Abstract:
Methods for fabricating foam cored items in which the foam core is tightly encased by an outer shell. The foam core is compressed, reducing a characteristic dimension, thereby facilitating installation and/or removal of the foam. The foam is then allowed to expand to the desired size. The methods are particularly suited for fabricating foam collars that are located above the chine of a boat and extend longitudinally along the sides of the boat to provide stabilization for the boat during high performance maneuvering and/or provide a fendering system.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation-in-part of prior application Ser. No. 10/462,088, filed Jun. 13, 2003, priority from the filing date of which is hereby claimed under 35 U.S.C. § 120. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention generally relates to a method for manufacturing items that includes a relatively flexible shell-like sleeve that tightly encapsulates a core of expanded polymeric foam material. The invention is particularly suitable for and directed to the manufacture of foam core collars that serve as boat sponsons or fenders.  
       BACKGROUND OF THE INVENTION  
       [0003]     Plastic foam material manufactured by expanding polymeric beads of polyethylene, polypropylene, and polyurethane is used in a variety of situations. In some situations, finished products are formed by, for example, casting or molding the polymeric material in the presence of a blowing agent. In other cases, sheets or a block of foam that can be used for protective packaging or for additional processing by machining or other techniques are molded or otherwise formed that result in a desired product or product component. Advantageously, the process used to form the foam material and foam products can be controlled to establish a relatively wide density range. Further, the foam material and products exhibit a number of desirable properties, such as relatively high energy absorption, resistance to denting or scarring caused by impact, and light weight and resistance to chemicals and other substances. However, situations exist in which it is necessary or desirable to either coat the exterior of an item formed of expanded polymeric plastic foam with protective material to form a shell-like skin layer or to encase the foam with a relatively flexible sleeve formed of fabric that is coated or impregnated with protective material. Applying a protective coating to the exterior of an item formed of expanded polymeric plastic foam is somewhat disadvantageous in that several additional manufacturing steps are often required to obtain the desired protective coating. For example, it may be necessary or desirable to sequentially coat the foam item with different types of material. Typically, each coat must be allowed to cure or dry prior to proceeding with additional steps of a manufacturing process. On the other hand, encasing an item formed of expanded polymeric plastic foam with a protective sleeve can result in problems from the standpoint of serviceability, appearance, and performance unless the sleeve is placed under tension so that the sleeve is of a uniform, desired contour and shape.  
         [0004]     Among the situations in which polymeric plastic foam material is either coated with protective material or is located within a protective sleeve is the fabrication of foam members, commonly called collars, that are affixed to the external surfaces of boat hulls to serve as stabilizers or fenders. By way of example, U.S. Pat. No. 5,282,436, No. 5,647,297, and No. 5,870,965, issued to Hansen, incorporated herein in their entirety by this reference, disclose high performance boats that are stabilized through the use of polymeric foam stabilizers. In the arrangement of Hansen, the foam stabilizers are mounted on the sides of the hull above the chine and extend from stern to bow. The foam stabilizers of the Hansen patents are not in contact with the water when the boat is at rest or is being operated at cruising speed. However, when the boat lists during high-speed turns, the stabilizers enter the water and provide a righting moment that decreases list relative to what would otherwise be present. Although the stabilizers used in the Hansen patents are preferably formed from a foam such as closed cell polypropylene or polyethylene that does not absorb water and exhibits fair resistance to dents and chemicals, increased damage tolerance and tolerance to sunlight can be achieved by coating the exterior of the foam stabilizers with a protective material.  
         [0005]     Examples of boat collars that employ sleeves that contain polymeric foam material include published U.S. Patent Application No. 2002/0096101 of Hansen and U.S. Pat. No. 6,371,040 to Hemphill et al. (each of which is hereby incorporated by reference). Although the Hansen patent application and the Hemphill et al. patent differ in several aspects, the arrangements disclosed in both of these references employ a cylindrical sleeve that is similar to conventional inflatable flotation collars and is only partially filled with expanded polymeric foam. More specifically, the polymeric foam used in the arrangement of Hemphill et al. is tubular, circumferentially surrounding and encasing an inflatable air bladder. In the Hansen patent application, polymeric foam inserts are employed that do not completely fill the sleeve with inflatable air bladders being located in regions of the sleeve that do not contain the foam inserts. In both the Hemphill et al. and Hansen arrangements, the air bladders are inflated to place the sleeve under tension to thereby provide a collar of desired shape, contour, and firmness.  
