The present invention relates to a foil arrangement for boats or ships as well as to a hull of a boat or a ship, a rudder and the boat or ship itself.

Especially for motor-powered boats, it has been common for decades that boats may be fully lifted out of the water by hydrofoils. However, experimental sailboats on hydrofoils were developed more than 50 years ago. Progress in material technology and especially carbon composite materials allowed new designs so that foiling sailboats with many configurations are available on the market now.

There are following common configurations for boats on hydrofoils:

1. 1. system of fixed foils (or pivotable foils) like engine-powered boats with multiple fixed foils, often used as ferry boats.
2. 2. small powerboat with front and rear foil
3. 3. multihull sailboat with foil construction outside the hulls
4. 4. monohull sailboat with foil construction outside the hull which may be taken out of the water by rotation.

Recent developments include the so-called T-foils, which have symmetrically provided the typical shape of a L or J and extend from the hull in a perpendicular direction, L- or J- foils connected to a respective hull of a multihull sailboat, as well as L- or V- foils on both sides of a monohull sailboat.
Further there are straight foils whose angles can be adjusted by hydraulic jam during sailing.

The US 3,561,388 discloses a hydrofoil trimaran adapted to be supported fully by hydrofoils. The hydrofoil construction is non-movably fixed to the hulls of the trimaran.

The US 7,644,672 B2 teaches a monohull sailing vessel having a lifting hydrofoil for improving the performance of the monohull sailing vessel. The foil is movably connected to the hull between a towed position and a deployed position in which the hydrofoil extends from one side of the hull.

In the US 20110259254 A1 a tri-foil sailboat is described having retractable hydrofoils with independently adjustable angles of attack. The two forward hydrofoils are adapted to have extendable sections at least partially retractable into said monohull.

However, when using foils on sailboats, some problems still exist, namely when the wind is not constant, sometimes the boats are faster without the foils. Therefore, the foils should be retractable. Second, side forces on the sails are high, giving a considerable heeling moment on the boat. Therefore, if two foils on each side of a boat or on each hull of a catamaran are used, the lifting forces shall be different on each side. This can be resolved either by changing the angle of attack of the foil or by partially or fully retracting one of the foils.

The possibility of fully or partially retracting the foils is the key to performance. This is realized either by a pivotable concept which, depending on the pivot axis, might only work when the boat is not moving. Alternatively, the retracting is done by allowing the foils to slide in a casing. Most L- or J- foil solutions allow the foil to slide in a casing in order to at least partially retract it.

One solution of the problem is to fully retract the foils. For this purpose, the foils are guided on bearings to allow a bended part of the foil to slide through.
However, there are some disadvantages to this solution, too.

The cross section of the foils should be as thin as possible for performance reasons. Thus, the foils are structurally very challenging to engineer and build, as no supporting strut can be applied to the foil without restricting the sliding ability in the casing. This makes the construction complicated and quite expensive.
In order to be guided firmly in a casing, the foil should have a constant cross-section. However, the bending forces vary along the profile, requiring a larger cross-section in many places along the profile than structurally required.
Thus, the problem to be solved by the present invention is to provide a foil arrangement allowing high performance together with the ability to be retracted easily.

This problem is solved by the subject-matter of the independent claim 1 claiming a foil arrangement, as well as independent claims 12, 13 and 14 claiming a hull, a rudder and a boat or a ship comprising the foil arrangement.

As a first aspect of the invention, a foil arrangement is provided, comprising at least one foil section having a wing profile which extends along a flow direction and comprising a connection section connected to the foil section along a connection direction, wherein the connection direction extends angularly to the flow direction and the connection section is adapted to be mechanically fixed in a movable way, so that the foil arrangement is rotatorily and/or translationally movable relative to a hull of a boat or ship. The foil arrangement comprises a stiffening element connecting the foil section and the connection section to each other so that the foil arrangement has a closed hollow profile.

