Patent Publication Number: US-2013247807-A1

Title: Anti-Heeling Apparatus for Sailboats

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application 61/614,875 filed on Mar. 23, 2012. 
    
    
     OBJECTIVE 
     The apparatus provides a safe and stable means of increasing the sail area of a single or double-handed dinghy class sailboat by using an anti-heeling apparatus which is simple, effective and inexpensive. Meeting this objective will enhance the enjoyment of sailing games such as sailball or sailing frisbee and will result in faster and more exciting racing boats for young and old alike. 
     TECHNICAL FIELD 
     Small monohull sailing vessels and specifically dinghy class vessels and increasing the speed and stability of such vessels. 
     BACKGROUND 
     A sailboat cannot sail directly into the wind. The wind must come from one side of the boat or the other, or, in a special case, directly from behind. Since the wind usually hits the sail from the side, the boat heels to leeward. This causes some of the wind to spill over the top the sail thereby reducing the forward driving force of the sail. Also the sail area presented to the wind is less, reducing the force generated. In addition because the boat is tipped, the forward force generated by the sail is normally centered off to leeward and therefore often causes the boat&#39;s bow to try to turn into the wind. To counter this effect, the helmsman must pull on the tiller to adjust the rudder so the boat goes straight. This has a braking effect on the boat due to induced drag, additionally causing it go more slowly than if the mast were straight up. 
     In large monohulls, heeling is countered by using a heavy weight on the keel. The heavier the weight, the more upright the boat will be, but it will go more slowly because of the bigger keel, which increases the displacement and frictional drags of the hull. In monohulls with daggerboards or centerboards, the crew hikes out to windward to reduce heeling. However, as the wind speed increases, the crew reaches the limit on how far they can hike so the boat heels anyway. 
     In catamarans, the hulls are a large distance apart. This enables the crew to get farther out to windward to reduce heeling. Because the catamaran design produces greater anti-heeling force, it enables the use of taller masts and more sail area, which results in boats which go faster than monohulls. A tall mast also allows a smaller attack angle to the wind, similar to operation of long wings on gliders. In sailing, going at a smaller angle to the wind is called pointing up. When beating, boats which point higher will usually reach their destinations sooner. However, the catamaran design sometimes results in inconveniently wide boats. Also they are more difficult to tack. 
     An object is to provide an apparatus which facilitates anti-heeling so tall masts and large sail areas can be used, resulting in fast boats which can point high, thus performing comparably to catamarans. 
     SUMMARY 
     In one embodiment, a Sunfish® sailboat, shown in  FIG. 1 , is equipped with two hydrofoil holding assemblies near the daggerboard well, one on the starboard side and one on the port side. An outwardly curved hydrofoil can be placed in each assembly. Each can be inserted in two possible positions—to produce negative lift or to produce positive lift. As viewed from starboard, for negative lift the hydrofoil is rotated clockwise with respect to an upright position, and for positive lift it is rotated counterclockwise. The hydrofoil&#39;s holders align their hydrofoils substantially parallel to the leeway angle so they produce little or no leeway forces. For optimal operation, the hydrofoils are retained at the leeway angle. 
     When both hydrofoils are used for anti-heeling, the leeward one also lifts the hull toward the surface of the water, thereby reducing displacement and skin friction hull drags. The hydrofoils can be manually adjusted up and down to accommodate different wind and boat speeds and wind directions. 
     On the windward side of the boat, the hydrofoil is usually inserted for negative lift. On the leeward side the hydrofoil is usually set for positive lift. The hydrofoils provide forces which counter the heeling force of the wind on the sail. 
     If inwardly curved hydrofoils are used for both lift and leeway control such as on catamarans or trimarans, the flow of water around the hydrofoils which produces the hydrodynamic force to prevent sideslipping is interfered with by the flow which produces lift. Leeway control is provided by a daggerboard and lift by the hydrofoils. 
     When the boat comes about from starboard tack to port tack, the hydrofoil on the windward side of the boat, is partly withdrawn, rotated to the positive lift position and pushed back down, and the hydrofoil on the leeward side is changed from the positive to the negative position. This shifts the anti-heeling function from one side to the other. 
     The slots in the hydrofoil holders through which the hydrofoils pass are designed such that the slot the upper level of the holder allows the hydrofoil to be rotated without the hydrofoil being completely removed from the holder. This reduces the chances that the crew will accidentally drop the hydrofoil into the water. The slot in the lower level is designed so that the hydrofoil cannot accidentally transfer between the positive and negative lift positions. This functionality is enabled by having the center of rotation at the upper level, and the lower level is at a sufficient distance from the center of rotation so that the hydrofoil cannot shift from negative lift to positive or vice versa while it is immersed. 