         [0006]     The solid foam boat collars described in the Hansen patents and the partially foam filled collars described in the Hemphill et al. patent and the Hansen patent application all function satisfactorily from the standpoint of stabilizing a boat and/or providing a fendering system. Nonetheless, a need exists for boat collars that incorporate the structural simplicity, ruggedness, and durability of solid foam collars while simultaneously presenting advantages from the standpoint of ease of fabrication and the efficient manufacture and repair of foam collared boats.  
       SUMMARY OF THE INVENTION  
       [0007]     In its most general aspect, the invention provides a method for fabricating items of manufacture in which polymeric foam that defines the size and shape of the item is firmly encased by a shell-like skin layer. In accordance with the invention, the encased foam is formed of a compressible polymeric foam material that returns to its original shape and volume when compressive forces are removed. One step of the method of the invention includes casting or machining the foam material so that it corresponds in shape and contour to the manufactured item, with the cast or machined foam being larger than the finished item of manufacture. The cast or machined foam is then compressed so that its size and volume is less than that of the item being manufactured. In some applications of the invention, the compressed foam is inserted into a relatively flexible shell or sleeve that corresponds to the shape and size of the item being manufactured. The opening that allows placement of the foam in the shell is then closed. Because the shell does not allow the foam to totally return to its original size, the shell is placed under tension to tightly enclose the foam. By suitably selecting the density of the foam and the degree to which the fully expanded foam is oversize, a desired degree of rigidity can be attained. In other applications of the invention, a portion of the foam that will fill the shell or sleeve is compressed while it is in place within the shell or sleeve. Following compression, an additional foam piece is inserted in the sleeve or shell with the compressed foam portion. The opening of the shell is then closed and the foam expands to place the shell under tension.  
         [0008]     In the specific application of the invention for manufacturing foam boat collars, the relatively flexible sleeve is tubular and is fabricated from fabric such as woven or knitted polyester and/or nylon coated with polyurethane or polyurethane blended with polyvinylchloride (PVC). Synthetic rubbers such as chlorosulfonated polyethylene (commonly identified by the trademark “HYPALON”) may also be used. Regardless of the material employed, the tubular sleeve is dimensioned and shaped to match the contour of the boat on which the collar is to be mounted and, in addition, to define a desired cross-sectional geometry (e.g., round, oval, or D-shaped). To allow placement of foam within the tubular sleeve, an opening extends along the perimeter of the sleeve. Preferably, the opening is either equipped with a single zipper or two zippers that are sewn or thermally welded one on top of the other and operated by a common opening and closing pull.  
         [0009]     In one method of practicing the invention, polymeric foam that matches the entire cross-sectional geometry of the collar being manufactured, but is dimensionally larger than the interior of the tubular sleeve is compressed and is placed inside the tubular sleeve while it is in a compressed state. In a second method of practicing the invention, foam that matches a portion of the cross-sectional geometry of the collar is placed within the sleeve and compressed while it is located inside the sleeve. Additional foam that completes the collar cross-sectional geometry is then placed in the sleeve with the compressed foam. In many cases, sections of compressed foam that collectively will make up the boat collar are placed in abutment with one another along the length of the tubular sleeve, thus allowing the foam to be easily be inserted in the sleeve, especially with respect to long sleeves and regions that are curved or angled to match hull shape.  
