SE2050857A1

SE2050857A1 - A hydrofoil vessel

Info

Publication number: SE2050857A1
Application number: SE2050857A
Authority: SE
Inventors: Gustav Hasselskog
Original assignee: Candela Speed Boat Ab
Priority date: 2020-07-06
Filing date: 2020-07-06
Publication date: 2022-01-07
Also published as: SE544119C2; EP4175872A1; WO2022010404A1; SE2051092A1; US20230294797A1; SE544574C2

Abstract

The invention involves a hydrofoil vessel (1) comprisinga hydrofoil assembly (4),- and a hull assembly (2) presenting, when the vessel is floating at rest, a vertical symmetry plane (SP), and a horizontal plane (HP) coinciding with a waterline of the hull assembly (2),wherein the hydrofoil assembly (4) comprises two struts (401) extending from the hull assembly (2) on opposite transverse sides of the symmetry plane (SP), mainly within a respective plane which is parallel to the symmetry plane, or mainly partly away from the symmetry plane and partly downwards when the vessel is floating at rest,wherein each strut (401) comprises a strut foil (402) with a non- symmetrical cross-section, and with a pressure side (402P) facing at least partly towards the symmetry plane, and a suction side (402S) facing at least partly away from the symmetry plane (SP),wherein the hydrofoil assembly (4) comprises two main foil portions (411) each extending from a respective one of the struts (401), towards the symmetry plane (SP) and substantially in parallel with the horizontal plane (HP), and/or towards the symmetry plane and partly towards the horizontal plane (HP), and wherein each main foil portion (411) has a non-symmetrical cross-section, and a pressure side (411P) facing at least partly away from the horizontal plane (HP), and a suction side (411S) facing at least partly towards the horizontal plane (HP).

Description

A HYDROFOIL VESSEL TECHNICAL FIELD The invention relates to a hydrofoil vessel comprising a hydrofoil assembly, and a hullassembly presenting, When the vessel is ﬂoating at rest, a vertical symmetry plane, and ahorizontal plane coinciding with a waterline of the hull assembly. The invention also relates to a hydrofoil set for a hydrofoil vessel.

BACKGROUND In the field of hydrofoil vessels, there has traditionally been two types of hydrofoils. Oneof them is a submerged, or immersed hydrofoil, i.e. a foil that is designed to be fullysubmerged during a cruising mode of the vessel. An immersed foil may have an adjustablepitch orientation so as to change the angle of attack of the adjustable hydrofoil. The other hydrofoil type is a surface piercing hydrofoil.

A known problem with hydrofoil vessels is that the vessel may lean outwards in turns, andbe difficult to operate in high seas. This is the case with both submerged and surfacepiercing hydrofoils. In a hydrofoil vessel with an immersed foil the inherent lack of rollstability creates a challenge. Roll may be defined as a movement around a roll axis whichis substantially parallel to a direction of forward travel of the vessel. The roll axis couldextend within the hull assembly symmetry plane, and it could be substantially horizontal.Where the hull assembly comprises a single hull, the roll movement could be a movementaround an axis which extends from the bow to the stern of the hull. An immersed hydrofoilmay, for the roll stability, be arranged to be controlled so as to present different liftcoefficients, and/or different angles of attack, along the length of the foil, e. g. as described in SE540588C2.

However, there is nevertheless a desire to achieve a good roll stability of hydrofoil vessels.

SUMMARY An object of the invention is to improve the roll stability of a hydrofoil vessel.

The object is achieved with a hydrofoil vessel according to claim 1. Thus, the inventionprovides a hydrofoil vessel comprising a hydrofoil assembly. The vessel comprises a hullassembly presenting, when the vessel is ﬂoating at rest, a vertical symmetry plane, and ahorizontal plane coinciding with a waterline of the hull assembly. The hydrofoil assemblycomprises two struts extending from the hull assembly on opposite transverse sides of thesymmetry plane, mainly within a respective plane which is parallel to the symmetry plane,or mainly partly away from the symmetry plane and partly downwards when the vessel isﬂoating at rest. Each strut comprises a strut foil with a non-symmetrical cross-section, andwith a pressure side facing at least partly towards the symmetry plane, and a suction sidefacing at least partly away from the symmetry plane. The hydrofoil assembly comprisestwo main foil portions each extending from a respective one of the struts, towards thesymmetry plane and substantially in parallel with the horizontal plane, and/or towards thesymmetry plane and partly towards the horizontal plane. Each main foil portion has a non-symmetiical cross-section, and a pressure side facing at least partly away from the horizontal plane, and a suction side facing at least partly towards the horizontal plane.

