WO2008017118A1

WO2008017118A1 - Air supported cover

Info

Publication number: WO2008017118A1
Application number: PCT/AU2007/001117
Authority: WO
Inventors: Gary Keith Thorpe
Original assignee: Department of Agriculture and Fisheries
Current assignee: Queensland Department of Primary Industries and Fisheries
Priority date: 2006-08-09
Filing date: 2007-08-09
Publication date: 2008-02-14
Anticipated expiration: 2009-02-09
Also published as: AU2007283455A1

Abstract

An air supported cover (10) is described formed from a central panel (14) and peripheral weight pipe arrangement. The weight pipe arrangement is formed from one or more weight pipes 12. The weight of the weight pipe arrangement may be varied by addition of more weight pipes or introduction of material into one or more internal cavities of the weight pipe or pipes. The central panel 12 may have a peripheral sleeve 22 to receive the weight pipes. The cover may include a side curtain (94) and internal purge vent or vents (140). Adjacent covers may be joined by a joining strip (115). The cover is particularly suitable for use on water.

Description

TITLE

"AIR SUPPORTED COVER " FIELD OF THE INVENTION

The present invention relates to an air supported cover. The cover is particularly useful for a body of water such as a pond, pool, dam or other substantial body but is not so limited. In one application, the invention is directed to a floating cover which holds a volume or air or other gas adjacent to a water surface. The floating cover or covers may be particularly suitable for use in aquaculture. BACKGROUND OF THE INVENTION

Bodies of water such as pools, ponds, dams, tanks and similar are used for a variety of applications such as recreational use in swimming and industrial purposes such as aquaculture. The need often arises to attempt some control of the temperature of such a body or to otherwise cover its surface or part thereof. The need to provide covers in other environments, such as on land, also often arises.

One of the most common responses to the need to cover a body of water is the swimming pool blanket which is a flat blanket positioned on the surface of the body of water and which may be rolled onto and off that surface as required. This blanket is usually formed of a transparent or semi- transparent material which allows sunlight entry into the water body to thereby heat it and at the same time restricts heat loss through convection and wind effects. The pool blanket however prevents gaseous exchange at the air/water interface. This latter effect is undesirable in situations where gaseous exchange is important for maintaining the quality of the water for applications such as aquaculture and maintenance of the health of animals in a husbandry situation. In these cases, it may be important to increase the oxygen transferred from air into the water body while at the same time releasing unwanted gases such as carbon dioxide from the body of water.

US Patent No. 5,839,391 to Shaar discloses an aquaculture system which includes floating surface panels to provide thermal insulation. The circular panels allow an air bubble to form between the pond surface and the panel to aid in thermal insulation. The device has a floatable frame configured to float on a surface of the pond and a flexible water impermeable sheet disposed within the floatable frame to form a thermal and evaporative insulating seal on a surrounded portion of the pond.

The floating frame may be constructed of PVC pipe. The frame members may be constructed of any buoyant or floatable material and the preferred panels are 8 by 8 feet in size. This is a limitation in the disclosed invention. Due to the relatively light weight of the PVC pipe, the anchoring effect of the frame is limited. Any significant size of the cover will lead to instability in operation particularly during periods of wind. The overall structure will be inclined to sail readily before the wind and also will be subject to deformation and lifting due to the lightweight nature of the structure. This presents a problem in covering substantial areas such as in a commercial aquaculture centre where ponds may be several hectares in size. This lightness of construction is a result of the components and also leads to the need to provide drainage from the plastic sheeting in the devices. The drains are provided at each corner and allow run-off under the water. In the absence of the drains, rainwater will tend to flatten the domed sheeting, accumulate and expel air under the sheeting and virtually "sink" the device or at least reduce it to a flat blanket type effect. This then creates a problem in returning each of the panels to a proper operative configuration.

Given the size limitations of the device, it is necessary to use a substantial number of covers to provide significant coverage. This is less cost effective in manufacture and also leads to increased rubbing, abrasion and damage between adjacent covers. The cost of manufacture is significant as a 1 hectare pond may need over 1000 units of 3 metres x 3 metres. Multiple small units also require a large effort in after-season cleaning and storage. Further, the presence of multiple small units requires a complex air delivery system to provide individual supply. The presence of many covers may also interfere with artificial currents in a pond necessitating larger paddlewheels, more of them and increased capacity in drive motors for the paddlewheels and aerators.

The inability to tension the covers with air limits the size of the device and precipitates the above problems. The presence of numerous covers also makes dismantling more difficult, particularly if urgently needed as in the onset of severe weather conditions.

