US3747549A

US3747549A - High speed sailboat

Info

Publication number: US3747549A
Application number: US00261076A
Authority: US
Inventors: S Shutt
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-06-08
Filing date: 1972-06-08
Publication date: 1973-07-24
Anticipated expiration: 1990-07-24

Abstract

The present invention is an improved downward pulling hydrofoil for use with a sailboat by extending the foil from the windward side of the hull to provide a stabilizing moment equal and opposite to the sail heeling moment. The hydrofoil is provided with a second horizontal foil mounted behind the main holddown foil which second foil is controlled thru a mechanical linkage to keep the main holddown foil tracking in the water for varying wind and sea conditions.

Description

' United States Patent [191 Shutt [451 July 24,1973

[ HIGH SPEED SAILBOAT [76] Inventor: Sidney G. Shutt, 612 Briarwood Dr.,

Brea, Calif.

[22] Filed: June 8, 1972 [21] Appl. No.: 261,076

[52] U.S. Cl 144/39, 114/121, 114/66.5 H [51] Int. Cl B63b 35/00 [58] Field of Search 114/39, 66.5 H, 121-123,

[56] I References Cited FOREIGN PATENTS 0R APPLICATIONS 743,359 9/1966 Canada 114/123 Primary Examiner-Milton Buchller Assistant Examiner-D. C. Butler Att0meyEdward Dugas 7] ABSTRACT The present invention is an improved downward pulling hydrofoil for use with a sailboat by extending the foil from the windward side of the hull to provide a sta bilizing moment equal and opposite to the sail heeling moment. The hydrofoil is provided with a second horizontal foil mounted behind the main holddown foil which second foil is controlled thru a mechanical linkage to keep the main holddown foil tracking in the water for varying wind and sea conditions.

8 Claims, 5 Drawing Figures PATENTEUJULZMQH SHEET 2 [IF 2 HIGH SPEED SAILBOAT BACKGROUND OF THE INVENTION The present invention pertains to the field of high speed sailboats and more particularly to the field of sailboats using hydrofoil sections.-

All sailboats provide in their design and construction a means for producing a counter heeling moment to prevent the sail force from capsizing the craft. The conventional approach to achieve a counter heeling moment is to allow the separation between the crafts center of mass and center of buoyancy to continuously vary to provide an equal and opposite moment to the sail heeling moment. Several variations of positioning the center of mass of the boat with respect to the center of buoyancy have evolved over many years. The single hull craft, with weighted keel, represents the conventional concept of sailboat roll stability. Improvements have been made to gain a wider mass-buoyancy separation by increasing the keel weight, by the crew hiking out over the rail, and by using a trapeze to allow a crew member to hike out beyond the rail. The multihull crafts achieve greater counter heeling moments by using greater separation of the mass center and the buoyancy center, but the basic idea is the same. These crafts have evolved into catarmarans, out-riggers, trimarans, and proas. All of these can be made light, with small displacement hulls having low drag. These boats have a large counter heeling moment which allows the use of larger sails; therefore, very fast boats have been made of these types.

Two or more hulls have the disadvantage that they cost more and although their drag is low it would be even lower if only one hull having a low drag were used. Also, all of the designs presently on the market use a mass displaced from the center of buoyancy to achieve stability, this places a limit on the wind velocity the craft can be sailed without capsizing.

In a co-pending U.S. Pat. application, Ser. No. 179,068, filed Sept. 9, 1971, entitled HIGH SPEED SAILBOAT; there is disclosed a holddown fin which is supported from the windward side of a high speed sailboat with the foil being designed to run just below the waters surface to provide a counter force to the heeling moment. The foil disclosed in the co-pending application is satisfactory for a large variation in wind and sea conditions but it has been found that under certain wave conditions the holddown foil described in the copending application will tend to tear out of the water, thereby eliminating its effectiveness.

The present improved holddown foil is designed to eliminate this tearing out condition for all except the most extreme of conditions.

SUMMARY OF THE INVENTION The present invention is comprised of an improved holddown foil assembly for a sailboat. The foil assembly is supported from the windward side of the boat such that a main horizontal foil rides below the surface of the water pulling downward with a force that is proportional to the angle of incidence of the foil and the square of the speed at which the foil is moved thru the water. A second horizontal foil is pivotly affixed to a vertical rudder and is mechanically linked to a planing surface such that the position of the planing surface with respect to the position of the foil assembly above the water surface controls the angle of attack of the second horizontal foil so as to maintain the angle of incidence of the main horizontal foil at a constant depth below the water surface.

It is therefore an object of the present invention to provide an improved holddown foil for a sailboat.

It is another object of the present invention to provide a holddown foil having capability of maintaining itself a fixed distance below the water surface.

It is another object of the present invention to provide a hydrofoil with an automatic depth holding feature.

