The present invention is directed generally to the field of water craft.
Generally, the force of the wind on a sail can be resolved into a force that drives a boat forward and, a force that causes the boat to slide sideways and heel (tip to the side). In a typical sailboat, the boat is restrained from sliding sideways by one or more foil(s) in the water (e.g., keel(s), centerboard(s), rudder(s)), and the tipping moment is counteracted by such things as a heavy weight on the bottom of a keel, the weight of the crew leaning out to windward, or for example, in the case of a catamaran, the weight of the windward hull and the buoyancy of the leeward hull.
The speed of a sailboat typically is constrained by drag, particularly drag due to dynamic displacement of water by (a) the hull, steering foils (e.g., a rudder) and tracking foils (e.g., keel, centerboard), and (b) skin friction on the hull and foils. Displacement drag results from the energy required to move water out of the way of the moving hull. Friction drag results from the water sticking to the hull as a result of molecular attraction. The loss of energy through drag decreases the energy available to push the boat forward. Generally, the amount of force needed to overcome these drags increases as the square of the speed, which tends to put a practical limit on possible speed.
To increase forward driving force, techniques such as increasing sail area are needed, but increasing the sail area can result in a variety of problems such as decreased control and increased tipping moment, which causes the boat to heel over too far. Also, as the speed of a sailboat increases, it becomes more difficult to balance the large driving forces and large drags so constant adjustment of sails and boat direction is required.
Recent advances in sailboat design have resulted in the development and construction of sailboats which can travel at much higher speeds than sailboats many years ago. For example, it is now common for high-speed sailboats to go faster than the wind, in some cases twice or as much as almost three times as fast. Such increase in performance has been largely due to changes in design which use better sails, reduce weight, make use of planing hulls that raise the boat out of the water, hydrofoils, novel sail configurations, or some combination of these.
Some of the advances in boat design are described in the books “The Physics of Sailing Explained” by Bryon Anderson, Sheridan House, 2003, ISBN 1-57409-170-0 and “Aero-hydrodyanmics of Sailing” by C. A. Marchaj, Dodd, Mead & Company, 1979, ISBN 0-396-07739-0.
With such technologies, some modem high speed sailboats can occasionally achieve high speeds, but their maximum speeds have been limited to somewhat less than 50 knots (approx. 57 mph). In 2004, for example, the speed sailing record for water borne-sailing craft was set at 46.85 knots (53.95 mph) by a windsurfer. Prior to that it was held for eleven years by an Australian boat, the Yellow Pages Endeavour (YPE), (http://innovoile.free.fr/YPE_e.html); at 46.52 knots (53.57 mph). This modest increase in recent years illustrates the difficulties of increasing speed.
One of the early contributions to increased speed was the refinement of the planing board, which is designed to lift water craft up out of the water. Water skis, surf boards and windsurfers are examples of water craft which use planing boards. Also some modem high speed sailboats such as the Hobie Trifoiler (http://www.hobiecat.com/sailing/models_trifoiler.html ) use planing boards which are similar to water skis.
In addition, very wide sailboats with multiple hulls, such as the YPE, have improved balancing of the tipping moment of the sail with the righting moment of the weight of the crew, allowing larger sail areas. Also, improvements have been made with such innovations as stiff sails, which avoid driving force loss due to sail twist; solid sails similar to airplane wings which are more aerodynamically efficient than soft sails; steering and tracking foils having shapes that result in reduced drag; and taller sails for better wind attack angles. Nevertheless, significant limitations due to displacement drag and skin friction drag have remained. In addition, with current designs, at very high speeds, cavitation on the steering, tracking foils and hydrofoils, if employed, reduce control because the cavitating foils lose contact with the water. Moreover, many high-speed sailboats are designed so they can only operate with the wind coming from one side of the boat, and are therefore not suitable for purely recreational use.
Jean Margail of France, the leader of the Water.Resist speed sailing team (http://foxxaero.com/indsail—013.html), has noted that “everybody knows that for speed sailing the craft should be out of the water . . . hydrofoils generate too much drag—max speed 45 knots.” He published a design on his web site that appears to use airfoils (e.g., wings) to lift the boat up from the water, but the fixed steering and tracking foils that he proposes remain submerged, which still limit the speed at which his proposed sailboat can travel because of the displacement and skin friction drags on those vertical foils.