     In other embodiments the hydrofoil holding assemblies automatically move the hydrofoils to an angle substantially parallel to the leeway angle as water flows across them. One such embodiment is shown in  FIG. 20   a . This embodiment uses “L” shaped hydrofoils. These foils can be manually pulled completely out of their hydrofoil assemblies only by tipping the boat and pulling them out from the bottom; however, the entire hydrofoil holding apparatus can be manually removed, just as pintles and gudgeons often used on rudder assemblies can be detached from each other to remove rudders. In this embodiment, since raising the hydrofoil does not change the lift generated, the attack angle of the hydrofoil is continuously adjustable to perform this function. 
     The hydrofoils can be manually adjusted up and down to engage or disengage them from the water. 
     On the windward side of the boat, the hydrofoil attack angle is usually positioned for negative lift. On the leeward side the attack angle is usually set for positive lift. The leeway angle is set by a daggerboard, keel or centerboard. 
     When the boat comes about from starboard tack to port tack, the hydrofoil on the windward side of the boat is rotated to the positive lift position, and the hydrofoil on the leeward side is changed from the positive to the negative position. 
     This shifts the anti-heeling function from one side to the other. Since the hydrofoil holding assemblies can rotate in the plane of the deck, the water flowing past them forces them to assume the proper leeway angle. 
     A bar connects the two hydrofoil holders so that they are both at the same angle. This is necessary because since the hydrofoils are canted outward, drag generated at their outward extremities would cause them to deviate from the proper leeway angle. Since the rotational forces are equal but opposite on the two hydrofoils, the bar forces the two hydrofoils to be at the same leeway angle. 
     On a run, the two hydrofoils should be set to have the same attack angle, either positive or negative, or they can be withdrawn. The leeway angle is substantially zero, and the daggerboard is usually fully withdrawn. If both hydrofoils are set for positive lift, the boat will rise up, reducing the form and skin friction drags of the hull, which will cause the boat to go faster. For greater boat stability, the attack angles can both be negative. 
     An additional advantage is that as the wind increases, thereby increasing heeling force, the boat will speed up, and the hydrofoils will exert greater anti-heeling force. A similar effect occurs in monohulls with heavy keels in which the anti-heeling effect of the keel increases as the boat heels more in increasing winds; however, in that case the boat suffers loss of speed due to increased heeling angle, whereas using the apparatus, the boat stays upright as long as the increased boat speed equals the increased wind speed. If the change in boat speed lags the increased wind speed, additional righting moment can be generated by lowering curved hydrofoils or increasing attack angle of “L” shaped ones. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of the anti-heeling apparatus for sailboats. 
         FIG. 2   a  is a top view of the embodiment of the apparatus of  FIG. 1 . 
         FIG. 2   b  is a rear view of the embodiment of the apparatus of  FIG. 1 . 
         FIG. 2   c  is a side view of the embodiment of the apparatus of  FIG. 1  viewed from the starboard side. 
         FIG. 3  is a perspective view of an embodiment of a starboard hydrofoil holder for use with the apparatus of  FIG. 1 . 
         FIG. 4  is a top view of the embodiment of the hydrofoil holder of  FIG. 3 . 
         FIG. 5  is a bottom view of the embodiment of a hydrofoil holder of  FIG. 3 . 
         FIG. 6  is a perspective view of an embodiment of a typical hydrofoil for use with the apparatus of  FIG. 1 . 
         FIG. 7   a  is a diagram showing apparent wind and leeway in relation to a sailboat on starboard tack when using the apparatus of  FIG. 1 . 
         FIG. 7   b  is a diagram showing typical starboard and port tack hydrofoil settings on upper and lower levels of the hydrofoil holder of  FIG. 3 . 
         FIG. 7   c  is a diagram showing typical pressures on inward curved hydrofoils when using the apparatus of  FIG. 1 . 
         FIG. 7   d  is a diagram showing typical pressures and flows on outward curved hydrofoils when using the apparatus of  FIG. 1 . 
         FIG. 7   e  is a diagram showing typical pressures and flows on outward curved hydrofoils set at the leeway angle when using the apparatus of  FIG. 1 . 
         FIG. 8  is a diagram showing typical forces and moments when using the apparatus of  FIG. 1 . 
         FIG. 9  is a diagram showing operation of the embodiment of the apparatus of  FIG. 1 . 
         FIG. 10  is a diagram showing operation of the embodiment of the apparatus of  FIG. 1  in very light wind. 
