Field of the Invention There is described a sail comprising at least a portion of self-reinforcing

polypropylene (srPP). The described sail is particularly advantageous for use in sail boats or windsurfers.

Background to the Invention

Sails are commonly used on boats or other equipment. For instance, sails can be used within sports equipment including sail boats (such as yachts, dinghies or model boats) or windsurfers or types of kitesurfers. In strong wind conditions when in use, or during handling and transportation, a sail can be prone to rips or tears. Such rips and tears can severely reduce the performance of the sail, even once repaired. Preferably, the sail should be as lightweight as possible, in order to avoid additional load during transportation or in use and so as to improve the performance of the boat, surfer or vessel to which it is connected.

Performance of the sail can be improved by shaping or reinforcing areas of the sail. Shaping the sail can be achieved by providing battens which are formed using flexible or semi-flexible rods of wood, plastic or other material placed in pockets within regions of the sail. Battens can be used to shape the sail to better 'catch' the wind and/or reduce drag when the sail is in use. In some examples, battens are used to keep portions of the sail flat or planar when in use. However, such battens can be heavy and increase the overall weight of the sail.

Some known sails include small window regions or transparent panels in the body of the sail (which is otherwise formed of opaque or near-opaque material). The windows are provided to allow the user to see objects on the opposite side of the sail, which would otherwise be obscured from view. However, the types of transparent material used to form such panels can be particularly susceptible to stretching or cracking, which thereby forms weaknesses in the body of the sail. For this reason, the windows are kept fairly small in area. However, this reduces visibility for the user.

Thus there is required a sail and sail equipment that would overcome these shortcomings. Summary of the Invention

In a first aspect, there is described a sail comprising at least a portion of self- reinforcing polypropylene (srPP). The sail may be formed entirely of srPP, or may by formed from a plurality of materials, including at least a portion of srPP.

Advantageously, srPP is both strong and lightweight. Thus a sail comprising at least a portion of srPP is more robust than sails formed from known or standard sail making materials. Furthermore, the sail may be more conveniently transported, due to the reduction in weight. As polypropylene is recyclable, sails made from srPP may also be easily recycled at the end of life.

The sail may comprise a panel of srPP which makes up a proportion, and optionally a substantial proportion, of the surface area of the entire sail. Sails may be formed of a plurality of layers of material, of which srPP comprises one or more of the plurality of layers. The sail may comprise panels or strips of srPP, arranged to reinforce sails formed of other materials. In a further example, srPP panels may be retrofitted to existing sails.

Beneficially, srPP panels can provide reinforcement to areas of the sail under particular stress during use. This takes advantage of the strength and lightweight properties of srPP. Panels of srPP can be included at certain areas of existing sails, in order to reinforce vulnerable areas of the sail such as around the head clew or tack of the sail.

The sail may comprise at least a portion of srPP which is formed or shaped to have properties suitable for improving sail performance. For instance, the portion of srPP may provide reinforced areas, areas of stiffness within the sail, or areas having a specific shape or contour. The portion of srPP may be bonded to other layers of srPP, or to layers of other materials, using methods such as thermoforming, stitching, gluing, riveting etc.

In an example, the portion of srPP that is formed or shaped to have properties suitable for improving sail performance can be shaped so as to be used to provide draft wing shapes. Alternatively, the sail may comprise one or more strips of srPP arranged as sail battens. In other words, the portion of srPP that is formed or shaped to have properties suitable for improving sail performance can be strips of srPP used in place of tapered battens within the sail, running traverse across the sails. Use of srPP to replace battens, for example, provides improved performance resulting from maintaining certain wing shapes whilst being more lightweight than using traditional sail battens.

In some examples, the srPP strips or battens may each be formed of a plurality of laminated layers of srPP, the srPP layers including aramid fibres. In still further embodiments the srPP layers may be arranged so that the aramid fibres in each layer are arranged perpendicular to the aramid fibres in the preceding layer. The layer of srPP may be arranged such that the aramid fibres are configured to be about or approximately 45 ^e to the longitudinal direction of the srPP strips. This can improve flexibility of the srPP

'battens'.

The sail may further comprise a panel or insert of expanded polypropylene (ePP).

For instance, such an insert could be placed next to the mast in order to provide definition of the wing shape of the sail. SrPP or other materials can be stitched to surround the ePP inserts (in other words, the ePP is enclosed in a 'pocket' of srPP) to encase the ePP.

