WO2020234456A1

WO2020234456A1 - Sail

Info

Publication number: WO2020234456A1
Application number: PCT/EP2020/064283
Authority: WO
Inventors: Anders HAUGEN
Original assignee: Tvibit As
Priority date: 2019-05-22
Filing date: 2020-05-22
Publication date: 2020-11-26
Also published as: NO20190661A1

Abstract

There is disclosed a structural device for placement within a double-skin of a double-skin propulsive device having an external shape of an airfoil or a hydrofoil for adjustment of the external shape of the double-skin. The structural device comprises an internal structure having a leading edge and a trailing edge and an attachment device that is attached to the leading edge of the internal structure and extends outwards from the internal structure and, when the internal structure is placed within the double-skin, through the double-skin for attachment to a holding device located externally of the propulsive device such that the internal structure is rotatable relative to the holding device and the double-skin whereby the external shape of the double-skin is adjustable.

Description

SAIL

The present invention is related to a structural device, a propulsive device comprising a plurality of structural devices and a propulsive system comprising one or more propulsive devices.

Sails on modern sailboats function as single skin airfoils taking advantage of the Bernoulli principle to create a fluid suction area across the foil and thereby a force for moving forward. The same principles and natural laws that govern aircraft flight, govern a wind-propelled vessel.

It is believed that for any given airfoil size, a double-skin air foil more similar to an aircraft wing will produce more thrust and less drag than a single skin airfoil normally used on most sailboats. Eltringham (2004:44) discusses the theoretical implications for such a notion on large yachts and concludes that“for the entire range of results the thrust force of a double luff wing sail is just under half that of the heeling force. The heeling force of conventional sails is between three and four times the thrust force”.

Many researchers and vessel airfoil propulsion projects have widely discussed and tested out the possibility of producing a double-skin wing shaped airfoil for gained thrust on vessels. Two of the most successful are The Vestas Sail Rocket, the world’s fastest wind propelled vessel, and the AC 70 Americas Cup racing catamaran. Both use double-skin air foils to create propulsion. The AC 70 Americas Cup boats can tack, i.e. turn its bow through the wind and sail equally fast with the wind on both port and starboard side. The AC 70 air foil cannot be reefed and needs a huge mobile crane to change sail. The Vestas sail Rocket can only sail in one direction.

Several initiatives have been launched for wind powering of commercial ships. Neither the Sky sail (with a kite for propulsion) nor the Ecoliner (with a set of modern square sails) has proved commercially successful. There has not been a large-scale wing sail initiative, presumably because until now the wing sail technology has been perceived unsuitable to propel commercial shipping.

One tackable double-skin airfoil is presented in US patent application

2013/0233229 Al, wherein the airfoil has internal rigid structures enabling mirroring of the airfoil and therefore enabling tacking of the vessel.

Another way of designing a tackable double skin airfoil is presented in WO

03039948 Al. This publication discloses a complicated design with a predominantly horizontal rotational device constituting most of the leading edge of the foil, moving and bending battens in an inner casing with many moving parts. Yet another double-skin tackable airfoil is presented in US patent 7,114,456 B2.

This has rotating inner ribs much like the present invention, but 7, 114,456 B2 have serious faults and drawbacks. First, the outer skin of the airfoil will not able to stretch tight over the ribs due to the fact that the skin is tightened around the whole airfoil with no way of loosening and tightening the skin during tack. Since the ribs are set in an angle of 90 degrees or more to each other (a steeper angle is not possible due to the internal mast), the distance between the outer boundaries or edges of the two ribs will be longer than the width of the rib (according to

Pythagoras' theorem). A tight outer skin will not permit this, and it is therefore doubtful that this patent will create a working tackable airfoil. The internal mast is in itself a hindrance for this invention.

Furthermore, none of the above mentioned airfoils can be hoisted on a conventional sailboat without removing or seriously altering the mast and rigging. They all have internal vertical structures making a conventional mast obsolete. The removal of the mast is, however, not particularly advantageous since the airfoils with an inner vertical structure is unsupported (US patent 7, 1 14, 456 B2) or without spreaders (the AC 70 rigid airfoil). Unsupported masts will have to be many times bigger, stronger and more expensive. The owner will have to choose only one means of propulsion on a sailboat; either conventional sails or a double-skin airfoil. Changing sail setup will need a large crane and the changing of masts and rigging.

In US 4,074,646 A a hydrofoil is disclosed having a variable foil keel. This also has an internal vertical structure that are needed to change the shape of the foil.

Thus, there is a need for a double-skin airfoil which can be hoisted on any conventional sailboat since a double-skin airfoil produces more thrust and less heeling force than present single skin sails. Said double-skin airfoil would preferably be able to tack and it should be reefed, packed and trimmed much like a single skin sail.

Hence, an object of the present invention has been to create a double-skin airfoil or hydrofoil that can be hoisted on any conventional sailboat.

Another objective of the present invention has been to create a double-skin airfoil or hydrofoil that can be tacked, trimmed, reefed and packed much like a fully battened single skin sail.

Furthermore, a further object of the present invention has been to provide more effective wind powered propulsion on any vessel, including but not limited to leisure boats and commercial ships.

