AU2016204704B2

AU2016204704B2 - Novel pool shell and method

Info

Publication number: AU2016204704B2
Application number: AU2016204704A
Authority: AU
Inventors: David Pain
Original assignee: North Star Tech Ltd
Current assignee: North Star Technology Ltd
Priority date: 2009-10-02
Filing date: 2016-07-07
Publication date: 2018-05-10
Anticipated expiration: 2030-10-01
Also published as: AU2016204704A1

Abstract

A method of forming a swimming pool shell is described using a vinylester resin and, preferably, with a reinforcing section with high performance fibres. Those fibres are preferably selected from carbon fibres, 5 basalt fibres and aramid fibres, particularly Kevlar. The reinforcing sections are located preferably intermediate walls of a fibre glass pool shell. The invention extends to a swimming pool including the reinforcing section having at least one high performance fibre and/or formed from fibre reinforced vinylester resin. 2795421v '-Il

Description

TITLE “NOVEL POOL SHELL AND METHOD”

FIELD OF THE INVENTION

The present invention relates to shells for use in swimming pools, spas and similar arrangements. The invention more particularly relates to a method of constructing and reinforcing a shell for a swimming pool, spa and the like and a shell formed according to that method.

BACKGROUND OF THE INVENTION

Swimming pools have been traditionally formed from concrete poured and/or sprayed into an excavation in the ground. With the advent of modern synthetic materials such as resins and fibreglass, it became possible to provide a lightweight shell with high strength to weight characteristics for a swimming pool, spa or the like. This form of shell being in this context “fiberglass” is understood to refer to composite materials more accurately known as a glass fibre-reinforced polymer or glass-reinforced plastic shell or fibreglass shell.

As manufacturing techniques improved, the size and complexity of such shells increased. Manufacturers may provide a fiberglass synthetic shell for in-ground installation or above-ground installation, the latter particularly for spas. While the majority of the discussion in the specification is directed to swimming pools it is to be understood that other like structures such as spas may also within the scope of the present invention.

There are however a number of problems that arise with the use of glass-reinforced plastic synthetic materials such as fibreglass for swimming pool shells. The first factor is the suitability of resins to be used to manufacture a shell. The use of unsuitable resins may lead to a failure of the swimming pool shell.

As a further factor, there are a number of stress lines and points in shells, especially where panel sections such as walls and the floor meet. In a rectangular pool for example, two wall sections and the floor meet at a bottom corner. With increasing complexity of shape, often for aesthetic reasons, the stress areas have increased in number.

As a further factor, an issue arises with increasing depth in a pool as the hydrostatic pressure of the water column applies a consistent and considerable pressure to the lower regions of the pool shell, also resulting in a stress area.

These stress areas may be vulnerable to cracking or weakening in a number of situations including manufacture itself, transport, installation and during the life of the pool when movement or pressure results in leaks.

An ongoing problem in relation to prior art pool shells is the tendency to suffer from “osmosis”. This refers to the ingress of water into a fiberglass layer. This results in hydrolysis of conventionally used resins (in particular unsaturated orthophathalic polyester resins or UPE) within the fibre reinforced plastics (FRP) layer. This in turn results in internal pressure buildup and blistering and structural weakening of the FRP material. Ultimately the pool shell may lose its waterproof integrity with subsequent failure.

Another problem that arises with prior art pool shells is a certain fragility or brittleness arising from restricted flexural properties. This renders them susceptible to damage during manufacture, transport, installation and operation in situ.

SUMMARY OF THE INVENTION

In one form although it need not be the only or indeed the broadest form, the invention resides in a method of manufacturing a reinforced composite shell for use as a swimming pool, spa or similar, the method comprising the steps of: (a) forming a gelcoat layer in or on a mould; and (b) applying multiple layers of vinylester resin after the gelcoat layer to form the shell.

The vinylester resin is preferably applied with a catalyst and, in at least one or more layers, fibre reinforcement, preferably gun rovings;

The method preferably also includes the steps of: (c) applying at least one reinforcing section to the shell, wherein: the at least one reinforcing section comprises a composite material including a plurality of high performance fibres.

In another form, the invention may reside in a method of manufacture of a reinforced composite shell for use as a swimming pool, spa or similar, the method comprising the steps of: (a) forming a shell in or on a mould, said formation including the steps of applying two or more layers of fiber reinforced plastic comprising vinylester resin and in one or more of the layers, fibre reinforcement; (b) applying at least one reinforcing section to the shell; wherein the at least one reinforcing section comprises a composite material including a plurality of high performance fibres.

