Patent Application
20150274266
Monohull sailing vessels using hydrofoils and increasing the speed and stability of such vessels.
The objective of the boat is to provide a monohull sailboat which has a substantially greater speed and stability than current monohull sailboats. It (1) enables the use of sails with much larger areas than common sailboats, in some cases larger by a factor of two or more, (2) constrains heeling to low angles, (3) enhances planning and (4) provides a boat with greater stability in a larger range of sailing conditions than usual. In addition the apparatus used to control heel can also reduce the apparent weight of the boat, thereby decreasing displacement and skin friction drags, which then increases boat speed.
A further objective of the boat is to use dual purpose foils which can act as both hydrofoils and planning boards and provide smooth adjustment over a wide range of operating conditions. Yet another objective is to provide boats which combine performance advantages of both monohulls and catamarans.
It is well known to those familiar with the art that heeling reduces the speed and stability of a sailboat, and if heeling exceeds certain limits, the boat can capsize. Heeling produces several phenomena which reduce the speed of the boat. Most importantly, the effective area of the sail is reduced to the product of actual area and the cosine of the heel angle. For small heel angles this effect is small, but at heel angles over 20° it is substantial.
Also the hull of a boat is designed to produce the least drag when the boat is upright or almost upright. In addition boats with lightweight hulls will suffer from additional heeling if the heeling angle is large enough that the weight of the sail, rigging and spars contribute to heeling.
To counteract heeling monohulls are often equipped with deep, heavy keels, sometimes cantilevered to increase anti-heeling. However, as wind speed increases, heeling forces increase, but the anti-heeling force does not, so eventually the boat will capsize.
Multi-hull boats use hulls wide apart to counter heeling, but this results in vessels which do not tack easily and are often more difficult to moor and dock.
It is also known to those practiced in the art that there is a maximum speed, which is call the “displacement speed,” “critical speed” or “hull speed,” at which monohull sailboats can travel. This value varies as the square root of the length of the boat at the waterline, and therefore is much smaller for small boats than for large ones. As wind speed increases and critical speed is approached, using larger sail area has little or no effect.
Using hulls designed to plane allows critical speed to be exceeded, but often the result is not substantial. If monohulls are equipped with enough sail to plane at low wind speed, they generally heel excessively in moderate winds and are prone to capsizing.
It is well known that if hydrofoils are used to inhibit heeling and if the hydrofoils are outwardly canted, the hydrodynamic forces produced by the hydrofoils and those produced by their supporting strut oppose each other, thereby reducing the heeling suppression force. Outwardly canted hydrofoils can be used on a monohull if the opposing force problem is avoided by allowing the strut to self-align to the leeway angle established by the daggerboard or keel or to be manually set by the crew each time the boat comes about. However self-alignment increases the complexity and cost of the boat and manual operation is often inconvenient, particularly for single-handed boats.
To combat heeling due to propeller torque or uneven weight distribution on motor boats, planning foils, called trim tabs, are sometimes mounted on the stern. One is tilted up and the other down to rotate the boat in the opposite direction of the undesired heel. This heeling suppression technique would be less effective on sailboats because the boat's stern is generally narrow, limiting the lever arm available.
Foils which have historically been used for heeling suppression have been either submerged or at the surface of the water in the planning mode, but not used both ways.
The design of the current boat avoids the disadvantages of prior techniques and combines the most useful features of several of them.
Ketterman
Ketterman, in his college dissertation, Senior Project Trifoiler, determined that if hydrofoils are canted outward, the hydrodynamic forces generated by vertical struts, which on catamarans determine the leeway angle the boat travels at and the forces generated by horizontal hydrofoils used to lift the boat conflict with each other.
Welbourn
Welbourn, U.S. Pat. No. 7,644,672, describes means of counteracting heeling by use of a laterally translatable hydrofoil which is mounted in the hull of a boat, provides positive lift, and can be moved from the windward side of a boat to its leeward side and vice versa. In this situation, leeway angle issue is not a concern because there are no struts.
Coffman
Coffman, US Patent Application 20110259254, covers an apparatus which converts a monohull into a trifoiler at a wind speed sufficient to cause the boat to be foil borne.
The boat described herein is intended to overcome the performance and cost constraints of previous techniques and combines the advantages of several of them.
The boat employs one or more outwardly canted hydrofoils on both the starboard and port sides of the boat. The hydrofoils can be adjusted for attack angle and depth of immersion enabling a wide range of anti-heeling action correction and can act either as ordinary hydrofoils or planning foils.
The struts holding the hydrofoils are designed to reduce or eliminate the conflict of hydrodynamic forces which normally reduces the effectiveness of outwardly canted hydrofoils. Furthermore, the immersed area of a strut is kept small compared to the area of the hydrofoil attached to it, on the order of 10% of the hydrofoil area or less in normal operation.
