routed through a center of the watercraft lift.  
         [0039]      FIG. 20  is an isometric view of the watercraft lift of  FIG. 1  with the floating pontoons removed and swing arms pivotally attached to a slip. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]     This section illustrates aspects of the invention, and points out certain preferred embodiments of these aspects. This section is not intended to be exhaustive, but rather to inform and teach the person of skill in the art who will come to appreciate more fully other aspects, equivalents, and possibilities presented by invention, and hence the scope of the invention is set forth in the claims, which alone limit its scope.  
         [0041]     Several embodiments of the invention are set forth in the following description:  FIGS. 1 through 20  provide a thorough understanding of such embodiments. One skilled in the art will understand that the present invention may be practiced without several of the details described herein. In the following description of the embodiments, it is understood that a watercraft includes any vehicle that is at least partially waterborne, which includes boats and similar vessels, but may also include amphibious vehicles including various amphibious automobiles or aircraft. Moreover, in the description that follows, it is understood that the figures related to the various embodiments are not to be interpreted as conveying any specific or relative physical dimension, and that specific or relative dimensions related to the various embodiments, if stated, are not be considered limiting unless future claims state otherwise.  
         [0042]     An isometric view of a watercraft lift  10  in a fully lowered position is shown in  FIG. 1 . The watercraft lift  10 , having a port side A and a starboard side B, includes a lifting cradle  50  comprising two air tanks  40  each having a lifting bunk  51 , and a pair of port and starboard floating pontoons  60  with the lifting cradle positioned between the laterally spaced apart rearward portions of the floating pontoons. Fore and aft pivotal connectors  80  pivotally connect the lifting cradle  50  to the floating pontoons  60 . Each pivotal connector  80  includes a torsion bar  81  extending through the lifting cradle  50  and two swing arm  70  attached to the torsion bar, one on each side of the lifting cradle. One swing arm  70  of the pivotal connector  80  is pivotally connected to the port floating pontoon  60 , and the other swing arm of the pivotal connector is pivotally connected to the starboard floating pontoon  60 . As best seen in  FIG. 9  for the port side A, the swing arms  70  of the fore and aft pivotal connectors  80  are pivotally attached at points  91  and  92  on the port floating pontoon  60  and are also pivotally attached to the lifting cradle  50  at points  43  and  44 . The lower ends of the swing arms  70  rotate forward and upwardly towards the forward floats  61  as air volume is increased within the air tanks  40 . The lifting bunks  51  provide support to the hull of a watercraft  111  when in engagement therewith as shown in  FIG. 12 .  
         [0043]     Again referring to  FIG. 1 , each floating pontoon  60  has a forward float  61 , three side floats  62 , side ballasts  63  and forward ballast  64 . As will be described below, these floats are connected together to form a dock like structure for access to the watercraft  111  using the watercraft lift  10  from three sides.  
         [0044]      FIG. 2  shows the watercraft lift  10  in a partially raised position from the lowered position shown in  FIG. 1  which results from the pumping of air into the air tanks  40  of the lifting cradle  50  and the resulting purging of the water therein. As the air volume is increased within the air tanks  40 , the lifting cradle  50  increases in buoyancy and rises to engage the lifting bunks  51  with the hull of the watercraft  111  thereabove. Thereafter, the lifting cradle  50  carries the watercraft on the lifting bunks  51  upward with the lifting cradle. If the watercraft lift  10  starts to list to the port side A, the side floats  62  on the port side A and the side ballast  63  on the starboard side B will provide the righting moment to stabilize the watercraft lift and prevent the watercraft  111  from rolling off of the lifting bunks  51 . In the same manner, if the watercraft lift  10  lists to starboard side B, the side floats  62  on the starboard side B and the side ballast  63  on the port side A will provide the righting moment to stabilize the watercraft lift and prevent the watercraft  111  from rolling off of the lifting bunks  51 . This provides increase laterally stability for the watercraft lift  10 .  
