US3298346A

US3298346A - Sail construction

Info

Publication number: US3298346A
Application number: US450087A
Authority: US
Inventors: Steven M Cochran
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-04-22
Filing date: 1965-04-22
Publication date: 1967-01-17
Anticipated expiration: 1984-01-17

Description

1967 s. M. COCHRAN SAIL CONSTRUCTION Filed April 22, 1965 INVENTOR STEVEN M. COCHRAN ATTORNEYS United States Patent 3,298,346 SAIL CONSTRUCTION Steven M. Cochran, Winchester, Mass. (6847 Country Lane, Dearborn Heights, Mich. 48127) Filed Apr. 22, 1965, Ser. No. 450,087 Claims. (Cl. 114-103) My invention relates to an improved sail construction for sailing craft. In particular, it relates to an inflatable sail defined by a pair of closed surfaces which are capable of assuming the form of an asymmetric air foil in response to wind pressure at the surface thereof.

Conventional sails are formed from a single sheet of material which deforms in response to wind pressures on the surface of the sail to provide a thrust component in the forward direction. These one-dimensional air foils are, however, aerodynami-cally inefiicient and do not provide the thrust that may be obtained from a two dimensional air foil of comparable dimensions. Various attempts have been made to utilize two dimensional air foils for sails but such attempts have, until now, introduced attendant disadvantages such as greater complexity and increased weight aloft. These disadvantages have outweighed the advantages obtained by adding another surface to the sail. I

Accordingly, it is an object of my invention to provide an improved sail construct-ion whose cross section is that of a two dimensional airfoil. A further objectof my invention is to provide a light-weight sail that has an aerodynamic cross section. Another object of my invention is to provide an improved sail of the double-surface type which is capable of maintaining an airfoil shaped cross section without requiring the use of battens or other rigid shaping structures. Yet another object of my invention is to provide an inflatable sail that is capable of assuming a cross sectional shape resembling that of an asymmetric airfoil in response to wind pressures on the surface thereof. Still another object of my invention is to provide an inflatable sail having an airfoil shaped cross section-which may readily be attached to, and detached from, the mast of a conventional sail boat and which may easily be hoisted for sailing or lowered for storage.

Other and further objects and features of my invention will in part be obvious and will in part appear below in the following detailed description of a preferred embodiment of my invention which has been selected for purposes of illustration and which is shown in the accompanying drawings in which:

FIGURE 1 is a side elevational view of a sail constructed in accordance with a preferred embodiment of my invention;

FIGURE 2 is a cross section taken along the lines 2--2 of FIGURE 1 which illustrates one method of securing the leech of the sail to the mast;

FIGURE 3 is a cross section taken along the lines 33 of FIGURE 1 which illustrates one method of securing the foot of the sail to the boom;

FIGURE 4 is a fragmentary cross section taken in a horizontal plane through the sail and similar to FIGURE 2 Which shows in an enlarged scale the positioning of the bolt rope and the bolt rope cover;

FIGURE 5 is an expanded view in partial side elevation of the sail of FIGURE 1 showing the construction of the sail in more detail with the bolt rope cover omitted for the sake of clarity; and

FIGURE 6 is a cross section taken in a horizontal plane through the sail and illustrating the shape the sail assumes in response to wind pressure on the surface thereof.

In accordance with my invention, I provide an inflatable sail having a pair of surfaces or sail segments positioned adjacent to each other and secured to each other at their edges in a manner to form an airtight seal. Transverse "ice ' nicates with the air pockets formed between the sail segments, thereby providing a means of inflating the sail. A bolt rope and bolt rope cover, secured to one edge of the still, provides means for attaching the sail to the mast I and boom in conventional fashion; the bolt rope may be omitted along the foot of the sail if the sail is to be used loose-footed. 1

In the drawings, FIGURE 1 shows one embodiment of a sail constructed according to my invention. For purposes of illustration, there is shown a saillt) of conventional triangular form and having a luff 12, a leech 14, and a foot 16. The sail 10 has two panels or segments of identical shape positioned adjacent to each other and secured to each other at the edges thereof to form an airtight seal. A first segment forming a first sail surface is shown in FIGURE 1 and is indicated generally at 18; a second segment is more readily seen in FIGURE 2, and is indicated by the reference numeral 20.