One of the objectives of the technology described here is to reduce displacement and skin friction drags described above. A further objective is to provide more stable control of a boat that is lifted out of the water, by reducing cavitation, which results in loss of control. A further objective is to enable high speed sailboats to operate more like conventional sailboats so a larger part of the sailing public can enjoy high-speed sailing.
In general, in one aspect, the disclosed technology relates to high-speed sailing craft. In one aspect the high-speed sailing craft has one or more airfoils. The airfoil may be shaped, for example like a wing, such as an airplane wing. The airfoil may extend from the craft or be integral to the craft, for example, may be designed into a deck, or used to connect portions of the craft. The airfoil is preferably approximately (and relative to vertical foils) horizontal, although generally at a slight angle, and is configured for lifting the craft up from the water, such that in operation of a portion of, and in some cases, much of, the craft can be out of the water.
The craft also has one or more rotating foils. Just as one example, the rotating foils can be, or can be mounted on, wheels, that are configured to rotate according to the direction of travel of the boat. In one embodiment, a rotating foil(s) typically is partially submerged in the water for providing tracking and/or steering. The rotating foil is preferably approximately (and relative to horizontal foils) vertical. For tracking, the top of the rotating foil preferably rotates in line with the direction of travel, such that the rotation of the bottom of the rotating foil is approximately stationary with respect to the water as the boat travels. To provide steering, one or more rotating foils can also be configured to pivot, such that the foil rotates in a direction that is at an angle from the direction from the front to the back of the craft, thereby providing a force that will direct other than straight ahead. This is analogous to the pivot of a rudder or the wheels of a car that are controlled by a steering wheel.
By lifting the craft up from the water, the airfoil allows the craft to travel faster by reducing the displacement drag and friction drag of the water on hull(s) and/or float(s). The rotating action of tracking and/or steering foil(s) reduces the friction on them, also resulting in reduced drag and reduced cavitation. In combination, one or more airfoils and one or more rotating tracking and/or steering foils have the combined effect of significantly reducing the forces holding back and impeding control of a water craft, thereby improving speed and performance.
In general, in another aspect, the disclosed technology relates to a sailing craft that can attain high speeds by using one or more airfoils alone or in combination with one or more planing boards to lift the board and boards out of the water. Rotating foils are used in combination with the boards. In increased-speed operation, the craft is lifted almost entirely out of the water. As the boards and foils for steering and tracking rise, displacement and skin friction drags are greatly reduced. In addition, the steering and tracking foils needed for control are free to turn, further reducing skin friction.
In some such embodiments, at rest and at very low speeds, planing board buoyancy is the primary source of lift, but at higher speeds, the boards plane (lift up in the water), and at yet higher speeds, aerodynamic lift from the airfoils provides lift, and the planing boards lift out of the water.
The rotating steering and tracking foils can be implemented as wheels. One exemplary implementation, for example, uses three varieties of wheels. Wheels near the front of the boat include a body, a tread and a peripherally mounted foil for tracking. These wheels protrude through planing boards such that their bottoms are below the boards' bottom surfaces. At top speed, only the foils and a small part of the wheel body of the wheels are submerged.
In one implementation, these wheels are spring-loaded such that the wheels descend downward as the airfoils lift the boat and raise it from the water. The descending motion also is coordinated with control of an aileron on the adjacent foils such that lift is reduced. This action prevents the boat from becoming airborne and keeps the tracking foil submerged so it can perform its function.
For example, in one embodiment, the wheel is attached to an arm that activates a mechanism to adjust aileron position. When enough lift has been provided to lift the wheel bodies mostly out of the water, leaving the bottoms of the foils submerged, any further lift causes ailerons to reduce lift and prevent the boat from becoming airborne. Other embodiments use electronic sensors and aileron position motors to accomplish this function. In other embodiments, wind speed is sensed, and when the wind exceeds the level at which the boat would become airborne, the ailerons are raised to reduce lift. In another embodiment, a water level sensor is used, alone or in combination with the above, to control the ailerons.
In one embodiment, the wheel(s) in the aft section of the boat have only the wheel body and tread, with no foil, but are connected to a lift-reducing apparatus which is configured to coordinate with the nearby aileron.
In one embodiment, in a third type of wheel, only the foil portion is used, the body and tread are omitted, and the wheel is used as a rudder. The foils on the aft wheels can be omitted so that they do not interfere with rudder function.
In one embodiment, the craft includes a combination of a planing board, an airfoil and a rotating wheel at one or more locations. The wheel and planing board comprise an assembly referred to as a pod.