Preferably two layers of fibre reinforced plastic including vinylester resin are applied over an initial layer of gel coat. A first layer may be applied over an entire surface of the gel coat. Preferably, a second layer of the two layers is applied on all walls and a radius of the pool, although it may also extend over all surfaces including a floor of the shell. A floor layer may be applied, the floor layer formed from vinylester resin and catalyst.

Applying the at least one reinforcing section in forming the shell includes applying the reinforcing section to or into one or more of a wall, a floor, step sections and feature sections.

The step of forming the shell preferably further comprises applying the at least one reinforcing section to the shell intermediate two layers. The reinforcing section may be applied to preferably one or more of junctions of walls, the floor, the steps and feature sections.

Applying the at least one reinforcing section preferably comprises applying a band of the composite material in the section or sections selected. A plurality of reinforcing sections may be applied to the shell.

High performance fibres are to be understood as having one or more characteristics superior to glass fibres. The high performance fibres may include one or more aramid fibres (including para-aramid fibres) carbon fibres and basalt fibres.

The preferred section or sections for reinforcing may be selected from wall to wall junctions, wall to floor junctions, coping to wall junctions, step section junctions to wall, pool features such as shallow sections and junctions to wall and/or floor as well as panels of the shell.

In a particularly preferred embodiment, the pool shell includes a third layer of fibre reinforced plastic including vinylester resin. This third layer is preferably positioned over the radius of the pool (i.e. the curved junction between two walls or panels). In one embodiment, a fourth layer is applied, the fourth layer comprising fibre reinforced plastic including high performance fibres, vinylester resin, and gun rovings and is applied in combination with a catalyst.

The high performance fibres are preferably provided as a woven material including Kevlar®, carbon fibre and basalt.

It is preferred that a fifth layer is provided comprising fibre reinforced plastic formed from vinylester resin, catalyst and gun roving. This layer is preferably applied over the entire outside area of the pool shell.

The method may include installing conventional reinforcement structures.

It is preferred that a final layer is applied and is formed from a combination of vinylester resin and catalyst.

In a further aspect, the present invention may reside in a reinforced composite shell for use as a swimming pool, spa or similar, the reinforced composite shell formed from: 1. a first inner layer of gel coat; 2. at least two overlapping layers of fibre reinforced plastic formed from vinylester resin, catalyst and gun rovings preferably with a vinylester resin and catalyst floor coat; 3. a further layer of fibre reinforced plastic formed from vinylester resin and catalyst and gun rovings, preferably localized to a radius or curved area of the shell formed primarily between side walls and a bottom of the shell; 4. a layer of high performance fibres preferably formed as a woven material and preferably including one or more of e-glass, Kevlar®, carbon fibre and basalt; 5. a further layer integrated with the high performance fibres, the further layer formed from a combination of vinylester resin, catalyst and gun roving; 6. a second further layer formed from a combination of vinylester resin, catalyst and gun roving preferably applied over the entire surface of the reinforced shell; 7. a final sealing coat formed from a combination of vinylester resin and catalyst applied over an entire surface of the reinforced shell.

It is to be understood that the invention may extend to various combinations and permutations of the layers described above and a single layer may be formed from one or more passes and/or the number of layers may vary accordingly or as required.

In a further form, the invention may reside in a shell for a swimming pool and the like, the shell formed according to the above method.

In yet a further form, the invention may reside in a shell for a swimming pool and the like, the shell including at least one composite fibre reinforcing section, the at least one reinforcing section including a plurality of one or more high performance fibres in a composite material. The reinforcing section/s applied to one or more sections of the shell may be formed from a material including a plurality of substantially parallel fibres and a resin. The reinforcing section may include one or more of carbon fibres, aramid fibres and basalt fibres. A preferred material for the at least one reinforcing section comprises a woven material formed from glass fibres with interspersed carbon fibres, aramid fibres and basalt fibres. The aramid fibres are preferably Kevlar®. The glass fibres may be E-glass fibres.

In a further aspect, the invention may reside in a method of reinforcing weight bearing features such as steps and benches.

