GB2247221A

GB2247221A - Aerofoil-section sails

Info

Publication number: GB2247221A
Application number: GB9111434A
Authority: GB
Inventors: Philip John Boys
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-05-25
Filing date: 1991-05-28
Publication date: 1992-02-26
Anticipated expiration: 2011-05-28
Also published as: GB9111434D0; GB2247221B

Abstract

A flexible, aerofoil-section sail 1A, e.g. for a windsurfer, has two spaced, flexible sheets defining the aerofoil surfaces, the sheets being stiffened by pocketed battens 6. The two sheets are formed by one sheet extending round the mast, thus also forming the leading edge of the sail section. The battens are secured as pairs to leading edge batten holders. The sail may be swung about the mast to lie centrally, Fig.3, to lie to starboard, Fig.4 or to port, Fig.5. A single sail arrangement is also described (Fig 18). <IMAGE>

Description

AEROFOIL SECTION SAILS WITH ALTERNATELY VARIABLE CAMBER & VARIABLE CONTOUR SAILS. USING THIS PRINCIPLE This invention relates to all Sails that can be used to generate propulsive power by airflow passing on both sides of the sail.

Sails are well known on Yachts, Dinghys, Land Yachts & BR< Windsurfers, with the exception of Spinnakers and Square rigged ships, They are all basically of triangular side view.

Jib or Foresails are attached at the leading edge (luff) and set by adjusting the Jib sheet (rope) at the bottom of the trailing (leech) edge to give the reguired angle of attack into the wind.

Leading edges of Main sails are attached at the mast on Dinghys, Yachts & Land Yachts. The bottom of the 'triangle' shape is wholly or partially attached to a boom. The angle of attack required into the wind is set by tensioning the main sheet (rope) between the Boom end and a centrally mounted pulley close to the aft end of the vessel.

Similarly on a windsurfer, except that the boom is attached to the mast at approx shoulder height. The angle of attack of the sail into the wind required is adjusted by hand. The sail is often extended out from the basic triangle shape by battens.

A part of the triangle sail shape is below the boom.

Fully battened sails ( Rotational sails) have battens from luff to leech held in pockets stitched into the Sail, that rotate around the side of the mast soley for port or stbd use.

All the above examples of completed sails are produced as a single piece of sail - even though they may be manufactured from several pieces of different material. There is no sectional width apart from the material used, with the exception of some windsurfer sails wh-ich are called : (a) "camber induced" where approx 1/10 of the sail from luff towards leech, has a cross section, in reality a widened 'luff tube'. Inside of which there are 'Camber Inducers', whose function is to hold the leeward side of the sail only, in a cambered shape to gain propulsive power on their port or stbd settings onlv. which they have to be 'Jerked into'.

(b) Similarly some mast attachments claim to give some sail power adjustment by holding the main batten in a straighter or curved position as required.

These two separate patented inventions, in use, doubtless give some benifit to propulsive power and control of it, if used together, but are totally different from the present linked inventions that can either be a truly adjustable aerofoil sail or a variable contour sail with power settings between Port & Stbd extremes and a neutral 'flat' setting, enabling it to do essentially the same as the full aerofoil sail, able to:1. To form a true neutral streamline section sail of minimum profile drag.

2. To automatically assume this position during the uphauling of the rigged sail from the water.

(The most common method of starting sailing a windsurfer) 3. To form an alternate & variable aerofoil section sail, or either a variable contour sail to adjust, while in use, for propulsive power required.

Previous sails will generate a lot of induced drag during the 'tacking' manoeuvre, either by the sails flapping in the wind or by presenting the reverse curve into the wind, in the, case of 'camber induced' or 'rotational' sails, which cannot be reset, by yanking into position, until the tack is completed.

With the exception of Roller Reefing Mainsails, and windsurfer masts fitted with the central batten clamp. There is little or no facility for using less power while set & in use.

An excessive increase in wind speed necessitates - dropping the sail & raising a smaller one.

With regard to the present invention, optional full aerofoil sail, there are patented aerofoil sails, these fall broadly into one or more of the three following categories:1. They are not true variable aerofoils, and are not capable of forming, old, known and proven aerofoil sections such as,'Clark W', 'STCYR 24', to name two only out of many, which have the required high 'lift' factor, gained in part from the necessary curvature on both sides of the aerofoil.