It is a further object of the present invention to provide a hydrofoil having a high frequency response for maintaining its depth below the water surface at a constant.

It is a further object of the present invention to provide a holddown fin for a high speed sailboat which fin has its angle of incidence changed in proportion to the upward force exerted on the fin and its distance below the water surface.

These and other objects of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein like characters indicate like parts, and which drawings form a part of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a prospective view of the improved holddown foil in place on a high speed sailboat;

FIG. 2 is a top view of the improved holddown foil;

FIG. 3 is a side view, partially sectioned, of the hold down foil of FIG. '1, in a neutral running position;

FIG. 4 is a side view, partially sectioned, of the holddown foil for an increasing angle of incidence in response to an upward translation; and

FIG. 5 is a side view, partially sectioned, of the holddown foil for a decreasing angle of incidence in response to a rotation.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the unimaran sailboat 10 uses a single slim hull 11 from which extends upwards a mast 13 for supporting a sail 12. A centerboard 16 extends from the bottom of the hull to minimize the leeward movement of the hull through the water 17. A hiking board 14 provides a seat for the helmsman and also allows the helmsman to add his weight to the counter heeling force. Attached to the hiking board 14 is a fin supporting assembly 15 which is also connected to the mast 13 by means ofa guy cable 18. A holddown fin 20 is gimbaled to the supporting assembly 15 and creates a downward force when the hull 11 moves through the I water 17. This downward force is transmitted to the hull through the cable 18 and the mast 13. The holddown fin 20 creates the variable force which counteracts the varying heeling force. Steering is accomplished with the aid of a rudder 19.

Referring to FIGS. 2 and 3, the foil 20 is gimbaled to the fin support assembly 15 by means of a shaft 23 and a sleeve 24 which is affixed to the support assembly 15 to allow the shaft 23 to rotate about the axis labeled B. The shaft 23 is an integral part of an L-shaped member 26. A vertical rudder 22 normally positioned well behind the pivot axis B is pivotly mounted to the L-shaped member 26 at the pivot point labeled A, by means of pins 43. As the rudder 22 moves through the water it is forced to track directly behind the shaft 23.

Connected to the bottom portion of rudder 22 is a forward projecting arm 27. Attached to the end of arm 27 is the main horizontal hydrofoil section 21. The crosssection of the foil is inverted to provide a downward lift, or force F, as the foil is moved thru the water. A planing surface 25 which is constructed to operate on the water surface is pivotly connected to the L- shaped member 26, at point D, by means of linkage 28, and

pins

29 and 30. A torsional spring 52 connects between the L-shaped member 26 and the linkage 28 to help gravity hold the planing surface 25 to the back side of waves. The planing surface 25 is normally positioned in front of the pivot axis B to sense the level of the water surface with respect to the holding sleeve 25. The end of linkage 28 opposite the end connected to the planing surface is connected by

linkages

31 and 32 to a spring 34 and shaft 33. The shaft 33 extends downward thru the center of rudder 22 to a lever arm 35. the lever arm 35 is connected to a horizontal stabilizing foil 24, which is pivotly mounted to the rudder 22 by a shaft 42.

Connected at approximately the mid-point on lever arm 35 is a cylinder 40, which in combination with a piston 41 forms a dash-pot. The piston 41 is connected by a rod 39 to a linkage 38. The linkage 38 is connected thru

linkages

37, 45 and 44 to the linkage 31. One end of linkage 44 is pivotly connected to the rudder 22 at 51. The dash-pot piston 41, under the influence of the linkages moves approximately 4 times as far as the shaft 33. This provides a mechanical amplification of about 8, of the dash-pot linkage, as compared to the spring linkage of shaft 33 in producing a change in the angle a for the stabilizer 24. In servomechanism theory the afore-described linkage produces a lead compensation to the feedback control system. The main horizontal foil 21 is shown inclined downward at an angle 0. When the foil 21 is moved forward at a velocity v in the water it creates a downward force F which counteracts the heeling force P pulling upwards on the gimbal sleeve 25. A streamlining shroud 50, shown in dotted lines, protects the linkages from mechanical damage.

In operation the planing surface 25 rides on the water surface, continuously sensing the displacement, y, between the holding gimbal 25 and the water surface. A close approximation of Ay is y -y which is the actual input to the linkage. The linkage connects the input Ay to the stabiilizing foil, to control the angle of incidence a of the stabilizing foil, so as to produce a variable force F2 which will rotate the rudder 22 and the horizontal foil 21 until the inverted foil angle of incidence 0, is at the correct angle to maintain foil force F,, equal and opposite to the pull force P. Operating on a smooth water surface, if the pull force, P, increases the device moves upwards since P is greater than F,. The planing surface remains on the water surface resulting in an increase of Ay which is transmitted through linkage 28 to linkage 31. Two parallel linkage paths connect to the stabilizing foil; to linkage 32, spring 34, shaft 33 to linkage 35, and also to

linkages

45, 37, 38, shaft 39, piston 41, cylinder 40 to linkage 35. Thru the displacement of spring 34 and shaft 33,