In one embodiment, the boat is designed generally as a rectangle, similar to a catamaran. However, instead of a starboard and a port hull, at each corner of the catamaran, is a pod, such that there are two pods on the starboard side of the boat that replace the right hull of a traditional catamaran, and likewise two pods on the port side replace the left hull of a traditional catamaran. Airfoils are attached to the center of the boat and extend out to the pods. Wheels are mounted in the planing boards and their foils, if any, protrude below the bottoms of the boards.
In one embodiment, planing hulls are not used, and the boat floats on its buoyant wheels.
In one embodiment, the boat is in the form of a trimaran with two pods to starboard of a center hull and two to port. In such a configuration, the planing boards in the pods may be omitted with a planing board added to the center of the boat. This embodiment can result in a boat which is lighter and simpler to construct since the boat is not held up at the ends of the airfoils while at rest or in light winds since the pods at the ends of the airfoils contribute little to floatation.
In some embodiments, the pods and/or wheels are spring loaded to adjust to waves. This reduces the drag experienced by the planing hull plowing into a wave.
In some embodiments, there are multiple wheels in each pod.
In some embodiments, the tread of the wheels are honeycomb structures bonded to the wheel on one side and open to the water on the other. As the wheel revolves, the honeycomb pockets become submerged, trapping air in each one. At rest or at low speeds, the buoyancy of the boat is enhanced by these air pockets, and the wetted surface of the boat is reduced, and the tread has less tendency to contribute to loss of energy caused by throwing water into the air at the back of the wheel. Essentially the honeycomb decouples the boat from the water.
In some embodiments, a water level sensor is mounted in each pod to determine how much the pod has been lifted by its associated planing board, air foil and wheel. This sensor is used to adjust the position of an aileron on one or more the associated airfoils to control the amount of lift provided by the airfoil and to prevent the foil from coming completely out of the water. The adjustment can be automatic so that at high speeds the planing board is above the water surface and only a small portion of the wheel tread and body is submerged, leaving only the foil portion of the steering/tracking foil completely submerged. The adjustment could also (or instead) be controlled by the crew.
In some embodiments, a trampoline deck is used and configured so that the crew can move out toward or beyond the windward pods countering the tipping moment of the sail. In other embodiments, the leeward airfoils are adjusted to increase lift to balance sail tipping moment and in still further embodiments the windward foils are adjusted to decrease lift or produce reverse lift to balance sail tipping moment. In some embodiments, the deck is a net so that its interference with air circulation necessary to produce lift is minimized.
In some embodiments, the aft and forward airfoils are separately controlled to keep the boat level fore to aft. This is particularly useful when the boat is on a run (with the wind behind it). In this situation, some boats can be prone to tip over bow first. Control of the boat angle can prevent such a forward pitch.
In some embodiments a wind shield is mounted on each pod to reduce drag due to wind similar to aerodynamic designs used in land vehicles (e.g., cars).
In one embodiment, in which there are no ailerons on the airfoils, the boat is prevented from becoming airborne by adjusting the trim of the sail so that as the lift-off speed is approached, the pulling force of the sail is reduced. The trim may be automatically adjusted in response to a water level sensor or may be adjusted by the crew. In other embodiments in which there are no ailerons on airfoils, the angle of the airfoils may be adjusted to control lift.
In one embodiment, the boat is operated by a single skipper and in others by a crew of two of more.
In one embodiment, the boat is small, similar in size to a windsurfer, and the skipper operates the boat in a standing position and trims the sail by rocking the sail forward and aft as in a windsurfer. In this embodiment there is no rudder.
The boat can be any sort of sailing craft, with any sort of configuration of sails and propulsion. In some embodiments there are multiple masts and sails. In some embodiments, the boat is equipped with a jib and/or a spinnaker.
In one embodiment, an engine or other propulsion is used to accelerate the boat to the speed necessary for the airfoils to lift all but the wheel foils out of the water, thereby taking advantage of the resulting reduced displacement and skin friction drags. Once the necessary lift has been achieved, the engine is turned off.
In some embodiments, the mast is taller than would typically be found in a similar-sized sailboat, reducing leakage of air off the top of the sail and decreasing the angle of attack of the boat to the apparent wind. The taller mast is facilitated by the availability of using the airfoils to counteract tipping moment. Masts twice the length of the boat or more are possible.
In one embodiment, steering is controlled by a tail fin, like an airplane's. The tail fin can be used instead or in combination with a rudder.
