GB2225760A

GB2225760A - Windsurfer spar and sail

Info

Publication number: GB2225760A
Application number: GB8921614A
Authority: GB
Inventors: Richard Dryden
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-12-07
Filing date: 1989-09-25
Publication date: 1990-06-13
Anticipated expiration: 2009-09-25
Also published as: WO1990006254A1; GB2225760B; AU4746190A; GB8828598D0; GB8921614D0

Abstract

A wind-propelled vehicle such as a sailboard has a body (1), an unstayed spar (2) connected to the body (1) through a universal-type joint (3), a pair of arcuate booms (5, 6) connected onto the spar, and a sail (4) held taut between the booms. The spar (2) comprises a top section (11), a middle section which includes front and rear struts (9 and 10), and a lower section (8), the sections all being pivotally coupled together to permit flexing of the spar, under the control of the user, predominantly in the plane of the sail with a subsidiary lateral rotation of the middle section. The sail (4) is formed of a resiliently extensible material and has a sleeve (25) running along its front edge to receive the spar (2). The sail is additionally supported by rods (28) which extend transverse to the spar.

Description

WIND-PROPELLED VEHICLE TECHNICAL FIELD OF THE INVENTION This invention is concerned with wind propelled vehicles of the kind comprising body means, an unstayed spar connected to the body means through a universaltype joint, a sail attached at one edge region thereof to the spar, and a pair of booms, first ends of the booms being connected together and connected onto the spar, and second ends of the booms being connected together and connected to the sail such that the sail is held taut between the booms.

The invention is applicable to any lightweight windpropelled craft, examples of which include watercraft

such as sailboards (popularly known as wlndsurterst, iceboats, and landcraft such as landyachts. In use, the unstayed spar and sail are held in an operational position by the user (who will hereinafter be referred to as a "sailor"). The sailor uses control movements and his/her bodyweight to counter the forces produced by the air flowing across the sail and produce the desired movements of the vehicle over the appropriate surface, i.e. water, ice or land.

BACKGROUND In conventional sailboards and other wind propelled vehicles of the kinds described above, the spar supporting the sail is by the nature of its construction slightly flexible, as may be seen by the curve produced by the spar when the sail is rigged and tautened. Furthermore, minor changes in sail shape take place under the loads normally encountered during sailing. For example, the trailing edge of the upper part of the sail "washes out" (twists) to a greater degree as aerodynamic loads increase. Within limits, this tends to improve the control that the sailor has over the movement of the vehicle. However, a given sail still tends to work effectively over only a relatively narrow range of wind strengths, and most serious sailors find it necessary to have several sails to cope with the range of sailing conditions normally encountered.Previous attempts have been made to increase the useful range of a sail, for example by including removable portions secured by zip fasteners, but these have not gained widespread acceptance.

In light wind conditions and during racing, a technique known as "pumping" is often used to enhance the speed of the sailboard. This comprises oscillating the sail back and forth across the centreline of the board to accelerate the airflow across the sail and give increased propulsion. However, in a conventional sailboard this technique is limited in its effectiveness.

SUMMARY OF THE INVENTION Two major objects of the present invention are to provide: (i) a form of spar and sail that is suitable for use under a wider range of wind conditions than that afforded by a conventional spar and sail, and (ii) a form of spar and sail which allows the pumping technique to be used to greater effect.

According to the present invention, a wind-propelled vehicle of the kind specified in the opening paragraph above is distinguished by the fact that the spar comprises a plurality of sections which are pivotally connected together, and the sail is of a resiliently extensible material, such that the spar and sail can adopt an extended or flexed configuration in use.

Normally bias means will be included for biassing the spar towards the extended configuration. The main flexing movement of the spar will normally be in the plane of the sail, although the pivotal connections preferably permit flexing of the spar in a direction perpendicular to the plane of the sail.

The spar preferably comprises upper, middle and lower pivotally connected sections. The middle section preferably comprises first and second spaced struts which are connected to the respective upper and lower sections by spaced pivotal connections. The bias means may comprise a resiliently extensible element which is tensioned between anchoring portions of the upper and lower sections that extend beyond the pivotal connections. Preferably the first strut is connected to the upper section for pivotal movement about a single axis and to the lower section by a universaltype joint, and the second strut is connected to the upper section by a universal-type joint and to the lower section for pivotal movement about a single axis.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is exemplified in the accompanying drawings in which: Figure 1 is a side view of a sailboard equipped with a spar and sail of the invention, and showing the spar and sail in an extended configuration, Figure 2 is a similar view to Fig. 1 but showing the spar and sail in a flexed configuration, Figure 3 is a detailed view of the main structural members of the spar, Figure 4 is a side view of the sail alone, Figure 5 shows a section through the spar and sail at the level of the booms, and Figures 6 to 9 show details of the way in which the tensioning webbing is secured to the spar.

