Hydrofoil stabilizer of list, pitch and roll for sail vessels
A sailboat having a hull, a sail assembly and a keel is additionally equipped with an assembly of stationary or pivoted hydrofoils—the object of the present invention. The foils are mounted on both sides of the hull and placed above and below center of mass (C.G.) of a sailboat in a biplane manner that allows efficiently compensating yacht's roll. The assembly of stationary hydrofoils of the present invention, which upper foils can go out of water when a yacht is heeling over also develop momentums efficiently compensating wind list. Another embodiment of the present invention, which comprises hydrofoils assembled in a triplane manner, allows efficiently compensating wind list at low sailboat speed. Biplane assembly of pivoted hydrofoils of the present invention allows compensation all adverse momentum affecting a sailing vessel.
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTNot Applicable.
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INCORPORATED-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISKNot Applicable.
FIELD OF THE INVENTIONThe present invention relates to sailboats, and more particularly to improved hydrofoil list, roll and pitch stabilizers for a sailboat.
DESCRIPTION OF THE RELATED ARTA type of conventional sailing boat is one, which comprises a hull, a sail assembly, and a keel structure, wherein the function of the keel is to operate as a vertical hydrofoil which resists lateral movement of the boat partially compensating wind and turn list so the boat can travel on an angled course in an upwind direction. For this, the keel has to be weighted so as to add ballast and lower the center of gravity of the boat to provide the stability of the boat. Despite of many modifications introduced in sailing boats, this basic design of sailing boats has for many centuries been the one most commonly used; but, the practice reveals that this solution is not enough to compensate wind and turn list, roll, pitch and yaw, which affect speeding yachts. Therefore, there were numerous attempts to solve this problem by means of underwater wings—hydrofoils—installed in different parts of yachts. Today it becomes even more important, because ship designer try to utilize “green energy”—the well-known power of wind—not only for small yachts, but also for large ships.
It is known in the prior art a number of applications of hydrofoils in boats. One of the oldest hydrofoils, which is known from beginning of XX century, is the bilge keel—the long underwater hydrofoil placed along a hull. Although not as effective at reducing roll, bilge keels are cheaper, easier to install, and do not require special internal space inside the hull.
One of the best known applications of hydrofoils is to lift the hull of the boat out of the water in such a way that the hull is being supported entirely by the lifting force provided by such hydrofoils—underwater wings—traveling through the water in high speed. This application is perfectly working in motor boat, but it can not be utilize in sail boat because of dangerous list that can turn the sailboat over keel.
There have been other proposed applications of hydrofoils—underwater fins—in boats to provide stability. One such application is shown in U.S. Pat. No. 1,499,900 issued to Zukucker, wherein a plurality of hydrofoils are mounted on two sides of a power boat. These fins may be adjusted both upwardly and downwardly to improve the stability of the boat. In two other patents, U.S. Pat. Nos. 3,377,975, Field, and 3,842,777 issued to Larsh, laterally extending fins are provided on opposite sides of a ship to alleviate any roll condition of the ship.
There have also been other various attempts in the prior art to stabilize sailing vessels by the use of hydrofoils. For example, in U.S. Pat. No. 1,356,300 issued to McIntire there are pair of bulky “stabilizing planes” mounted at the outer end of outrigger arms. Each stabilizing plane is slopped at a downward and inward inclination so, according to the author, compensating forces causing boat's list and yaw.
The similar solution dedicated to multi-hull boats is shown in U.S. Pat. No. 3,949,695 issued to Pless, which comprises pair of hydrofoil members mounted at the outer ends of outrigger arms on opposite sides of the hull.
As was noted above, hydrofoil members proposed in these patents are bulky, significantly increase width of the vessel and, because of this, useless.
U.S. Pat. No. 4,058,076 issued to Danahy shows hydrofoil members functioning in the similar way as those in the previous patents. In this patent the hydrofoil members look like triangle extending downwardly to end of the keel.
This solution has obvious disadvantages: the strange shape of hydrofoil members proposed in U.S. Pat. No. 4,058,076 makes the yacht ugly, and, because the hydrofoils is extended below the center of gravity of the yacht, the hydrodynamic forces applied to parts of such hydrofoils above and below the center of gravity produce momentums applied in opposite direction which can not effectively compensate the list.