Alternatively, the ePP may be glued to a srPP panel (or a panel of another material), or be glued between layers of srPP or one or more other materials. As ePP and srPP are both lightweight, water resistant and have good floatability properties, they are ideal for use within sails.

The sails may further comprise at least a portion of transparent or translucent srPP. The transparent or translucent srPP may form panels within the sail, or may be used to form the entire sail. The panels of transparent or translucent srPP may be used in addition to other srPP panels (for instance, which are opaque or near opaque), or be used alone or in addition with other materials within the sail.

The sails may further comprise at least a portion of srPP comprising an additive, the additive being added to the srPP material for prevention of UV degradation. In another example, the sails may further comprise one or more layers of plastics resistant to UV degradation. The one or more layer of plastics may be used in a laminated formation with the srPP material, in order to protect the srPP material from UV damage.

In a further aspect, there is a method of manufacturing a sail comprising at least a portion of self-reinforcing polypropylene (srPP). The sail may be formed or shaped by techniques such as thermoforming, gluing, stitching or riveting the srPP, either combining a plurality of srPP layers or in combination with layers of other types of material or fabric.

For instance, a sail may be formed entirely of srPP, in which seams or edges are thermoformed, stitched, glued or riveted. Alternatively, srPP panels may be used within or together with sheets or panels of other materials to form a sail, wherein the srPP panels are fastened or secured to the other sail materials by stitching, gluing, riveting or thermoforming (or thermofusing).

The method of manufacturing a sail may include fastening additional panels of srPP within a sail formed of other materials, in order to reinforce an area of the sail. Alternatively or additionally, the method may include bonding (by stitching, gluing, riveting or

thermoforming) regions of srPP with layers of other material to provide a sail with improved sail performance. For instance, regions of a sail may be stiffened by adding a srPP portion, to form portions that are more difficult to bend or fold, or in order to form certain shapes for the sail or portion of the sail. For instance, strips of srPP may be applied to the sail to achieve this (either by retrofitting to an existing sail, or by adding to a sail formed of another material, or formed of srPP). Shaping or stiffening regions of the sail in this way can improve drag and other performance characteristics for the sail. In this way, the srPP regions can replace traditional sail battens.

The method of manufacturing a sail may further include providing a panel of transparent or translucent srPP and fastening the panel of transparent or translucent srPP within the sail. For instance, the transparent or translucent panel may be attached or fastened within a panel of more opaque srPP or a panel of one or more other types of material (or a mixture of srPP and other material) in order to form the sail. Such

transparent panels are particularly advantageous in order to improve the visibility of a user (and avoid obstruction of a user's line of sight by the sail). Transparent or translucent panels formed of srPP are strong and robust. The transparent or translucent srPP material can be used without stretching or cracking. The transparent or translucent srPP materials can be used as panels within the sail, or can even be used to form the whole sail.

An example of srPP is Armadon™.

The sail may be used on any type of vessel. For instance the vessel may be a windsurfer, sail boat, yacht etc.

In a further aspect there is a sail comprising at least a portion of self-reinforcing polypropylene (srPP) material. For instance, the self-reinforcing polypropylene material may make up part of the surface area of a sail, the entire surface area of the sail or at least one layer of a sail incorporating at least a portion having a plurality of laminated layers. The portion of srPP may be a patch or panel applied to an area of a sail (formed either of self-reinforcing polypropylene material or another material).

Optionally, the portion of self-reinforcing polypropylene material is a first portion, the sail further comprising at least a second portion, and wherein the first and second portion are bonded to form the sail. Although the first portion is formed of a self-reinforcing polypropylene material, the second portion may also be formed of a self-reinforcing polypropylene material, or of another type of material. The first portion and second portion may be a first and second panel, joined at their edges to form the sail. Alternatively, the first or second portion may be a first and second layer, bonded to form a sail comprising at least a region having a plurality of laminated layers.

Optionally, the portion of the self-reinforcing polypropylene material comprises a substantial proportion of the surface area of the entire sail. For example, the srPP portion may make up more than 50%, more than 75%, or more than 90% of the sail surface area. The self-reinforcing polypropylene material may also make up the entire sail surface area.

Optionally, at least a portion of the sail is formed from a plurality of laminated layers, wherein the portion of self-reinforcing polypropylene material comprises at least one of the plurality of laminated layers. The entire sail area may be formed of a plurality of laminated layers. Alternatively only parts of the sail surface area may be formed of a plurality of laminated layers. These parts of the sail surface area may be areas of the sail benefitting from reinforcement (such as the clew or tack area), and the portion comprising a self- reinforcing polypropylene material may be a reinforcement panel or patch.

