WO1998005552A1

WO1998005552A1 - Propulsive rigging for sail boats and a sail boat provided with such rigging

Info

Publication number: WO1998005552A1
Application number: PCT/EP1997/004229
Authority: WO
Inventors: Paolo Chiaves
Original assignee: Paolo Chiaves
Priority date: 1996-08-07
Filing date: 1997-08-04
Publication date: 1998-02-12
Also published as: AU4297797A; IT1284736B1; ITTO960684A1

Abstract

The rigging includes an outrigger structure (32; 34) and a sail (18) so dimensioned that, at least during close hauled sailing, the line of action of the aerodynamic forces on the sail (18) passes close to the centre of lateral resistance (CD).

Description

Propulsive rigging for sail boats and a sail boat provided with such rigging

The present invention relates to propulsive rigging for sail boats comprising at least: a substantially vertical mast carried by the hull of the boat ,- a sail with non-bent leading and trailing edges situated to leeward and substantially forward of the mast and having a head, a clew and a tack; running rigging which connects the head of the sail to an upper part of the mast and the tack and clew to the hull, and an outrigger structure which interconnects the hull or mast and at least one of the tack and clew of the sail to keep the lower edge or foot of the sail away from the edge of the hull.

The preceding definition corresponds to a rigging which is considered as the nearest prior art, that is to say a rigging in which the sail is a spinnaker or a non-stayed, boomed jib.

In traditional sailing boats the transverse component of the aerodynamic force on the sail and the presence of leeway cause a heeling couple which tends to make the boat heel to leeward about its longitudinal axis .

There is a continuing wish to avoid or reduce the heeling of a sail boat both for the greater comfort and safety of the crew, and to conserve or alter as little as possible the hydrodynamic efficiency of the hull when it is not heeled.

In ballasted boats the heeling moment is resisted mainly by the ballast.

On dinghies and large racing yachts the heeling moment of the sail is resisted by the crew by displacing the centre of gravity of their weight to windward with respect to the centre of buoyancy. This measure is, however, not always desirable on a cruising boat.

The problem of heeling has been resolved, at least in part, in multihull boats which, however, have the dual disadvantage of being very wide which makes them difficult to manoeuvre in port, and of capsizing irreversibly if a certain heeling angle is exceeded.

The object of the present invention is to provide a propulsive rigging of the type defined above by virtue of which the heeling of the sail boat on all points of sailing between close hauled and running is nil or drastically reduced.

According to the present invention this object is achieved by a rigging characterised in that: the outrigger structure is arranged to extend to leeward of the boat ; and the outrigger structure and the sail are so dimensioned that, at least when close hauled, the resultant of the aerodynamic forces on the sail stretched between its head, tack and clew, in addition to having a propulsive component, has a centre of pressure situated to leeward of the boat, and an upwardly directed supporting component .

In all of the present description and in the claims, the following is conventionally understood: the tack of a sail is a point of attachment of the sail situated forwardly, independently of whether this point is fixed or movable with respect to the hull; the clew of a sail is a point of attachment of the sail situated furthest to the aft, independently of whether this point is movable or fixed with relation to the hull; running rigging is any device, not necessarily constituted by a rope, which serves to tense one of the points of the sail.

By virtue of the proposed idea, the present invention makes use of a principle which is different from traditional principles since it exploits the reduction (or absolute cancellation) of the heeling moment which is achieved by inclining the plane of the sail in such a way that the line of action of the aerodynamic resultant passes at least relatively close to the centre of lateral resistance.

Even in normal boats, the idea on which the present invention is based is contained in a very small way: a jib (possibly boomed), or the current "gennakers" are, in fact, positioned to leeward and their drive has a small upward component parallel to the mast; moreover, in multihull boats, trimarans and catamarans, the clew of the spinnaker or gennaker is often sheeted to the hull to leeward. The position of these sails is adapted for running, when the drive component in a direction transverse to the motion is small .

The problems with normal rigging arise in the tightest points of sailing (close hauled, or when the boat is travelling very fast and the apparent wind is thus displaced towards the bow) , since : the tack of the sail is positioned substantially on the vertical plane of symmetry of the boat or even distinctly leeward of this; the sail in these points of sailing is hauled tightly aft and, consequently, its foot is almost parallel to the axis of the boat .

