Patent Publication Number: US-7216602-B2

Title: Seasonal, multi-use, multi-level structure transportable both by ground and water for use in a body of water

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part of application Ser. No. 11/150,048 filed Jun. 10, 2005. 

   TECHNICAL FIELD 
   This invention relates to a structure used in a body of water such as a lake. More particularly, this invention relates to a structure that is installed in and removed from the body of water in a seasonal fashion, i.e. installed in and used in the body of water during the spring and summer and removed from the body of water and stored on land during the fall and winter. 
   BACKGROUND OF THE INVENTION 
   The recreational boating industry involves the use of a watercraft, such as a jet ski or boat, on a body of water. Many different structures have been developed to facilitate the use of and enjoyment of such watercraft. One such structure is a boat lift and an adjoining dock. The boat lift includes a movable cradle that may be raised and lowered to lift the watercraft into a storage position out of contact with the water or drop the watercraft into a use position in which the watercraft floats on the water. The cradle of the boat lift may be powered either manually or by some type of motor. 
   In northern locales where the body of water freezes during the winter, boat lifts and docks are typically used seasonally. Usually, a boat lift/dock is installed in the body of water in the spring and used throughout the summer. Then, prior to the onset of cold weather in the late fall, the boat lift/dock is removed from the body of water and stored on land during the winter. This prevents the boat lift/dock from being damaged by ice formed in the body of water during the winter. 
   Installing and removing a boat lift or dock from a body of water is often a very strenuous and difficult operation. While docks come in sections to allow a dock to be disassembled and removed piece by piece, the same is not true of a boat lift. A boat lift is typically provided as one assembled, unitary structure. Thus, a boat lift often has to be manhandled into and out of the water using brute force. This usually requires a number of strong, fit people who often must be specifically hired for the job. 
   The boat lift installation and removal problem is made even worse if the shorefront property over which the boat lift must travel to the body of water is steep, rocky or uneven or the beach is narrow or non-existent. Most prime shorefront property having relatively wide, smooth and flat beaches has already been developed. Thus, owners of more newly developed shorefront property may have an impossible time of installing and removing a boat lift or dock from the water. It often can&#39;t be done if there is a large drop or highly uneven terrain between where the boat lift or dock must be stored out of season and where the boat lift or dock is to be installed and used during the season. 
   In addition, some boat lifts are part of larger, multi-level structures that include an entertainment area, such as a patio or sundeck, in a second level located above the boat lift. Obviously, such multi-level structures are considerably heavier and more complex than a boat lift or dock alone. To date, such multi-level structures are only used in climates where they can be assembled in place in the body of water and left year round. Thus, the use of such multi-use, multi-level structures has been restricted to bodies of water that remain open and ice free year round. 
   There is a need in this art for a simpler, easier way of installing and removing structures such as boat lifts and docks from a body of water. In addition, there is a need to find some way of being able to install and remove a multi-use, multi-level structure from a body of water without having to assemble and disassemble such structure in place. This invention addresses these and other needs. 
   SUMMARY OF THE INVENTION 
   One aspect of this invention relates to a structure that may be used in a body of water. The structure comprises a multi-level structure having a lower level and an upper level. The lower level is tall enough to accommodate at least a watercraft therein. The upper level includes a weight bearing deck that is strong enough to support a plurality of people and furniture in a first entertainment area on the structure. At least a pair of wheels can be at least temporarily attached to the lower level of the structure to allow the structure to be transported by ground to and from the body of water and to be rolled into and out of the body of water. A buoyancy system is carried on the structure to selectively provide the structure with a buoyant state in which the structure floats on the body of water and a non-buoyant state in which the structure does not float on the body of water. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention will be described more completely in the following Detailed Description, when taken in conjunction with the following drawings, in which like reference numerals refer to like elements throughout. 
