Patent Publication Number: US-11027801-B2

Title: Boat lift

Description:
This Application is a continuation of application Ser. No. 16/238,849 filed Jan. 3, 2019, now U.S. Pat. No. 10,597,127, issued Mar. 24, 2020, which was a continuation in part of U.S. application Ser. No. 16/143,737, filed Sep. 27, 2018, U.S. Pat. No. 10,370,073 issued Aug. 6, 2019, which is a continuation of U.S. application Ser. No. 15/467,399, filed Mar. 23, 2017, U.S. Pat. No. 10,086,919 issued Oct. 2, 2018, which is a continuation in part of U.S. application Ser. No. 15/160,372, filed May 20, 2016, U.S. Pat. No. 9,604,709 issued Mar. 25, 2017. 
    
    
     BACKGROUND OF THE INVENTION 
     It is desirable to store boats out of the water when not in use. Particularly in saltwater environments, water can lead to rapid corrosion of metal parts, and depreciation of other parts of the boat. Further, in many saltwater environments, storage of the boat hull in the water leads to fouling of the hull, propellers and through hulls that communicate with boat utilities. Barnacle growth, for example, occurs in many saltwater environments, and such fouling reduces performance of the boat hull and propulsion systems. 
     It is also desirable to lift boats out of the water for maintenance. 
     Many boats and ships are very large. There is a need for boat lifts that can accommodate larger vessels, and can be transported on highways for installation in water, without obtaining special permits due to the width and/or length of the transported boat lift. 
     SUMMARY OF THE INVENTION 
     A boat lift has one or more pumps that evacuate water from a first flotation tank construct and a second flotation tank construct to create flotation of the boat lift. Modular boat lifts may be constructed according to the invention that have substantial width while being transportable by truck for assembly on site. 
    
    
     
       BRIEF DRAWING DESCRIPTION 
         FIG. 1  is a perspective view of a boat lift and catwalk according to an embodiment of the invention. 
         FIG. 2  is a top plan view of the boat lift and catwalk of  FIG. 1 . 
         FIG. 3  is a perspective view of a modular section of a boat lift according to an embodiment of the invention. 
         FIG. 4  is an elevation of the modular section of  FIG. 3 . 
         FIG. 5  is a perspective view of the boat lift and catwalk as shown in  FIG. 3 , with the boat lift and catwalk covered according to an embodiment for use. 
         FIG. 6  is an elevation of a connecting guide construct for connecting the floating lift of the invention to a catwalk or other object. 
         FIG. 7  is an elevation of the connecting guide construct of  FIG. 6 . 
         FIG. 8  is a perspective view demonstrating the connecting guide construct of  FIG. 8  connecting a boat lift and catwalk. 
         FIG. 9  is a perspective view of a pile guide. 
         FIG. 10  is an elevation of the pile guide of  FIG. 9 . 
         FIG. 11  is an exploded view of another embodiment of the boat lift and catwalk. 
         FIG. 12  is a perspective view of the boat lift and catwalk of  FIG. 11 . 
         FIG. 13  is a top plan view of the of the boat lift and catwalk of  FIG. 12 . 
         FIG. 14  is an isolation of connecting guide construct joining the boat lift. 
         FIG. 15  is an isolation of flotation tanks for the catwalk and boat lift with a pile guide as shown in  FIG. 10  in position in the catwalk flotation tank. 
         FIG. 16  is a side elevation of a connecting guide construct demonstrating connection of a catwalk to a flotation tank of a boat lift. 
         FIG. 17  is a perspective view of connecting guide constructs of  FIG. 14  and demonstrating connection of a catwalk to flotation tanks of a boat lift. 
         FIG. 18  is a side sectioned view of a transverse member of the boat lift. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  and  FIG. 2  show a preferred embodiment of a boat lift  2  surrounded by a catwalk  4 . In this embodiment, the boat lift is characterized by two generally parallel flotation tanks  6 , 8  that are connected by transverse tanks  10 , 12  positioned near each end of the longitudinal flotation tanks and may be intermediately positioned  14 . 