Unlike other heeling suppression techniques used on keel boats and catamarans, as wind and boat speed increase, heeling suppression automatically increases using the techniques described herein. This dramatically reduces the probability of capsizing.
The hydrofoil apparatus increases the stability of sailboats partly by increasing the apparent beam of the boat.
The apparatus can be employed by monohull sailboats of various sizes. It can be incorporated during manufacture or as an accessory to existing boats.
Many of the methods of increasing the speed of sailboats function best in a narrow range of wind speeds. For instance when a catamaran becomes foil borne, its speed increases significantly, but below that hydrofoils offer little advantage. Thus adding hydrofoils to a catamaran is most useful only at high winds, and, in general, in most parts of the world, consistently high winds are rare. Because the boat described herein relies on a very large sail(s) to provide extra speed, its benefits are evident at all wind velocities. Particularly good results have been measured at low to moderate speeds.
Recently development has been done on the use of hydrofoils on sailboats to combat heeling. Early work was done by Ketterman who studied inwardly and outwardly canted hydrofoils on catamarans. His analysis proved that if the struts holding the hydrofoil contribute to setting the leeway angle, the hydrodynamic forces produced by the hydrofoil and the strut oppose each other if the hydrofoil is outwardly canted. This consideration is particularly important in catamaran or trimaran designs which rely exclusively on the struts setting the leeway angle.
The boat described herein can be used in the hydrofoil, planning or hybrid mode and in some embodiments smoothly transforms without skipper intervention from one to the other as wind ebbs and flows and the boat's heel lessens or increases. In some embodiments the apparatus can be altered by the crew from one mode to the other or adjusted in attack angle and/or depth of immersion to increase or decrease the anti-heeling force.
In most operating modes the leeway force produced by the strut is small (preferably 10% or less) as compared to the positive lifting force of the hydrofoil. In many embodiments this accomplished by making the submerged area of the vertical strut which holds a hydrofoil much smaller than the submerged area of the hydrofoil so that the conflict between the lifting and leeway producing forces is minimized.
In one embodiment, the boat, shown in
A hydrofoil can operate in lifting mode or in the planning mode or can be raised above the water level, where it performs neither function. Either, both or neither hydrofoil can be set to engage the water. How much a hydrofoil engages the water depends on how far it is lowered, which is determined by how much heeling suppression force is desired.
a is a front view of the high performance planing monohull sailboat with heeling control showing operation of the boat in light winds.
b is a front view of the high performance planing monohull sailboat with heeling control showing operation of the boat and reduction of the apparent weight of the boat.
a is a side view of the hydrofoil apparatus of the high performance planing monohull sailboat with heeling control showing the hydrofoil set at an attack angle of zero.
b is a side view of the hydrofoil apparatus of the high performance planning monohull sailboat with heeling control showing the hydrofoil set an attack angle of plus twelve degrees.
c is a side view of the hydrofoil apparatus of the high performance planning monohull sailboat with heeling control showing the hydrofoil set an attack angle of minus twelve degrees.
a and 22b illustrate an embodiment in which the hydrofoil apparatuses can be rotated into a stowed position.
Referring to
Note in
In this figure and other figures referred to in this section, a horizontal arrow, 2-5 shows wind direction, and if the hydrofoils produced any lift, either positive or negative, it would be shown by one of the arrows, 2-6, aimed up or down. The angle, 2-7, of the bottom of the boat with respect to the waterline in this embodiment is approximately 10°, flat enough to enable planning.
If the crew can know for certain that the wind will stay low enough that the skipper hiking out can hold the boat level or nearly level, then he may opt to go sailing without the hydrofoils as shown in
In very low winds the heel, if any, is controlled by the position of the crew, or in the case of single-handed operation, by the position of the skipper. Normally the skipper does not choose to sail the boat in a perfectly upright position. If the boat is on a beat or reach, the boat sails heeling slightly to leeward so that gravity causes the sail to take a smooth camber rather than to wrinkle up. A smooth camber causes air to flow smoothly across the sail which, increases the power of the sail. If the boat is on a run, it is usually heeled slightly to windward so the center of force on the sail is directly over the centerline of the boat. This prevents the force on the sail from trying to rotate the boat, i.e., to produce a weather helm. A weather helm must be opposed by a force on the tiller, and that force increases rudder drag.
At low wind speeds heeling is countered both by the skipper hiking out and the actions of the hydrofoils.
This situation is illustrated in
The angle of the heel is determined by the position of the skipper hiking to windward, the force of the wind, and the lift, 5a-3, of the leeward hydrofoil, 5a-2. The attack angle is set positive as shown by the plus sign, 5a-4. The windward hydrofoil, 5a-5, is out of the water and is set at a zero attack angle, 5a-6.