       FIG. 1  is a perspective view of a first embodiment of a structure according to this invention, particularly illustrating a multi-level structure providing a boat lift on the lower level and an entertainment area on the upper level, the structure being shown disposed on the ground for ground transport; 
       FIG. 2  is a side elevational view of the structure shown in  FIG. 1 ; 
       FIG. 3  is a rear elevational view of the structure shown in  FIG. 1 ; 
       FIG. 4  is an enlarged side elevational view, partly shown in cross-section, of that portion of the ballast system shown in the circled portion of  FIG. 2 , particularly illustrating a pair of interconnected ballast tanks and a bilge pump inside one of the tanks for pumping water out of the interconnected ballast tanks; 
       FIG. 5  is a side elevational view of the structure shown in  FIG. 1 , particularly illustrating the structure floating on water for water transport, the ballast system providing a desired amount of buoyancy for such water transport; 
       FIG. 6  is a side elevational view similar to  FIG. 5 , but illustrating the structure having been sunk into the bottom of a body of water adjacent a shoreline, the ballast system having been filled with water to provide ballast for the structure; 
       FIGS. 7 and 8  are diagrammatic rear elevational views of the structure of  FIG. 1 , particularly illustrating placement of the ballast tanks inboard on the structure with the ballast tanks being shaped to provide clearance to the boat lift; 
       FIG. 9  is a side elevational view of another structure according to this invention, particularly illustrating a multi-level structure providing a deck on the lower level and an entertainment area on the upper level, the structure being shown disposed on the ground for ground transport; 
       FIG. 10  is a diagrammatic bottom plan view of the structure of  FIG. 9 , particularly illustrating a single array of ballast tanks; 
       FIG. 11  is a side elevational view of the structure of  FIG. 1 , particularly illustrating an alternative in which the ballast tanks are carried on each side of the structure in an array comprising two horizontal rows of tanks that are vertically stacked on top of each other; 
       FIGS. 12 and 13  are diagrammatic side elevational views of an array of ballast tanks used with the structure of  FIG. 1 , particularly illustrating two alternatives in which the tanks within the array are shaped to have an overall front to back hull or torpedo like configuration, respectively, to aid in towing the structure through the water; 
       FIG. 14  is a diagrammatic side elevational view of a single large ballast tank used with the structure of  FIG. 1 , particularly illustrating a plurality of partial height baffles within the ballast tank; 
       FIG. 15  is a partial side elevational view of one of the telescopic legs of the structure shown in  FIG. 1 , illustrating an alternative in which the ballast tanks are carried on the telescopic legs of the structure rather than on the sides of the structure; 
       FIG. 16  is a cross-sectional view of the ballast tank alternative shown in  FIG. 15  taken along lines  16 — 16  in  FIG. 15 ; and 
       FIG. 17  is a side elevational view of another structure according to this invention, particularly illustrating an alternative buoyancy system comprising an inflatable bag or bladder system for selectively providing buoyancy to a multi-level structure, the structure being shown disposed on the ground for ground transport. 
   

   DETAILED DESCRIPTION 
   One embodiment of a structure according to this invention is shown in  FIG. 1  generally as  2 . Structure  2  preferably has two stories or levels comprising a lower level  4  and an upper level  6 . Lower level  4  preferably contains a vertically movable boat lift  8  for holding a watercraft such as a boat  10  or jet ski. Lower level  4  is open along a rear end to allow boat  10  to be driven from a body of water into lower level  4  of structure  2  and positioned atop a cradle  12  of boat lift  8 . 
   Upper level  6  preferably provides an entertainment area for people and their guests. Structure  2  includes a stairway  14  at the front end for allowing people to ascend to the entertainment area provided by upper level  6  of structure  2 . Stairway  14  can extend down only a portion of the height of lower level  4  as shown in  FIG. 2 . This allows the bottom of stairway  14  to mate with a landing or dock  18  extending from the shoreline at an elevation above the base  20  of lower level  4  as shown in  FIG. 6 . 
   Lower level  4  has a substantially rectangular base  20  formed as an open framework by a plurality of longitudinal and transverse beams  22  that are rigidly connected together by being welded or bolted together. Base  20  comprises an open framework. By this, it is meant that base  20  is open to the passage of water and lacks a hull or solid bottom that would permit direct flotation of structure  2 . Thus, without the ballast system  38  of this invention whose operation will be described hereafter, structure  2  would otherwise sink when placed into a body of water. 
   Lower level  4  of structure  2  is formed by a plurality of uprights  24  that extend vertically upwardly from base  20  along the peripheral sides of base  20 . Some of the uprights  24   a  extend full height to upper level  6  of structure  2 . Other uprights  24   b  extend only a few feet up from base  20 . Side rails  26  can extend between uprights  24   a  and over the tops of partial height uprights  24   b  to form partial height, open side walls along three sides of lower level  4 . No partial height side wall is present at the open rear end of lower level  4  to allow a boat to be driven into lower level  4  and to have access to boat lift  8 . 
   A standard boat lift  8  is housed in lower level  4  of structure  2 . Boat lift  8  comprises a V-shaped cradle  12  having a plurality of rollers or pads  27  for engaging against the hull of a boat  10 . See  FIGS. 11 and 12 . Cradle  12  vertically slides up and down on some of the full height uprights  24   a  of structure  2 . A lifting apparatus  28 , such as an electrically powered or hand powered winch, lifts and lowers cradle  12  from a lowered watercraft receiving position to a raised watercraft storage position shown in  FIG. 6 . Such boat lifts  8  are well known in the boating industry and need not further be described herein. 