     In this embodiment, the boat lift  2  is disposed within a catwalk  4 . The catwalk as shown in  FIG. 1  and  FIG. 2  has generally parallel flotation tanks  20 , 22  joined at one end by a transverse tank  24 . The catwalk is open at one end to permit ingress and egress of a boat from the boat lift. 
       FIG. 3  and  FIG. 4  show an embodiment of a transverse member  24  for joining the parallel flotation tanks  20 ,  22  of the catwalk. This transverse member may be formed to a desired length, which is determined based upon the desired width of the boat lift and catwalk. The flanges  54  on the ends of the transverse member or tank may be inserted into slots formed in the catwalk flotation tanks and fixed in place, such as by welding. Assembly may be performed after transportation of the catwalk to the site of installation. As with other embodiments described herein, flotation tanks and other members of the boat lift and the catwalk may be formed in multiple sections for later assembly at the point of installation, along with the transverse member or tank for the catwalk being attached to the flotation tanks of the catwalk after transportation and at the point of installation, allow a boat lift and associated catwalk of large length and/or width to be constructed without concern for highway transportation limitations. 
     The catwalk  4  floats with a water level of a body of water in which the construct is placed. The flotation tanks may be filled with water to a level that positions the catwalk at a desired height. As the water level of the body of water rises and falls, the catwalk will also rise and fall. The catwalk is secured by piles that are driven into the earth. The piles are generally vertical members that are inserted through pile guides  30 . 
     In the embodiment as shown in  FIG. 1 , the pile guides  30  are inserted into voids formed in the flotation tanks. The pile guides are preferred to be positioned at the ends of the flotation tanks  22 , 24  as shown, so that they are out of the way of covering or planking  26  that covers the catwalks, and do not interfere with the person walking on the catwalk. As shown in  FIG. 5 , the boat lift  2  may be covered with a covering or planking  16 . 
     The boat lift  2  is secured by a connecting guide construct  32  that is attached to the catwalk  4  in a preferred embodiment. In another embodiment, the connecting guide construct is connected to the boat lift, and if a catwalk is not used, the connecting guide construct is attached to a stationary member such as a pile, or a bulkhead, or a seawall. 
     An embodiment of a connecting guide construct is shown in  FIG. 6  and  FIG. 7 . The upper guide  34  is attached to the catwalk  4  or other fixed object. The upper guide vertically traverses the stanchion  36  of the construct. The boat lift guide  38  is attached to the boat lift. 
     In one embodiment, the boat lift guide  38  and the accompanying stanchion  36  are fixed to the boat lift  2 . In another embodiment, the stanchion is driven as a pile into the earth, and the boat lift guide moves vertically along the stanchion as does the upper guide. The use of multiple guide constructs  32  allows the boat lift to raise and lower vertically relative to the catwalk  4 .  FIG. 1 . The catwalk floats vertically with the water level relative to the stanchion. The stanchion fits within the upper guide with very little “slop.” The upper guide moves freely in a vertical direction, but the fit with the stanchion inhibits horizontal movement of the upper guide relative the stanchion. Accordingly, the catwalk (or a fixed member) resists horizontal movement from waves, wind and other forces. 
     Similarly, when the boat lift guide  38  is fixed to the stanchion  36 , the boat lift can move vertically, but the horizonal movement of the boat lift  2  is inhibited. If the stanchion is driven as a pile into the earth, the stanchion fits within the upper guide  34  with very little “slop.” The upper guide moves freely in a vertical direction, but the fit of the boat lift guide with the stanchion inhibits horizontal movement. Accordingly, the boat lift resists horizontal movement from waves, wind and other forces. 
     When at least two connecting guide constructs  32  are associated with each flotation tank and are spaced apart as shown in the drawing figures, the boat lift and the catwalk resist horizontal forces applied by wave action, wind and other forces. The boat lift and catwalk are very stable, although they move vertically as the water level raises and lowers in the case of the catwalk, or the boat lift is raised or lowered. 