International Application No. WO 00/02443 to Becchi discloses a floating apparatus consisting of an inflatable cover for positioning above known devices for aeration of the water. It is provided with a shut-off valve controlled by a float for regulating the flow of oxygen to the inside of the floatable cover. As a result, oxygen is used efficiently while the cover is always kept in the floatable condition. The device is not a thermal or evaporation cover. It is relatively complex and uses a jet pulsed upwards by a fixed pipe into the cover which is supported on a raft. The frame is supported by four floats which are rigidly connected to it.

Neither of the above documents disclose a mechanism for providing a relatively stable cover water which may be dimensioned to cover a significant surface area of, for example, water. SUMMARY OF THE INVENTION

In a first broad form, the invention may reside in an air supported cover for a surface, the cover comprising: a weight pipe arrangement positioned peripherally to secure the cover to the surface, the weight pipe arrangement including one or more weight pipes; and a central panel connected to the weight pipe arrangement and adapted to trap a layer of air or gas adjacent the surface; wherein: the weight pipe arrangement is adapted to allow variation of its weight. The weight pipes may comprise tubular elements. The tubular elements may extend around the weight pipe arrangement and may comprise a single tubular element extending around the periphery of the cover. In one embodiment, the weight pipe arrangement may comprise two independent tubular elements to facilitate variation of the weight pipe arrangement by adding or removing one or more of the weight pipes to the air supported cover. One may be positioned medially to the other and extend around the periphery of the cover. The two tubular elements may be abutting or spaced. They may be attached each to the other. They may be formed integrally with different materials introduced to their internal chambers. Alternatively, one tubular element may be positioned internally in the other tubular element.

The weight pipe arrangement may be adapted to allow variation of the contents of one or more internal chambers in the weight pipe/s to vary its weight.

One form of suitable tubular element is a polyvinyl chloride pipe preferably in the range of 200 to 600 mm diameter. A particularly suitable form of tubular element may be a flat tubing or "lay fiat" form of pipe or a polyethylene type. In a further alternative embodiment the weight pipe arrangement may comprise three or more tubular elements. A plurality of tubular elements may be located internally in another tubular element. The weight pipe arrangement may include a telescopic portion to allow variation of the circumference of the tubular element or elements and thereby variation of the circumference of the weight pipe arrangement. The central panel may be formed as a single sheet member connected to the weight pipe arrangement and extending across an internal space defined by the weight pipe arrangement. The central panel may be formed of a transparent or translucent material. The central panel may be formed as two spaced sheets where a first sheet is positioned under the second sheet such that it sits above the water surface and below the second sheet in operation, preferably with an air layer between the two sheets.

The central panel may include reinforcing means to reinforce the sheet or sheets. The reinforcing means may be reinforcing bands. Alternatively, the reinforcing means may be formed as a mesh-like reinforcing material preferably extending substantially over the entirety of the sheet material. Other means of reinforcing may be used as appropriate.

The central panel may be connected to the weight pipe arrangement by a sleeve formed on a periphery of the central panel and adapted to receive the weight pipe arrangement. A separate sleeve may be formed for each tubular element, or alternatively where there are two or more tubular elements, all may be located within a single sleeve.

The tubular element or elements may be formed from flat tubing ("lay flat") which is expanded by the introduction of contents into a central lumen or chamber.

The contents of the internal chamber of the one or more tubular elements may comprise one or more of a liquid, a gas and a solid. The liquid may preferably comprise water, although other liquids may be suitable. The gas may be air. The solid may include an expanded foam, such as a Styrofoam type material. The contents of the internal chamber may be pressurised.

The weight pipe arrangement may be adapted to allow variation of the contents of each internal chamber through an entry port. The entry port is preferably resealable in operation. The entry port may be formed as one or more valve type arrangements to allow introduction of contents to the internal chamber. A separate entry port or valve may be provided for gas and a further valve arrangement provided for liquid.

In another aspect, the invention may reside in a system of two or more covers substantially as disclosed above in co-operating position. The two or more covers may be adjoining and connected by adjacent weight pipe arrangements overlapping.

Alternatively, a first cover may be located or nested inside a second larger cover to provide a double layer of covering. The central panel of each may be formed of polarised material. Relative rotation between the first inside cover and second larger, outer cover may vary penetration of light through the two covers.

The invention may include or comprise a joining strip or strips having two slots, each slot having a mouth narrower than the slots widest dimension and adapted to receive an inflatable tube. Inflation of the tube locks it in the slot and the tube is secured to a flap on a cover to thereby lock the cover to the joining strip. An adjoining cover is locked to the same strip to thereby secure the cover and adjoining cover together.

In a further embodiment, the invention may include or comprise an internal purge vent. The internal purge vent may comprise a base, a weight and an open-ended tube mated to or adapted to mate to the central panel. The purge vent may be connected directly or indirectly to the central panel. The invention may reside in venting an air supported cover by installing one or more internal purge vents in the cover. In a further aspect, the invention may reside in a method of providing a cover for a surface, the method comprising the steps of: forming a peripheral frame structure from one or more elongate members each preferably having an internal compartment or compartments; providing means to vary the contents within the internal compartment or compartments to thereby vary the density of the peripheral frame structure; and fixing a flexible sheet material to the peripheral frame structure to enclose the area defined by the frame structure and thereby forming a central cover.

