Patent Publication Number: US-8117729-B2

Title: Methods of deploying a portable floating hot tub

Description:
RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 60/903,567, filed Feb. 27, 2007. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to methods for deploying a portable hot tub that floats in a body of water and, in particular, to an easily and rapidly deployable, portable floating hot tub that can be used in bodies of water that are turbulent and cold. 
     BACKGROUND OF THE INVENTION 
     Hot tubs or spas are excellent ways for relaxing and rejuvenating, as well as therapeutically soothing sore muscles and body parts. The conventional hot tub is mounted in or above the ground, has rigid sidewalls, typically a molded fiberglass shell for containing water, and a relatively sophisticated and expensive electronically monitored and controlled water heating system relatively permanently connected an existing water supply system. Hot tubs are often combined with standard swimming pools, either close to but spaced from the pool or immediately adjacent thereto separated by a low dividing wall. The ability to switch back and forth from the cold pool water to the hot spa water is extremely exhilarating. 
     To date, there has not been an economically feasible portable hot tub for use in remote locations away from the backyard. One difficult hurdle in constructing a portable hot tub is the necessity of providing extremely strong sidewalls to contain the large amount of water therein. Of course providing sturdy sidewalls increases the size and weight of the device which hinders portability. One possible answer to this practical problem is to immerse the hot tub in a larger body of water, which equilibrates the hydraulic forces across the spa wall and therefore reduces the structural strength requirements. 
     Several designs for floating hot tubs, spas and pools are known, including U.S. Pat. Nos. 4,126,905, 4,135,256, 4,754,502, 5,470,480, 6,795,983, and 7,032,258. For a number of reasons, these designs lack one or more of the following: easy portability, easy and rapid setup, stability in turbulent water, or economic practicality. Some relatively recent floating hot tubs, such as in U.S. Pat. No. 6,795,983, commercially available as the HOT POD floating spa, are primarily designed for use in a pool with relatively flexible and lightweight construction, which makes them ill-suited for use in very cold and turbulent water. Indeed, the &#39;983 patent promotes the ability to easily depress the hot tub upper rim to facilitate entry and exit of both people and surrounding ambient water. Hot tubs have been built into larger boats, including crew ships and luxury yachts. Though technically “floating,” these hot tubs are not portable by themselves, and are relatively permanently structurally installed and connected to the electrical and water systems of the boat. 
     Consequently, there remains a need for a floating hot tub that is portable, easy and quick to set up by one person, stable in rough waters, and within the budget of ordinary consumers. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a hot tub that is portable and may be placed in a body of water such as a pool, a lake, river or the ocean. A primary application is to use the hot tub behind a boat. Boaters in particular would appreciate the ability to quickly deploy a hot tub in the water behind their boat wherever they are moored. The hot tub can also be used next to a dock or floating independently in a body of water. 
     In general, the present invention provides a hot tub that is portable, easily assembled, easy to enter and exit, provides for comfortable seating, and can be used in environments where there is cold and turbulent water. The hot tub has a collapsible, rigid frame that makes it operable in turbulent water such as in a river or on the ocean. Walls of the hot tub are constructed from a thermally insulating material so that it retains heat and can be operated in cold water environments found in lakes, rivers and oceans. The hot tub is portable and can be carried and assembled easily by a single individual in confined environments such as on a boat or on the dock. Finally, the rigid frame structure of the tub provides for comfortable seating. 
     In one embodiment, the hot tub is constructed from three independent components: a pontoon, a frame and walls. The hot tub is supported in the water by a floating inflatable pontoon. The pontoon can be constructed from one or more bladder units. The pontoon must be large enough to stabilize the tub when people enter or leave the tub. The support frame of the tub is made with structural materials such as pipes or rods, or any other structural material that may be easily disassembled. The frame may include provisions for seating of one or more people in the hot tub. Extra material may be placed between the frame arms and the pontoon to distribute the weight of the frame on the pontoon. The walls of the hot tub are made from a thermally insulating material such as neoprene rubber. The insulating material helps to keep the water in the tub from losing heat too rapidly to the external body of water. When the hot that is filled with water, the majority of the tub is submerged below the surface of the external body of water, providing stability. The hot tub is designed such that when filled with water, the water level inside the tub is approximately the same level as the external body of water. 
     In accordance with one aspect of the invention, a portable floating hot tub comprises a collapsible frame of connected rigid members having a collapsed configuration and a deployed configuration. The deployed frame forms an interior volume, at least one seat for a person within the volume, and an upper periphery. An insulated liner is sized and shaped to fit closely against and attach to the deployed frame to form a subassembly and define a hot tub fill volume within the liner. An inflatable pontoon buoyantly supports the deployed frame and liner subassembly. Cooperating means on the collapsible frame, the insulated liner, and/or the inflatable pontoon couples the frame and liner subassembly to the pontoon. The inflated pontoon has sufficient buoyancy to support the frame and liner subassembly in a body of water with the upper periphery of the frame above the water level. Finally, a source of hot water connects to circulate water to and from the hot tub fill volume. 