         FIG. 11  is a diagram showing operation of the embodiment of the apparatus of  FIG. 1  in light wind, when beating. 
         FIG. 12  is a diagram showing operation of the embodiment of the apparatus of  FIG. 1  in moderate wind. 
         FIG. 13  is a diagram showing operation of the embodiment of the apparatus of  FIG. 1  while intentionally heeled. 
         FIG. 14  is a diagram showing operation of the embodiment of the apparatus of  FIG. 1  in high winds. 
         FIG. 15  is a diagram showing operation of the embodiment of the apparatus of  FIG. 1  while running. 
         FIG. 16  is a diagram showing operation of the embodiment of the apparatus of  FIG. 1  while running heeled to windward. 
         FIG. 17  is a side view of the embodiment of the apparatus of  FIG. 1  on a sailboat with a standard sail. 
         FIG. 18  is a side view of the embodiment of the apparatus of  FIG. 1  on a sailboat with a larger than normal sail. 
         FIG. 19  is a side view of the embodiment of the apparatus of  FIG. 1  on a sailboat with a sail optimized for racing. 
         FIGS. 20   a, b  and  c  are perspective, front and side views of another embodiment of the anti-heeling apparatus for sailboats. 
         FIGS. 21   a, b  and  c  are perspective exploded views of the embodiment of the apparatus shown in  FIGS. 20   a, b  and  c.    
         FIGS. 22   a, b  and  c  are side views of the embodiment of the apparatus shown in  FIGS. 20   a, b  and  c  showing attack angle variations. 
         FIG. 23  is a top view of the embodiment of the apparatus shown in  FIGS. 20   a, b  and  c  showing adjustments to leeway angle. 
         FIG. 24  is a perspective view of the embodiment of the apparatus of  FIGS. 20   a, b  and  c  with curved hydrofoils. 
         FIG. 25  is a perspective view of the embodiment of the apparatus of  FIGS. 20   a, b  and  c  with inverted “T” shaped hydrofoils. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The Sunfish® is a single-handed sailboat approximately 14 feet long, manufactured by the Laser Performance Company located in Portsmouth, R.I. 
     Referring to  FIG. 1 , an embodiment of the apparatus is mounted on to the hull,  1 - 1 . The starboard and port parts  1 - 2  and  1 - 3  of the apparatus are each composed of a hydrofoil,  1 - 4 , and a hydrofoil holder,  1 - 5 . The upper area of the holder,  1 - 6 , is a plate made of fiberglass/resin composite or similar material which fits on the deck,  1 - 7 , of the boat and is held in place with adhesive or mechanical mounting mechanisms, such as bolts or clamps. Materials for constructing composite materials can be obtained Fibre Glast Developments Corporation in Brookville, Ohio. Alternatively, parts  1 - 2  and  1 - 3  can be integrally formed with hull  1 - 1 . 
       FIG. 2   a  shows the view from the top. The settings of the hydrofoils are those which would be used on a starboard tack in a high wind. The starboard hydrofoil,  2   a - 1 , is positioned in the holder,  2   a - 2 , so that it produces negative lift, while the port hydrofoil,  2   a - 3 , is set in its holder,  2   a - 4 , to generated positive lift. The hydrofoils are held at the leeway angle expected in normal up-wind operation, normally in the range of 1 to 5 degrees, depending on boat design and expected wind velocities. 
       FIG. 2   b  shows the view of the boat from the back. The hydrofoil holders,  2   b - 1 , have open ends so that water can pass through them from front to back as the boat moves forward. The center of curvature,  2   b - 2 , of the hydrofoil is at or near the deck level,  2   b - 3 . 
     In  FIG. 2   c , the starboard hydrofoil,  2   c - 1 , and its holder,  2   c - 2 , are shown from the starboard side of the boat. This figure shows more of the center part of the Sunfish® than  FIGS. 1 ,  2   a  and  2   b , but not the front and back of the boat. In this figure the hydrofoil is shown rotated by the holder clockwise around a pivot point,  2   c - 3 . Of course there is no hub at this position because that would prevent the hydrofoil from being manually lowered and raised in the holder. The starboard hydrofoil is set at the attack angle of α,  2   c - 4 . Since the attack angle is negative with respect to the water level, the hydrofoil generates negative lift. Attack angles for the invention generally range from 1 to 10 degrees. In the figure the attack angle is 6 degrees. 
     A typical holder is shown in  FIG. 3 . The hydrofoil is kept in place by slots,  3 - 4  &amp;  3 - 5 , in the upper level,  3 - 1 , of the holder and its lower level,  3 - 2 . The holder is attached to the deck of the boat by the flange,  3 - 3 . Alternatively, the holder can be formed integrally with the hull. 