   Upper level  6  of structure  2  comprises a weight bearing floor or deck  30  supported by the upper ends of the full height uprights  24   a . A safety railing  32  is preferably provided around the periphery of deck  30  to prevent people and objects from falling off deck  30 . Stairway  14  provides access to deck  30  and may join deck  30  through an opening (not shown) in deck  30 . Obviously, people can ascend stairway  14  to be able to pass through such opening and gain access to deck  30 . Alternatively, stairway  14  could be placed along one side of deck  30  with access to deck  30  being provided through an opening in safety railing  32 . 
   Deck  30  which forms upper level  6  of structure  2  provides an entertainment area in which people, such as the owners of structure  2  and their guests, may gather for entertainment. Deck  30  is sufficiently strong to bear the weight of various people standing thereon along with pieces of furniture (e.g. patio chairs, tables, etc.) or entertainment equipment (e.g. barbecues, stereos, etc.) carried thereon. Play equipment suited for water recreation (e.g. diving boards, water slides, ropes, etc.) can be attached to the sides of deck  30  and/or extended out from deck  30 . In addition, all or part of deck  30  could be covered with a removable roof or canopy (not shown) to help protect the people using deck  30  from the elements. Thus, upper level  6  of structure  2  provides a conveniently located entertainment area that complements the outdoor, water based environment in which structure  2  is used. 
   Base  20  includes a tow hitch and a pair of ground engaging wheels  36  to allow structure  2  to be towed over the ground, such as over a road or the like. The tow hitch comprises a tow tongue  34  that extends from the front end of base  20  of lower level  4  of structure  2 . Tow tongue  34  is connected in any suitable manner, i.e. by a ball and socket hitch, to a tow vehicle (not shown), such as a pickup truck, SUV, or the like. 
   Wheels  36  are rotatably carried on the underside of base  20  of lower level  4  by any suitable axle and bearing structure. Wheels  36  and their associated axles and bearings are all rated for highway use. Wheels  36  can be permanently mounted on base  20 . However, wheels  36  are preferably of a removable type to allow wheels  36  to be selectively installed on and removed from base  20 . This removal is indicated in  FIG. 6  by the phantom line illustration of wheels  36 . 
   Preferably, wheels  36  are the usual pneumatic type rubber wheels that are typically used on cars and on boat trailers with wheels  36  being inflated by air. This allows structure  2  to be towed at reasonably high towing speeds, such as 25 to 35 mph, that are substantially above walking speeds. Thus, if structure  2  is towed at such speeds, then structure  2  will not impede the flow of traffic at least on most non-freeway type roadways. In addition, such wheels  36  allow structure  2  to be towed over long distances if need be. 
   Structure  2  preferably includes a ballast system  38  that provides positive buoyancy for structure  2  when ballast system  38  is completely or even partially empty of water, but that provides sufficient weight to structure  2  to substantially anchor structure  2  in place in a body of water when ballast system  38  is full of water. In addition, ballast system  38  can be partially filled with water to any desired degree to provide a desired mix of buoyancy and weight such that structure  2  can be stably transported across a body of water. For example, given the relatively top heavy nature of structure  2 , ballast system  38  might always be at least partially filled with water to provide enough weight to prevent structure  2  from capsizing or being blown over while structure  2  is floating or being transported on the water. The amount of ballast weight provided by ballast system  38  can be easily adjusted by adding water to ballast system  38  to take into account any environmental conditions that might be present, such as high winds on the body of water. 
   Ballast system  38  comprises a plurality of substantially rigid, hollow ballast tanks  40 , made from either metal or a strong, durable plastic material, secured as low as possible to lower level  4  of structure  2 . As shown in  FIGS. 1–5 , ballast system  38  can comprise a horizontal row of five tanks  40  along one side of lower level  4  of structure  2 . A similar row of five tanks  40  is disposed along the opposite side of lower level  4  of structure  2 . Each row of tanks  40  is secured to lower level  4  of structure  2  substantially adjacent base  20  of lower level  4 . 
   Each row of tanks  40  is preferably outboard of each side of lower level  4  of structure  2  to not intrude into the space occupied by boat lift  8 . Each individual tank  40  is rectangular but could have other shapes. Tanks  40  within each row are oriented generally vertically to minimize the width of structure  2  when tanks  40  are in place thereon. See  FIGS. 1 and 3  which illustrate the outboard, vertical orientation of tanks  40 . Tanks  40  can be secured to structure  2  in any suitable manner, e.g. by strapping tanks  40  to the sides of structure  2 , etc. 