     In one embodiment, the cooperating means comprises at least one lateral extension from the frame and liner subassembly that engages the pontoon. For instance, the cooperating means may be flexible straps. The source of hot water desirably comprises a hand-carried portable heater having an inlet and an outlet and hoses connected therewith for circulating water to and from the hot tub fill volume. A preferred insulated liner comprises a foam core and protective outer layers, and is easily separable from the frame. In one form the collapsible frame comprises a plurality of lightweight rigid struts connected at junctions. For autonomous navigation of the hot tub a small motor may be mounted on the pontoon. Advantageously, the inflatable pontoon has a closed geometric form surrounding a central aperture within which the deployed frame and liner subassembly are peripherally supported. 
     Another portable floating hot tub of the invention comprises a collapsible frame of connected rigid members having a collapsed configuration and a deployed configuration, wherein the deployed frame forms an interior volume, at least one seat for a person within the volume, and an upper periphery. An insulated liner is sized and shaped to fit closely against and attach to the deployed frame to form a subassembly and define a hot tub fill volume within the liner. A pontoon buoyantly supports the deployed frame and liner subassembly such that the upper periphery of the frame is above the water level. A hand-carried portable heater having an inlet and an outlet and hoses connected therewith circulates water to and from the hot tub fill volume. The heater has a tilt sensor that shuts off operation of the heater if the heater tilts more than a predetermined amount from an upright orientation. Cooperating means may be provided on the collapsible frame, the insulated liner, and/or the pontoon for buoyantly coupling the frame and liner subassembly to the pontoon. The collapsible frame desirably comprises a plurality of rigid struts hinged together. The heater may have a gas burner and an electric control therefore, and a heating capacity of at least 30,000 BTUs. Another element of the system may be a submergible water pump having an inlet and an outlet with an outlet hose connected to the inlet of the heater. The pontoon desirably has at least one inflatable bladder that is capable of being collapsed and hand-carried in a bag. 
     A still further embodiment of a portable floating hot tub comprises a collapsible frame, an insulated liner attached to the deployed frame to form a subassembly, and an inflatable pontoon arranged to buoyantly support the deployed frame and liner subassembly. A hand-carried portable heater is provided to circulate water to and from the hot tub fill volume, and the hot tub components can be collapsed and stored in one or more carry bags with a combined weight of less than 100 pounds. Preferably, the collapsible frame comprises a plurality of lightweight rigid struts connected at junctions, some of which are dedicated hinges and some of which are detachable. The inflatable pontoon may have a closed geometric form surrounding a central aperture within which the deployed frame and liner subassembly are peripherally supported. Desirably the insulated liner is easily separable from the frame, and more particularly the insulated liner has a plurality of tabs secured thereto for attaching the liner to the deployed frame. 
     A method for rapidly deploying a floating hot tub of the present invention includes deploying a collapsible frame of connected rigid members having a collapsed configuration and a deployed configuration, wherein the deployed frame forms an interior volume, at least one seat for a person within the volume, and an upper periphery. An insulated liner sized and shaped to fit closely against and attach to the deployed frame is provided, and the deployed frame and the liner are coupled to form a subassembly and define a hot tub fill volume within the liner. An inflatable pontoon arranged to buoyantly support the deployed frame and liner subassembly is inflated placed it in a body of water. The user fills the hot tub fill volume with water so that the upper periphery of the frame is buoyantly supported by the pontoon above the water level, and then circulates heated water to the hot tub fill volume. 
     The pontoon preferably defines a central aperture and the step of filling causes the frame and liner subassembly to descend through the aperture. Furthermore, cooperating means may be provided on the collapsible frame, the insulated liner, and/or the inflatable pontoon that prevent the subassembly from passing completely through the central aperture. For instance, the cooperating means may be at least one lateral extension from the frame and liner subassembly that engages the pontoon. Desirably, the source of heated water comprises a hand-carried portable heater having an inlet and an outlet and hoses connected therewith for circulating water to and from the hot tub fill volume. The collapsible frame may be a plurality of lightweight rigid struts connected at junctions, and the step of deploying the frame comprises unfolding the rigid struts and securing at least one junction to maintain the deployed configuration. Further, the step of coupling the deployed frame and the liner preferably involves inverting the frame, draping the insulated liner over the frame, righting the frame and liner, and coupling an upper edge of the liner to the upper periphery of the frame. The insulated liner may have a plurality of tabs secured thereto for attaching the liner to the deployed frame. 