U.S. Pat. No. 4,193,366 issued to Salminen proposes a single hydrofoil—underwater wing—profiled in such a way that provides vertical downward forces that, according to the author, have to compensate lateral aerodynamic force component exerted by wind against the sail assembly, thus diminishing the list and yaw angle in the travel of the boat. Analysis of forces and momentums (see
There have been other attempts in the prior art to utilize hydrofoils in combination with a set of “ailerons” lifting the hull of the sailing vessel totally out of the water. One of such devices is shown in U.S. Pat. No. 3,373,710 issued to Steinberg, in which a hydrofoil is positioned beneath the boat, wherein the “ailerons” are works as ailerons on an aircraft to maintain the sailboat in an upright position.
The similar, but more complex arrangement is proposed in U.S. Pat. No. 3,800,724 issued to Tracy. It shows a “winged sailing craft” which has a vertical airfoil to provide a force for forward travel, and a horizontal airfoil to provide stability. In addition, there are provided upper and lower hydrofoils. The upper hydrofoil lifts the vessel out of the water at lower speeds, and the lower hydrofoil provides either positive or negative lifting forces as required.
As was noted above, solution proposed in these two patents can not be applied to sail vessels, unlike to motor boats. All sail vessels are affected by wind forces applied high above the center of gravity of the vessel. These forces power the vessel, but also generate high momentum that is heeling over the vessel and tries to turn it upside down. To make sail vessel stable, a heavy ballast is placed below its center of gravity. Because of this, hydrofoils lifting a sail vessel from water make it very unstable. Analysis shows that it is necessary to install large hydrofoils or airfoils (having size of a sail) to stabilize such vessel. Obviously, such solution can not be utilized in yacht design.
Another solution is represented in U.S. Pat. No. 3,505,968 issued to Gorman and U.S. Pat. No. 3,968,765 issued to Menegus. They show a hydrofoil mounted below a hull of a sailboat and working as a conventional keel, but rotating about a horizontal longitudinal axis so that its lifting force can be exerted laterally to one side or another one. In one of embodiments, the hydrofoil is turned in such a way that provides an upward dynamic lifting force.
The task of vessel stability is a complex one, where all forces, —static and dynamic ones—affecting the vessel, particularly, sailing vessel, have to be taken in account. Moreover, because vectors of these forces do not pass through the center of gravity of the vessel, they produce momentums that try to turn the vessel in all three planes that in many cases decrease the vessel stability. As analysis of the prior art shows that the authors of the prior art miss some forces and momentums; in the result, the task of eliminating of adverse factors affecting sailing vessels has not been solved yet. Also, the hydrofoils proposed in the previous art affect yacht stability causing unnecessary vertical lifting and yaw.
SUMMARY OF THE INVENTIONIn the present invention, there is a sailing vessel comprising a hull and a sail assembly that is mounted to the hull and arranged to be positioned relative to wind which is blowing at an angle to the longitudinal axis of the hull so that the sail develops an aerodynamic force having a lateral aerodynamic force component and a forward aerodynamic force component. The lateral aerodynamic force component causes list and yaw—the adverse factors affecting sailing vessels. The solution proposed in the present invention is based on analyses of all momentums affecting a sailing vessel; therefore it overcomes the unsolved problems of the prior art by means of utilization of specially positioned above and below the center of gravity of the vessel stationary and pivoted hydrofoils—the object of the present invention—which compensate forces causing wind list and yaw also minimizing roll and pitch.
The scheme of sailboat of the preferred embodiment of the present invention is shown in
The sail assembly is or may be of conventional design, and as shown on
As shown on
The hydrofoils 6, 7, 8, 9, 10, 11, 12 and 13 are placed below vessel's waterline and hydrodynamically profiled to provide a carrying power, wherein the hydrofoils 6, 10 and 8, 12 provide upward lifting forces and the hydrofoils 7, 11 and 9, 13 provide downward forces. This arrangement of the hydrofoils of the preferred embodiment together with the hydrofoil shape provides compensation of adverse momentums affecting a sailing vessel equipped with the hydrofoils of the previous art; also, the assembly proposed in the preferred embodiment of the present invention develops momentum compensating roll and pitch (working as a shock absorber).