         [0010]     Regardless of whether the foam is compressed prior to placement in the sleeve or a portion of the foam is compressed while positioned within the sleeve, the zipper or other arrangement used to access the interior of the sleeve is closed while the foam is still compressed. In practicing the invention to manufacture boat collars, the degree of oversize to which the foam was originally fabricated does not allow the foam to fully expand. Specifically, the expanding foam presses against the tubular sleeve placing it under tension. Since the tubular sleeve exhibits limited stretching or flexure, the foam remains under compression. As a result, a collar fabricated in accordance with the invention exhibits physical properties such as energy absorption and resistance to dents, dings, and chemicals that match or surpass the corresponding physical properties of prior art boat collars. Moreover, the buoyancy of the foam collars provides substantial flotation to keep a boat afloat under emergency situations such as swamping or capsizing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0012]      FIGS. 1-4  depict methods of compressing polymeric foam that are alternatives to the hereinafter-described mechanical and pneumatic methods. Specifically,  FIGS. 1-4  depict exemplary arrangements for compressing polymeric foam using air bladders to exert the compressive force, with:  
         [0013]      FIG. 1  illustrating, in cross-section, an arrangement in which elongate sections of foam can be compressed for fabricating foam core boat collars;  
         [0014]      FIG. 2  illustrates an arrangement that can be used as an alternative to the arrangement of  FIG. 1 ;  
         [0015]      FIGS. 3A-3C  illustrate an arrangement that can be used to implement a two-step process in which polymeric foam boat collars are fabricated and installed on a boat; and  
         [0016]      FIG. 4  illustrates another alternative arrangement utilizing an inflatable bladder that is installed in situ with the foam core. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     The invention will now be described as it specifically relates to the fabrication of foam collar stabilization and fendering systems for boats. Upon understanding the use of the invention in that particular context, those skilled in the art will recognize that the invention can be employed to fabricate other items that primarily consist of a polymeric foam core that is encased by or coated with a protective and/or decorative skin layer. Use of the invention can be especially advantageous as an alternative to prior art processes in which multiple steps are used to coat an item formed of polymeric foam in order to provide a reinforced skin layer.  
         [0018]     Regardless of whether the item being fabricated is a foam boat collar or another item, the invention basically comprises four primary operations. The first operation is the fabrication of a relatively flexible sleeve or shell that, at the end of the process, will define the object&#39;s size and shape and will fully enclose a foam core. The fabricated sleeve or shell includes an opening that allows access to the interior of the sleeve or shell and is of sufficient size to allow placement of the polymeric foam in the sleeve or shell. A zipper or other means of closing the opening is also included.  
         [0019]     The second operation is forming (e.g., casting or machining) the polymeric foam that is to be enclosed by the sleeve or shell. The type of foam to be used is selected on the basis of the desired weight of the item being manufactured (i.e., determined by foam density and object size), impact resistance, and other physical properties of the foam that are specified by the manufacturers that supply polymeric foams. In all cases, the foam that is used in the practice of the invention is compressible and exhibits a “memory” that restores the foam to its original shape and size (within at least a few percent) when the compressive force is removed. Further, regardless of the technique used to form the polymeric foam material, the foam core that results from the forming operation corresponds to the shape of the object that is being fabricated but is dimensionally larger.  
         [0020]     The third operation is compressing of the foam core. In the current practice of the invention, the foam core (or individual foam sections that can be assembled to make up the core) is compressed by a mechanical compression technique by pneumatically compressing the foam in a hyperbaric chamber or by compressing the foam with air bladders that are inflated while the foam and one or more air bladders are positioned within a surrounding structure that causes the air bladders to exert pressure on the surface of the foam.  
         [0021]     The mechanical compression technique is useful in fabricating objects such as foam collars that are of substantially circular or other smooth and uniform cross-sectional geometry. Specifically, polycarbonate sheeting or other suitable material is wrapped about the periphery of the foam object with edges of the sheeting overlapping one another and with the sheeting extending over at least the full length of the foam object. A series of ratchet equipped tensioning straps or other similar devices are placed around the sheeting at spaced-apart locations along the length of the formed foam core. The straps or equivalent devices are then sequentially tightened to compress the foam by the desired amount, with the sheeting protecting the surface of the foam core and distributing the compressive force that results by tightening the straps. In some cases, such as large foam cores and/or relatively dense foam, it may be necessary to tighten the tension straps in stages, pausing between stages to allow the foam to reach the state then caused by the tension straps.  
         [0022]     As one alternative to mechanical compression, the formed foam object is pneumatically compressed by inserting the foam object in a conventional hyperbaric chamber and increasing the air pressure within the chamber to achieve the desired amount of compression. Use of the hyperbaric chamber is especially advantageous in situations in which the foam core is small or is of irregular geometry that does not provide a smooth and uniform surface that is easily compressed by means of mechanical compression.  