At least a second one of the plurality of laminated layers forming a sail may comprise a plastic material that is resistant to ultra-violet (UV) degradation. For instance, one layer may be formed of a plastic material that does not degrade under UV radiation (for example, in sunlight).

The portion of self-reinforcing polypropylene material may be at least one panel of self-reinforcing polypropylene material, the at least one panel having a surface area less than the whole surface area of the sail. For example, the panel may be a reinforcement patch, or a may be a panel at a relatively small area of the sail having a specific function (such as a sail batten, or in the Luff area) and connected to other portions of the sail. The sail may be formed by joining two or more (a 'patchwork') of panels, at least once of which is formed from srPP.

Optionally, the portion of self-reinforcing polypropylene material is resilient. For example, the self-reinforcing polypropylene material may be semi-rigid, or able to recoil or spring back into its original shape after bending, stretching, or being folded or compressed.

Optionally, the portion of self-reinforcing polypropylene material is shaped or contoured. For example, the portion may be formed to have a resilient three dimensional shape, so as to be curved (for example in a shallow "U" or other shape).

The at least one panel of self-reinforcing polypropylene material may itself comprise a plurality of laminated layers of self-reinforcing polypropylene. The panel could comprise 2, 3 or more layers of self-reinforcing polypropylene material. This may be the case even if the panel forms part of a sail that, at least in part, also comprises a plurality of layers.

Preferably, each layer of self-reinforcing polypropylene of the plurality of laminated layers of self-reinforcing polypropylene (forming the panel) comprises reinforcing fibres arranged approximately parallel to each other, in a direction parallel to the plane of the layer. A first layer of self-reinforcing polypropylene in the plurality of laminated layers of self-reinforcing polypropylene may be arranged to have fibres configured to be

approximately perpendicular to the fibres in a second layer of self-reinforcing polypropylene in the plurality of laminated layers of self-reinforcing polypropylene. In other words, the reinforcing fibres in subsequently layers of self-reinforcing polypropylene material may be arranged to be around 90 ^e to each other, to improve the strength and tear resistance of the panel.

Preferably, at least one panel of self-reinforcing polypropylene material is arranged to form a sail batten, the sail batten having a longitudinal dimension greater than a dimension in a direction perpendicular to the longitudinal direction. For example, a sail batten may be approximately rectangular prism shaped, wherein the longitudinal direction is the longest dimension. At least one layer of self-reinforcing polypropylene in the plurality of laminated layers of self-reinforcing polypropylene may be arranged to have fibres configured to be about 45 ^e to the longitudinal direction of the sail batten. In other words, the reinforcing fibres are arranged to be diagonal to the longitudinal direction of the batten. This improves resilience and flexibility of the batten.

Preferably, at least one panel of self-reinforcing polypropylene material is arranged to provide a sail batten. The self-reinforcing polypropylene material may be particularly useful for sail battens, due to its resilience but lightweight characteristics.

The sail may comprise a plurality of laminated layers and the sail batten may be enclosed between two layers of the plurality of laminated layers of the sail. For example, the sail batten formed of srPP may be enclosed, enveloped or encased between two layers forming part of the sail.

Optionally, the sail batten is formed from at least one layer of self-reinforcing polypropylene having a thickness of 0.5 mm or greater. A thicker layer of srPP may have greater resilience, but still be lightweight.

Preferably, the at least one panel of self-reinforcing polypropylene material is configured to provide a draft wing shape in a Luff area of the sail. This can be useful to provide a panel having a resilient shape that helps the sail to "catch the wind". This can improve the performance of the sail.

Preferably, the sail further comprises a panel of expanded polypropylene (ePP), the expanded polypropylene being contoured and shaped. Such a panel or insert can also be used to provide a draft wing shape in the Luff area, for instance. A sail incorporating both a srPP potion and an ePP insert (or panel) is both lightweight and very buoyant.

Optionally, the sail comprises a plurality of laminated layers and the panel or insert of expanded polypropylene (ePP) is enclosed between two layers of the plurality of laminated layers of the sail. For example, the panel or insert of ePP may be enclosed, enveloped or encased between layers forming the sail. Preferably, the portion of self-reinforcing polypropylene material comprises at least one seam formed by at least one of a group consisting of: thermoforming, stitching, gluing, riveting. The seam may bond a part of the self-reinforcing polypropylene material portion to itself (for example, at an edge seam). Alternatively, the seam may bond the self-reinforcing polypropylene material to another portion, panel or layer (either of srPP or another material).