   Referring now to  FIG. 4 , each individual tank  40  of ballast system  38  includes an air vent comprising an upwardly extending snorkel tube  42 . The lower end of tube  42  enters into the top of tank  40 . The upper end of tube  42  extends upwardly along the side of lower level  4  and is secured to one of the uprights  24 . Tube  42  is long enough so that the upper end of tube  42  remains above the water line even when ballast system  38  is completely filled with water and structure  2  has sunk to its maximum depth in a body of water. 
   Referring further to  FIG. 4 , one ballast tank  40  in each row has a hand operated fill valve  44  in one end thereof. In addition, all tanks  40  in each row are interconnected or plumbed together by a plurality of hydraulic couplings  46  with one coupling  46  extending between and interconnecting each two adjacent tanks  40 . Thus, from a hydraulic standpoint, the individual tanks  40  in each row of tanks act collectively act as a single long tank and, in fact, could be replaced by such a single tank. However, it is more practical and economical to join a plurality of smaller tanks  40  together along each side of structure  2  than to use one long tank. 
   One tank  40  in each row of tanks has an electrically operated bilge pump  48  installed in the bottom of tank  40  as shown in  FIG. 4 . Bilge pump  48  is coupled to a drain line  50  that is routed out through the side of tank  40  adjacent the top of tank  40 . Drain line  50  is sealed where it passes through the wall of tank  40  to prevent water from leaking into tank  40  around drain line  50 . The only path for water to enter ballast system  38  is through the manually operated fill valve(s)  44 . 
   Bilge pump  48  is powered by an electrical supply line  49  that brings electrical power to bilge pump  48  from a source of electrical power. Preferably, this electrical power source is carried on structure  2  and comprises a simple battery placed somewhere on structure  2 , i.e. on deck  30  of upper level  6 . This battery could be rechargeable using solar power. Alternatively, the source of electrical power could be external to structure  2 , such as a battery on a boat or a land based electrical power line extending to structure  2 . 
   To fill each row of ballast tanks, the user need only manually open fill valve  44  to allow water to flow into tanks  40  on that side of structure  2 . Desirably, fill valves  44  on both rows of ballast tanks are opened at the same time to allow the dual rows of ballast tanks to fill evenly. As water enters each row of ballast tanks, the water will fill all tanks  40  in each row in an even progressive manner due to the interconnecting couplings  46  between tanks  40 . The air vents  42  provided in the tops of tanks  40  allow air to escape from tanks  40  during the tank filling process. When tanks  40  have been filled to a desired amount, the user need only close fill valves  44  by turning the handle on each fill valve  44  to a closed position. 
   Conversely, to empty each row of ballast tanks, the user need only energize bilge pump  48  for that row of tanks using any suitable switch or control (not shown) in the electrical supply to bilge pump  48 . Bilge pumps  48  in the dual rows of ballast tanks desirably have identical pumping rates. In addition, bilge pumps  48  are preferably actuated at the same time so that water is pumped out of each row of ballast tanks at the same rate and at the same time. To ensure bilge pumps  48  are always activated at the same time, a single control or switch could be wired into the electrical supply circuits to both pumps so that they both operate together whenever the control or switch is selectively closed by the user. 
   Preferably, each bilge pump  48  will pump water out of whatever tank  40  in which it is contained at a rate that is less than the rate at which water can flow through the interconnecting couplings  46 . Thus, water within the row of tanks will lower in a steady, even fashion, i.e. tank  40  containing bilge pump  48  is not pumped dry ahead of the other tanks in the same row. This is done by oversizing the hydraulic couplings  46  relative to the size of drain line  50  and the pumping rate of pump  48 . 
   Structure  2  provided by this invention can be easily installed in a body of water or removed from a body of water to allow seasonal use even though structure  2  is a multi-level structure. For example, assume that it is spring and structure  2  has been stored out of the water on land as is necessary in northern climates where the body of water in which structure  2  is normally used freezes. In this condition, wheels  36  are in place on base  20 . At some point during the spring, the body of water will thaw and the user of structure  2  will decide to put structure  2  into the water. 