         [0045]      FIG. 3  shows the watercraft lift  10  in a fully raised position with the lifting cradle  50  in a raised position sufficient to hold the watercraft  111  out of the water as shown in  FIG. 12 . The air volume in the air tanks  40  is selected to be sufficient that in combination with the buoyancy of the floating pontoons  60  the watercraft  111  will be held in a raised position above the water (see  FIG. 12 ). It is noted that the floating pontoons  60  stay floating in the water throughout the operation of the watercraft lift  10 , and that when the lifting cradle  50  is in the fully raised position of  FIG. 3  the lifting cradle and the floating pontoons are spaced apart at a first distance, and when the lifting cradle is in the fully lowered position of  FIG. 1  the lifting cradle and the floating pontoons are spaced apart at a second distance with the second distance being greater than the first distance.  
         [0046]      FIG. 4  shows an isometric view of the air tank  40  of the watercraft lift  10 . The air tank  40  serves as the lower structural bar of a 4-bar linkage  90 . The air tank  40  is made from a hollow rotationally molded structural plastic shell with a longitudinally extending, upwardly projecting, integrally formed strengthening rib  41 , laterally extending, upwardly projecting, integrally formed forward and rearward bunk towers  48 , and longitudinally extending, upwardly projecting, integrally formed gussets  47 . The rib  41  provides stiffness and rigidity, and the bunk towers  48  and gussets  47  distribute the load over the entire air tank without the need for an external structure to provide the main load support and also would increase the height of the lifting cradle. The air tank  40  further has a water inlet and outlet port  45 , an air inlet and outlet port  42 , an adjustable relief port  46  and horizontally adjustable pivot points  43  and  44  using the adjustment brackets  49 .  
         [0047]     As shown in  FIG. 5 , the lifting cradle  50  has two air tanks  40 , each with one lifting bunks  51  mounted to a top side thereof atop the bunk towers  48 . The lifting bunks  51  is rigidly attach to the air tanks  40  on bunk towers  48  thus adding bending stiffness to the air tank of the lifting cradle  50 . The lifting cradle  50  lifts the watercraft  111  by introducing air through the air inlet and outlet port  42 , and thereby evacuating water within the air tank  40  through water inlet and outlet port  45 , thus increasing the buoyancy of the air tank. If watercraft lift  10  lists, air will escape through the adjustable relief port  46  of the air tank  40  which is the least submerged, thus reducing its buoyancy and preventing the watercraft lift from rolling. The relief port  46  comprises a column of through-holes in the wall of the air tank, each to be at a different height relative to the water line. The relief port  46  is adjustable in that based on the size of the watercraft to be supported by the lifting cradle  50 , plugs can be used to close selected ones of the through-holes and thereby control the ones which are operable. The adjustable relief port  46  is provided on the laterally outward side of each of the air tanks  40 . When it is desired to lower the lifting cradle  50  to lower the watercraft  111  supported, the air within the air tanks is released through the air inlet and outlet port  42 , and thereby allowing water to enter within the air tank  40  through water inlet and outlet port  45 , thus decreasing the buoyancy of the air tank.  
         [0048]     The air tanks  40  each include a longitudinally extending, laterally outward projecting lower portion  40 A. As best seen in  FIG. 12 , the lifting cradle  50  is sized so that when positioned between the floating pontoons  60 , the laterally outward projecting lower portion  40 A of the port air tank  40  when the lifting cradle  50  is in the fully raised position extends laterally outward to under the lower side of the port floating pontoon and engages the lower side of the port floating pontoon, and the laterally outward projecting lower portion  40 A of the starboard air tank  40  when the lifting cradle  50  is in the fully raised position extends laterally outward to under the lower side of the starboard floating pontoon and engages the lower side of the starboard floating pontoon. With this arrangement, the floating pontoons  60  serve as stops for the upward movement of the lifting cradle  50 . Further, the contact of the laterally outward projecting lower portions  40 A of the air tanks  40  with the lower sides of the floating pontoons  60  provides the watercraft lift  10  with increased rigidity and stability when the lifting cradle  50  is in the fully raised position shown in  FIG. 12 .  