     As shown, the boat lift guide  38  and the upper guide  34  of the boat lift construct each comprise a sleeve  42 , 44 . In a preferred embodiment, the sleeves are formed of high density polyethylene. High density polyethylene is extremely strong but has a low co-efficient of friction that allows movement of the guides relative to the stanchion  36 . High density polyethylene (HDPE) can be formed to an inside diameter that has minimal slop relative to the stanchion to inhibit horizontal movement, but the co-efficient of friction is sufficiently low to permit the required vertical movement. High density polyethylene is also resistant to corrosion, which is particularly important in saltwater applications. 
     The guides  34 , 38  each have a mounting bracket  46 , 48  that is configured for mounting to the boat lift in the case of the boat lift guide, or to a catwalk in the case of the upper guide as attached to a catwalk, or otherwise configured as required for attachment to a fixed object. 
       FIG. 8  shows the connecting guide construct attached to a flotation tank  20  of a catwalk and a flotation tank  6  of a boat lift. The upper guide  34  is attached to flotation tank  20 , and the boat lift guide  38  is attached to the flotation tank  6 . In the embodiment of  FIG. 7 , the stanchion  36  is fixed to the boat lift guide. As can be seen, the boat lift can move vertically and independently of the catwalk, and the catwalk can move vertically and independently of the boat lift, each moving substantially only vertically to produce a stable boat lift and catwalk construct even when horizontal forces from wave action, wind, or other horizontal forces are applied to the boat lift and catwalk construct. 
     The boat lift guide  38  and upper guide  34  may be formed entirely of one material, and preferably HDPE. In another embodiment, the guide sleeves  42 , 44  are attached to mounting brackets  46 , 48 , which may be formed of metal or other strong and durable materials. The boat lift guide and the upper guide may be mounted to the boat lift and catwalk (or other fixed object) by bolting or in the case of HDPE, welding to the flotation tanks that are preferred to be formed of HDPE. 
     In a preferred embodiment, the pile guides  30  are inserted through a void in the catwalk flotation tanks  20 , 22 , 120 , 121 , 122 , 123 . Preferred constructs of pile guides for this application are shown in  FIG. 9  and  FIG. 10 . The pile guide is characterized by a generally vertical sleeve  50  from which a planar flange  52  extends. The catwalk flotation tanks are shown as having a void  64  formed into which the pile guides are poisoned and fastened, such as by welding. The flange limits the travel and assists in positioning the pile guide into the flotation tanks. 
     In a preferred embodiment, the pile guide is formed of HDPE, and formed by welding the sleeve to the flange. It has been found that welding the sleeve to the flange provides greater strength in forming the pile guide as a unitary member, although the pile guide may be formed as unitary member in some embodiments. 
     A void is formed in the flotation tanks  20 , 22  for the catwalk  4 , preferably near ends of the flotation tanks of the catwalk, as shown in  FIG. 1 . The pile guides  30  are inserted into the void in the flotation tanks of the catwalk in a manner that allows removal of the pile guides in case maintenance of the pile guides is required due to breakage or wear. The flange  52  limits the travel of the pile guide into the void of the catwalk flotation tanks, with a portion of the pile guides extending above the flotation tanks in a preferred embodiment. The sleeve  50  of the pile guides accepts a pile that is driven into the earth and which fixes the catwalk or other object to the earth. Through the use of connecting guide constructs  32 , the piles also position the boat lift, substantially negating horizontal movement of the boat lift but permitting free vertical movement of the boat lift. 
     It is preferred that the pile guides  30 , 32  and other components disclosed herein are formed of high density polyethylene (HDPE). High density polyethylene is extremely strong and can withstand substantial impact. Floating docks and pile guides used with them are subject to impact from boats and other objects. High density polyethylene is also abrasion resistant. Importantly, high density polyethylene exhibits a low coefficient friction; therefore, the sleeve of the device glides easily relative to the pile or similar securing object, whether the pile or object is constructed of wood, concrete or other materials. This feature is particularly important for applications wherein the associated floating dock is subject to frequent tidal changes or boat lift movement approaching two (2) meters or more. Further, because high density polyethylene is abrasion resistant, the sleeve is not subject to substantial wear over time as the pile moves within the opening or interior of the sleeve  50 . 