DETAILED DESCRIPTION OF THE DRAWINGS Fig.s 1 and 2 show a wind-propelled vehicle in the form of a sailboard. The sailboard comprises a base 1 in the form of an elongate board of known design. An unstayed spar 2 is connected to the board through a universal-type joint 3 (i.e. a joint having three axes of rotation), and a sail 4 is attached along its front edge to the spar. A pair of arcuate booms 5, 6 are located one on each side of the sail 4. The front ends of the booms are connected together and connected onto the spar part way along its length, and the rear ends of the booms are connected together and connected to the sail such that the sail is held taut between the booms.

As shown in Fig.s 1 and 2 and more particularly in Fig.

3, the spar comprises a lower strut 8, substantially parallel front and rear middle struts 9 and 10, and an upper strut 11. The struts are pivotally connected together. The upper end of the lower strut 8 is secured to the lower end of the rear middle strut 10 for pivotal movement about an axis 12 which extends transverse to both the lower strut 8 and to the general plane of the sail. The upper end of the rear middle strut 10 is connected by a universal-type joint 14 to a region slightly inset from the extreme lower end of the upper strut 11. The lower end of this upper strut is secured to the upper end of the front middle strut 9 for pivotal movement about a respective axis of rotation 15. This axis is again orientated transversely in relation to the upper strut 11 and the general plane of the sail.The lower end of the front middle strut 9 is coupled by a further universal-type joint 16 to the lower strut 8 at a region slightly below its extreme upper end. Thus, the spar can be woved from an extended position shown in Fig. 1 to the rearwardly flexed position shown in Fig.s 2 and 3, but at the same time, the twin middle struts 9 and 10 ensure that the angular relationship between the upper and lower struts 11 and 8 remains unchanged. In addition, the universal joints 14 and 16 permit the spar to adopt, to a limited extent, a combined rotational and flexing movement in a lateral direction.

The importance of this movement will be explained below.

The lower end of the upper strut 11 carries an eye formation 18 which extends beyond the axis 15, and the lower end of the rear middle strut 10 carries a similar eye formation 19 extending beyond the axis 12. The structure and function of these will be described in more detail below.

The sail 4 is of a tear-resistant and resiliently extensible material. A sleeve 25 (Fig.s 1, 2 and 4) is formed along the front of the sail to receive the spar 2. The middle region of the lower portion of the sleeve is widened in a rearward direction to accommodate the angulation of the spar. The sleeve is reinforced on each side by strips of inextensible webbing 26 that follow the general line of the mast and are tied to the foot 27 of the mast (Fig. 4). In addition to being tied to the rear ends of the booms 5 and 6 the sail is tensioned by a number of rods (battens) 28 which extend generally perpendicular to the spar 2 and are secured at the rear edge of the sail. The front ends of the upper rods simply end at the sleeve 25 without making contact with the mast, while the middle rods impinge directly against the rear middle strut 10 by way of camber inducers of known design, The lowermost rods end at the sleeve 25, but each is supported in that position by further rods 29, one in each side of the sleeve, that are anchored at the front to the webbing strips 26. This arangement of rods ensures that the sail maintains the correct camber (aerofoil shape) as the mast flexes, extends and rotates. The leading edge of the sail is reinforced with a resiliently extensible cord 30. This extends from the region of the joint between the upper section 11 with the middle sections 9 and 10 to the foot of the sail. A similar length of cord 31 extends along the trailing edge of the sail.These cords are under tension when the sail is rigged for use, and reduce flutter at the leading and trailing edges of the sail.

Referring now to Fig. 5, the arcuate booms 5 and 6 are joined together and secured to the rear edge of the sail 4 in known manner. The front ends of the booms are likewise joined together and attached to the front middle strut 9 by means of a clamp or rope tie (not shown) of known design. The rear middle strut 10 is free to move from side to side between the booms 5, 6, the range of movement being defined by stops 7 attached to the inner aspect of each arcuate boom 5, 6.

Referring now to Fig. 6, a loop of resiliently extensible tensioning web 38 is used to bias the spar 2 towards the extended condition. This web is secured in a loop 39 (Fig. 7) around the lower end of the upper strut 11 and both limbs of the web pass through the associated eye formation 18 (Fig. 8). The limbs of the web pass either side of the middle struts 9, 10 to pass through the other eye formation 19. The eye formations 18 and 19 are both of similar form and each comprise a passage 41 of generally rectangular section which is open along its length by a slot 42 through which the web can be inserted. The limbs of the web then travel down the rear of the lower strut 8 and loop through a tensioning ring 43 (Fig. 9). This ring is connected by a tensioning rope 44 to a tie-off point 45 at the foot of the spar.By adjusting the effective length of the tensioning rope 44 the tension in the web can be adjusted to suit the weight of the sailor and the manner in which the sail is to be used.