Diagram of forces and momentums applied to sailing vessel having biplane hydrofoils of the preferred embodiment is depicted in
The diagram shows that all momentums and lifting forces developed by the hydrofoils compensate each other. Therefore, the arrangement of the symmetrically-positioned biplane hydrofoils proposed in the present invention utilizes hydrodynamic drag forces; it works as a shock absorber to compensate roll and pitch without other dynamic momentums and forces affecting a sailing vessel.
The shock absorption force (hydrodynamic drag) of a hydrofoil depends on surface of the hydrofoils and relative water-hydrofoil velocity.
This force is determined by formula:
F=Cx×s×ρ×V2/2 [1],
where Cx—coefficient depending on shape of hydrofoil (for rectangular flat plate Cx≈1.1), s—projection of the surface of hydrofoil on the plane that is in perpendicular to vector of velocity, V—relative water-hydrofoil velocity, ρ—density of water.
When a yacht rolling, vector of water-foil velocity is lying on tangent to circumference having the center in C.G; so projection of the surface of hydrofoil on the plane that is in perpendicular to vector of velocity can be calculated by the formula:
s=S×cos β [2],
β—angle between radius connecting C.G to geometrical center of the foil and horizontal plane of the yacht (see
S—hydrofoil surface.
For periodical roll with amplitude of A (maximal movement of the foil about horizontal plane) and period T, the force will be approximately determined by the following formula:
F=4π2×s×ρ×A2/T2 cos2(2πt/T).
According to this formula, this drag force is a periodical function. Amplitude and mean value of the force—Fa and Fm respectively—applied to the hydrofoil will be determined by the formulas:
Fa=4π2×s×ρ×A2/T2 and Fm=1/2Fa=2π2×s×ρ×A2/T2.
Thus, mean value of momentum developed by the single foil can be determined by approximate formula:
Mm=2π2×(a−L)×s×ρ×A2/T2 [3],
where a—½ of wing (foil) span, L—width of the foil.
Therefore, all 8 foils of this assembly will produce the compensating momentum of 8 Mm.
As an example, if amplitude of pitch is 1 m and period of the pitch is 10 sec, the single hydrofoil having surface of 0.5 m2 produces the amplitude of the resistance force Fa of 2200 N or 440 lbs; the mean value of this force producing by all hydrofoils will be about 1,760 lbs (800 kg), and mean value of the momentum determined by formula [3] (for large racing yacht with B=28 ft) will be about 24,600 lbs-ft (3,300 kg-m).
The hydrofoils of the present embodiment can be additionally profiled in such a way that plane of each foil is bent and have shape of “seagull wing” as depicted in
The hydrofoils of the present embodiment can be utilized in “combined yachts”—yachts jointed together in the process of utilization of old-model yachts. The scheme of such yachts and position of the hydrofoils on the hull of such yachts are shown on
The hydrofoil assembly of this embodiment comprises two pairs of rows of hydrofoils—upper and lower ones—positioned in biplane manner, wherein upper rows (left and right) are positioned on both sides of the yacht above and below yacht's C.G on equal distances from said C.G. Each row contains three hydrofoils—front 43, middle 44 and rear 45, wherein the middle foil 44 is positioned in the place where the two hulls 41 and 42 are jointed. This position of hydrofoils allows compensating momentum bending yacht's hull that is important in the case of high pitch. The solution of this embodiment becomes even more efficient when the hydrofoils are pivoted and computer-controlled ones as described below in the following embodiment.
Description of the Second Variant of the Preferred Embodiments of the Present Invention Biplane Assembly of Partially Submerged Hydrofoils Counteracting Vessel's ListThe static hydrofoil assembly of the first variant of the previous embodiment can stabilize a sail boat in the cases of roll and pitch, but does not compensate wind and turn lists and yaw. This problem can be solved by means of a static hydrofoil assembly arranged in such a way that one of upper foils can be partially submerged (or completely out of water) when a sailing vessel is heeling over. In this case momentums generated by upper foils do not compensate each other and the resulting momentum is applied in opposite direction to the momentum generated by lateral wind so compensating wind list.