Preferably providing means to vary the contents of the internal compartments includes the step of providing one or more apertures to access the internal compartment or compartments to introduce different content elements. This step may involve providing one or more valve type arrangements to permit access into the internal compartment. Alternatively, the method may comprise providing two or more separate or attached elongate elements of the frame structure each able to contain variable contents which may be in the form of liquid, gas or solid as preferred.

The central cover preferably is adapted to hold a volume of air or other gas adjacent a surface of a body of water.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of a first embodiment of an air supported cover of the present invention suitable for use on water.

FIG. 2 is a cross sectional view of the air supported cover of FIG. 1 taken along the line AA.

FIG. 3 is a cross sectional view of an alternative view of a weight pipe arrangement.

FIG. 4 is a cross sectional view of a further embodiment of a weight pipe arrangement.

FIG. 5 is a side view of a feature in a weight pipe for the variation of contents.

FIG. 6 is a cross sectional view of two adjacent floating covers engaged by overlapping. FIG. 7 is a top plan view of an arrangement for a pond with adjacent overlapping floating covers.

FIG. 8 is a top view of a series of alternative arrangements which may be utilised in substantially the same pond surface area to provide alternative coverage. FIG. 9 is a cross sectional view of two nested weight pipe arrangements for overlaid covers.

FIG. 10 is a sectional view of a telescopic portion of a weight pipe arrangement.

FIG. 11 is a cross sectional view of a two cover arrangement. FIG. 12 is a cross sectional view of multiple weight pipes positioned within an outer weight pipe to provide a weight pipe arrangement.

FIG. 13 is a view of an alternative embodiment of a reinforced cover.

FIG. 14 is a cross sectional view of a further embodiment of an air supported cover with a side curtain. FIG. 15 is a cross sectional view of two nested air supported covers with side curtains.

FIG. 16 is an isometric view of a joining strip for coupling adjoining air supported covers. FIG. 17 and FIG. 18 are cross sectional views of a retaining tube being positioned and inflated in the joining strip of FIG. 16.

FIG. 19 is an isometric view of adjoining air supported covers coupled by joining strips.

FIG. 20 is a sectional view of another embodiment of the invention including an air purge vent.

FIG. 21 is an isometric view of an air purge vent. FIG. 22 is a schematic perspective view of a straight sided air supported cover with numerous spaced air purge vents.

DETAILED DESCRIPTION OF THE DRAWINGS The following description is primarily directed to a floating cover for use in water. It should be understood that the cover could be used on land, inside a building or elsewhere if its functionality renders it appropriate.

Referring to FIG. 1 there is seen a floating cover 10 comprising a peripheral frame formed by a weight pipe arrangement which describes a rectangle. The weight pipe arrangement is formed by weight pipe 12 and its contents. The rectangle defines a central space or void which is covered by an internal panel in the form of flexible sheet 14 to provide a central cover. The flexible sheet is preferably transparent although this is not essential. It is also dimensioned to allow the entrapment of a layer of air or other gas between the flexible sheet 14 and a surface of a body of water. The flexible sheet may be formed from a suitable plastics material such as polyethylene but may be formed of other material such as polyvinyl chloride. In this embodiment the flexible sheet 14 is shown as reinforced by reinforcing straps 16 which are dimensioned to allow expansion of the flexible sheet when entrapping a layer of air and then limit that expansion at a preferred level of distension and tension in the flexible sheet. This decreases distension of the flexible sheet and limits the tendency to tearing particularly during periods of stress such as during high winds or even, in some cases, when an operator walks across the surface of the floating cover. In an alternative embodiment the reinforcement means may be formed from a mesh cover which substantially extends across the entirety of the surface of a flexible sheet. Other methods or reinforcement will also be apparent to a person skilled in the art. FIG. 2 shows a cross sectional view taken along the line AA of FIG. 1.

The flexible sheet 14 can be seen to be elevated above water surface 18 thereby entrapping a layer of air 20 above the water surface. The air may be maintained in constant turnover by the use of a pump (not shown) delivering air into the cover either directly or indirectly through the water. The flexible sheet 14 terminates in a peripheral sleeve 22 which preferably extends around the entirety of the periphery. Other means of attaching the weight pipe 12 to the flexible sheet 14 may be utilised. For example, the sleeve may not extend completely around the periphery and may be intermittent. However, it should be arranged so that the edge of the flexible sheet substantially seals against or under the water surface 18 around its length to limit discharge of the body of air 20.