Therefore, with the usual arrangements, the foot of the sail in the tight points of sailing is certainly close the longitudinal axis of the boat when, instead, in these points of sailing it would be more suitable to reduce the heeling moment .

The present invention offers the major benefits over traditional riggings in these points of sailing.

The principle of inclining the plane of the sail has already been used in some boats, but has not been widely diffused because of the limited practicality of the structures used. Examples of boats which make use of this principle are the boats "Objectif 100" and "Longshot" , designed to establish speed records and, also, kite-drawn boats.

The boat "Objectif 100" is provided with a rigid wing of asymmetric wing profile which, to change tack, is tipped from one side to the other by rotating substantially about the longitudinal axis of the boat.

The boat "Longshot" was, on the other hand, inspired by the "pyramid" rig conceived at the end of the 50' s. It is provided with two sails positioned on the two sides of the boat so that one is to windward and the other to leeward, inclined in such a way that the leeward sail works according to the principle explained above and the windward sail has, on the other hand, a downwardly inclined aerodynamic resultant (in such a way that it also has a small heeling moment) ; when the boat changes tack the sails each remain on the same side and simply change incidence to operate on the new tack.

Both these boats are delicate and difficult to sail, and are affected by limitations which make them unsuitable for safe and autonomous navigation. One of the problems they have is that of not allowing an easy reduction in the sail area with a change in wind conditions.

Kite-drawn boats represent the most radical development of the idea for nullifying the heeling moment of the sail; their completely mastless rig is, however, difficult to manoeuvre, complicated by the large number of lines present and, moreover, is unstable in operation.

Finally, it is to be noted that the same principle is not utilised in sail boards or "windsurfers" : when sailing, their sail does have a vertical, upwardly directed component of thrust, but the centre of pressure is positioned to windward of the boat and therefore requires that the athlete resists the heeling moment by leaning to windward.

The rigging according to the invention eliminates all the above-stated problems since it utilises a sail which can be traditional or suitably cut, but which does not depart much from the traditional geometry adopted in particular for jibs.

As will be understood better from the description with reference to the drawings, the advantages of a rigging according to the invention can be summarised as follows: a possibility of carrying more sail for the same available righting moment and, therefore, the availability of a greater propulsive force; better "centring" of the drive of the sail in all points of sailing: the outrigger structure can be disposed largely to leeward in the tightest points of sailing, and more towards the bow when the wind is more abeam so that the resultant of the drive of the sail always passes relatively close to the centre of lateral resistance; the boat is therefore almost always neutral on the helm; if the outrigger structure is constituted by a simple spar, such as a swinging boom, and if, as is preferred, the mast has no forestay and is supported toward the bow by two shrouds positioned laterally of the angular sector within which the boom swings, the passage of the swinging boom from one side to the other takes place by making it turn towards the bow about its point of attachment with a manoeuvre which is just as simple as the passage of a mainsail boom; facilitates hoisting and lowering the sail; facilitates replacement of the sail, for example, to reduce its surface area in strong wind conditions; little or no heeling and a consequent reduction of the tendency to griping when close hauled; moreover, the little or no heeling contributes to the comfort of the crew, and safety against falling overboard; reduced dimensions in port in comparison with multihull boats .

Rigging according to the invention can be also adopted in a mixed rig, equally including a mainsail of usual type, with the advantage of reducing the heeling moment with respect to a conventional rig having the same total propulsive component .

Thus a boat can also be provided with two or more masts rigged according to the invention.

The invention also relates to a boat provided with a rig as claimed.

The invention will be better clarified from a reading of the following detailed description, made with reference to the attached drawings and given by way of non-limitative example, in which: Figures 1, 2 and 3 respectively illustrate in side-view, from above and from the bow, of a dinghy provided with a rig according to a first embodiment;

Figures 4, 5 and 6 are three views similar to the above, which illustrate a second embodiment;

Figure 7, 8 and 9 are again three views similar to the above, which illustrate a third embodiment; and

Figures 10, 11 and 12 are again three views similar to the above, which illustrate a fourth embodiment.

