Abstract:
A cover ( 200 ) for inhibiting corrosion of a metallic object over which the cover is placed. The cover has an inner surface ( 104 ) defined by a liquid-permeable layer ( 202 ) and an outer surface ( 102 ) defined by a liquid-impermeable layer ( 204 ). A moisture-absorbing layer ( 206 ) is sandwiched between the liquid-permeable layer and the liquid-impermeable layer. The liquid-permeable layer allows vapor and liquid moisture beneath the cover to be absorbed into the moisture-absorbing layer to reduce the amount of moisture beneath the cover. The liquid-impermeable layer repels environmental liquid moisture, such as rain, sea spray, dew and the like and prevents such moisture from penetrating the cover. A radar-influencing layer ( 308 ) and vapor corrosion inhibitors ( 214 ) may be included in the cover. A method of protecting an object is also disclosed. The method includes covering a metallic object with cover ( 200 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation of U.S. application Ser. No. 09/557,845, filed on Apr. 26, 2000, the entire disclosure of which is incorporated by reference into this application. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention generally relates to the field of covers for protecting materials from environmental elements. More particularly, the present invention is directed to a flexible cover that actively inhibits the corrosion of a metallic object on which the cover is placed.  
       BACKGROUND OF THE INVENTION  
       [0003]     Corrosion and corrosion mitigation have become increasingly important for economic and safety reasons. Based on estimates made in the mid 1990&#39;s, overall costs attributable to corrosion account for over $100 billion a year in the United States alone. These costs typically account for only the direct costs of corrosion and do not include the associated indirect costs, such as safety, plant downtime, loss of product, contamination and over-design.  
         [0004]     Corrosion is defined as the destructive result between a metal or metal alloy and its environment. Nearly every metallic corrosion process involves the transfer of electronic charge in aqueous solution, and most corrosion reactions take place in the presence of water in either liquid or condensed vapor phases and also in high humidity.  
         [0005]     Corrosion is particularly a problem in marine environments, such as shipboard, off-shore drilling rigs, coastal regions and the like, where seawater enhances corrosion reactions due to increased ion transport, pH effects and elevated dissolved oxygen levels that in turn enhance levels of hydrogen ions. Corrosion reactions are further accelerated in marine environments by contaminants, such as chloride ions, present in seawater. Corrosion damage to equipment stored and used in marine environments is a tremendous problem, impacting maintenance costs, availability, repair and reliability.  
         [0006]     Equipment stored, for example, onboard a ship or in coastal regions, is often stored in protective storage systems that have proved to be less than optimally effective. At best, such equipment is covered with waterproof tarpaulins, although often, especially for shipboard equipment, it is not stored properly and is directly exposed to a marine environment, which leads to rapid corrosion. Even when equipment is covered by waterproof tarpaulins, seawater still penetrates through and/or around the tarpaulins into the protected spaces where it collects and corrodes the underlying equipment. Also, conventional storage systems can be cumbersome to use and maintain, and are often avoided. As a result, corrosion continues to be a significant and costly problem, requiring many hours of rust removal, painting and repair that lead to premature equipment replacement.  
         [0007]      FIG. 1  shows a conventional waterproof cover  20  used to protect metallic objects, such as metallic block  22  shown resting on a surface  24 , from moisture, such as rain, sea spray, dew and the like. Cover  20  has an outer surface  26 , an inner surface  28  and an area  30  defined by a peripheral edge  32 . Cover  20  is shown covering block  22  in a typical manner, wherein a micro-environment, is generally defined by the space enclosed by cover  20 . The micro-environment comprises a number of interior regions, such as regions  34 , located between cover  20  and block  22 .  
         [0008]     Generally, prior art covers comprise at least one liquid-impermeable layer made of, for example, a tightly-woven polymer fabric. More complex prior art covers may include one or more additional layers that provide the inner surface with a non-abrasive texture to minimize mechanical damage to the object covered. Other prior art covers are made of vapor-permeable materials, such as expanded polytetrafluoroethylene or the like.  