In embodiments of the invention, the hydrofoil vessel may be a hydrofoil boat. The hullassembly may comprise a single hull. In some embodiments, the hull vessel may comprisea multihull assembly. For example, the vessel may have catamaran or a trimaran hulls. Thevertical symmetry plane, and the horizontal plane may be imaginary. The horizontal plane may coincide with the waterline of the hull assembly when the vessel is ﬂoating at rest.

The strut foils and the main foil portions may be surface piercing. For this, the main foilportions may have cross-sectional shapes, orientations, and dimensions, adapted tominimize or avoid air being sucked down when the main foil portions are under the watersurface, in particular under but close to the water surface, or at the surface. However, in some embodiment the main foil portions may be submerged.

The main foil portions may each extend from a respective one of the struts, towards thesymmetry plane and substantially in parallel with the horizontal plane, and/or towards thesymmetry plane and partly upwards when the vessel is ﬂoating at rest. The pressure side ofeach main foil portion may face at least partly downwards when the vessel is ﬂoating atrest, and the suction side may face at least partly upwards when the vessel is ﬂoating atrest. The main foil portions may extend inwards from distal ends of the respective struts. Insome embodiments however, the main foil portions may be connected to the respectivestruts at a distance from the distal ends of the struts. Each main foil portion may extendinside and/or below the respective strut. The main foil portions may be located below thehull assembly when the vessel if ﬂoating at rest. The non-symmetrical cross-section of each main foil portion may extend substantially fore and aft in relation to the vessel.

The struts may extend substantially within a respective plane which is parallel to thesymmetry plane. The struts may extend downwards when the vessel is ﬂoating at rest,substantially within the respective plane which is parallel to the symmetry plane. In someembodiments, a main extension of the struts may be partly away from the symmetry planeand partly downwards when the vessel is ﬂoating at rest. The strut foils may form therespective struts, or the strut foils may form parts of the respective struts. Preferably, thelength of each strut foil is at least 50%, at least 70%, at least 80%, or at least 90%, of thelength of the respective strut. The non-symmetrical cross-section of each strut foil mayextend substantially fore and aft in relation to the vessel. The strut foil pressure sides mayface at least partly inwards in relation to the hull assembly. The strut foil suction sides may face at least partly outwards in relation to the hull assembly.

The asymmetry of the strut foils creates, when the vessel heels over, a lift force directed atleast partly outwards from the vessel, and in some embodiments partly upwards. The force causes a righting moment, thereby providing roll stabilization, e. g. in rough conditions.

More specifically, by the struts extending from the hull assembly on opposite transversesides of the symmetry plane, mainly within a respective plane which is parallel to thesyinmetry plane, or partly away from the symmetry plane and partly downwards when the vessel is floating at rest, and by each strut foil having a non-symmetrical cross-section a pressure side facing towards the symmetry plane, and a suction side facing away from thesymmetry plane, it is ensured that the strut foils provides a force in relation to the center ofgravity of the vessel, that serves to roll the vessel in a direction which opposes heeling ofthe vessel. Particularly, the strut foils may serve to provide a smallest angle between aresultant hydrodynamic force acting on one of the strut foils, and a vector from the centerof gravity of the vessel to a center of pressure of the hydrodynamic force, which angleserves to rotate the vessel in a direction which is opposite to a heeling direction of thevessel. Said angle may be equal to or greater than 10 degrees, equal to or greater than 20degrees, equal to or greater than 30 degrees, equal to or greater than 40 degrees, or equal toor greater than 50 degrees. The center of pressure of the hydrodynamic force may also be referred to as the point of attack of the hydrodynamic force.