         [0049]      FIG. 6  shows the port and starboard floating pontoons  60  without the lifting cradle  50 . Each of the floating pontoons  60  includes three side floats  62  and one forward float  61 . The side floats  62  and the forward float  61  of each floating pontoon  60  are mechanically link together with a tube  67  to which each is attached at its laterally inward side. The side ballast  63  is removably attached to a top side of the side floats  62 , and the forward ballast  64  is removably attached to a top side of the forward floats  61 . The side ballast  63  includes heavy concrete tiles that provide ballast for the watercraft lift  10  as described above. The forward ballast  64  helps keep the watercraft lift  10  in an acceptable fore-aft attitude in the event air pressure within the air chambers  40  is lost or compromised and the floating pontoons  60  must support the watercraft  111  when the watercraft lift  10  is in a locked raised position which will be described below. The forward ballast  64  is shown as a heavy grate that covers a through opening in the forward float  61 . The through opening reduces the light blocked by the watercraft lift  10 .  
         [0050]     The side floats  62  and the forward floats  61  are constructed of a sealed rotationally molded plastic shell with a foam filled or an air filled inner core for buoyancy. The buoyancy is selected to be sufficient to keep the watercraft  111  supported high enough above the water and in sufficient frictional contact with the lifting bunks  51  to keep the watercraft from floating off and away from the lifting cradle  50  when the lifting cradle is in the locked raised position even if all air pressure in the air tanks  40  is lost and the air tanks provide no buoyancy. The forward floats  61  are shaped on an inward side to accept and position the bow of the watercraft  111  must like a boat slip, and are designed to be used as mirrored parts as shown in  FIG. 6 .  
         [0051]     The port and starboard floating pontoons  60  are attached together at a connection location  69  with a mechanical connection  68  which connects together the front floats  61  of the two floating pontoons. The floating pontoons  60  can be split at the connection location  69  and a spacer float (not shown) can be added therebetween to increase the distance between the side floats  62  of the floating pontoons to accept a boat with a wider beam.  
         [0052]      FIG. 7  shows the swing arms  70  as having an upper pivot point  71  at an upper end thereof and a lower pivot point  72  at the opposite lower end thereof. The upper end of the swing arm  70  is pivotally attached to the floating pontoon  60  for pivotal movement relative thereto about the upper pivot point  71 , and the lower end of the swing arm is rigidly attached to one end of the torsion bar  81  of the pivotal connector  80  for pivotal movement relative to the lifting cradle  50  about the lower pivot point  72 . The pivotal connector  80  is shown in  FIG. 8  with one of the swing arms  70  rigidly attached to each of the two opposite ends of the torsion bar  81 . As shown in  FIG. 7 , the swing arm  70  has a substantially straight lower end portion with a shorter upper end portion at an angle relative to the lower end portion such that when the swing arm is rotated forward with the lower end shape aligned with a horizontal axis  73  with the upper pivot point  71  on the horizontal axis, the lower end portion of the of the swing arm and the lower pivot point  72  are offsets below horizontal axis.  
         [0053]     In  FIG. 9 , the 4-bar linkage  90  on the port side of the watercraft lift  10  is shown as the tube  67  of the port floating pontoon  60  being a first upper bar, the air tank  40  of the lifting cradle  50  being a second lower bar, and the forward and rearward swing arms  70  of the two pivotal connectors  80  being the third and fourth bars. Of course, there is a similar 4-bar linkage  90  formed at each of the port and starboard floating pontoons  60 . The upper pivot points  71  of the swing arms  70  are pivotally attached to the tube  67  of floating pontoons  60  at points  91  and  92 , and the lower pivot points  72  of the swing arms are pivotally attached at points  93  and  94  to the pivots  43  and  44  of air tanks  40  by the torsion bars  81 . The use of the 4-bar linkage  90  provides the watercraft lift  10  with a level lift and lowering of the watercraft  111  by the lifting cradle  50 .  