Scheme of hydrofoil assembly and diagram of forces and momentums applied to sailing vessel having biplane hydrofoils of this embodiment is depicted in
As was noted above, the conventional way of yacht stabilization is the hydrostatic one utilizing heavy keel, when C.G. of the yacht is positioned maximally below waterline. In the case, when a yacht is heeling over, the center of buoyancy (C.B.) of the yacht is shifted horizontally about its center of gravity (C.G.) on the distance named Righting Arm (G.Z.), so hydrostatic forces provide momentum compensating yacht's list and pitch. Even though exact calculation of G.Z is difficult, for small angle of list the hydrostatic compensating momentum can be defined by the approximate formula:
Mh=Disp×G.Z=Disp×sin φ×(b+δ) [4],
where:
(b+δ)—distance from waterline to C.G.,
Disp—displacement (weight of the yacht),
φ—angle of roll (list).
Maximal angle of roll (list) for racing yachts is known as LPS (Limit of Positive Stability). It is the roll angle at which a boat will no longer right itself and become inverted (capsized). All racing yachts is designed for LPS of about 100-120 arc degrees. LPS roll angle is the extreme limit and the practical value of maximal roll (list) can be determined by the condition when yacht's deck touches water. It is approximately described by the formula:
φm=arctan(2h/B) [5],
where:
h—elevation of yacht deck above waterline,
B—yacht's overall beam.
Therefore, for the yacht with LOA (Length Overall) of 141 ft, B (Overall Beam) of 28 ft, D (Draft) of 19 ft, when height of yacht's deck of fully loaded yacht is 5 ft, the maximal list will be about 20 arc degrees.
As depicted in
Height of end of the foil rising above water can be determined by the formula:
H=a−b×(1−cos h)/sin φ−δ/sin φ,
where:
a—½ of wing span of the hydrofoil (wing),
b—distance from C.G to hydrofoil plane,
δ—depth of the hydrofoil plane,
φ—angle of the list.
Dry width of the hydrofoil (width of part of the foil that is out of water), can be determined by the formula:
wdry=a−(b+δ)/sin φ+b/tgφ [6].
The dry width wdry may be larger than real width W of the hydrofoil. It means that all surface of the hydrofoil is above water. When it happens, only hydrofoils, which still in water produce the lifting force and compensating momentum.
For the large racing yacht (mentioned above) with LOA=141 ft, B=28 ft, D=19 ft, which is equipped with hydrofoil assembly of the present embodiment and having depth of the upper wing plane δ=2 ft, distance from C.G to wing plane b=6.7 ft, ½ of wing span of the hydrofoil a 32 14 ft, the possible dry length wdry of the foil determined by formula [6] is shown on the Table 1:
The calculation shows that end of the foil starts going out of water at φ=9 arc degrees.
The lifting force F1 of this foils declines because only part of the foil stills in water, so the lifting force can be determined by the formula:
F1=Fy×(1−wdry/W) [7],
where:
Fy—total lifting force of the underwater foil,
wdry—dry width of the foil,
W—width (lateral dimension) of the foil.
Total lifting force of a wing is determined by the formula:
Fy=Cy×S×ρ×V2/2 [8],
where:
Cy—lifting coefficient,
P—density of media,
V—water-foil velocity,
S—surface of the foil.
Coefficient Cy depends on many factors and can be determined by approximate formulas or by the graphs in textbooks.
For non-profiled foil (thin plate) Cy can be determined by the formula:
Cy=2π×sin α [9],
where:
α—angle of attack.
For airplane-like wing coefficient Cy can be estimated as shown on the Table 2.
Below it is the example of operation of the hydrofoil assembly of the present embodiment dedicated to the large racing yacht mentioned above.
Thus, for single profiled foil having surface of 1.5 m2 the upward lifting force will be about 6,360 N (918 kg of force or 1,890 lbs) at V=10 kt (18.5 km/hour) and α=0.
If two upper foils are dry (>10 arc degree list) and two opposite foils still in water, the total lifting force compensating wind list will be about 1840 kg and produce the compensating momentum of 7730 kg-m. Hydrostatic momentum Mh (see formula [4]) will be around 18,000 kg-m.