         [0023]     Once the formed foam is mechanically or pneumatically compressed to the desired state of compression, the fourth operation is placing it in the interior of the sleeve or shell. The zipper or other arrangement allowing access to the interior of the sleeve or shell is used to close off the interior of the sleeve or shell. As the compressed foam expands, its outer surface contacts the interior surface of the sleeve or shell. As expansion of the foam continues, the sleeve or shell is placed under tension that is sufficient to cause the outer surface of the sleeve or shell to be uniform and of the desired shape and contour.  
         [0024]     In an alternative to the above-described mechanical and pneumatic compression techniques, the foam object is compressed using inflatable air bladders to assert the compressive force. The use of this technique can be advantageous in that it is portable in the sense that it can easily be employed at sites other than the location at which a boat is manufactured. Moreover, this alternative technique can be used to compress oversized foam cores that correspond to the full shape and geometry of the sleeve or shell that is to encase the foam core. On the other hand, this technique can be used to compress oversize foam cores that correspond to only a portion of the full shape and geometry of the encasing sleeve or shell. When a compressed foam core that corresponds to the full shape and geometry of the sleeve or shell is compressed, it is placed in the interior of the sleeve or shell; the sleeve or shell is zipped or otherwise closed off; and the foam core is allowed to expand so that it presses against the interior surface of the sleeve or shell to thereby form an object of desired shape and rigidity. In situations in which an oversized foam core that corresponds to a portion of the size and shape of the object is being formed, the compressed foam core and a suitably sized insert of foam or other material is placed in the encasing sleeve or shell that may already be mounted to the boat. As is the case with the above-discussed use of foam cores that correspond to the full shape and geometry of the sleeve or shell, the sleeve or shell is then zipped or otherwise closed off and the compressed foam core is allowed to expand toward its original size.  
         [0025]     Shown in  FIG. 1  is an exemplary arrangement in which air bladders are used to compress elongate sections of oversize foam cores of the type used in the manufacture of foam boat collars. In the arrangement of  FIG. 1 , two elongate foam cores having a D-shaped cross-sectional geometry are placed in back-to-back relationship within a longitudinally extending tubular enclosure  12  that extends at least the full length of the D-shaped foam cores  10 . Located between the inner wall of the tubular enclosure  12  and the outer surface of each D-shaped foam core  10  is an air bladder  14 , which extends over at least a major portion of the curved surfaces of foam cores  10 . Also indicated in  FIG. 1  are two elongate spacers  16 , with each spacer  16  being located between the back-to-back foam cores  10  and the inner surface of tubular enclosure  12  and, in addition, extending between spaced-apart end boundaries of air bladders  14 . Elongate spacers  16  may be formed of any material that undergoes little or no compression when air bladders  14  are inflated to compress the shaped foam cores  10 . Elongate spacers  16  are optional, not being necessary in order to practice the invention. However, in some situations, spacers such as elongate spacers  16  of  FIG. 1  can advantageously be employed to control the distribution of the compressive force that is exerted on the surface of the foam core.  
         [0026]     Tubular enclosure  12  of  FIG. 1  may be formed of a fabric membrane, metal, a composite material or various types of plastic. In particular, tubular enclosure  12  is preferably constructed of material that exhibits little or no expansive stretching when air bladders  14  are inflated to a pressure that compresses foam cores  10  to a desired size. In that regard, sufficient compression is needed so that the foam cores  10  can be removed from the elongate enclosure  12  and can be installed within a shell or sleeve while the compressed foam core is small enough for easily placing it within the shell or sleeve.  
         [0027]     Although tubular enclosure  12  of  FIG. 1  is shown as being cylindrical, it should be recognized that various other cross-sectional geometry can be employed to accommodate foam cores of different geometry. Further, it should be recognized that tubular enclosure  12  need not be structures having a single continuous wall. For example, tubular enclosure  12  of  FIG. 1  could be two symmetrical sections with latches being located diametrically opposed to a longitudinally extending hinge. In such an arrangement, tubular enclosure  12  can be swung open and closed for positioning foam cores  10  and air bladders  14  within tubular enclosure  12 , as well as swung open for removal of the foam cores  10  after compression by air bladders  14 .  