In addition, each main foil portion extending from a respective of the struts, towards thesymmetry plane and substantially in parallel with the horizontal plane, or towards thesymmetry plane and partly towards the horizontal plane, and each main foil portion havinga non-symmetrical cross-section, and a pressure side facing at least partly away from thehorizontal plane, and a suction side facing at least partly towards the horizontal plane,provides an additional force in relation to the center of gravity of the vessel, that serves toroll the vessel in the direction which is opposite to the heeling direction of the vessel.Particularly, the main foil portions may serve to provide a smallest angle between aresultant hydrodynamic force acting on one of the main foils, and a vector from the centerof gravity of the vessel to a center of pressure of the hydrodynamic force, which angleserves to rotate the vessel in a direction which is opposite to a heeling direction of thevessel. Said angle may be equal to or greater than 10 degrees, equal to or greater than 20degrees, equal to or greater than 30 degrees, equal to or greater than 40 degrees, or equal to or greater than 50 degrees.

Thereby, through the combined hydrodynamic contributions of the strut foils and the mail foil portions, a particularly high roll stabilization of the vessel may be provided.

It should be noted that in some embodiments, the hydrofoil assembly may comprise one or more additional struts. The additional struts may have non-symmetrical cross-sections, similarly to the struts described above, or the additional struts may have symmetrical cross-sections.

Preferably, each strut further comprises a major portion and a transition portion, thetransition portion forming a transition from the major portion to the respective main foilportion, wherein the length of the transition portion is no more than 30%, no more than20%, no more than 10%, or no more than 5%, of the length of the respective strut. Thelength of the transition portion may be defined by the length of a trailing edge thereof. Thelength of the strut may be defined by the length of a trailing edge thereof.

By the transition portion, sharp corners between the struts and the main foil portions maybe avoided. Sharp corners may otherwise create a need for reinforcements to avoidstructural damage. A structurally beneficial arrangement may thereby be provided, whilethe hydrodynamic features improving roll stability, are retained. As understood, featurescontributing to the roll stability include the struts extending mainly within a respectiveplane which is parallel to the symmetry plane, or mainly partly away from the symmetryplane and partly downwards when the vessel is floating at rest, and each strut foil having anon-symmetrical cross-section, a pressure side facing towards the symmetry plane, and asuction side facing away from the symmetry plane. Each strut foil may be fonned by a respective strut major portion or a part thereof.

The transition portion may be provided at, or form, a distal end of the respective strut. Thetransition portion may be provided as a bend from the strut major portion to the main foilportion. The transition portion may form a smooth transition from the strut major portionto the main foil portion. Specifically, the transition portion may have a radius to form sucha smooth transition. Alternatively, the transition portion may have a straight part, or it may be entirely straight.

In some embodiments, each main foil portion extends to the other of the main foil portions.

Thereby, the main foil portions may form together a main foil. The main foil may extend from one strut to the other of the struts.

Each main foil portion extending to the other of the main foil portions allows a simpleintegration of the main foil assembly with the hull assembly, since the main foil assemblymay be connected to the hull assembly only by the struts. Nevertheless, in someembodiments, each main foil portion extends from a respective of the struts to the hull assembly.

In some embodiments, the main foil portions may extend substantially in parallel with thehorizontal plane. Thereby the main foil may be horizontal when the vessel is at rest.

Thereby, the manufacturing of the main foil may be relatively simple.

However, in some embodiments, the main foils may extend from the respective strut,partly towards the symmetry plane and partly towards the horizontal plane. By suchextensions, partly towards the symmetry plane and partly upwards, the main foil portionsmay be inclined when the vessel is at rest. Thereby, the main foil may present the shape ofan inverted V. In some embodiments, each main foil portion may present an outer inclined part, and an inner horizontal part.

The inclination of the main foil portions may serve to provide a beneficial angle between aresultant hydrodynamic force acting on one of the main foil portions, and a vector from thecenter of gravity of the vessel to a center of pressure of the hydrodynamic force. Morespecifically, by the inclination of the main foil portions, the hydrodynamic force acting onone of the main foil portions may be brought closer to being perpendicular to the vectorfrom the center of gravity of the vessel to the center of pressure of the hydrodynamic force.

Thereby, the vessel righting effect of the force may be high.

Preferably, the strut foils each extend substantially within a respective plane which isparallel to the symmetry plane. Thereby, the struts, or at least the strut foils thereof, mayextend vertically as seen in the direction of travel of the vessel. In a side view of the vessel,the struts, or at least the strut foils thereof, may extend vertically, or in a non-zero angle to a vertical direction.