These objects are achieved with a propulsive device as defined in independent claim 1 and a propulsive system as defined in claim 9. Further preferred embodiments of the propulsive device are defined in the dependent claims 2-8, and the propulsive system in dependent claims 10-11.

Hence, according to the present invention there is provided a structural device for placement within a double-skin of a double-skin propulsive device having an external shape of an airfoil or a hydrofoil for adjustment of the external shape of the double-skin. The structural device comprises an internal structure having a leading edge and a trailing edge and an attachment device that is attached to the leading edge of the internal structure and extends outwards from the internal structure, and when the internal structure is placed within the double-skin, through the double-skin for attachment to a holding device located externally of the propulsive device such that the internal structure is rotatable relative to the holding device and the double skin whereby the external shape of the double-skin is adjustable.

However, a person skilled in the art would know that the attachment device, instead of being attached to the leading edge of the internal structure, could be attached to the trailing edge of the internal structure in order to allow for adjustment of the external shape of the double-skin.

The double-skin may be made of a flexible or foldable material such as a canvas or other types of materials that are sufficiently strong and non-elastic to stand the loads during use of the propulsion device. For example, sailcloth used in

conventional sails may be used in the double-skin in many embodiments of the present invention. Alternatively, the double-skin may also be made of a hard material such as metal plates and/or wooden panels.

The structural device may be a substantially rigid device or a device that has at least one or more parts that are at least to some degree elastic. With the exception of a part of the attachment device that extends out of the double-skin of the propulsive device, the structural device is arranged within the double-skin, i.e. on the inside of the double-skin. The attachment device is attached to the leading edge of the propulsion device and extends out of the double-skin of the propulsive device and is preferably connected to a holding device arranged externally of the propulsion device. The attachment device is preferably passed through a dedicated opening for the attachment device in the double-skin.

The leading edge of the internal structure preferably corresponds to the leading edge of the propulsive device in which it is arranged. Similarly, the trailing edge of the internal structure preferably corresponds to the trailing edge of the propulsive device in which it is arranged.

The leading edge and the trailing edge are well known features of an airfoil-shaped or hydrofoil-shaped device, such as the present invention. The leading edge should therefore be understood herein as the front part of the propulsive device that first meets air or water in use and the trailing edge should be understood herein as the rear part of the propulsive device where airflow or waterflow separated by the leading edge rejoins. It should be noted that the leading edge should be understood to comprise the entire front part of the internal structure and the propulsive device that faces the airflow or waterflow, and not just the frontmost “line” or“edge” of the internal structure and the propulsive device.

The relative rotatability between the internal structure within the double-skin of the propulsive device and the holding device located externally of the propulsive device can be provided in various ways. In one embodiment the attachment device may be rotatable relative to the internal structure. In another embodiment the attachment device may be fixedly attached to the internal structure and the attachment device is adapted to be rotatably attached to the holding device. In a further embodiment the attachment device may be provided with internal rotatability such that the internal structure can be rotated relative to the holding device when the attachment device is attached to the holding device.

Hence, preferably the attachment device is:

- rotatable relative to the internal structure, and/or

- fixedly attached to the internal structure and adapted to be rotatably attached to the holding device, and/or

- provided with internal rotatability such that the internal structure can be rotated relative to the holding device when the attachment device is attached to the holding device.

The structural device is preferably rotatable about a rotational axis that is co-axial with a longitudinal axis of the attachment device.

The attachment device can obviously have many different designs. In a preferred embodiment, the attachment device is bolt-shaped with a longitudinal axis that is co-axial with the rotational axis of the attachment device.

The internal structure may comprise a first section and a second section that are attached to each other forming an internal angle larger than 0° and smaller than 180° between the first section and the second section. The first section is preferably attached to the second section along corresponding longitudinal edges on the first section and the second section, forming an attachment edge, such that a cross- section along the attachment edge of the internal structure is generally V-shaped.

Preferably the first section and the second section fixedly attached to each other, i.e. the internal angle between the first section and the second section is fixed. Furthermore, the first section and the second section are substantially flat-shaped, i.e. the first section and the second section are substantially plate-shaped.

Alternatively, the first section and the second section may be adjustably attached to each other, i.e. the internal angle between the first section and the second section is adjustable. The first section may for example be connected to the second section with a hinge device that allows the internal angle to be adjusted. Preferably, there is further provided one or more locking devices that allows the internal angle between the first section and the section to be locked at a desired internal angle.

The first section may be made of a first plate element and/or the second section may be made of a second plate element. The first plate element and the second plate element may be provided with one or more through-going holes or may simply be made without through-going holes.

In another embodiment of the structural device according to the present invention, the two sections are attached to each other with the leading edge and the trailing edge arranged in opposite directions, i.e. the leading edge of the first section is located and attached to the trailing edge of the second section and the trailing edge of the first section is located at the leading edge of the second section. The first section is attached to the second section along the attachment edge forming a cross- section that is generally V-shaped. This design of the internal structure allows for interchanging of the leading edge and trailing edge of a propulsion device are provided with structural devices having this design. By rotating the structural devices in the propulsion device, the leading edge of the propulsive device will become the trailing edge and vice versa. The airfoil-shaped or hydrofoil-shaped propulsive device will not only tack, but also interchange the leading edge and trailing edge as the structural devices rotates relative to the holding devices that the structural devices are attached to.