         [0028]     Air bladders  14  can be constructed of a variety of fabrics and membranes of the type used for inflatable devices. Examples include urethane-coated nylon membranes, and various fabrics having a rubber-based interior coating and unsupported urethane film. A conventional air valve (not shown in  FIG. 1 ) is located in an accessible region of each air bladder  14  so that the air bladder  14  may be inflated with the foam core or cores  10  and air bladder or bladders  14  encased by a suitable enclosure  12 . For example, with respect to the arrangement shown in  FIG. 1 , the air valves may be located at one or both ends of the longitudinally extending air bladders  14 . Although the arrangement of  FIG. 1  includes two air bladders  14 , it should be recognized that more than two, or even one, air bladder may be employed. In that regard, the shape, size, and number of air bladders used are dependent upon the size and shape of the foam core or cores that will be subject to compression. Further, the pressure to which the air bladders are inflated may vary from as little as 0.5 pounds per square inch to 50 pounds per square inch, depending upon the size and shape of the foam cores, the type of foam being used, the density of that foam, and other factors. Likewise, the time required to suitably compress a foam core is dependent upon various factors such as the size and shape of the foam, foam density, and the rate at which the air bladders are (or, in some cases, can be) inflated. Because the invention has various applications using various types and densities of polymeric foam, it may be necessary to empirically determine parameters, such as the amount of air pressure used to compress the foam by a desired amount and the rate at which the air bladders are inflated, and further, whether it is necessary to use a sequence of inflation steps that allow the foam core or cores to reach a partially-compressed state before introducing additional air pressure. Additionally, in some cases it may be desirable (or even necessary) to empirically determine the number, size, and shape of air bladders to be employed. For example, in some situations, it may be desirable or even necessary to compress only selected portions of the foam core.  
         [0029]      FIG. 2  illustrates an alternative arrangement of the present invention in which a single inflatable air bladder  18  is used to compress an elongate section of foam core  20  with the foam core  20  and air bladder  18  being positioned within a compression fixture  22 . As can be seen in  FIG. 2 , the depicted foam core  20  is essentially D-shaped in cross-sectional geometry and includes an elongate channel that extends longitudinally along the center of the flat surface of the foam core  20 . Compression fixture  22  includes a back plate  24  and an enclosure panel  26  that encompasses air bladder  18  and the curved surface of foam core  20 . In the depicted arrangement, back plate  24  can be formed of various materials, such as metal, or machined or composite plastic material that is essentially incompressible under the forces exerted on the back plate  24  during compression of foam core  20 .  
         [0030]     In the particular arrangement shown in  FIG. 2 , back plate  24  is similar in size and shape to a mounting plate (not shown) that extends longitudinally along the sides of a boat that employs foam sponsons having a foam core that corresponds to foam core  20  in  FIG. 2 . Although back plate  24  of  FIG. 2  matches the mounting plate on a boat on which foam core  20  will be installed, it should be noted that foam core  20  could be compressed without the use of this matching feature. Further, two foam cores configured in the manner of foam core  20  can be placed back to back and compressed in the arrangement described relative to  FIG. 1 .  
         [0031]     Like tubular enclosure  12  of  FIG. 1 , enclosure panel  26  of  FIG. 2  can be formed of fabric, a synthetic membrane, metal, a composite material, or various other materials. In  FIG. 2 , enclosure panel  26  is secured to the top and bottom of back plate  24  by retainers  28 . A variety of devices can be used for retainers  28  with the requirement being that the retainers allow access for placement of foam core  20  and air bladder  18  against back plate  24  in the manner shown in  FIG. 2 , and allow foam core  20  to be removed after the compression process. In some situations, it may be advantageous to use a single hinge or spaced-apart hinges as a replacement for one of the retainers  28  so that enclosure panel  26  remains connected to back plate  24  and can be swung between an open and a closed position.  
         [0032]      FIGS. 3A-3C  depict an arrangement in which an oversized foam core corresponding to a portion of the shape and geometry of the shell or sleeve that is to encase the foam core is compressed, combined with a spacer formed of uncompressed foam or other material encased with the sleeve or shell with the compressed foam expanding to exert pressure on the shell or sleeve. In the arrangement of  FIGS. 3A-3C , the sleeve is located on a boat and is the covering for a sponson. Thus, the arrangement can be used for producing a foam boat collar when a boat is manufactured and, in addition, used for retrofitting a boat with foam collars or replacing foam collars at locations remote from the facility at which the boat was built.  
