Stabilizing foils for a hydrofoil craft

Abstract

 A hydrofoil (11) is provided on an underwater portion thereof with rolling preventing movable flaps (17) projecting from the hydrofoil approximately at right angles therewith. Each of the movable flaps (17) is turnable about a rod (25) extending in the direction of the projection.

Description

[0001] The present invention relates to a hydrofoil craft. Fig. 1 shows a hydrofoil craft heretofore known. The hydrofoil craft is adapted to travel with its hull 2 lifted clear of the water by the dynamic lift generated by a hydrofoil 1. The craft is so constructed as to reduce rolling when subjected to the force of waves or like external force during the foilborne operation. More specifically, when the craft, while travelling stably in an upright position relative to the water surface A shown in Fig. 1, is inclined clockwise in the drawing by rolling as represented by a water surface B, a larger portion of the hydrofoil 1 is sub- . merged on the right-hand side of the drawing than on the left side. This causes the hydrofoil 1 to generate a lift force F1, which exerts a counterclockwise restoring or righting moment M1 on the hull 2 to restore the hull 2 to the original upright position. A foilborne- operation movable flap attached to the rear edge of the front hydrofoil 1 may also be operated to increase the righting moment M1. However, since the lift force F1 acts perpendicular to the hydrofoil 1, the distance between the line L1 of action of the force and the center of gravity G, namely, the arm al of the righting moment M1, is small, and the righting moment is therefore small relative to the lift force. The horizontal component F3 of the lift force F1 further drifts the craft sidewise. When the movable flap on the hydrofoil 1 is operated to increase the righting moment M1, a malfunction of the flap or the control means therefor, if occuring, renders the craft unoperable in foilborne condition.

[0002] An object of the present invention is to provide a hydrofoil craft involving a greatly reduced likelihood of rolling and comfortable to board.

[0003] The hydrofoil craft of the invention has rolling preventing movable flaps projecting from an underwater portion of a hydrofoil thereof approximately at right angles with the foil, each of the movable flaps being turnable about a rod extending in the direction of the projection. With the hydrofoil craft of the present invention, the movable flap for preventing rolling is controlled to a suitable angle to generate a lift force in this portion to give a righting moment. Since this righting moment is added to the righting moment of a lift force usually generated by the hydrofoil, an increased overall righting moment is available. Further because the rolling preventing movable flap is projected from the hydrofoil approximately at right angles thereto, the line of action of the lift force generated in this portion is approximately parallel to the foil, thus lengthening the righting moment arm, with the result that a great righting moment can be obtained from a relatively small lift force. This' greatly mitigates the rolling of the craft and gives greatly enhanced comfort to the passenger. The sidewise horizontal component of the lift force generated in the conventional hydrofoil is offset by the sidewise horizontal component of the lift force generated in the movable flap, so that the craft can be prevented from drifting sidewise. This also renders the craft more comfortable to board. Further because the vertical component of the lift force generated in the flap portion is small, the craft can travel, for example, with the aid of the rudder in the event of a malfunction of the flap or the control means therefor.

[0004] It is desirable that the hydrofoil be provided with fixed fins in addition to the rolling preventing movable flaps. The flaps can then be easily attached to the hydrofoil which has a relatively small thickness by utilizing the fixed fins for supporting the flaps. Other features of the present invention will become apparent from the following description.

Fig. 1 is a front view showing a conventional craft;

_Fig. 2 is a front view showing a first embodiment of the invention;

Fig. 3 is a perspective view of the same;

Fig. 4 is an enlarged view partly broken away and showing the main portion of Fig. 3;

Fig. 5 is a front view of a front hydrofoil showing another embodiment of the invention;

Fig. 6 is a front view of a front hydrofoil showing another embodiment of the invention;

Fig. 7 is a front view of a front hydrofoil showing another embodiment of the invention;

Fig. 8 is a front view of a front hydrofoil showing another embodiment of the invention;

Fig. 9 is a front view of a front hydrofoil showing another embodiment of the invention; and

Fig. 10 is a front view of a front hydrofoil showing still another embodiment of the invention.