         [0009]     Interior regions  34  generally never have a moisture content less than that of the ambient environment. If the moisture content of the ambient environment rises, the moisture content of regions  34  also rises due to the inflow of moisture (illustrated by arrow  36 ) through gaps between cover  20  and surface  24  at peripheral edges  32 . Eventually, the moisture content of the ambient environment  38  and regions  34  equalize. Once the additional moisture is in the micro-environment, it can become trapped, as illustrated by arrows  40 . Moisture levels can quickly become elevated and the air saturated. In such a case, condensation could occur on the block  22 . Because the moisture content of interior regions  34  never falls below that of ambient environment  38 , prior art covers are not very effective in high moisture environments, such as marine and high-humidity environments. Moreover, once moisture enters the micro-environment, it can take a long time to dissipate, if at all.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention is directed to a cover for inhibiting corrosion of a metallic object. The cover includes a first layer having a first face and a second face. The first layer comprises a super-absorbent material adapted to absorb and store moisture. A second layer is located adjacent the first face of the first layer. The second layer is liquid permeable. A third layer is located adjacent the second face of the first layer. The third layer is liquid-impermeable. A radar-influencing layer is located within or adjacent at least one of the first layer, second layer and third layer. The radar-influencing layer comprises a radar-influencing material.  
         [0011]     In another aspect, the cover of the present invention includes a first layer having a first face and a second face. The first layer comprises a super-absorbent material adapted to absorb and store moisture. A second layer is located adjacent the first face of the first layer. The second layer is liquid permeable. A third layer is located adjacent the second face of the first layer. The third layer is liquid-impermeable. A vapor corrosion inhibitor layer is located within or adjacent at least one of the first layer, second layer and third layer. The vapor corrosion inhibitor layer comprises a vapor corrosion inhibitor.  
         [0012]     In yet another aspect, the cover of the present invention includes a panel having a first face, a second face and a peripheral edge. The panel includes a first layer having a first face and a second face. The first layer comprises a super-absorbent material adapted to absorb and store moisture. A second layer is located adjacent the first face of the first layer. The second layer is liquid permeable. A third layer is located adjacent the second face of the first layer. The third layer is liquid-impermeable. The panel includes a fastening means located adjacent the peripheral edge adapted to removably fasten said panel to a similar panel.  
         [0013]     The invention is also directed to a method of inhibiting corrosion on a metallic object. First, a cover is provided. The cover includes a first layer having a first face and a second face. The first layer comprises a super-absorbent material adapted to absorb and store moisture. A second layer is located adjacent the first face of the first layer. The second layer is liquid permeable. A third layer is located adjacent the second face of the first layer. The third layer is liquid-impermeable. Next, at least a portion of the metal object is covered with the cover such that the second layer faces the object. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     For the purposes of illustrating the invention, the drawings show a form in which the invention may be embodied. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.  
         [0015]      FIG. 1  is a cross-sectional view of a prior art cover shown covering an object;  
         [0016]      FIG. 2  is a cross-sectional view of a corrosion inhibiting cover of the present invention shown covering an object;  
         [0017]      FIG. 3  is a cross-sectional view of a portion of one embodiment of the corrosion inhibiting cover of the present invention;  
         [0018]      FIG. 4  is a cross-sectional view of a portion of an alternative embodiment of the corrosion inhibiting cover of the present invention;  
         [0019]      FIG. 5  is an enlarged view of one edge of the cover shown in  FIG. 2 , for one specific embodiment of the present invention;  
         [0020]      FIG. 6  is a perspective view showing an embodiment of the corrosion inhibiting cover of the present invention comprising a plurality of panels removably secured to one another; and  
         [0021]      FIG. 7  is an enlarged cross-sectional view of one of the peripheral edges of one of the panels taken along line  7 - 7  of  FIG. 6 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     Referring now to the drawings, wherein like numerals indicate like elements,  FIG. 2  illustrates a corrosion-inhibiting cover, which is generally denoted by the numeral  100 . Cover  100  is preferably made of flexible materials and includes an outer surface  102  and an inner surface  104 . In some cases rigid materials, often formed with a configuration corresponding to that of the object to be covered, may be used for cover  100 . Cover  100  has a peripheral edge  106  that defines an area  108 , which may be shaped as desired to suit a particular application. When draped over an object, such as a metallic block  10  resting on a surface  112 , outer surface  102  is exposed to an ambient environment  114  and inner surface  104  defines a micro-environment comprising a number of interior regions, such as those denoted as  116 , located between inner surface  104  and block  110 .  