         [0033]     With reference to  FIG. 3A , it can be noted that similarity to the arrangement of  FIG. 2  exists in that a section (or sections) of foam core  30  is positioned in abutment with a back plate  32  and an air bladder  34  is placed about the curved periphery of foam core  30 . However, unlike the arrangement of  FIG. 2 , foam core  30  corresponds to only a portion of the interior shape of the boat collar being formed and back plate  32  is welded or otherwise secured to the side of the boat (designated by numeral  44  in  FIGS. 3A-3C ). Extending from the top and bottom of back plate  32  are an upper sponson panel  36  and a lower sponson panel  38 . The mating portions of a zipper (indicated by numerals  40 - 1  and  40 - 2  in  FIG. 3A ) are located along the edges of upper and lower sponson panels  36  and  38  that are not affixed to back plate  32 . As is shown in  FIG. 3B , upper and lower sponson panels  36  and  38  are dimensioned to enclose air bladder  34  and foam core  30  by closure of zipper elements  40 - 1  and  40 - 2 . In that regard, the dimensions of upper and lower sponson panels  36  and  38  also determine the dimensional characteristics of the sponson, once the process associated with  FIGS. 3A-3C  is complete. As can be recognized with respect to  FIG. 3B , inflation of air bladder  34  compresses foam core  30  in the same way that foam cores  10  and  20  of  FIGS. 1 and 2  are compressed.  
         [0034]      FIG. 3C  illustrates the manner in which foam core  30  (in its compressed state) is installed to form the boat sponson. A spacer  46  formed of polymeric foam, which may be the same material as the foam used in fabricating foam core  30  (or another suitable material), is received by back plate  32 . Foam core  30  (in its compressed state) is positioned in abutment with the outer face of spacer  46 . As is indicated in  FIG. 3C , when the zipper  40  is closed to join together the edges of upper and lower sponson panels  36  and  38 , the compressed foam core  30  and spacer  46  are positioned in close relationship with one another and back plate  32 . As the compressed foam core  30  expands, joined-together upper and lower sponson panels  36  and  38  are placed under tension to thereby form a boat collar (in this case, a sponson) exhibiting physical properties—such as energy absorption and resistance to dents and dings as well as fuel or chemicals that may come in contact with the boat collar.  
         [0035]     With continued reference to the fabrication of foam core collars for boats, the sleeve or shell that encloses the foam core (e.g., sponson panels  36  and  38 ) is constructed of material such as a woven or knitted polyester and/or nylon fabric that is coated with polyurethane or polyurethane that is blended with polyvinylchloride (PVC). Synthetic rubbers may also be used such as chlorosulfonated polyethylene, which is commonly identified by the trademark “HYPALON.” As will be recognized by those skilled in the art relating to boat collars, the same types of material are used in the construction of inflatable floatation collars. Each of these materials is relatively flexible within the context of the present invention. That is, when the inner surface of a sleeve or shell formed of the material is placed under tension by the encased polymeric foam, the outer surface of the sleeve becomes firm and assumes the desired size and shape.  
         [0036]     With respect to foam boat collars, the tubular sleeve is dimensioned and shaped to match the contour of the boat on which the collar is to be mounted. Currently, design work has been completed or is under way to produce foam collars for boats ranging in length from approximately ten feet up to approximately fifty feet. With respect to cross-sectional geometry, the designs that have been completed or are under way utilize both D-shaped sponsons, like those disclosed in the previously referenced Hansen patents, and sponsons of circular cross-section, as disclosed in the previously referenced Hansen patent application and the Hemphill et al. patent. The preferred width or diameter of the tubular collar ranges from approximately eight inches for smaller boats up to approximately 36 inches for the largest boats. Similarly, the weight of the material used to form the tubular sleeve varies according to boat size and the use for which the boat is designed (e.g., recreational, commercial, etc.). Material suitable for use in the manner in which the invention will be initially practiced range between what is known as 20-ounce material and 50-ounce material. In extremely demanding situations, even heavier material (e.g., up to 90-ounce) can be used.  
         [0037]     The way the tubular sleeve is fabricated from the selected material is substantially the same as the way inflatable floatation collars are manufactured. That is, the fabric is cut in accordance with a pattern for the boat on which the collar is to be used and the patterned pieces of fabric are thermally welded or otherwise bonded together. To allow access to the interior of the tubular shell for placement of the foam, an opening is included along the perimeter of the tubular shell. In the currently preferred practice of the invention, a zipper is sewn into the opening. Most preferably, and especially with respect to large foam collars, a double-zipper configuration is used in which two zippers are sewn together, one on top of the other with a single conventional tabular zipper pull being used to open and close both zippers simultaneously.  