[0005] Fig. 3 shows a surface-piercing hydrofoil craft, which is provided with a front hydrofoil (front foil) 11 and a rear hydrofoil (rear foil) 12 below its hull 10. Movable flaps 13 the same as those already known for foilborne travel are attached to and continuous with the rear edges, of oppposite slanting portions of the front foil 11. Propellers 14 and a rudder 15 are mounted on the rear foil 12. The craft is equipped with a rolling preventing system. This system consists essentially of a pair of opposite fixed fins 16 secured to the lower side of the front foil 11, a pair of opposite rolling preventing movable flaps 17 attached to the rear side of the fixed fins 16 individually, a pair.of opposite hydraulic cylinders 18 disposed in the interior of the front foil 11 for driving the flaps, a pair of opposite valve panels 20 connected to the hydraulic cylinders 18 by hydraulic ducts 19 individually, a control panel 22 connected to the valve panels 20 by signal lines 21, and a rolling sensor 24 connected to the control panel 22 by a signal line 23. The fixed fins 16 which are arranged symmetrically with respect to the center line of the craft, are secured to the slanting portions of the front foil 11 which are to be submerged at all times so as to project from the lower side of the front foil 11 at right angles thereto. Although unillustrated, brackets are attached to the rear end of each fin 16. A movable flap support rod 25 at right angles to the front foil 11 is rotatably supported by the brackets. The movable flap 17 is attached at its front end to the rod 25 and positioned at right angles to the front foil 11. The upper end of the flap support rod 25 extends into the front foil 11 and has a tiller 26 fixed thereto. A connecting rod 28 for interconnecting the tiller 26 and the rod 27 of the hydraulic cylinder 18 is pivoted at its opposite ends to the forward ends of the tiller 26 and the rod 27. The rod 27 of the hydraulic cylinder 18, when reciprocatingly moving forward and backward over a predetermined distance, reciprocatingly turns the movable flap 17 through a predetermined angular range. When stopped at a desired position, the rod 27 holds the flap 17 at an angle corresponding to that position. Although not shown, the front foil 11 is internally provided with an angle sensor for detecting the angle of the movable flap 17 by detecting the position (displacement) of the rod 27 or the angle (amount of rotation) of the tiller 26. The angle sensor is connected to the corresponding valve panel 20 by a signal line.

[0006] Each valve panel 20 is provided, for example, with a servo valve (not shown) and disposed within the hull 10 at a suitable location, for example, under the floor. Although unillustrated, a movable flap driving hydraulic pump to be driven by the main machine of the craft is connected to the valve panel 20.by_.a hydraulic duct. The control panel 22 is provided with a computer, etc. and disposed in the pilothouse of the hull 10. The rolling sensor 24 is disposed at a suitable location, for example, under the floor of the pilothouse. The hydraulic ducts 19, the signal lines 21,23, are arranged within the front foil 11 and the hull 10 at suitable locations.

[0007] When the start button (not shown) on the control panel 22 is manipulated, the rolling preventing system functions automatically, automatically controlling the angle of the movable flaps 17 to reduce the rolling of the craft as will be described below. The rolling sensor 24 detects the rolling of the craft to deliver a signal to the computer housed in the control panel 22. The computer calculates the angle of -each movable flap 17 to reduce the rolling and feeds an-angle command signal to the valve panel 20. In accordance with the command from the computer and the output from the angle sensor for the movable flap 17, the servo valve of the valve panel 20 controls the amount of oil to be fed to the hydraulic cylinder 18 from the hydraulic pump so that the flap 17 is turned to the angle calculated by the computer. Thus the flap 17 is controlled to the proper angle to mitigate the rolling.

[0008] The function of the rolling preventing movable flap 17 will be described in detail with reference to Fig. 2.

[0009] When the craft, while cruising stably in an upright position as represented by the water surface A in Fig. 2, is inclined clockwise in the drawing owing to rolling as represented by the water surface C, the angle of each flap 17 is so controlled that a lift force F2 acting obliquely rightward in the drawing will be generated -in the flap portion, whereby the hull 10 is subjected to a counterclockwise righting moment. At the same time, the inclination of the hull 10 produces a difference in the submerged area between the opposite sides of the hydrofoils 11 and 12. Consequently, as is the case with the conventional hydrofoils, a lift force F1 is generated in the foils 11 and 12, exerting a counterclockwise righting moment on the hull 10 in the drawing. The righting moment of the lift force F1 generated in the foils 11,12 and the righting moment of the lift force F2 generated in the movable flaps F7 combine to give a great righting moment M2, which restores the hull 10 to the initial position. Furthermore, the line L2 of action of the lift force F2 generated in the flap 17 is parallel to the front foil 11 to lengthen the arm a2 of the righting moment, so that a great righting moment can be obtained from a relatively small lift force. Meanwhile, experiments have shown that the rolling preventing system is most effective for reducing marked rolling at the resonance (tuning) point of rolling and waves, greatly decreasing the rolling angle at the resonance point to render the craft very comfortable to board. Moreover, the sidewise horizontal component of the lift force F1 generated in the foils 11 and 12 is offset by the sidewise horizontal component of the lift force F2 in the movable flap 17 to prevent the craft from rolling. This also gives enhanced comfort to the passenger.