Abolt rope 46, fastened along the luff 12 and the foot 16 of the sail, is secured to the sail by means of a bolt rope cover which fits over the bolt rope and attaches to the edges of the sail on opposite sides thereof. This construction is shown in detail in FIGURE 4 and will be described at greater length in connection with that figure. The lufl 12 of the sail is fitted into a track formed in the after edge of the mast 22; the foot 16 of the sail is fitted into a similar track in the boom 24. A clew cringle 26 and a tack cringle 28 are provided to secure the tack and clew of the sail to the fitting 40 on the boom 24 and the outhaul 36 by means of a shackle pin 38 and a line 34 respectively, while a peak cringle 30 is provided to haul the sail up the mast by means of a haliard 42 in order to secure the head to the mast. A valve 32 which is attached to the sail at one side thereof to provide a means of inflating the sail, communicates with the air pocket formed between the two

segments

18 and 20 of the sail and is provided with a resilient tube 33 which may be attached to a source of air pressure. Obviously the tube 33 is attached to the valve 32 in an airtight fashion. Transverse webs 19 running parallel to the foot of the sail extend between the

sail segments

18 and 20. These webs are provided with vent holes to allow the free passage of air or other gas throughout the interior of the sail from one portion of the sail to another, and will be more fully described in connection with FIGURE 2.

After the sail of FIGURE 1 has been set and made fast to the mast 22 and the boom 24, it is inflated through the valve 32 and the tube 33. With the ship headed into the wind, the sail assumes the shape of a symmetric airfoil as shown in FIGURE 2, and the forces on each side of the sail are balanced. Under this condition no useful lift is obtained from the sail.

FIGURE 2 of the drawing shows a cross sectional view of the sail taken along the lines 2--2 of FIGURE 1. The mast 22 has a track 44 into which a bolt rope 46 is fitted for securing the sail to the mast. The bolt rope cover 48 is fitted around the bolt rope and attached to the

opposite segments

18 and 20 of the sail 10. The bolt rope cover may be fitted to the sail by means of stitching, high-strength adhesives, or other known means. The valve 32 is attached to one segment of the sail, here shown as the segment 18, and communicates with an interior air pocket 60 formed between the

segments

18 and 20 to allow the sail to be inflated. The web 19 extends between the sail segments 18 and 2t and is provided with vent holes 21 which allow the air within the sail to flow freely past the web in either direction. The webs 19 may be fastened to the sail segments 18 and by stitching, adhesives, thermal bonding techniques, or other known means. It will be noted that the cross sectional shape of the sail in FIGURE 2 is that of a symmetric airfoil when the sail is inflated, the chord of the airfoil being denoted by the dimension B and the maximum thickness of the airfoil being denoted by the dimension A. In practice, it has been found that the sail need only be inflated to a thickness approximately equal to one-tenth of its maximum chord in order to provide the desired lifting characteristics for the sail.

FIGURE 3 is a cross sectional view taken along the lines 3-3 of FIGURE 1 and showing the sail secured in the boom 24. The boom is shown as having a track 50 formed therein in which the bolt rope 46 and bolt rope cover 48 are firmly secured.

FIGURE 4 is a view in enlarged scale illustrating the attachment of the bolt rope and bolt rope cover to the sail 10. As stated previously, any of a number of known means may be used to attach the bolt rope cover to the sail; for purposes of illustration only, the bolt rope cover is shown as being secured to the

segments

18 and 20 of the sail by means of a high strength waterproofadhesive layer 52 interposed between the bolt rope cover and the sail segments. It will be apparent that the bolt rope cover may also be attached to the sail segments by stitching, an airtight seal being formed around the stitched areas by means of a sealer or adhesive material applied thereto.

FIGURE 5 is a view in enlarged detail of the tack section of the sail with the bolt rope 46 positioned against the edges of the sail along the luff and the foot, the bolt rope cover being removed to show the crimping 54 along the luff and the foot by means of which an airtight pocket is formed between the segments of the sail. sail segments may be joined together by any of a number of conventional means, including vacuum molding,

heat sealing, chemical bonding, or any other means which is capable of providing an airtight seal at the edges of the segments so joined; illustratively in FIGURE 5, the segments are shown as being adhesively bonded and pressure sealed along the crimping lines 54.