2. They are impractical for real use as Sails, but satisfy the legal critera for grant of a patent. However they specifically state "curvature on one side only" and or "shall be held taught to keep other side flat" or other such descriptions / claims substan'tially the same.

3. Mention is not made or claimed, for using1 varying degrees of asymetric aerofoil sectional shape, as the ideal means of varying the propulsive power obtained, from the maximum (as explained in 1) down to zero propulsive power c/w the benefit of absolute minimum drag when set in the neutral streamline position.

Part of the present invention, is an aerofoil section sail of alternate & variable camber, that can be fitted over or substan'tially attached to a mast & set to form a variable power sail by rotating the low drag leading edge formed in conjuntion with attached, pairs of removable battens, held in opposite pockets stitched in the sail, on both sides of the aerofoil. The battens are secured at the trailing edge (leech) by the method shown in Fig. 16 & Fig. 17 section 'DD' of The leech is also acted upon by the boom as per normal.

The aerofoil sail described can be set to a neutral streamline position, approaching the optimum 'fineness' ratio, depending on it's size & application. t possess's a true alternately variable mean camber line, with a straight chord line when set to the neutral streamline section.

The completed full aerofoil sail option will be made to deter water from entering the aerofoil, by the use of inset stretch panels shown in fig 1. Facility (not shown) would be provided if required, to expel any such water by discharging a small compressed gas cylinder inside the aerofoil, to make the sail buoyant, for saftey, when in the water, e.g. after a capsize.

The aerofoil sail described would posses a rounded leading edge leading back to a thicker section, before gradually thinning to the minimum at the trailing edge (leech).

The present invention, full aerofoil or variable contour sail, would use battens to extend the sail out from the basic triangle shape, if reqd., as do previous sails.

The leading edge swivelling, adjustable / lockable sytems, would be constructed, so that they could be engaged, partially engaged or disengaged manually.

In the windsurfer application, either in the full aerofoil sail or the variable contour sail, the system can be set to work in conjunctin with the uphaul rope, so as to give an automatic, semi-automatic or soley manual facilitys. Achieved by the quadrant adjusting lever's locking pin position (fig 10). Technically essential on whatever application of the present invention is the ability of the leading edge to turn in conjunction with the battens & still rotate as reguired achieved by adjustable - lockable mast leading edge swivels, by which camber or contour is achieved, in conjunction with clamped on leading edge formers or 'contour formers'.

The contours (luff to leech) of the sails mentioned will be formed in Dart onlv by using tapered battens of any type, number, made in as many pieces as necessary with the required stiffness / flexibility as is old and known.

They will cooperate with the new mast / or leading edge formers and extend back & be fitted in normal pockets stitched into the sail until they reach the trailing edge (leech), where they will either be held loosley together by a stitched in sealed end (Fig. 16) & tensioned from the luff end.

In the case of the variable contour sail they will end conventionally with tensioning batten straps CFig. 18) after starting in the new batten holders 'contour foners' that. are clamped or fixed to the mast when the sail is set and in use.

A specific embodiment of the present invention, for the windsurfer aerofoil sail application will now be described by way of example with reference to the accompanying diagramatic drawings 1 to 17 and 20 to 2N C not to scale ) in which: Figure 1 shows 'opened out' partially finished sail, CIW bottom inset stretch panel, to deter ingress of water into the aerofoil. A similar panel shown will be fitted inside the boom attachment area. The finished sail is as Figures 2 & 12.

Figure 2 shows sidle view of a rigged windsurfer sail, with two types of battens randomly shown. It also indicates where the section 'AA' is-taken from, and shows the swivel position for the following diagrams.

Figure 3 plan view of section on 'AA', sail set in neutral streamline position.

Figure 4 plan view of section on 'AA',sail on Port Tack.

Figure 5 plan view of section on 'AA', sail set on Stbd Tack.

Figure 6 Shows various batten arrangements, on new mast / L.E.

Figure 7 Shows section on 'AA' (fig 2) of new mast, boom clamp and rotational assembly.

Figure 8 Shows utilization of original mast, for use with Leading edge formers - batten holders (Figure 14).

Figure 9 Shows front view of contour adjusting lever, c/w lever line attached to uphaul rope.

Figure 10 shows contour adjusting lever, as part of, the leading edge rotational quadrant assembly. Plan view from underneath, it also shows where the section 'BB' is taken from for figure 11.