         [0054]     The adjustment brackets  49  (best seen if  FIG. 4 ) each have an aperture through which the end portion of the torsion bar  81  extends and in which it is rotatably mounted. The adjustment brackets  49  are positionable during manufacture of the watercraft lift  10  along the rib  41  of the air tank  40  to achieve the desired longitudinal separation between the torsion bars  81  of the fore and aft pivotal connectors  80  even if the molding process used for the air tank produces a variation in the size of the air tank from one to the other.  
         [0055]     A lock mechanism  100  is shown in  FIG. 10  as being associated with one of the swing arms  70  pivotally attached to the port floating pontoon  60  and with one of the swing arms pivotally attached to the starboard floating pontoon. The lock mechanism  100  is selectively rotatable about a vertical axis to engage the adjacent swing arm  70  and limit the downward movement thereof, and thus locking the floating pontoon  60  to the lifting cradle  50  with the lifting cradle in the raised position. The lock mechanism  100  includes an engagement lever  104  at its top end, a lock shaft  101  to which the engagement lever is attached, a lock plate  103  for lock position indication, a load holding shoulder  105 , and an engagement foot  102 . The lock mechanism  100  is mounted through one of the side floats  62  and is bolted to the tube  67  using a clamp  106  which allows the lock shaft  101  to rotate therein relative to the side float. When the engagement lever  104  is rotated into a locked position D, the lock shaft  101  is rotate about the vertical axis to rotate the engagement foot  102  into position below the swing arm  70 , thus limiting the downward rotational travel of the swing arm toward the lowered position shown in  FIG. 1 . When swing arm  70  rotates downward sufficient to engage the engagement foot  102 , the load holding shoulder  105  transfers the load placed thereon by the swing arm and the lifting cradle  50  to which it is connected, to the side float  62  of the floating pontoon  60  through the clamp  106  and the tube  67 . As discussed above, the ability to lock and hold the lifting cradle  50  in the raised position and providing the forward floats  61  and the side floats  62  of the floating pontoons  60  with sufficient buoyancy to support the full weight of the watercraft  111  and keep the watercraft above the water even should the entire air pressure in the air tanks  40  be lost, provides the watercraft lift  10  with a significant safety feature in the event of a failure that results in air pressure loss in the air tanks.  
         [0056]     When engagement lever  104  is rotated along path E to an unlocked position C, the engagement foot  102  rotates to a position where it will not engage swing arm  70  and hence not limit downward rotation of the swing arm toward the lowered position shown in  FIG. 1  and allow its unimpeded upward movement.  
         [0057]     When the engagement lever  104  is rotated into the locked position D, the lock mechanism  100  prevents accidental or unintended lowering of the watercraft  111  into the water. Even should air pressure be released from the air tanks  40 , the locking mechanism will prevent lowering of the lifting cradle  50 . When the engagement lever  104  is rotated into the locked position D, the engagement lever  104  may be padlocked to the lock plate  103  or in alternative embodiments otherwise locked to prevent rotation of the lock shaft  101  and hence rotation of the engagement foot  102  from under the swing arm  70 . This provides protection against theft of the watercraft  111  when on the lifting cradle  50  in the raised position since without being able to rotate the engagement lever to the unlocked position C, the lifting cradle cannot be lowered to place the watercraft in the water, thus preventing unauthorized removal of the watercraft from the watercraft lift  10 .  
         [0058]      FIG. 11  shows a rear view of the watercraft lift  10  in the lowered position with the watercraft  111  in the load/unload position. The lock mechanism  100  is in the unlocked position C. The watercraft  111  is shown floating with respect to a waterline  112  and the lifting cradle  50  is submerged below and does not touch the watercraft  111 .  