In another embodiment of the internal structure, the internal structure is

substantially flat-shaped, i.e. the internal structure is substantially plate-shaped. In this embodiment, the internal structure may comprise one section only.

In an embodiment, the internal structure may comprise:

- a first beam element that is substantially straight and has a leading edge end and a trailing edge end,

- a second beam element that is curved and has a leading edge end and a trailing edge end,

- a third beam element that is curved and has a leading edge end and a trailing edge end,

where the leading edge ends of the first beam element, the second beam element and the third beam element are attached to each other, and the trailing edge ends of the first beam element, the second beam element and the third beam element are attached to each other. For example, the leading edge end and the trailing edge end of the first beam element can be attached to the leading edge end and trailing edge end of the second beam element respectively, forming a first section of the internal structure. Furthermore, the leading edge end and the trailing edge end of the first beam element can be attached to the leading edge end and trailing edge end of the third beam element respectively, forming the second section of the internal structure.

As mentioned above, the internal angle between the first section, i.e. the plane in which the first beam element and the second beam element lie, and the second section, i.e. the plane in which the first beam element and the third beam element lie, is preferably larger than 0° and smaller than 180°. The first section is preferably attached to the second section along corresponding longitudinal edges on the first section and the second section, forming an attachment edge, such that a cross- section along the attachment edge of the internal structure is generally V-shaped.

The internal structure may also comprise at least one spreader element that extends between and is attached to the first beam element and the second beam element. The internal structure may further comprise at least one spreader element that extends between and is attached to the first beam element and the third beam element.

As indicated above, the first beam element and the second beam element may be arranged so that they lie in substantially the same plane. The first beam element and the third beam element may be arranged so that they also lie in substantially the same plane.

In an embodiment of the present invention, the at least one spreader element attached to the first beam element and the second beam element may have an adjustable length and/or the at least one spreader element attached to the first beam element and the third beam element may have an adjustable length. Thereby the curvature of the first beam element and/or the curvature of the second beam element and/or the curvature of the third beam element can be adjusted. The length may be made adjustable for example by using piston/cylinder arrangements.

In another embodiment, the internal structure may comprise:

where the leading edge end and the trailing edge end of the first beam element are attached to the leading edge end and trailing edge end of the second beam element respectively. The internal structure may further comprise at least one spreader element that extends between and is attached to the first beam element and the second beam element. Preferably the first beam element and the second beam element lie in substantially the same plane. Thereby the internal structure may be considered to be formed by a single section.

The at least one spreader element attached to the first beam element and the second beam element has an adjustable length and/or wherein the at least one spreader element attached to the first beam element and the third beam element has an adjustable length, whereby the curvature of the first beam element and/or the curvature of the second beam element and/or the curvature of the third beam element can be adjusted. The length may be made adjustable, for example by using piston/cylinder arrangements.

The internal structure preferably has an external shape that is substantially airfoil shaped or hydrofoil-shaped, i.e. a longitudinal section through the internal structure is substantially airfoil-shaped or hydrofoil-shaped and provides the propulsive device with its airfoil-shape or hydrofoil-shape when the internal structure is placed within the double-skin of the propulsive device.

As indicated above, in an embodiment of the structural devices the two sections of each structural device may be attached to each other with the leading edge and the trailing edge arranged in opposite directions, i.e. the leading edge of the first section is located and attached to the trailing edge of the second section and the trailing edge of the first section is located at and attached to the leading edge of the second section. The first section is attached to the second section along the attachment edge forming a cross-section that is generally V-shaped. By rotating the structural devices in the propulsion device, the leading edge of the foil will become the trailing edge and vice versa. The airfoil-shaped or hydrofoil-shaped propulsive device will not only tack, but also interchange the leading edge and trailing edge as the structural devices rotates relative to the holding devices that the structural devices are attached to. The same embodiment of the structural device may also be rotated so as only to change direction of the foil, without tacking.

According to the present invention, there is also provided a propulsive device having a double-skin and an external shape of an airfoil or a hydrofoil, the propulsive device comprising a plurality of structural devices comprising respective internal structures that are placed within the double-skin for adjustment of the external shape of the double-skin. The internal structures have a leading edge and a trailing edge, and the structural devices comprises respective attachment devices that are attached to the leading edge of the structural devices and extend outwards from the structural devices and through the double-skin for attachment to respective holding devices that are located externally of the propulsive device and support the propulsive device. The internal structures are rotatable relative to respective holding devices and the double-skin. Thereby the external shape of the double-skin is adjustable. Hence, the attachment devices are adapted to be attached to their respective external holding devices such that the internal structures are rotatable relative to the external holding devices and the double-skin.

The relative rotatability between the internal structures within the double-skin of the propulsive device and the holding device located externally of the propulsive device can be provided in various ways. In one embodiment the attachment devices may be rotatably attached to their respective internal structures. In another embodiment the attachment devices may be fixedly attached to their respective internal structures and the attachment devices may be adapted to be rotatably attached to respective holding devices or to respective rotatable parts of the holding devices.