Where the struts, or at least the strut foils thereof, extend substantially within a respectiveplane which is parallel to the symmetry plane, the hydrofoil assembly may be relativelysimple to manufacture, in particular where the main foil portions extend substantially inparallel with the horizontal plane. The struts may be fixed to the hull assembly at lateraledges thereof. Thereby the hydrofoil assembly may have a horizontal main part fonned bythe main foil, and two vertical parts, formed by the struts, connecting the horizontal part with the hull assembly.

Preferably, the strut foils and the main foil portions are fixed in relation to the hullassembly. The strut foils and main foil portions are preferably surface piercing foil.Thereby, the strut foils and main foil portions can go in and out of the water without sucking down air and loose lift.

Preferably, the vessel comprises, in addition to the hydrofoil assembly, an adjustablehydrofoil having an adjustable pitch orientation so as to change the angle of attack of theadjustable hydrofoil. The adjustable hydrofoil may be, compared to the hydrofoilassembly, further away from the horizontal plane. The adjustable hydrofoil may be, when the vessel is ﬂoating at rest, below the hydrofoil assembly.

The adjustable hydrofoil may be arranged to be submerged at speeds when the hullassembly is lifted out of the water. At such speeds also the hydrofoil assembly may belifted out of the water. The angle of attack control allows control of the vertical position ofthe adjustable hydrofoil. The adjustable hydrofoil may, for the roll stability, be arranged tobe controlled so as to present different lift coefficients, and/or different angles of attack, along the length of the adjustable hydrofoil foil.

Problems with known hydrofoils include a submerged foil typically being most efficientwithin a rather small speed range, due to the need to provide a compromise between agood take-off performance and a good cruising performance. Another disadvantage with asubmerged hydrofoil is that it can lose lift in high seas due to ventilation, causing the vessel to suddenly drop down. A surface piercing hydrofoil has a problem of an overall low efficiency.

In embodiments of the invention, the main foil portions will provide, in addition to theadjustable hydrofoil, a lifting force at relatively low speeds of the vessel. This will allowfor a relatively small propulsive force, and hence a relatively small engine or motor, fortaking off from a hull displacement state of the vessel, to a foil carried state. In addition, oralternatively, the adjustable hydrofoil may be made relatively small, and hence moreefficient at relatively high speeds. Furthennore, the main foil portions will allow for thevessel to be supported in rough sea by giving it extra lift when the hull assembly tends tofall down into the water. In addition, a slow speed rough sea mode is made possible, wherethe vessel runs on the adjustable hydrofoil and the main foil portions, with the hull assembly relatively close to the water.

Thereby, a hydrofoil vessel may be provided with a combination of an immersed foil, anda further foil, achieving, while combining a good high speed performance with a good take-off and high seas performance, a good roll stability of the vessel.

The adjustable hydrofoil may be connected to the hull assembly independently of thehydrofoil assembly, by means of one or more foil holding members. This simplifies the production of the hydrofoil vessel.

The object is also reached with a hydrofoil set according to claim ll, the hydrofoil setcomprising the hydrofoil assembly. Where the hydrofoil set also comprises the adjustablehydrofoil, the adjustable hydrofoil may be adapted to be connected to the hull assembly by means of the one or more foil holding members.

Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS Below, embodiments of the invention will be described with reference to the drawings, in which: - fig. 1 shows a perspective view a hydrofoil vessel according to an embodiment ofthe invention, - fig. 2 shows a side view of the vessel in fig. 1, - fig. 3 shows a view of the vessel in fig. 1 from in front of the vessel, - fig. 4 shows a cross-sectional view with the section oriented as indicated by thearrows IV in fig. 2, - fig. 5 shows a detail in fig. 3, - fig. 6 shows the view of fig. 3, when the vessel is heeling over, - fig. 7 shows a hydrofoil vessel according to an alternative embodiment of theinvention, in a view corresponding to the view in fig. 3, - fig. 8 shows a hydrofoil vessel according to a further alternative embodiment of theinvention, in a view corresponding to the view in fig. 3, - fig. 9 shows a hydrofoil vessel according to another embodiment of the invention,in a view corresponding to the view in fig. 3, - fig. 10 shows a hydrofoil vessel according to a further embodiment of theinvention, in a view corresponding to the view in fig. 3, and - fig. ll shows a hydrofoil vessel according to a yet another embodiment of the invention, in a view corresponding to the view in fig. 3.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Fig. 1 and fig. 2 show a hydrofoil vessel 1. The vessel comprises a hull assembly 2 comprising a single hull.