         [0023]     Although metallic block  110  is generally protected from elements present in ambient environment  114  by cover  100 , moisture from ambient environment  114  tends to infiltrate (as illustrated by arrow  118 ) interior regions  116  through gaps between peripheral edge  106  of cover  100  and surface  112 . However, the materials and structure of cover  100  allow it to absorb and store such infiltrating moisture (as illustrated by arrows  120 ) from within interior regions  116  and maintain the moisture content of the micro-environment at a low level, below that of ambient environment  114 . Cover  100  is also able to absorb and store by wicking action any water present on the surface of block  110  that comes into contact with inner surface  104 . This low-moisture micro-environment inhibits metallic block  110  from corroding. In addition to the ability to absorb and store moisture, cover  100  may be provided with the ability to passively regenerate its moisture-absorbing and storing features by allowing stored moisture to diffuse to the outer surface of the cover, where it can evaporate (as illustrated by arrows  122 ) into ambient environment  114  when conditions there are suitable for evaporation.  
         [0024]     Beneficial features of the flexible cover  100  of the present invention are that it can be made to any size and shape necessary to protect an object having virtually any size and surface profile. Some diverse examples of such objects are containers for container ships, deck-mounted guns on naval ships, construction equipment, stored construction materials, air conditioning units and barbeque grills, to name just a few. Pouches of flexible cover  100  could be fashioned to store munitions, tools, handguns and telephones and other electronic devices to name just a few. One skilled in the art will recognize that there is a vast range of applications for cover  100 .  
         [0025]     Referring now to  FIG. 3 , there is shown one specific embodiment of corrosion-inhibiting cover  100  of the present invention, which is identified at  200 . Cover  200  comprises three layers consisting of a liquid-permeable layer  202 , a liquid-impermeable layer  204  and a moisture-absorbing layer  206  sandwiched between liquid-permeable layer  202  and liquid-impermeable layer  204 . With reference to  FIGS. 2 and 3 , liquid-permeable layer  202  forms inner surface  104  of cover  200  and retains the constituent materials of moisture-absorbing layer  206  within cover  200 . Liquid-permeable layer  202  is vapor permeable to allow moisture vapor within interior regions  116  to reach moisture-absorbing layer  206 , and liquid-permeable to allow any liquid water contacting inner surface  104  of cover  200  to be wicked into moisture-absorbing layer  206 . Preferably, liquid-permeable layer  202  has a water transmission rate of greater than 10 g/m 2 -hr. Liquid-permeable layer  202  should be made of a durable woven or non-woven material that can withstand repeated use and continual contact with a wide variety of surfaces. It is also preferable that liquid-permeable layer  202  be relatively smooth and/or soft so that damage to any object contacted by liquid-permeable layer  202  is avoided. A preferred material for liquid-permeable layer  202  is polyester mesh Style No. 9864, available from Fablock Mills, Murry Hill, N.J. Other suitable materials include nylon, polypropylene, or the like and are available from Fablock Mills Inc., Murry Hill, N.J., Jason Mills Inc., Westwood, N.J., and Apex Mills, Inwood, N.Y. among others. Moisture-absorbing layer  206  includes a fiber matrix  210  and a super-absorbent material  208 , such as hydrogel. Preferably, the super-absorbent material  208  is in particulate or fiber form, which allows it to be dispersed throughout the fiber matrix. Alternatively, however, super-absorbent material  208  may be located in a generally discrete layer within fiber matrix  210 , which may comprise either a woven or non-woven material. Examples of acceptable materials for fiber matrix  210  include wool, fiberglass, polymer fleece, fluff wood pulp and the like. It is desirable that fiber matrix  210  have a high capillarity, preferably greater than 10 g/m 2 -hr., so that moisture coming into contact with moisture-absorbing layer  206  through liquid-permeable layer  202  may be wicked deep into moisture-absorbing layer  206  to take advantage of the super-absorbent material located there. Although a fiber matrix is shown, it may be eliminated in an alternative embodiment having a hydrogel or other super-absorbant material in a form that need not be supported by and/or located within a fiber matrix.  
         [0026]     Hydrogel, one example of a class of super-absorbent materials, is capable of absorbing up to 400 times its weight in water. With such a large absorption capability, the particles of hydrogel can swell to many times their original size. If the hydrogel particles are not distributed properly throughout fiber matrix  210 , moisture-absorbing layer  206  may experience hydroblocking, wherein the hydrogel particles closest to the moisture source swell so much that they block moisture from being wicked farther into the fiber matrix. Although some of the absorbed moisture eventually reaches the hydrogel located deep within fiber matrix  210  by diffusion, diffusion is a slow process that would degrade the usefulness of a cover experiencing hydroblocking, particularly in high-moisture conditions. Therefore, care must be taken to distribute super-absorbent material  208  within fiber matrix  210  in a manner such that when the super-absorbent material adjacent the mesh layer is saturated, the fiber matrix is still able to wick water deeper into the moisture-absorbing layer.  
