US20110030600A1

US20110030600A1 - Sailboard with slotted winglets

Info

Publication number: US20110030600A1
Application number: US12/880,360
Authority: US
Inventors: John H. Keller
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-05-31
Filing date: 2010-09-13
Publication date: 2011-02-10

Abstract

A winglet in a planing hull for sailboards with longitudinal length at least three times its transverse width, or a top slot that covers at least half the winglet area, and a forward slot and or a top slot, which allows dynamic lift from both the top and bottom surface of the winglet when the board is traveling at a transition speed between displacement mode and planing mode, but at high planing speed it does not normally have lift from the top surface of the winglet. This winglet may have a camber/slope step on the planing surface. In addition the transverse section of the nose of the hull can have the shape of an upside down wing.

Description

FIELD OF THE INVENTION

The present invention generally relates to a winglet with a forward and/or a top slot in a planing hull for sailboards/windsurfers for improving the transition from displacement operation to planing operation and the transition to higher planing speed.

BACKGROUND OF THE INVENTION

U.S. patent application Ser. No. 10/157,875 filed May 31, 2002, provisional application 61/166,569, filed Apr. 3, 2009 and PCT/US2009/051138 filed Sep. 16, 2009, are hereby fully incorporated by reference.
U.S. patent application Ser. No. 10/157,875 teaches the use of winglets on the outer surfaces of a sailboard for increasing the lift to drag of the sailboard when transitioning from a displacement mode to a planing mode. These winglets have been found to be quite effective in reducing the amount of wind needed to cause the sailboard to plane. However, the front nose of these winglets can be above the flat undisturbed water surface thus preventing or reducing the water flow and lift from the top surface of the winglet.
When the sailboard is designed so that the water will easily go above the front of the winglet, the board needs to be slightly concave and slightly longer in the nose. One would also like the lift from the winglet to be nearer the back of the board. Also the flow over the top of the front of the winglet may stop at a slower board speed than desired, while the camber of the winglet is limited by the thickness to length ratio. In addition one would like the winglet to be a larger percentage of the back of the board to further reduce the wave and turbulent drag at transition speeds.
U.S. patent application Ser. No. 10/157,875 also teaches the use of a wing grid which is a plurality of winglets with slots between the winglets. However, each winglet has drag from the separation of the water at its nose, thus if the number of winglets is too large there will be increased drag from this wing grid.
On wings of many airplanes there are “Fowler type flaps” which, when they are moved down and back from the wing, have slots in front of the flap or winglet. At some positions of these flaps, the top part of the wing in front of the slot partially covers the nose or beginning of the flap. In this position there is a Coanda flow of energized fluid that flows through the slot and over the flap thus creating a vacuum lift on top of the flap.
PCT/US2009/057138 teaches a step design which at slower planing speed the water contacts the surface close to and behind the step, producing lift, while at faster planing speed it does not contact this surface, thus reducing drag.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a to increase the dynamic lift of a winglet behind a slot in the side of a sailboard hull.
It is another object to have an efficient winglet on a shorter or smaller sailboard.
It is a further object to move the lift further back closer to, or behind, the center of gravity of the board and sailboarder.
It is yet another object of the present invention to have the nose of the winglet covered such that water from the front of the winglet does not spray up onto the sailboarder.
Another further object of the invention is to have the top of the winglet clear of water above about 15 mph.
It is still another object of this invention to reduce the variation of the optimum position of the center of gravity of the sailboard and sailboarder.
Another further object of the invention is to prevent weeds from catching in the slot.
To achieve the foregoing and other objects of the invention, winglets with a forward slot in accordance with the invention start at a location on the order of 130 cm, generally in the range of 90 to 160 cm, from the back of the sailboard or less. That is where, when the sailboard is transitioning from displacement mode to a planing mode, the pressure under the board is near the maximum in the slot in front of the winglet. This slot in front of the winglet may be roughly 30 cm long (range of 15 to 80 cm). The vertical distance of the slot between the winglet and the bottom of the surface in front of the winglet can be roughly one-half the thickness of the winglet. This front surface can cover the nose of the winglet to the point were the winglet has a thickness of about 50% of the maximum. Thus any spray off of the nose of the winglet is reduced, while the slot allows energized water from under the front of the board to produce a Coanda effect (lift) over the top surface of the winglet.
The winglets according, to this invention may have a slot on the top of the winglet, particularly near the end of the winglet such that the turbulent and wave rag at the back of the board is decreased. That is, the top, slot allows the winglet be extended under the top surface of the board. This also allows the top surface of the sailboard, which is above top slot, to have a foot strap and a top surface, for sailing and jibing the sailboard.
If desired, the transverse end of the forward slot, i.e. the outside, can be covered or partially covered so that water and waves, particularly on the windward side do not enter the slot and strike the nose of the winglet when sailing at high planing speeds, such as over 15 mph. When partially covered, an opening between the cover or partial cover and the winglet will allow any weeds or grass going into the slot to escape.
While the slot can be perpendicular, angled back, angled forward or curved, it is preferred that it be swept back. This will both allow it to shed weeds and direct the water on top of the winglets away from the front foot straps.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which:

FIG. 1 shows a longitudinal slightly curved cross section of the preferred embodiment of the region of the slots and winglet,

FIG. 2A the top plane-form and side view of a sailboard winglet with a front slot and top slot,

FIG. 2B shows the bottom view of the sailboard,

FIG. 2C shows and exemplary cross-section of a preferred shape of the nose of the sailboard,

FIG. 3 shows Multiple Slotted winglets with a camber/slope step,

FIG. 4 shows the Cover over the front slot extending over the top of the winglet,

FIG. 5 shows a detail of the step in FIG. 3, and

FIG. 6 shows a winglet with a top slot or channel.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, a cross section of a side part of a sailboard hull 1 is shown with a preferred embodiment of a winglet 2 with a front slot 3 and the top slot 6, hereafter called a slotted winglet 1. This winglet 2 is similar to super sonic winglets on jet planes such as on the SR 71. It has a length, in the long direction of the sailboard hull, at least 2 or 3 times its transverse width. Thus it is distinguished from a fin or skeg at the side of the hull as in some racing catamaran sailboats. The front slot 3 is behind a front planing or displacement section 4, which can be part of the nose or front of the sailboard. When the sailboard is starting to plane, the underside of the slot is located in the region of high water pressure on the hull near the slot 3. For a nearly flat planing surface, this maximum pressure occurs at about 1/10 the wetted surface length back from the start of the wetted surface length. Thus water is forced through the slot and over the top surface of the winglet 2. This causes vacuum lift on the winglet. The cross section shown in FIG. 1 is slightly curved to approximate more closely the path of the water at a transition speed.
When the board is planing at a higher speed either the water off of the front section 4 goes below the nose of the winglet or, on average, the slot and the nose of the winglet are above the water and thus only the bottom surface of the winglet is in the water. The slot 3 in front of the winglet allows the winglet to start further back on the sailboard and, if desired, the sailboard can be shorter. This in turn makes the front of the sailboard lighter and the sailboarder or sailor is able to sail at an optimum planing attack angle of about 3 to 5 degrees.
The bottom end 4′ of section 4 can have a smooth upward curvature such that the water will remain in contact with both sides of the winglet 2 at transition speed, but at faster planing speeds the water flow from waves will Separate from said curvature and go below the nose of the winglet 2. The surface behind the said upward curve 4′ on section 4 can be straight or preferably have a negative second derivative (height with respect to longitudinal distance) curvature.
If desired, more than one set of slotted winglets 1 can be used on the board as shown, for example, in FIG. 3. Winglets with a forward slot in accordance with the invention start at a location on the order of 130 cm, generally in the range of 90 to 160 cm, from the back of the sailboard. That is where, when the sailboard is transitioning from displacement mode to a planing mode, the pressure under the board is near the maximum. This slot in front of the winglet may be roughly 30 cm long or a range of 15 to 80 cm at the bottom in the longitudinal direction of the board. The vertical distance of the end of said slot between the winglet and the surface that makes the top of slot 3 can be roughly one half the thickness of the winglet. This surface formed by the lower surface of section 4 can cover the nose of the winglet to the point where the winglet has a thickness of about 50% of the maximum thickness of the winglet. Thus any spray off of the nose of the winglet is reduced, while the slot allows energized water from under the front of the board to produce a Coanda effect over the top surface of the winglet.
Referring now to FIGS. 2A and 2B, FIG. 2A shows the top and side view of the sailboard and the location of the cross section shown in FIG. 1. If desired, the transverse end of the slot can be covered or partially covered by a cover 12 so that water and waves, particularly on the windward side, do not enter the slot and strike the nose of the winglet when sailing at high planing speeds, such as over 15 mph. When partially covered by cover 12, an opening between partial cover 12 and the winglet will allow any weeds going into the slot to escape.
