Multi-hull vessel

Abstract

 The present invention relates to a multi-hull vessel having two slim, symmetrically placed hulls (1,2) on which are provided two submerged transverse wings or foils (4,5,11) which, at normal running speeds, will contribute to determination of the vessel's draft, trim and movement in all six degrees of freedom. The invention is characterized in that the wings (4,5,11) are positioned below and spaced apart from the plane of the keel (BL) with the aid of downward projecting struts (6,7,12,13), each of said hulls (1,2) being provided with a separate forward wing (4,5) with the aid of a respective controlled strut (6,7) projecting downward from the hull for limited pivotal movement about a vertical axis. The hulls (1,2) are connected at the stern to a common stern wing (11), supported by a rear strut (12,13) projecting downward from each hull. Each of the separate forward wings (4,5) and the stern wing have actuator operated (8) flaps (9). There is described the use of water jet drive, with a water jet intake (14) in the lowermost submerged sections of the rear struts (12,13) that are directed at a slant forwards and downwards in the water.

Description

[0001] The invention relates to a multi-hull vessel having two slim, symmetrically placed hulls on which are provided submerged transverse wings or foils which, at normal running speeds, will contribute to determination of the vessel's draft, trim and movements in all six degrees of freedom.

[0002] The very rapid pace of development in the entire area of high-speed boats, i.e., single-hull boats, hydrofoils, catamarans, air cushion boats, air-cushion catamarans, etc., both for civil and military use, has accentuated the need for higher speed and improved seagoing properties.

[0003] High-speed boats of the type mentioned above have a speed of at least 25 knots and a length of at least 20 meters.

[0004] A vessel that moves in water is subjected to frictional resistance at the wet surface below the water line. With increasing speed for the vessel, the friction produced by the movement of the hull through the water continues to increase until a limit is reached where the frictional forces will impose a practical limitation on attainment of a higher speed. The propulsion energy for the vessel increases accordingly.

[0005] A second important factor in addition to speed which affects the vessel's efficiency is the vessel's capability of retaining so-called trim. Trim is the condition the vessel is designed to assume when it is stationary. For displacement vessels this will vary to a high degree with the vessel's speed through the water. For practical reasons it is convenient that the deck, equipment, etc., should retain substantially the same relationship to the horizontal, both when the vessel is stationary and when it is underway.

[0006] A steadily increasing demand for higher speed also for larger boats has led to the development of a more or less planing hull. In practice, however, planing hulls are suitable only for relatively small craft. The planing surfaces on the hull will cause the vessel to lift up in the water when the speed increases.

[0007] The wet surface area is reduced, thereby also reducing the frictional resistance. This may entail a quite substantial reduction in resistance. There will always remain, however, a considerable area of wet surface, with attendant resistance, and here the trim limitations will also play a role in a negative sense. As the speed increases, also the water flowing along even very streamlined planing surfaces will be subjected to friction. The friction increases with the speed, and will lead to limitations in the attainable level of speed. The greatest disadvantage of planing vessels, however, is the pressure exented beneath the bottom of the boat in a seaway; this pressure may be very high, resulting in powerful movements in the vessel. Under particularly unfavorable conditions it may also result in damages to the hull itself.

[0008] In recent decades the development of hydrofoil boats and catamarans, in particular, has accelerated rapidly. Characteristic of hydrofoils is that they are provided with support wings, in the same manner as airplanes, which support wings will provide a lifting power when moved through the water; the boat hull itself will thereby finally be lifted up from the surface of the water, and the hydrofoil will then "fly" over the water surface at its cruising speed.

[0009] Multi-hull vessels, e.g., catamarans, are based on the concept that each of the hulls may be designed in such manner as to take into consideration the hydrodynamic conditions that are important, while the hydrostatic considerations can be accommodated by an appropriate separation of the hulls. This possibility does not exist for single-hull vessels, since the hydrodynamic and hydrostatic conditions must be accommodated by the same hull, thereby giving rise to conflicts with respect to selection of the main parameters. There have also been attempts to use the tunnel between the catamaran hulls to provide a certain lifting force, utilizing the air stream pressed through the tunnel when the catamaran is in motion. A major advantage of multi-hull vessels is their high stability.