Lateral wind of 20 kt (37 km/hour) produces listing momentum of 24,000 kg-m (at SA=400 sq.m. and height of center of wind pressure of 12 m).
Thus, the compensating momentum of the hydrofoils (7,730 kg-m) together with hydrostatic compensating momentum of the yacht (18,000 kg-m) provides total compensating momentum exceeding 25,000 kg-m that can successfully counteract wind listing momentum keeping the yacht at the list not exceeding 10 arc degrees (at mentioned above conditions).
Another example of calculation is dedicated to medium-size Alberg 30 yacht having Displacement=9,000 lbs, LOA=30.2 ft, D=4.2 ft, Beam=8.8 ft and SA=410 sq.ft. Maximal roll (list) will be φm=40 arc degrees (see formula [5]).
For the upper hydrofoils positioned 1.5 ft below waterline, wing (hydrofoil) span of 8.8 ft and the distance from C.G. to wing (hydrofoil) plane of 1 ft (δ=1 ft, a=4.4 ft, b=1 ft, see formula [6]) the value of the dry width wdry of hydrofoil for different angles of the list is shown on TABLE 3.
As Table 3 shows, the hydrofoil with width W=2 ft is completely above water at 28-degree list.
For single profiled foil having surface of 10.8 sq.ft (1 m2) the lifting force will be about 1260 lbs (612 kg) at V=10 kt and α=0.
If the row of two upper foils is dry (>28 arc degree list) and the opposite row stills in water, the total lifting force will be about 1220 kg that produces the compensating momentum of 1610 kg-m. Hydrostatic momentum Mh determined by the formula [4] will be about 1,150 kg-m at list of 28 arc degrees.
Lateral wind of 20 kt (37 km/hour) produces listing momentum of about 2,000 kg-m at SA=410 sq.ft (38.1 m2) and height of the center of wind pressure of 14 ft (4.2 m).
Thus, the hydrodynamic compensating momentum of hydrofoils (1,614 kg-m) together with hydrostatic compensating momentum of the yacht (1,150 kg-m) provides total compensating momentum of 2,764 kg-m that can successfully counteract the wind listing momentum.
At the list angle of 20 arc degrees only part of hydrofoils is involved in wind list compensation. Here, the hydrostatic compensation momentum determined by formula [4] will be about 837 kg-m; and hydrodynamic compensation momentum will be about 1,047 kg-m (at yacht speed of 10 kt.). Totally they provide 1,900 kg-m compensating momentum counteracting wind listing momentum of 2,000 kg-m. Thus, complete compensation will be achieved at list angle of about 21 arc degrees.
Thus, at the list below 15 degrees, the hydrofoils do not works as list compensator, but still working as roll and pitch stabilizer; and list compensation is provided by conventional hydrostatic forces. The lifting force of the hydrofoils starts counteracting listing momentum at list angle of 15 degrees and produce full compensating momentum at list angle of 28 degrees. Therefore, such hydrofoil assembly protects the yacht from the list exceeding 21 degrees. The lower hydrofoils positioned below C.G produce downward lifting force, which stabilizes the yacht.
The hydrofoil assembly can be installed on a yacht when it is on service in a dry dock; the foils can be rigidly mounted on yacht's hull, or the foils can be clipped to a harness that is attached to yacht's hull. The possible position of hydrofoil assembly of the present embodiment on Alberg 30 yacht is shown on
The symmetrical position of the hydrofoils is the preferable one, but for some sailing vessels having shallow C.G and complicated underwater shape it is difficult to keep upper and lower foils on the same distance from C.G. In this case these distances can be different, but lifting forces of upper foils and lower foils have to be equal.
Description of Another Embodiment of the Present Invention Biplane Assembly of Pivoted HydrofoilsUnlike the first embodiment of this invention—biplane assembly of static (non-pivoted) completely submerged (never out of water) hydrofoil members rigidly mounted on the hull above and below C.G.—that can partially compensate roll and pitch, but can not compensate wind list, an assembly of similar pivoted hydrofoils allows compensating all adverse momentums caused by roll, pinch and lateral wind.