In a further embodiment the attachment devices of the internal structures may be provided with internal rotatability such that the internal structures can be rotated relative to respective holding devices when the attachment devices are attached to the holding devices. For example, the attachment devices may be designed as two- part attachment devices where the two parts are rotatable relative to each other about the longitudinal axes of the attachment devices.

Hence, preferably the attachment devices are:

- rotatably attached to their respective internal structures, and/or

- fixedly attached to their respective internal structures and adapted to be rotatably attached to their respective holding devices, and/or

- provided with internal rotatability such that the internal structures can be rotated relative to respective holding devices when the attachment devices are attached to the holding devices.

Preferably, the structural devices are rotatable about respective rotational axes that are co-axial with the longitudinal axes of their respective attachment devices.

As mentioned above, the attachment devices may obviously have many different designs. The attachment devices may for example be bolt-shaped with a

longitudinal axis that are co-axial with the rotational axes of their respective structural devices.

The internal structures preferably have an external shape that is substantially airfoil shaped or hydrofoil-shaped, i.e. a longitudinal section through the internal structures are substantially airfoil-shaped or hydrofoil-shaped and provides the propulsive device with its airfoil-shape or hydrofoil-shape. The propulsive device is preferably provided with an adjustment system for rotation of one or some or all the structural devices within the double-skin of the propulsive device.

The adjustment system may for example comprise one or more cords that are attached to the structural devices. Alternatively, the attachment devices may be adapted for rotatable attachment to the external holding device, such as batten cars of a boat mast, where the external holding devices comprise an electric or hydraulic mechanism for rotation of the attachment devices. It could also be an option to adapt the attachment devices for rotatable attachment to the external holding devices, such as batten cars of a boat mast, where the holding devices comprises an automatic mechanism utilising the power from the horizontal movement of the foil to rotate the internal structures when the vessel tacks.

If the external holding devices comprise an electric or hydraulic mechanism, where the electric or hydraulic mechanism, for instance, may be in form of an electric or hydraulic motor, the electric or hydraulic motor may be connected to the attachment device attached to an internal structure of the structural device in order to rotate the structural device.

A plurality of structural devices arranged within a double-skin, each structural device being attached to an external holding device comprising an electric or hydraulic mechanism may form a propulsive system for large boats and ships.

In an alternative embodiment it could also be envisaged that the attachment device could comprise an electric or hydraulic mechanism, where the electric or hydraulic mechanism, for instance, may be in form of an electric or hydraulic motor, the electric or hydraulic motor may be connected to the attachment device attached to an internal structure of the structural device in order to rotate the structural device.

The propulsive device may further be provided with one or more support devices that support the internal structures of the structural devices and allows the internal structures to rotate relative to the double-skin of the propulsive device. A part of the support device may be attached to the trailing edge of an internal structure, or possibly somewhere between the trailing edge and the leading edge, and ensures that the structural devices may be supported at a second location, i.e. in addition to the attachment devices, which are supported by the holding devices.

The support device may comprise a first support member, for example in form of a pin element, securely attached to the internal structure of the structural device and a cooperating second support member, for example in form of a through-going support hole in the double-skin, allowing the internal structure to rotate relative to the double-skin when the pin element is supported by the second support member. An alternative support device is a string/cord/wire element or similar that is attached to the double-skin of the propulsive device and passing around the internal structure of the structural device in a loop, possibly arranged in a groove dedicated for the string/cord/wire element, thereby supporting the internal structure and at the same time allowing the internal structure to rotate relative to the double-skin of the propulsive device. Other support devices that supports the internal structure and at the same time allows the internal structure to rotate relative to the double-skin of the propulsive device may obviously also be used.

As mentioned, the attachment devices may be adapted for rotatable attachment to respective batten cars of a boat mast.

The double-skin may be made of a flexible material such as a canvas or other types of materials that are sufficiently strong to stand the loads during use of the propulsion device. For example, sailcloth used in conventional sails may be used in the double-skin in many embodiments of the present invention. Alternatively, the double-skin may also be made of a hard material such as metal plates and/or wooden panels and/or composite panels.

The propulsive device preferably has the shape of an airfoil or a hydrofoil.

The structural devices of the propulsive device are preferably structural devices according any one or more of the features of the structural device according to the present invention described above.

According to the present invention, there is also provided a propulsive system comprising a plurality of holding devices and a propulsive device having a double skin and an external shape of an airfoil or a hydrofoil. The propulsive device comprises a plurality of structural devices that are placed within the double-skin for adjustment of the external shape of the double-skin. The structural devices each comprises an internal structure having a leading edge and a trailing edge. The structural devices further comprise respective attachment devices that are attached to the leading edge of respective internal structures and extend outwards from the structural devices and through the double-skin for attachment to respective holding devices that are located externally of the propulsive device. The internal structures are rotatable relative to the respective holding devices and the double-skin whereby the external shape of the double-skin is adjustable. The holding devices are adapted for movable or fixed connection to an external structure, for instance a mast of a boat or the like.