     High density polyethylene can also be formed to be resistant to ultraviolet (UV) light such as sunlight. The addition of carbon black to high density polyethylene provides UV stability. Further, UV absorbers and light stabilizers (HALS) either alone or in combination with each other, and/or in combination with carbon black, may be added to the high density polyethylene to improve UV resistance and reduce UV deterioration. 
     The planar flange  52  may be formed from a sheet of high-density polyethylene. High density polyethylene may be cut or formed to the shapes shown in the drawing figures to form the planar flange. A hole or void may be cut or formed in the high-density polyethylene. Extruded high-density polyethylene pipe may be cut to form the sleeve  50 . The sleeve may be welded in the hole or void of the planar flange to form the pile guides shown in the drawings. 
     While the sleeve  50  as shown in the drawings is cylindrical, it is not necessary that the sleeve have the circular cross section of a cylinder. The sleeve of the pile guide may be formed in other geometric shapes, such as rectangles or squares. The shape of the sleeve of the pile guide will typically depend upon the geometric shape of the cross section the pile on which it is mounted. 
     In another embodiment of the boat lift, elements of the boat lift and catwalk are formed as separate parts that permit the catwalk and boat lift to be assembled after the boat lift is transported to a destination for installation. Due to limitations of highway transportation, very wide and/or very long and previously assembled boat lifts and catwalks cannot be transported by truck. 
       FIG. 11  and  FIG. 12  demonstrate a catwalk and boat lift that may formed in parts for later assembly after transportation of the parts to a site. This construction is referred to herein as a modular boat lift and modular catwalk. The longitudinal flotation tanks  120 ,  121 ,  122 ,  123  are formed in two or more pieces for each side of the catwalk, and the flotation tanks of the boat lift are formed as separate tank constructs  106 ,  108  for the boat lift. 
     In one embodiment, the longitudinal members are joined by inserting a connecting sleeve  104  to each end of the longitudinal flotation tanks  120 ,  121 ,  122 ,  123 . As shown in  FIG. 11  and  FIG. 13 , a plate  110  is present at or near the end of the longitudinal tanks. This plate is attached, such as by welding, to form a water seal in the end of the tanks. The flotation tanks are inserted into the inside diameter of the connecting sleeve to join the flotation tanks in a construct to support the catwalk. In another embodiment the connecting sleeve is inserted into the inside diameter of the flotation tanks to join the flotation tanks together. The sleeve is fixed to the floatation tanks, such as by welding. When the flotation tanks are formed of the preferred material, which is HDPE, the sleeve may be welded to the ends of the flotation tanks. The connection of the flotation tanks as described may be done after transportation of the individual parts of the boat lift and/or catwalk construct with assembly performed onsite where the boat lift and/or catwalk are installed. 
     The boat lift flotation tank constructs  106 , 108  each join a transverse flotation tank  130 . In a preferred embodiment the transverse flotation tank comprises one or more pump receptacles  102 . The transverse flotation tank is in water (hydraulic) communication with the flotation tank constructs. That is, the pumps  140  that are positioned in the transverse flotation tank pump water from the flotation tank constructs to cause the boat lift to float to the desired level. The transverse flotation tank in the embodiment shown has two (2) receptacles on each side that receive two (2) corresponding ends of the flotation tank constructs in hydraulic communication that permits water flow from tank to tank.  FIG. 11 ,  FIG. 12 . 
     The pumps  140  pump water from the transverse flotation tank  130  and the flotation tank constructs  106 , 108 , which are in hydraulic communication with the transverse flotation tank. Water may be pumped out of the flotation tanks through lines such as lines  142 .  FIG. 18 . 