An enlarged view of one edge is shown in FIG. 2A wherein the weight pipe 12 is located in the peripheral sleeve 22. The weight pipe 12 has an internal compartment 24. The preferred option is for the weight pipe to be formed from a tubular element.

In one arrangement, polyethylene pipe of around 110 mm diameter is used for the weight pipe arrangement. A 600 mm sleeve may be formed around the periphery to receive the pipe through one or more entrance apertures. The pipe may be inserted into the preformed sleeve preferably after heating the pipe along its length as it is introduced in the sleeve to facilitate bending when forming a circular floating cover. The ends of the pipe may be joined by a suitably sized socket which receives the ends preferably with a sealant or suitable adhesive material. The peripheral sleeve may be formed by stitching or even plastics welding.

In the present application the weight pipe 12 is filled by liquid contents within its internal compartment 24. A volume of water 26 is introduced to fill the space. Addition of more or less water will effect the density of the weight pipe and its functional characteristics in relation to retention of the air body 20 and the level of tension or pressure on the air body. Increasing the amount of water will cause an increasing density and subsequent changes in the floating or sinking characteristics of the weight pipe 12. It is also possible to introduce a liquid denser than water. Indeed, saltwater is heavier than freshwater and may be used as ballast in freshwater situation. It may also be used in seawater but the performance characteristics will change slightly. Addition of the heavier material will change the tensioning characteristics of the frame as formed by the weight pipe 12. A solid material may be introduced. Variation of the density provides variation of the ballasting effect of the weight pipe arrangement to thereby allow increased or decreased tension in the flexible sheet 14. The density may be varied to accommodate both a different size of the floating cover as well as shape and the climatic conditions in which it is located. In higher wind conditions, it is preferred by have a reasonably low profile, high-tension, flexible sheet 14 which requires increased ballast in the weight pipe. Alternatively in smaller covers or in benign conditions, the volume of the body of air may be increased while maintaining a relatively low density in the weight pipe. Further the ability to vary the contents means a pond cover may be easily positioned in its functioning location with no ballast and then have contents to provide increased density and/or weight introduced when in position. Likewise, if the need for the cover decreases, such as coming into warmer weather in an application where the cover is used for heating, the ballast material may be discharged to allow easier handling of a relatively light weight frame and cover arrangement to facilitate its removal and storage. In general, it is to be preferred to fill the weight pipe if a flowable material or liquid is used as ballast. This avoids the potential for the flowable material to run to one section of the weight pipe arrangement while leaving only air in a remaining section or sections. This would unbalance the cover leading to a heaving "sunken" side and a relatively light, lifted side. Such a tendency may be avoided by the use of baffles or spaced, discrete chambers or may not be a particular problem in small covers. Different volumes of liquid may be used in an elastic weight pipe where the diameter will increase with increasing pressure. FIG. 3 shows an alternative weight pipe arrangement 30 comprising a first weight pipe 32 located in a first sleeve 34 and a second weight pipe 36 located in a second sleeve 38. The contents of the first and second weight pipes may be different to provide an overall ballasting effect or density that is desired. For example the first weight pipe 32 may be filled with water and the second weight pipe 36 may be filled with foam. The two weight pipes are functionally linked to form a weight pipe arrangement that provides a variability that is relatively sophisticated. The first weight pipe 32 may be set up on installation to remain relatively constant in density with the second weight pipe 36 allowing adjustment which may be quite subtle adjustment in operation. The second weight pipe may be removed in operation.

FIG. 4 shows a further alternative weight pipe arrangement 40 in which a first weight pipe 42 abuts a second weight pipe 44 in a common sleeve 46. The two weight pipes 42, 44 may be simply loosely abutting or may be attached each to the other by an adhesive, welding or may even be formed integrally. The first weight pipe 42 may contain water or other liquid 48. The second weight pipe 44 may include a solid such as a foam, a liquid or a gas. It is clear that the various components of the contents may be mixed as required to give a desired result.

FIG. 5 shows an exemplary embodiment of an adaption to vary the contents of the weight pipe arrangement. A weight pipe 52 is joined by a sleeve 54 to close a peripheral frame. The peripheral frame may be any suitable shape. It may include right angles formed by appropriately sized elbows or may be circular. In this case the frame is closed by the sleeve 54 to unite the two loose ends of weight pipe 52. A collar 56 is provided on the sleeve 54. An air port or other gas port 58 is mounted to the collar providing a valve like access to the internal chamber of the weight pipe. A water port 60 or other liquid port is provided lower in the collar 52 to allow introduction and extraction of a liquid into and from the internal chamber of the weight pipe 52. Compressed air may be introduced to discharge water from the pipe when emptying the weight pipe at the end of a heating season.