[0010] It is only natural that in the course of further development there have been suggested various combinations of hydrofoil boats and catamarans, i.e., vessels having a catamaran hull on which are provided submerged transverse wings fore and aft which, at cruising speed, determine the draft and trim of the vessel. The intention here is to be able to combine the excellent stability properties of the catamaran with the technology of the hydrofoil, so that on high speed the catamaran hulls would be lifted up from the water and the hydrofoil catamaran would thus "fly" over the water surface, and on lower speeds or a full stop it would then behave like a conventional catamaran.

[0011] The higher speed with which a hydrofoil catamaran could operate, however, creates several problems of both of an operational and structural character, which will be further elucidated below.

[0012] According to the invention, therefore, there is proposed a multi-hull vessel having two slim, symmetrically placed hulls on which are provided submerged transverse wings or foils which, at normal cruising speed, will control the movement of the vessel about both a longitudinal and a transverse axis, as well as in the vertical direction, characterized in that the wings are positioned below and spaced apart from the plane of the keel with the aid of downward projecting struts, each of said hulls being provided with a separate forward wing with the aid of a respective controlled strut projecting downward from the hull for limited pivotal movement about a vertical axis, and each hull being connected at the stern to a common stern wing, supported by a rear strut projecting downward from each hull.

[0013] Through both theory and trial it has been proven favorable to have a smaller aspect ratio (the ratio between the length and chord of a wing) for the front supporting surfaces, since this means that a given trim angle produces greater lifting power on stern wings than on the forward wings, thus contributing toward reducing this trim angle. By dividing the front supporting surface into two parts, this advantage is further accentuated. These parts may be realized as two independent support surfaces or wings, each supported by its own limited, pivotable strut. The separate struts with their associated support wings will be capable of advantageously accommodating loads/strains resulting not only from possible collision with floating objects, but also the impacts from the sea and accelerational forces. A normal angular deflection would be in the range of ± 5° and maximum ± 10°, then with shock-absorbing effect, precisely for the purpose of sustaining varying loads. In normal operation, these 5° would not be exceeded. In reality, the front struts will function as front rudders. Such front rudders do per se introduce an instability into the system, but the fact that they are controlled and pivotable makes it possible to incorporate these front rudders into the vessel's overall balance system thereby achieving an effective steering function.

[0014] The controlled, limited pivotal movement of the forward struts may also be utilized advantageously with regard to speed in curves, thus being beneficial not only for the vessel's balance problems in a straight course. To drive the new vessel in an advantageous manner in curves, one combines rolling and rudder, i.e., one gives the boat roll in order to give it swing.

[0015] The swing radius may be reduced considerably because the front struts are pivotable. Use of separate forward wings, each connected to its own hull, solves a strength-related problem since the global torsional forces will not be transferred to the slim, hgdrodgnamicallg designed struts and wings. A particular advantage of having two separate struts and wings is that in the event of a breakdown in one of the strut/wing units, the vessel could maintain its position and thus "fly on three points". In addition, short struts may contribute toward reduced load/strains.

[0016] For vessels of the type referred to here, which operate at high speed, it is important to be able to control the vertical movement. One achieves this in an advantageous manner by means of the common support surface or wing at the stern, which serves to influence/regulate the lift at the rear. Actuator operated wing flaps on stern wings will improve the wings' mode of operation. At the same time, the common rear supporting surface will effectively provide a safeguard against the feared -- if exaggerated -- danger of the hulls' breaking apart, a danger which to the degree it exists is most evident at the stern.

[0017] It is particularly advantageous, according to the invention, for each of the separate forward wings to have an actuator operated (steered) flap. By this means, it is possible advantageously to influence the lifting effect of the forward wings, and to reduce the hydrodynamic resistance and attain increased rolling and pitching stability. Provision of wing flaps both forward and aft will, to a high degree, improve the vessel's movements in the sea. The actuators may to advantage be placed in the transitional area between strut and wing. (Shorter and more efficient transferral path for the forces).