The method may comprise: applying a layer of reinforcing material to the weight bearing features. The reinforcing material may comprise a bulker mat. A particularly suitable material is COREMAT™. The reinforcing material may be a core material for a centre of a laminate or similar function. It may be a nonwoven polyester compatible with one or more resins. The advantage of such a material includes the rapid build up of thickness and strength. Exemplary thickness are 1 to 10mm. In one example of COREMAT™ 1mm of thickness of used material contains 0.6kg/m2 of resin.

It is preferred the layer of reinforcing is applied after a first layer of reinforced methyl ester resin.

The method may be extended to the method or methods described above further including applying one or more layers of reinforcing material.

In one broad form the invention may reside in a method of forming a composite shell having at least two layers including vinylester resin and preferably at least five layers. The invention may extend to a shell formed from the method. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a schematic representation of production of a shell according to the present invention; FIG. 2 is a perspective view of a shell for a swimming pool manufactured according to the method of the present invention; and FIG. 3 is a top view of a woven material suitable for use in a reinforcing section. DETAILED DESCRIPTION OF THE FIGURES Referring to FIG. 1, there is a seen a schematic outline of process steps for a shell of the present invention. The production arrangement includes a mould at a station, 1, where a first step (“a first pass”) is executed. Initially a layer of gelcoat is applied to the mould. Swimming pool shells are typically formed on an outside surface of a male mould.

The gelcoat is most commonly a blue colour but this may vary. It is applied in a layer of approximately 0.5 - 1 millimetre. One example of a suitable material is FGI Gelcoat. This is a composition including styrene, fumed silica, pigments and extenders, synthetic resin, hydroxyethyl methacrylate and dibutyl maleate. Other minor ingredients may also be included.

At step 2, a second pass is completed. The outer side of the gelcoat is sprayed with a chopper gun. This device is driven by compressed air and delivers a resin, a catalyst and chopped glass fibres.

The resin is a vinylester resin such as VIPEL FOIO-LSE Resin - 45. This comprises styrene and synthetic resin.

An example of a suitable catalyst is SUPEROX 46-701 which comprises methyl ethyl ketone peroxide, dimethylphthalate, hydrogen peroxide and methyl ethyl ketone.

The glass fibres are produced from gun rovings passed through rotating blades on the gun and introduced into the mixture of catalyst, resin and air. The layer applied at this pass is usually around 2mm thick and is rolled to even it out and remove air. A third pass (step 3) is made wherein the mixture is applied to radii only. In this case the resin used is vinylester resin. A suitable example is VIPEL FOIO-LSE Resin - 45. The composition includes styrene and synthetic polyester resin. This resin allows addition of thickness and strength.

The gun roving is also known as continuous filament fiberglass. Typically the composition comprises around 95% fibrous glass (E-glass, continuous filament) and organic surface binder or sizing.

In this pass, woven rovings of fiberglass are layered onto radii of the shell after they are sprayed with vinylester resin, catalyst and gun rovings. Once laid, the woven rovings are oversprayed again with the same combination.

In the present invention, one or more reinforcing sections with a plurality of high performance fibres may be now, preferably, fixed in position. A preferred material is a woven glass product including aramid fibres and/or carbon fibres and/or basalt fibres and/or ECR glass in a woven and/or non-woven form. Preferred glass may comprise ECR glass which is similar to E-glass but without boron fluorine. This improves and provides the product with additional strength. In an alternative process, described below, the reinforcing sections may be applied later in the sequence.

The aim may be to form composite engineered materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished material.

In the present case, composites are considered to include fibre reinforcement surrounded by plastic or other binder. In this specification, the term composite may, where the context allows, also refer to the fibrous, preferably woven, reinforcing material including at least one high performance fibre.

One suitable material comprises a woven glass base with longitudinal multi strand carbon fibres and angled strands of an aramid fibre such as Kevlar®. The material may be placed onto the pool shell after a priming layer of catalyst and resin and subsequently have additional catalyst and resin applied to saturate the material and provide, ultimately after setting, a high strength composite reinforcing section with high performance fibres.

In an alternative embodiment, the high performance fibres may be purely aramid or basalt fibres or a combination of the two. A knitted fabric incorporating high performance fibres may be used. A further pass (4) is made using a vinylester resin, gun roving and catalyst.

At this stage strengthening ribs are applied in selected positions such as along the wall and closed box reinforcement sections are also applied before another pass (5) is made with a vinylester resin, gun rovings and catalyst.