In a broad form the invention may reside in the mounting of the weight pipe in a peripheral sleeve. One of the advantages of this arrangement is demonstrated in FIG. 6 where a first floating cover 62 abuts or adjoins a second floating cover 64 in operation. The two covers are interconnected by sliding the weight pipe arrangement and sleeve 66 containing water of the second cover 64 over the weight pipe arrangement in sleeve 68 containing air of the first cover 62. This is a very simple arrangement which keeps the covers together during operation and prevents their separation in most climatic conditions. A disparity in densities of the respective weight pipes is preferred so that the denser sits over the lighter, but this is not essential.

The present invention provides considerable utility. FIG. 7 shows an arrangement in which a primary cover 70 is formed as a circle with a diameter of around 40 metres. This size is over and above anything contemplated by the prior art. The enclosing effect of the primary cover 70 is enhanced by secondary covers 71-74 which are attached in position as lobes to the primary cover. The present invention allows the interoperability of adjacent floating covers to provide extensive coverage even of irregularly shaped water bodies such as occurs with some ponds.

This versatility is further shown in FIG. 8 where a variety of arrangements is demonstrated on the same basic pond shape. The pond is shown as a square of around 42 metre sides with truncated corners. Different variations of the air supported covers are shown generally 10. FIG. 8A provides 90 per cent coverage of the pond. FIG. 8B uses more circular covers with diameters of 13.9 metres and one with a diameter of 11.5 metres to give 75 per cent total coverage. The advantage of this arrangement is that the pond covers are relatively small and easy to handle. The pond covers may be fixed in position by attachments to lines stretching from side to side of the pond. An attachment bracket or brackets may be mounted to the weight pipe arrangement.

FIG 8.C shows 81 per cent total coverage using two 24 metre diameter covers plus two 17 metre diameter covers. FIG. 8D shows 78 per cent total coverage using 20.5 metre diameter covers and FIG. 8E approximately 89 per cent coverage using rectangular cover configurations.

The present arrangement is particularly suitable for use in an aquaculture environment. For example, in raising prawns it is preferred to maintain water temperature at at least 28⁰C throughout winter. This allows the juvenile prawns to maintain growth and be ready for the full growth season in spring. A preferred means of heating the pond involves the use of gas heating. Once such heating arrangement is described below for a volume of around 3.2 megalitres of water.

EXAMPLE 1 : Gas Heating: 2 heating banks each consisting of 6 outdoor Bosch commercial 250 MJ/Hr heaters - each bank capable of 1500 MJ/Hr heat output - banks can be configured for independent or dual operation.

A 5 ton steel gas storage cylinder on site stores approx. 10,000 litres of LPG for the gas heaters. Heat exchangers: Heated distilled water from the boilers enters an M6 titanium plate heat exchanger at 84°C and out at 46°C at 3.56 litres/second. Pond water enters the other side of exchanger at 28°C and out at 35°C returns to the pond at 10.5 litres/second.

A heat recovery interchanger preheats the 5% exchange raw seawater from (in mid-winter) 16°C to 26⁰C from the 28°C pond water being discharged to waste through the interchanger at 18°C at a flow rate of 2 litres/second.

A third heat exchanger takes heat from distilled water pumped through a 1500 square meter solar collector array on a 75 mm "Fibre mesh" reinforced 40 mPa concrete slab approx. 100 metres by 15 metres.

Heated water from the solar collector is pumped through the heat exchanger at 13.4 litres/second and enters at ~40°C and out at 34°C. Pond water enters at 28°C and out at 35⁰C at 10.5 litres/second.

Floating Covers: 4 x 20.5 metre diameter circular floating covers provide heat retention overnight whilst allowing solar heat input throughout the day. Each cover has a sealed 100 mm poly pipe inserted into a 600 mm pocket sown into the cover around its circumference. This pipe has an inner weight pipe providing the necessary counterweight to the air pressure under the inflated cover. The ratio of weight/metre around the cover to air pressure maintains the shape and profile of the covers.

In one embodiment the weight pipe may be formed as collapsible plastic pipe thereby making it easily packed and easy to insert into the peripheral sleeve due to its flexibility and light weight when collapsed. These types of pipe are often referred to as "lay flat". Appropriate contents may then be introduced when it is in position to provide suitable ballast. One advantage of the present system is that it can be deployed progressively as multiple floating covers as water temperature in a pond drops. It can also be removed quickly from the pond if water temperatures increase too much. The system does not impede access to the pond, it may be formed of rust resistant material, it can be repaired easily and can be removed and stored easily when not required. Despite the substantial size of some of the proposed covers, they are relatively lightweight and can be flat stacked one on the other, when the contents are removed from the internal chambers of the weight pipes.