[0018] At cruising speed it is intended that the vessel's hull will be lifted up and lie just above the undisturbed water surface. The propulsive force in this connection may advantageously be provided by means of water jet aggregates, having high efficiency, and it is suggested in this connection, according to the invention, that the water jet intakes be placed in the respective lowermost submerged sections of the rear struts. It is particularly advantageous that the rear struts be forward-directed, i.e., that they slant downwards and forwards in the water. The combination of the water flow channel in the strut with a strut configuration favorable to flow is made possible by the fact that the vessel according to the special features mentioned above is able to move low above the water surface. Thus it is possible for the danger of inward suction of air during operation in the sea to be reduced to nearly zero, because the water intakes are situated as deep as possible down in the sea, at the same time as the forward-directed configuration of the struts provides for favorable water flow, with minimal velocity change from intake to water jet outlet.

[0019] According to the invention, it is advantageous to mount each rear strut in the associated hull with the aid of an adaptor frame. This is a structural solution that is particularly advantageous when the hull is of aluminum, or another material having low module of elasticity, because an adaptor frame, e.g., made of steel, will provide for secure attachment of the respective rear struts to the hull, effectively incorporating the prevailing forces.

[0020] Further, according to the invention, each hull may to advantage have a so-called "step", in the bottom of the rear section. Such steps serve to provide a gentle transition with respect to the pressure gradients which on a more conventional hull would have resulted in negative pressure effects and vertical forces in those situations where the rear part of the hull is partly in and partly above water. With the steps it is possible, in fact, to reduce the force of bouyancy step by step, or to raise the stern step by step in a gentle manner. As is known, a stern has an inherent tendency to dig itself down into the water as velocity increases, until reaching the planing speed.

[0021] The invention and its advantages will be explained in more detail with reference to the drawings, where:

Fig. 1

shows a side view of a catamaran according to the invention,

Fig. 2

shows the catamaran in Fig. 1 seen from the front,

Fig. 3

shows the catamaran seen from the rear,

Fig. 4

shows a bottom view of an adaptor frame, and

Fig. 5

shows a schematic section of a rear hull section, where the adaptor frame in Fig. 4 is placed.

[0022] The catamaran shown in Figs. 1-3 has two catamaran hulls 1,2 extending down from a center, common hull bridge member 3. Each of the catamaran hulls 1,2 is designed with a sharp, pointed bow, and the water lines are very slim, with a high bottom raising angle, particularly in that part of each hull furthest forward.

[0023] Each hull 1,2 is provided at the front with a separate, transverse symmetrical forward wing 4,5 with the aid of a respective downward projecting strut 6,7. Each such strut 6,7 is in suitable manner (not shown) pivotably mounted about a vertical axis and each strut is, in this regard, connected with its own actuator 8. The actuator is designed so as to be capable, in normal operation, of imparting to the associated strut 6 or 7 a guided pivotal movement of ± 5o about said vertical axis, at the same time having the possibility of dampening an externally caused pivotal movement of the strut over an angular area of ± 10°.

[0024] Each of the forward support wings 4,5 has a trim flap 9 provided at the rear edge thereof. For controlled movement of flap 9 there is positioned in the lower part of the strut an actuator (not shown in more detail) in a housing 10 which forms the lower part of the respective struts 6 and 7. Each support wing 4,5 is transversely symmetrical about the longitudinal center plane through each of the provided struts 6,7 and has an expanse in width equal to B.

[0025] Each hull 1,2 is provided at the stern thereof with a common stern wing 11, supported by a downward projecting strut 12,13 from each hull 1, 2, and also having controlled wing flaps, as mentioned above for the forward wings. The two rear struts 12, 13 are, as shown, designed to slant downwards and forwards. This configuration was chosen because each rear strut 12, 13 is, in addition to its strut function, also utilized advantageously as a water jet intake. Thus, in the respective lowermost submerged section of each rear strut 12, 13, there is formed a water jet intake 14 through which water may flow in a uniformly curved conduction channel 15 in the strut and up to a respective water jet aggregate 16 in the stern end. The water jet aggregate 16 is designed in a manner known per se and, in this respect, comprises an impeller with a power source 17 connected thereto.