     Another method for deploying a floating hot tub embodied herein, comprises deploying a collapsible frame and coupling an insulated liner thereto to form a subassembly. A user places a pontoon in a body of water, positions the frame and liner subassembly adjacent the pontoon, and fills the hot tub fill volume with water so that the flame and liner subassembly descend until the upper periphery of the frame is buoyantly supported by the pontoon above the water level. Heated water is circulated to the hot tub fill volume, and the floating hot tub is detached from any mooring in the body of water and a means of propulsion is used to return to the original or another mooring. Desirably, the means for propulsion comprises a small motor mounted on the pontoon. In one embodiment, the pontoon comprises at least one inflatable bladder, and the method includes inflating the bladder. The pontoon may have a closed geometric form surrounding a central aperture within which the frame and liner subassembly is peripherally supported. In the latter instance, the step of filling causes the frame and liner subassembly to descend through the aperture, and cooperating means are provided on the collapsible frame, the insulated liner, and/or the pontoon that prevent the subassembly from passing completely through the central aperture. 
     A still further method for rapidly deploying a floating hot tub, comprises:
         a. deploying a collapsible frame of connected rigid members, wherein the deployed frame forms an interior volume, at least one seat for a person within the volume, and an upper periphery;   b. coupling an insulated liner to the deployed frame to form a subassembly and define a hot tub fill volume within the liner;   c. inflating a pontoon;   d. placing the inflated pontoon in a body of water of ambient temperature;   e. positioning the deployed frame and liner subassembly adjacent to the pontoon;   f. filling the hot tub fill volume with ambient temperature water so that frame and liner subassembly descends until the upper periphery of the frame is buoyantly supported by the pontoon aperture above the water level;   g. circulating heated water to the hot tub fill volume to heat the water to at least 100° F.; and   h. performing the preceding steps in about an hour.       

     The pontoon may define a central aperture, such that the step of filling causes the frame and liner subassembly to descend through the aperture, wherein cooperating means are provided on the collapsible frame, the insulated liner, and/or the inflatable pontoon that prevent the subassembly from passing completely through the central aperture. The source of heated water preferably comprises a hand-carried portable heater having an inlet and an outlet and hoses connected therewith for circulating water to and from the hot tub fill volume, the heater having a gas burner and an electric control therefore, and a heating capacity of at least 30,000 BTUs. The collapsible frame may be a plurality of lightweight rigid struts connected at junctions, and the step of deploying the frame comprises unfolding the rigid struts and securing at least one junction to maintain the deployed configuration. The step of coupling the deployed frame and the liner desirably comprises inverting the frame, draping the insulated liner over the frame, righting the frame and liner, and coupling an upper edge of the liner to the upper periphery of the frame. The insulated liner may have a plurality of tabs secured thereto for attaching the liner to the deployed frame. All of the aforementioned steps may be performed by a single person. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and advantages of the present invention will become appreciated as the same become better understood with reference to the specification, claims, and appended drawings wherein: 
         FIG. 1  is a perspective view of an exemplary potable floating hot tub of the present invention deployed off the back of a boat, and illustrating a portable heater having hoses connected thereto for circulating hot water to an inner volume of the hot tub; 
         FIG. 2  schematically illustrates an exemplary rigid frame and insulated liner in a deployed configuration, prior to filling an inner volume with water, and positioned within a central aperture of a buoyant pontoon on a body of water; 
         FIG. 3  schematically illustrates the rigid frame and insulated liner after having an inner volume filled with water such that the assembly descends within the central aperture of the pontoon; 
         FIG. 4  is a perspective view of an exemplary rigid frame of the present invention in a deployed configuration; 
         FIG. 5  is a perspective view of the rigid frame of  FIG. 4  in a collapsed configuration; 
         FIG. 6  is a perspective view of the deployed frame above an insulated liner representative of one step in an assembly process of the floating hot tub; 
         FIG. 7  is a perspective view of the assembled flame and insulated liner above an inflated pontoon representative of another step in the assembly process of the floating hot tub; 
         FIG. 8  is a sectional view through a portion of a wall of an exemplary insulated liner of the present invention; and 
         FIG. 9  is a schematic diagram of an exemplary portable heater used to rapidly heat water within the floating hot tub of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a portable floating hot tub that is an improvement over previous designs. The exemplary hot tub of the present invention is easy to set up and take down by one person in any confined space and in a short amount of time, is stable in even choppy waters, and retains heat for a significant length of time. Moreover, the components of the hot tub can be carried in two small luggage-sized bags that are easily transported and stored in a small space. A number of desirable features described herein combine to provide a truly advanced portable floating hot tub, though it should be understood that certain features by themselves and some combinations thereof are believed novel and may be incorporated into other portable floating hot tubs for a similar advantage. Therefore, the present invention should not be considered limited to the exemplary system described herein, but instead should be evaluated by reference to the appended claims. 