[0010] Any method suited to the craft is usable for controlling the angle of the movable flap 17 by the control panel 22.

[0011] The rolling preventing movable flap 17 is usable also as a rudder. When the flap is coupled to the usual rudder 15 attached to the rear foil 12, the craft can be steered with improved efficiency.

[0012] The arrangement of the fixed fins 16 and the rolling preventing movable flaps 17 can be modified suitably, for example, as shown in Figs. 5 and 6.

[0013] With reference to Fig. 5, a pair of opposite fixed fins 16 is secured to the lower side of a front foil 11, and a movable flap 17 is turnably attached to the lower end of each fin 16.

[0014] With reference to Fig. 6, a pair of opposite fixed fins is secured to the upper side of a front foil 11, while movable flaps 17 are turnably attached to the lower side of the front foil 11 in corresponding relation to the fins 16. The fixed fins 16 can be disposed below the movable flaps 17 in reverse relation to the arrangement shown in Fig. 6.

[0015] Although the front foil 11 is provided with the fixed fins 16 and the rolling preventing movable flaps 17 in the foregoing embodiments, an equivalent effect will be also achieved if the turnable movable flaps 17 only are provided on the upper or lower side of the front foil 11 at suitable locations, for example, as shown in Figs. 7 to 10.

[0016] While the fixed fin 16, the movable flap 17 and the turning rod (support rod 25) for the flap extend from the front foil 11 at right angles thereto according to the foregoing embodiments, these members may be slightly inclined sidewise relative to the front foil 11. To increase the righting moment of the lift force F2 to be generated in the movable flap 17 to the greatest possible extent, it is desirable that the axis of rotation of the movable flap 17 extent through, or in the vicinity of, the center of gravity G of the craft. The number of the fixed fin 16, as well as that of the movable flaps 17, is suitably variable.

Claims

1. A hydrofoil craft comprising a hydrofoil (11) having an underwater portion, characterized by movable flaps (17) projecting from the underwater portion of the hydrofoil (11) approximately at right angles with the foil, each of the movable flaps being turnable about a rod (25) extending in the direction of the projection.

2. A hydrofoil craft as defined in claim 1, characterized in that the hydrofoil (11) provided with the movable flaps (17) is a front hydrofoil.

3. A hydrofoil craft as defined in claim 1 or 2, characterized in that the movable flaps (17) are provided on the lower side of the hydrofoil (11).

4. A hydrofoil craft as defined in claim 1 or 2, characterized in that the movable flaps (17) are provided on the upper side of the hydrofoil (11).

5. A hydrofoil craft as defined in one of the preceding claims, characterized by fixed fins (16) and movable flaps (17) for preventing rolling, the fins and the flaps projecting from an underwater portion of a hydrofoil (11) approximately at right angles with the. foil.

6. A hydrofoil craft as defined in claim 5, characterized in that the hydrofoil provided with the fixed fins (16) and the movable flaps (17) is the front hydrofoil (11).

7. A hydrofoild craft as defined in claim 5 or 6, characterized in that the fixed fins (16) are provided on the lower side of the hydrofoil immediately in the rear of the fixed fins.

8. A hydrofoil craft as defined in claim 5 or 6, wherein the fixed fins are provided on the lower side of the hydrofoil (11) and the movable flaps (17) are provided at the lower ends of the fixed fins (16).

9. A hydrofoil craft as defined in claim 5 or 6 wherein the fixed fins (16) are provided on the upper side of the hydrofoil (11) and the movable flaps (17) are provided on the lower side of the hydrofoil under the fixed fins.

10. A hydrofoil craft according to one of claims 5 to 9, characterized by two symmetrically arranged fixed fins (16) and movable flaps (17) positioned in the transition area between a central horizontal portion and opposite slanting portions of the front.foil (11), respectively.

Drawing