Standard additions including lifting points for movement of the shell, stainless end wire ties for attachment to steel reinforced concrete are included in the shell.

Preferably multiple reinforcing sections are applied such as at the joins between two walls, the walls and the floor and other sections if required. These other sections may be any part of the shell but typically would extend from joins between sections such as walls, floors, steps, features or other structures. It may be desirable to apply reinforcing sections to straight and/or curved panel areas formed with more aesthetically directed shapes such as billabong, kidney or tear-drop shaped pools. The composite fibre reinforcing material is preferably applied internally in the shell and then activated to set. A particularly preferred material will include reinforcing aramid fibres. In some embodiments the reinforcing sections may be applied externally.

Aramid fibres form a core of heat resistant and strong synthetic fibres. They are typically used in the aerospace industry and military applications. The name is a shortened formed of aromaticpolyamide. The chain molecule has chemical characteristics for which the fibre can be exploited. The aramid fibres are able to be handled similarly to normal textile clothing fibres and are characterised by their excellent resistance to heat as they neither melt nor ignite in normal levels of oxygen. The expression aramid fibres should be understood to extend to variants and analogs such as a meta-aramid.

Aramid fibres also include the well known trade named product Kevlar® which is a trade mark of E I Du Pont de Nemours and Company. This material combines high strength with light weight to improve the performance of the present reinforcing sections. Kevlar® is light weight, flexible, strong and safe.

The fibres may also be selected from the carbon fibre group of materials. These are also known as graphite fibre or carbon graphite and form a material consisting of extremely thin fibres and composed mostly of carbon atoms. Typically the fibres will be in a range of around 0.005 to 0.010mm. The carbon atoms are bonded together in a way that more or less aligns them parallel to the long axis of the fibre. The crystal alignment makes the fibre very strong for its size. Several thousand carbon fibres are twisted together to form a yarn, which may be used by itself or woven into a fabric.

Carbon fibre has many different weave patterns and is usually combined with a plastic resin and wound or moulded to form composite materials. This carbon fibre reinforced plastic (also referenced as carbon fibre) provides a high strength to weight material. The density of carbon fibre is also considerably lower than the density of steel making it extremely strong for its weight. The properties of carbon fibre include it being high tensile, low weight and low thermal expansion.

Basalt fibres are made from extremely fine fibres of basalt, comprising the minerals plagioclase, pyroxene and olivine. It has better physiomechanical properties than fibreglass. Fibres typically have a diameter between 9 and 13 micrometres. The fibres are produced by extruding molten basalt.

One preferred embodiment of composite fibre reinforcing material is a knitted fabric material which is applied to some of the swimming pool shell and is wet through with a resin. Referring to FIG. 2 there is a seen a shell 20 comprising a floor 21 a side wall 22 and end wall 23. The walls 22, 23 terminate in an upper lip 24 which extends around the pool top surface. The present alignment shows a shell during manufacture when it is inverted on a mould and allows access to stress sections such as wall to wall junctions 25, wall to floor junctions 26 and other areas such as formation of steps, curves, shall sections or “beaches” which are not shown in this view. A composite fibre reinforcing section 28 is shown and positioned along the adjoining paneled sections such as walls and floors. The resin is vinylester resin in at least two layers. FIG. 3 shows a preferred woven material for use in reinforcing sections. The material 30 comprises woven strands based on a glass fibre 32 mat. A preferred glass fibre is E-glass.

The mat is interspersed with three high performance fibres. Broad bands of carbon fibre 34 are spaced evenly through the mat.

Transverse to the carbon fibres 34 are Kevlar® fibres 36. Parallel to the Kevlar® fibres 36, and positioned between adjacent Kevlar® fibres, are basalt fibres 38.

This material in itself is considered novel and inventive.

The composite fibre reinforcing section is positioned preferably as a woven band into position with a resin which impregnates the material and sets to incorporate it into a solid reinforcing section adhered to shell 20. The preferred method is incorporation of the reinforcing section internally in the walls as they are layered. Further layers may be applied. The reinforced shell is allowed to dry completely and obtain full strength. It is then moved by appropriate lifting gear such as a crane, a forklift or pulley system onto a transport vehicle for transfer to a an installation site. EXAMPLE 1

One example of a formation of a shell of the present invention is set out below:

Pass 1 - Using a spray gun a combination of gelcoat and catalyst is sprayed onto a male mould. This pass is approximately ,5mm to 1mm in thickness.