FIG. 2B shows the bottom view.
While the slot and winglet can be perpendicular, angled back, angled forward or curved, it is preferred that it be swept back, preferably at 2.0° to 50°. This amount of sweep-back can both allow it to shed weeds and direct the water on top of the winglets away from the front foot straps and the board sailor.
A top slot 6 can be cut into the back of the hull of the sailboard. This allows the width of the back of the winglet to be a larger percentage of the back width of the board thus a larger percent of the water, when the board is beginning to plane, can flow smoothly off the back of the winglet. Thus the drag of the board at transition speeds is further reduced and the lift is increased. This top slot 6 also allows for a wider spacing of the foot straps and a wider top sailboard surface 8, which can be easily used by the sailor for sailing and jibing the sailboard. The top slot 6, if desired, can have a plurality of support vanes 6′ in them. These vanes should be curved to match the typical water flow through slot 6 at transition speed.
FIG. 3 shows multiple slotted winglets. The main winglet 2 is shown in the back. It may have a camber 16, step 21 and slope 18, i.e. a camber/slope step, on the planing surface. In front of the main winglet is an auxiliary winglet 5. Tests of wings with auxiliary airfoils are given by Fred E. Weick and Robert Sanders NACA Report 472 pp 567-584. This arrangement of winglets allows for a larger total slot height in front of the main winglet. Thus it allows more water to flow over the top of the winglet at transition speed and a correspondingly larger lift coefficient. Both the main winglet 2 and particularly the auxiliary winglet 5 can start at a height above that of the center rocker line of the sailboard. This arrangement also allows the camber 16 of the camber/slope step to be the whole length from the start of the main winglet to the step. The camber 16 depth can also be large, on the order of 1.5 cm (range 0.5 to 4 cm) thus increasing the planing lift at high planing speed as well as total lift of the winglet at transition speed. Part of this camber 16 depth can start above the centerline depth of the hull and part can be below the centerline depth near the step. The depth of the step 21 is preferably about 2 to 3 mm, as shown at 7 in FIGS. 3 and 4 and in the enlarged detail shown in FIG. 5.
In front of the auxiliary winglet 5 is again the planing or displacement section 4, which may or may not be in the water depending on the hull speed. FIG. 3 shows the hull at a typical planing attack angle of 3.5 degrees.
If desired, the auxiliary winglet 5 can be changed from a winglet and made part of section 4. In such a case, a long slot is produced that has a long cover. It is believed, however that the auxiliary winglet configuration is preferable over the long single slot from the standpoint of the lift to drag ratio. However, the single slot may be stronger and easier to fabricate.
Referring now to FIG. 4, the length of the slot 10 over and on top of the winglet can be extended to the back of the board thus it would include slot 6. This configuration allow the foot straps on the top surface 8 of the sailboard to be placed further to the outside as in a Formula sailboard or other sailboards in which it is desired to use a longer fin.
As shown in FIGS. 2A-4, the back planing surface of the winglet and bottom, surface 23, which is outside of the of the planing region 24 near and in front of the fin 9 contain slope 18. This slope can have a positive rocker on the order of a 30 meter (3000 cm) radius or a positive second derivative of 3×10⁻⁴cm⁻¹(range of 0 to −8×10⁻⁴cm⁻¹) or it can have a negative rocker. In addition, camber 16 and surface 23 with possible camber 25 produce lift at transition speed but dewet the surface 23 behind the steps 21 at faster planing speeds. The step 21 is shown in the bottom view of the sailboard of FIG. 2B. The camber 16 depth can be small, about 2-6 mm and consists of a downward curved section of about 10 cm length with a maximum angle on the order of 5 degrees. The camber can also be larger, on the order 1.5 cm (range 0.4-4 cm) as shown in FIG. 3. This camber is followed by a smooth upward curve with a radius on the order of 1 cm or range of 0.3 to 4 cm. These camber/slope steps allows the sailboard to be sailed at an optimum attack angle (3° to 5°) from transitional speeds to speeds greater than 20 mph.