In one trial of 20 metre diameter floating covers, they were responsible for a 4 to 5 degree temperature rise in a grow-out pond for prawns. The trial covers were stable in winds of up to 20 to 25 knots with occasional gusts up to 30 knots. In higher winds, the present inventor has found it safer to collapse the covers although this is not compulsory. Collapsing the covers may be accomplished easily by simply raising one edge of the frame with one or more floats and allowing the air to be expelled passively by the weight of the central panel. Prior art arrangements have been unstable at any significant size and have tended to lift in winds. The present arrangement may function to automatically collapse in high winds rather than lifting off the surface. The increased tension available using the present invention also allows rain to simply drain off the central sheet material and over the edge of the weight pipe arrangements via the outside layer of the sleeves. This has been apparent even in quite heavy downpours of rain.

EXAMPLE 2:

A 20.5 metre diameter floating cover was constructed. The cover was fabricated from sheets of "Solar Shield" ®. This is a woven high density polyethylene scrim, double lamination of low density polyethylene. The sheets were taped welded to make it 22.1 x 22.1 metre²from which a 22.1 metre diameter circle was cut. A 600 mm pocket was sewn around its circumference and later coated with contact adhesive on both sides of the cover to render the stitching holes airtight. A cut was made on the underside of the cover in a pocket to allow a weight pipe to be inserted. The weight pipe was formed from 64 metres from 110 mm diameter HDPE polypipe. Manufacturing stresses within the polypipe were reduced with a quantity of boiling water being passed through the pipe and in this case that was approximately 800 litres. The water entered the pipe through one end and discharged from the other at a controlled rate to give enough residual time to heat up the polypipe for it to soften. This process took many of the undulations out of the pipe and allowed it to float uniformly on the surface of the pond. A flexible lay flat tubing has also been used for the pipe. Polypipe was chosen due to its inherent buoyancy and its significant compartment size.

In the present case, the pipe was inserted in the pocket and then flooded with pond water before sealing. Although the pipe floats in the water it weights 9.5 kg per metre out of the water thereby providing a significant resistance to lifting and also allowing tensioning of the internal screen and pressurisation of the entrapped air or gas. Variation of the length of the weight pipe in relation to the outer circumference of the pocket determines the final profile of the inflated cover. A shorter length a higher profile. A longer length gives a lower profile. The lower the profile is formed the less susceptible the cover is to wind loading. The weight of the pipe contributes to the amount of tension the material will have when inflated. This tension also contributes to the rigidity of the floating cover in operation and therefore its stability. The cover may be deployed onto the surface of the pond and air is injected under the cover either directly or into the water. As the pocket of air grows in its entrapped position the cover floats and the air is increasingly pressurised as the weight pipe arrangement is lifted and flotation effects decrease. The inventor has used a net lift of around 1 -2 kg/m² in prototypes.

However, it is clear that the lift, ballast weight, materials and differential pressures may be varied as required. While application as a thermal and evaporation control means is preferred it is not the only use for the present covers. Other uses may include use as gas collection units from anaerobic digesters, odour control covers for effluent ponds and as floating stills for collection of fresh water. These uses are not limiting. The covers may be used on land or supported on land to cover water.

The present covers are particularly well suited to minimise heat lost due to evaporation, convection, conduction and radiation mechanisms occurring at the interface of the water surface and the atmosphere. Translucent polyethylene sheet material is one many non-permeable membranes suitable for this application. A high degree of light transmission allows solar radiation to enter the pond through the cover. This material is buoyant in fresh water. In one embodiment, different size floating covers may be formed and dimensioned for one to locate into the other ("nest") to provide double layer of protection.

FIG. 9 shows a first outer cover 70 with a weight pipe arrangement comprising a weight pipe 72 filled with water over a second inner cover 74 and weight pipe arrangement comprising a weight pipe 76 filled with air. The different float characteristics of the two weight pipe arrangements maintains position of the covers relative to each other. The perimeter of weight pipe 72 is preferably just less than weight pipe 76 and air may be directly injected into each air space 78, 80. Other gases, such as oxygen, may be used if appropriate.

FIG. 10 shows a telescopic portion 81 of a weight pipe which allows alternation of the perimeter of the weight pipe. The length of the section may be increased by introduction of fluid or simple manual expansion. The reverse may also be conducted by removal of fluid and/or manual reduction.

Fluid may be introduced through valve 181 in FIG. 1OA to enter chamber 182 and expand the telescopic portion 81 as seen in FIG. 1OB. An alternative is shown in FIG. 1OC where the valve 282 is positioned in a different location but still expands chamber 182.

FIG. 11 shows two covers 82, 83 in cross section originating from the same weight pipe arrangement 84 comprising an inner tube or weight pipe 85 and outer tube or weight pipe 86. The covers 82, 83 may overlap and be zipped or stuck together in a removable fashion. Air pressure under the inner cover 83 is preferably more than under the outer cover 82 to best maintain shape.