In one embodiment, the pods are arranged in a triangular configuration rather than a rectangle. Preferably, in such embodiment, the frame of the craft may be triangular. Generally in such embodiments the rudder will be at the point of the triangle, either forward or aft, and the wheel at that location will have a body and tread as well as a rudder foil.
In some embodiments one or more pods pivot, or turn, like the wheels of a car, to provide a steering function. In some embodiments, just the wheels, not the pods, are configured to pivot, or turn, to provide steering. In a further embodiments, only forward pods or wheels pivot, only aft pods or wheels pivot, or pods or wheels in forward and aft positions pivot.
In one embodiment, the pods are wide and are in the form of airfoils. In such an embodiment, the pods act both as planing boards at low speeds and airfoils at high speeds.
In one embodiment the airfoil is designed to produce a stalling action at a desired maximum speed to assist in preventing the boat from becoming completely airborne. For example, as wind speed increases, airfoils with large lift angles will produce turbulence in the air flow pattern, which reduces lift. The angle of airfoils also may be adjustable to control lift.
In various embodiments, commercially available boats may be modified, or designs for commercially available boats may be modified to include embodiments of the invention. In one exemplary embodiment, an A Class catamaran is modified to provide a lower cost version of the invention. An A Class catamaran is a light (e.g., 165 pound), fast catamaran, typically with a 30 foot mast, which can be sailed single or double-handed. In one embodiment, the hulls of such a boat are separated further than normal, the trampoline is tilted back, and in some configurations it is cambered to provide greater lift. In addition, airfoils may be placed in front of the mast to provide lift. In some such embodiments, the usual daggerboards and rudders may be replaced by rotating foils. The result is a boat that may lift substantially off the water in true wind speeds as low as 10-15 knots and may reach very high forward speeds in high winds. It should be understood that this embodiment is exemplary, and other boats may be modified in an analogous manner.
In various embodiments, two or more airfoils may be used, e.g., a port-side airfoil or set of airfoils and a starboard-side airfoil or set of airfoils. The lift generated by each of the airfoils may be adjusted during operation, for example but not limited to by using ailerons, adjusting the airfoil angle, or by another technique, so that the airfoils can be used help control the angle of the boat to avoid tip-over. In this way, a boat may travel at speeds that might otherwise cause tip-over. For example, in a boat in which a skipper is hiking out, airfoils (and/or ailerons) on one or both sides may be adjusted to help hold the windward side down, and so control tipping. The adjustment of airfoils (and/or ailerons) may be automatic, for example but not limited to based on distance from water surface and/or boat angle and/or based on the weight distribution within the boat. Adjustments may be made manually instead of or in addition to automatic adjustment.
In some embodiments, a sailing craft may include a frame, a sail connected to the frame, a port side airfoil for providing lift, and a starboard side airfoil for providing lift. The lift provided by the port side airfoil and the lift provided by the starboard side airfoil may be adjusted automatically to control tipping. The lift may be adjusted for example but not limited to by adjusting airfoil angle, adjusting ailerons, or some other method. In some implementations, there may be a set of two, three or more port side airfoils and/or a set of two, three or more starboard side airfoils. There may be additional airfoils not associated with one side or the other.
As mentioned, the principles described here can be used in any suitable craft or configuration. For example, in one embodiment, a craft has a proa configuration in which the mast is on either the starboard or port side of the boat rather than in the middle. As another example, another embodiment has catamaran hulls instead of or in combination with the pods described above. In yet another embodiment, the craft is a trimaran, and all three·hulls lift out of the water at high speeds, and one or more of the hulls have rotating foils built-in or affixed thereto.
In general, in one aspect, the invention uses the teachings of co-pending International PCT Application No. PCT/US2004/012241, entitled “Sailing Craft with Wheels,” which is incorporated herein by reference in its entirety. The technology described here, such as the use of airfoils and planing boards can be used effectively with the foils and crafts described therein.
a shows a wheel with a peripheral foil such as might be used in the embodiment illustrated in
b is a side view of a tracking wheel and
d is an isometric view of a wheel such as would be used in the aft portion of the illustrative embodiment. Here the foil is omitted as it might interfere with the operation of the rudder.
e shows a rotating foil used for steering.
a shows the forward airfoil of the illustrative embodiment.
b shows a top view of the forward airfoil illustrative embodiment with its associated pods while
d is a top view of a forward airfoil for an ultra high speed embodiment in which the planing board is on the bottom of the central torsion box and the planing boards are omitted from the pods.