   To put structure  2  in the water, the user need only connect a tow vehicle to tow tongue  34 . The vehicle is then used to tow structure  2  to the body of water in which it is be installed. The use of conventional pneumatic, rubber wheels  36  and a conventional hitch allows structure  2  to be towed over at roadway at normal non-freeway type speeds. Once the user reaches the body of water, the user can then back structure  2  into the water. This can be done either proximate to where structure  2  is to be installed in the body of water, i.e. on the user&#39;s own property, or remotely from where structure  2  is to be installed, i.e. at a boat ramp that may be remote from the user&#39;s own property such as a boat ramp located on the other side of the lake. 
   Of course, when structure  2  is first backed into the water during the spring, tanks  40  in ballast system  38  will be largely or completely dry since structure  2  has been out of the water over the winter. Thus, structure  2  upon entering the water will be naturally buoyant without having to do anything since the dry tanks  40  will provide their maximum buoyancy. If structure  2  is situated at its final desired location immediately upon entry into the water, fill valves  44  may be used to completely flood tanks  40 . However, some amount of final positioning or even extended transport over the body of water may often be required. Thus, the user will preferably open fill valves  44  on ballast system  38  and partially flood tanks  40  on either side of structure  2  until some water enters tanks  40  and provides some stability to structure  2  but structure  2  as a whole is still buoyant. 
   With a partially flooded ballast system  38 , structure  2  will still float on the water but will have sufficient stability to allow structure  2  to be accurately positioned. For example, the user can then push or pull on structure  2  to float it however many feet or yards is required until structure  2  is positioned exactly where it is to be installed. If structure  2  has been put into the body of water at a remotely located boat ramp, then structure  2  may have to be towed across the body of water to reach its destination and then positioned by hand. In either case, the use of partially flooded ballast tanks  40  allows such water transport to occur, either over short or long distances.  FIG. 5  illustrates structure  2  in this condition floating on a body of water. 
   Once structure  2  has been exactly positioned where the user likes, then fill valves  44  can be opened again and ballast system  38  completely flooded to provide the maximum ballast weight to structure  2 . This will sink structure  2  in the body of water to the maximum possible depth as shown in  FIG. 6 . In this condition, at least some of lower level  4  of structure  2  up as far as the top of tanks  40  will be submerged Ideally, however, legs  52  (described hereafter) will be adjusted so that the tops of tanks  40  are somewhat below the water surface when structure  2  is resting on the bottom to prevent tanks  40  from collecting waterborne debris. This is shown in  FIG. 6 . 
   The amount of weight added by ballast system  38  is significant and is preferably large enough so that structure  2  becomes substantially immovable in the water. For example, with ten ballast tanks as shown on structure  2  of  FIG. 1  and with each ballast tank holding 60 gallons of water, the amount of weight added to structure  2  when ballast system  38  is completely filled with water is about 5000 lbs. (600 gallons*8.34 lbs. per gallon). The gross weight of structure  2  shown in  FIG. 1  without any water in tanks  40  is only 2450 lbs. Thus, ballast system  38  when fully filled approximately triples the dry gross weight of structure  2  to help anchor structure  2  in place. Obviously, ballast system  38  when partially filled will help provide such additional weight to structure  2  needed to provide dynamic stability to structure  2  when structure  2  is being transported or floated on the surface of the body of water. If structure  2  were built with only a single lower level comprising a boat lift  8  covered by a canopy, the additional weight provided by ballast system  38  would help keep structure  2  and boat lift  8  in place even in strong winds and with boat lift  8  empty, thus solving another problem faced by conventional non-ballasted boat lifts. 
   Hydraulic couplings  46  between tanks  40  in each row of tanks could have individual shut off valves (not shown) therein to allow tanks  40  to be trimmed between the front and rear ends of structure  2 . Suppose a relatively heavy hot tub or spa is carried on one end of deck  30 . Then, when tanks  40  are filled with water, the tanks  40  beneath the end carrying such hot tub or spa could be individually shut off before all the tanks  40  in the row are completely filled with water. This would selectively provide the shut off tanks  40  with less water and more air to make such tanks  40  at least partially buoyant to better support the heavier loads on that end of structure  2 . Side to side trimming of structure  2  can be done by selectively filling the ballast tanks  40  on one side of structure  2  to a greater or lesser degree than the ballast tanks  40  on the opposite side of structure  2 . 
   At least some of the uprights  24  of structure  2  have telescopic legs  52  extending out of the bottom thereof. Such legs  52  can be selectively extended from the bottom of such uprights  24  to engage against the bottom of the body of water at the location where structure  2  is being installed. Any suitable means can be provided for locking legs  52  in their extended lengths, e.g. locking pins (not shown) selectively insertable through one of a plurality of locking holes  54  provided along the length of legs  52 . See  FIG. 15 . Such legs  52  further secure and support structure  2  in place as shown in  FIG. 6 . 