     The transverse floatation tank  130  of the boat lift and may be produced to multiple desired lengths and kept in stock with pumps assembled in the transverse flotation tank. The transverse flotation tank may also comprise the valves  146  that prevent or allow water to flow into the boat lift flotation tanks  106 , 108 , 130 . The transverse member or tank  126  of the catwalk may be produced in lengths that complement the transverse flotation tank  130 , so that boat lifts of varying widths may be efficiently produced. The boat lift and catwalk can be assembled on site due to the modular construction, so that the resulting width of the boat lift and cat walk is not limited by the width of trucks that transport the tanks. 
     The boat lift flotation tank constructs  106 , 108  may be constructed to be assembled on site. For example, the flotation tank constructs may be formed of HDPE and the center or transverse members  132  welded to the outer or longitudinal members  134 . It is preferred that the center members  132  and the outer members  134  are in hydraulic communication with each other and with the transverse flotation tank  130 . Transportation of the boat lift by truck is not limited due to width, and the boat lift according to the invention may be made to many widths and lengths as required by the user. 
     In a preferred embodiment, the boat lift flotation tank constructs  106 , 108  and the transverse flotation tank  130  are formed of cylindrical members, such as cylinders formed of HDPE. The ends of the cylinders may have a wall positioned therein to form a water seal. The wall may be circular member welded or otherwise attached in the ends of each of the circular openings of the flotation tanks. The voids  124  are exterior to the water seals so that the voids do not hydraulically communicate with the tanks and cause leakage. The cylinders may have baffles inserted therein that regulate movement of water within the flotation tanks as they are flooded or evacuated, since movement of water that is too rapid may impact the balance of the boat lift. The baffles may be a series of vertical members positioned within the flotation tanks. 
     Similarly, one or more additional flotation tank constructs like  106 , 108  may be joined to one or more additional transverse flotation tanks  130  to obtain the overall required boat lift length. The width may be changed according to the width of the transverse flotation tanks. 
     The teachings of pile guides and connecting guide constructs for the boat lift and catwalk as described above and shown  FIG. 1 ,  FIG. 2  and  FIG. 5  may also be applied to the modular boat lift and catwalk depicted in  FIG. 11  and  FIG. 12 . 
       FIG. 14  shows another embodiment of a connecting guide construct. In this embodiment, the flotation tanks of the boat lift  106 , 108  have voids  124  formed near an end thereof that is adjacent to the catwalk for receiving the connecting guide construct.  FIG. 12 ;  FIG. 13 . The voids as shown are vertical voids. The voids are outside of the water receiving portion of the flotation tank constructs  106 , 108 . The voids are exterior to water seals of the flotation tank constructs. 
     A stanchion  60 , which may be formed of aluminum or stainless steel, is inserted into the void  124  of the boat lift flotation tanks  106 , 108 , as demonstrated by  FIG. 14 , and fixed to the flotation tanks in one embodiment. An upper guide  56  as described herein accepts the stanchion therein and permits vertical travel of the boat lift relative to the catwalk or other fixed object but negates or minimizes horizontal movement of the boat lift. The boat lift can move up and down relative to the upper guide that is mounted to a floating catwalk, or to a fixed object, such as a bulkhead or pile or seawall.  FIG. 14  shows the upper guide  56  mounted to a flotation tank  106  or  108  of a catwalk, with a stanchion  60  inserted and affixed to the boat lift. As with other guides disclosed herein, the upper guide is preferred to be formed of HDPE. 
       FIG. 16  demonstrates a variation of the connecting guide construct of  FIG. 14 , wherein the stanchion  60  is driven as a pile and fixed into the earth. In this embodiment, the flotation tank  106  of the boat lift is not fixed to the stanchion, but vertical movement is permitted relative to the stanchion, as the guide  56  is also permitted vertical movement. As described above, the size of the stanchion relative to the sleeve in the upper guide  56  and the opening in the flotation tank of the boat lift permit vertical movement of the boat lift and the catwalk, while negating horizontal movement from wave action, wind or other forces. It is preferred that at least two connecting guide constructs are associated with each flotation tank  106 , 108  of the boat lift. 