f illustrated a forward airfoil with the wings swept forward.
a is a top view of a pod.
b shows a side view when the airfoil has lifted the boat to the level which leaves only the wheel's foil submerged as would occur at top speed.
e shows the position of the wheel in the pod and the position of the aileron with the boat as rest or a very low speed.
c and 4d are the end views corresponding to 4b and 4e.
a is a top view of the rudder assembly of the illustrative embodiment while 5b is the side view with the boat at rest or at low speed.
a, 6b, 6c and 6d are vector diagrams showing motion of the boat for various true wind directions.
a and 7b illustrate a pod in which the planing board can pivot to accommodate waves.
Referring to
In this embodiment, the sail 102 is attached to a mast 104 by conventional means. The mast 104 is held in place by a fore stay 105, a starboard shroud 106 and a port shroud (mostly hidden behind the sail). The skipper controls the trim of the sail 102 using the main sheet 117 which is attached to the boom 118 and passes through the block 119. This may be a conventional sail 102 and rigging, or may be a sail that is specially configured for operation of this boat.
The skipper controls the boat from the deck, which in this embodiment is a trampoline 112. The skipper steers the boat using a tiller extension 113 attached to a tiller 114 which in turn is attached to a tiller post 15. This can be a conventional tiller and assembly. As in a conventional craft, the boat is steered by tiller operation that results in turning the rudder 121. In this boat, however, the rudder is a freely rotating disk, such as a wheel as described below with reference to
Forward and aft airfoils 109, 110 are attached to the frame 103. These are equipped with ailerons 111, which are adjusted to control the amount of lift provided by the airfoils.
Each pod 101 includes a freely rotating wheel 107, also with reference to
A central structural member 116 of the frame runs fore to aft, and in this embodiment is in the form of a torsion box so that the pressure on the sail results in minimal twist to the boat, keeping the pods at approximately the same level with respect to the frame each other. In the preferred embodiment, this structure is approximately one foot square in cross section. It is fabricated from aluminum extrusions, but could instead be manufactured as a tube of composite material. Torsion boxes, for example, were widely used in early biplanes to prevent the wings from twisting. The supports used in them can be made from struts and cables.
In the absence of wind, the boat floats on the planing boards 108, such that the outer portions of the wheels 414 (
In moderate winds the planing boards 108 will move more rapidly, and it becomes more difficult to move the water out of the way fast enough, so drag increases. This is called the forced mode. As the wind increases further, the planing boards 108 will begin to plane, i.e., rise up, and the boat enters a planing mode. In this mode the drag continues to increase with increased velocity by not at the same rate as in the forced mode because less and less water is displaced. For most boats, the displacement drag generally increases as the square of velocity in the displacement and planing modes and as the cube of velocity or higher in the forced mode. A second form of drag, skin friction drag, begins to significantly add to drag as the boat accelerates. This drag also generally increases as the square of velocity. Since the wetted surface area of the boat in the planing mode is less than in the displacement or forced modes, planing somewhat mitigates the increase in skin friction drag.
As the boat continues to go faster, the airfoils provide lift, which raises the boat with its planing boards out of the water, thereby dramatically reducing both displacement drag, because less volume of water needs to be displaced, and skin friction drag because (i) the planing board is out of the water (ii)the bottom of the wheel is almost stationary relative to the surface of the water and (iii) the tread 205 (
The lift of an airfoil varies as the square of wind velocity. Since displacement drag varies as the volume of water displaced by the hull which varies with depth of immersion, and skin friction varies as the wetted area which also varies as the depth of immersion, the lift of the airfoils counters some of the typical drag increases that result from increased velocity. This decrease in drag due to the airfoils will greatly facilitate the boat's acceleration compared to ordinary boats.
As speed increases, the boat will lift until only portions of the wheels and the rudder wheel are immersed, and drag from the water is reduced to its minimum. This is the ideal running elevation. If the airfoils were to continue to increase lift, the boat might become completely airborne, and the wind will push it sideways and backwards, allowing the boat to descend back into the water but at a lower velocity.
In one embodiment control of the airfoils is provided by a mechanism which senses the depth of the tread in the water. In this embodiment the tread does not fully lift out of the water as described below and illustrated in
As wind speed increases, drag due to the airfoils increases. However, due to the lower density and viscosity of air compared to water, this drag increases at a much slower rate than the decreases in drag due to the planing board and wheel treads being lifted out of the water.