Reference is made also to fig. 3. The hull assembly 2 presents, when the vessel is ﬂoatingat rest, an imaginary vertical symmetry plane SP, and an imaginary horizontal plane HP coinciding with a waterline of the hull assembly 2.

The vessel comprises an adjustable hydrofoil 301 having an adjustable pitch orientation soas to change the angle of attack of the adjustable hydrofoil. The adjustable hydrofoil 301 is connected to the hull assembly by means of two foil holding members 302. The adjustable hydrofoil 301 may be, as exemplified in fig. 2, in the direction of travel of the vessel 1,located substantially at a center of gravity CG of the vessel.

The vessel also comprises a propulsion arrangement. The propulsion arrangementcomprises a propeller 501. The propulsion arrangement is provided at a stem of the hull. Inthis example, the propulsion arrangement comprises an electric motor in a pod 502. Themotor is arranged to drive the propeller, which is mounted on the pod. The pod is mountedto the hull assembly via a pod carrying element 503. The motor is arranged to be poweredby a power source such as a battery pack 504. The propulsion arrangement may be controlled so as to steer the vessel.

The vessel could be provided with any suitable alternative propulsion arrangement, e. g. comprising an outboard or an inboard engine.

The vessel further comprises an aft foil 601. The aft foil is arranged to support, in ahydrofoil driving mode, an aft part of the hull assembly. The aft foil is mounted to the hullassembly via an aft foil carrying element 503. ln this embodiment, the aft foil carrying element is also the pod carrying element.

The vessel further comprises a hydrofoil assembly 4. As exemplified in fig. 3, theadjustable hydrofoil 301 is, compared to the hydrofoil assembly, further away from thehorizontal plane HP. As exemplified in fig. 2, the hydrofoil assembly 4 may be, in thedirection of forward travel of the vessel 1, located further forward than the adjustablehydrofoil 301. Alternatively, the hydrofoil assembly 4 may be located behind theadjustable hydrofoil 301. As a further alternative, the hydrofoil assembly 4 and theadjustable hydrofoil 301 may be in substantially the same position in the direction of travel of the vessel 1.

The hydrofoil assembly 4 comprises two struts 401 extending from the hull assembly 2 onopposite transverse sides of the symmetry plane SP, mainly within a respective plane which is parallel to the symmetry plane. Each strut 401 comprises a strut foil 402.

As exemplified in fig. 4, each strut foil 402 has a non-symmetrical cross-section, and witha Suction side 402S facing away from the symmetry plane SP, and a pressure side 402P facing towards the symmetry plane.

The hydrofoil assembly 4 comprises two main foil portions 411 each extending from arespective of the struts 401, towards the symmetry plane SP and substantially in parallelwith the horizontal plane HP. Each main foil portion 411 extends to the other of the main foil portions 411. The main foil portions 411 form together a single main foil.

Each main foil portion 411 has a non-symmetrical cross-section, and a pressure side 411Pfacing downwards when the vessel is ﬂoating at rest, and a suction side 411S facing upwards when the vessel is ﬂoating at rest.

The strut foils 402 and the main foil portions 411 are fixed in relation to the hull assembly2. The strut foils 402 and the main foil portions 411 are surface piercing. In someembodiments, the strut foils 402 and/or the main foil portions 411 may be adjustable and/or retractable.

Reference is made also to fig. 5. Each strut 401 further comprises a major portion 403 anda transition portion 404. The transition portion forms a transition from the major portion tothe respective main foil portion 411. The transition portion 404 is provided as a bend fromthe major portion 403 to the main foil portion 411. The transition portion forms a smoothtransition from the maj or portion to the main foil portion. The length Ltp of the transitionportion 404 is preferably no more than 30% of the length Ls of the respective strut. In theexample in fig. 1 - fig. 5, the length Ltp of each transition portion 404 is about 10% of thelength Ls of the respective strut. A trailing edge TE of the hydrofoil assembly is indicatedwith a broken line in fig. 5. The length Ltp of the transition portion may be defined by thelength of a trailing edge thereof. The length Ls of the strut may be defined by the length of a trailing edge thereof.

