WO1987007234A1

WO1987007234A1 - Sail assembly with camber inducing means

Info

Publication number: WO1987007234A1
Application number: PCT/GB1987/000346
Authority: WO
Inventors: Paul Donald Zink
Original assignee: Paul Donald Zink
Priority date: 1986-05-22
Filing date: 1987-05-20
Publication date: 1987-12-03
Also published as: DK26488A; AU7399687A; DK26488D0

Abstract

A sail assembly for a sailboard comprises a sail having a luff pocket (16) and camber inducing means comprising leading edge support inside the luff pocket and battens (20) extending from the leading edge support to the leech of the sail. The leading edge support comprises a number of vertically spaced, tear-drop shaped rib elements (30) and a pair of vertical strips (32) of sail cloth stretched taut over the rib elements.

Description

Sail assembly with camber inducing means

THIS INVENTION relates to a sail assembly. More particularly, it relates to a sail assembly provided with camber inducing means.

The invention finds particular application in boardsailing sails. In its simplest form, a boardsailing sail comprises a sail having a luff pocket into which the sailboard mast is a close sliding fit. Such a sail provides a far from optimum aerofoil shape when in use, the main imperfection being at the luff of the sail, where the sail proper and the luff pocket meet. The transition here is abruptly from the luff pocket (which is distended into a substantially round cross-sectional shape by the mast) to the single foil of the sail proper.

Applicant is aware of the use of camber inducing means to improve the aerofoil shape of a sail. In one such construction the camber inducing means comprises resiliently flexible full length battens each having a split leading or luff end. The luff end of the batten is then splayed apart, with one half extending to one side of the mast and the other half to the other side of the mast. The sail is shaped such that when the sail is stretched in the luff-to-leech direction along the battens, the battens are placed under longitudinal compression and the mast (which is resiliently flexible) bows slightly. This causes a camber to be induced in the sail, the camber being able to reverse when changing tack. In another construction the camber inducing means comprises full length battens, each having associated therewith a bifurcated element located between the luff end of the batten and the mast. The bifurcated leading ends of the elements straddle the mast. To accommodate the splayed apart luff end of the batten or the bifurcated element, as the case may be, the luff pocket is widened somewhat. The main drawback of these constructions is that the maximum effective width of the luff pocket is extremely limited due to the lack of control over the flexible luff ends of the battens. The tighter the sail, the more the luff ends of the battens tend to flex beyond the optimum aerofoil shape. Secondly, the thickness of the sail, immediately behind the mast, is limited to substantially the diameter of the mast. Thirdly, the greater the width of the luff pocket, the more does the luff pocket have to be able to slide across the mast upon changing tack. The tighter the sail, the more difficult this sliding movement becomes. On the other hand, when the sail is too slack, it tends to wrinkle, and any camber which is induced in the leading edge of the sail is not continued through to the the regions of the sail between adjacent battens.

It is an object of the present invention to provide a sail assembly with camber inducing means which is able to support a substantially wider part of the luff of the sail in the form of a reversible double surface assymetrical foil, without the difficulties heretofore experienced, and which is better able to approximate the optimum aerofoil shape.

According to the invention there is provided a sail assembly which comprises: a sail having a head, a tack, a leech, and a luff pocket, a mast being receivable in the luff pocket; and camber inducing means which includes a leading edge support accommodated in the luff pocket, and one or more battens extending from the leading edge support to the leech, the leading edge support comprising a plurality of vertically spaced, transversely extending, rib elements, and a web of flexible sheet material which, in use, can be stretched taut over the rib elements.

By the leading edge is meant the forward part of the sail, which extends rearwardly from the mast, on the leeward side of the sail.

Each of the rib elements may have a nose portion for bearing against the mast, and a pair of resiliently flexible limbs which extend rearwardly from the nose portion, the limbs diverging rearwardly when in a relaxed, inoperative condition, and, when in a flexed, operative condition with the rear ends thereof brought together, forming the rib element into a tear-drop shape.

The nose of each of the rib elements may be forwardly concave, for locating the rib element laterally with respect to the mast.

At least one of the rib elements may have an adjustable nose portion for adjusting the angle at which the limbs thereof diverge rearwardly when in the relaxed, inoperative condition.

Said web may be attached at its head end to the head of the sail and may, at its tack end, be provided with adjustment means for adjusting the tension of the web in a head-to-tack direction, relative to the tension of the sail in that direction. Said web may be in the form of two vertically extending strips of sheet material, one on each side of the leading edge support, there further being a strap at the height of each of at least some of the rib elements, each strap being arranged to extend across the nose of the respective rib element and to interconnect said vertical strips.