     A view of the top level of a hydrofoil holder is shown in  FIG. 4 . There is a slot,  4 - 2 , in the holder,  4 - 1 , through which the hydrofoil is inserted. The slot is shaped so that the hydrofoil can be changed from the position for negative lift to positive and vice versa without withdrawing the hydrofoil out of holder. It must, however, be withdrawn above the bottom level to be shifted. 
     The hydrofoil is the black area,  4 - 3 , in  FIG. 4 , and is in the negative position so that it is at angle equal to the leeway angle, λ,  4 - 4 , for starboard operation. When shifted to positive lift operation on port tack, it is rotated by twice the leeway angle so that it still aimed in the direction of boat travel. For embodiments which do not incorporate automatic leeway adjustment, the leeway angle chosen for any particular embodiment of the invention is the one for wind direction most commonly expected. 
     The bottom level,  5 - 1 , of the hydrofoil holder is shown in  FIG. 5 . The black area is the position of the starboard hydrofoil,  5 - 2 , in the bottom level when in the negative lift position when the boat is on starboard tack. It takes into account the leeway angle and the fact that the bottom level is below the plane containing the pivot point of the hydrofoil, and thus there is an offset fore to aft experienced by the hydrofoil due to its curvature. The figure shows that when on starboard tack and in the negative lift condition, the hydrofoil,  5 - 2  cannot accidently shift into position reserved for positive lift,  5 - 3 . 
       FIG. 6  illustrates the form of a curved hydrofoil,  6 - 1 . The foil cross section is shaped much like an airplane wing with a blunt forward edge,  6 - 2  and sharp trailing edge,  6 - 3 . 
       FIGS. 7   a  and  7   b  describe the influence of leeway angle on the design of the apparatus. In  FIG. 7   a  the symbols used correspond to those conventionally used in the industry. 
     The apparent wind,  7   a - 1 , VA, propels the boat forward at a velocity,  7   a - 2 , VS. This produces a headwind,  7   a - 3 , VHD. The true wind velocity is VT,  7   a - 4 . When wind velocity is steady, the heeling component of the apparent wind must be balanced by a force produced by the daggerboard,  7   a - 5 , in the opposite direction of the heeling force so the boat will be in equilibrium. This force is generated by the daggerboard operating at the leeway angle, λ,  7   a - 6 . The leeway angle is the angle between the centerline of the boat,  7   a - 7  and the direction of travel,  7   a - 8 . For optimal operation, the hydrofoils,  7   a - 9 , must be substantially parallel to the leeway angle with respect to the centerline of the boat because otherwise when hydrofoils are curved outward, there is conflict between the flow of water which sets the leeway and the flow of water which produces lift. 
     The settings of the hydrofoils for starboard and port operation are shown in  FIG. 7   b . The upper two hydrofoil holder diagrams,  7   b - 1 , are for starboard tack operation. The lower ones,  7   b - 2 , are for port operation. Hydrofoils,  7   b - 3 , are in black. The centerline,  7   b - 5 , of the boat is the line with long dashes. The line with the arrow,  7   b - 4 , is the direction of travel of the boat. The directions of the wind are  7   b - 6  and  7   b - 7 . The horizontal arrows are the true wind vectors and the slanted ones are the apparent wind vectors. 
       FIGS. 7   c ,  7   d  and  7   e  illustrate the why outward curving hydrofoils need to be set substantially parallel to the leeway angle.  FIG. 7   c  shows a Sunfish® on starboard tack viewed from aft. The boat has been configured to operate much like a trimaran with the hydrofoils aiming in toward the center of the boat.  FIG. 7   d  shows the hydrofoils aiming out. In  FIGS. 7   c  and  7   d  the hydrofoils are set parallel to the fore-aft axis of the boat, and thus are not aligned to the leeway angle. These figures are adaptations of  FIG. 14  of Greg Ketterman&#39;s paper Design Modifications for a Model Sailboat, his thesis at California State Polytechnic University. The figures show forces and water pressures. Water pressures are identified by two letter symbols. The first letter indicates the amount of pressure, with “H” being high and “L” low. The second letter indicates the source of pressure. “1” is for leeway action and “h” for anti-heeling action. 
     In both figures the starboard foil generates negative lift and the port one positive lift. 
     In  FIG. 7   c  the wind,  7   c - 1 , causes the boat to more forward, i.e., into the page. Since the starboard foil is set at a negative attack angle with respect to forward motion of the boat, the water flowing over it from fore to aft produces a pressure differential, the negative lift force,  7   c - 4 . The pressure differential is the difference between the high pressure, Hh,  7   c - 2 , and low pressure, Lh,  7   c - 3 . The port foil is set at a positive attack angle and thus produces a positive lift force, Lh,  7   c - 5 . These negative and positive forces produce an anti-heeling moment,  7   c - 8 . 