The holding devices are preferably adapted to be movably mounted to an external structure. The holding devices may for example be adapted to be arranged in and guided along a guide element in a manner well known in the art. Furthermore, the holding devices may be adapted to be movable relative to each other. Thereby the propulsive device, for example a sail for a vessel, is collapsible into a storage position, i.e. the propulsive device can easily be mounted to the external structure, hoisted into its operational position and later lowered again and demounted from the external structure.

The propulsive device may preferably be provided with an adjustment system for rotation of one, some or all the structural devices within the double-skin of the propulsion device.

The adjustment system may for example comprise one or more cords that are attached to the structural devices. Alternatively, the attachment devices may be adapted for rotatable attachment to the external holding device, such as batten cars of a boat mast, where the external holding devices comprises an electric or hydraulic mechanism for rotation of the attachment devices.

A plurality of structural devices arranged within a double-skin, each structural device being attached to an attachment device comprising an electric or hydraulic mechanism may form a propulsive system for large boats and ships.

It could also be envisaged that an external holding device could comprise an electric or hydraulic mechanism, where the electric or hydraulic mechanism, for instance, may be in form of an electric or hydraulic motor, the electric or hydraulic motor may be connected to the attachment device attached to an internal structure of the structural device in order to rotate the structural device.

It could also be an option to adapt the attachment devices for rotatable attachment to the external holding devices, such as batten cars of a boat mast, where the holding devices comprises an automatic mechanism utilising the power from the horizontal movement of the foil to rotate the internal structures when the vessel tacks.

As mentioned above, the external holding devices may be batten cars that are movably mountable or attachable to a mast, for example a mast of a sail boat. The propulsive device may typically be a double-skin sail which is thereby easily attached to and detached from the batten cars of the mast or from the batten car track of the mast. The structural devices of the propulsive device are preferably structural devices according to any one or more of the features of the structural device according to the present invention as described above.

The propulsive device of the propulsive system is preferably a propulsive device according to any one or more of the features of the propulsive device according to the present invention as described above including structural devices according to the present invention as described above.

There is further provided a use of a structural device according to any one or more of the features of the structural device according to the present invention as described above in a double-skinned sail.

There is further provided a use of a propulsive device according to any one or more of the features of the structural device according to the present invention as described above for propulsion of a vessel.

There is further provided a use of a propulsive system according to any one or more of the features of the propulsive system according to the present invention as described above for propulsion of a vessel.

The present invention will enable any owner of almost any type of sailboat to purchase a double-skin airfoil, and without much ado hoist a sail that has more thrust and less heeling force than what is currently available on the market.

For a better understanding of the device according to the present invention, it will be referred to the enclosed figures, where:

Figure 1 illustrates a first embodiment of a structural device according to the present invention.

Figure 2 illustrates a second embodiment of a structural device according to the present invention.

Figure 3 illustrates a third embodiment of a structural device according to the present invention.

Figure 4 illustrates a fourth embodiment of a structural device according to the present invention.

Figure 5 illustrates a first option for attachment of an attachment device to an internal structure of a structural device according to the present invention.

Figure 6 illustrates a second option for attachment of an attachment device to an internal structure of a structural device according to the present invention. Figure 7 illustrates a first embodiment of a propulsive device according to the present invention comprising a plurality of structural devices according to the present invention arranged within the double-skin of the propulsive device.

Figure 8 illustrates a second embodiment of a propulsive device according to the present invention comprising a plurality of structural devices according to the present invention arranged within the double-skin of the propulsive device.

Figure 9 illustrates a propulsive device according to the present invention comprising a plurality of structural devices arranged within the double-skin of the propulsive device where the attachment devices of the structural devices are attached to respective holding devices mounted to an external structure.

Figure 10 illustrates an alternative option for attachment of an attachment device to an internal structure of a structural device according to figure 5.

Figure 11 illustrates an alternative option for attachment of an attachment device to an internal structure of a structural device according to figure 6.

In figure 1 there is depicted an embodiment of a structural device 25 according to the present invention for placement within the double-skin of a double-skin propulsive device 10 having an external shape of an airfoil or a hydrofoil for adjustment of the external shape of the double-skin propulsive device 10. A few examples of propulsive devices are shown in figures 7-9. The structural device 25 comprises an internal structure 27 that has a leading edge 28 and a trailing edge 29. The embodiment of the structural device 25 shown in figure 1 is a substantially rigid version.

The structural device 25 comprises a first beam element 2, i.e. a first batten, which is substantially straight and extends from the leading edge 28 to the trailing edge of the internal structure 27.

The structural device 25 further comprises a second beam element la that is pre bent or bendable, i.e. a second curved or bent batten. The second beam element la is at its end portions attached to the corresponding end portions of the first beam element 2. The first beam element 2 and the second beam element la lie in substantially the same plane which forms a first section 31 of the internal structure 27. The first section 31 is further provided with two spreader elements 3 which are attached to the first beam element 2 and the second beam element la in order to provide rigidity to the first section 31 and the internal structure 27. It should be understood that the number of spreader elements 3 obviously may be different from the two shown in figure 1 depending on the size and required rigidity of the internal structure 27. The structural device 25 further comprises a third beam element lb that is pre-bent or bendable, i.e. a second curved or bent batten. The third beam element lb is at its end portions attached to the corresponding end portions of the first beam element 2. The first beam element 2 and the third beam element lb lie in substantially the same plane which forms a second section 32 of the internal structure 27. The second section 32 is also provided with two spreader elements 3 which are attached to the first beam element 2 and the third beam element la in order to provide rigidity to the second section 32 and the internal structure 27. It should be understood that the number of spreader elements 3 obviously may be different from the two shown in figure 1 depending on the size and required rigidity of the internal structure 27.