Pass 2 - Using a chopper gun a combination of vinylester resin, catalyst and gun rovings is sprayed over the top of Pass 1. This pass is over the entire pool. Rollers are used to roll flat and remove air from the sprayed laminate. This pass is approximately 2mm in thickness.

Pass 3 - Using a chopper gun a combination of vinylester resin, catalyst and gun rovings is sprayed over the top of Pass 2. This pass is approximately 2mm to 3mm in thickness. Rollers are used to roll flat and remove air from the sprayed laminate. This pass is done on all of the walls and radii of the pool. With regards the floor, a chopper gun is used to spray a combination of vinylester resin and catalyst. Fibreglass is not applied on this pass on the floor only. One reason for this is that thickness on the floor is not as necessary as for the walls. As Pass 3 is curing, at certain designated locations various additional reinforcement structures are attached. For example, foam strips may be placed onto the walls of the pool spaced approximately 400mm to 600mm apart running vertically. Cardboard box sections may be located into the coping of the pool. Cardboard angle may be located on the step ledge of the pool. Steel lifting hooks may be located in designated locations on the pool coping.

Pass 4 - Using a chopper gun a combination of vinylester resin, catalyst and gun rovings is sprayed down over the radius of the pool (being where the floor of the pool meets the walls of the pool). Rollers are used to roll flat and remove air from the sprayed laminate. A woven material is applied over the radius consisting of a combination of E-glass, Kevlar, Carbon Fibre and Basalt. A combination of vinylester resin, catalyst and gun rovings is sprayed over this woven material and then rolled flat using a roller to remove air from the sprayed laminate. The use of the new material with Kevlar, Carbon Fibre and Basalt is later in the sequence than in the earlier described method.

Pass 5 - Using a chopper gun, a combination of vinylester resin, catalyst and gun rovings is sprayed over the top of Pass 3 (which has the reinforcement material) and Pass 4. This pass is over the entire pool. Rollers are used to roll flat and remove air from the sprayed laminate. This pass is approximately 2-3mm in thickness.

Pass 6 - Using a chopper gun a combination of vinylester resin and catalyst is sprayed over the entire pool as a final sealing coat. No gun rovings are sprayed and there is no rolling required. This mass is approximately ,5mm in thickness.

On site the pool shell is arranged in an excavation or alternatively as an above ground pool typically with a surround support wall. Water is then added along with the appropriate plumbing for filtration purposes.

The shell of the present invention once in place and filled is highly resistant to cracking due to the application of the present invention. The present invention provides numerous advantages. One particular advantage is the increased strength of the pool shell to resist fracture and leakage. The present invention provides a safe long lasting and strengthening addition to a traditional pool shell. The composite fibre reinforcing section is reasonably expected to extend the life of the shell and to avoid manufacturing defects and faults especially at the stress sections of a pool shell.

The inventors have surprisingly found that the use of vinylester resin provides a marked improvement in two aspects of the pool shell function. The first is an increase in resistance to osmosis. Vinylester resins are synthesized from epoxy resins addition-esterified with acrylic acids (especially methacrylic acid) and later diluted with styrene.

Conventional pools are largely formed from unsaturated orthophathalic polyester resins (UPE). When used in FRP materials, the end products absorbs around 1-2% of its weight when constantly immersed in water. This water eventually permeates through the thickness of the FRP and begins to hydrolyse the ester linkages of the UPE resins. The vinylester resins in trialing by the applicant has been found to absorb much less water than UPE based FRP materials and has displayed better inherent hydrolysis resistance meaning that the opportunity for osmosis of these materials is reduced. A further advantage of the present invention arises from improved flexural properties of vinylester resin FRP material when used in the shell compared to the prior art use of polyester resin FRP materials. This provides greatly increased resistance to stresses during manufacture, transport, installation and operation particularly in the ground.