   Preferably, the lower ends of legs  52  terminate in feet  56  for engaging against the bottom of the body of water when legs  52  are extended. It is preferred that legs  52  be extended and feet  56  placed against the bottom of the body of water when ballast system  38  is partially flooded but not completely flooded. Then, when ballast system  38  is completely flooded, the additional weight will help sink feet  56  on legs  52  into the bottom of the body of water. This will enhance the ability of legs  52  to help secure structure  2  in place. 
   In shallow locations where the depth of the bottom is relatively shallow and constant, wheels  36  may be removed from structure  2  as indicated by the use of dotted lines in  FIG. 6 . Such wheels may also be removed even if the bottom depth would be sufficient to accommodate them simply to prevent wheels  36  from being constantly submerged in water during the length of time that structure  2  is installed in the water and is in use. This will help prevent wheels  36  and, more importantly, the wheel bearings from deteriorating due to too much water exposure. The bearings will typically be protected by a seal on the wheel axle which seal is often called a Bearing Buddy, but such seals are not guaranteed for prolonged water submersion. 
   As shown in  FIG. 6 , once structure  2  is in place in the water, a landing or dock  18  may be extended from the shoreline to structure  2  to facilitate access to structure  2 . Desirably, dock  18  will be at the level of the bottom of stairway  14  so that a person walking on dock  18  may simply ascend stairway  14  to access the entertainment area provided by upper level  6 . Dock  18  may be installed so that it is simply adjacent to structure  2  but not connected thereto. Alternatively, structure  2  may be provided with various connectors or sockets (not shown) so that dock  18  may be physically coupled or attached to various portions of structure  2 . 
   Structure  2  of this invention for the first time allows a user to transport a multi-level structure over a road via ground engaging wheels  36  on structure  2  and to install and remove such a structure from a body of water for seasonal use. In addition, ballast system  38  allows this to be done with a minimum of manpower and effort. Ballast system  38  when partially flooded allows the user to achieve a desired balance between buoyancy and weight so that structure  2  can be floated on the surface of the water even over long distances. Ballast system  38  when completely flooded provides sufficient weight to substantially anchor structure  2  in place in the body of water. 
   Moreover, ballast system  38  of this invention is particularly safe, durable and easy to use. Tanks  40  will normally be dry and buoyant when structure  2  is being placed into the water, during the spring or early summer. Thus, the user need do nothing to make structure  2  buoyant and must only back structure  2  into the water where it will float. The user can then adjust the buoyancy to partially flood tanks  40  to make structure  2  more stable to allow structure  2  to be more safely transported across the water. With structure  2  in its intended final destination, the user can then completely flood tanks  40  to sink structure  2  down into the water to its desired maximum depth, after having first extended legs  52  to engage the bottom of the body of water. If necessary, wheels  36  can be removed at any point in this process after structure  2  has been backed into the water. All of this can be done without needing any power or compressed air since tanks  40  are flooded merely by opening the manually openable and closable fill valves  44 . 
   Once the season ends and structure  2  is to be removed from the water, wheels  36  need to be reinstalled if they have been removed and telescopic legs  52  raised. Ballast system  38  needs to be emptied of water. This is done merely by switching on the electrically operated bilge pumps  48  in each row of ballast tanks  40 . Such bilge pumps  48  can be used to partially or fully empty tanks  40  of added water. Structure  2  can then be pulled out of the water and towed to a desired storage location using tow tongue  34  and ground engaging wheels  36 . 
   When structure  2  is being pulled over public roads and the like, the height and width of structure  2  must conform to any applicable governmental limits. Accordingly, upper level  6  of structure  2  can be no higher than the prescribed maximum height permitted by law. In this respect, it may be necessary to dismount safety railing  32  provided on deck  30  as shown in  FIG. 5  or alternatively to pivotally mount such railing to deck  30  to allow railing  32  to be folded flat against deck  30  or to hang down from the sides of deck  30 . Obviously, any removable roof or canopy provided on upper level  6  would also have to be removed from deck  30 . 
   The width of structure  2  can be minimized by judicious placement of tanks  40 . As shown in  FIGS. 1–6 , vertical placement of tanks  40  along the sides of structure  2  (i.e. the long axis of tanks  40  being parallel to the sides of structure  2 ) is one way to do this. Another way to do this is to place such tanks largely or completely inboard of the sides of structure  2 . 