The first section 31 and the section 32 are joined through the first beam element and forms an attachment edge. The first section 31 and the second section 32 are with an acute internal angle between them so that the first section 31 and the second section 32 forms a generally V-shaped internal structure 27 as can be seen in figure 1. The internal angle lies between 0° and 180°.

At the leading edge 28 of the internal structure 27, there is provided an attachment device 44 as indicated in figure 1. Two embodiments of the attachment device 44 are shown in figures 5 and 6 and will be described in further detail in connection with those figures.

The structural device is further provided with a support device 39 for additional support of the structural device 25 within the double-skin of the propulsive device 10. The support device 39 comprises a first support member 40 that is attached to the trailing edge 29 of the internal structure 27 and is adapted to be support by or suspended from a second support member of the propulsive device 10 as indicated in figures 7-9 where the first support member 40 is supported in a dedicated hole (not shown clearly in the figures). Other types of support devices 39 may obviously also be used as long as it allows the internal structure 27 to rotate within the double skin of the propulsive device 10. It should be noted that the support device 39 is optional and may, as shown in figure 3, be left out if that is desired.

In figure 2 there is depicted a similar embodiment of the structural device 25 for placement within the double-skin of a double-skin propulsive device 10 having an external shape of an airfoil or a hydrofoil for adjustment of the external shape of the double-skin propulsive device 10. A few examples of propulsive devices are shown in figures 7-9. The structural device 25 comprises an internal structure 27 that has a leading edge 28 and a trailing edge 29. The embodiment of the structural device 25 shown in figure 1 is also a substantially rigid version.

The structural device 25 comprises a first section 31 which in this embodiment is a substantially flat plate provided with a desired number of holes or openings 34. The number of holes 34 and the size of the holes are determined by the desired rigidity and weight of the internal structure 27.

The structural device 25 further comprises a second section 32 which in this embodiment is also a substantially flat plate provided with a desired number of holes or openings 34. The number of holes 34 and the size of the holes are determined by the desired rigidity and weight of the internal structure 27.

The first section 31 and the second section 32 are joined to each other along an attachment edge 33 forming an acute internal angle between them so that the first section 31 and the second section 32 forms a generally V-shaped internal structure 27 as can be seen in figure 2. The internal angle lies between 0° and 180°.

At the leading edge 28 of the internal structure 27, there is provided an attachment device 44 as indicated in figure 2. Two embodiments of the attachment device 44 are shown in figures 5 and 6 and will be described in further detail in connection with those figures.

The structural device is further provided with a support device 39 for additional support of the structural device 25 within the double-skin of the propulsive device 10. The support device 39 comprises a first support member 40 that is attached to the trailing edge 29 of the internal structure 27 and is adapted to be support by or suspended from a second support member of the propulsive device 10 as indicated in figures 7-9 where the first support member 40 is supported in a dedicated hole (not shown clearly in the figures). Other types of support devices 39 may obviously also be used as long as it allows the internal structure 27 to rotate within the double skin of the propulsive device 10. It should again be noted that the support device 39 is optional and may, as shown in figure 3, be left out if that is desired.

In figure 3 there is depicted a further embodiment of the structural device 25 for placement within the double-skin of a double-skin propulsive device 10 having an external shape of an airfoil or a hydrofoil for adjustment of the external shape of the double-skin propulsive device 10. A few examples of propulsive devices are shown in figures 7-9. The structural device 25 comprises an internal structure 27 that has a leading edge 28 and a trailing edge 29. The embodiment of the structural device 25 shown in figure 1 is also a substantially rigid version.

The structural device 25 of this embodiment comprises only one section, a first section 31 which in this embodiment is a substantially flat plate provided with a desired number of holes or openings 34. The number of holes 34 and the size of the holes are determined by the desired rigidity and weight of the internal structure 27.

At the leading edge 28 of the internal structure 27, there is provided an attachment device 44 as indicated in figure 3. Two embodiments of the attachment device 44 are shown in figures 5 and 6 and will be described in further detail in connection with those figures.

The structural device 25 in this embodiment is not provided with a support device 39 for additional support of the structural device 25 within the double-skin of the propulsive device 10 as the embodiments shown in figures 1-2 and 4. As mentioned above, the support device 39 is optional feature of the structural 25 and may, as shown in figure 3, be left out if that is desired.

In use, the embodiment of the structural device shown in figure 3 will have to be rotated 180° to adjust the external shape of the double-skin propulsion device 10 from one tack to another (To tack is to change course by turning a boat’s head into and through the wind, so as to bring the wind on the opposite side).