Preferably, the one or more seam can bond the portion of self-reinforcing polypropylene material to at least one portion or layer of another type of material or to at least one other portion or layer of self-reinforcing polypropylene material, or to another area of the same portion of self-reinforcing polypropylene material.

The at least one seam may be jagged or uneven. For example, the seam may form a join that is dog-toothed or saw-toothed. Ideally, the length of the seam (and the join between the self-reinforcing polypropylene material portion and another portion or layer) is increased beyond the length of a straight or curved seam. This helps to dissipate energy at the seam, and can help to avoid tearing.

Preferably, the portion of self-reinforcing polypropylene material is translucent or transparent. The entire sail may be formed from translucent or transparent self-reinforcing polypropylene material. Alternatively, the portion may form a translucent or transparent window in a sail otherwise formed of an opaque or semi-opaque material (either in srPP, or another material).

Optionally, the portion of self-reinforcing polypropylene material that is translucent or transparent is a first portion, the sail further comprising at least a second portion formed of opaque or near opaque self-reinforcing polypropylene material.

Optionally, the portion of self-reinforcing polypropylene material further comprises an additive for prevention of ultra-violet (UV) degradation. For example, the additive may be added during manufacture of the self-reinforcing polypropylene material.

In a still further aspect there is a method of manufacturing a sail comprising forming a sail comprising at least a portion of self-reinforcing polypropylene (srPP) material.

The method may comprise forming a first portion of the sail, forming a second portion of the sail and bonding the first and second portion to form the sail, wherein at least the first portion comprises self-reinforcing polypropylene material. The first and second portion may be a first and second panel, joined at their edges to form at least part of the sail. The first and second portion could alternatively be a first and second layer to form at least a portion of a sail including a plurality of laminated layers.

Optionally, the second portion comprises self-reinforcing polypropylene material.

However, the second portion could instead be formed of another type of material. Optionally, the first portion is a first layer and the second portion is a second layer, and wherein bonding the first and second portion comprises bonding the first and second layer to form at least part of a sail comprising a plurality of laminated layers. For example, the first portion could be a reinforcement patch, which, in the areas where it is applied, the sail incorporates a plurality of laminated layers.

Optionally, the first portion is a first panel and the second portion is a second panel, and wherein bonding the first and second portion comprises bonding the first and second panel to form at least part of a sail comprising a plurality of panels. For example, the surface area of the sail may be formed from two or more joined panels, at least one of which is formed from self-reinforcing polypropylene material.

Optionally, the first portion is a panel or patch of self-reinforcing polypropylene used to reinforce an area of the sail. For example, the panel or patch may be applied to the sail at the areas of greatest stress (for instance around the clew or head, or where the tack or rope is attached to the sail). The reinforcement panels of srPP may be retrofitted to an existing sail.

Preferably, forming a first portion comprises forming the first panel comprising a plurality of laminated layers of self-reinforcing polypropylene. In other words, the panel or patch of self-reinforcing polypropylene material may itself comprise a plurality of laminated layers of self-reinforcing polypropylene material, even if the sail also comprises regions including a plurality of layers.

Preferably, each layer of self-reinforcing polypropylene of the plurality of laminated layers of self-reinforcing polypropylene comprises reinforcing fibres arranged approximately parallel to each other, in a direction parallel to the plane of the layer. Forming the first panel comprising a plurality of laminated layers of self-reinforcing polypropylene may comprise arranging a first layer of self-reinforcing polypropylene of the plurality of laminated layers to have fibres configured to be approximately perpendicular to the fibres in a second layer of self-reinforcing polypropylene of the plurality of laminated layers. For instance, subsequent layers in the plurality of layers forming the panel may be arranged having their fibres at 90 ^e to the previous layer.

Optionally, prior to bonding the first and second portion to form the sail, the method further comprises configuring the panel of self-reinforcing polypropylene to provide a sail batten. The portion or panel of self-reinforcing polypropylene material may be especially advantageous for use as a sail batten, due to its resilient and lightweight characteristics.

Optionally, prior to bonding the first and second portion to form the sail, the method further comprises configuring the panel of self-reinforcing polypropylene to provide a draft wing shape in a Luff area of the sail. The self-reinforcing polypropylene material panel or portion may be shaped or contoured to provide the draft wing shape.

Preferably, prior to bonding the first and second portion to form the sail, the method further comprises arranging a panel of expanded polypropylene (ePP) between the first and second portion, and bonding the first and second portion comprises enclosing the panel of expanded polypropylene between the first and second portion. The ePP panel or insert may be shaped, for example to have a draft wing shape for use in the Luff area of the sail.