Referring to Figures 1 to 3 , the hull of a drop keel boat is indicated 10.

The hull 10 carries a substantially vertical mast 12.

The mast 12 is supported by aft shrouds 14 and a pair of lateral shrouds 16, which extend towards the bow.

For reasons which will be explained below, the mast 12 has no forestay .

The boat is provided with a triangular sail 18 which can, for example, be a normal jib or a gennaker.

The sail 18 is not bent to the mast 12 and is supported from this only by its head 20.

The clew is indicated 22 and the tack is indicated 24. The lower edge or foot of the sail is indicated 26. The reference number 28 indicates its trailing edge- or leech, and the leading edge is indicated 30. According to the invention the propulsive rig comprises an outrigger structure which interconnects the hull 10 and the mast 12 to the clew 22 and tack 24 so as to maintain the lower edge or foot 26 of the sail offset to leeward of the edge of the hull. The distance of the foot 26 from the edge of the hull can also be equal to or greater than 50% of the height of the mast 12.

In the embodiment of Figures 1 to 3 the outrigger structure includes a pivoted spar 32 such as a swinging boom, which connects the tack 24 to a lower part of the mast 12, (or to an adjacent part of the hull), and a substantially fixed spar 34 which extends laterally from the hull 10. The spar 34 connects the hull 10 to the clew 22 by means of a sheet 36 led to the cockpit of the boat.

The tack 24 of the sail 18 is connected to a point adjacent the bow of the hull 10 by means of a sheet or outhaul rope 38 also led back to the cockpit.

The spar 34 is preferably connected to the hull 10 by means of stays 40 and possibly by a downhaul, not shown.

The swinging boom 32 is provided with a downhaul 42 and possibly an uphaul , not shown.

The sheet 36 has the dual function of maintaining the sail 18 extended, and of permitting its angle of attack to be regulated. The outhaul or sheet 38 resists the tendency of the swinging boom 32 to rotate towards the leeward side under the pull of the sail, and makes it possible to adjust its position in the different points of sailing.

As can be seen, the outrigger structure represented by the spars 32 and 34 maintains the general plane of the sail, indicated P in Figure 3, inclined with a descending slope to leeward starting from the masthead.

Preferably, the boat is provided with a second rigid spar 34', symmetrical with respect to the spar 34.

The two spars 34 and 34' can be folded along the hull for manoeuvring in port or in restricted places.

By virtue of the absence of a forestay, the swinging boom 32 is free when going about to change tack, passing over the bow of the boat and assuming a symmetrical position with respect to that of Figure 2. The clew 22 may advantageously be provided with another sheet (not shown) led back permanently to the boom 34' and which allows the sail 18 to be pulled to the other side and then hauled aft .

The following considerations, with reference to Figure 3, are also valid for the embodiments of Figures 4 to 12, and will not be repeated for these further Figures .

In Figures 1 to 3 , the sail 18 is shown in an aspect corresponding to a close hauled point of sailing. In Figure 3 , the centre of lateral resistance of the boat is indicated C_D, and the centre of pressure of the sail is indicated C_p . As can be seen, according to the invention, the centre of pressure C_p is situated very much to leeward.

F_R indicates the resultant, having a moment arm B_R, of the pressures acting on the sail in the plane transverse the boat. This resultant, which is perpendicular to the plane P of the sail, breaks down into the known components of leeward drift F_D, of moment arm B_D, and resisted by the reaction R_D of the keel or centre board, and a drive component F_L, that is to say directed upwardly, of moment arm B_L.

The boat, to a first approximation, is subjected to a heeling moment

B_R = F_n X B_r F_τ. X B_r

In Figure 3 there is also illustrated, in chain line, a sail V of dimensions equivalent to those of the sail 18, and bent in traditional manner to a forestay.

In the plane transverse the boat, the sail V is subjected to substantially the single almost horizontal component F'_R, with a moment arm B'_R.

As is easily understood, for the same sail dimensions

^F' R 2 ^FB ' but since

^BR ^B'R ' one will have F_R x B_R < F ' _R x B ' _R ,

that is to say that, in the case of the invention, a very much reduced heeling moment with respect to that which there would be for the same sail dimensions if it were traditionally bent.

According to the invention it is possible to attain a zero heeling moment by making the line of action of the resultant F_R pass through, or close to, the centre of lateral resistance C_D.

However, by utilising rigging according to the invention, and thus as illustrated in Figure 3, it is not in general convenient to allow the foot of the sail to move to leeward up to the point where the heeling moment F_R x B_R is entirely nullified by making the line of action of the resultant F_R pass through the centre of lateral resistance C_D . This can give rise to the following disadvantages: excessive dimensions and weight of the outrigger structure ; an excessive inclination of the aerodynamic resultant of the sail, with a worsening of the overall efficiency because of a reduction in the propulsive component.

On the other hand, a light residual heeling moment can offer the following advantages : guarantee an improved sea holding; obtain, when hoisting or lowering the sail, a behaviour of the same type as that of normal boats, thus facilitating sailing (in a first approximation, when hoisting the sail, the boat will also tend to incline to leeward) ; avoid the risk of lifting of the boat from the water if the drive from the sail increases sharply, for example due to a gust of wind: the boat will in fact tend to incline rather than lift and the crew will be led to slacken the sail as in a normal boat .

Rather than utilise a sail similar to normal foresails, as in the embodiment of Figures 1 to 3 , specialised sails with a rhomboidal or segmented shape in plan can advantageously be used.

One embodiment including a sail 18 with a rhomboidal plan form is utilised in the embodiment of Figures 4 to 6 , to which reference will now be made . In this embodiment a segment-shape sail such as that of Figures 7 to 9 could also be used.

In Figures 4 to 6, the same or similar parts to Figures 1 to 3 are, for simplicity, designated with the same reference numerals .

The sail 18 of Figures 4 to 6 is of substantially rhomboidal form with a leading edge 30 at an obtuse angle extending between the head 20 and tack 24.

A batten 44 extends between the clew 22 and a point 46 of maximum convexity of the leading edge or luff 30. The batten 44, as well as maintaining the sail 18 extended, allows the sheet 36 to be drawn in a direction not belonging to the plane of the sail. The batten 44 may be substituted with a wishbone .

The sail 18 of Figures 4 to 6 can also include other reinforcing battens (not shown) . A pivoted swinging boom 32, which could be replaced by a rigid spar, extends from the mast 12 to the tack 24.

A sheet 36, which connects the clew 22 to the hull 10 allows the angle of attack of the sail to be adjusted.

An outhaul rope 38, which can be led back to the cockpit for the purpose of adjustment, prevents the rotation of the swinging boom 32 towards the aft.

In the case of Figures 4 to 6 as well, thanks to the absence of the forestay, when going about the swinging boom 32 is free to pass from one side to the other to dispose itself onto the other side, in a symmetrical position to that of Figure 5. The clew 22 can advantageously be provided with another sheet passing forward of the mast 12 and which allows the sail 18 to be pulled across to the other side and then hauled aft .

Referring to Figures 7 to 9, the embodiment shown there includes a segmented sail, again indicated 18, but could include a rhomboidal sail such as that of Figures 4 to 6. The same or corresponding parts as those of the preceding Figures are again, for simplicity, designated with the same reference numerals. In the sail 18 of Figures 7 to 9 the foot 26, which is oblique, the trailing edge or leech 28, and the leading edge or luff 30 all have a convex form with a discontinuous line. A batten 44, similar to that of Figures 4 to 6 , extends between the tack 24 and the point 48 of maximum convexity of the leech 28. Another two battens, respectively 44a and 44b, extend parallel to the batten 44, the first between two inclined points of the leech 28 and luff 30, and the second between two inclined points of the foot 26 and the leech 28. In this arrangement, the battened sail illustrated in Figures 7 to 9 is preferred but is not essential, and could be replaced by a non-battened, substantially triangular sail, with the advantage of an easier replacement of the sail.

Contrary to tradition, the point 22 called the clew is, as a rule, intended to be maintained fixed and is connected to the mast 12 by means of a swinging boom 32 via a sheet passed through a block situated at the end of the swinging boom. The end of the swinging boom 32 is moreover connected to the bow of the hull by means of an adjustment rope 38 which serves as a downhaul .