Referring to
Referring briefly to
Referring again to
The core of the wheel may be formed using lightweight foam such as polystyrene or polystyrene foam sheets, such as those manufactured by the Owens Corning Company of Midland Michigan, available in standard two inch thickness, and which can be purchased in lumber supply stores. The sheets may be cut to the needed diameters and bonded together using Resorcinol glue, which can be obtained from Allerd & Associates 2 South St., Auburn N.Y. 13021. In one embodiment, on the periphery of each cylindrical section of the wheel a layer of honeycomb 205 such as that shown in
The axle 201 can be made from any suitable material, and in the illustrative implementation is made from stainless steel. Preferably, in general, the metal materials used are preferably corrosion resistant or plated to prevent attack by salt water. Aluminum boat parts, for example, can be anodized.
Referring to
Referring now to both
In an illustrative embodiment, the L-brackets 405 are attached to the airfoil 406 by posts 408. The wheel mounting is strengthened by braces 409 that form a torsion box to enhance the stability of the assembly. Referring to
An aerodynamic shell 122 (
Referring to
Information on hydrodynamic planing can be found in the book “High Performance Sailing” by Frank Bethwaite, International Marine,1993, ISBN 0-07-05799-0.
Referring to
It sometimes comes as a surprise to some people that a boat can go faster than the wind because often people view a boat as being pushed from behind by the wind. In reality, a boat is propelled by the difference in air pressure between the air on the front of the sail and on the back of the sail. As the pressure in front of the sail is less than that behind it, the boat will move forward.
If the wind is coming directed from the front of a sailboat, the sailboat will be driven backwards. However, if the wind is coming largely from the front, e.g., at an angle of 45 degrees from the front, if the flow of air along the front of the sail is faster then than behind it, the air pressure in front of the sail will be less than behind it, and the boat will be pushed forward. The keel and rudder are needed to prevent the boat from going sideways. This situation by itself places no limit on how fast the boat can go. Ice boats, for example, have been known to go as much as five times as fast as the wind.
The direction of the wind experienced by the sail, called the apparent wind, is combination of the true wind, i.e., the direction sensed by a person standing on the shore and the wind generated by the motion of the boat, i.e., the wind experienced by the skipper of a motor boat traveling on a windless day. In technical terms this combination is the vector sum of the two winds, the true wind and the boat speed wind. For instance if the true wind is coming directly from the side of a sailboat, and the boat is traveling forward at same speed as the true wind, the two winds will have equal speeds but will be a right angles to each other and the apparent wind, i.e., the wind experienced by the sail will be coming at an angle of 45 degrees to the forward direction of the boat. This is the direction of the apparent wind. The angle of the sail with respect to the boat, normally called the trim of the sail, is adjusted to apparent wind to maximize the boat speed. (For a conventional boat a typical relationship between boat speed and wind speed as a function of the angle between the boat direction and the wind is illustrated on page 71 of the book by Marchaj previously mentioned.)
For high speed sailboats, the relationships between the true wind, the boat speed wind and the apparent wind and the significance of these relationships to the performance of the airfoil can be better understood by referring to
Referring to
The
In the example of
In the example of
In the example of
In the example of
As illustrated in these figures, for a large variety of true wind angles, for example in 601a and 601b, the angle that the apparent wind makes with the sail is the same if the skipper uses ideal sail trim.
Then airfoil responds best to wind coming head on to the boat, but a 20 degree angle such as that shown in
Referring to
When the boat is moving in very light winds, the skipper would operate the boat from the center of the trampoline. As wind increases, he may move out to windward to counter the tipping moment of the sail and keep the boat level. Eventually, as wind continues to increase, he cannot go any further out, and the ailerons on the windward side can be raised to decrease lift and assist in countering the tipping moment. In one embodiment, this happens automatically: when the windward pods are lifted out of the water leaving only the foils submerged, this initiates an automatic aileron-raising mechanism, such as that described with reference to
In this embodiment, the trailing edge of the airfoil 301 with the aileron in its normal position is aimed about 12 degrees downward. Other embodiments with larger and smaller angles are possible, and since lift is directly proportional to the sine of the angle, larger angles can facilitate narrower airfoils. Lift is also directly proportional to airfoil length and width, and is proportional to the square of wind velocity.
b shows a top view of the forward airfoil 301 for the illustrative embodiment, and depicts a torsion box 303, pods 304 and the location of the wheels 305.
c is a side view of this assembly which shows the position of the wheels for the highest 306 and lowest 307 lift positions and their associated water levels 308, 309.