The adjustable hydrofoil 301 is in the embodiment in fig. 1 - fig. 4 connected to the hullassembly, independently of the hydrofoil assembly 4, by means of the two foil holding members 302. In alternative embodiments, the adjustable hydrofoil 301 may be mounted tothe hydrofoil assembly 4, by means of the one, or more than two, foil holding members 302.

Reference is made also to fig. 6. When the vessel is not heeling over, the strut foils 402may be, depending on the speed of the vessel, above the water, or partly submerged in thewater. When the vessel heels over, one of the strut foils 402 becomes lower than the otherof the strut foils. Thereby, the lower strut foil may be further submerged in water than thehigher strut foil. The lower strut foil may be partly or fully submerged in the water whilethe higher strut foil may be less submerged than the lower strut foil, or above the water.Thereby, the hydrodynamic force will be larger on the lower strut foil than on the higher strut foil.

The orientation of the lower of the strut foils serves to provide a smallest angle ASlbetween a resultant hydrodynamic force Fl acting on the lower strut foil, and a vector Vlfrom the center of gravity CG of the vessel to a center of pressure of the hydrodynamicforce Fl, which is at least 10 degrees, in this example 29 degrees. Thereby, the force Fl will counteract the heeling of the vessel.

Further, when the vessel heels over, one of the main foil portions 411 becomes lower thanthe other of the main foil portions. Thereby, the lower main foil portion may be furthersubmerged in water than the higher main foil portion. The lower main foil portion may thepartly or fully submerged in the water while the higher main foil portion may be lesssubmerged than the lower main foil portion, or above the water. Thereby, thehydrodynamic force will be larger on the lower main foil portion than on the higher main foil portion.

The orientation of the lower of the main foils portion serves to provide a smallest angleAS2 between a resultant hydrodynamic force F2 acting on the lower main foil portion, anda vector V2 from the center of gravity CG of the vessel to a center of pressure of thehydrodynamic force F2, which is at least 10 degrees, in this example 32 degrees. Thereby, the force F2 will also counteract the heeling of the vessel.

Fig. 7 shows an alternative embodiment, which is similar to the embodiment shown in fig.1 - fig. 6, except for the following features: Outer parts of the main foil portions 411 eachextend from a respective one of the struts 401, towards the symmetry plane and partlyupwards when the vessel is ﬂoating at rest. Inner parts of the main foil portions 411 eachextend towards the symmetry plane SP and substantially in parallel with the horizontalplane HP. The outer parts of each main foil portion 411 has a pressure side 41lP facingpartly downwards when the vessel is ﬂoating at rest, and a suction side 41lS facing partlyupwards when the vessel is ﬂoating at rest. The inner parts of each main foil portion 411has a pressure side 411P facing downwards when the vessel is ﬂoating at rest, and a suction side 411S facing upwards when the vessel is ﬂoating at rest.

Fig. 8 shows a further alternative embodiment, which is similar to the embodiment shownin fig. 1 - fig. 6, except for the following features: The main foil portions 411 each extendfrom a respective one of the struts 401, towards the symmetry plane and partly upwardswhen the vessel is ﬂoating at rest. Each main foil portion 411 extends to the hull assembly2. Thereby, the main foil portions may be mounted to the hull assembly. Each main foilportion 411 has a pressure side 411P facing partly downwards when the vessel is ﬂoating at rest, and a suction side 41 1S facing partly upwards when the vessel is ﬂoating at rest.

Fig. 9 shows a further alternative embodiment, which is similar to the embodiment shownin fig. 1 - fig. 6, except for the following features: The struts 401 extend from the hullassembly 2 on opposite transverse sides of the symmetry plane SP, mainly partly awayfrom the symmetry plane and partly downwards when the vessel is ﬂoating at rest.Thereby, the strut foil pressure sides 402P face partly towards the symmetry plane SP, andthe strut foil suction sides 402S face partly away from the symmetry plane SP.

Fig. 10 shows another embodiment, which is similar to the embodiment shown in fig. 1 -fig. 6, except for the following: The vessel does not comprise an adjustable hydrofoil. The vessel comprises a surface piercing hydrofoil assembly.

Fig. 11 shows yet another embodiment. The vessel comprises a hydrofoil assemblycomprising two struts 401 extending from the hull assembly on opposite transverse sidesof the symmetry plane SP, mainly within a respective plane which is parallel to thesymmetry plane. Each strut 401 comprises a strut foil 402. Each strut foil 402 has a non-symmetrical cross-section, and with a suction side 402S facing away from the symmetry plane SP, and a pressure side 402P facing towards the symmetry plane.