     As the boat moves forward, the foils must assume a lateral attack angle, the leeway angle, relative the direction of boat motion, which produces pressure differentials,  7   c - 7  and  7   c - 9 , that produce a force,  7   c - 6 , to balance the force of the wind,  7   c - 1 . 
     Note that the on the starboard side the high and low pressures producing negative lift and leeway control are both on the same side of the foil, and a similar situation occurs on the port side. 
     However, examination of  FIG. 7   d , which shows outward aiming foils, reveals a completely different situation. Here high and low pressures, for instance  7   d - 2  and  7   d - 3 , occur on the same side of a foil. Thus instead of flowing properly over foil to generate pressures which produce lift and leeway control, water will flow between the low and high pressure areas on the same sides of the foils diminishing lift and leeway control, as illustrated by the dotted arrows,  7   d - 4  and  7   d - 5 . Ketterman confirmed this phenomenon experimentally. The wind,  7   d - 1 , produces a heeling force and the daggerboard generates a leeway force,  7   d - 6   
     Note that in  FIGS. 7   c  and  7   d  the port foil is immersed deeper than the port one which causes the boat to lift out of water, helping to simulate hydrofoil equipped trimaran performance. 
     As illustrated in  FIG. 7   e , the apparatus resolves problems associated with outward aiming foils by using a large and deep daggerboard,  7   e - 1 , which dominates setting the leeway angle and the foils,  7   e - 2  and  7   e - 3 , are aligned substantially parallel to the leeway angle so that they do not produce lateral pressures. The pressures, on each side of a foils, i.e., the daggerboard or either hydrofoils, do not interfere with pressures near other foils. 
     Generally the leeway angle does not vary substantially with apparent wind angle and varies little with wind velocity so for any particular sailboat a fixed leeway angle used for the hydrofoils, though not perfect, will perform fairly well. For more ideal performance an embodiment which incorporates automatic leeway angle adjustment, as described later, can be used. For the Sunfish® embodiment with a large sail, the leeway angle varies +−15% over apparent wind angles from 65 to 25 degrees. At apparent wind angles of less than 65 degrees, heeling is not as great a problem so the hydrofoils generally can be pulled up, which reduces their drag. 
     Referring to  FIG. 8 , when the wind is blowing from the starboard side of the boat, there is a force,  8 - 1 , exerted on the sail, which causes the boat to heel to port. This heeling moment is counteracted by the outward curving hydrofoils,  8 - 2  and  8 - 6 , which produces a negative lift and positive lifts respectively. The heeling force on the sail causes the boat to rotate counterclockwise on the axis of the boat, while the lifts causes it to rotate clockwise, as seen from aft. The hydrofoil,  8 - 2  is submerged just far enough to overcome the heeling force when its force,  8 - 3 , is added to the additional clockwise effect of the weight of the crew,  8 - 4 , which is hiking out, and the positive lift,  8 - 5 , of hydrofoil  8 - 6 . 
     The starboard negative lift,  8 - 3 , of the windward hydrofoil causes the boat to appear heavier than it is, which would result in slower speed due to increased displacement and skin friction drags. To overcome this effect the hydrofoil,  8 - 6 , is submerged into the water, and produces a lifting force,  8 - 5 . This force opposes the combined downward forces of the starboard hydrofoil,  8 - 3 , the weight of the crew,  8 - 4 , and the weight of the boat,  8 - 7 . The buoyancy of the hull,  8 - 8 , also opposes the downward forces. The hydrodynamic force,  8 - 9 , is generated by the daggerboard leeway angle and equals the heeling force,  8 - 1 . Leeway angle forces on the hydrofoils are minimal since the hydrofoils are set at the leeway angle. 
     The two hydrofoils are adjusted so the boat remains upright and floats high enough in the water for optimum speed while maintaining stability. 
     When the boat goes on port tack, the hydrofoils,  8 - 2  and  8 - 6 , are retracted, rotated and reinserted in their holders so their attack angles to the water are reversed. And, they are set for the port tack leeway angle. 
     The forward force generated by the sail depends on the speed of the wind and the attack angle of the sail, as does the heeling force. Each part of the boat generates drags, which oppose the forward force. The hull generates displacement and skin friction drag. Each part which produces aerodynamic or hydrodynamic lift produces fluid dynamic drag, displacement drag and skin friction drag. 