   When a boat lift  8  is housed in lower level  4  of structure  2 , tanks  40  when placed inboard can also be shaped to nestle beneath the V-shaped cradle  12  of boat lift  8 . For example, tanks  40  can have either a slanted or L-shaped cross-section as shown in  FIGS. 7 and 8 . This minimizes interference with boat lift  8  while permitting inboard mounting of tanks  40 . Obviously, even rectangular ballast tanks  40  extending transversely from one side of lower level  4  to the other could be used beneath boat lift  8  if so desired. However, this would entail an increase in the vertical height of structure  2  to provide sufficient clearance between the downwardly pointing midpoint of the V-shaped cradle  12  and such a tank  40 . 
   Another embodiment of structure  2  is one where lower level  4  is not used to house a boat lift, but is instead used to provide a second or additional entertainment area. This is shown in  FIG. 9 . A solid weight bearing floor or deck  60  is installed on lower level  4  of structure  2  in place of boat lift  8 . Such a lower deck  60  can be placed at the level of the bottom of stairway  14  and can itself be extended out from one end of structure  2  to form the landing for stairway  14 . Lower deck  60  on lower level  4  can be braced or held above base  20  by a plurality of vertical spacers  62  or the like extending upwardly from base  20  to the underside of lower deck  60 . 
   In this embodiment of structure  2  as shown in  FIGS. 9 and 10 , a plurality of ballast tanks  40  can be arranged in a single array beneath base  20  rather than being arranged in separate arrays along the sides of structure  2 . All of tanks  40  in this single array can be interconnected together by hydraulic couplings  46 . A bilge pump and fill valve are installed in one or more of the tanks  40  in the array. The single array of ballast tanks  40  is filled and operated in much the same way as when tanks  40  were disposed in multiple arrays, except that only a single pump and fill valve are used. Preferably, each ballast tank  40  still has its own individual air vent (not shown in  FIGS. 9 and 10 ). 
   In another arrangement of ballast tanks as shown in  FIG. 11 , each row of ballast tanks in the embodiment of  FIGS. 1–6  can be replaced by a multi-level row of ballast tanks to increase the amount of weight that can be added to structure  2  when tanks  40  are completely filled with water. In such a multi-level row, tanks  40  in upper rows can be offset relative to tanks  40  in the lower rows like bricks in a brick wall. Again, all tanks  40  in such a multi-level row will be interconnected together and a single bilge pump and fill valve can be placed into one of the tanks  40  in the lowest level of the plural stacked rows. 
   Referring now to  FIGS. 12 and 13 , tanks  40  in each row of tanks can be shaped relative to each other so that each row of tanks has an overall shape or configuration that more easily passes through the water during water transport of structure  2 .  FIG. 12  shows the five tanks  40  in each row thereof shaped much like a keel or hull (with the gaps between tanks  40  and couplings  46  being omitted for the sake of clarity).  FIG. 13  shows the five tanks  40  in each row having an overall torpedo or bullet shape. Either of these configurations allows for smoother towing with less drag than the merely rectangular shape of the row of tanks as shown in  FIGS. 1–6 . Moreover, structure  2  will be very stable during water transport if structure  2  is towed with tanks  40  partially flooded and the torpedo or bullet shape of  FIG. 13  largely submerged. 
     FIG. 14  shows a ballast tank that can be used along each side of structure  2  or underlying structure  2  comprising a single long ballast tank  40  having an overall hydrodynamic shape like that shown in  FIG. 12 . Such a single large tank  40  would perhaps be more difficult and expensive to obtain, but actually presents less drag in the water than an array of separate, smaller, interconnected tanks even when such an array is hydrodynamically shaped as in  FIGS. 12 and 13 . Such a single large tank  40  would preferably have a plurality of internal, partial height, vertical baffles  41  that would have lower holes therein (not shown) to let the water slowly flow through the baffles  41  when water is being added or pumped from tank  40  so that tank  40  fills and drains evenly. However, during water transport of structure  2 , baffles  41  would prevent any ballast water within tank  40  from sloshing to the rear of tank  40  as structure  2  crests a wave, thereby preventing instability and possible capsizing of structure  2 . 
     FIGS. 15 and 16  illustrate an alternative way to carry tanks  40  on structure  2 . Each ballast tank can be carried on one of the extendible legs  52  either in a fixed or slidable fashion. As tanks  40  are filled with water, the weight of tanks  40  will cause legs  52  to extend downwardly out of structure  2  until feet  56  on the lower ends of legs  52  engage against the bottom of the body of water. Alternatively, if tanks  40  are slidably carried on legs  52 , legs  52  could be extended downwardly before tanks  40  are filled and then tanks  40  will slide down legs  52  as they are being filled. In any event, legs  52  can still be locked in place on structure  2  after they have engaged the bottom. 