The scheme of assembly of the pivoted hydrofoils is depicted in
Here, the assembly of submerged hydrofoils is the similar to one shown on
Thus, the lifting force of the single foil proposed above for Alberg 30 yacht (at yacht speed of 10 kt) will vary from 1260 lbs (612 kg) at α=0 up to 2,900 lbs (1,400 kg) at α=9 degrees. In this case, momentum (in vertical lateral plane) developed by the single foil will vary from 805 kg-m up to 1,850 kg-m respectively; and the lifting force is equal to 0 at the angle of attack of −4.5 degrees.
Also, the foil develops momentum in vertical longitude plane. If each foil is positioned on the horizontal longitude distance of 12 ft from C.G, the foil produces momentum that varies from 2,200 kg-m (α=0) up to 5,060 kg-m (α=9).
In the first embodiment all foils are submerged ones and have pre-installed angle of attack of 0 degree; and upper foils provide upward lifting, whereas the lower foils provide downward lifting force. Thus, such hydrofoil assembly works as a roll compensator, but does not produce any rotating momentum because the momentums developed by the hydrofoils compensate each other.
In the case of pivoted foils, they can produce rotating momentums that can be used to compensate roll, pitch and wind list. For roll and pitch compensation, the foils have to be turned synchronically with movements of yacht's hull, but counteracting them. So, the lifting forces have to be in opposite direction to vector of velocity of yacht's hull.
To compensate wind listing, the foils have to develop rotating momentums counteracting listing momentum caused by wind. This compensation can be estimated for the hydrofoil assembly proposed above for Alberg 30 yacht.
As was noted above, the lateral wind of 20 kt (37 km/hour) produces listing momentum of about 2,000 kg-m at SA=38.1 m2 (410 sq.ft) and height of the center of wind pressure of 4.2 m (14 ft). Hydrostatic compensating momentum of the yacht calculated by the formula [4] is 690 kg-m at 10-degree list. So, the hydrofoil assembly has to develop additional 1,310 kg-m momentum. If the assembly is symmetrical about C.G and the yacht is heeling to left side, the left upper and right lower foils have to be turned on the same angle of attack of 5 arc degrees (see formula [8] and Table 2). It provides additional upward (for upper foils) and downward (for lower foils) forces developing momentum that, together with hydrostatic momentum, compensates the wind list.
Because the lifting forces produced by hydrofoils are dynamic ones that depend on yacht speed (Fγ˜V2), angle of attack of the foils has to be regulated according to the vessel's speed. In the case of low speed when the lifting forces of the mentioned above foils are not enough to compensate the wind list, other hydrofoils can be involved. So (see example above), if the yacht is heeling to left side at low speed, the right upper and left lower foils have to be turned on the negative angle of attack of −4.5 arc degrees (see formula [8] and Table 2) where Cy=0. Hydrostatic compensating momentum of the yacht calculated by the formula [4] is 690 kg-m at 10-degree list. The lateral wind of 20 kt produces listing momentum of 2,000 kg-m. So, the hydrofoil assembly has to develop 1,310 kg-m momentum. At the yacht speed of 5 kt the compensating momentum produced by these four foils (at the same angle of attack of 5 degrees) will be only 327 kg-m that is not enough. So, if the left upper and right lower foils is turned on the angle of attack of 9 arc degrees (see formula [8] and Table 2) and the right upper and left lower foils are turned on the angle of attack of −4.5 arc degrees, the hydrofoil assembly produce rotating momentum of 3,500 kg-m counteracting with the wind list. This momentum will be enough to compensate lateral wind of 28 kt at the vessel speed of 5 kt. Also these hydrofoils (at the angles of attack mentioned above) can compensate lateral wind of 20 kt at the yacht speed of 3 kt.
The pivoted foils of this embodiment can be controlled by electromechanical or hydraulic actuators placed inside of the hull (
Therefore, when the power is on, the electromotor 33 together with foil 32 starts rotating about the shaft 35 in the direction depending on polarity of voltage applied to the electromotor 33.