The wing profile has a cross section showing the typical shape of a profile producing a lifting effect when deflecting a flow. For instance, the cross section may have the shape of an NACA profile. The wing profile or the cross section showing the typical wing profile extends along the direction of attack. The connection direction extends angularly and in particular transversal to the direction of attack on the foil section. The connection section can be adapted to be mechanically fixed in a movable way in a rigid clamping installed in a hull of a boat or of a ship.

However, the invention is not restricted to a foil arrangement having the wing profile merely in the foil section. The wing profile may also be provided in the connection section so that depending on the position of the connection section and/or of the hull connected to the foil arrangement also at least a region of the connection section may function as a hydrofoil.

The closed hollow profile is defined perpendicularly to the flow direction or direction of attack, wherein when the closed hollow profile is shown by lines a closed polyline is provided.

Due to the stiffening element, a bending moment applied to the foil section is not merely transmitted by the connection section into a bearing, but by the connection section as well as by the stiffening element. That is, not only the connection section is loaded by the bending moment but also the stiffening element so that there is an additional element on which the bending element is applied. Thus, the load applied onto the connection section is reduced. As a result, the foil arrangement has a better bending stiffness than common foil constructions. In turn, the connection section is provided with a quite small geometrical moment of inertia. Thus, the connection section is quite thin. Hence, the cross section of the connection section may be adapted to the cross section of the foil section so that the connection section may also have the shape of a profile producing a lifting effect when deflecting a flow. This leads to more flexibility for the user regarding the position of the foil section and the connection section, respectively. That is, also the connection section and/or transition regions between the actual foil section and the connection section may be used as a foil.

Additionally, the foil arrangement according to the invention having the same or nearly the same cross section can be manufactured with less effort and expense. Furthermore, there are no stress peaks because there are no steps between the sections.

The connection section can be connected to a first end of the foil section by a first connection section end, and the stiffening element can be connected to a second end of the foil section, positioned opposite the first end of the foil section, so that the closed profile comprises the second end of the foil section.

Further, the connection section can be connected to a first end of the foil section by a first connection section end, and the stiffening element can be connected to a second connection section end, positioned opposite the first connection section end, so that the closed profile comprises the second connection section end.

Preferably, the connection section is non-linear formed. That is, the connection section is non-linear formed in a direction transverse to the flow direction. The stiffening element is provided to bypass or to bridge the curve of the foil section.

In a special embodiment, the connection section is curved so that the connection section comprises a first subsection connected to the foil section and a second subsection connected to the first subsection, wherein the subsections form an angle of 80° to 130°. Preferably, the first and second subsections are connected to each other by a curved third subsection. Therefore, the foil section having a longitudinal extension extending in a longitudinal direction, and the second sub section form an angle of 80° to 130°, in particular an angle of 90° to 100°. Thereby, the longitudinal extension is defined in an area of the foil arrangement having the typical cross-section of a wing that is in the foil section.

In order to allow reversible opening of the closed profile, the foil arrangement comprises at least one separating unit. By means of the separating unit the foil arrangement can be opened and closed for installation and/ or maintenance reasons.

Furthermore, the foil arrangement may comprise at least one winglet positioned between the foil section and the stiffening element. That is, the foil arrangement can be profiled and shaped in a way to provide a wingtip-type device to improve the fluid dynamic efficiency of the main foil.

Also, a pre-tension may be applied in the foil arrangement. As the peak force is located at the point where the foil comes out of a bearing fixing the connection section, a pre-tension or pre-bending in the foil arrangement can be applied to counteract the working bending forces. This can be implemented by pressing the opposite ends of the foil section and the connection section apart from each other when mounting the stiffening element between them. By doing this, a static pretension load can be applied to the foil arrangement, which may at least partially counteract the bending moment at the critical point.

Preferably, the foil section is made of one or a combination of the following materials:

• Carbon composite which may be locally reinforced with titanium; high performance fibre composites, glass composites, aluminum, steel and wood.

