EP0005343B1

EP0005343B1 - A wind-propelled vehicle

Info

Publication number: EP0005343B1
Application number: EP79300690A
Authority: EP
Inventors: Amiram Steinberg
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-05-03
Filing date: 1979-04-24
Publication date: 1982-03-31
Also published as: EP0005343A3; EP0005343A2; DE2962381D1; IL54633A0; AU4655279A; AU523541B2; IL54633A

Description

The present invention concerns wind-propelled vehicles comprising a sail mounted on an unstayed mast and in which essentially all the steering and control is accomplished through the sail. One kind of vehicle to which the invention pertains is surfboards and the invention will hereinafter be described with reference thereto, it being understood that it is not confined to surfboards and is also applicable to other wind propelled vehicles such as, for example, iceboats and sleds.
From U.S. Patent Specification 3,487,800 and the corresponding British Patent Specification 1,258,317 and German Patent Specification 1,914,604, there are known surfboards of the kind specified in which the mast is connected to the hull through a joint which provides universal-type movement of the mast, and a pair of arcuate booms are mounted on the mast in such a way that the booms have 2-3 degrees of freedom relative to the mast. During operation, the user stands on the board and grips the windward boom. For acceleration, turning and tacking, manipulation of the sail is required and for this purpose the user must change the position of the sail in various ways according to need and must also change his own position and/or shift his weight in order to counterbalance the wind action. For example, if the craft is sailing with the wind abeam and the user wishes to steer leeward, the sail must be tilted forwardly and downwardly from its balanced position whereby a steering moment of the wind is applied to the surfboard which causes the craft to turn. If the user wants, on the other hand, to steer to windward, the sail is tilted backwards from its balanced position. In the known surfboards said tilting, and in particular the forward tilt, reduces the aerodynamic efficiency of the sail.
Moreover, in sailing in general and in a surfboard in particular, for every wind angle in relation to the central line of the hull, there must be a corresponding angle between the chord of the sail and the central line of the hull, the chord in this case being a straight line between the lowermost edge of the luff and the clew of the profiled, operational sail. The greater this angle the more the forward section of the boom moves away from the windward side of the craft and consequently, the user gripping the boom for steering has to move with the boom in order not to lose his grip. In doing so, he may have to move out from a position in which he would normally by his own weight create a righting moment. This in turn, may cause a heel to leeward which may lead to the user falling off board and even to capsizing. To avoid this, the user has to hike out, i.e. to bear windwards and in doing so he may pull the entire rigging with him, creating an excessive windward inclination which affects adversely the performance.
All in all, it has been found that operation of a surfboard of the kind described in the above U.S., British and German patent specifications puts high demand on the athletic skills of the operator who is at times forced to twist and bend his body in unnatural and inconvenient ways.
Moreover for operation of such a surfboard the user has normally to be in a position in which his shoulder line is essentially parallel to the central line of the craft, which means that to be able to steer he must turn his head towards the stem by nearly 90° which is a further source of discomfort.
Operation of wind-propelled vehicles in general and of a surfboard in particular puts high demand on the user's skill, requiring a high degree of mental alertness, physical fitness and motoric coordination capacity. There is thus a demand for improvement of existing wind-propelled vehicles of the kind specified and it is the object of the present invention to provide a wind-propelled vehicle of the kind specified that is more convenient to operate.
In accordance with the present invention it has surprisingly been found that the reduction of the aerodynamic efficiency upon tilting of the sail in the above known surfboard is due to the fact that the mast is essentially straight. It has further been found that the operational discomfort is due to the fact that the booms are angularly displaceable around the longitudinal axis of the mast and that the booms are two distinct members capable of being bent and twisted relative to each other.
Based on these findings, the invention provides a wind-propelled vehicle comprising an unstayed mast (5) connected to a hull (2) through a joint (7, 8, 10) which will provide universal type movement of the mast (5), a boom assembly attached to the mast (5) and consisting of two booms (15, 16) joined to each other at their free ends, and a sail (25) carried by the mast (5) and the boom assembly (15, 16), characterised in that the mast (5) has a longitudinally curved form, the boom assembly (15, 16) is substantially rigid, and the connection (19, 20, 21, 22) between the mast (5) and the boom assembly (15, 16) is such that no relative angular displacement is possible between them around an axis defined by the centre line of the mast (5) at the point of the connection.
In sailing crafts in general, masts are as a rule straight, possibly short of a small uppermost stretch. To the best of applicant's knowledge the only exception to this general rule is a sailing craft known by the name of Jangada which is a raft made of logs of light wood with a sail, seat, steering oar and daggerboards (see, for example, Websters 3rd International Dictionary, page 1209). This raft which is steerable in the normal way, which has no booms and in which the mast is rigidly connected to the raft, represents a different art than the present invention.
There are thus no prior art teachings suggesting in any way the features which in combination characterise the wind-propelled vehicle according to the invention.
In one of its embodiments the wind-propelled vehicle according to the invention is a surfboard. Preferably the hull of such surfboard comprises at least one leeboard.
The invention is illustrated, by way of example only, in the accompanying drawings in which:

Fig. 1 is a diagrammatic perspective view of a surfboard according to the invention;
Fig. 2 is a perspective view from above showing the rigging in the same operational position as Fig. 1;
Fig. 3 shows for comparison a prior art surfboard in a similar operational position;
Fig. 4 is a detail of Fig. 1 showing the mounting of the booms on the spar; and
Fig. 5 is another detail of Fig. 1 showing the joint that connects the spar to the body.

The surfboard 1 according to the invention here illustrated comprises a hull 2 fitted with a central leeboard 3 and a stern leeboard 4. A curved tubular mast 5, e.g., of aluminium, is joined to the hull 2 in such a way as to enable universal-type movement. This joint is shown more specifically in Fig. 5. As seen there, a flexible, cylindrical rod 6, e.g. of rubber, having a broadened lower tip 7 is received by a correspondingly shaped recess 8 of the hull. The lower hollow conical portion 9 of the mast 5 receives the upper end of the flexible rod 6 and is connected thereto by a connecting pin 10, which in turn is secured by a cotter pin 11.
The rigging of the craft further comprises a boom assembly comprising booms 15 and 16 joined together at both the mast and clew ends to form an oblong, basically rigid annular body having at the mast end a fulcrum 28. The connection between the mast end of this assembly and the mast is shown in Fig. 4. As shown there, the boom assembly 15, 16 which is located in a plane P₂ (see Fig. 1) comprises near the mast end two identical brackets 17 and 18 with integral pins 19 and 20, respectively, symmetrically positioned with respect to the central line of the boom assembly. Mast 5 comprises securely mounted onto opposite sides thereof two identical, slotted suspending members 21 and 22 whose slots are adapted to receive pins 19 and 20, respectively, the slotted suspending members slid onto the pins from above. Stops are provided (not shown) to prevent the pins 19, 20 from sliding out of the slots.
A sail 25 is mounted on mast 5 by means of a suitably shaped hem of the sail which receives the mast. The clew of sail 25 is connected to booms 15 and 16 by means of outhauls 26, 27 which engage the booms in any suitable way known in the art, e.g. by means of cleats. The luff, clew and chord of sail 25 are all located in a plane P, forming a right angle with plane P₂ of the boom assembly.
The above described connection between the boom assembly 15, 16 and the mast is such that no relative angular displacement between them is possible around an upright axis through said connection. When mast 5 is swung from windward to leeward and vice versa, the boom assembly swings with it and the right angle between planes P, and P₂ is maintained.
The connection between the mast and the boom assembly enables a certain up and down leverage of the boom with respect to the mast around pins 19 and 20 which serve as pivots. However, due to the fact that the boom assembly 15, 16 is rigid no part of it can move out of plane P and when the boom assembly is levered up or down plane P₂ follows suit so that the assembly always remains in the plane. In consequence the leeward boom 16 does at no time interfere with an efficient aerodynamic profile of the sail 25.
The prior art surfboard 101 of Fig. 3 is essentially of the kind described in U.S. patent specification 3,487,800. It comprises a hull 102, a straight mast 105 connected to the hull by a joint which provides universal-type movement, a sail 125 and a pair of curved booms 115, 116 interconnected at both ends. As described in the said U.S. patent specification the connection between the booms and the mast is such as to enable a relative angular displacement around an upright axis extending through the connection. Moreover the booms do not form together a rigid annular assembly.