Figure 11 Partially sectioned side view of the leading edge rotational quadrant assembly, showing the front portion of the boom. The contour adjusting lever, the uphaul rope, attached or loose'ly attached by a line shown to contour adjusting lever & the disengagement locking pin. Springs may be fitted, similar to those shown, to ensure the quadrant returns to the centre readily if required.

Figure 12 Shows side view of rigged windsurfer aerofoil sail, Standard mast used in conjunction with leading edge batten holders ( Figs. 14 & 15 ) & also shows fitted, a compatible standard adjustable length boom. It also shows where the view 'EE' is for fig 13 & view 'DD' for figure 15 Figure 13 shows waterproofed 'zipped' sail access panel.

Figure 14 Shows plan view of a Leading Edge former - batten holder, and how it is capable of being clamped onto a round (std. windsurfer) mast at the correct position.

Figure 15 Shows front view of fig.13 with clamp locked shut.

Figure 16 Shows section 'DD' for Fig. 17 Figure 18 Shows plan view, example of new 'contour former' single batten holder. fixed on for use with present invention of variable contour sail, shown on port tack.

Figure 19 Shows a diapramatic plan view, of a 'contour former', unclamped, shown out of the sail for clarity.

Referring to the windsurfer aerofoil sail application.

The sail 1A is pulled down & around the mast 13A, through the inset stretch panels, sail foot 20 & boom attachment area 22, the sail 1A is folded back at the reguired boom height to leave the mast exposed, (to enable boom to be clamped on) through the respective sealing rings 21 and 23 & tensioned by the downhaul line 9 and held by the standard jambcleat 11, part of the standard mast to deck assembly 10, at the mast foot. The sail battens 6 are fitted into their pockets 4 in the sail at the luff access panels and pushed in until they lock into the leading edge batten holders SA, the holder is then aligned with a vertical line down the mast and clamped to it. This process is repeated until all batten (pairs) are in.

The front of the boom 14A, new rotational assembly 15A (fig 8) is then clamped to mast 13A at the required height, by placing clamp around the mast & affixing the over - centre clamp.

The Contour adjusting lever 16A is set in the neutral streamline position. The sail la is then tensioned by the outhaul line 17 between the trailing edge (leech) of the sail 1A and the boom 14A and held in the clew outhaul line jambcleat 18, and adjusted until required streamline effect is achieved.

The Sail is now ready for use, after setting the contour lever 16A, as required.

Derigging is the reverse of rigging above.

The above aerofoil sail can also be used on a nearly all sail powered vessels / vehicles, as can, the variable contour sail.

now described in it's windsurfer application merely for ease of description.

Refering to the drawings the variable contour sail will now be described with reference to the accompanying drawings in which: Fig. 18 is a sectional plan view of the sail at a batten pocket and shows a 'Contour Former' 5B clamped onto a windsurfer mast 13A c/w attached batten 6 held in place by a batten strap and buckle 7 at the leech.

Fig. 19 Plan view of a 'Contour Former around a mast but open & not clamped shut or in it's normal position in the sail.

Fig 20 is a plan view of an alternative 'Contour Former' BC shown attached to a streamline mast 13C.

Fig. 21 Shows a variable contour sail rigged on a windsurfer mast, ready for use after attaching to a windsurfer.

Shown to illustrate a application of the present invention.

Shown with a optional one piece boom, obviously could be manufactured to form the front part of a standard boom as shown in fig. 12. The standard batten straps have not been shown. A foot batten is shown as is known & old, though not shown as such could easily be ending in a 'contour former' on the mast, as could a top batten, not shown. All battens which end in the new 'contour formers' have zipped acsess panels as is old & known.

Fig. 22 Shows a variable contour sail rigged as a main sail on a Dinghy or Yacht, it is fitted over a streamlined mast 13C and uses the shown variation of 'Contour Former' Fig. 20.

Simple means for swilleving to Boom to the Mast will be provided,-either by lines or a lever and catch assembly, not shown. All examples of sails according to the present invention may use a 'leech line' to vary the taughtness of the leech as is old and known.

Facility would be provided, if required for the application of the present invention, of variable tension outhaul lines and variable tension batten straps.

Kev to numbers used on Diagrams 1A = AEROFOIL SAIL.

1B = VARIABLE CONTOUR SAIL.

2 = LUFF TUBE OF SAIL.