It should be understood that in the broadest scope the present invention is directed to the wide spread use of vinylester resin in FRP materials in a pool shell. EXAMPLE 2

Layer 1 - Gelcoat (entire pool)

Layer 2 - Vinyl Ester Resin, catalyst and gun roving (entire pool)\

Layer 3 - Vinyl Ester Resin, catalyst and gun roving (radius, walls, steps and benches with vinyl ester resin, catalyst and gun rovings and a misting of vinyl ester and catalyst on the floor only)

Layer 4 - Vinyl Ester Resin and woven high performance fibres (Radius and key stress points);

Layer 5 - Vinyl Ester Resin, catalyst and gun rovings (entire pool). On this layer the applicator would lay down Coremat that is between 2mm to 4mm in thickness and wet out the Coremat with Vinyl Ester Resin on weight bearing structures such as steps and benches.

Layer 6 - Vinyl Ester Resin and catalyst sealing layer (entire pool). COREMAT™ is a polyester nonwoven material that contains microspheres which are closed. They therefore take up space without absorbing resin. It or any similar products can be used to increase stiffness, reduce weight, reduce costs and improve surface consistency. This product is representative only.

This method provides a shell that resists deformation of weight carrying features such as steps and benches. It decreases deflection in use. The invention may include a shell formed according to the method.

Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features. It will therefore be appreciated by those of skill in the art that, in light of the instant disclosure, various modifications and changes can be made in the particular embodiments exemplified without departing from the scope of the present invention.

Claims

CLAIMS:

1. A method of manufacturing a reinforced composite shell for use as a swimming pool or spa, the method comprising the steps of: (a) forming a gelcoat layer in or on a mould; and (b) applying multiple layers of reinforced vinylester resin over the gelcoat layer to form the shell; and (c) applying at least one reinforcing section to the shell, wherein: the at least one reinforcing section comprises a composite material including a plurality of high performance fibres, and the high performance fibres comprise a combination of glass fibres, aramid fibres, carbon fibres and basalt fibres.
2. A method of manufacturing a reinforced composite shell for use as a swimming pool or spa, the method comprising the steps of: forming a shell in or on a mould, said formation including the steps of applying two or more layers of fiber reinforced plastic comprising vinylester resin and in one or more of the layers, fibre reinforcement; and applying at least one reinforcing section to the shell; wherein the at least one reinforcing section comprises a composite material including a plurality of high performance fibres, and the high performance fibres comprise a combination of glass fibres, aramid fibres, carbon fibres and basalt fibres.
3. The method of claim 2 including the steps of applying a first layer of fibre reinforced plastic, including vinylester over an entire surface of an initial gel coat, and a second layer on all walls and a curved area or areas of the pool.
4. The method of claim 2 wherein applying the at least one reinforcing section to the shell includes applying the reinforcing section to or into one or more of a wall, a floor, step sections and feature sections.
5. The method of claim 4 wherein the step of forming the shell further comprises applying the at least one reinforcing section to the shell intermediate two layers.
6. The method of any one of claims 2, 3, and 5 wherein the at least one reinforcing section is applied to one or more of wall to wall junctions, wall to floor junctions, coping to wall junctions, step section junctions to wall, pool features and junctions to wall and/or floor as well as panels of the shell.
7. The method of claim 6 further comprising the step of applying a third and fourth layer of fibre reinforced plastic including vinylester resin.
8. The method of claim 7 further comprising the step of applying a fifth layer comprising fibre reinforced plastic formed from vinylester resin, catalyst and gun roving, applied over the entire outside area of the pool shell.
9. The method of claim 8 further comprising applying a final layer over the composite shells formed from a combination of vinylester resin and catalyst.
10. A shell for a swimming pool or spa, the shell formed according to the method of any one of claims 1 to 9.
11. A reinforced composite shell for use as a swimming pool or spa, the reinforced composite shell formed from: a. a first inner layer of gel coat; b. at least two overlapping layers of fibre reinforced plastic formed from vinylester resin, catalyst and gun rovings preferably with a vinylester resin and catalyst floor coat; c. a further layer of fibre reinforced plastic formed from vinylester resin and catalyst and gun rovings, preferably localized to a radius or curve of the shell formed primarily between side walls and a bottom of the shell; d. a layer of high performance fibres preferably formed as a woven material and the high performance fibres comprise a combination of glass fibres, aramid fibres, carbon fibres and basalt fibres; e. a further layer integrated with the high performance fibres, the further layer formed from a combination of vinylester resin, catalyst and gun roving; f. a second further layer formed from a combination of vinylester resin, catalyst and gun roving preferably applied over the entire surface of the reinforced shell; and g. a final sealing coat formed from a combination of vinylester resin and catalyst applied over an entire surface of the reinforced shell.