This hydrofoil-mounted actuator can be also utilized in pivoted “seagull wing” hydrofoils (see
For the accurate compensation of wind list, the actuators have to be computer-controlled ones, wherein the controlling computer 311 has to have information about yacht's speed, wind speed and direction (
If the actuators are fast enough (time response is less than about 2 seconds), this hydrofoil assembly can be utilize to compensate not only the wind list, but also other adverse momentums affecting the yacht, such as roll, pitch and yaw. In this case, the controlling computer has to have additional real-time information about position of the vessel and its dynamic, which can be obtain from onboard gyroscope 314. To achieve fast and reliable response, advanced fuzzy logic expert system and processors can be utilized.
Description of Another Embodiment of the Present Invention Passive Triplane Assembly of HydrofoilsThe scheme of the hydrofoil assembly of the present embodiment is depicted in
The assembly works as follows:
When a yacht is heeling over (for example to left side), the left upper row of foils 26 and 28 enters water providing upward lifting force. The right middle row of the foils 10 and 12 (see
The assembly of the present embodiment is the passive one; it does not require any foil alignment and computer-controlled rotation. This solution allows significantly increasing momentum counteracting wind list that is especially important at the conditions of low yacht's speed. Below is an example of such assembly dedicated to Alberg 30 yacht. For single profiled foil having surface of 10.8 sq.ft the lifting force will be about 1260 lbs (612 kg) at V=10 kt and angle of attack of α=0.
If two upper foils enter in water, the total lifting force compensating wind list will be about 2,690 lbs (1 220 kg) and produce the compensating momentum of 11,820 lbs-ft (1610 kg-m).
If two middle foils are out of water and two opposite foils still in water, the total lifting force compensating wind list will be about 1220 kg and produce the compensating momentum of 1610 kg-m.
Hydrostatic momentum Mh determined by the formula [4] will be about 690 kg-m at list angle of 13 arc degrees, 427 kg-m at 8 degrees and 267 kg-m at 5 degrees. Lateral wind of 20 kt (37 km/hour) produces listing momentum of about 2,000 kg-m at SA=38.1 m2 (410 sq.ft) and height of the center of wind pressure of 4.2 m (14 ft).
Thus, the maximally possible hydrodynamic compensating momentum of hydrofoils (3,200 kg-m) achieved at yacht's speed of 10 kt together with hydrostatic compensating momentum provides the rotating momentum that is well enough for wind list compensation. Because the list momentum and compensating momentum have to be in balance, the upper and middle foils can be partially submerged to provide together with hydrostatics the total value of rotating momentum of 2,000 kg-m.
If the yacht is traveling with lower speed, such as 6 kt, the hydrodynamic momentum of foil assembly will decline to 1,300 kg-m; so the complete compensation of the lateral wind will be achieved when the left foils of upper row are completely in water and the right foils of the middle row are completely out of water.
Optionally, the distance between the upper row and waterline can differ from the distance between the middle row and waterline; so, for example, the right middle foils can leave water at lower list and the left upper foils enters water at higher list. Such solution provides smoother regulation of yacht's position.
Thus, if yacht's list is less than some angle (depending on upper and middle hydrofoils position), the hydrofoil assembly does not work as a list compensator, but still working as roll and pitch stabilizer; here the list compensation is provided by conventional hydrostatic forces. The lifting force of the hydrofoils starts counteracting listing momentum at list angle when the upper foils touch water and middle foils leave water; and the assembly produces full compensating momentum at list angle when the left upper foils are completely in water and right middle foils leave water completely. The lower hydrofoils positioned below C.G produce downward lifting force, which counteracts upward lifting forces (not the momentums) generated by upper and middle hydrofoils so stabilizes the yacht in vertical direction.
Claims
1. A sailboat comprising:
- a displacement hull, a sail assembly mounted to said hull, a keel mounted beneath said hull,
- a one or more submerged hydrofoils mounted on said keel,
- wherein the improvement, which allows said hydrofoils counteracts sailboat roll without adverse momentums, comprises:
- an upper hydrofoil assembly and a lower hydrofoil assembly rigidly mounted on both sides of said hull above and below center of gravity (C.G.) of said sailboat in a biplane manner, wherein said upper hydrofoil assembly consists of a two rows—right and left—containing two or more hydrodinamically profiled hydrofoils each, and said lower hydrofoil assembly consists of a two rows—right and left—containing two or more hydrodinamically profiled hydrofoils each; and said upper hydrofoil assembly generates upward lifting forces, whereas said lower hydrofoil assembly generates downward lifting forces; wherein surfaces of the hydrofoils are equal that allows compensating hydrofoil upward and downward lifting forces so vertically stabilizing said sailboat, compensating yaw momentum and counteracting sailboat roll.