As disclosed in the above-incorporated PCT/US2009/057138 there should be an increased attack angle or cusp at least on the fin side of the intersection of the planing surface region 24 and the region 23. Surface region 24 is shown with dotted lines in FIG. 2A, side view, so that it does not obscure rocket surface region 23. The board's bottom can be essentially flat near the fin, except for the increased attack angle or cusp at the intersection between regions 23 and 24, or it can have multiple concave or slight “Vee” shape in region 24 with variation of about 5 mm or less, or region 23 can be deeper than region 24, in which case the increased attack angle can be on the outer edge of section 24. Since the steps 21 are small, an exemplary step is shown in more detail in FIG. 5. The camber, step slope and cusp are easy to fabricate into the bottom planing surface of the board. They can be constructed from an additional piece of Divinycell under the fiberglass or carbon skin of the sailboard. FIG. 5 shows the region of the camber 16, rocker/slope 18 in more detail.
If one wishes a particular board to plane at lower speed, another camber 25 can be added at the end of the region 23 and slope 18. This camber should have a cup angle of 5 degree or less. In FIGS. 4 and 5, the hull is shown with at a planing attack angle of zero.
Referring now to the front of the hull in FIGS. 1-4, the nose 30 of the hull of the sailboard should be shaped like an upside down or inverted wing, asymmetric from bottom to top with more transverse curvature on the bottom than on the top as shown in FIG. 2C. This inverted wing shape can be symmetric from the left side to the right side. In this way the area shown as 31 can have less positive (e.g. convex) curvature or, preferably, a negative (e.g. concave) curvature as also shown it the exemplary cross-section of FIG. 2C, while the bottom area 32 of the nose 30 will have greater curvature. The purpose of this nose shape is to reduce or counteract the lift of the true wind on the nose of the board, which can cause the sailboard to be unstable and the nose to fly up into the air. This effect is often referred to as the board “tail-walking”. Thus, by employing this nose shape of the sailboard, one can use a larger sailboard and take advantage of the greater lift to drag of this invention.
FIG. 6 shows a winglet 33 in the shape of a hydrofoil. This winglet may have any desired aspect ratio of length to width and may be provided as a set of winglets. This set, left and right, of winglets have top slots 10 (channels 10) on top of winglets 33, which covers at least half of the winglets 33. It is preferred that these winglets be swept back both to shed weeds and for better directional stability. The bottom of the end of winglet 33, at least on the outside, is below that of the rest of the hull. In addition the top surface of the top slot should roughly follow the shape of the top of the winglets so there is not a pressure increase in the channel due to the width in the channel or top slot changing. At high planing speed only winglet 33 and the back section of the board, preferably with camber/slope steps as discussed above are in the water. Thus these slotted winglets aid in the stability of the planing attack angle at high planing speed.
Those skilled in the art will appreciate that two or more applications of winglets with a front slot or top slot can be used in a row in accordance with the invention and that slotted winglets 2 can be used with known hydrofoils nearer the front or middle of the hull to better maintain an optimum planing angle at even faster planing speeds.
While the invention has been described in terms of a single preferred embodiment and variations thereon, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims.