The stiffening element is made of one or a combination of the following materials: Carbon composite, high performance fibre composites, glass composites, aluminum, steel, and wood.

Fittings and connecting pieces are preferably made of carbon composite, titanium, stainless steel and/ or aluminum, wherein also alternative materials as high performance fibre composites, glass composites, steel, wood, or any mix of these materials may be used. It is pointed out that the named materials may be combined with Aramid (Kevlar), PBO, spectra, dyneema and/ or vectran (liquid crystal polymers).

In another embodiment, the foil arrangement at the connection section comprises a fixation means for mechanical fixation of the foil arrangement. That is, the foil arrangement can be fixed by the fixation means to or on a hull of a boat or ship.

The fixation means can be a rigid clamping allowing movement of the foil arrangement along the longitudinal direction of at least one part of the connection section. The movement can be carried out along the first, the second and the third subsection of the connection section. Dependent on the shape of the foil section and/ or the shape of the connection section, the movement can be carried out along the foil section. In order to allow the movement, the rigid clamping is provided with rolls pressing onto the connection section as well as a brake fixing the position of the connection section between the rolls.

Here, the stiffening element may be formed and positioned to bypass the fixation means.

The invention provides a foil arrangement having a stiffening element as a structural reinforcement by a construction going from the top part of the foil arrangement, passing outside of a hull connected to the foil arrangement, to a point on the lower part of the foil arrangement.

The foil arrangement remains almost fully retractable, but the structural loads acting on the main parts are significantly reduced and distributed more equally along the profile, thus allowing a smaller cross section of the profile.

A further topic of the invention is a hull of a boat or a ship, comprising at least one foil arrangement according to the invention. However, the invention is not restricted to foil arrangements running through the hull, but the foil arrangement can be fixed by a support mounted to the hull.

Additionally, a rudder is provided, comprising a foil arrangement according to the invention, wherein the rudder is rotatably mountable on a boat or a ship. Here, the foil section is essentially mounted horizontally to respective connection sections positioned at both ends of the foil section. In this case, the connection sections likewise function as respective stiffening elements.

Preferably, the rudder has a triangular shape with a horizontal foil section provided between two perpendicular or tilted parts acting as the connection sections and stiffening elements.

A further aspect of the invention is a boat or ship having at least one hull and/ or at least one rudder according to the invention. The invention is not restricted to monohull boats or ships but can be easily applied also on multihull boats or ships. Here the structural reinforcement can pass outside the respective hull, but also inside the platform on the space between the hulls.

The foil arrangement or the rudder is fixed to a hull of the boat or the ship by means of the fixation means.

The invention is further illustrated by the following examples and figures, from which further embodiments and advantages can be drawn. These examples are meant to illustrate the invention but not to limit its scope.

The following is shown in the figures:

• Fig. 1: a diagram showing the bending moment in dependence of the span,
• Fig. 2: a boat 100 having a hull 70 with two foil arrangements 1,
• Fig. 3: a boat 100 on which both foil arrangements 1 are fully retracted,
• Fig. 4: a boat 100 having a recess 71,
• Fig. 5: a foil arrangement 1 having a winglet 50,
• Fig. 6: a diagram showing the bending moment in dependence of the span when pre-tension is applied,
• Fig. 7: a boat 100 comprising a rudder 80.

Figure 1 shows in a diagram the bending moment in dependence of the span fs of a common foil (dashed line) as well as of a foil arrangement according to the invention (continuous line) when the foil arrangement is fully lowered into the water and loaded. Here it is obvious that the bending moment bm in the arrangement according to the invention is much smaller than the bending moment bm in a common foil. In particular, there is a significant reduction of the bending moment over almost the whole foil span and a large reduction of the peak bending force at the exit of the bearing.