3 = LEECH LINE IN EITHER SAILS.

4 = BATTEN POCKETS IN SAILS.

4B = TWIN BATTEN HOLDER IN LEECH OF AEROFOIL SAIL = = LEADING EDGE FORMER IN AERFOIL SAIL (TWIN BATTEN HOLDER AT LUFF) SB = 'CONTOUR FORMER' IN VARIABLE CURVED SAIL (SINGLE BATTEN HOLDER AT LUFF) SC = 'CONTOUR FORMER' ALTERNATIVES 6 = BATTENS VARIOUS 7 = BATTEN STRAPS & HOLDING BUCKLES.

8 = BATTEN END CAP.

9 = DOWNHAUL LINE 10 = STANDARD MAST FOOT (WINDSURFER) 11 = DOWNHAUL LINE JAMBCLEAT 12 = MAIN HALYARD.

13A = MAST (ROUND SECTION ) 13B = MAST (SLOTTED SECTION) 13C = MAST (STREAMLINE SECTION) 14A = BOOM (WINDSURFER) 14B = BOOM (MAIN SAIL) 1SA = BOOM TO MAST QUADRANT ASSEMBLY CWINDSURFERS ETC) 15B = BOOM TO MAST ASSEMBLY (MAIN SAILS) 16A = CONTOUR ADJUSTING LEVER.

(PART OF 1SA) 16B = CONTOUR ADJUSTING LEVER (PART OF 15B) 17 = LEECH OUTHAUL LINE.

18 = LEECH OUTHAUL LINE JAMBCLEAT 19 = KICKING STRAP.

20 = INSET MAST FOOT APERATURE AEROFOIL SAIL.

21 = SEALING RING MAST FOOT APERATURE IN AEROFOIL SAIL.

22 = INSET BOOM TO MAST APERATURE IN SAIL 23 = SEALING RINGS BOOM TO MAST APERATURE IN SAIL. (22) 24 = UPHAUL ROPE (windsurfer) 25 = CONTOUR ADJUSTING LEVER LINE ATTACHED TO 24 26 = LUFF ACSESS ZIPPED PANELS 26 = MAIN SHEET 28 = CONTOUR LEVER LOCKING PIN 29 = CONTOUR ADJUSTING LEVER LOCKING HINGE 30 = CONTOUR ADJUSTING LEVER RETURN SPRING

Claims

CLAIMS 1. An aerofoil section sail with alternate & finitely variable camber,that can be fitted over, or substant'ally attached to, a mast & set to form a variable power sail by rotating the low drag leading edge formed in conjunction with attached pairs of removable battens held in opposite pockets stitched in the sail, on both sides of the aerofoil. Said sail to be capable, for example, as nearly as possible, within, limits imposed by the application of the present invention of forming old known and proven 'high lift' aerofoil sections, such as the 'Clark W', which has predetermined curvature on both sides of the aerofoil. However said sail will also be capable of inverting them quickly while sailing, for use on either Port or Stbd tack, under the control of a contour lever.

The sails described all have one common linking feature, i.e.

they can all be set to a variable aerofoil section sail, or alternatively a single sided variable contour sail to adjust, while in use, for propulsive power required. All applications of the present invention rely on the leading edge formers being clamped to or affixed to the mast used that is able to rotate under control of a quadrant to boom attachment assembly, resulting in the cooperating batten pairs curving both the sail surfaces to achieve the aformentioned section.

Alternatively a single sided variable contour sail, the 'contour former' single batten holder would be clamped or held to the mast used resulting in the cooperating batten achieving a variable contour sail. In direct contrast to known and used systems that rely totally or partly on the freedom of previous devices to rotate around the mast at will, in an effort to create a predetermined full port & stbd setting only.
2 An aerofoil section sail as described in claim 1, that can be manually set by a lever or a rope, which is part of the boom to mast attachment clamp that allows the front portion of the boom to rotate around the mast to any reguired position while sailing. In a windsurfer application or any sail propelled vehicle / vessel that uses the same or substantally the same rigging arrangement.
3 An aerofoil section sail as described in claims 1 & 2, that can be manually set and held at varying degree's of camber and foil section, for use on port or starboard tack.
4 An aerofoil section sail as described in claims 1,2 4 3 that automatically set's to neutral streamline section when uphauling the sail from the water, prior to starting sailing by pulling on the uphaul rope which is attached or partially attached to the lever locking system.
5 An aerofoil section sail as described in claims 1,2,3 and 4 that can be locked to stay in its previous position & not automatically reset itself to a neutral streamline position when uphauling the sail from the water when applied to a windsurfer.