         [0038]     With respect to polymeric foam for use in fabricating a boat collar in accordance with the invention, the use of closed cell polypropylene and polyethylene material is preferred since objects formed of that material can be compressed and when no longer subjected to compressive forces will return to their original state, typically having no more than two percent residual compression. Further, polypropylene and polyethylene foam materials exhibit very low water absorption, thus remaining buoyant even under circumstances where the sleeve of a foam collar has been damaged. The density of the foam material generally is selected as a trade-off between collar buoyancy (low-density foam) and resistance to impact during maneuvers such as docking (higher density foam). This trade-off is affected by both the size and intended use of the boat employing the foam collar. Currently, the practice of the invention can use foams having densities ranging from approximately 0.05 pounds per cubic foot to 5 pounds per cubic foot, thus allowing a high degree of design latitude. By way of example and not limitation, a foam density of 1 pound per cubic foot has been used in fabricating a foam collar for a 25-foot boat with the diameter of the sponsons being 21½ inches. With further regard to selecting an appropriate foam material, reference may be taken to ASTM 3575, which is entitled “Structural Properties of Plastics,” and is published by the American Society for Testing and Materials. That publication is used by the manufacturers of polymeric foam material to determine and publish material properties that are important to the design of foam collars, including material density, buoyancy, tensile and tear strength, as well as the degree to which an item formed of the foam will return to its original shape and size after being compressed.  
         [0039]     Although it is possible to cast or mold the polymeric foam for use in small boat collars, it often will be more practical to machine the foam material to a shape that matches the expanded interior shape of the tubular sleeve (i.e., the shape of the collar being made). As mentioned with respect to the tubular sleeve, the cross-sectional geometry typically used for boat collars is circular or D-shaped. Regardless of the exact cross-sectional geometry, the cross-sectional dimensions of the foam core that is constructed of the foam material exceed the corresponding dimensions of the interior of the tubular sleeve. For example, with reference to the previously mentioned collars for a 25-foot boat, the interior diameter of the sleeve (when fully expanded) is 21½ inches, an uncompressed diameter of the foam core is 23 inches. At this point in time, an appropriate “rule of thumb” appears to be an unexpanded foam core size that is oversized by approximately eight percent.  
         [0040]     With continued reference to the foam core, it sometimes is necessary to fabricate the core in sections that are not as long as one side of the collar being produced. Specifically, the curvature or tangential angle of the boat hull near the bow of the boat or other areas may require the use of shorter sections of foam that are placed in the tubular shell in lengthwise abutment with one another. In such cases, it can be advantageous to dimension the foam sections slightly longer than required so that lengthwise expansion of the sections within the sleeve will press the sections together and tension the tubular shell in the longitudinal direction. By way of example, with respect to the foam core used in the fabrication of a collar for a 25-foot boat, foam sections having an intended final length of 24 inches were 24½ inches prior to being compressed and placed in the tubular sleeve.  
         [0041]     Compressing the foam core or core sections for placement in the tubular shell can be accomplished by the previously discussed mechanical means, the use of a hyperbaric chamber, or by the use of inflatable air bladders. With respect to foam collars having a circular or “D” cross-sectional shape, the use of the mechanical compression technique or the air bladder technique may be more advantageous than compression in a hyperbaric chamber. In that regard, the compressed foam core sections can be stored while remaining under compression, thus allowing efficient production scheduling and, in the case of relatively large foam collars, the ability to process the number of foam core sections required to completely fill the tubular sleeve. Preferably, the degree to which the foam cores are compressed is determined by the density of the foam, the ease of compressing the foam, and the expansion rate of the foam once the compressive force is no longer present. In particular, the minimum amount of compression must allow time for the foam to be placed in the tubular sleeve and, additionally, should be established so that the time required for the foam to expand within the tubular sleeve is of reasonable length. With reference to the exemplary situation of fabricating a foam collar for a 25-foot boat, the foam core is formed so that it is approximately eight percent (8%) oversize relative to the diameter of the foam collar, and the core is compressed to eighty-two percent (82%) of its original size.  