     The  1  illustrates an exemplary floating hot tub  20  of the present invention deployed in an external body of water W with a woman enjoying a soak in a volume V of hot water therein. The hot tub  20  is shown floating just off the back of a boat B with a portable heater  22  supported on a transom platform P thereof. The boat B represents any number of solid surfaces from which to deploy the hot tub  20 , such as the edge of the swimming pool, a dock, shoreline, etc. Likewise, the body of water W represents any number of larger bodies of water, including the ocean, lakes, rivers and ponds, swimming pools, etc. 
     The present invention is particularly well adapted for deploying off the back of the boat because of its small portable size and minimal space requirements for set up. Although the floating hot tub  20  desirably remains tethered to the boat, its particularly effective insulating properties and stability permit it to float freely for some time before the inner volume V loses heat. A series of spaced handles  24  around the outside of the hot tub  20  enhance maneuverability and provide anchoring members through which to tether a line. In one particular configuration, the inner volume V is about 250 gallons and the heated water can remain hot for hours, even in the coldest environments. 
     With reference those to  FIGS. 1-3 , the hot tub  20  comprises three main components: a floating pontoon  30 , a rigid frame  32 , and an insulated liner  34  that forms walls dividing the inner volume V from the exterior body of water W. The three main components are separable for transport and assembled just prior to deployment in the water W.  FIG. 2  illustrates the pontoon  30  floating on the water W and a subassembly of the frame  32  and liner  34  buoyantly supported by the pontoon. A procedure for assembling the hot tub  20  will be described below, in particular with reference to  FIGS. 6 and 7 . 
     As seen in  FIG. 1 , the pontoon  30  comprises a closed geometric form of continuous air-filled tubular bladders defining a central aperture  40 . In the exemplary embodiment the closed geometric form is rectangular. The subassembly of the frame  32  and liner  34  is positioned within the central aperture  40  and peripherally supported by the pontoon  30 . Of course, those of skill in the art will understand that the principles of the present invention described herein are not solely limited to a rectangular closed configuration, and other shapes as well as multiple independent or connected pontoons are contemplated. For instance, only two parallel sides of the illustrated pontoon  30  may be utilized, either connected together with rods or deployed independently and separately coupled to the subassembly of the frame  32  and liner  34 . The illustrated hot tub  20  provides two comfortable seats for the enjoyment of two people at once, as will be explained. Of course, by doubling the width of the various components a four-person hot tub could be formed. Similarly, a round, hexagonal, or other shaped hot tub could be constructed based on the principles described herein. 
     The pontoon  30  may be constructed from one or more bladder units inflated with air. That is, the entire rectangular pontoon  30  may be constructed from a single bladder unit having a common interior inflation chamber. Alternatively, the pontoon  30  maybe constructed of a series of connected and separate bladder units having separately inflated chambers. The latter configuration will provide a measure of redundancy for safety in case one of the bladder units fails or is punctured. One useful configuration is to provide at least two inflation chambers separated by one-way valves, yet only a single exterior insulation. In such a system, the setup time remains about the same, though leakage from of one of the inflation chambers will not affect the entire pontoon. The bladder units should be large enough to keep outside water from entering the hot tub  20 , and the pontoon should be large enough to stabilize the hot tub when people enter or leave directly from the surrounding body of water, from a dock, or from the swim platform P of the boat B. In one exemplary embodiment, the bladders are made of 0.9 mm PVC tarp material, and are approximately 1 foot in diameter. 
     As mentioned above,  FIG. 2  illustrates the subassembly of the rigid frame  32  and insulated liner  34  in the central aperture  40  of the pontoon  30 . In this configuration, the insulated liner  34  closely surrounds the deployed frame  32  and defines a hot tub fill volume therewithin. That is, the walls around the frame  32  formed by the insulated liner  34  are relatively water-impervious so as to contain the volume V therein. In  FIG. 2 , no water has been added to the volume V, while in  FIG. 3  water fills the volume V such that the subassembly of the frame  32  and liner  34  sinks down through the aperture  40 . 
     The frame  32  possesses at least one, and preferably multiple lateral extensions  50  that engage the pontoon  30  and prevent complete passage of the frame  32  and liner  34  subcombination through the central aperture  40 . In the illustrated embodiment, the lateral extensions  50  comprise rigid arms that project outward from the frame  32  at least partly across the radial dimension of the tubular pontoon  30 . As seen in  FIG. 3 , the lateral extensions  50  rest on the top surface of the pontoon  30  and thus prevent the frame  32  and liner  34  subassembly from sinking through the central aperture  40 . In a preferred embodiment, the operator fills the inner volume V of the hot tub  20  with water to a level that is just below the level of the external body of water W, such that when the users of the hot tub immerse themselves in the hot tub water, the inner and outer water levels are approximately the same. This creates an equilibrium such that the lateral extensions  50  rest lightly on the pontoon  30 , and therefore reduces any deleterious effects of excess rubbing and the like. The lateral extensions  50  may also be shaped so as to reduce friction on the pontoon, and in the illustrated embodiment are bent down at their outer ends which helps to prevent injuries to someone entering or leaving the hot tub. 