     The invention increases the forward driving force of the sail while increasing the sum of all drags by a smaller amount than the increase in driving force and improving the pointing capability. 
     For each combination of wind speed and angle, the settings of the hydrofoils, the sail and the daggerboard can be adjusted for optimum performance. Also in various embodiments the boat&#39;s mast height, sail area and sail shape can be designed for best performance.  FIG. 18  shows an embodiment in which the mast and sail have been redesigned, but the hull and rudder are standard for the Sunfish®.  FIG. 17  shows a Sunfish® with a standard sail plan and the apparatus.  FIG. 19  shows a Sunfish® with a sail optimized for racing. 
       FIGS. 9 through 16  illustrate how the hydrofoils might be set for operation in winds of various strength and direction. They also show how the crew would shift their weights to assist in heel compensation. The position of the crew is identified by the icon of a man. The actual size of the crew would be much larger than the icon. 
     In moderate to heavy winds, the settings of the hydrofoils are shown in  FIG. 9 . The starboard hydrofoil,  9 - 1  generates negative lift,  9 - 3 , which counters the heeling force on the sail,  9 - 4 . The port hydrofoil,  9 - 2 , generates positive lift,  9 - 5 , 
       FIG. 10  shows that both hydrofoils,  10 - 1  and  10 - 2 , are withdrawn in very light winds. In this situation the anti-heeling action of the hydrofoils is not needed to keep the boat upright. The figure shows that the crew,  10 - 3 , is sitting approximately in the center of the boat. 
     In light wind on a beat the crew hikes out on the windward side. The wind in  FIG. 11  is not strong enough to require much hydrofoil action for righting. 
     As the wind increases, the crew hikes out as far as possible, as shown in  FIG. 12 , and lowers the port lifting hydrofoil,  12 - 1 , which produces lift,  12 - 3 , to counter the heeling force,  12 - 2 , and decreases the effective weight of the boat. 
     In  FIG. 13  the boat is heeling at about 14 degrees to leeward. Often a heeling angle between 5 and 20 degrees is considered ideal. Allowing a small amount of heel does not reduce forward driving force much and increases the righting moment,  13 - 1 , of the crew,  13 - 3 , so the increased induced drag which would have been generated by lowering the foils does not slow the boat. In this mode care must be taken to avoid heeling so much that the windward hydrofoil,  13 - 2  emerges from the water.  FIG. 13  also illustrates that using a Sunfish® hull, a heeling boat enhances the onset of planning since the bottom and water level are approximately parallel. 
     If the wind continues to increase, it is ultimately necessary to lower the negative lift generating hydrofoil to keep the boat upright as shown in  FIG. 14 . In this situation the heeling force,  14 - 1  requires the combined righting forces of the hiking crew,  14 - 2 , the lifting port hydrofoil,  14 - 3 , and the negatively lifting starboard hydrofoil,  14 - 4 . 
     The hydrofoil settings in light to moderately heavy winds with the boat on a run are shown in  FIG. 15 . The figure shows the boom,  15 - 1  off to port. 
       FIG. 16  shows a boat on a run in which the hydrofoils have been lowered to improve stability and to assist in heeling to windward. Heeling to windward is used to place the center of force of the sail directly over the center line of the boat so there is little or no pressure on the helm, which reduces induced drag and improves speed. Since there is no leeway attack angle, operating a boat in this way requires slots in the holders which are parallel to the center line of the boat. 
     Normally best performance of the boat is achieved if the hydrofoils are submerged a little as necessary because the drag produced by the hydrofoil will oppose the driving force of the sail. However, the hydrofoils may be submerged more than optimum for speed considerations in situations where a crew may want to sacrifice speed for stability and safety. 
     An embodiment which enables the hydrofoils to automatically conform to the leeway angle at which the boat is operating is illustrated in  FIGS. 20   a, b  and  c.    
     In these drawing the dotted lines represent the boat. The apparatus straddles the hull of the boat as shown in  FIG. 20   b.    
     Referring to  FIG. 20   a , a starboard “L” shaped hydrofoil,  20   a - 1 , is contained in a hydrofoil holder apparatus,  20   a - 2 . Likewise a second hydrofoil,  20   a - 3 , is held by a port hydrofoil holder apparatus,  20   a - 4 . The hydrofoils can slide in the their holders, as shown by the arrow,  20   a - 5 , which allows their depths in the water to be adjusted. A hydrofoil holder apparatus is composed of two parts, the leeway adjustment assembly,  20   a - 6 , and the attack angle adjustment assembly,  20   a - 7 . The leeway adjustment assembly permits the apparatus to conform to the leeway angle. The attack angle adjustment assembly can rotate within the leeway adjustment assembly and contains slots,  20   a - 8  in which the hydrofoil can be adjusted up or down. Thus, as shown by the coordinate system,  20   a - 9 , the hydrofoil can be slid in the x-z plane, and as shown in  FIG. 1   a , the attack angle holder assembly can be rotated in the x-z plane (around the y axis,  20   a - 10  as described in relation to  FIG. 21 ), and the entire hydrofoil holder assembly can rotate in the x-y plane (around the z axis,  20   a - 11 ). 