0. An increase in 0 results in an increase in F until F is equal to P.

Referring now to FIG. 4, if the water surface increases in height, as for example thru wave action, causing the planing surface to rise. The linkage to the stabilizing foil will decrease or resulting in a downward force F2 causing a decrease in 0. A decrease in 0 will reduce F1 resulting in P larger than Fl which will cause the entire assembly to move upward over the incoming wave. If the wave is decreasing in height the reverse will occur causing F1 to be larger than P resulting in the assembly moving downward. The assembly will therefore follow the water surface moving in the direction which tends to make F1 P for variations in pull force or wave inputs.

Referring to FIG. 5, the stabilizing foil also responds to body rotations with the linkage described above. If the rudder assembly 22 is rotated clockwise by a wave disturbance, the linkage changes to produce a downward force F2 which rotates the rudder 22 counterclockwise back to the correct 0. The same linkage, dash-pot and spring provide lead to rotation as well as 1 translation. The device is arranged so that the spring and piston 41 and cylinder 40, a change is made in the 6 angle of incidence of the stabilizing foil, so as to rotate the rudder in the direction M to thereby stably increase and dash-pot are nominally centered for all operating values of 0. Inverting the main foil 21 results in a stabilized lifting hydrofoil.

While there has been shown what is considered to be the preferred embodiment of the present invention, it will be manifest that many changes and modifications may be made therein without departing from the essential spirit of the invention. It is intended, therefore, in the annexed claims, to cover all such changes and modifications as fall within the true scope of the invention.

I claim:

1. A holddown fin assembly for attachment to a support assembly which support assembly normally projects from the windward side of a sailboat hull comprising in combination:

a. a vertical rudder;

b. means for mounting said vertical rudder to said support assembly with at least 2 of freedom such that said rudder normally tracks behind the support assembly as it is pulled thru the water;

c. a horizontal holddown fin;

d. means projecting forward from said rudder to support said horizontal fin below the water surface;

e. a planing surface coupled to said vertical rudder, for riding on the water surface and for providing an indication of the displacement of the support assembly with respect to the water surface;

a horizontal stabilizing foil pivotly affixed to said vertical rudder; and

g. means responsive to the indicated displacement of the planing surface for controlling the angle of incidence of the stabilizing foil so as to cause the horizontal holddown fin to change its angle of incidence in the water thereby maintaining the displacement between the support assembly and the planing surface.

2. The holddown fin assembly of claim 1 wherein said means responsive to the indicated displacement is comprised of:

a. amplifying linkage for sensing the indicated displacement and for increasing the indicated displacement;

b. a spring means connected between said amplifying linkage and said horizontal stabilizer for rotating said stabilizing foil about said pivot; and

c. a dash-pot connected between said amplifying linkage and said horizontal stabilizer for damping high frequency vibrations in said stabilizing foil.

3. A holddown fin assembly for attachment to a support assembly which support assembly normally projects from the windward side of a sailboat hull comprising in combination:

a. a vertical rudder pivotly affixed to said support assembly;

b. a horizontal holddown fin;

c. means projecting forward from said rudder to support said horizontal fin below the water surface;

(1. a planing surface mechanically linked to said rudder for determining the displacement between the support assembly and the water surface;

e. a horizontal stabilizing foil pivotly affixed to said vertical rudder; and

f. means for controlling the angle of said stabilizing foil in response to said determined displacement for maintaining said displacement at a constant value.

4. The holddown fin assembly according to claim 3 wherein said means for controlling the angle of said stabilizing foil is comprised of:

a. amplifying linkage connected between said planing surface and said stabilizing foil, for pivoting said horizontal stabilizing foil in response to the displacement of said planing surface; and

b. damping means connected between said amplifying linkage and said horizontal planing surface for eliminating high frequency vibrations in said horizontal stabilizing foil.

5. The means for controlling the angle of said stabilizing foil according to calim 4 and further comprising:

a. a spring inserted between said amplifying linkage and said horizontal stabilizer for providing a time lag between the displacement sensed by said planing surface and the resultant position of the horizontal stabilizing foil.

6. A holddown fin particularly adapted to be mounted from the windward side of a sailboat to counteract heeling moments, said holddown fin comprising in combination:

a. a horizontal holddown foil;

b. means for pivotly mounting said holddown foil to said sailboat such that said foil normally rides below the water surface;

c. a planing means for sensing the displacement between the water surface and a reference level and for providing a signal proportional to the sensed displacment;

d. a horizontal stabilizing foil positioned behind said horizontal holddown foil; and

e. servomechanism means for receiving said sensed displacement signal and for controlling the incidence angle of said horizontal stabilizing foil so as to cause said horizontal holddown foil to change its incidence angle to be driven deeper or shallower in the water to thereby maintain said sensed displacement signal at a preselected level.