[0026] Each rear strut 12, 13 is securely fastened to the associated hull 1, 2, respectively, via an adaptor frame 14. In the embodiment example the catamaran hulls 1, 2 are made of aluminum. The rear struts 12, 13 (as well as the front separate support wing struts 6, 7) are of steel, and the attachment of the rear struts in the respective hulls is facilitated considerably by use of such an adaptor frame; see, in addition to Fig. 1, also Figs. 4 and 5. The adaptor frame is of steel and is fixedly secured in hull 1 (Fig. 5), with an intermediate layer of a suitable lining/smoothing material 19. Rear strut 13 is also made of steel and is attached to the adaptor frame. This adaptor frame will solve in excellent manner the problem of attachment/adaptation between the hull and rear strut. The adaptor frame is, of course, designed with a suitable opening 20 adapted to the water flow channel 15 in rear strut 13, for conduction of water through the water jet propulsion system.

[0027] In Fig. 1 are drawn in the catamaran's water line VL and base line BL. It is apparent that when the catamaran is stationary its water line will be VL. When starting up and with gradually increasing speed, the catamaran hulls 1, 2 will lift up and finally run totally free, i.e., they will lie above the undisturbed water line, with their base line BL. Each of the hulls 1, 2 are provided in the stern section thereof with steps 21, 22, which will be of advantage with respect to the hulls' necessary transition between displacement position and flying position, and which will therefore enable a more precise use of the control forces. Both during ascent and descent the steps 21, 22 will contribute toward providing gentle transitions with respect to bouyancy/lift.

[0028] The invention is shown and described above as a catamaran. The catamaran embodiment is considered the best practical embodiment, but the invention may of course also be realized with, e.g., three hulls, i.e., with a central third hull. As indicated by the dotted line in Fig. 3, the rear wing may be provided with an extra central strut.

Claims

1. A multi-hull vessel, having slim, symmetrically placed hulls (1,2) on which are provided submerged transverse wings or foils (4,5,11) which, at normal running speeds, will contribute to determination of the vessel's draft, trim and movement in all six degrees of freedom, said wings (4,5,11) being positioned below and spaced apart from the plane of the keel (BL) with the aid of downward projecting struts (6,7,12,13), and said hulls (1,2) being connected at the stern to a common stern wing (11), supported by a downward projecting rear strut (12,13) from each hull,
characterized in that each of the said hulls (1,2) is provided with a separate forward wing (4,5) with the aid of a respective controlled strut (6,7) projecting downward from the hull for limited pivotal movement about a vertical axis.

2. The multi-hull vessel according to claim 1,
characterized in that each of the separate forward wings (4,5) has an actuator operated (8) flap (9).

3. A multi-hull vessel according to claim 1,
characterized in that the stern wing has actuator operated flaps.

4. A multi-hull vessel according to claim 2 or 3,
characterized in that the actuators (8) are placed in the transition between strut and wing.

5. The multi-hull vessel according to claim 1, 2, 3 or 4, and having water jet operation (16), characterized by a water jet intake (14) in the respective lowermost submerged sections of the rear struts (12,13).

6. A multi-hull vessel according to claim 5,
characterized in that each rear strut (12,13) slants downwards and forwards in the water and comprises a water flow conduction channel (15) from the water jet intake (14) and up to the water jet aggregate (16) provided above.

7. A multi-hull vessel according to claim 5 or 6,
characterized in that each rear strut (12,18) is attached to the associated hull (2,1) by an adaptor frame (18).

8. A multi-hull vessel according to claim 7,
characterized in that between the adapter frame (18) and the associated hull (1,2) is provided an intermediate layer/smoothing material (19)

9. A multi-hull vessel according to one of the preceding claims, characterized in that one or more hulls (1,2) has (have) a step (21,22) in the bottom of the stern section thereof.

Drawing