     A hydrofoil holder apparatus rotates to conform to the leeway angle of the boat, just as a weathervane conforms to the direction of the wind. To avoid conflict between the hydrodynamic forces generated by the daggerboard and the hydrofoils, the hydrofoils should conform to the leeway angle. It is a primary object of this embodiment that the hydrofoils substantially assume the leeway angle by virtue of the water passing along them as the boat moves forward. Thus the invention utilizes a mechanism which is similar to that used to mount the rudder on a small sailboat. Just as the rudder will align with the flow of water if the tiller is unconstrained, the hydrofoil will align if the holder assembly is free to rotate in the x-y plane,  20   a - 11 . The mounting mechanism uses a gudgeon and pintle,  20   a - 12 , arrangement like those employed to hang shutters on a house or rudders on boat. In the invention the pintle must be constrained at both ends since the pressures produced by the hydrofoil can be either upward or downward. Also so that the entire hydrofoil holder apparatus can be detached from the boat when the boat is stored or beached, the pintle must be detachable from the gudgeon. A gudgeon/pintle arrangement with this property is used employed on the Sunfish® sailboat and other boats and the small boats and can be obtained from Annapolis Performance Sailing in Annapolis Md. 
     If each hydrofoil is allowed to freely rotate, since the tip,  20   a - 13 , of a hydrofoil experiences displacement and skin friction drags as water passes by it, the starboard hydrofoil will tend to rotate clockwise as viewed from above, causing it to deviate from the proper leeway angle. The port hydrofoil will rotate in the counterclockwise. If the two hydrofoil holder assemblies are connected by a rod,  20   a - 14 , and if both hydrofoils are immersed by equal amounts, the two rotating forces will cancel each other, and both hydrofoils will both assume the desired leeway angle. This rod should be detachable from the hydrofoil holder apparatuses, to facilitate storage. In  FIG. 20   a  the gudgeon,  20   a - 15 , is shown by dotted lines to indicate that it is mounted on the hull, not the hydrofoil holder apparatus. The pintle,  20   a - 16 , is detachable from the gudgeon so the hydrofoil, and its hydrofoil holder apparatus can be removed. This arrangement allows the boat to sail without the anti-heeling feature, which is sometimes desirable in light airs. 
     The apparatus can be further understood by examining  FIGS. 21   a ,  21   b , and  21   c , which show an exploded view of a starboard hydrofoil holder apparatus and its hydrofoil. 
       FIG. 21   a  shows the leeway adjustment assembly. The dotted lines indicate the position of the hull. The leeway angle adjustment assembly,  21   a - 1 , attaches to the hull via the mechanism,  20   a - 12 . Its gudgeon,  20   a - 15  is attached to the hydrofoil holder mounting surface,  20   b - 2 , which is an integral part of the hull. The mechanism allows an entire hydrofoil holder apparatus to rotate per the arrow,  21   a - 2 , in the x-y plane. Between the outer member,  21   a - 3 , and the inner member,  21   a - 4 , of the leeway adjustment assembly, there is a slot,  21   a - 5 , which contains the attack angle adjustment assembly,  21   b - 1 . On the leeway adjustment assembly there is a pin at the position,  21   a - 6  which goes from the inner member,  21   a - 4 , to the outer member,  21   a - 3 , and passes through the attack angle adjustment assembly and at position  21   b -S providing the pivot point for the attack angle adjustment. The pin does not extend to hydrofoil. 
     FIG.  21 - b  shows the attack angle adjustment assembly. The back wall,  21   b - 2 , fits inside the leeway adjustment assembly&#39;s slot,  21   a - 5 . The assembly rotates in the x-z plane,  21   b - 3 , as shown in the diagram of the coordinates,  21   a - 7 . This rotation sets the attack angle. 
     The assembly contains a top slot,  21   b - 4  and a bottom slot,  21   b - 6  into which the hydrofoil,  21   c - 1  fits. The cross-sectional profile of the hydrofoil is rectangular in the illustration, which would be acceptable in embodiments having very thin hydrofoils, but in other embodiments an NACA defined shape such as used in airplane wings is preferred as seen in  FIG. 6 . Various embodiments use detents, pins, clamps, springs, locking mechanisms or other devices to hold the hydrofoil at its attack angle. Similar means may be used to prevent the hydrofoil from slipping up or down from the desired depth of immersion. 