7. The holdown fin according to claim 6 wherein said means for pivotly mounting said holddown foil to said sailboat is comprised of:

a. a vertical rudder gimbaled to said sailboat for two degrees of angular freedom;

b. a forward projecting member affixed to said vertical rudder for supporting said horizontal holddown foil substantially below the gimballed point of said vertical rudder, such that the forces acting on said horizontal holddown foil are transmitted directly thru the gimbal point.

8. The holddown fin according to claim 6 wherein said servomechanism means is comprised of:

a. a mechanical linkage connected between said planing means and said horizontal stabilizing foil for converting the displacement of said planing surface into a corresponding change in the incidence angle of the horizontal stabilizing foil.

* l= lk

Claims

1. A holddown fin assembly for attachment to a support assembly which support assembly normally projects from the windward side of a sailboat hull comprising in combination: a. a vertical rudder; b. means for mounting said vertical rudder to said support assembly with at least 2* of freedom such that said rudder normally tracks behind the support assembly as it is pulled thru the water; c. a horizontal holddown fin; d. means projecting forward from said rudder to support said horizontal fin below the water surface; e. a planing surface coupled to said vertical rudder, for riding on the water surface and for providing an indication of the displacement of the support assembly with respect to the water surface; f. a horizontal stabilizing foil pivotly affixed to said vertical rudder; and g. means responsive to the indicated displacement of the planing surface for controlling the angle of incidence of the stabilizing foil so as to cause the horizontal holddown fin to change its angle of incidence in the water thereby maintaining the displacement between the support assembly and the planing surface.

2. The holddown fin assembly of claim 1 wherein said means responsive to the indicated displacement is comprised of: a. amplifying linkage for sensing the indicated displacement and for increasing the indicated displacement; b. a spring means connected between said amplifying linkage and said horizontal stabilizer for rotating said stabilizing foil about said pivot; and c. a dash-pot connected between said amplifying linkage and said horizontal stabilizer for damping high frequency vibrations in said stabilizing foil.

3. A holddown fin assembly for attachment to a support assembly which support assembly normally projects from the windward side of a sailboat hull comprising in combination: a. a vertical rudder pivotly affixed to said support assembly; b. a horizontal holddown fin; c. means projecting forward from said rudder to support said horizontal fin below the water surface; d. a planing surface mechanically linked to said rudder for determining the displacement between the support assembly and the water surface; e. a horizontal stabilizing foil pivotly affixed to said vertical rudder; and f. means for controlling the angle of said stabilizing foil in response to said determined displacement for maintaining said displacement at a constant value.

4. The holddown fin assembly according to claim 3 wherein said means for controlling the angle of said stabilizing foil is comprised of: a. amplifying linkage connected between said planing surface and said stabilizing foil, for pivoting said horizontal stabilizing foil in response to the displacement of said planing surface; and b. damping means connected between said amplifying linkage and said horizontal planing surface for eliminating high frequency vibrations in said horizontal stabilizing foil.

5. The means for controlling the angle of said stabilizing foil according to calim 4 and further comprising: a. a spring inserted between said amplifying linkage and said horizontal stabilizer for providing a time lag between the displacement sensed by Said planing surface and the resultant position of the horizontal stabilizing foil.

6. A holddown fin particularly adapted to be mounted from the windward side of a sailboat to counteract heeling moments, said holddown fin comprising in combination: a. a horizontal holddown foil; b. means for pivotly mounting said holddown foil to said sailboat such that said foil normally rides below the water surface; c. a planing means for sensing the displacement between the water surface and a reference level and for providing a signal proportional to the sensed displacment; d. a horizontal stabilizing foil positioned behind said horizontal holddown foil; and e. servomechanism means for receiving said sensed displacement signal and for controlling the incidence angle of said horizontal stabilizing foil so as to cause said horizontal holddown foil to change its incidence angle to be driven deeper or shallower in the water to thereby maintain said sensed displacement signal at a preselected level.

7. The holdown fin according to claim 6 wherein said means for pivotly mounting said holddown foil to said sailboat is comprised of: a. a vertical rudder gimbaled to said sailboat for two degrees of angular freedom; b. a forward projecting member affixed to said vertical rudder for supporting said horizontal holddown foil substantially below the gimballed point of said vertical rudder, such that the forces acting on said horizontal holddown foil are transmitted directly thru the gimbal point.

8. The holddown fin according to claim 6 wherein said servomechanism means is comprised of: a. a mechanical linkage connected between said planing means and said horizontal stabilizing foil for converting the displacement of said planing surface into a corresponding change in the incidence angle of the horizontal stabilizing foil.