Preferably, bonding the first and second portion comprises forming at least one seam to join the first and second portion, the seams formed by at least one from the group comprising: stitching, gluing, riveting, thermoforming or thermofusing. A seam may be formed between the self-reinforcing polypropylene material portion and a second portion of self-reinforcing polypropylene material, or a second portion of another material. A seam may also be formed at the edge of the self-reinforcing polypropylene material portion (i.e. forming a seam with itself).

Preferably, forming the at least one seam comprises forming a jagged or uneven seam. Ideally, the length of the seam is increased compared to a straight or curved seam. This helps to prevent tearing.

Preferably, the portion comprising self-reinforcing polypropylene comprises a portion of translucent or transparent self-reinforcing polypropylene. The portion of transparent or translucent self-reinforcing polypropylene material may be used as a window section in a sail of an opaque self-reinforcing polypropylene material, or as a window in a sail of another opaque material. The entire sail may be formed of transparent or translucent self-reinforcing polypropylene material.

Preferably, the portion of translucent or transparent self-reinforcing polypropylene is formed by using a release agent during manufacture of the self-reinforcing polypropylene material.

Optionally, forming a first portion comprises applying heat and pressure to the portion of self-reinforcing polypropylene to permanently soften the self-reinforcing polypropylene material.

Optionally, forming a first portion comprises inclusion of an additive for prevention of ultra-violet (UV) degradation.

In a still further aspect there is a patch or panel of self-reinforcing polypropylene material for bonding to a sail, for reinforcement of areas of the sail. Brief description of the Figures

A sail and its method of manufacture in accordance with aspects of the present disclosure is described, by way of example only, with reference to the following drawings, in which:

FIGURE 1 is a plan view of a sail according to the invention;

FIGURE 2 is a plan view of a further embodiment of a sail;

FIGURE 3 is a plan view of a sail with reinforcing panels;

FIGURE 4 is a representation of a sail comprising transparent srPP, in use;

FIGURE 5 is a further representation of a sail comprising transparent srPP, in use;

FIGURE 6A is a plan view of a sail;

FIGURE 6B is a plan view of a sail according to an embodiment of the invention; FIGURE 7A is a plan view of a sail according to a further embodiment of the invention;

FIGURE 7B is a plan view of a sail according to a still further embodiment of the invention;

FIGURE 8A is a plan view of a sail including sail battens;

FIGURE 8B is a cross-sectional view of a sail batten area;

FIGURE 9A is a cross-sectional view of a sail batten area according to an embodiment of the invention;

FIGURE 9B is a cross-sectional view of a sail batten area according to a further embodiment of the invention;

FIGURE 9C is a perspective view of the sail batten area of FIGURE 9B;

FIGURE 10A is a plan view of a sail according to an embodiment of the invention; FIGURE 10B is an example of a batten for use in the sail of FIGURE 10A;

FIGURE 10C is a further example of a batten for use in the sail of FIGURE 10A;

FIGURE 10D is a still further example of a batten for use in the sail of FIGURE 10A;

FIGURE 10E is a yet further example of a batten for use in the sail of FIGURE 10A;

FIGURE 1 1A is a plan view of a sail according to an embodiment of the invention; FIGURE 1 1 B is a plan view of a sail according to a further embodiment of the invention;

FIGURE 12A is a plan view of a sail according to a still further embodiment of the invention; and

FIGURE 12B is an alternative plan view of the sail of FIGURE 12A. Where appropriate, like reference numerals denote like elements in the figures. The figures are not to scale.

Detailed description of embodiments of the invention

There is described herein a sail comprising at least a portion of self-reinforcing polypropylene (srPP). The sail may be formed entirely of srPP, or as panels of srPP in combination with other materials.

The use of srPP within sails would present some advantages over current sail materials, as it is stronger and more lightweight.

In addition, with novel changes in manufacturing techniques by using a different release agent during the hot pressing stage of forming the srPP, the material can be transparent or near transparent rather than an opaque cloudy colour. This would present significant advantages for use in sails, as the entire sail could then be manufactured from transparent and strong material, whereas currently only small windows can be inserted into sails (this is because known transparent materials are not strong enough for an entire sail and are susceptible to stretching or cracking etc.).

It presents significant advantages for a sail to be fully transparent, as it allows an oncoming obstacle to be visible, e.g. when racing - other boats, or when wave sailing then the tip of a wave.