   One advantage of placing tanks  40  on legs  52  of structure  2  is the fact that the weight or ballast provided by tanks  40  is located as low as possible, even lower than base  20  of lower level  4 . However, one disadvantage of placing tanks  40  on legs  52  of structure  2  rather than somewhere else is the need to have individual pumps and fill valves for each tank along with snorkel tubes  42  that have a maximum length that will keep the upper ends of tubes  42  above the water line. One approach for such a snorkel tube would be to have a tube that would be a flexible, coiled tube that could unroll as tank  40  sinks to the bottom of the body of water. 
   Various other modifications will be apparent to those skilled in the art. For example, fill valve  44  could be placed in tank  40  that is at the rear end of structure  2  furthest from tongue  34 . Then, when structure  2  is first removed from the body of water at the end of the season, structure  2  can be tipped to the rear about wheels  36  by elevating tongue  34 . Fill valve  44  will then be the lowermost portion of the array of ballast tanks  40  and if opened can be used to drain any water that remains the ballast tanks  40  prior to storage of structure  2 . Moreover, structure  2  could simply comprise a single level, weight bearing deck forming a section of a dock. 
   The use of one or more electrically operated bilge pumps  48  is preferred for evacuating ballast tanks  40  since such pumps  48  can pump the water out at synchronized, controllable, relatively slow rates. External manually operated pumps could also be used. However, a compressed air system could be substituted for pumps  48  to blow the water out of ballast tanks  40 . 
   Ballast system  38  represents one type of buoyancy system that provides structure  2  with buoyant and non-buoyant states to float structure  2  on the body of water or to sink structure  2  in the body of water. Ballast system  38  does so by evacuating water therefrom or by adding water thereto, respectively. 
     FIG. 17  illustrates an alternative buoyancy system which may be used in place of ballast system  38 . In this alternative system, ballast tanks  40  are replaced with a plurality of flexible, inflatable air bags or bladders  70 .  FIG. 17  shows three such bladders  70  on structure  2  with two bladders  70  being shown fully inflated and expanded and one bladder  70  being shown fully uninflated and collapsed. The number of bladders  70  and their placement on structure  2  could obviously vary just as the number and placement of tanks  40  can vary. 
   Bladders  70  would have suitable air valves (not shown), similar to those used on pneumatic tires, to allow compressed air to enter and inflate bladders  70  and to allow such compressed air to be bled from and permit bladders  70  to collapse. Such bladders  70  would be inflated from a source of compressed air provided on structure  2  or externally of structure  2 . 
   A buoyancy system comprised of inflatable bladders  70  is not preferred over ballast system  38 . Bladders  70  are much more prone to being punctured and uninflated by being snagged or hooked on something than are ballast tanks  40 , at least when such tanks  40  are made from a rigid plastic or metallic material as would usually be the case. One could attempt to protect bladders  70  by placing them well inside structure  2  beneath base  20 , but even so it would still be somewhat likely that one or more bladders  70  would be punctured at some time, either when structure  2  was in the water or was out of the water. This would mean the repair or replacement of the damaged bladder(s)  70 , which is obviously inconvenient and expensive. 
   While bladders  70  could be pneumatically linked together in groups or arrays to allow the groups or arrays to be simultaneously inflated and collapsed, the danger of bladder puncture would militate against this. Instead, it would be safest to use separate bladders  70  that are individually inflated and collapsed so that the puncture of one bladder  70  would not affect the inflated state of the remaining bladders  70 . However, it would take more time and be more work to have to inflate and collapse each bladder  70  individually. 
   Yet another reason for preferring the use of ballast system  38  is that ballast system  38  adds significant weight to a light structure while inflatable bladders  70  have to provide buoyancy to a heavier structure. If one wants structure  2  to weigh 7,500 pounds when in the water, then one can build a 2,500 pound structure  2  equipped with ballast tanks  40 . The ballast in the form of the water added to ballast tanks  40  makes up the difference. Thus, one only needs 2,500 pounds of materials to construct structure  2  and only this amount has to be towed by a tow vehicle. 
   The situation is the reverse if one uses a buoyancy system made of inflatable bladders  70 . One has to start with a structure weighing 7,500 pounds meaning more material must be used in the construction of structure  2  and one now has to tow a 7,500 pound structure. Bladders  70  then must be sized to provide more than 7,500 pounds of buoyancy to allow structure  2  to float. Thus, ballast system  38  is far more economical and efficient when used on structure  2  than an inflatable system of flexible bladders  70 . 
   Thus, the scope of this invention is to be limited only by the appended claims.