     It should be understood that the illustrated lateral extensions  50  are merely one configuration for coupling the frame  32  and liner  34  subassembly with the pontoon  30 . Another configuration is one or more flexible straps that extend from an upper periphery  52  of the frame  32  and attached to rings or other such anchors provided on the upper or outer surface of the pontoon  30 . A still further alternative is to extend straps or a web of straps across the pontoon  30  and under the frame  32  and liner  34  subassembly, such as shown in phantom at  54  in  FIG. 3 . In the latter arrangement, the frame  32  and liner  34  subassembly are filled with water until they come to rest on the straps  54 . In general, therefore, one or both of the frame/liner subassembly and pontoon  30  includes cooperating means for preventing passage of the subassembly entirely through the pontoon aperture. Those cooperating means could be rigid arms such as shown at  50  in  FIG. 2 , or flexible straps similarly connected to the frame  32 . Alternatively, flexible straps could be provided on the liner  34 . The cooperating means could also be mounted to the pontoon  30 , such as the straps shown in phantom at  54  in  FIG. 3 . If straps connected to the frame  32  or liner  34  are used, they may couple to D-rings or cinches mounted to the pontoon  30 , in which case the cooperating means are located on both components. Those of skill in the art will understand that there are numerous possible configurations of cooperating means, each of which functions to prevent passage of the subassembly of the frame  32  and liner  34 , and thus sinking, entirely through the central aperture  40  of the pontoon  30 . 
       FIGS. 4 and 5  illustrate an exemplary collapsible frame  32  for use in the hot tub  20  of the present invention.  FIG. 4  shows the frame  32  in a deployed configuration, while  FIG. 5  shows the frame in a collapsed configuration. In its deployed configuration, the frame  32  defines a substantially rectangular upper periphery  52  which, in a preferred embodiment, has a long dimension of about 5 feet and a short dimension of just under 3 feet. The frame  32  comprises a pair of end sections  64  separated by a middle section  66 . The middle section  66  is approximately twice as deep as the end sections  64  and has a lower floor  68 . Each of the end sections  64  includes a seat  70 . The deployed frame  32  defines a volume therewithin suitable for two adults to sit facing each other on the seats  70  with their feet resting on the lower floor  68 . Although not shown, a small removable step-ladder having hooks for resting on the upper periphery  52  of the frame  32  may be provided to make getting into the hot tub easier.  FIG. 4  shows an alternative to the lateral extensions  50  in that flexible straps  50 ′ may be used, while  FIG. 5  shows the rigid extensions  50  as they would be folded in line with the struts of the frame  32 . 
     In a preferred embodiment, the frame  32  comprises a series of members such as rods or struts  74  made of a rigid lightweight material such as aluminum or fiberglass and connected at junctions  76  that may be hinges or fasteners. Exemplary struts  74  include hollow pipes or rods of plastic, metal, or composites. Likewise, the lower floor  68  and seats  70  are constructed of lightweight panels of nylon or other flexible and strong material. As seen in  FIG. 5 , the frame desirably collapses upon itself to a relatively small profile; in the preferred embodiment, the size of the collapsed frame is approximately 28×28×10 inches in dimension, and weighs approximately 40 pounds. To facilitate rapid assembly and disassembly, some of the junctions  76  will be dedicated hinges (e.g., bolted or riveted), while some will be detachable. Some of the hinges may be freely rotating while others are lockable to fix the angle between two connected struts. In one embodiment, the two upper side panels in the middle section  66  completely detach from the rest of the frame  32  to facilitate collapse of the remainder of the frame about parallel hinge axes. Advantageously, no tools are required to set up or take down the frame  32 . The struts  74  may be secured in their deployed orientations with large thumb screws at the hinged joints, and the resulting deployed frame  32  seen in  FIG. 4  is firmly held in its desired form; that is, in a three-dimensional form defining a volume within which users of the hot tub sit. 
       FIGS. 6 and 7  schematically illustrate two of the steps in assembling the main components of the hot tub  20 .  FIG. 6  shows the deployed frame  32  above the insulated liner  34 . The liner  34  is formed of the number of panels connected together so as to closely mirror the exterior shape of the deployed frame  32 . Of course, the liner  34  is desirably formed of a flexible material such as NEOPRENE rubber, and only assumes the shape shown in  FIG. 6  once draped around the deployed frame  32 . An upper edge  78  of the liner  34  defines an opening through which the deployed frame passes. Because of the relative lack of form of the fabric-like liner  34 , a preferred method of assembly is to invert the deployed frame  32  and pull the liner  34  down around it. In this respect, the lightweight nature of these two components facilitate their assembly in that one person can invert the frame  32 , cover it with the liner  34 , and invert the assembly  80 . In an alternative arrangement, the insulated liner  34  is sized to fit closely within the deployed frame  32 , rather than surrounding it. In either arrangement, the insulated liner  34  fits closely against the deployed frame  32 , and may include a series of fasteners or hook and loop straps to secure the walls and floor of the liner against the frame, not just the upper periphery. 