Transparent srPP has other uses, for example in bags and cases, see through documents wallets, or strong transparent cases. In other words, the material can be used for any purpose where visibility is of importance but protection is too (such as at security gates for carry-on items at airports, for example).

SrPP can also be utilised in sails made from normal sail materials as add-on lightweight reinforcing strips around the head clew and tack of the sail.

SrPP sails can be formed either through thermoforming processes or by stitching, gluing, riveting etc. to form a draft wing shape to a sail, improving its performance without the need for heavy tapered battens running transverse across the sails (as currently used in sails that are wing shapes).

Additionally, an ePP insert next to the mast could aid the definition of a wing shape and srPP would be stitched or glued to encase the ePP. As ePP and srPP are lightweight and water resistant and float, they are ideal sail materials.

In addition, polypropylene is 100% end of life recyclable and old sails could be easily recycled. Benefits of the described sail comprising at least a portion of srPP include; the strength and robustness of the material resulting in a more robust sail with less weight; the speed and ease of workmanship to form the sail; that only a small number of panels or reinforcement sections are required to significantly improve the performance and durability of the sail.

In addition, it will be understood that the sail can be formed from a plurality of layers, including coupling at least a portion of srPP with layers of Kevlar, Endumax or aramids. Furthermore, tapes or ropes can be inbuilt to save sewing and laying in extra ridged areas of the sail.

Furthermore, the sail can be formed from a srPP material including a compound or additive within the srPP polymer. The compound can be used to reduce UV degradation. Alternatively, the srPP may be combined or layered with one or more layers of plastic sheeting or material which have a UV protective quality, in order to protect the srPP material from UV degradation. In one example, the plastic sheeting is polyethylene terephthalate (PTE). In a further example, the srPP layer is laminated between two sheets of plastic with good UV degradation qualities.

FIGURE 1 shows an example of a sail 1 formed of srPP attached to a mast 2 of a vessel (such as a sail boat or windsurfer). The sail can be shaped or pre-formed to create a sail draught and wing shape. For instance, the sail can be shaped by thermoforming the srPP material, or by gluing or stitching layers of srPP.

FIGURE 2 shows a sail 1 formed of srPP connected to a mast 2, but with an ePP insert 3 next to the mast. The insert is enclosed between layers of srPP. The ePP insert is shaped to create a wing shape. The ePP / srPP combination is rigid but flexible, and also adds to flotation (for instance, in a windsurfer). The ePP / srPP is very light.

FIGURE 3 shows a sail 10 comprising portions of srPP 12a, 12b, 12c. SrPP sections or portions are attached around the clew head and tack of the sail, in order to provide strong and lightweight reinforcement. These reinforcing sections can be used in addition to the main region of the sail formed of srPP, or the main region of the sail can be formed from other materials.

FIGURE 4 shows a sail 20 formed from the transparent srPP. The whole sail is formed from the transparent or translucent srPP material, so that the user can see through the sail and see oncoming obstacles. For example, the transparent sail of FIGURE 4 means an approaching wave in the water 22 is visible to the user of the vessel (the arrows in FIGURE 4 show the direction of travel of the vessel). Only a portion of the sail could be formed from the transparent or translucent srPP material to form a window. Transparent srPP has significant advantages over current sail materials as the entire sail could be transparent and yet still strong and robust. Known "sail windows" are sewn into sails made from Mylar or similar materials, and it is often a weak point in sails (especially at the seam or join). Mylar is susceptible to cutting, abrasion and cracking, for instance. Use of srPP overcomes these weaknesses.

For instance, windsurf sails usually use materials for a transparent section of a sail that need reinforcement due to their thin nature. These portions are vulnerable to damage / tearing. An srPP transparent section of sail would allow a larger transparent area to be used in the sail, or even for the whole sail to be formed of the material.

In current sails, where Dacron or other known materials are used, reinforcing aramid lines of materials can be used to strengthen the sails. Where the srPP material is used (especially the transparent srPP material), then these aramid materials can be removed, thereby saving costs, reducing sewing times, and also increasing transparency of the sail.

A fully transparent sail allows you to see the horizon, other boats when racing, the wave when wave windsurfing etc., and so is highly desirable.

FIGURE 5 shows the transparent or translucent srPP material sail in use. As shown, the visibility of the user is improved in whichever direction the sail is orientated compared to the user, as the whole sail can be made transparent whilst remaining strong and lightweight. For instance, the transparent sail allows a full view of an oncoming craft.