Wind impinging on the boat is rarely directly from the front of the boat because such a wind would merely drive the boat backwards. As previously described, under ideal operating conditions, the wind is about 20 degrees off the direction of the boat. Thus, unlike the airfoils of an airplane, the wind does not come head-on. The wind directions 310, 311 for starboard and port tacks are shown in
In the illustrative embodiment the torsion box may interfere with air flow. This latter effect can be mitigated by using an embodiment such as shown in
In general, the airfoils are positioned as low as convenient to the water so that the airfoils operate in the ground effect region. In this mode of operation, speed is enhanced because induced drag from the vortices generated at the wingtips is less.
f shows an airfoil configuration in which the wings sweep forward by the angle of best performance between wind direction and boat direction. If the wind is approaching somewhat from starboard, the leeward airfoil lift will be enhanced at the expense of the windward airfoil. Since it is desirable for the leeward lift to be larger in any case to counter tipping moment, the sweep wing approach can improve overall performance. In the figure, the direction of the wind 312 is shown for starboard tack.
Referring again to
A wheel 403 protrudes into the water through an opening 404 in the planing board.
The wheel 403 has an axle 410, 201 (
In light air, the wheel can go up to the position shown in
The operation of the illustrative embodiment's automatic system used to reduce lift as wind reaches or exceeds an acceptable limit is shown in
Using this arrangement, the skipper of the boat does not have to control the four ailerons. In other embodiments, the skipper can control the ailerons manually or in combination with an automatic system. For example, the height of the wheel can be measured using a displacement sensor that generates a signal that is used to control a motor that moves an aileron. Arrangements for moving ailerons are common in airplanes.
In some embodiments, the aileron can be raised far enough so that air leaving the aileron is aimed upward. This is useful if it is desired to use reverse lift on the windward side of the boat to compensate for the tipping moment of the sail. Again the action can be automatic, since the tipping action will cause the windward wheels to lift and the leeward wheels to lower. The aileron adjustment mechanism described above decreases and perhaps reverses the lift of the windward airfoils, while the lift of the leeward airfoils is increased. Thus the overall effect will be to keep the boat more level.
As an added benefit, if a lifted pod encounters a wave, its wheel will rise due to the buoyancy of the wheel, tipping the aileron down thereby increasing lift and assisting the boat to ride over the wave. Likewise at a wave trough, the lift will decrease forcing the boat down into the trough.
In embodiments which use airfoil/pod assemblies spring loaded at the central torsion box, the ability of the boat adjust to waves and ride at the appropriate height above the water is further enhanced. Such an embodiment is illustrated in
The airfoils mount on posts 804 and attached to hinges 805 which include a pivot point 806. Springs 807 hold the airfoils in place.
In other embodiments accommodation to waves can be implemented as shown in
a shows a top view of the illustrative embodiment's rudder assembly. A side view is shown in
The tiller 512 is attached to the second pulley 511, and a tiller extension 513 is connected to the tiller. This assembly can be obtained from marine supply retailers such as Layline in Rayleigh N.C. The steering assembly thus operates as in normal sailboats such that as the tiller is pulled to starboard, the boat turns to port. As a rotating foil, this rudder has the advantage described above of decreased drag in the direction of travel.
The advantages of rotating foils are further illustrated with reference to
The speeds of various points on the wheel's foil are depicted using vectors. The vectors represent the velocity of the boat 905a, 905b, 905c and 905d as shown by the solid arrow at points a, b, c, and d in the vector diagrams. The vectors representing the velocities 909a, 909b, 909c and 909d due to rotation at points a, b, c, and d are the heavy dotted line with the small dashes. The resultant vectors representing the actual speeds and directions of the points are represented by the fine dotted lines 910a, 910c, 910d with the long dashes.
At point b, the resultant vector has a value of zero, indicating that point is approximately stationary with respect to the water. At a and c, the result vector has speed about 90% of the boat speed for the embodiment shown. At d the speed is about 57% of boat speed. On average, the points on the submerged portion of the foil will be traveling at about half the boat speed. As a result, the onset of serious cavitation occurs at a much higher boat speed than if the foil were being dragged forward through the water, as happens in conventional boats. Furthermore the lowest part of foil, which performs most of the function of the foil, travels at the lowest speed relative to the water.