In light wind conditions the sailboard may be used in the conventional way. Under stronger wind conditions the sailor leans out more over the water. The sailor's body weight acts on the spar through the booms 5, 6 causing the spar to adopt a flexed position against the action of the tensioning web. The centre of effort is thus lowered making the sail easier to control.

When the pumping technique is used under light wind conditions the variable geometry of the spar enables the sail to be more effective in imparting energy to the airflow. At the start of the pumping cycle the mast is fully extended under the action of the tensioning web. As the spar is pulled vigorously towards the sailor in the power stroke the mast begins to flex rearwardly and the sail changes shape causing an enhanced air flow across the sail. During the return stroke the spar returns to the extended position assisted by the tensioning web so that the energy stored in the sail during the power stroke is utilised in the return stroke, thereby improving the efficiency of the pumping action.

The combined lateral flexing and rotational movement of the spar referred to above has a subtle but important effect on the overall geometry of the sail. Under sailing loads the joint between the lower and middle struts of the spar rotates away from the sailor. This has the effect of incre-asing the camber of the lower part of the sail. In so doing the joints and struts become reorientated such that they conform to a substantially conical surface, and this configuration is maintained even during flexion and extension movements. The main advantage of this is that the angle of attack of the sail changes from being high at the base of the sail, where the airflow is slower, to low at the top where the airflow is appreciably faster.

This considerably enhances the efficiency of the sail.

When the sailboard changes tack the sail has to adapt to the new tack by reversing its aerofoil curvature.

Under such conditions the struts of the middle section automatically rotate in response to the changed pressure relationships experienced by the sail and produce the reverse conical geometry.

Although the invention has been illustrated in the drawings in relation to a sailboard it will be appreciated that the new spar and sail could also be used with other wind propelled vehicles of the kind specified in the opening paragraphs above.

Claims

1. A wind propelled vehicle comprising body means, an unstayed spar connected to the body means through a universal-type joint, a sail attached at one edge region thereof to the spar, and a pair of booms, first ends of the booms being connected together and connected onto the spar, and second ends of the booms being connected together and connected to the sail such that the sail is held taut between the booms, the vehicle being distinguished by the fact that the spar comprises a plurality of sections which are pivotally connected together and a major part of the sail is resiliently extensible, the arrangement being such that, in use, the spar and sail can be moved between an extended and a flexed configuration under the control of a user.

2. A vehicle according to Claim 1, in which the spar is provided with bias means for biassing the spar and sail towards the extended configuration.

3. A vehicle according to Claim 1 or 2, in which the pivotal connection/s between the spar sections are arranged to permit flexing of the spar predominantly in the plane of the sail with a subsidiary lateral rotation.

4. A vehicle according to any preceding claim, in which the spar comprises upper, middle and lower sections which are pivotally connected together.

5. vehicle according to Claim 4, in which the middle section of the spar comprises first and second spaced struts which are connected to each of the upper and lower sections of the spar by spaced pivotal connections.

6. A vehicle according to Claim 4 or 5, in which the first strut is connected to the upper section of the spar for pivotal movement about a single axis which is transverse to the general plane of the sail, and to the lower section of the spar by a universal-type joint; and the second strut is connected to the upper section of the spar by a universal-type joint, and to the lower section of the spar for pivotal movement about a single axis which is transverse to the general plane of the sail.

7. A vehicle according to Claim 5 or 6, in which the front ends of the booms are connected onto the first strut of the middle section, the second strut being arranged for lateral movement between the booms.

8. A vehicle according to any of Claims 4 to 7 as appended to Claim 2, in which the bias means comprises a resiliently extensible element which is tensioned between portions of the upper and lower sections that extend beyond their respective pivotal connections with the middle section of the spar.

9. A vehicle according to Claim 8, in which one end of the resiliently extensible element is anchored to the upper section of the spar and the other end of the element is anchored to the foot region of the spar by an inextensible element, the effective length of which can be adjusted to alter the tension in the extensible element.

10. A vehicle according to any preceding claim, in which the spar is contained within a sleeve extending along a front edge portion of the sail, and in the region of the sleeve, the sail is substantially inextensible in the longitudinal direction of the spar.

11. A wind propelled vehicle substantially as described with reference to the accompanying drawings.