As so far described, my sail construction provides a closed, double-surfaced sail whose cross-sectional shape The 7 in a horizontal plane is that of an airfoil and, in partic ular, a symmetric'airfoilwhen the surfacesof the sail segments are symmetrically disposed with respect to the wind.

If the sail were to maintain a symmetric shape under r all conditions, however, it would be found that its lift.

component would often be less than that of a singlesurfaced sail and the hoped-for advantages of using a closed, double-surfaced sail would not be achieved. Forturnately, the shape of the sail distorts as the magnitude of the angle between the centerline 'of the chord of the wing and the wind direction (the so-called angle of attack) increases, the sail becoming increasingly asymmetric in response to the increased angle of attack. It is well known in aerodynamic theory that the lift generated by an asymmetric airfoil increases as the angle of attack increases, the lift obtainable with this type of section being nearly four times that obtainable with a single-surfaced sail. Accordingly, it will be seen that my sail assumes the desired shape in response to a wind blowing on the surface thereof, the cross sectional shape of the sail becoming increasingly asymmetric as the sail is inclined at greater angles to the wind.

This feature of my invention is illustrated more clearly in FIGURE 6 which shows a horizontal cross section of the sail of FIGURE 1 under the influence of a wind 58 acting upon the sail. The pressure in the air pocket formed between the

segments

18 and 20 of the sail prevents the segments from adhering to each other under the influence of the wind and maintains the desired cross sectional shape, thereby providing a highly efficient asymmetric air foil for the generation of a greater lift then was heretofore available with conventional sails. be noted that with the wind blowing on the sail as in FIGURE 6, there will be an inward pressure on the sail segment 20 which is on the windward side and an outward pressure on the sail segment 18 which is on the leeward side. Under certain conditions, namely conditions of heavy air and high angles of attack, the low pressure conditions existing along the luff of the sail directly behind the mast cause the center of pressure of the sail to shift forward and create bulges in the sail which impair its aerodynamic characteristics. Accordingly, I have provided a series of transverse webs 19 which limit the amount of distortion which the sail can undergo under all conditions. These webs add little to the Weight of the sail but add to its desirable characteristics in heavy air conditions and at high angles of attack. The webs may be omitted if the sail is not to be used under these adverse conditions.

It will be apparent from this figure that the exact shape the sail assumes will be determined by the extent to which the sail is inflated (as measured by the ratio of the thickness A to the chord B) as well as by the magnitude and direction of the wind at the surface of the sail. As stated previously, a ratio of A/B=1/ 10 has been found to be a practicable value for inflation of the sail.

Various constructions and details of my invention may be altered to suit the needs of the user. Thus, the sail of my invention may be formed of identical sail segments which are joined together along the corresponding edges thereof or may be formed from a single sheet of material folded over along a line of symmetry of the material and joined together at the corresponding remaining free edges; the latter construction is shown in FIGURE -l. The shape of the sail, of course, need not be triangular and any desired sail shape may be used with my invention; also, loose-footed sails may be used if desired. It will also be apparent that the sail need not be secured to the mast by means of a bolt rope and bolt rope cover but may use any of a number of known means of securing the sail to the mast which need not be described herein detail. I

The means utilized to secure an air tight compartment between the segments of the sail will be dictated largely by economic considerations and any fastening technique which secures the desired seal under the conditions in which the sail will be used is acceptable in the practice of my invention. It will be found, for example, that rubber or plastic materials readily lend themselves to vacuum molding, heat sealing, and chemical bonding techniques, and such materials may economically be used. A prefered material for use in my sail is the polyester film formed as the condensation product of ethylene glycol and terepthalic acid and sold under the trademark MYLAR by E. I. duPont de Nemours & Co., Inc. This material has the desired properties of strength, light weight, and relative impermeability to fluids that are desirable in practicing my invention. The desired characteristic of my sail may also be obtained by forming a laminate structure of one or more materials, at least one of the materials being chosen to have superior impermeability to fluids. Thus the MYLAR film described above may advantageously be laminated to the polyester fiber also formed from ethylene glycol and terepthalic acid and sold under the trademark DACR ON by E. I. duPont de Nemours & Co., Inc. This DACRON fiber is also of light weight and high strength, and is commonly used in the persent conventional sails. It will be apparent, of course, that the MYLAR film laminate may be used with other types of fabric coverings such as cloth or canvas. It will also be apparent-that the airretaining structure need not be laminated to the outer It will fabric, as this fabric will conform to the air-retaining structure when the latter is properly inflated.