Referring to
An illustrative example boat shown in the figure is an A Class catamaran (“Acat”) that has been modified to include features of the invention. The figure shows the boat going up-wind (beating) on starboard tack in a high wind.
An Acat typically has hulls that are approximately 18 feet long, separated by 8 feet, and a mast which is 30 feet tall, with a total sail area of 150 square feet. A Class catamarans may be obtained, for example, from Performance Catamarans, 1800 East Boarchard Ave., Santa Ana Calif. 92705.
As shown in the figure, a modified Acat has hulls, 1001 and 1018, that are separated by approximately 12 feet, four feet more than normal. Additional separation increases the sizes of the trampoline 1002 and airfoils 1003, 1005 that may be used for lift and may allow the boat to become substantially airborne at lower wind speeds.
As is typical, a trampoline 1002 is mounted between the two hulls 1001, 1018. To provide lift in this modification, however, the trampoline 1002 is tilted upward in front and cambered (curved) in a manner that enhances lift (e.g., in the shape of an airplane wing, or other suitable shape). Thus, in this exemplary implementation, the trampoline also may be referred to as an airfoil, in that it serves both the functions of a trampoline and an airfoil. The trampoline also may be made of any other suitable material, for example but not limited to a solid material such as foam or sailcloth.
Two additional airfoils, 1003 and 1005, are mounted in front of the mast 1004. In some embodiments, these airfoils are made from sailcloth, but these also may be made of any suitable material, including but not limited to rubber or foam. If made of sailcloth, the airfoils 1002, 1003, and 1005 may be adjusted to control lift, for example manually and/or automatically, and it should be understood that various techniques may be used to control the angle of the airfoils 1002, 1003, and 1005. It should be understood that various embodiments may include only the modified trampoline, additional airfoils, or both.
In this exemplary implementation, a rotating foil 1006 is in a position that may typically hold a dagger board in an Acat. In this exemplary implementation, a rotating foil is also used for rudder 1007. As shown, the top portion of the foil may be covered by a shield 1017 to prevent a sailor from disturbing the foil. For example, the skipper of the boat may operate the boat from this area in strong winds. The rotating rudder 1007 is held by forked bracket 1008, similar to that used to hold the front wheel of a bicycle. The forked bracket is held in place by a fixed bracket 1009 affixed to the hull 1001. The rudder is turned by a tiller assembly 1010.
The boat's sail 1011 is attached to the mast 1004 and the boom 1012 in a manner typical for sailboats. The trim of the sail is adjusted by a main sheet 1013, also in typical fashion. The hulls are held in place by rods 1014, 1015 and 1016.
Each of the forward airfoils, 1003 and 1005, is mounted on a rectangular frame 1018. The sailcloth airfoils are loosely affixed to the forward and aft parts of the frames so they assume an upward camber if the frame is tilted up and a downward camber if it is tilted down. The fames are attached to brackets 1019. The brackets contain a pivot point 1020 at the position in the airfoil representing the center of lift for the airfoil. At the front edge of an airfoil's frame a bracket 1021 is attached with a small water ski 1022 on its bottom. A spring at the pivot point 1020 of the bracket causes slight pressure on the frame to cause the ski to push down slightly into the water.
In the absence of wind both airfoils 1003 and 1005 assume a tilt shown by the port airfoil 1003. As the wind increases, all three of the airfoils, 1002, 1003 and 1004 contribute to lifting the boat out of the water thereby reducing displacement and frictional drag. As the boat rises the lowering skis cause the tilt of the airfoil frame to lessen, thereby reducing lift and diminishing the tendency of the boat to become airborne in a puff.
As wind speed continues to increase, the weight of the skipper hiking out on the windward hull may be insufficient to hold the windward hull down on the water. In this condition, the starboard hull 1001 is lifted out of the water sufficiently far that it is desirable to reduce the lift on the starboard side of the boat so that the boat does not tip over. The port hull 10018 is either at the surface of the water or its bottom is slightly submerged.
As shown in
In some embodiments adjustment of the tilts of the forward airfoils 1003 and 1005 could be done by the crew, but since the skipper needs to trim the sail and steer the boat, a second crew member would be needed and his extra weight would slow the boat down.
A boat as configured in this exemplary figure may not achieve the speeds of an embodiment such as that shown in
This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 60/716,168, filed Sep. 12, 2005, entitled “High Speed Sailing Craft,” attorney docket number XYP-002PR, incorporated herein by reference.
Number | Date | Country | |
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60716168 | Sep 2005 | US |