     The operation of the invention can be further understood by examining orthogonal views shown in  FIGS. 20   b  and  20   c.    
       FIG. 20   b  shows the invention as viewed from the front. The boat,  20   b - 1 , hydrofoil holder mounting surface,  20   b - 2 , and gudgeon,  20   a - 15 , are shown by the dotted lines. The pintle,  2   a - 16 , being part of the apparatus is in solid lines. Both the angle of attack and leeway angles are zero in this illustration. The hydrofoils,  20   a - 1 , are shown in the fully descended positions. 
       FIG. 20   c  is the embodiment as seen from the port side. 
       FIGS. 22   a ,  22   b , and  22   c  illustrate three possible attack angle, α, positions for a hydrofoil.  FIG. 22   a  shows the hydrofoil in the neutral position, i.e., with the attack angle at 0 degrees. The upper arrow,  22 - 1 , aiming left, is the direction the boat is traveling. The lower arrow,  22   a - 2 , is the direction of the water relative to the hydrofoil. In the  FIG. 22   b  the attack angle, α,  22   b - 3 , is −6°. As in an airplane wing, this denotes negative lift. In  FIG. 22   c , the attack is +6°, which is positive lift, i.e., the hydrofoil pulls the boat up out of the water. 
       FIG. 23  is a top view of a hull and illustrates that the hydrofoils,  23 - 1 , of the invention conform to the leeway angle, λ,  23 - 2 , of the boat. The figure assumes a leeway angle of 3°, which would be normal for a boat of this type. The arrow,  23 - 3 , is the direction of the wind. The hydrofoil holder apparatus,  23 - 4 , pivots on the shaft,  23 - 5 . A rod,  23 - 6 , connects starboard and port hydrofoil holding assemblies. This rod keeps the angles of the starboard and port hydrofoils the same. 
     Other features to facilitate use and manufacturing of the apparatus can be incorporated into the embodiments described above as would be apparent to a person of ordinary skill in the art. For example, the hydrofoils can be spring loaded so that the retract or rotate to the level of the hull when the boat is beached. In addition, the connector connecting the hydrofoil holders in the automatically adjusting embodiment can be a removable rod. Also, an additional hydrofoil can be placed on the rudder to provide enhanced operation when running. 
     A Sunfish® with a normal sail and the invention is shown in  FIG. 17 . The boat is shown on starboard tack. The dotted outline,  17 - 1 , of the hydrofoil is the position of the port hydrofoil. 
       FIG. 18  shows the invention mounted on a Sunfish® with a sail much larger than the normal Sunfish® sail. 
     In  FIG. 19  the Sunfish® is equipped with sail designed for improved performance beating up wind, which facilitates racing. 
     The invention can take be implemented in other ways and on different boats. In one embodiment the hydrofoil holders are installed on the hull of a boat. In another embodiment, the holders are integral with the hull. 
     In another embodiment the invention can be applied to single-handed dinghies such as the Laser, two-handed monohulls such as the Laser 2, or larger boats. 
     Still another embodiment could be applied to a catamaran, such as a Class A catamaran or Tornado. In this embodiment, the hulls of the catamaran could be brought closer together to make it easier for the crew to adjust the positions of the hydrofoils and to decrease the weight of the boat and improve its maneuverability. For catamarans, the daggerboards must be retained to provide leeway angle control. 
     In yet another embodiment, the starboard and port hydrofoil holders can use separate positive and negative hydrofoil holder slots on each side of the boat, and when coming about the hydrofoil is shifted from one to the other. 
     For varying wind conditions the holders can be designed for easy removal and replacement so holders set for different attack angles can be used. 
     The invention can be used on monohulls with keels. 
     Further embodiments which exhibit self-alignment to the leeway angle appear in  FIGS. 24 and 25 . The embodiment in  FIG. 24  uses curved hydrofoils, while the one In  FIG. 25  employs has hydrofoils in the shape of an inverted “T”. The embodiment in  FIG. 24  features hydrofoils which can be totally removed from their holders and whose lifts are adjustable by varying depth of immersion allowing fixed attack angles. The embodiment in  FIG. 25  narrows the beam of the boat; however, since the hydrofoils to not extend as far out as other embodiments, it exhibits reduced righting function. 
     The foregoing description of the preferred embodiments of the invention have been presented only for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention only be limited by the claims appended hereto.