         [0027]     Liquid-impermeable layer  204  defines outer surface  102  of cover  200  and prevents liquid in ambient environment  114 , such as rain, sea spray, dew and the like, from reaching interior regions  116  beneath the cover. It is preferable, however, that liquid-impermeable layer  204  be vapor-permeable material to allow moisture stored in moisture-absorbing layer  206  to escape into ambient environment  114  by diffusion and evaporation as described above. Preferably, liquid-impermeable layer  204  has a vapor transmission rate of greater than 1 g/m 2 -hr. The liquid transmission rate through the liquid-impermeable layer  204  should be less than the employed vapor transmission rate for the liquid impermeable layer. For the stated lower bound of 1 g/m 2 -hr. of vapor transmission through the liquid-impermeable layer  204 , a liquid transmission rate through the liquid-impermeable layer  204  could be any value less than 1 g/m 2 -hr. If the vapor transmission rate were greater, the corresponding acceptable level of liquid transmission would be greater, as long as it remained less than the vapor transmission rate. By allowing stored moisture to escape, cover  200  is capable of regenerating itself during periods of low ambient moisture so that it is capable of storing more moisture during a subsequent period when interior regions  116  again become moisture laden. Beneficially, the liquid-impermeable layer should also be able to absorb solar energy to provide heat to cover  200  that accelerates regeneration of moisture-absorbing layer  206 .  
         [0028]     Liquid-impermeable layer  204  may comprise a woven material, a non-woven material or a combination of the two. A preferred vapor-permeable material for liquid-impermeable layer  204  is a laminate of  200  denier nylon inner layer and a breathable urethane outer layer, available from LAMCOTEC Incorporated, Monson, Mass. Other vapor-permeable materials, such as expanded polytetrafluroethylene, GORE-TEX® fabric (W. L. Gore &amp; Associates, Inc., Newark, Del.), SUNBRELLA® fabric (Glen Raven Mills Inc., Glen Raven, N.C.), Hub Semi-Permeable fabric (Hub Fabric Leather Company, Everett, Mass.) or the like, may alternatively be used.  
         [0029]     In an alternative embodiment, cover  200  may further include a heating element  212  that would allow moisture-absorbing layer  206  to regenerate more quickly or regenerate when the conditions in ambient environment  114  would otherwise not permit evaporation of the stored moisture. Such a heating element may comprise an electrical resistance wire grid located within one of the layers or between adjacent layers. Alternatively, the heating element may comprise arrays of thin, flexible heating elements consisting of etched-foil resistive elements laminated between layers of flexible insulation like KAPTON®, NOMEX®, silicone rubber, or mica, or arrays of thin film ceramic elements available from Minco Products Incorporation, Minneapolis, Minn. and Watlow Gordon, Richmond, Ill. among others (KAPTON® and NOMEX® are registered trademarks of E.I. DuPont de Nemours and Company, Wilmington, Del.).  
         [0030]     In another alternative embodiment, the cover may further include a Vapor Corrosion Inhibitor (also known as “Volatile Corrosion Inhibitor”) (VCI)  214  incorporated into one or more of layers  202 ,  204  and  206 , preferably in the fiber matrix the moisture-absorbing layer, or into an additional layer. VCIs  214  are volatile compounds that emit ions that condense on metallic surfaces to form a mono-molecular layer that interacts with corrosion agents to protect the surface. VCIs  214  are continuously self-replenishing and environmentally benign. Examples of VCIs that may be used with the cover of the present invention include mixtures of materials selected from amine salts, ammonium benzoate, triazole derivatives, alkali dibasic acid salts, alkali nitrites, tall oil imidazolines, alkali metal molybdates, and the like which can be supplied by Cortec Corporation, St. Paul, Minn., Daubert Coated Products Incorporated, Westchester, Ill., Poly Lam Products, Buffalo, N.Y., Mil-Spec Packaging of Georgia Incorporated, Macon, Ga., and James Dawson Enterprises Limited, Grand Rapids, Mich., among others.  