FIGURE 6B shows a further example of the use of srPP regions or portions to reinforce areas of the sail under most stress or most prone to damage. The srPP regions can be added to existing sails for reinforcement. Increasing the size of the srPP and the length of the join with the existing sail material increases the energy dispersion and further reduces the likelihood of damage or tearing.

For instance, looking to FIGURE 6A, in a standard main boat sail 60, a number of regions of stress 62 are common. In the invention, these regions of stress can be reinforced with srPP portions or panels 64 attached to a panel of standard sail material 66. The srPP portions form regions of the sail having laminated layers (comprising the srPP portions or panels 64 and the standard sail material 66).

Also shown in FIGURE 6B is a jagged or uneven edge 68 of the srPP panel. This provides an increased area for maximum energy dispersion. In particular, the seam connecting or bonding the srPP portions or panels to the standard sail material is jagged to uneven, to maximise its length. This helps to reduce the likelihood of tearing at the seam.

FIGURES 7A and 7B show examples in which the srPP makes up portions of the sail. For instance, an srPP region can be applied to the large flat section of the sail, to improve sail performance, whilst a monolayer (or a plurality of layers) of an alternative material is joined to the srPP section to complete the sail. Certain regions of the sail can be reinforced with srPP strips to prevent the monolayer of sail material becoming overstretched or over strained and thereby damaged.

In an alternative, FIGURE 7 A shows a sail formed using an srPP panel 70 for the greater proportion of the sail surface area. This srPP panel 70 can be formed of a stiffer or thicker form of srPP to provide flatter and faster sails. A region of the sail nearest the mast 72 is formed from a panel of a soft monofilm 74. This monofilm 74 may be stretchable. The soft monofilm 74 can more easily bend and starch compared to the srPP panel 70, improving the aerodynamics of the sail. The soft monofilm 74 is connected to the srPP panel by a seam.

In addition, FIGURE 7A shows srPP strips 76 attached at the monofilm 74. The srPP strips 76 are attached so that the monofilm 74 can only stretch to a certain point. In other words, the srPP strips 76 reinforce the monofilm 74 to prevent the monofilm 74 stretching too far and tearing.

FIGURE 7B shows a further example of a sail formed using a region of monfilm and a region of srPP. The monofilm or monolayer 78 of a suitable sail material surrounds or borders a panel of srPP 79. The srPP is used particularly in the regions of greatest stress and strain on the sail. Use of panels of the srPP as described reinforces the most vulnerable areas of the sail, whilst maintaining a lightweight sail overall. This is due to the advantageous properties of srPP.

Sails may be formed with a monofilm or by using a monofilm with a reinforcement section. FIGURE 8A shows a sail of a windsurfer (having a deck 80, boom 81 and mast 82) in which battens are enclosed within pockets 83 in the sail 84. FIGURE 8B shows a cross-section of a batten pocket area 83. The battens 85 are stitched between two overlapping portions of material (including a first piece 86 and a second piece 87, having stitching 88 to connect them). The battens are used to stiffen and shape the sail for improved performance. However, the sail can be prone to tearing or damage at the regions where the battens are incorporated into the sail (shown as area 89).

FIGURES 9A and 9B shows two options according to the invention for using srPP to replace the battens of FIGURE 8. In a first option (option 1 , FIGURE 9A) the batten 90 can be sewn into a section of a first material at the sail 91 (formed of srPP or another material, as a single piece), by enclosing the batten with a second piece of material 92 formed of srPP or another material. Advantageously, the first and second pieces of material can be stitched together (at stitching points 93) without damage to the reinforcing structure of the srPP. The batten 90 can be formed of srPP. Furthermore, the batten 90 may be 0.5mm or greater in thickness, for greater stiffness.

As a second option (option 2, FIGURE 9B) the battens can be replaced entirely by use of a strip of thicker srPP 94 sewn on to the sail 95 in specific points (using stitching 96). The strips of srPP may have a thickness of 0.5 mm, or greater, for instance. The srPP strips can be stitched to the sail material directly, and thereby provide stiffness and shape to the overall sail. FIGURE 9C shows a perspective view of the battens of FIGURE 9B, once attached to the sail.

Advantageously, srPP has low stretch and creep, and so can be stitched to the sail without damage. Furthermore, the described method of stiffening and shaping the sail, using strips of srPP in place of battens, can reduce manufacturing time and manufacturing complexity (as the amount of sewing or stitching is reduced).