The hydrofoil assembly 4 comprises two main foil portions 411 each extending from arespective of the struts 401, towards the symmetry plane SP and substantially in parallelwith the horizontal plane HP. Each main foil portion 411 extends to the other of the main foil portions 411.

Cantilevered foil portions 412 each extend from a respective of the struts 401, away fromthe symmetry plane SP. The cantilevered foil portions 412 extend substantially in parallelwith the horizontal plane HP. The main foil portions 411 and the cantilevered foil portions412 fonn together a single main foil. The main foil has a non-symmetrical cross-section,and a pressure side facing downwards when the vessel is ﬂoating at rest, and a suction side411S facing upwards when the vessel is ﬂoating at rest. The main foil has an adjustablepitch orientation so as to change the angle of attack of the adjustable hydrofoil. The main foil is an immersed hydrofoil.

It is to be understood that the present invention is not limited to the embodimentsdescribed above and illustrated in the drawings; rather, the skilled person will recognizethat many changes and modifications may be made within the scope of the appended claims.

Claims

1. 1. l. A hydrofoil vessel (l) comprising a hydrofoil assembly (4), and a hull assembly (2) presenting, when the vessel is ﬂoating at rest, a verticalsymmetry plane (SP), and a horizontal plane (HP) coinciding with a waterlineof the hull assembly (2), characterized in that the hydrofoil assembly (4) comprises two struts (401)extending from the hull assembly (2) on opposite transverse sides of thesymmetry plane (SP), mainly within a respective plane which is parallel to thesymmetry plane, or mainly partly away from the symmetry plane and partlydownwards when the vessel is floating at rest, in that each strut (401) comprises a strut foil (402) with a non-symmetricalcross-section, and with a pressure side (402P) facing at least partly towards thesymmetry plane, and a suction side (402S) facing at least partly away from thesymmetry plane (SP), in that the hydrofoil assembly (4) comprises two main foil portions (4l l) eachextending from a respective one of the struts (401), towards the symmetry plane(SP) and substantially in parallel with the horizontal plane (HP), and/or towardsthe symmetry plane and partly towards the horizontal plane (HP), and in that each main foil portion (411) has a non-symmetrical cross-section,and a pressure side (4l lP) facing at least partly away from the horizontal plane(HP), and a suction side (4l lS) facing at least partly towards the horizontalplane (HP).

2. A hydrofoil vessel according to claim l, wherein each strut (401) further comprises a maj or portion (403) and a transition portion (404), the transition portion forming a transition from the major portion to the respective main foil portion (4l l), wherein the length of the transition portion is no more than 30% of the length of the respective strut. A hydrofoil vessel according to any one of the preceding claims, Wherein each main foil portion (411) extends to the other of the main foil portions (411). A hydrofoil vessel according to any one of the preceding claims, Wherein the main foil portions (411) extend substantially in parallel with the horizontal plane (HP). A hydrofoil vessel according to any one of the preceding claims, Wherein the strutfoils (402) each extend substantially Within a respective plane Which is parallel to the symmetry plane (SP). A hydrofoil vessel according to any one of the preceding claims, Wherein the strutfoils (402) and the main foil portions (411) are fixed in relation to the hull assembly (2). A hydrofoil vessel according to any one of the preceding claims, Wherein the strut foils (402) and the main foil portions (411) are surface piercing. A hydrofoil vessel according to any one of the preceding claims, Wherein the vesselcomprises, in addition to the hydrofoil assembly (4), an adjustable hydrofoil (301)having an adjustable pitch orientation so as to change the angle of attack of the adjustable hydrofoil. A hydrofoil vessel according to claim 8, Wherein the adjustable hydrofoil (301) is, compared to the hydrofoil assembly, further away from the horizontal plane (HP). A hydrofoil vessel according to any one of claims 8-9, Wherein the adjustablehydrofoil (301) is connected to the hull assembly independently of the hydrofoil assembly, by means of one or more foil holding members (302). A hydrofoil set (301, 302, 4) for a hydrofoil vessel (1) according to any one of thepreceding claims, the hydrofoil set comprising the hydrofoil assembly (4).