     The preferred catwalks are supported by longitudinal flotation tanks  120 , 121 , 122 , 123 . The longitudinal flotation tanks  121 , 123  may be connected by a transverse tank  126 . The flotation tanks for the catwalk  120 , 121 , 122 , 123  are water tight but provide a water inlet  136  and/or outlet for filling the tanks or withdrawing water from the tanks. During construction and/or positioning of the boat lift, catwalks are positioned alongside the boat lift construct (which comprises  106 ,  108  and  130  in the embodiment shown in the drawings). The flotation tanks are filled with water to a level of the flotation tanks that holds the catwalk in the desired floating position relative to the boat lift construct, so that the top decking  26  of the catwalks, which may be covered similarly or identically to the boat lift frame, are at the desired position relative to the decking of the boat lift when the boat lift is raised to its maximum vertical position. Once the water level in the flotation tanks of the catwalks is sufficient to hold the catwalk in the desired position, it should not be necessary to frequently adjust the flotation tanks&#39; water level. In a preferred embodiment, when the boat lift has lifted the boat to the full upper position, so that the hull of the boat is out of the water, the decking of the boat lift, where it joins the catwalk, and the decking of the catwalk will be relatively even each with the other and above the water line. Occupants of the boat may ingress and egress the boat by traversing the catwalk, without the decking of any of these elements presenting a tripping hazard. 
     The force of gravity holds openings  144  that communicate with the transverse flotation tank  130  and the boat lift flotation tanks  106 ,  108  below the water line. Water enters the flotation tanks when valves  146  that communicate with the openings  144  in the flotation tanks of the boat lift are open. The valves may be controlled by one or more actuators. The actuator(s) are preferred to be pneumatically controlled with an air compressor providing air pressure for actuating the valve by means of the actuator. Operation of the valves, and therefore filling of the flotation tanks, may further be controlled by a timer, or by a water level sensor. When the flotation tanks are filled with water, the boat lift construct, and any associated boat or vessel, is submerged to a depth that allows the boat to float over the boat lift. The boat may be driven on or off of the boat lift and any decking of the boat lift. In one embodiment, an inlet, valve and actuator are positioned at opposite ends of the transverse flotation tank  130  so that water enters the boat lift in a balanced manner relative to flotation tank constructs  106 , 108  that receive water from the transverse flotation tank. 
     Air vents  148  communicate with air vent lines. Each air vent has a valve associated with it, and the valve may also have an actuator that operates the valve to a fully opened or fully closed or partially open or partially closed position. The actuator may be pneumatically operated and controlled. By controlling the rate of flow of air out of the air vent, the rate of submersion of the boat lift can be controlled as the submerged openings to the flotation tanks are opened to flood the flotation tanks. In a preferred embodiment, the openings into the flotation tank are of sufficient size to allow the boat lift to travel from fully raised to fully submerged in less than one minute. However, by limiting the degree of opening of the air vents, and thereby limiting the rate of flow of air out of the flotation tanks, the rate of water entering the flotation tanks through the openings, and therefore the rate of submersion, may also be controlled, and accelerated or reduced as preferred. 
     The boat lift is raised by evacuating water from the flotation tanks  106 , 108  and replacing the water with air. In a preferred embodiment, evacuation of the water is performed by pumping the water from the flotation tanks, using one or more water pumps  140 . To accomplish water evacuation from the flotation tanks, the valves that associated with water inlets to the floatation tanks are closed, such as by the actuators. Water is pumped from the flotation tanks through water pump out lines  142  that communicate with each of the flotation tanks. The air vents  148  are opened to replace water that is being pumped from the flotation tanks with air. 