     Subsequently, the frame  32  and liner  34  subassembly  80 , seen in  FIG. 7 , inserts through the central aperture  40  of the pontoon  30 . Desirably, the pontoon  30  has first been inflated and placed in the body of water in which the hot tub  20  will float. 
       FIG. 8  is a sectional view through a portion of the insulated liner  34 . A number of materials having good insulating properties may be utilized, but preferably the liner  34  has an insulating core  81  made of a flexible, preferably foam, material such as NEOPRENE rubber. A protective internal barrier  82  and a protective external coating  84  sandwich the insulating core  81 . The protective barrier  82  and coating  84  help prevent damage from sharp objects, and may be coated to help resist the growth of algae or barnacles. The insulated liner  34  may be made similar to standard wetsuit material, with an inner foam layer sandwiched by outer layers of polymer stretchy fabric. In one configuration, the hollow spaces in the foam liner are filled with nitrogen for its insulation value, as is typical in diving and exposure protection applications. This also makes the material quite buoyant, which supplements the buoyancy of the pontoon  30 . Liners  34  for extremely cold water protection may be made of 7 mm thick NEOPRENE. 
       FIGS. 6 and 7  also illustrate an exemplary arrangement for coupling the frame  32  and liner  34 . In particular, the liner  34  includes a plurality of pairs of tabs  86  spaced around and extending from its upper edge  78 . Each pair of tabs  86  is sized to pass around one of the struts  74  of the frame  32  and couple to each other. The mating tabs may be coupled using hook and loop fasteners, snaps, or the like. In this regard, the process of assembling the liner  34  to the frame  32  is easy and quick, and can be reversed with the same speed. 
     With reference again to  FIG. 1 , the exemplary hot tub  20 , once deployed, is filled with water from a source such as a hose, or from the surrounding body of water W utilizing a submergible pump  88 . In this regard, submergible pump  88  can also be used to empty the hot tub  20  when it is time to disassemble the device. 
     As mentioned above, the portable heater  22  preferably includes a control and monitoring panel  90  and inlet and outlets  92  to which circulatory hoses  94  connect. In a preferred embodiment, the heater uses liquid propane (LP) gas, has a 12 V, 40 W power usage, and an output of 88,000 BTUs. The heater may be powered by a 12 V power source such as a cigarette outlet, or an optional 12 V battery. One particularly useful embodiment is to use a 36 V rechargeable wheelchair battery. An internal pump circulates water two and from the hot tub volume V through the hoses  94 . The preferred heater  22  can heat 250 gallons of water from 60° F. to 105° F. in about one hour. 
       FIG. 9  is a schematic diagram of preferred elements of the portable heater  22 . Desirably, a portable gas heater is used that requires minimal electric power, is relatively small in size, and simple to install or couple to the portable hot tub  20 . The water heater should include safety features such as a tilt shut-off switch, a flow switch, and a thermal shut-off switch. Desirably, the heat exchanger is a continuous-flow type made from thermally conductive material such as copper. Other materials may be used if the heater is used extensively in corrosive environments, such as in proximity to saltwater. The burner typically uses natural or LP gas and should have a heating capacity of 30,000 BTUs or greater. 
     In the embodiment illustrated in  FIG. 9 , a microcontroller receives input from the control panel  90  and various sensors, such as a flame temperature monitor, an exit water temperature monitor, and a hot tub water temperature monitor. Additionally, the portable heater  22  desirably includes a tilt switch connected to shut off the burner and pump if the housing of the heater tips a predetermined amount from upright. The tilt switch is extremely important for the present application, as the portable heater  22  may be placed in a boat where malfunction from tipping over and potential fire are extremely dangerous. The microcontroller is provided with a reset switch function that enables the heater  22  to be restarted shortly after being placed upright. 
     The microcontroller measures the temperature in the hot tub water with a thermocouple or thermistor, temperature T 3 . If the water temperature is too low, the microcontroller turns on the pump and ignites the burner. Once the desired temperature is reached, the microcontroller turns off the burner and then the pump. The microcontroller communicates to a burner controller which starts the burner. When switch on, the burner controller outputs a high-voltage pulse train to a piezo-igniter (P), opens the gas solenoid, and monitors a burner thermocouple output (T 1 ). After the gas ignites, and the burner thermocouple is hot, the burner controller shuts off the piezo-igniter. If at any point the flame thermocouple (T 1 ) or temperature out thermocouple (T 2 ) is not hot, the gas solenoid shuts off immediately, thus turning of the gas burner. Optionally, the functions of the gas solenoid, thermocouple monitoring, etc., can be incorporated into the microcontroller. 