If the sail 18 is the only one bent to the mast 12, the swinging boom 32, as illustrated in Figures 7 to 9 , can be articulated about the mast 12 and have an extension 32a situated aft of the mast 12 and connected by shrouds or guys 49 to the head and foot of the mast itself. In this way, the point load of the swinging boom does not stress the central part of the mast to flex.

The hull 10 is provided with a bowsprit 50. A rope 52, which really and truly acts as an adjustment sheet, is connected contrary to tradition to the tack 24 and led back to the cockpit by means of a block situated at the end of the bowsprit 50.

The bowsprit 50 can be provided with a downhaul (not shown) which connects its end to the lower part of the stem.

In a modification, the bowsprit 50 can pivot laterally about a substantially vertical axis to displace the turning point of the sheet 52 to leeward.

The adjustment of the angle of attack of the sail in Figures 7 to 9 takes place by manipulating the sheet 52.

In the case of Figures 7 to 9 , the presence of a single swinging boom 32 and the absence of a forestay also permit an easy change of tack.

The use of a twin sheet matching that indicated 52 is definitely not necessary for change of tack.

Reference will now be made to Figures 10 to 12 to describe an embodiment which has various similarities to that of Figures 7 to 9.

All the same or similar parts to those of Figures 7 to 9 are designated with the same reference numerals in Figures 10 to 12 and their description will not be repeated. The embodiment of Figures 10 to 12 differs from that of Figures 7 to 9 essentially in that the hull 10 is provided with two fixed lateral structures 58, one on each side.

These fixed lateral structures 58 may be foldable so as to reduce the dimensions of the boat in port or when manoeuvring in restricted spaces .

The two lateral structures 58 are preferably in the form of "terraces" as in Lake Garda racing yachts or in certain Australian boats, to permit the crew to move more effectively to windward .

A rigid spar 34, similar to that of Figures 1 to 3 , and which constitutes the outrigger structure according to the invention, forms part of each lateral structure.

The clew 22 of the sail 18 is connected to the end of the spar 34 by means of a sheet or downhaul 36. A manoeuvring sheet 52 is connected to the tack 24 of the sail 18 and, after having been returned around the end of a bowsprit 50 (which can be fixed or laterally pivotable as already explained) is led back to the cockpit.

The clew is provided with a second sheet 36' passing round the other rigid spar 34, and which runs free when the sheet 36 is working as in the drawings.

With the embodiment of Figures 10 to 12, manoeuvring to change tack is very simple: the leeward sheet 36 is released; whilst the bow of the boat passes through the eye of the wind, the rope or sheet 52 connected to the tack 24 is hauled in a little to pull the sail 18 towards the bow so that it does not interfere with the mast 12 and its shrouds 16; finally, the leeward sheet 36' is hauled aft and the sail 18 is adjusted on the new tack.

The main advantage of the fixed structures 58 is their greater ruggedness and rigidity with respect to a swinging boom if it should touch the water whilst the boat is travelling at speed; thus, these structures 58 can be placed closer to the water than a swinging boom or other devices and allows a greater reduction in the heeling moment of the sail for the same leeward lateral extension.

In a modification, the lateral structures 58 can moreover be provided with floats or hydrodynamic wings (not shown) for the purpose of skimming over the surface of the water rather than stopping the boat sharply if for any reason they touch the water.

Claims

1. Propulsive rigging for sail boats comprising at least: a substantially vertical mast (12) carried by the hull (10) of the boat; a sail (18) with non-bent leading (30) and trailing (28) edges situated to leeward and substantially forward of the mast itself and having a head (20) , a clew (22) and a tack (24) ; running rigging which connects the head (20) of the sail to an upper part of the mast (12) and the tack (22) and clew (24) to the hull (10) ; and an outrigger structure (32; 34) which interconnects the hull (10) or mast (12) and at least one of the tack (22) and clew (24) of the sail (18) to keep the lower edge or foot (26) of the sail away from the edge of the hull (10) , characterised in that the outrigger structure (32; 34) is arranged to extend to leeward of the boat; and the outrigger structure (32;34) and the sail (18) are so dimensioned that, at least when close hauled, the resultant of the aerodynamic forces on the sail stretched between its head (20) , tack (22) and clew (24) , in addition to having a propulsive component, has a centre of pressure (C_p) situated to leeward of the boat, and an upwardly-directed supporting component (F_L) .