     While raising the boat lift during the water evacuation process, the air vents  148  remain open so that air replaces water that is evacuated. The water flow rate may be regulated by partially closing valves associated with the air vents. However, in most cases, the air vents will remain fully open, since rapid evacuation of water, and the associated lifting action, is desired to occur relatively rapidly. Sensors may be provided so that when there is no water flow to the water pumps, or an individual pump of a plurality of water pumps, operation of the pump or pumps is terminated. 
     In a preferred embodiment, a central control panel for operating the boat lift is provided. The control panel may have a simple command selector to raise or lower the boat lift. Other controls may control the rate of flow of water and/or air in and out of the flotation tanks by operation of the valves as discussed herein. In other embodiments, manual controls for actuating the pumps or terminating operations of the pumps may be provided. 
     In a preferred embodiment, submersible pumps  140  are positioned in the transverse flotation tank  130  to communicate with the flotation tanks  106 , 108 . Pumps  140  may be inserted and retained in a pump receptacle  102  that houses each pump.  FIG. 18 . The submersible pumps are preferably positioned so as to balance the flotation tank construct, and also to remove water relatively uniformly from the flotation tank construct, thereby maintaining balance during the process of pumping water from the flotation tank construct. The submersible pumps may be submersible pumps such as those manufactured by Gorman-Rupp. 
     In one embodiment, the water receiving inlet or inlets  144  are positioned near the center of the flotation tank construct. The water receiving inlets are preferred to communicate with the flotation tanks  106 , 108 . By positioning the water receiving inlets in this embodiment near the center of the flotation tank construct, such as near the generally centralized transverse flotation tank  130 , water enters the flotation tank construct near the center thereof, balancing the boat lift construct as it fills with water. 
     Opening and closing of the water receiving inlets  144  that communicate with the flotation tanks  106 , 108  is preferred to be formed by a valve  146  for each inlet. The valves may be remotely controlled and may be electrically, hydraulically or pneumatically actuated. The valves and electric actuator may be those such as those manufactured by ROTORK. 
     Flotation of the boat lift of the embodiment of the invention shown in  FIGS. 1-4  operates in the same fashion as the embodiment of  FIGS. 11-13 . Water is pumped from the flotation tanks  6 , 8  by pumps that may be located in one or more of housings  62 . Regulated openings or inlets allow water to enter the tanks, with vents provided to equalize air pressure as described above. 
     In the preferred embodiment, flotation tanks for the boat lift and the catwalks are constructed of high density polyethylene (HDPE) and may be formed of HDPE pipe. HDPE components may be joined by welding or fusing methods for HDPE. 
     Optionally, or additionally, water receiving inlets may be positioned near an end of the flotation tank construct. Positioning water receiving inlets at the end of these flotation tanks may be preferred where water is shallow and the bottom of the body of the water slopes upwardly from the rear of the boat lift toward the front of the boat lift. The water receiving inlets may have electrically actuated valves. 
     In use, the boat lift flotation tank construct (includes  106 , 108 , 130 ) is partially or completely filled with water to increase specific gravity so that the boat lift is below the water line. A boat may be driven or otherwise positioned onto the deck of the boat lift. After the boat is secured in position on the boat lift the water receiving inlets  144  are closed, such as by actuation of the valves  146 . The submersible pumps are actuated, and water is pumped from the flotation tank construct. Air enters the flotation tank construct through the air vents to replace the water. The air vents are preferred to be above the water line when the boat lift is submerged. 
     As water is expelled from the boat lift flotation tank construct and air enters the flotation tank construct, the boat lift construct floats. The submersible pumps  140  are actuated until the boat lift reaches the desired level, which is typically after the bottom of the boat is completely above the water line, and the boat is at a level such that entering and exiting the boat by means of the catwalks is convenient. 
     The boat may subsequently be lowered for use by opening the valves  146  to the water receiving inlets  144  and allowing water to enter the flotation tank construct. The boat lift is submersed sufficiently to allow a boat positioned on the boat lift to float above the boat lift and exit the boat lift. In one embodiment, submersible pumps are used that reverse the flow of water so as to pump water into the flotation tank construct to rapidly flood the flotation tank construct.