In figure 4 there is depicted a further embodiment of a structural device 25 according to the present invention for placement within the double-skin of a double skin propulsive device 10 having an external shape of an airfoil or a hydrofoil for adjustment of the external shape of the double-skin propulsive device 10. A few examples of propulsive devices are shown in figures 7-9. The structural device 25 comprises an internal structure 27 that has a leading edge 28 and a trailing edge 29. The embodiment of the structural device 25 shown in figure 4 is similar to the embodiment shown in figure 1, but the internal structure 27 is not rigid. This embodiment is a semi-rigid version of the internal structure 27 comprising adjustable tension elements 5 or adjustment units 8, 1 1. The internal structure may in one embodiment have tension elements 5 to produce the wanted curve of the battens la, lb, and it may have and first adjustment unit in form of a moving car 8 or a second adjustment unit 11 in form of a movable section at the trailing edge to make the structure even more trimmable.

The structural device 25 further comprises a second beam element la that is bendable, i.e. a second curved batten. The second beam element la is at its end portions attached to the corresponding end portions of the first beam element 2. The first beam element 2 and the second beam element la preferably lie in substantially the same plane which forms a first section 31 of the internal structure 27. The first section 31 is further provided with two spreader elements 3 which are attached to the first beam element 2 and the second beam element la.

The structural device 25 further comprises a third beam element lb that is bendable, i.e. a second curved batten. The third beam element lb is at its end portions attached to the corresponding end portions of the first beam element 2. The first beam element 2 and the third beam element lb preferably lie in substantially the same plane which forms a second section 32 of the internal structure 27. The second section 32 is also provided with two spreader elements 3 which are attached to the first beam element 2 and the third beam element lb.

In this embodiment of the structural device 25, at least the second beam element la and the third beam element lb are bendable.

To facilitate bending of the second beam element la, the structural device 25 may be provided with at least one extendable and retractable tension element 5 that is attached to the first beam element 2 and the second beam element la. The tension element 5 may for example comprise a piston/cylinder arrangement that may be mechanically operated or operated by hydraulic or pneumatic or electric power. By extending and retracting the tension element 5 the curvature of the second beam element la can be adjusted as desired.

Similarly, to facilitate bending of the third beam element lb, the structural device 25 may be provided with at least one extendable and retractable tension element 5 that is attached to the first beam element 2 and the third beam element lb. The tension element 5 may for example comprise a piston/cylinder arrangement that may be mechanically operated or operated by hydraulic or pneumatic or electric power. By extending and retracting the tension element 5 the curvature of the third beam element lb can be adjusted as desired.

Alternatively, the second beam element la may be bent by moving the end portions of the two spreader elements 3 along a guide element 58 arranged in the second beam element la as indicated in figure 4. The opposite end portions of the two spreader elements 3 may be hingedly or slidingly attached to the first beam element 2. To facilitate the movement of the end portions of the two spreader elements 3 along the guide element 58 of the second beam element la, the structural device 25 may be provided with a first adjustment unit 8 as indicated in figure 4. The first adjustment unit 8 may be mechanically operated or operated by hydraulic or pneumatic or electric power. Although not shown in figure 4, this way of bending the second beam element la may of course also be used to bend the third beam element lb.

It should be understood that the number of spreader elements 3 and tension elements 8 obviously may be different from the two shown in figure 4 depending on the size of the internal structure 27 and the desired degree of adjustability of the curvature of the second beam element la and/or the third beam element lb.

To compensate for the bending of the third beam element lb and/or the second beam element la, the structural device 25 may further be provided with a second adjustment unit 11 as indicated in figure 4. The second adjustment unit 11 allows the end portion of the third beam element lb to slide along guide element 60 arranged in the first beam element 2 and/or the end portion of the second beam element la to slide along a guide element (not visible in figure 4) arranged in the first beam element 2. The second adjustment unit 11 may be mechanically operated or operated by hydraulic or pneumatic or electric power.

In figures 5 and 6 two embodiments of the attachment device 44 is shown. The attachment device 44 attaches the internal structure 27 and thereby the propulsive device 10 to a holding device 52 that is located externally of the propulsive device, such that the internal structure 27 can be rotated within the double-skin 20 of the propulsive device 10 and thereby alter the external shape of the propulsive device 10. A propulsive device 10 will normally be provided with a plurality of structural devices that are connected to respective external holding devices 52 such that the internal structures 27 of the structural devices 25 are rotatable relative to their respective holding devices 52 and relative to the double-skin 20 of the propulsive device 10 that the internal devices are located within.

A propulsive device 10 is shown in figures 5 and 6 with the double-skin 20 cut off around the leading edge 28 of the internal structure 27. The cut-off part 24 of the double-skin 20 is indicated with a dashed line. The double-skin comprises a first skin section 21 and a second skin section 22 both extending from the leading edge 28 to the trailing edge 29 of the internal structure 27 forming a closed unit in which at least one, but preferably a plurality of structural devices 25 are arranged.

Each attachment devices 44 of the structural devices 25 of a propulsive device 10 connect an internal structure 27, and thereby the propulsive device 10, to a holding device 52 which is located externally of the propulsive device 10 as shown in figures 5 and 6.