         [0042]     In the final steps of fabricating the foam collar, one or more sections of foam core that are needed to fill the tubular sleeve are placed in the sleeve, the sleeve is closed by means of the zipper, and the foam is allowed to expand. As previously noted, the interior volume of the tubular sleeve does not allow the foam core to fully expand so that the tubular sleeve of the foam collar is placed under tension.  
         [0043]     Various factors determine the amount of time required for the foam core to expand to the point at which the tubular sleeve is under tension to the point at which no further expansion takes place. The factors include the degree to which the foam core has been compressed, the size of the foam core, the density of the foam being used, ambient temperature, and even the technique that was employed to compress the foam core. In particular, the expansion rate of foam cores that have been mechanically compressed tends to be slower than the expansion rate of foam cores that have been compressed in a hyperbaric chamber or with air bladders. With respect to boat collars, some foam cores, especially larger cores, may not reach the point at which the sleeve arrests further expansion for two days or more.  
         [0044]     In some situations, eliminating the delay associated with a low foam core expansion rate may be desirable. For example, in the manufacture of foam cored boats, the installation of the boat collars may be one of the final steps of a production schedule. In such a case, a final inspection and delivery of the boat could be delayed longer than desired. Shown in  FIG. 4  is an arrangement that allows the foam collars to be fully serviceable when a compressed foam core is installed to form the boat collar. This arrangement also facilitates removal of the foam core from the collar should replacement or repair be required.  
         [0045]      FIG. 4  differs from previously described  FIG. 3C  in two respects. First, in its uncompressed state, foam core  50  of  FIG. 4  is an oversized core that corresponds to the full cross-sectional geometry of the containment sleeve (formed by the zipped-together upper and lower sponson panels  36  and  38 ). Second, an air bladder  52  occupies all or a portion of the space occupied by spacer  46  in  FIG. 3C . That is, air bladder  52  is positioned between back plate  32  and compressed foam core  50 .  
         [0046]     Although not specifically shown in the figures, it can be recognized that foam core  50  and air bladder  52  are installed on a boat in the same manner as was described relative to  FIG. 3A-3C . That is, with zipper  40  open, air bladder  52  (in a deflated state) is placed in abutment with back plate  32  and the flat surface of D-shaped foam core  50  is placed against the outboard side of air bladder  52 . The upper and lower sponson panels  36  and  38  are then zipped together with zipper  40  to fully encase compressed foam core  50  and air bladder  52 . Air bladder  52  is then inflated to a pressure at which foam core  50  presses against the interior surfaces of zipped-together upper and lower sponson panels  36  and  38  in a manner substantially the same as what would occur if foam core  50  were allowed to expand without air bladder  52  being inflated. To allow inflation and deflation, air bladder  52  includes a valve such as, or similar to, the valve stems used for inflation of vehicle tires. In  FIG. 4 , a valve stem  54  is shown projecting downwardly from the lower leg of back plate  32 . In arrangements in which the sponson extends aft of the boat transom, air valve  54  preferably extends through the sidewall of back bracket  32  at a position aft of the transom. Regardless of the location of air valve  54 , foam core  50  of the arrangement shown in  FIG. 4  is allowed to expand by periodically allowing air to escape from air bladder  52  via air valve  54 . When foam core  50  has expanded to the maximum state allowed by zipped-together upper and lower sponson panels  36  and  38 , air bladder  52  will contain little or no air.  
         [0047]     As previously noted, the arrangement of  FIG. 4  also allows foam core  50  to be easily removed for replacement or repair. Specifically, to gain access to or remove foam core  50 , air bladder  52  is inflated to compress foam core  50  to a point at which it easily can be removed by unzipping zipper  40 . In that regard, when foam core  50  has been compressed sufficiently, air bladder  54  is deflated, zipper  40  is opened, and foam core  50  is exposed for removal or repair.  
         [0048]     While the invention has been described in terms of its currently preferred implementation, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention. For example, although the arrangements discussed relative to  FIGS. 1-4  utilize air bladders, bladders inflated with other gases and/or various fluids, such as water, can be used. Additionally, the various materials that encompass the foam cores both during compression and as the sleeve or shell that surrounds the finished foam core item may depart from those that have been described. Specifically, any materials that provide the described functional characteristics can be employed.  
         [0049]     The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: