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US4044702: High efficiency aerodynamic sail system for boats, and method for sailing
39 Claims, No Drawings
A high efficiency aerodynamic sail system for boats comprises a triangular fabric sail pivotally suspended at its head from the apex of a tripod mast structure such that air impinging upon the luff of the sail is free from the turbulent wake of any upwind structure. The foot of the sail is attached only at its tack and clew ends to opposite ends of a spar which is pivotally attached at its center to a short stub mast centrally positioned in respect to the tripod mast. The sail luff and leech side deflections are caused to be identical by cables to provide a constant angle of attack of the sail to the wind along the entire sail height. A sail-shaping batten having a longitudinally varying cross section is employed along the foot of the sail. Loading of the batten by pressure generated by the wind causes the batten, and thus the sail, to assume an optimum airfoil shape. The sail luff and leech are cut to the deflection shape of the luff and leech cables, respectively, to assure a substantially constant camber along the entire height of the sail. In two variations the sail head is hung from a conventional single mast. In the first variation the sail tack and the sail clew are attached to opposite ends of a boom, the tack end of which is pivotally attached to one end of a second, shorter boom, which is, at its other end, rotatably attached to the mast. The sail may be positioned aweather of the mast to create a slot effect between the sail and the mast. In the second variation the sail tack is attached to one end of a short boom and the sail clew is attached at one end of a second, longer boom. The other ends of both booms are rotatably attached to the mast.
- 1. A high efficiency aerodynamic sail system, comprising:a. a sail having a luff, a leech, a head and a foot,said sail having a center of area at, or below, mid-height,b. means for supporting said sail,said supporting means being adapted to suspend said sail from every corner,said supporting means being adapted for mounting on a sailing craft,said supporting means including means to adjust the angle between said sail and said sailing craft while sailing, and to maintain said angle independently of the strength of the incident wind,c. means for causing the luff-to-leech airfoil chords of said sail to be virtually parallel each with the others when said sail is generating an aerodynamic lift force,said means for causing the luff-to-leech airfoil chords of said sail to be virtually parallel with each other when said sail is generating an aerodynamic lift force being capable of adjustment while said sail is in use, and,d. means for connecting said sail to said means for matching the leeward deflections of said luff and leech.
- 19. An aerodynamic sail system comprising:a sail having a head and a foot,said foot having tack and clew corners,means for supporting said head aloft,said means including a generally vertically extending mast, and further including means for securing said head to said mast,means for positioning said sail with respect to the wind,said positioning means including means for downhauling said sail to change the vertical curvature of said sail,means for attaching said foot to said positioning means,said means including tack and clew attaching means, andmeans for outhauling said foot to change the horizontal curvature of said sail wherein said outhauling means includes an arcuate track connected to said positioning means and a movable trolley connected to the end of one said luff or leech attaching means, said trolley being adapted to slide along said arcuate track whereby the distance between said luff and leech may be varied without affecting the distances between said head and said tack and between said head and said clew, and the said vertical curvatures of said sail.
- 20. A high efficiency aerodynamic lift-generating sail system, comprising:a. at least one generally triangular sail having a luff, a leech, a head, a tack, a clew and a foot, and having a batten pocket along said foot,b. means for supporting said sail at said head, tack and clew, with said luff away from the wake of any supporting structure, said supporting means being adapted for attachment to a sailing craft,c. means for matching the leeward deflections of said luff and leech whereby a virtually constant angle of attack of sail chords to the wind is provided along the height of said sail,said means including adjustable luff and leech countertension elements connected to said luff and said leech of said sail, said countertension elements acting in concert to move said luff and leech generally apart against the inwardly-directed tensile forces in said sail,d. an elongate sail-shaping batten adapted to fit in said batten pocket and having ends adapted for attaching to said luff and leech countertension elements,said batten having a longitudinally varying cross section whereby when said batten is laterally flexed it bends into an outline of an optimum airfoil, and,e. means for adjusting and maintaining the magnitude of said angle of attack independently of the velocity of said wind.
- 23. An aerodynamic sail system comprising:at least one generally triangular sail having a luff, a leech, a head and a foot,said foot having a tack and a clew,means for supporting said sail at said head and foot with said luff away from the wake of any supporting structure,said supporting means being adapted for attachment to a sail-powered craft,said supporting means including a streamlined mast,said supporting means also including a short boom having an end pivotally mounted to said mast,said supporting means further including a long boom having one end pivotally mounted to said mast,said head being adapted to hang from said mast,said clew being adapted to connect to the free end of said long boom,said long boom being rotatable to position said sail with respect to the wind whereby said sail generates lift, and,said tack being adapted to connect to the free end of said short boom,said short boom being rotatable to position said luff away from the wake of said mast and to position said sail abreast of and to the weather side of said mast to create a slot effect between said mast and said sail to increase said lift,said rotation of said short boom being in the direction to move said luff around to the rear of said mast when changing tacks.
- 24. A high efficiency aerodynamic sail system, comprising:a. at least one generally triangular sail having a luff, a leech, a foot, a tack and a clew,b. means for supporting said sail by said head and said tack and said clew, said supporting means being adapted for attachment to a sailboat,c. means for outwardly tensioning said luff and said leech of said sail, including a tension element, one portion thereof being attached along said luff and another portion thereof being attached along said leech, ends of said tension element being attached to a portion of said supporting means to support said tack and clew of said sail,one of said tension element ends adjacent to said clew being slidably attached to an arcuate track on said supporting means,said track having a radius of curvature to said head of said sail, whereby said tension element end adjacent to said clew may be moved toward or away from the other said end thereof which is adjacent to said tack without directly affecting the tension of said tension element, andd. means for causing said sail to assume an optimum airfoil shape, including an elongate batten having a longitudinally varying cross section,said batten being installed along said sail foot and having ends thereof attached to opposite ends of said tension element.
- 31. A method for making and using a sail, comprising the steps of:a. providing a flexible sail capable of assuming a smooth continuous airfoil shape in cross section responsive to the flow of air along its surfaces,b. providing deflection control elements for at least the luff and leech of said sail to oppose the tendency of said sail to belly greatly to leeward, said deflection control elements each having substantially the same characteristic taken laterally to a chord drawn across the foot of said sail,c. providing twist control elements for changing the magnitudes of lateral deflection of said luff and leech with respect to each other,d. connecting said deflection elements to said luff and leech,e. connecting said twist control elements to said deflection control elements,f. positioning said sail in respect to the wind to create a sail lift force, and,g. adjusting said twist control elements until the lateral components of deflection of said luff and leech are substantially matched along lines of airflow.
U.S. Patent Documents
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