Each vertical strip may have, at the height of each of the rib elements, a transversely extending pocket, for accommodating, and thereby locating, the corresponding limb of that rib element.

There may be a flexible connection between each of the battens and a respective one of the rib elements, the luff end of the batten extending forwardly between the limbs of the respective rib element.

The sail may be provided, at the tack thereof, with an inverted U-shaped fitting having one leg thereof located with respect to one side of the luff pocket and the other leg thereof located with respect to the other side of the luff pocket, for attachment thereto of a tack downhaul rope in such a manner that the downhaul rope is accommodated at least partly in the luff pocket.

The invention extends to a rib element for a sail assembly as defined above, which has a nose portion for bearing against the mast, and a pair of resiliently flexible limbs which extend rearwardly from the nose portion, the limbs diverging rearwardly when in a relaxed, inoperative condition, and, when in a flexed, operative condition with the rear ends thereof brought together, forming the rib element into a tear-drop shape. The invention will now be described in more detail, by way of example, with reference to the accompanying drawings. In the drawings :

Figure 1 is a diagrammatic plan of a sail assembly in accordance with the invention, for use with a sailboard;

Figure 2 is a diagrammatic section of-the sail assembly, on line II-II in Figure 1;

Figure 3 is a detail cross-section through the luff pocket of the sail assembly, showing the camber inducing means which forms part of the assembly; Figure 4 is a perspective view of the camber inducing means, folded open to show the internal parts; Figure 5 shows a rib element forming part of the camber inducing means, in a relaxed, inoperative condition;

Figure 6 shows the rib element in a flexed, operative condition; Figure 7 shows the construction of the tack region of the sail assembly; and

Figure 8 shows the nose portion of an alternative form of rib element.

Referring first to Figures 1 and 2, reference numeral 10 generally indicates a sail assembly for a sailboard, fitted on a sailboard mast 12. The sail assembly 10 comprises a sail 14 having a luff pocket 16 (the cross-hatched portion in Figure 1), and camber inducing means comprising a leading edge support 18 (the dotted portion in Figure 1) inside the luff pocket and a number of vertically spaced, full length battens 20 extending from the leading edge support 18 to the leech 22 of the sail. The width of the luff pocket 16 (in the luff-to-leech direction) is about 60% of the overall width of the sail. Further battens 23 are provided, one at the head of the sail and another at the foot of the sail. The battens 23 do not, however, form part of the camber inducing means.

The sail 14 is provided with a cut-out 24 to enable a wishbone boom (not shown) to be tied to the mast 12, and an eyelet 26 for the outhaul rope (not shown). The sail 14 also has suitably located windows 27. Because of the extent of the luff pocket 16, the windows lie wholly within the region of the luff pocket, transparent material being required on each side of the luff pocket. Dotted lines 28 indicate permanent stiffeners which are located in pockets sewn to the material of the luff pocket 16. There are two of the stiffeners 28 on each side of the luff pocket.

On each side of the luff pocket 16, along the trailing edge thereof and at the height of each of the battens 20, a half-moon shaped opening 29 is cut into the material of the luff pocket. These openings will facilitate drainage of water from the luff pocket, and also provide access when guiding the battens 20 during insertion thereof.

Referring now also to Figures 3 and 4, the leading edge support 18 comprises a number of vertically spaced rib elements 30 (there being a rib element for each of the battens 20 and, in addition, a further rib element midway between each pair of battens 20), and a pair of vertically extending strips of sail cloth 32 which, in use, are drawn taut over the rib elements.

The rib elements 30 and the battens 20 are of a resiliently flexible material such as, for example, glass-fibre reinforced resin. The rib elements 30 have a concave nose portion 34 and, when in the relaxed condition as shown in Figure 5, a pair of rearwardly diverging limbs 36. When the free ends of the limbs 36 are brought together, the rib element takes up a symmetrical tear-drop shape as illustrated in Figure 6. The limbs 36 of the rib elements 30 at mid-height of the sail assembly are longer than those of the rib elements towards the head and foot of the sail, according to the width of the leading edge support 18 at that point. It will be appreciated that the rib elements could be pre-moulded in the shape illustrated in Figure 6, instead of being formed into that shape by resilient flexing.