In such a case, the air-retaining structure, which is preferably thin walled so as to be sufficiently flexible, will form a closed surface or envelope which may be inflated by connecting the gas-valve to the interior of the envelope. For structural puroses, however, a unitary configuration such as is formed by laminating the air-retaining material to the outer fabric is preferred.

It will thus be seen that I have provided an improved sail whose cross sectional shape is that of an airfoil. Further, it will be seen that I have provided an inflatable sail having an aerodynamic cross section which is maintained without requiring the use of battens or other mechanical structures of excessive weight. I have also provided a simple yet efficient sail which is capable of assuming the shape of an asymmetric airfoil in response to wind pressure on the surface of the sail.

It is clear that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having thus described my invention, I claim:

1. An inflatable sail for sailing craft comprising, in combination, first and second sail segments of material which is substantially impermeable to fluids positioned adjacent to each other and secured to each other adjacent the edges thereof to form an air chamber having an airtight seal around the periphery thereof, a plurality of horizontally disposed transverse webs parallel to each other extending between said sail segments and secured thereto, said webs dividing said air chamber into segmented chambers, and means forming a gas valve secured to said sail and communicating with said air chamber whereby said sail may be inflated to form an aerodynamic cross-section throughout said sail, said webs maintaining said cross section in both light and heavy winds.

2. The combination defined in claim 1 in which each of said webs contains a perforation through at least one portion thereof whereby the segmented chambers between said webs may communicate with each other.

3. The combination defined in claim 2 in which said sail segments are formed in a generally triangular shape and include securing means formed along at least one of the edges of said sail for securing said sail to a mast in a generally vertical position.

4. The combination defined in claim 3 wherein said I first and second sail segments are formed from a single sheet of material, said segments being obtained by symmetrically folding the sheet upon itself.

5. The combination defined in claim 3 wherein said first and second segments are formed from at least two sheets of material, said segments being formed to have substantially equal dimensions in all directions.

References Cited by the Examiner UNITED STATES PATENTS 2,569,318 9/1951 Kersten 114103 2,979,287 4/ 1961 Ross 244-44 3,016,860 1/1962 Johnson 114-39 FOREIGN PATENTS 445,639 6/ 1927 Germany.

MILTON BUCHLER, Primary Examiner.

T. M. BLIX, Assistant Examiner.

Claims

1. AN INFLATABLE SAIL FOR SAILING CRAFT COMPRISING, IN COMBINATION, FIRST AND SECOND SAIL SEGMENTS OF MATERIAL WHICH IS SUBSTANTIALLY IMPERMEABLE TO FLUIDS POSITIONED ADJACENT TO EACH OTHER AND SECURED TO EACH OTHER ADJACENT THE EDGES THEREOF TO FORM AN AIR CHAMBER HAVING AN AIRTIGHT SEAL AROUND THE PERIPHERY THEREOF, A PLURALITY OF HORIZONTALLY DISPOSED TRANSVERSE WEBS PARALLEL TO EACH OTHER EXTENDING BETWEEN SAID SAIL SEGMENTS AND SECURED THERETO, SAID WEBS DIVIDING SAID AIR CHAMBER INTO SEGMENTED CHAMBERS, AND MEANS FORMING A GAS VALVE SECURED TO SAID SAIL AND COMMUNICATIING WITH SAID AIR CHAMBER WHEREBY SAID SAIL MAY BE INFLATED TO FORM AN AERODYNAMIC CROSS-SECTION THROUGHOUT SAID SAIL, SAID WEBS MAINTAINING SAID CROSS SECTION IN BOTH LIGHT AND HEAVY WINDS.