         [0031]     The addition of a VCI  214  to cover  200  enhances the corrosion inhibiting ability of the cover by allowing the cover to continue to provide protection when the moisture-absorbing layer is overwhelmed. In addition, the VCI  214  benefits from moisture-absorbing layer  206  because the moisture-absorbing layer removes the burden from the VCI by not requiring it to offer protection at all times. One or more VCIs may be added to any embodiment of the cover of the present invention, such as those shown in  FIGS. 4-7 .  
         [0032]     The layers of cover  200  are preferably bonded to one another throughout area  108  of cover  200  in a manner that does not interfere with its liquid and vapor transport features, yet retains the layers in physical proximity to one another. Bonding processes known in the art may be used to bond or join the layers of cover  200 . Bonding processes such as thermal bonding or multi-component adhesive bonding could be used to bond individual layers or the entire cover  200 . Other bonding processes known in the art, however, may be used.  
         [0033]     Alternatively, the layers may be secured to one another by other means such as stitching. Depending on the size and materials of the cover, it may only be necessary to provide stitching adjacent peripheral edge  106 . Otherwise, it may be necessary to provide quilt-stiching throughout the area. In a further alternative embodiment, liquid-impermeable layer  204  may be removably secured to the other two layers  202  and  206  to allow it to be removed to speed regeneration of the moisture-absorbing layer. Re-fastenable fasteners, such as hook-and-loop fasteners, snaps, zippers and the like, may be provided to facilitate this feature. Additionally, the moisture-absorbing layer  206  could be bonded or formed via an airlaid process known in the art as a process of producing a nonwoven web of fibers in sheet form where the fibers are transported and distributed via air flows where the entire sheet is then set with a mixture of binders and resins.  
         [0034]      FIG. 4  shows another specific embodiment of corrosion inhibiting cover  100  of the present invention, which is identified at  300 . Cover  300  comprises the three basic layers of cover  200 , shown in  FIG. 3 , i.e., a liquid-permeable layer  302 , a liquid-impermeable layer  304  and a moisture-absorbing layer  306  (these layers being identical, respectively, to layers  202 ,  204  and  206 ). In addition to these layers, cover  300  further includes a radar-influencing layer  308 . Radar-influencing layer  308  may comprise a radar-absorbing material  310 , a radar-reflecting material  312  or a combination of both, depending upon the desired radar profile of cover  300 . With reference to  FIG. 2 , it may be preferable to have entire area  108  of cover  300  be radar-attenuating. For example, in a military application it may be necessary to reduce the radar profile of a large object to conceal its identity. On the other hand, it may be preferable to have entire area  108  be radar-enhancing. For example, in a civilian application it may be advantageous to increase the radar profile of a small water craft to accentuate its presence. In another instance, it may be desirable to provide area  108  with alternating discrete radar-attenuating and radar-enhancing regions to give the cover a custom radar profile.  
         [0035]     Although radar-influencing layer  308  is shown located between liquid-impermeable layer  304  and moisture-absorbing layer  306 , it may be located elsewhere. For example, the radar-influencing layer may be located between moisture-absorbing layer and the liquid-permeable layer, adjacent outer surface  102  of cover  200  or the like. In addition, radar-absorbing material  310  and radar-reflecting material  312  may be incorporated into one or more of liquid-permeable layer  304 , moisture-absorbing layer  306  and liquid-permeable layer  302 . Care must be taken, however, to select a material that does not interfere with the vapor and liquid transport features of cover  300 .  
         [0036]     Radar-absorbing material  310 , may comprise polypyrrole-coated polyester fibers or the like which may be made into a thread that is then woven into a discrete fabric layer or the outer layer. Such textiles are available from Milliken &amp; Co., Spartanburg, S.C. under the trademark CONTEXT®. Alternatively, radar-absorbing material  310  may comprise discrete particles of graphite or the like dispersed within the fiber matrix or within a coating that is applied to liquid-impermeable layer  304  or is applied to a separate layer that is then incorporated into the cover. Other examples of radar-absorbing materials are REX radar-absorbing mats (Milliken &amp; Co., Spartanburg, S.C.) and RFWP Weatherproof Foam (R&amp;F Products, Inc., San Marcos, Calif.). Similar techniques may be used for radar-reflecting material  312 , except that a metal or the like, which may be provided as a thread or as discrete particles is incorporated into one or more layers of cover  300 .  