As the wind increases, the boat speeds up and the lift, 5b-1, of the leeward hydrofoil increases as shown in
At moderate wind speeds, the skipper hikes out further than at lower wind speeds and/or uses a larger leeward foil attack angle to maintain the boat at the desired heeling angle. However, eventually, as wind speed increases, these adjustments cannot overcome the heeling force.
When this occurs, the windward foil is lowered so it engages the water as shown in
In moderate winds expert sailors may be able to adjust the immersion depths and attack angles of the windward and leeward hydrofoils so that the leeward foil operates in the planning mode and the windward one produces a normal hydrofoil action. This would result in a minimum apparent boat weight.
If a sudden and intense puff is encountered, the skipper can quickly lower the windward hydrofoil if it has been previously set at a negative attack angle, but is not fully engaged with the water.
When the wind is strong, both hydrofoils are generally deeply immersed and set at high attack angles, the windward one negative and the leeward one positive. The depths of immersion are chosen so that the hydrofoils do not suffer significantly from loss of power due to being too near the water surface yet not deep enough to cause the foils and the struts to produce significant conflicting hydrodynamic forces. If maximum lifting forces from both hydrofoils are not needed, the leeward one is set to produce the greater force in order to lower the apparent weight of the boat and reduce displacement and skin friction drags. The apparent weight of the boat is its true weight less the net positive lift of the hydrofoils. Typical settings are shown in
In this figure it is seen that on the leeward side, the vector, 7-1, representing the sideways force produced by the hydrofoil pushes the boat to leeward, while on the windward side it, 7-2, pushes the boat to windward. In some cases it is possible balance these two forces so the hydrofoils do not affect to the leeway angle.
But if the boat is heeled to windward, the center of force can be placed directly over the boat's centerline, eliminating the weather helm. As shown in the figure, the boom, 8-6, extends to leeward and the boat heels to windward. This situation results from the positions of the two hydrofoils which are acting as planning foils. If change in wind speed causes the boat of change the heeling angle, one or the other planning foil will exhibit increased lift opposing any further change in heeling. The if a strong puff causes a sharp increase in heeling angle, the leeward foil will dip much further into the water, which converts its heeling action from planning to hydrofoiling, a change which ultimately increases lifting force by a factor of three. As the boat rights, the lifting force decreases because the foil approaches the water surface until a new equilibrium is reached.
The foil settings used for improved stability in light airs are similar to those used for running. Both foils are set at positive lift angles and normally operate in the planning mode. The value of the attack angle depends on the amount of stability desired, with larger angle producing greater stability.
Another feature of the boat is the ability to use the drags of the hydrofoils to combat weather or lee helms. If the boat's trim produces excessive weather helm, some compensation can be obtained by relying more on the leeward hydrofoil for righting moment than on the windward one.
The design of the boat is analyzed by starting with the hydrofoil because its performance influences all aspects of the boat.
The strut, 11-1, in
Laterally the angle of the hydrofoil with respect to horizontal is the angle A, 12-2. In the preferred embodiment it is same angle each side of the bottom makes with the deck, an arrangement which enhances planning when the boat heels at this angle.
The hydrofoil assembly holder mounts on the hull of the boat. The hull without the hydrofoil assembly holders is shown in
The hull is fabricated from Kevlar and carbon fiber textiles, or similar materials. Kelvar is puncture resistant and carbon fiber textiles are strong and stiff. The result is a light-weight, durable hull.
Details of the parts of the hydrofoil apparatus which are parts of the hull are shown in
When in use, any positive or negative lifting force produced by the hydrofoil passes from the hydrofoil assembly to the hydrofoil assembly holder and then to the hull. The design of the apparatus allows the hydrofoil assembly holder to be varied over the attack angle adjustment range.
The hydrofoil assembly, 16-2, is inserted upward through the slot in the hydrofoil assembly holder.
Several other parts of the boat are shown in
The boat's daggerboard, 18-1, is shown in
A typical rudder, 19-1, appears in
Because the boat permits adjustment of both attack angle and depth of immersion, the skipper may have many adjustments to perform when tacking. In addition to operating the tiller and the sheet, he can adjust the attack angles and immersion depths of both hydrofoils. He must keep one hand on the tiller at all times so all the adjustments ordinarily must be made with one hand. The adjustments of the hydrofoils are made to optimize the amount and polarity of lift (positive or negative). When the hydrofoil is below water level but near the surface of the water, lift can be varied over a wide range from zero to the maximum possible for the attack angle chosen by changing the depth of immersion. And, if the attack angle is set at maximum, there is little usefulness to backing down on attack angle since nearly the entire range of lift can be selected by changing foil depth. Thus the number of adjustments can be reduced merely by using only the maximum attack angle.