Each rib element 30 is located in position by its limbs 36 entering into pockets formed by transverse fabric strips 38 sewn to the inside of the vertical strips 32. At the level of each of the battens 20 the construction is further as follows. A length of webbing is doubled up and sewn along its upper and lower edges to form a rearwardly open pocket 40 for the leading end of the batten 20. Each end of the webbing is folded back once again so that four layers are now formed. These are sewn together top and bottom to form, on each side of the pocket 40, a strong fowardly open pocket 42. The free ends of the webbing are each sewn to the respective one of the vertical strips 32. The ends of the limbs 36 enter into the pockets 42, the pockets 42 being strong enough to keep the ends of the limbs together.

At the level mid-way between each pair of battens 20, the construction is similar to that described above, except that the pocket 40 is omitted and that a single forwardly open pocket 42 is formed into which the ends of both limbs 36 enter.

That part of each batten 20 which extends rearwardly beyond the trailing edge of the luff pocket 16 is located in a batten pocket formed in the sail 14 and which extends from the trailing edge of the luff pocket to the leech 22 of the sail. At the leech end, the batten pocket is provided with a conventional buckled strap (not shown) for tensioning the sail along the batten and thus placing the batten under longitudinal compression.

At the level of each of the rib elements 30, the vertical strips 32 are each provided, along their forward edges, with a strap 44, the two straps 44 being provided with complementary pile and hook fastener means such as that available under the registered trademark 'Velcro¹. After insertion of the limbs 36 into the pockets 38, the strips 44 are fastened together so as to extend across the nose portion 34 of the rib element 30. This will pre-tension the vertical strips 32 transversely, i.e. in the luff-to-leech direction. If it is desired to remove the rib elements 30, the pile and hook fasteners are undone. A number of vertically spaced webbing strips 46 (only one of which is shown in the drawings) are provided which permanently interconnect the forward edges of the vertical strips 32.

The upper ends of the vertical strips 32 are sewn to the sail 14 at the head 48 thereof. As illustrated in Figure 7, the lower end of each strip 32 is connected to the sail 14 at the tack 50 thereof via a twin ring buckle 52 and a strap 54, the lower end of the strap 54 being sewn to the respective side of the luff pocket 16. The strips 32 are otherwise unconnected to the sail. The twin ring buckle 52 and the strap 54 enable the vertical strip 32 to be drawn taut vertically.

Still referring to Figure 7, at the tack 50, c the sail is provided, on each side of the luff pocket 16, with an upwardly open pocket 60 (only one of which is shown). A U-shaped fitting 62 of a stiff material has each of its legs inserted downwardly into one of the pockets 60. A tack downhaul (not shown) for the 1_Q sail 14 is attached to the rounded, uppermost part of the fitting 62. This construction enables the downhaul to be located inside the luff pocket 16 and permits the tack 50 of the sail to be hauled down until it virtually touches the sailboard (shown dotted 15 at 64 in Figure 1). Thereby the gap between the sailboard 64 and the foot 66 of the sail can be reduced to a minimum.

In rigging up the sail assembly the mast 12 is inserted into the luff pocket 16 so that it lies in

20 front of the straps 44 (i.e. with the straps 44 being disposed between the mast and the nose portions 34 of the rib elements 30) and behind the webbing strips 46, as illustrated in Figure 3. The buckled straps at the leech ends of the battens 20 are now tightened so as

25 to stretch the sail 14 along the battens (i.e. in the luff-to-leech direction) and thus place the battens under longitudinal compression. This has the effect of bringing the nose portion 34 to bear against the mast 12, causing the straps 44 to be depressed by the

30 mast 12 into the concavity of the nose portion. This further tensions the strips 32 transversely ie in the luff-to-leech direction.

Rigging of the sail is now completed by tightening the outhaul and the downhaul ropes. The straps 54 by which the bottom ends of the vertical strips 32 are tied to the tack 50 are adjusted so that the strips 32 are tensioned longitudinally (i.e. in the head-to-tack direction) to a greater extent than the sail 14. On the one hand this will ensure that the strips 32 are drawn taut over the rib elements 30 so that not only those parts of the strips 32 immediately adjacent the rib elements, but also the parts intermediate the rib elements, will take up the tear-drop shape of the rib elements and are so able to support the leeward side of the luff of the sail. On the other hand, the sail 14 can remain sufficiently slack so that, when changing tack in use, it can easily slide over the strips 32 and the mast 12 in the direction of double headed arrow A in Figure 2.