         [0059]      FIG. 12  shows a rear view of the watercraft lift  10  in the raised position with the watercraft  111  in the stored position with the lifting bunks  51  engaging the hull of the watercraft. The locking mechanism  100  is in the locked position D. The watercraft  111  rests on the lifting bunks  51  which supports it in a position above the waterline  102 .  
         [0060]     The floating pontoons  60  can be tied or attached to a dock, sea wall or quay at tie points  66 . The watercraft lift  10  is shown in  FIG. 13  in a 4-point tie configuration with dock lines  131  tied to a slip  132  and to the lift tie points  66  on the floating pontoons  60 .  
         [0061]     The watercraft lift  10  is shown in  FIG. 14  in a forward mounting configuration with dock lines  141  tied to a dock  142  and the front lift tie points  66  on the floating pontoons  60 .  
         [0062]     The watercraft lift  10  is shown in  FIG. 15  in a side tie configuration with dock lines  151  tied to a dock  152  and the lift tie points  66  on the floating pontoons  60 .  
         [0063]     The watercraft lift  10  is shown in  FIG. 16  with a canopy  161  mounted to floating pontoons  60  using four canopy uprights  162 .  
         [0064]     The watercraft lift  10  is shown in  FIG. 17  with a hydrodynamic brake element  171  used to control the acceleration and velocity of the raising and lowering of the lifting cradle  50 . This reduces hull impact on raising of the lifting cradle  50  to provide a smooth lift. The hydrodynamic element  171  is removably attached to the lifting cradle  50  in position between the air tanks  40  and extends substantially fully between the air tanks. The hydrodynamic element  102  has a configuration selected to create increased water resistance to movement of the lifting cradle  50  as it moves upward and downward beyond the water resistance that would be experience otherwise. This is accomplished by the hydrodynamic element  102  catching the water and thereby forcing the water to flow over and around it. The hydrodynamic element  102  configuration provides water resistance that supplements the natural water resistance experienced by the lifting cradle  50  to control the acceleration and velocity of raising and lowering the lifting cradle.  
         [0065]     A plurality of the watercraft lifts  10  are shown in  FIG. 18  with the watercraft lifts mounted side-by-side. The front ends of the forward floats  61  of the floating pontoons  60  have a straight forward portion  183  that engages a straight side of a dock  181 , and are mechanically connected to the dock. The adjacent outward sides  182  of the floating pontoons  60  of the watercraft lifts  10  are in engagement and the adjacent floating pontoons are mechanically connected together. In this arrangement, the watercraft lifts  10  can be used with a simple dock to provide a plurality of boat slips with floating watercraft lifts and allows the convenient construction of a marina.  
         [0066]     The watercraft lift  10  is shown in  FIG. 19  with a conduit  191  having a length centrally routed between the floating pontoons  60  and air tanks  40 . The conduit  191  contains two air hoses. With this arrangement the conduit  191  and the hoses contained therein are below the watercraft  111  when on the lifting cradle  50  and hidden from view. Even when the watercraft  111  is not present, the conduit  191  provides an uncluttered appearance and reduces the chance of entanglement of the air hoses with foreign objects. The conduit  191  is corrugated and has an elastic member arranged to keep the conduit and hence the hoses out of the water and free from marine growth. The hoses within the conduit  191  connect to the air inlet and outlet port  42  of the air tanks  40  to provide pressurized air to the interior of the air tanks at sufficient pressure to evacuate the water therein and lift the lifting cradle  50  with the watercraft  111  thereon to the raised position, and to allow release of the pressurized air in the air tanks for lowering of the lifting cradle.  
         [0067]     The watercraft lift  10  is shown in  FIG. 20  with the floating pontoons  60  removed and the swing arms  70  of the pivotal connectors  80  pivotally attached to a slip  201  by their upper pivot points  71  at connection points  202 ,  203 ,  204  and  205 . This arrangement allows the watercraft lift  10  to be converted from a self-supported floating lift to a lift supported by a ground supported slip as desired.  
         [0068]     It will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without departing from the spirit or scope of the invention.