     The water pump associated with the portable heater  22  desirably uses minimal power, and may be submerged in water or not. Built pumps commonly used for boats can be used, but have very low power. Such pumps are capable of producing large flow rates with little water pressure. 
     The battery or power source used for driving the pump and the microcontroller may be integrated with the heater, which can be provided with an internal battery or a power lead for attaching to a 12 V outlet. Typically, the voltage of the pump within the heater is 12 V, and the current draw is less than 10 A. 
     The present invention enables extremely quick setup and takedown of the portable hot tub  20 . First of all, the components of the hot tub  20 , including everything shown in  FIG. 1 , can be collapsed and stored in one or more carry bags with a combined weight of less than 100 pounds. Desirably, the system components fit into one or more, and preferably two small luggage-sized bags that are easily transported and stored in a small space. In a preferred embodiment, the components of the system are collapsed and stored/transported in at least two bags to reduce the weight of each bag to less than 50 pounds. A frame bag that holds the pontoon  30 , frame  32 , and insulated liner  34 , measures 28×28×10 inches, and weighs about 40 pounds full. A heater bag measures 24×24×9 inches, and weighs about 30 pounds full. The entire volume of the disassemble system is 9 ft 3  or less. The only other components are a small 12V blower, a bottle of LP gas, and an optional 12 V battery. 
     Setting the hot tub up occurs in the following steps:
         a) Inflate the support pontoon  30 —The pontoon may be adapted for manual inflation, but typically includes a valve that receives a nipple of a small 12V electric blower, commonly used with inflatable rafts, chairs, etc. The time required to deploy and inflate the pontoon  30  is under five minutes.   b) Construct the frame  32 —Time required to deploy the frame  32  from its collapsed configuration is between 5-10 minutes, depending on the familiarity and dexterity of the person doing the work. Quick-connect joints such as spring-loaded pins greatly facilitate the process. Once finished, the frame  32  is inverted onto its upper periphery  52 .   c) Place the insulating liner  34  over the frame—As mentioned above, the liner  34  closely surrounds the frame  32  and then the subassembly is turned right side up so as to join all of the pairs of tabs  86  around the upper periphery  52  of the frame.   d) Set the frame/insulating material in the support pontoon—This step can be seen in  FIG. 3 , and takes mere seconds because of the lightweight nature of the frame  32  and liner  34  subassembly  80 .   e) Fill the tub with water—The time required to fill the inner volume V of the hot tub  20  depends on the capacity of the pump used, but typically a small submergible pump such as the one shown at  88  in  FIG. 1  can fill the hot tub  20  in under 10 minutes. As the tub is filled with water the frame and liner subassembly  80  will sink into the body of water and through the central aperture  40  of the pontoon  30 .   f) Heat the hot tub water—The preferred portable heater  22  described above can circulate water at 1-5, preferably 3, gallons per minute, and can heat 250 gallons from 60° F. to 105° F. in about 45 minutes.       

     The total setup operation from components being in the carry bags to the hot tub  20  floating and filled with hot water can be accomplished in less than two hours, and preferably in about one hour. That is, the setup time for the pontoon  30 , frame  32  and liner  34  is between 10-20 minutes, and filling and heating the water takes between 50-70 minutes. 
     The process for taking down the hot tub  20  involves first pumping the water out from the internal volume V, which can be done with the submersible pump  88 . As the water is pumped out, the frame and liner subassembly  80  will rise relative to the pontoon  30 . Once the subassembly  80  has been substantially emptied, it can be separated from the pontoon  30  and inverted to completely empty it. Desirably, the liner  34  can be easily separated from the frame  32 , such as by coupling the two elements with the hook and loop tabs  86 . The user lifts the liner  34  off of the frame  32 , inverts the frame, and collapses or otherwise folds both elements and stores them in carry bags. The pontoon  30  preferably has a port that can be opened wide for rapid deflation, and it is also folded and stored. The portable heater  22 , submersible pump  88 , and any other ancillary equipment are placed in their carry bag, which is typically separate from the frame, liner and pontoon. Providing two bags of 30-40 pounds in weight each is preferable than a single heavier bag. The entire disassembly process may take 20-30 minutes. 
     Although the preferred embodiment includes separate frame  32  and liner  34  elements that the user assembles at the time of deployment, the subassembly  80  shown in  FIG. 7  may alternatively be provided as a single collapsible/expandable unit. The advantage of separate parts is that they can be collapsed into a smaller aggregate volume, facilitating transport and storage. On the other hand, a single unit can conceivably be designed for easier and faster deployment. Segments of the liner  34  may be pre-attached to corresponding frame struts  74  with straps, grommets, stitches, glue, etc. 