6 An aerofoil section sail as described in claims 1,2,3,4 & 5 that can be adjusted in the water for the best setting to accomplish the 'waterstart manouevre' when applied to a windsurfer.

7 An aerofoil section sail as described in claim 1,2,3.4 & 6 that can be manually set & held for sailing in its Streamline setting, as a low drag, lower propulsive power sail, requiring less controlling effort. Instead of changing the sail for one of a smaller area, as would previously have been necessitated.

8 An aerofoil section sail as decribed in claim 1 that can be used with no prior settings and apparently revert in operation to previous inventions of sails, i.e. "camber induced" & BR< "Rotational" types. Achieved by activating a locking device to prevent the quadrant locking between it's limits of adjustment.

9 An aerofoil section sail as described in claim 1 can be set by a lever in the windsurfer application, while sailing. Or such other levers / catches / lines, substancially as described herin with reference to Figures 1 to 17 & 22.

10 An aerofoil section sail as described in claims 1 to 10 that can be set to varying degrees of curvature as required in whatever application.

11 A sail as described in claim 1 with variable curvature caused by the interaction of three cooperating parts, a variable curve batten and retaining strap (as is old an known), a new 'contour former' that clamps or is affixed to the mast used and accepts the luff end of the batten preventing it from turning until action of the new third component part, a rotatable boom to mast quadrant assembly, under the control of contour adjusting lever. Said lever rotates the mast causing the interaction required for operation of a variable curvature sail, capable of inverting quickly in stages from max power on Stbd through to a minimum drag setting onto a max power setting on port tack all while sailing, under the control of a contour lever.

12. A sail as described in Claim 1 & 11 with variable curvature shown or partially shown in figs 18,19 & 21, or also capable substantially as described, of the same operations as described in Claims 2,3,4,5,6,7,8,9,10,13,14,15, & 6.

13 An aerofoil section sail as described in claim 1 for a main sail application ( All sailing Vessels including Land Yachts ) will be adjusted by means of a lever controlling the bottom end of the mast with respect to the boom, that can be manually set to varying degrees of camber as required, for propulsive power required.

14 An aerofoil main sail as described in Claim 1 that can be set to behave as a previous mainsail design would.

15 Any aerofoil section main sail as described in claims 1 & BR< 13 set by a lever in the main sail sail application, or such other levers / catches / lines, substantially as described herein with reference to Figures 1 to 22.

16 Any alternative truly variable camber aerofoil sail substantially as described herein in figures 1 to 22 in the accompanying drawings.

17. Any part substantially as described herein, in the text or shown in any of the figures, that is relevant part of the present invention but can be used to advantage alone or together with what is known elswhere.

18. Any 'contour former' or 'Leading edge former' that operates by virtue of being affixed to a mast as described or shown that performs essentially the same function.

19. Any Boom to mast rotation assembly that performs essentially the same function as herein described.

19 Any sail or parts of the present invention, as described in the previous claims that contain Buss words / slang that have become accepted English, and by doing so, apparently contradict aeronautical engineering terms. The meaning of which, is essentially the same, for the application of the present invention.

AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS.

1. An adjustable contour sail (single sided sail) with alternate & finitely variable contour, that can be fitted over, or substant'ally attached to, a mast & set to form a variable power sail when set and in use, by rotating a quadrant to boom attachment assembly enabling the contour formers which are clamped or affixed to the mast, so that they cause each cooperating batten to curve varying the contour of the sail and hence it's propulsive force. In direct contrast to old and known systems that rely totally on the freedom of the previous devices (camber inducers) to rotate around the mast at will, in an effort to create a predetermined full port or starboard setting only.

2. A variable contour sail as described in claln I, that can be manually set by a lever or a rope, which is part of the bc..Om t.D mast attachment clamp that allows the boorn to rotate around the not to any required port or starboard position while sai inc, in whatever application of the present invention tat s the same or substancially the same rigi arrangement.