Alternatively if the foil is keep nearly at full depth, changing immersion has little effect so changing lift can be accomplished by changing attack angle only. Using either strategy, the number of adjustments needed for ordinary hydrofoil operation can be cut in half. Another approach to making adjustments easier involves using the skipper's feet to adjust settings.
Ordinarily in light airs using fixed attack angles and varying only immersion depth is useful, while in heavy weather it is best to fix the depth of immersion and vary the attack angle. In any case, the boat is designed so all four possible adjustments may use either fixed or variable settings.
The operation of the equipment used to adjust attack angle can be examined by studying
In these figures solid lines, 20a-1, delineate parts which would be seen by an observer. Dark dotted lines, 20a-2, show parts of the hydrofoil assembly obscured by other parts of the apparatus, and light dotted lines, 20a-3, show obscured parts of the hydrofoil assembly holder. The very dark dotted line, 20a-4, is the surface of the water, and the water itself is the area with slanted dotted lines.
The arrow, 20a-5, shows the direction of boat travel.
The chine, 20a-6, is slightly above the water level, 20a-4.
The pivot point, 20a-7, for the hydrofoil holder assembly is the point about which the holder changes its angle to set the attack angle. In the preferred embodiment a cam clamp is used to lock the attack angle. There are a large number of techniques, know to those practiced in the art, which can be used to lock the attack angle and depth of immersion, including vliers, travelers and pins. In the preferred embodiment, the shaft, 20a-8, of a cam clamp passes through the outer freeboard, 20a-9, then through the hydrofoil assembly holder, and ends at the inner freeboard 20a-10. The shaft passes through a hole in the hydrofoil assembly holder. It moves in slots, 20a-11, in the two freeboards as attack angle is altered, and the hydrofoil assembly holder rotates. When the cam on end of the shaft in depressed, it pulls the outer freeboard toward the inner one securing the hydrofoil assembly holder in the chosen position. Because the end of the shaft at the inner freeboard must slide in its slot, there is a mechanism in the hull which provides it this freedom. The details of the operation of a cam clamp are familiar to those skilled in the art.
The pivot point hardware consists of a stainless steel bolt, threaded at the end which feeds into a blind threaded insert mounted in the inner freeboard. The entire interior of the apparatus can be removed from between the inner and outer freeboards by removing the bolt.
b and 20c illustrate the positions of the hydrofoil assembly at the ends of the attack angle adjustment range, i.e., +12 and −12 degrees. In both figures the hydrofoil assembly has been further lowered so it engages the water. For clarity a simplified, miniature drawing, 20b-1, is included.
b shows the hydrofoil is set for maximum positive lift, 20b-3, and
When the hydrofoil in
Embodiments of the boat can take a variety of forms, depending on size of boat and performance desired.
In various embodiments the dimensions and shapes of the hydrofoil and strut may differ. The maximum depth of immersion, the range of attack angles, the shape and camber of the hydrofoil, and the canting angle of the hydrofoil can take various values.
Means of changing the angle of attack, altering the hydrofoils depth of immersion, and holding the angle of attack and depth of immersion constant can take differing of forms. The adjustment of the angle of attack and depth of immersion can be manual or mechanized.
Various sail plans including plans utilizing jibs and spinnakers can be the utilized as can various hull designs including flat and curved bottoms. All these possibilities are well known to those familiar with the art.
In one embodiment of the invention two hydrofoil apparatuses are placed on each side of the boat. This arrangement is particularly appropriate for use by children who are just learning to sail since it improves the stability of the boat and diminishes the possibility of pitch-poling.
Embodiments which use various strut designs are helpful in some situations. For instance in high wind situations in which the hydrofoils are deeply immersed, and the conflict between the hydrodynamic forces of the hydrofoil and the strut becomes significant, an embodiment could use two rods instead of a flat strut. Also the lateral lift coefficient of the strut can be reduced in embodiments which have rough surfaces or slots to upset laminar flow around the strut.
An embodiment is possible in which the position of the boom—to leeward or to windward—determines whether the attack angle in positive or negative. This simplifies the task of manually setting the attack angle.
Having the hydrofoils increase the effective beam of the boat may be disadvantageous when the boat is operated in crowded fleets or harbors, and would make approaching a dock more difficult. An embodiment which allows the hydrofoil apparatus to rotate onto the deck or backward toward the stern addresses this issue as shown in
When the boat heels, a sidewise force is generated in addition to the usual upward or downward lift. In another embodiment means of adjusting the angle of the strut to hold it vertical can be utilized.