     It should be noted that hot water to fill the hot tub  20  can come from sources other than the portable gas-powered heater  22 . For example, hot water from a boat motor or other hot water reservoir may be utilized. Alternatively, a solar heat exchange system which is relatively slower but more efficient may be used. Also, other portable heaters than the one described above, such as one that uses electric heating elements, can be substituted. 
     In the case of an “independent” hot water system, such as a solar heater, the heater may be supported on the pontoons that are used to float the hot tub. Alternatively the heating system may be placed on a small independent pontoon. 
     Moreover, in certain circumstances the portable floating hot tub  20  may be used to provide cooler water than the surrounding ambient body of water, such as in a mid-summer tropical environment. In that configuration, a water cooler rather than a heater is used. 
     The floating hot tub  20  described herein provides substantial structural integrity, as opposed to other commercial designs that are relatively flimsy. Because of the rigid internal frame  32 , the overall shape of the hot tub  20  is maintained even in the presence of large external forces. The relatively large pontoon  30  helps to cushion the hot tub  20  in case of a collision with a boat or other objects, and the internal frame  32  prevents the shape from distorting. Moreover, the large pontoon  30  provides a relatively high barrier to keep cold water from entering the hot tub when there is turbulent or choppy water. 
     It is often enjoyable to float in the hot tub  20  a large distance from the boat or stock. In this case, a long line may be attached to the hot tub tether it to the boat or dock. Before floating away from the boat, the hoses  94  connecting the portable heater  22  from the internal volume V are removed. Alternatively, a separate pontoon for the heater unit  22  and an LP gas cylinder and battery pack can be floated next to the hot tub  20 . More ambitiously, the hot tub  20  can be made autonomous from land or a boat by providing it with a small motor, such as a small electric outboard motor of 5 to 80 horsepower (4 to 60 kW), as shown in phantom in  FIG. 1 ). Any means of propulsion may be supplied, including the aforementioned motor, oars, a double-ended paddle, even a small sail. Consistent with the principle that the hot tub  20  can be formed in a number of shapes, the exterior contours can be streamlined to resemble a small dinghy or Zodiac-style inflatable boat so as to facilitate trips around a harbor, for instance. The presence of the rigid frame  32  greatly enhances the ability for propulsion through the water as it supports the overall form of the hot tub. The relatively large pontoon  30 , preferably about 1 foot in diameter, also helps make the hot tub  20  seaworthy, as it provides a relatively high barrier to waves splashing over the edge and into the internal volume V. 
     It is also conceivable that certain inventive principles of the hot tub  20  described herein may advantageously be incorporated into a somewhat less portable structure. For example, the highly portable collapsible rigid frame and insulated liner may be deployed and placed with a somewhat less portable pontoon structure, such as a Zodiac-style inflatable boat. In other words, a Zodiac-style or other small boat having a relatively large central aperture may remain in the water, such as in a harbor, but the other components of the portable hot tub  20  are stored on land and only deployed when needed. In this configuration, the construction of the pontoon can be significantly more robust, as well as providing a rugged mount for a larger motor, thus improving the ability to transit distances across open water. In this regard, therefore, the term “pontoon” encompasses both a simple bladder structure collapsible into a bag that can be hand-carried, as well as a more permanent structure such as defined above. With such as system, all the components but the pontoon remain extremely portable. 
     Furthermore, the insulated liner  34  provides excellent heat retention for the hot tub  20 , even in water as cold as 32°. In a preferred embodiment, the insulated liner  34  has the capacity to lose only 1° F. of temperature of hot water (e.g., 105° F.) within the internal volume V every 20 minutes to surrounding water of 60° F. or less. The thickness of the insulating layer can be increased depending on the temperature of the surrounding environment, with a trade-off being a corresponding increase in weight and decreased portability. Also, a cover (not shown) over the top of the hot tub  20  may be provided to better retain heat when the hot tub is not in use. 
     One very useful option for the system shown in  FIG. 1  is to provide a rod-like extension from the lower end of the portal heater  22  so that it can be mounted in a fishing rod holder off the back of the boat. Such an extension can be rigidly connected to the housing of heater  22 , or a separate basket-like frame with the extension can be provided. In this way, the heater  22  is securely held in an upright position close to the hot tub  20 . 
     Another useful option is to use a “heater” pontoon to hold the heater shown in  FIG. 1  instead of a boat step or dock. The pontoon holds a battery, gas tank, and heater. Such an option allows attaching the tub and “heater” pontoon to a mooring and leaving the unit to go out boating. When returning from boating the water in the tub would be hot. 
     Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the scope of the invention, as hereinafter claimed.