2. Rigging according to Claim 1, characterised in that (Figures 4, 5, 6) the outrigger structure (32) is so arranged as to keep the tack (24) substantially fixed and away from the hull (10) , and to enable the distance of the clew (22) from the hull to be adjusted by means of running rigging (36) such as a sheet .

3. Rigging according to Claim 1, characterised in that (Figures 1, 2, 3; 7, 8, 9; 13, 14, 15) the outrigger structure (32; 34) is so arranged as to keep the clew (22) substantially fixed and away from the hull (10) , and to enable the distance of the tack (24) from the hull to be adjusted by means of running rigging (52) such as a sheet.

4. Rigging according to Claim 1 or Claim 3 , characterised in that (Figures 1, 2, 3) the sail (18) is substantially triangular, with the upper vertex in the head (20) , and the tack (24) and clew (22) in the lower corners, and in that the outrigger structure includes a pivoted spar (32), such as a swinging boom, which adjustably connects the tack (24) to a lower part of the mast (12) or an adjacent part of the hull, and a substantially fixed spar (34) which extends laterally from the hull (10) and connects the clew (22) to the hull.

5. Rigging according to Claim 3 , characterised in that (Figures 7, 8, 9) the sail has on its leading edge a tack (24) between an upper head (20) and a lower clew (22) , and forward with respect to the head (20) and clew (22) , the tack (24) being bent for adjustment to the bow of the hull (10) by running rigging (52), and in that the outrigger structure includes a spar (32) such as a swinging boom which connects the clew (22) to a lower part of the mast (12) or to an adjacent part of the hull.

6. Rigging according to Claim 2 or Claim 3, characterised in that the sail (18) is substantially rhomboidal (Figures 4, 5, 6; 10, 11, 12) or segmented (Figures 7, 8, 9) in shape.

7. Rigging according to Claim 6, characterised in that (Figures 4, 5, 6) the sail (18) has a convex leading edge or luff (30) , and in that the sail (18) is provided with at least one batten (44) which extends from the clew (22) to the point (46) of maximum convexity of the luff (30) .

8. Rigging according to Claim 6 , characterised in that (Figures 7, 8, 9) the sail (18) has a convex trailing edge or leech (28) , and in that the sail (18) is provided with at least one batten (44) which extends from the tack (24) to the point (48) of maximum convexity of the leech (28) .

9. Rigging according to any of Claims 1 to 8 , characterised in that (Figures 10, 11, 12) the outrigger structure includes a rigid spar (34) which connects the clew (22) to a part of the hull (10) .

10. Rigging according to Claim 9, characterised in that (Figures 1, 2, 3; 10, 11, 12) the or each rigid spar (34) is foldable .

11. Rigging according to any preceding Claim, characterised in that (Figures 10, 11, 12) it includes a pair of fixed lateral structures (58) , each associated with one side of the hull (10) and acting as "terraces" to enable the crew to move to leeward. ->2

12. Rigging according to Claim 11, characterised in that (Figures 10, 11, 12) the lateral structures (34; 58) are foldable .

13. Rigging according to any of Claims 9 to 12, characterised in that the lateral structures (58) are provided with floats or deflecting wings.

14. Rigging according to any of Claims 3 to 8, characterised in that (Figures 7, 8, 9) the rigid spar is a swinging boom (32) which has an extension (32a) situated to aft of the mast (12) and connected by guys (49) to the head and foot of the mast .

15. Rigging according to any preceding Claim, characterised in that the outrigger structure (32; 34) is so dimensioned as to maintain the foot (26) of the sail (18) away from the longitudinal axis of the hull (10) by a distance equal to or greater than 50% of the height of the mast (12) .

16. A sail boat including rigging according to any preceding Claim.

17. A sail boat according to Claim 16, characterised in that it includes rigging according to any of Claim 1 to 15, associated with a mast (12) without forestay and provided with a swinging boom (32) or similar pivoted spar, constituting the aforesaid outrigger structure or forming part thereof, the swinging boom or spar being able to change sides by passing over the bow of the boat .