Claims

1. A sailboard hull comprising

at least one set of winglets, whose length is at least 3 times the winglet width, with a forward slot in the front of said winglet and/or a slot on top of said winglet, and

a bottom surface in front of said forward slot, which acts as a planing surface and wherein said forward or top slots allows the winglet to have lift both on the top and bottom of said winglet when the board is transitioning from displacement mode to planing mode.

2. The sailboard hull as recited in claim 1, wherein said forward slot is mostly covered on the top of the said slot to reduce the spray behind the said slot, from the nose of the winglet.

3. The sailboard hull as recited in claim 1, wherein said winglets are configured as hydrofoils near the front or middle of the hull.

4. The sailboard hull as recited in claim 2, wherein said forward slot is near the maximum pressure location on the bottom edge of the said hull or roughly 1/10^thof the wetted length back from the front of the wetted length when the sailboard is in transition from a displacement mode to a planing mode.

5. The sailboard hull as recited in claim 2, wherein said slot is partially covered on the outer edge.

6. The sailboard hull as recited in claim 2, wherein the front of said winglet is swept back between 25° and 45°.

7. The sailboard hull as recited in claim 1 wherein the bottom surface of said winglet has at least one camber/slope step.

8. The sailboard hull as recited in claim 7 wherein a nose of said hull is shaped like an upside down wing.

9. The sailboard hull as recited in claim 7 wherein said sailboard hull further includes a fin and a surface in front of said step is below that of the center of the board in the region of the said step, such that the region near said fin is roughly, flat within 5 mm.

10. The sailboard hull as recited in claim 7 wherein said winglet is a main winglet and has an auxiliary winglet in front of said main winglet.

11. The sailboard hull as recited in claim 10 wherein a front of a bottom surface of said main and auxiliary winglets is above the bottom of said sailboard hull.

12. The sailboard hull as recited in claim 7 wherein the said step has a camber depth in the range of 0.5 to 4 cm.

13. A sailboard hull comprising at least one set of winglets in the shape of a hydrofoil, with a top slot, which covers at least half of the said winglets.

14. The sailboard hull as recited in claim 13, which further includes a camber/slope step.

15. A sailboard hull having a winglet and surface forming a front slot above said winglet wherein, in a displacement or transitional mode, said surface causes water flow over a top surface of said winglet to produce Coanda lift and wherein, in a planing mode, a bottom of said winglet provides a planing surface.

16. The sailboard hull as recited in claim 15 further comprising a top slot.

17. The sailboard hull as recited in claim 16 wherein said top slot includes a support vane.

18. The sailboard hull as recited in claim 15 wherein said front slot is partially covered.

19. The sailboard hull as recited in claim 15 wherein said surface is located near the maximum pressure location on the bottom edge of said hull or roughly 1/10^thof the wetted length back from the front of the wetted length when the sailboard is in transition from a displacement mode to a planing mode.

20. The sailboard hull as recited in claim 15 wherein said surface is provided on an auxiliary winglet.

21. A sailboard hull having a winglet configured such that, in a displacement or transitional mode, said surface causes water flow over a top surface of said winglet to produce lift and wherein, in a planing mode, a bottom surface of said winglet provides a planing surface.

22. A sailboard hull as recited in claim 21, wherein said winglet extends below a bottom surface region of said sailboard hull adjacent to or in front of a fin.

23. A sailboard hull as recited in claim 21, wherein a bottom surface region of said sailboard hull adjacent to or in front of a fin has a concave or “Vee” shape.

24. A sailboard hull as recited in claim 21, further including a further winglet configured such that, in displacement or transitional mode, said surface causes water flow over a top surface of said winglet to produce lift and wherein, in a planing mode, a bottom surface of said winglet provides a planing; surface.

25. A sailboard hull as recited in claim 24, wherein winglet and said further winglet are located to form a slot between them.