         [0037]     Referring now to  FIGS. 2 and 5 , there is shown yet another corrosion inhibiting cover  100  of the present invention, which is identified at  400 . In  FIG. 5 , cover  400 , which has a five layer construction, is shown with its peripheral edge  106  contacting surface  112 , such as a ship&#39;s deck, a tarmac or the like. In such applications, it is common for a large amount of liquid water to be absorbed by cover  400  at regions adjacent peripheral edge  106 . This is so because much of the water from ambient environment  144 , such as rain, sea spray, dew and the like, repelled by area  108  travels down the sloping portions of cover  400 , ending up adjacent peripheral edge  106 . In order to prevent saturation of cover  400  in regions adjacent peripheral edge  106 , additional layers may be added to the basic three layer structure of  FIG. 3  to provide a separate zone for absorbing and storing moisture that may accumulate on surface  112 .  
         [0038]     Accordingly, cover  400  includes an outer liquid-impermeable layer  402 , a first moisture-absorbing layer  404 , an intermediate liquid-impermeable layer  406 , a second moisture absorbing layer  408  and a liquid-permeable layer  410 , which are located adjacent one another in the named order, except at a stepped region adjacent peripheral edge  106 . The primary purpose of outer liquid-impermeable layer  402  is to prevent liquid water, such as rain, sea spray, dew and the like, from penetrating into the micro-environment beneath cover  400 . Outer liquid-impermeable layer  402  includes a return to provide a robust structure at peripheral edge  106 . The primary function of first moisture absorbing layer  404  is to absorb and store moisture that collects on surface  112 , whereas the primary function of second moisture absorbing layer  408  is to absorb and store moisture trapped in the micro-environment beneath cover  400 .  
         [0039]     Intermediate liquid-impermeable layer  406  prevents liquid moisture stored in each of the moisture-absorbing layers from migrating to the other of such layers. At regions adjacent peripheral edge  106 , this separation prevents second moisture-absorbing layer  408  from becoming over-burdened by moisture from surface  112 . Preferably, both liquid-impermeable layers are vapor permeable to allow cover  400  to passively regenerate by losing stored moisture to ambient environment  114  when conditions there permit.  
         [0040]     Peripheral edge  106  of the intermediate liquid-impermeable layer  406  is laterally spaced from peripheral edge  106  around the entire periphery of cover  400  to define an opening  412 . When cover  400  is draped over an object, such as metallic block  110 , opening  412  contacts or is slightly spaced from surface  112 , allowing any moisture present on surface  112  to be wicked into first moisture-absorbing layer  404 . Depending on design parameters, such as materials selected, volume of moisture to be absorbed and the like, the width  414  of opening  412  may be varied accordingly.  
         [0041]      FIGS. 6 and 7  show a corrosion inhibiting cover  500  according to the present invention, wherein cover  500  is penalized into a number of discrete panels, each denoted  502 , and having an outer surface, an inner surface and a peripheral edge. Panels  502  are removably secured to one another, and are removably securable to other panels (not shown) of similar construction, with fasteners  504  located adjacent the peripheral edge of cover  500 . Panelization allows cover  500  of the present invention to be assembled to fit the size and shape necessary for a particular application. To further enhance customization, one or more of the panels may be formed into a shape other than the rectangular shapes shown in  FIG. 6 .  
         [0042]     Fasteners  504  may be of the hook-and-loop type, which includes a flexible hook strip  506  secured to the outer surface of cover  500  and a flexible loop strip  508  secured to the inner surface. Loop strip  508  is preferably liquid-permeable so that its presence does not interfere with the moisture absorbing properties of cover  500  at its peripheral edge. Such hook-and-loop fasteners may be VELCRO® brand hook-and-loop fasteners (Velcro Industries B.V., Curacao, Netherlands) or the like. Alternatively, other fasteners such as buttons, zippers, snaps, hook and eyelet, eyelet and lacing or the like, may be used for fasteners  504 .  
         [0043]     In the embodiment shown, each panel  502  comprises the basic three-layer structure of a liquid-impermeable outer layer  510 , a moisture-absorbing layer  512  and a liquid-permeable inner layer  514 . Alternatively, each panel  502  may be modified to include the plural moisture-absorbing layer structure shown in  FIG. 5  and/or the radar-influencing layer  308  shown in  FIG. 4 .  
         [0044]     Although the invention has been described and illustrated with respect to the exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changed, omissions and additions may be made therein and thereto, without parting from the spirit and scope of the present invention.