FIG. 12 shows two views of weight pipe arrangements having outer weight pipes 87 with multiple inner small weight pipes 88, 89 positioned inside them thereby maximising adjustment options. Each inner pipe may be able to be filled with different contents.

FIG. 13 shows a web 90 stretching over the cover 91 to reinforce and protect it. In a particularly sophisticated arrangement, the internal sheet of the two cooperating overlaid covers may be formed from polarising material.

Rotation of one relative to the other may therefore vary the amount of light penetration through the two cover arrangements. Alternatively, a single frame may support two internal covers to provide a double layer insulation effect. Gas inlets may be provided to each body of air entrapped by each of the two covers to thereby inflate both. The gas is typically air but may be other types of gas such as an oxygen rich mixture. Alternatively, the lower cover may have a communication with the compartment between it and the other outer cover to allow bleeding of air or other gas into or under the second cover to thereby inflate both. Pressurisation of air or gas in the weight pipe increases its rigidity to enhance stability of the device. During installation, water or other liquid can be introduced into the liquid port under a predetermined pressure to displace air and maintain rigidity of the weight pipe arrangement.

FIG. 14 shows an air supported cover 92 further incorporating a side curtain 93. The side curtain comprises a curtain sheet 94 and lower weight 95 and hangs down into the water body 96. It may reach to the bottom of the pond or finish short of the bottom. The effect is to give a more isolated portion of the total water volume to provide better control. The curtain sheet 94 is attached to a weight pipe arrangement 97 through a gas permeable material 98, such as Velcro®. Air purged from the trapped layer 99 exits under the weight pipe arrangement 97 to disperse through the gas permeable material 98. A fine bubble plume aerator 99 is provided to aerate the water body, create water circulation as shown by arrows and inflate the cover 100. Cooler water 101 is kept separate from the contained volume 102 of heated, aerated water.

FIG. 15 shows a dual cover, dual curtain arrangement. The inner cover 103 has a weight pipe arrangement 104 and curtain 105. The outer cover 106 has an outer weight pipe arrangement 107 and curtain 108. By having the outer weight pipe arrangement 107 set slightly less than the inner weight pipe arrangement 104, a slight pressure decrease in outer contained gas 109 will arise relative to inner contained gas 110 thereby maintaining the form of the two covers.

FIGS. 16 to 19 show a joining strip for use with adjoining air supported covers. The joining strip 115 is preferably rigid and has two slots 116, 117. Each slot has a mouth 118, 119 respectively which is narrower than the slots' widest dimension 118A, 119A. The air supported covers 120, 121 each have a joining flap 122, 123 with an edge sleeve 124, 125 respectively. The edge sleeves 124, 125 are positioned in the slots 116, 117. Deflated retaining tubes 126, 127 are then inflated (see FIG. 18) to lock the joining flaps 122, 123 into the joining strip 115.

As seen in FIG. 19, the joining strip 115 is used in combination with identical joining strips 115A with a gap 130 between them. The gap 130 allows rain to flow into the pond 131 or purged air to be vented,. The purged air exits under the weight pipe arrangements 132 each comprising an outer perimeter pipe 133 (air filled) and inner weight pipe 134 (water filled) in a sleeve 135. The joining strip may be formed as one continuous strip with drainage/air vents formed in it.

FIG. 20 is a side view of an air supported cover 150 further incorporating an internal purge drain. The drain 140 is an air purge vent and water inlet. It comprises a base 141 , a weight 142 and an open-ended tube 143. An upper edge 144 of the open-ended tube 143 is mated to the central panel 144 so that water on the central panel 144 will drain into the open- ended tube 143 and hence into the body of water 145. Once the lift in the cover is sufficient, the drain 140 rises from the body of water 145, creates a patent flow path for gas under the panel 144, which is then discharged or purged until equilibrium is retained. The input from aerators 146 may be adjusted to keep the drain 140 constantly purging to ensure good oxygenation of the water. The relative proportions of the weight 142 and open-ended tube 143 may be varied for any preferred outcome. The weight may be a set weight or may also be variable, such as previously described in relation to adding or withdrawing contents from an internal chamber.

The circulation in the arrangement of FIG. 20 as shown by arrows leads to centralisation of sediment 180 under the cover which, in this case, is a circular cover. FIG. 21 is an isometric view of one embodiment of an internal purge drain 155 having a base 156, a weight 157 and open-ended tube 158 mated to a central panel 159.