The properties of srPP battens applied to a sail can be modified according to the composition of the battens. FIGURE 10A shows a sail 100 including battens (formed in batten areas 101 ) comprising srPP, the sail connected to a mast 105. These types of batten can be used to replace fiberglass, plastic or wooden battens, in order to stiffen and shape the sail.

In a first example at FIGURE 10B, battens 102 are formed of srPP material used in strips, in order to replace fiberglass battens at the sail. In a second example at FIGURE 10C, battens 103 are formed of srPP material incorporating aramid fibres 104. The aramid fibres 104 may be used to reinforce the strips of srPP material, wherein the strips are used as battens at the sail. In the example of FIGURE 10D, battens 103 are formed using layers of srPP material configured such that intervening layers have aramid fibres 104 arranged perpendicular to each other, and such that the longitudinal direction of the aramid fibres of a first layer of srPP run parallel to the longitudinal direction of the batten and so that the longitudinal direction of the aramid fibres of a second layer of srPP run perpendicular to the longitudinal direction of the batten. In other words, a second layer comprises aramid fibres arranged compared to the first layer such that the aramid fibres of the first srPP layer are at 90 ^e to the second layer. The arrangement of the fibres of intervening layers is called the "layup". In the example of FIGURE 10E, battens 103 are formed using layers of srPP material configured so that each layer is arranged having aramid fibres 104 at 90 ^e to the previous layer upon which it is arranged. However, in this example the aramid fibres are also arranged at 45 ^e to the longitudinal direction of the batten. This improves the flexibility of the batten, whilst still causing the batten to be semi-rigid.

Although the sail comprising at least a portion of srPP is robust, ideally the sail material will also be soft, pliable and easily conformable to new shapes when in use. Ideally, a sail is foldable to a compact volume when not in use. The pliability of the sail material must be balanced against the robustness of the sail material.

Improved robustness of the srPP sail may be provided by increasing the weight or density of the srPP material. However, increasing the weight or density of the srPP material may also increase stiffness. In order to soften the srPP material, the material may be heated and/or pressed (placed under pressure). This processing of the srPP material has been found to soften the material compared to an unprocessed portion of srPP of a given weight or density. In particular examples, srPP material having a density of 134 gm ^"3 is used to form a sail, and applied heat and pressure is used to soften the material prior to manufacturing the sail. A similar technique can be used with 100 gm ^"3 srPP material for use in sails.

FIGURES 1 1 A and 1 1 B show alternative sails (connected to a mast 1 1 1 ) in which a portion of the sail is reinforced using a plurality of srPP panels. In the example of FIGURE 1 1 A, the entire sail is formed of a panel of srPP 1 10 (ideally a single layer of srPP), with additional srPP panels 1 12 applied (or overstretched) to the sail area in regions of particular stress or that are particularly prone to damage. In an alternative embodiment, these additional panels could be comprised of a material other than srPP. In another example shown at FIGURE 1 1 B, srPP strips 1 13 are applied to the sail in manner described in reference to FIGURES 9A and 9B, in order to replace traditional sail battens. In each case, the panels or strips of srPP are applied to shape and stiffen the sail, and thereby improve sail performance whilst being lightweight and strong. The srPP strips can be comprised of one layer or two laminated layers of srPP, for example.

FIGURES 12A and 12B show a sail in which the Luff area 120 (the forward leading edge of the sail 122, which is commonly parallel to the mast 121 ) is formed from a pre-shaped or pre-formed region of srPP. FIGURE 12A shows a side view of the sail, whereas

FIGURE 12B shows a view of the sail 122 as if looking down on the top of the mast 121 , from above. For instance, the Luff area 120 can be formed form a pre-formed curve portion 124 (in srPP), stitched into the main sail. The Luff area 120 can therefore "catch the wind". For instance, the srPP can be formed as a semi-rigid shape designed to provide the best performance. Although the srPP is formed into a semi-rigid shape, the material retains some flexibility. Therefore, it is ideally suited for use in the sail. In the particular example of FIGURE 12A and 12B srPP strips 125 are also provided as sail battens, as discussed above in relation to FIGURES 9A to 10E for instance.

The sails may be entirely formed from a portion of transparent or translucent srPP material, or a sail may include regions or windows of transparent or translucent srPP material. Commonly, srPP may release chalk or other compounds when formed, which reduces visibility through the srPP material. This means that formation of sails with common srPP material would require a mono-film (or window area) to be added. However, the present inventors have overcome this problem, in order to produce transparent or translucent srPP material.

The whole sail can be formed out of translucent srPP. In a further example, a window of another transparent or translucent material can be added to a sail formed of srPP.