In all three Figures 1, 2 and 3 the hands of the user are shown to grip the windward boom.
In Figs. 1 and 2 the position of the rigging is the same. In that position the wind W forms an angle a with the central line B of the boom assembly and fulcrum 28 has moved windward with respect to the central line A of the hull. At the same time an angle f3 is formed between the central line A of the hull and the projection of the central line B of the boom assembly onto the hull surface. In that position the user may still conveniently stand on the hull 2 without need for any undue twist of the body. It can further be seen from Figs. 1 and 2 that in the two operational positions shown the shoulder line of the user will form an angle of about 45° with the central line A of the craft and consequently he needs to turn his head only by about 45° to face the stem. This contributes to the comfort of operation as compared to the known surfboards.
In contrast, in the prior art surfboard of Fig. 3 in which the wind direction is similar as in Figs. 1 and 2, fulcrum 128 is more leeward which compels the user to pull the entire rigging system back to windward. Due to this and also due to the degree of freedom between the mast and the booms and further due to the bending and twisting of the booms relative to each other the user is compelled to twist his body in an awkward position. Furthermore in that craft the shoulder line of the user will be approximately parallel to the central line of the craft which adds to the user's discomfort.
By comparing Figs. 2 and 3 it is further seen that in the former, i.e. according to the invention, the resultant driving force R attacks the sail along a line extending about mid-way between the user's hands, whereas in the latter, i.e. in the prior art craft, the resultant R extends along a line close to one of the hands. It is thus seen that in accordance with the invention the position of the user is more balanced with respect to the driving wind force, which is a further improvement.
Where it is required to turn or tack the surfboard according to the invention as shown in Figs. 1 and 2, the boom assembly 15, 16 is so manipulated that the mast is tilted forward or backward, as this may be required. Due to the curved shape of the mast such tilting does not adversely affect the aerodynamic properties of the sail.
During operation, it may occasionally become necessary to control the tension of the leech and foot of sail 25 and this is achieved by slightly levering the boom assembly 15, 16 around pins 19, 20. During such levering manipulations the right angle between planes P, and P₂ is maintained.

Claims

1. A wind-propelled vehicle comprising an unstayed mast (5) connected to a hull (2) through a joint (7, 8, 10) which will provide universal type movement of the mast (5), a boom assembly attached to the mast (5) and consisting of two booms (15, 16) joined to each other at their free ends, and a sail (25) carried by the mast (5) and the boom assembly (15, 16), characterized in that the mast (5) has a longitudinally curved form, the boom assembly (15, 16) is substantially rigid, and the connection (19, 20, 21, 22) between the mast (5) and the boom assembly (15, 16) is such that no relative angular displacement is possible between them around an axis defined by the centre line of the mast (5) at the point of the connection.

2. A wind-propelled vehicle according to Claim 1, characterized by being a surfboard.

3. A surfboard according to Claim 2, characterized in that the hull (2) comprises at least one leeboard (3).

4. A wind-propelled vehicle according to any one of Claims 1 to 3, characterized in that the boom assembly is so mounted on the mast (5) to enable its levering up and down thereby to enable tensioning and slackening of the sail (25), as may be required.