2. The sailboat of claim 1 having the upper hydrofoil assembly of claim 1 and the lower hydrofoil assembly of claim 1 containing two rows of the submerged hydrofoils of claim 1 each, wherein distance between said two rows of the upper hydrofoil assembly of claim 1 and sailboat waterline is low that allows one of said rows of said upper hydrofoil assembly, which is positioned on one sailboat side, rising from water when the sailboat is heeling over, whereas another said row of said upper hydrofoil assembly, which is positioned on opposite side of the boat, stills in water; therefore said hydrofoils that still in water continue producing upward lifting forces, whereas said hydrofoils that completely rise from water do not produces any lifting forces; thus said upper hydrofoil assembly generates rotating momentum counteracting sailboat list, whereas said lower hydrofoil assembly stills generating downward lifting force so stabilizing said sailboat.
3. The sailboat of claim 1 containing the upper and lower hydrofoil assemblies of claim 1 mounted on the sailboat hull in a biplane manner, wherein each of said hydrofoils is a pivoted one driven by a manual or computer-controlled actuator that allows efficiently counteracting all adverse momentum affecting said sailboat; wherein said actuator of each said hydrofoil is mounted inside said hydrofoil and comprises:
- a. a rigidly mounted inside said hydrofoil reversible electromotor having a shaft that is profiled as a worm-gear,
- b. a second shaft rigidly mounted on sailboat hull and supported inside said hydrofoil by bearings, so said hydrofoil can rotate about said second shaft, wherein a part of said second shaft is profiled as a gear that is engaged to said worm-gear; and said second shaft has a channel where an electrical cable is placed that allows feeding said electromotor from a source placed inside sailboat hull; therefore, when the power is on, said electromotor together with said hydrofoil starts rotating about said second shaft in a direction depending on polarity of voltage applied to said electromotor.
4. The sailboat of claim 2 having the hydrofoil assemblies of claim 2, which comprises additional upper hydrofoil assembly consisting of two rows of hydrofoils—a right and a left—positioned above sailboat waterline, so configuration of said hydrofoil assemblies is a triplane containing two rows of upper hydrofoils positioned above sailboat waterline, two rows of middle hydrofoils shallow submerged below waterline and two rows of lower hydrofoils that still submerged at any list angle; therefore, when the sailboat is heeling over, for example, to left side, said left row of said upper hydrofoils goes under water, whereas said right upper row stills above water; said right row of said middle hydrofoils rises from water, whereas said left middle row stills in water; thus, said upper row of hydrofoils that enters water starts producing upward lifting forces, whereas said upper row of hydrofoils that still above water do not produces any lifting forces; said middle row of hydrofoils that stills in water continue producing upward lifting forces, whereas said middle row of hydrofoils that rises from water do not produces any lifting forces; therefore, this configuration of hydrofoil assemblies allows to said upper and middle hydrofoil rows generating momentum strongly counteracting sailboat wind list even at low sailboat speed, whereas said lower rows of hydrofoils still compensating upward lifting force of said upper and middle rows of hydrofoils so stabilizing said sailboat.
5. The sailboat of claim 1 with the hydrofoils of claim 1 having an internal part and an external part each, wherein said external part of each said foil is angled about said internal part of said foil in a manner of “seagull wing”; wherein plane of said internal part passes through sailboat's C.G and plane of said external part is in parallel to horizontal plane of the sailboat; therefore, said internal part of said foil compensates sailboat's roll; and said external part of said foil, which is in parallel to horizontal plane of said sailboat, compensates sailboat's pitch.
Type: Application
Filed: Aug 27, 2009
Publication Date: Mar 3, 2011
Inventor: Eduard Leonidovych Zvenyhorodskyy (Toronto)
Application Number: 12/548,538
International Classification: B63B 39/06 (20060101); B63B 35/00 (20060101);