3. variable contour sail as described in claims 1, that automatically setts to it s neutral flat contour when aphauling the sail from the water in the windsurfer application, prior to starting sailing by pulling- on the uphaul repe which is attached cr partially attached to the ::c-r locking system A A variable contour sail as described in claims 1,2 and 3 that cnn be to =ra? in it its previous position, for xample full curvature for maximum propulsite power & not automatically reset itself to a neutral flat contour minimum propulsive power) when uphauling the sail from the water as when applied to a windsurfer 5. A variable contour sail as described in claim 1,2,3 and 4 that can be adjusted in the water for the best setting to accomplish the 'waterstart manouevre" when applied to a windsurfer.
6. A variable contour sail as described in claims 1,2,3,4 and 5 that can be manually set & held for sailing in its flat uncontoured setting, as a low drag, lower propulsive power sail, requiring less controlling effort. Instead of changing the sail for one of a smaller area, as would previously have been necessitated.
7. h variable contour sail as decribed in claim 1 that can be used with no prior settings and apparently revert in operation to previous inventions of sails, i.e. "camber induced11 & BR< "Potational" types. Achieved by activating a locking device to prevent the quadrant locking and stopping anywhwere between it's limits of full power port or Starboard adjustment.
8. A variable contour sail as described in claim 1 can be set by a lever in the windsurfer application, while sailing. Or such other levers / catches / lines. substancially as described her in with reference to Figures 7,8,9,10,11,12,,18,19,20,21.
9. A variable contour sail as-described in claims 1 to 8 that can be set to varying degrees of curvature as required in whatever application.
10. h sail as described in claim 1 with variable curvature caued by the interaction of three cooperating parts, a variable curve batten and retaining strap (as iS old an known) a new "contour former that clamps or is affixed to the r,ast use and accepts the luff end of the cooperating - ten preventing t from turning until action of the new third CThponent part, a roLatable ratl tci mast quadrant assembly, under the control of contour adjusting lever or ne. SaiJ lever or lie, rotates the mast causing the interaction required for operation of a variable curvature sail1 capable of inverting quickly in stages from max power on St to to a minimum drag setting onto a ma: power setting on port tack all while sailing under the control of a contour lever.
11. Any detachable Boom assembly capable of rotating the mast inside the boor. to effect the sane function as shown in figures 2,3,4ijr and 1.
12, Any boom assembly described in claim 11 that in addition is detachable from a standard boom assembles, as in figures 7,12.
13. Any Boom to mast rotation assembly that in claims 11 & 12 that performs essentially the same function as herein described.
14. Any 'contour former' or similar device that operates by virtue of being affixed to a mast as described or shown that performs essentially the same function of aligning the luff ends of each cooperating batten, so that each 'contour former' moves in unison with its batten from one predetermined angular position to another, on whatever mast is used. Due to being clamped or affixed in a vertically alligned position for example by aligning them before and durina affixing with a vertical line down the mast or by using a method of fixing that ensures this, examples figures 18,19 and 20.
15. Any contour former' or 'leading edge former for use with variable contour sails or aerofoiis sails respectively, that is capable of being clamped or affixed to a mast in any way to form the function as described in claim 14 and in addition may use the mast substancialy as the leading edge by design of the clamp so as to have just a thin affixing band forward of the actual mast.
16. An aerofoil section sail with alternate and variable camber that can be fitted over, or substancially attached to, a standard mast or substancially so, as to form a variable power sail by rotating the low drag leading edge formed by the formers that hold and locate the attached pairs of removable battens held in opposite pockets stitched into the sail, on either sides of the aerofoil.
17. Any part substantially as described herein, in the text cr shown i any y t the figures. that is a relevant part of the présent inventIon but can be used to advantage alone or together with what is known elsewhere.

An Any sail or parts of the present invention, as described in the previous claims that contain Buss words / slang that have become accepted English, and by doing so, apparently contradict aeronautical engineering terms. The meaning of which, is essentially the same, for the application of the present invention.

17. Any aerofoil section sail as descried in claim 16 once set (with batten pairs) that is capable by virtue of the same vttr. used of performing the same functions as the variable contour tail does (with single battens) in claims 2,3,4,5,6,7,8,: and 10 C.Any batten pocket for aerofoil section sails that allows each pair sf battens to be both compressed alongside each other at the leech when -et in the neutral streamline section an allows tc-. leeward one to slide partially under tension allowing that side of the sail to increase it's aerodynamic length it respect to the windward one whose batten remaIns compressed treb enabling the formation of the aerofoil ect iOfl.