In this case, the weight 157 is formed by a car tyre which is a resilient, cheap and easily obtained item. FIG. 22 shows a schematic representation of an air supported cover

160 with a plurality of internal purge drains 161. The cover 160 has straight sides 162 and can be positioned adjoining other straight sided covers. The multiple purge drains reduce the profile of the cover to that of a substantially flat cover. This provides a real advantage in that local control is provided over the entire surface cover. The purge drains may all be identical structures or they may have different weights. They may all service an identical area to the other purge drains or it may be preferred to provide different densities of purge vents across the cover to thereby provide different characteristics. For example, in one section there may be one purge vent per 10 square metres of cover while in a different section, there may be one purge vent per 20 square metres. The edge of the cover has its own weight pipe arrangement which may be decreased in weight due to the impact of the internal purge vents. The present invention provides great advantages in that it allows scaling up of covers, particularly for use on bodies of water. Variation of the physical characteristics of the arrangement allows for different performance characteristics of a single cover or a system of covers.

Introduction of ballast into a weight pipe arrangement stabilises the air supported cover while its removal allows easy handling and packing. Covers of the present invention may be deployed in Autumn and removed during Spring. This is particularly advantageous in extending productive growth time is aquaculture enterprises. Deflation of the cover in the face of harsh weather conditions may be accomplished by simply lifting the weight pipe with one or more floats. The dropped cover will then sit on the water surface and be held in position by the weight tube.

Throughout the specification, the aim has been to describe the preferable embodiment only, and is not intended to limit the scope, applicability, or configuration of the present invention. Rather, the detailed description of the preferred exemplary embodiments provides those skilled in the art with an enabling description for implementing the preferred exemplary embodiments of the invention. It should be understood that various changes can be made in the function and arrangement of elements and steps without departing from the spirit and scope of the invention.

Claims

1. An air supported cover for a surface, such as the surface of a body of water, the cover comprising: a weight pipe arrangement positioned peripherally to secure the cover to the surface, the weight pipe arrangement including one or more weight pipes; and a central panel connected to the weight pipe arrangement and adapted to trap a layer of gas adjacent the surface; wherein: the weight pipe arrangement is adapted to allow variation of its weight.

2. The air supported cover of Claim 1 , wherein the weight pipe arrangement comprises two or more separate weight pipes to facilitate variation of the weight of the weight pipe arrangement by adding or removing one or more of the weight pipes to the air supported cover.

3. The air supported cover of Claim 1 , wherein the weight pipe arrangement is adapted to allow variation of contents of one or more internal chambers in the weight pipe or weight pipes to thereby vary the weight of the weight pipe arrangement.

4. The air supported cover of Claim 3, wherein the one or more weight pipes are each tubular elements.

5. The air supported cover of Claim 1 further comprising at least one telescopic portion in the weight pipe arrangement to allow variation of the circumference of the weight pipe arrangement.

6. The air supported cover of Claim 1 , wherein the central panel is a single sheet member having a peripheral sleeve or sleeves housing the weight pipe arrangement and thereby connecting the central panel to the weight pipe arrangement.

7. The air supported cover of Claim 6, wherein the central panel is formed as two spaced sheets, one under the other, with an air layer between the sheets.

8. The air supported cover of Claim 1 further comprising reinforcing means to reinforce the central panel.

9. The air supported cover of Claim 1 , wherein at least one weight pipe is formed of lay flat tubing.

10. The air supported cover of Claim 3, wherein the contents of the one or more internal chambers is a liquid.

11. The air supported cover of Claim 3 including one or more entry ports, each entry port adapted to allow introduction or removal of contents from a corresponding internal chamber.

12. The air supported cover of Claim 1 further comprising a side curtain.

13. The air supported cover of Claim 1 further comprising one or more internal purge vents.

14. The air supported cover of Claim 13, wherein each of the one or more purge vents comprises a base, a weight and an opened-ended tube mated to the central panel.

15. The air supported cover of Claim 1 , when combined with one or more adjoining air supported covers to form a system of air supported covers.

16. The system of air supported covers of Claim 15, wherein the air supported cover is joined to at least one adjoining air supported cover by one or more joining strips, the joining strips having two slots, each slot having a mouth narrower than the slot's widest dimension; and an inflatable tube secured to an edge of a flap on each of the air supported cover and the at least one adjoining air supported cover, the inflatable tube positioned in a corresponding slot and inflated.

17. The air supported cover of Claim 1 when positioned underneath a second air supported cover, each having a side curtain.

18. The air supported covers of Claim 1 when positioned underneath a second air supported cover, each being formed of transparent, polarised material whereby relative rotation of the two air supported covers will vary the penetration of sunlight.

19. A method of providing a cover for a surface, the method comprising the steps of: forming a peripheral frame from a weight pipe arrangement comprising one or more weight pipes each having an internal compartment or compartments; fixing a flexible sheet material to the peripheral frame to enclose the area defined by the peripheral frame and thereby form a central cover adapted to trap a layer of air or other gas adjacent the surface; and varying the contents of the internal compartment or compartments to thereby vary the weight of the weight pipe arrangement.

20. The method of Claim 19 further comprising the step of positioning at least one internal purge vent in the flexible sheet.