Figure 2 shows a boat 100 having a hull 70 on which two foil arrangements 1 are fixed by means of fixation means 60. The respective foil arrangement 1 comprises a foil section 10, having a wing profile extending along the direction of the flow direction 11 which is essentially perpendicular to the extension direction of the foil section 10. Along a connection direction 21 a first end of the foil section 12 is connected to a first connection section end 22 of a connection section 20 of the foil arrangement 1. On the opposite side of the first connection section end 22 the connection section 20 comprises a second connection section end 23 which is connected to one end of a stiffening element 30 connecting the connection section 20 to the foil section 10. The stiffening element 30 is connected to a second end of the foil section 13. Thus, a foil arrangement 1 is provided showing a closed hollow profile.

The connection section 20 is bent, wherein a first subsection 24 of the connection section 20 extends in an angle 27 with respect to a second subsection 25 of the connection section 20, wherein the first subsection 24 is connected to the foil section 10 via the first end of the foil section 12 and the second subsection 25 is connected to the stiffening element 30 via a separating unit 40. The first subsection 24 and the second subsection 25 are connected to each other by a third subsection 26 which is curved.

The foil arrangement 1 is fixed by a fixation means 60 provided at the hull 70 of the boat 100. The fixation means allows for a movement of the foil arrangement 1 along the longitudinal direction 28 of at least one part of the connection section 20.

In order to realize the movement, the fixation means 60 comprises a (not depicted) rigid clamping provided with rolls pressing onto the connection section 20 as well as a brake fixing the position of the connection section 20 between the rolls. In figure 2, the left foil arrangement 1 is in a fully lowered position. Here, the stiffening element 30 extends through a recess 71 provided in the hull 70. The right foil arrangement 1 is slightly retracted.

In figure 3 a boat 100 is shown on which both of the foil arrangements 1 are fully retracted so there is nearly no water contact.

Figure 4 shows a boat 100 with a hull 70 provided with a recess 71 permitting the straight stiffening element 30 to pass.

However, as shown above, the connection section 20 can be curved near the second connection section end 23 to pass along the original hull shape without touching it in any position.

Figure 5 shows a special embodiment of the foil arrangement 1, having a winglet 50 provided between the second end of the foil section 23 and the stiffening element 30.

Another extreme configuration may be a fully circular, oval or any closed shaped foil arrangement 1. This embodiment allows to choose which part of the foil arrangement 1 having different profile or curvature along the foil section 10 and/or the connection section 20 is inside the water.

Further, the foil section 10 may have a curved form.

Figure 6 shows in a diagrame the bending moment in dependence of the span fs of a common foil (dashed line) as well as of a foil arrangement according to the invention (continuous line) when the foil arrangement is fully lowered into the water and when a pre-tension is applied to a foil arrangement according to the invention. The upper dashed line represents a loaded common foil without pre-tension, the continuous line represents a loaded foil arrangement according to the invention without pre-tension, the dotted line represents an unloaded common foil with pre-tension and the lower dashed line represents a loaded foil arrangement according to the invention with pre-tension.

In figure 7 a boat 100 is shown which additionally to the foil arrangements 1 comprises on the sides of the hull 70 a rudder 80 at the stern. The rudder 80 comprises one or two foil sections 10 extending essentially horizontally. The respective foil section 10 is fixed to a connection section 20 which in this case has the function of a stiffening element 30 as well as a rudder blade, too. This rudder 80 therefore has structural advantages, and the horizontal foil sections 10 provide a natural wingtip and improve the aerodynamic efficiency of the rudder 80. Foil arrangement 1 foil section 10 flow direction 11 first end of the foil section 12 second end of the foil section 13 connection section 20 connection direction 21 first connection section end 22 second connection section end 23 first subsection 24 second subsection 25 third subsection 26 angle between the first subsection and the second subsection 27 longitudinal direction 28 stiffening element 30 separating unit 40 winglet 50 fixation means 60 hull 70 recess 71 Rudder 80 boat 100 foil span fs bending moment bm