The connection between the battens 20 and the limbs 36 is flexible so that, as shown in Figure 3, when changing tack, the batten 20 can move from one limit position (indicated by dotted line 20.1) in which the leading end thereof abuts against the inside of the one limb 36 of the rib element 30, to the opposite limit position (indicated by dotted line 20.2) in which it abuts against the inside of the other limb 36. In each of the positions 20.1 and 20.2, the batten 20 forms in effect a smoothly curved, continuous extension of the corresponding limb 36.

Referring lastly to Figure 8, the modified rib element 30.1 shown there has a nose portion 70 which is in two arcuate parts 70.1 and 70.2, and a pair of straight, resiliently flexible limbs 72 each secured to a respective one of the parts 70.1, 70.2. The two arcuate parts 70.1, 70.2 can be adjusted with respect to one another in the direction of double headed arrow B to increase or decrease (as shown dotted) the angle at which the limbs 72 diverge when in the relaxed condition. Once in the desired angular position, the parts 70.1 and 70.2 can be locked together. The arrangement may be such that the parts 70..1 and 70.2 lock together automatically when the limbs 72 are flexed. This adjustability will provide added versatility in that the user can, to a certain extent, adjust the profile of the leading edge support 18 of the camber inducing means.

The construction described above provides a sailboard sail assembly with an operative shape which, it is believed, much better approximates the optimum aerofoil shape that is required for such a sail. It produces a pre-shaped and controlled aerofoil section, particularly of the leading edge or leeward side of the luff or forward part of the sail, and reduces turbulence on the windward side.

Claims

CLA IMS :

1. A sail assembly which comprises: a sail having a head, a tack, a leech, and a luff pocket, a mast being receivable in the luff pocket; and camber inducing means which includes a leading edge support accommodated in the luff pocket, and one or more battens extending from the leading edge support to the leech, the leading edge support comprising a plurality of vertically spaced, transversely extending, rib elements, and a web of flexible sheet material which, in use, can be stretched taut over the rib elements.

2. A sail assembly as claimed in claim 1, wherein each of the rib elements has a nose portion for bearing against the mast, and a pair of resiliently flexible limbs which extend rearwardly from the nose portion, the limbs diverging rearwardly when in a relaxed, inoperative condition, and, when in a flexed, operative condition with the rear ends thereof brought together, forming the rib element into a tear-drop shape.

3. A sail assembly as claimed in claim 2, wherein the nose of each of the rib elements is forwardly concave, for locating the rib element laterally with respect to the mast.

4. A sail assembly as claimed in claim 2 or claim 3, wherein at least one of the rib elements has an adjustable nose portion for adjusting the angle at which the limbs thereof diverge rearwardly when in the relaxed, inoperative condition.

5. A sail assembly as claimed in any one of the preceding claims, wherein said web is attached at its head end to the head of the sail and is, at its tack end, provided with adjustment means for adjusting the tension of the web in a head-to-tack direction, relative to the tension of the sail in that direction.

6. A sail assembly as claimed in claim 5, wherein said web is in the form of two vertically extending strips of sheet material, one on each side of the leading edge support, there further being a strap at the height of each of at least some of the rib elements, each strap being arranged to extend across the nose of the respective rib element and to interconnect said vertical strips.

7. A sail assembly as claimed in claim 6, wherein each vertical strip has, at the height of each of the rib elements, a transversely extending pocket, for accommodating, and thereby locating, the corresponding limb of that rib element.

8. A sail assembly as claimed in any one of claims 2 to 7, wherein there is a flexible connection between each of the battens and a respective one of the rib elements, the luff end of the batten extending forwardly between the limbs of the respective rib element.

9. A sail assembly as claimed in any one of the preceding claims, wherein the sail is provided, at the tack thereof, with an inverted U-shaped fitting having one leg thereof located with respect to one side of the luff pocket and the other leg thereof located with respect to the other side of the luff pocket, for attachment thereto of ^~ tack downhaul rope in such a manner that the downhaul rope is accommodated at least partly in the luff pocket.

10. For a sail assembly as claimed in any one of claims 2 to 8, a rib element which has a nose portion for bearing against the mast, and a pair of resiliently flexible limbs which extend rearwardly from the nose portion, the limbs diverging rearwardly when in a relaxed, inoperative condition, and, when in a flexed, operative condition with the rear ends thereof brought together, forming the rib element into a tear-drop shape.

11. A sail assembly substantially as herein described and illustrated.

12. A rib element substantially as herein described and illustrated.