Title:
SAIL RIG
United States Patent 3693571


Abstract:
This invention relates to a sail rig adapted for use with any sail propelled vehicle which permits both the tack and the clew of the sail to be positioned independently relative to the body of the vehicle (i.e. the hull). This arrangement permits the vehicle to be sailed much closer into the true wind than has heretofore been possible. In the preferred embodiment, the head or peak of a generally symmetrical generally triangular sail is rotatably fastened to a mast structure which mast structure is otherwise out-of-contact with the sail and the tack is fastened to a thrust spar which in turn is pivotally attached to the deck of the vehicle. Preferably the luff of the sail is provided with a stiffening member which may be a curved luff spar where the luff itself is curved and the foot of the sail with a boom. Manipulation of the thrust boom permits the leading edge or luff of the sail to be positioned at any angle of arc up to 90° or beyond on either side of the fore and aft centerline of the hull. The position of the clew is manipulated in the normal manner for a fore and aft rig by a main sheet.



Inventors:
HISCOCK EARLE F
Application Number:
05/097732
Publication Date:
09/26/1972
Filing Date:
12/14/1970
Assignee:
EARLE F. HISCOCK
Primary Class:
International Classes:
B63B15/00; (IPC1-7): B63H9/04
Field of Search:
114/39,102
View Patent Images:
US Patent References:
3396689Sailboat rigging1968-08-13Sommer
3195494Sail control for vessels1965-07-20Robin



Primary Examiner:
Blix, Trygve M.
Claims:
1. A sail rig for a sail propelled vehicle comprising a sail, means for supporting the head of said sail in an elevated position to pivot freely about a single point above said vehicle, which point is substantially fixed relative to said vehicle, means independent of said supporting means for positioning the tack of said sail relative to said vehicle along an arc centered at a fixed point on said vehicle substantially below said pivot point and separate means for positioning the clew of said sail relative to said vehicle along an arc centered approximately on said tack.

2. A sail rig as claimed in claim 1 wherein the foot of the sail is provided with a boom.

3. A sail rig as claimed in claim 1 where the luff of said sail is provided with stiffening means.

4. A sail rig as claimed in claim 3 wherein the luff stiffening means comprises a luff spar.

5. A sail rig as claimed in claim 1 wherein the means for positioning the tack includes a thrust boom, one end of which is pivotally attached to said vehicle.

6. A sail rig as claimed in claim 5 wherein the pivot to which the thrust boom is attached is substantially axially aligned with the pivot to which the head of the sail is attached.

7. A sail rig as claimed in claim 5 wherein means are provided to rotatably position said thrust boom relative to said vehicle.

8. A sail rig as claimed in claim 7 wherein said thrust boom positioning means includes a pair of fore sheets running between said thrust boom and said vehicle one on each side of said thrust boom.

9. A sail rig as claimed in claim 7 wherein retraction means are provided to return said thrust boom toward a fore and aft position if said positioning means are released.

10. A sail rig as claimed in claim 1 wherein said means for supporting the head of the sail includes a mast structure mounted on said vehicle which mast structure except for the point about which the head of said sail pivots is entirely out of contact with said sail.

11. A sail rig as claimed in claim 1, wherein the foot of the sail is provided with a boom, the luff is provided with stiffening means comprising a luff spar, and said boom is pivotally mounted at one end of said luff spar.

12. A sail rig for a sail propelled vehicle which comprises a sail, means including a mast structure mounted on said vehicle for pivotally supporting the head of said sail to pivot freely about a single substantially fixed point, said point being substantially above the centerline of said vehicle at a suitable position fore and aft, a boom at the foot of said sail to which at opposite ends the tack and the clew of said sail are attached, a thrust boom which at one end is pivotally attached to said vehicle and to which at the other end the tack end of said boom is pivotally attached, means for rotatably positioning said thrust boom relative to said vehicle and means including a main sheet for positioning the clew end of said boom.

13. A sail rig as claimed in claim 12 wherein the luff of the sail is provided with a stiffening member which extends between the pivot at the head of the sail and the free end of the thrust boom.

14. A sail rig as claimed in claim 12 wherein the pivot at the head of the sail and the pivot at which the thrust boom is attached to the vehicle are substantially axially aligned one vertically above the other relative to said vehicle.

15. A sail rig as claimed in claim 14 wherein means are provided at the junction between said thrust boom and said luff stiffening member to prevent the twisting of said stiffening member relative to said thrust boom.

16. A sail rig as claimed in claim 12 wherein the sail is symmetrical and wherein the effective length of the thrust boom is substantially one-half the length of the boom.

17. A sail rig as claimed in claim 15 wherein the sail has substantially the shape of a isosceles triangle.

18. A sail rig as claimed in claim 12 wherein the means for rotatably positioning said thrust boom includes a pair of fore sheets arranged between the thrust boom and the vehicle, one on each side of the thrust boom.

19. A sail rig as claimed in claim 18 wherein retractor means are provided between said thrust boom and the front of said vehicle to retain the thrust boom toward the fore and aft position whenever both fore sheets are released.

Description:
SUMMARY OF THE INVENTION

During the many thousands of years that sailing vessels have been in existence many different sailing rigs have been developed and used. While most any kind of rig is reasonably effective running before the wind or in a reach it is only relatively recently, at least in western civilization, that rigs have been developed that permit the vessel to point into the wind to any appreciable degree and with any efficiency. The greatest advances have come in the present century with the realization that a sail at least in a close hauled position, is in fact an airfoil subject to the same aerodynamic principles, as for example, the wing of an airplane. Thus, for example, in a close hauled position a major portion of the propelling force in a Bermuda rig, the most efficient close hauled sail rig known to date, is developed on the lee side of the main sail at a position just slightly aft of the mast. The presence of the mast however produces turbulence that appreciably reduces the theoretical efficiency of the sail as compared to e.g., the ideal airfoil and even the use of a genoa jib to produce a slot effect to minimize the turbulent eddies on the lee side of the main sail is only partially effective. In additional a symmetrical airfoil is theoretically more efficient than an asymmetical one but a symmetrical sail which is equally effective in all points of heading is difficult to produce when the luff is mounted on a mast even if the mast is raked. As a result, even a finely tuned bermuda rigged sloop such as the 12 meter yachts designed for the America's Cup Races with all of the advances in recent years in sail and sail cloth design, cannot head closer into the true wind than about 35° as compared for example with a glide ratio in excess of 40:1 for certain well designed sail planes.

In addition, while the asymmetrical triangular sail of the bermuda rig is the most efficient heading into the wind, it has certain rather marked disadvantages sailing before the wind in that, with the boom abeam, the center of force of the wind on the sail is well off of the centerline of the vessel. The resulting large moment of force or torque tends to steer the vessel toward the side opposite the boom -- to turn the vessel up to windward. This can be overcome either by the use of excessive rudder angle which tends to impose a substantial drag against the forward movement of the vessel or by rigging a counterbalancing sail, a spinnaker, on the opposite side of the mast. Raising a spinnaker is a relatively difficult task requiring a well trained crew and the time required for raising and lowering the spinnaker interferes with the maneuverability of the craft limiting its use to relatively long downwind courses. In addition, in the absence of a spinnaker or other counterbalancing sail, with the boom abeam, the tip of the boom, especially if the boom is relatively long compared to the beam of the vessel, can readily come into contact with the water submerging that portion of the sail near the clew which can easily cause the vessel to broach.

Finally, in a conventional fore and aft rig such as either the bermuda or the gaff rig, it is desirable to maintain a controlled downward force on the boom in order to shape the sail properly. THe main sheet is effective for this purpose only when the vessel is relatively close hauled. In other aspects it is conventional to use a boom vang to maintain a downward force on the boom. However, in a conventional rig the boom vang is only partially effective especially when the boom is relatively long since the downward pull of the boom vang can only be applied relatively close to the mast.

It is an object of the invention to provide a sail rig which permits the sail structure to be moved in relation to the vessel as a free airfoil.

It is a further object of this invention to provide a sail rig which permits almost unlimited choice of aerodynamic shape for the airfoil.

It is a further object of this invention to provide a sail rig wherein, if desired, the forces may be essentially balanced in every aspect or point of sailing.

It is a further object of this invention to provide a sail rig wherein the wind contacting the airfoil is not made turbulent by any structure on the vessel.

It is a further object of this invention to provide a sail rig which permits a closer tack into the true wind than heretofore possible.

It is a further object of this invention to provide a sail rig that can be sailed if desired as a conventional fore and aft rig especially in the sense that if the several sheets and the rudder are released the craft will automatically come to a luffing attitude.

It is a further object of this invention to provide a sail rig that can easily be handled by one person on a small or moderate sized vessel.

The essential elements of the sail rig are as follows. The head or apex of the sail is pivotally attached at a single pivot substantially above the centerline of the vessel at a suitable position fore and aft. The clew and the tack are attached to a boom. The tack end of the boom is pivotally attached to a spar which I refer to as a thrust boom which spar is preferably substantially one-half of the length of the boom and is in turn pivotally attached to the vessel at a point substantially below the point at which the head or apex of the sail is attached. The clew end of the boom is provided with a main sheet in the conventional manner. The thrust boom is provided with a pair of fore sheets on the port and starboard side respectively adapted to rotatably position the thrust boom to at least athwartships both to port and starboard. Normally the luff of the sail is provided with a stiffening member which in the case of a triangular sail would extend between the apex pivot and the tack.

Briefly then the apex of the sail, if the sail is triangular, or a point on the head of the sail, if the sail is a shape other than triangular, is fixed at a single point about which the sail may pivot. The tack of the sail may be positioned by regulating the proper fore sheet at any point along an arc centered substantially below the pivot point of the head of the sail. The clew moves along an arc centered on the tack and is positioned against the force of the wind on the sail by a conventional main sheet.

Superficially my sail rig bears some resemblance to a number of pre-existing rigs where the sail may be pivoted about a point other than the luff such as for example the lateen rig or certain lug rigs. In these pre-existing rigs however a movement of the clew about the pivot results in the proportional opposite motion of the tack about the same pivot. The same is true for example in Laurant U.S. Pat. No. 3,173,395, Robin U.S. Pat. No. 3,195,494 and Purvis U.S. Pat. No. 3,345,969, the first two of which show symmetrical triangular sails and the last shows a jib-main sail combination which pivots as a unit. The mast aft arrangement which I prefer but which certainly is not essential to my invention is shown in Robin U.S. Pat. No. 3,195,494, the article entitled "A Patented Sloop" by Philip T. Robin appearing at page 28 of the magazine "The Skipper", March 1970, and at page 51 of Amateur Yacht Research Society Publication No. 58 entitled "Practical Hydrofoils" published by John Morwood, Woodacres, Hythe, Kent, United Kingdom, Oct. 1966 in an article entitled "Semi-Elliptical Sail" by George Dibb and John Morwood. In the last mentioned arrangement the tack of the sail, while movable, may only be positioned at some point over the deck by lines which are therein also referred to as tacks.

It will be understood that, while the detailed description which follows describes the rig in relation to a conventional monohull sail boat, the rig itself, which is the subject matter of this invention, is equally useful for any type of sail propelled vehicle whether it be a monohull, a catamaran, a trimaran, a hydrofoil, an ice boat or even a land yacht and may well have special utility in connection with the last three enumerated in view of the improved ability of the rig to balance the forces imposed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a side elevation of a small sailboat rigged with the sail rig of the present invention;

FIG. 2 is a plan view corresponding to FIG. 1 but with the sail omitted and the booms displaced slightly to show details of the rigging;

FIG. 3 is a detailed view of the fitting between the luff spar and the thrust boom taken at line 3-3 of FIG. 1;

FIG. 4 is a side elevation in the region shown in FIG. 3;

FIG. 5 is a side elevation showing in detail and partially in section the region at the peak of the sail;

FIG. 6 is a side elevation showing a variation of the sail rig of the present invention;

FIG. 7 shows diagrammatically the possible positioning of the sail rig of the present invention in various aspects of sailing from running before the wind through close hauled.

DETAILED DESCRIPTION

FIGS. 1 and 2 show the sail rig of the present invention as mounted on a conventional small boat of the centerboard type. The boat, indicated generally at 15, comprises a conventional hull 16, rudder 17, tiller 18, centerboard 19, centerboard box 21, and is provided with a cockpit 22, forward deck 23, port and starboard gunwales 24 and 25 and transom 26.

Sail 31 is preferably symmetrical and, in the specific embodiment shown in FIG. 1, is a spherical isosceles triangle with a curved leach 32, a curved luff 33 and a curved foot 34. The luff 33 of sail 31 is provided with a reinforcing member or luff spar 35 which in the specific embodiment is a suitably curved piece of lightweight aluminum aircraft tubing. The luff 33 is fastened clew 39 is provided with outhaul 41 passing through a luff spar 35 by any of the means conventionally used to fasten the luff of an ordinary sail to the mast as indicated by rings 36. The foot 34 of sail 31, in the specific embodiment, is fastened to boom 37 by any conventional means, such as by the use of a roped edge in a channel, used for fastening the foot of an ordinary sail to a boom. Tack 38 of sail 31 is fastened to luff spar 35 in a conventional manner as by passing a loop of line through a grommet provided for this purpose and around luff spar 35 (see FIG. 4). Clew 39 is provided with outhaul 41 passing through grommet provided for this purpose to a cleat 42 mounted at the aft end of boom 37 to provide for adjustment of the tension on foot 34 of sail 31. It is, of course, not essential that the foot be attached to the boom along its entire length and a loose footed or semi-loose footed arrangement can be employed. Leach 32 of sail 31 may be provided with stiffening battens 43 if desired. Boom 37 is pivotally mounted on luff spar 35 as by U-shaped strap 40, the ends of which are mounted on opposite sides of boom 37 and the body of which passes around luff spar 35.

The mast 44 in the specific embodiment is curved sufficiently to permit the leach 32 of sail 31 to swing freely and extends from a point adjacent transom 26 to a point above the midpoint of boom 37 where it terminates in a horizontal (i.e. parallel to the waterline) plate 45. The mast 44 is formed from aircraft aluminum tubing and, in the specific embodiment, is bifurcated at its lower end as indicated at 44a and 44b to permit for the movement of tiller 18. Normally, where the rudder is mounted ahead of the stern, a single mast would be preferred.

The manner in which upper end of luff spar 35 is pivotally mounted to plate 45 of mast 44 is shown in detail in FIG. 5. Pivot 46 passes vertically downwardly through an aperture (not shown) in plate 45 through a large flat sided washer 47 of nylon or some other suitable low friction material to inverted U-shaped member 48 mounted below plate 45. The upper end of luff spar 35 is provided with a generally outwardly extending U-shaped member 49, the arms of which are adapted to cooperate with the arms of U-shaped member 48 and are pivotally joined thereto by horizontal pivot 51. Additional low friction washers and the like (not shown) may be provided to insure that member 48 pivots freely around pivot 46 and member 49 pivots freely around pivot 51.

The lower end of luff spar 35 is attached to boat 15 by means of a so-called thrust boom 55. One end of thrust boom 55 is provided with a horizontal plate member 56 which is pivotally attached to the upper horizontal surface of pulpit 57 or other suitable supporting member, which in turn is firmly attached to hull 16, by means of vertical pivot 58 which preferably is axially aligned with pivot 46. A suitable flat sided washer 59 of nylon or some other low friction material may be provided between plate member 56 and the upper horizontal surface of pulpit 57. The main portion of thrust boom 55, which can be made of any suitable stiff material as, for example, aircraft aluminum tubing, extends generally upwardly to provide clearance between thrust boom 55 and deck 23 on the one hand and clearance between thrust boom 55 and boom 37 on the other and at its outer end terminates in and is provided with a generally horizontal flat plate member 61 (see FIGS. 3 and 4). Plate member 61 is provided with a rectangular slot 62, the major dimension of which extends axially of thrust boom 55. The lower end of luff spar 35 is provided with a generally vertically extending tongue member 63 having a rectangular cross section adapted to extend through and closely cooperate with slot 62. This insures that as thrust boom 55 and luff spar 35 rotate about pivots 58 and 46, luff spar 35 will remain in the generally vertical plane extending through the pivots and along the centerline of thrust boom 55 without twisting. A removable member 64 such as a nut and bolt is provided on tongue 63 below plate member 61 to prevent the accidental disengagement of tongue 63 from plate 61. Preferably the horizontal distance between pivot 58 and tongue 63 is approximately half the length of boom 37.

The rigging for the most part is conventional. Thus, for example, sail 31 is raised by a halyard 71 which runs from grommet 72 at the head or apex of sail 31 through sheave 73 attached to some convenient portion of the mast head swivel such as pivot 51 through sheaves 74 mounted at convenient intervals along mast 44 to a cleat 75 mounted e.g. at the base of mast 44. At the lower end of the luff 33 of sail 31, a down haul 77 is provided which runs from eye 78 mounted on the bottom of boom 37 adjacent mounting strap 40 through sheave 79 mounted on the top of thrust boom 55 adjacent plate member 61 to a cleat 80 mounted on top of thrust boom 55 at a convenient position near pivot 58. Tension in the sail along luff 33 is controlled by controlling the tension on halyard 71 and downhaul 77.

A boom vang 83 may be provided. Boom vang 83 runs between a sheave 84 mounted on top of pivot 58 and a sheave 85 mounted on the bottom of boom 37 at approximately its midpoint to a cleat 86, preferably a jam cleat, mounted, in the case of the specific embodiment, on top of centerboard box 21. The boom vang 83 in the sail rig of this invention offers a great advantage over boom vangs in conventional rigs in that, as will be shown later, in practically any angle of sailing and especially in reaches, when the use of a boom vang is most desirable in order to put a downward pull on the boom (the sheet in such aspects being relatively ineffective for this purpose) to cause the sail to assume the desired aerodynamic shape, it is possible through the proper adjustment of the angle of thrust boom 55 to place sheave 85 directly over sheave 84 whereby boom vang 83 will exert a vertically downward pull at the midpoint of boom 37.

Main sheet 87 is rigged in any conventional manner. In the specific embodiment main sheet 87 runs from eye 88 mounted underneath the end of boom 37 to a sheave 89 on the starboard gunwale 27 to sheave 90 on the port gunwale 24 to sheave 91 mounted on the bottom of boom 32 inboard or forward of eye 88 to sheave 92 mounted on the bottom of boom 37 further inboard (forward) of sheave 91 thence to cockpit 22.

The non-conventional rigging comprises a pair of fore sheets and a retraction gear all for the purpose of positioning thrust boom 55. Starboard fore sheet 95 runs from eye 96 mounted on the bottom of thrust boom 55 approximately three-fourths of the way out from pivot 58 to sheave 97 mounted on starboard gunwale 25 at a position abaft the location of pivot 58 to sheave 98 mounted on the right side of thrust boom 55 at the position of eye 96 back to a cleat 99 preferably a jam cleat mounted on gunwale 25 at a convenient position. Port fore sheet 95' runs from eye 96 to sheave 97' mounted on port gunwale 24 opposite sheave 97 to sheave 98' mounted on the left side of thrust boom 55 opposite sheave 98 back to cleat 99' mounted on port gunwale 24 opposite cleat 99. By lengthening or shortening the appropriate fore sheet 95 or 95' the position of the free end of thrust boom 55 can be fixed at any position from slight abaft either beam through straight ahead. Normally only the windward fore sheet need be used, with the leeward fore sheet remaining slack, due to the pressure of the wind on sail 31.

The retraction gear comprises retraction line 101 which runs from eye 102 at the bow through sheave 103 mounted at the bottom end of tongue 63 to cleat 104 mounted on deck 23 amidship at some point forward of pulpit 57. In the specific embodiment, the retraction line 101 comprises an elastic shock cord and is so adjusted as to apply some tension at all times. The function of retraction line 101 is to return thrust boom 55 to, or toward, its bore and aft position wherever both fore sheets are released. In larger vessels springs or spring loaded drums or the like may be used instead of the shock cord. The retraction gear is intended as a safety feature in that if all three sheets (the main sheet and the two fore sheets) and the tiller are released, the vessel will automatically tend to face into the wind with the sail luffing as is the case with the ordinary bermuda rig.

To summarize and to recapitulate, in the sailing rig of the present invention, a thrust boom is provided which is mounted on the vessel at some convenient point to pivot in a horizontal plane. A vertically extending luff spar is provided at the free end of the thrust boom and the luff spar is mounted at its upper end to pivot about a horizontal plane with the axis of the two pivots in substantial alignment. A boom is provided mounted to swing freely about the lower end of the luff spar and a sail is mounted with its foot adjacent the boom and its luff adjacent the luff spar. A main sheet is provided to position the free end of the boom and a pair of fore sheets are provided to position the free end of the thrust boom. The primary if not sole function of the mast is to provide a support for the upper pivot so that, while a mast aft arrangement appears to be the most convenient and the most satisfactory especially in avoiding any possibility of disturbing the air before the air reaches the sail when the vessel is heading up into the wind, the mast structure can be arranged in any manner that is convenient provided the mast at all times remains free of the swing of the sail. Since the mast provides the primary support for the sail, the luff spar, whose primary function is to stiffen the luff of the sail, is desirably as thin as possible to avoid disturbing the flow of air especially on the leeward side when sailing up into the wind.

The sail is thus free to act in its primary function as an aerodynamic element, an airfoil. The only restraint on the sail is that its head pivot about a point, that it have a boom, one end of which pivots about a point which point lies on an arc centered on a point approximately axially aligned with the first recited pivot and that its luff be stiffened. Within these limits the sail can theoretically assume any number of shapes it being understood, of course, that if a gaff is provided for the head of the sail, that portion of the gaff forward of the upper pivot would be considered as a portion of the luff stiffening means. Because of the advantages of balancing the forces when going before the wind it is believed that the most satisfactory sail shapes would all be substantially symmetrical with the effective length of the boom being approximately twice the effective length of the thrust boom.

In the specific embodiment, the sail has been shown as a spherical isosceles triangle to approximate the elliptical shape that most theoreticians hold to be the most efficient shape for a sail. The fact is that, to my knowledge, no one has previously devised a means for mounting a sail as a free airfoil and for this reason there has not heretofore, before my invention of the present sail rig, been any means of thoroughly testing this theory. For this reason I do not intend to be bound to any particular shape of the sail realizing, for example, that there may be some advantages especially if a higher aspect is desired in providing the sail for example in the shape of an ordinary isosceles triangle as shown in FIG. 6 where only the major elements are shown and where corresponding elements have been given corresponding numbers but with one hundred added.

Some of the advantages of the present rig are shown in FIG. 7 where typical arrangements of boom 37 and thrust boom 55 are shown in various aspects of sailing with FIG. 7A representing going before the wind, FIG. 7B representing a broad reach, FIG. 7C a close reach, FIG. 7D a starboard tack and FIG. 7E close hauled.

In FIG. 7A, thrust boom 55 is oriented abeam to starboard with the boom 37 oriented, athwartships to port. With a symmetrical sail as shown in the specific embodiment, the resultant propelling force on the sail is directly amidship and the boat 15 can be kept on course with little or no rudder action. By tightening or easing both main sheet 87 and foresheet 95 the position of boom 37 fore and aft may be adjusted without changing the orientation of the sail. Thus, if the use of the boom vang to full effectiveness is desired, boom 37 can be moved aft slightly from the position shown to bring the center of boom 37 over the lower pivot. By easing both main sheets 87 and fore sheet 95, boom 37 can be positioned forward of the lower pivot while remaining precisely athwartships thereby sloping the foot of the sail outwardly to provide an upward resultant force which is desirable to overcome the normal tendency of the bow to be driven down when going before the wind. Such a movement of the boom of course would place the resultant force slightly to port of amidships.

This is shown more specifically in FIG. 7B where the dotted lines indicate the position of boom 37 if positioned directly over the lower pivot and the solid lines showing the positioning of boom 37 to provide a distinct slope to the sail.

It should be understood that the sail rig of the present invention can be sailed in any aspect as a conventional bermuda rig merely by positioning thrust boom 55 directly amidship. This is shown in FIG. 7D.

One of the more spectacular aspects of the sail rig of the present invention is that the vessel can in effect be twisted under the sail while retaining a constant aspect between the sail and the true wind. This is shown in FIG. 7E where boom 37 is positioned at 35° to the true wind and yet vessel 15 is headed somewhat closer into the wind. This is accomplished by moving the tack to leeward and the clew to windward as shown. In the initial test with a 13 foot boat so rigged it was possible to sail the boat to within about 15° of the true wind. This is much closer into the wind than any sail boat that I am aware of or has ever sailed before. Just how close into the wind it will be possible to sail with the sail rig of the present invention I do not know, but I believe that with a suitable refinement of the aerodynamic shape of the sail and especially with low drag hulls such as, for example, with an ice boat it will be possible to sail even closer into the wind. It will be noted from the diagram that, if a boom vang is provided, the boom vang may be used in lieu of the main sheet 87 in the event that it is desirable to position the aft end of boom 37 beyond the side of the vessel in sailing into the wind.

While the specific embodiment described herein sets forth the best and simplest way known to me to practice my invention, it will be obvious to those skilled in the art that many variations of the present invention are possible especially if some but not all of the advantages of the specific embodiment are desired. For example, in the course of the experiments leading to the development of the specific embodiment I made one model wherein the thrust boom was pivotally attached to the boom at a point about two-thirds of the way from the middle of the boom toward the tack end. This arrangement was quite satisfactory in every respect except that the sail would not come into a luffing position and the rig could not be sailed as a conventional bermuda rig. This defect was in part overcome by providing means for selectively disengaging the boom from the thrust boom while at the same time connecting the tack to a line running from the bow whenever it was desired that the sail come to a luffing condition. Such an arrangement while workable is certainly more complicated and much less convenient than the arrangement shown in the specific embodiment. Many other similar modifications which however come within the scope of my invention as defined in the claims I am sure will occur to those skilled in the art.