The attachment device 44 may obviously have many different designs and two different designs are shown in figures 5 and 6. In figure 5 the attachment device 44 is bolt-shaped having a longitudinal axis that is the same as the rotational axis R of the internal structure 27. The internal structure 27 is provided with an opening in the leading edge 28 region of the internal structure 27. The attachment device 44 comprises an attachment member 45 that extends through the opening in the internal structure 27 and is securely attached in one end to an attachment element 54 of the holding device 52. In the other end, on the other side of the opening in the internal structure 27, the attachment member 45 of the attachment device 44 may be secured to the internal structure 27 with a fastening element 46, for example with a nut that is screwed onto the attachment member 45. The attachment element 54 of the holding device 52 may be mounted to a holding unit 53 of the holding device 52 with a bolt element 55 rotatably about an axis T as indicated in figures 5 and 6. Alternatively, the attachment element 54 of the holding device 52 may be fixedly mounted to the holding unit 53 of the holding device 52.

The holding device 52 is attached to an external structure 12 which for example can be a framework or a mast of a vessel. The holding device 52 is preferably, but not necessarily, slidingly mounted to the external structure 12 along a guide device 13 in a well-known manner as indicated in figures 5 and 6.

The only difference between the embodiment shown in figure 5 and the embodiment shown in figure 6 is the location where the rotation of the internal structure 27 relative to the holding unit 53 of the holding device 52 and relative to the double skin 20 is enabled.

In the embodiment shown in figure 5, the attachment member 45 of the attachment device 44 is securely attached to the attachment element 54 of the holding device 52 so that no relative movement between the attachment member 45 and the attachment element 54 is allowed. To enable the internal structure 27 to rotate, the attachment member 45 of the attachment device 44 is rotatably connected to the internal structure 27. The attachment member 45 is passed through the opening through the internal structure 27 located in the leading edge region of the internal structure in manner that allows the internal structure 27 to rotate around the attachment member 45, i.e. about axis R shown in figure 5. As indicated in figure 5, there is preferably provided a bushing 37 or a similar device that is capable of reducing wear and tear on the internal structure 27 and the attachment member 45.

The embodiment of the attachment device 44 shown in figure 6 comprises an attachment member 44 that is passed through the opening in the leading edge region of the internal structure 27 and is securely attached to the internal structure internal structure 27. The internal structure 27 is therefore incapable of rotating relative to the attachment member 45 of the attachment device 44. The rotation of the internal structure 27 relative to the holding device 52 and the double-skin 20 is obtained by attaching the attachment member 45 of the attachment device 44 to the attachment element 54 of the holding device 52 such that the attachment member 44 can rotate relative to the attachment element 54 about the rotational axis R and that

substantially no axial movement along the axis R is allowed and that bending moments can be transferred from the attachment member 45 to the attachment element 54. A possible design is shown in figure 6 where the end portion of the attachment member 45 is provided with a cylindrically shaped head part 48 that is arranged within a correspondingly shaped but slightly larger housing part 49 of the attachment element 54. The head part 48 and the housing part 49 are shaped so that the head part 48 is capable of rotating within the housing part 49 about axis R and substantially no axial movement of the head part 48 in the axial direction along axis R is possible. Furthermore, bending moments can be transferred from the

attachment member 45 to the attachment element 44 and further into the external structure 12.

Hence, figures 5 and 6 disclosed the attachment of a double-skin propulsive device 10 to an external structure 12, for example attachment of a sail to a mast. The propulsive system 70 comprising a propulsive device 10 and holding devices 52 that enables easy adjustment of the external shape of the propulsive device 10 and at the same time easy and quick hoisting and lowering of a double-skin propulsive device 10.

In figures 7-9 there is shown the use of the structural device 25 according to the present invention in three different propulsion devices 10 attached to external structures 12.

In figure 7 there is shown an embodiment of the present invention where the propulsive device 10 according to the invention has four structural devices 25 arranged within a double-skin 20 propulsion device 10. This particular figure shows the foil on port tack. By adjusting tension in tension elements 9, for example ropes, the structural devices 25 can rotate in concert around the axis of the attachment device enabling the foil to tack.

In figure 8 there is shown an embodiment of the invention where the propulsive device 10 is connected to an external structure 12 in form of a framework. In this particular embodiment of the invention, the double-skin 20 of the propulsion device 10 is wrapped around both the internal structural devices 25 and the external structure. By rotating the external structure 12 as indicated by arrow R on, the propulsive device 10 is rotated.

In figure 9 there is shown a propulsive system 70 including a plurality of structural devices 25, corresponding holding device 52 that the attachment devices 44 of the structural devices 25 are attached and the double-skin 20 of the propulsive device 10. The propulsive device 10 on this embodiment of the invention is a sail that is attached to a common sailboat mast and boom.

In figures 10 and 11 two alternative embodiments of the attachment device 44 and external holding device 52 according to figures 5 and 6 are shown, where the attachment device 44 and external holding device 52 in these embodiments comprises an electric or hydraulic mechanism 100. The attachment device 44 attaches the internal structure 27 of the structural devices 25 and thereby the propulsive device 10 to an external holding device 52 that is located externally of the propulsive device 10, such that the internal structure 27 can be rotated within the double-skin 20 of the propulsive device 10 and thereby alter the external shape of the propulsive device 10. A propulsive device 10 comprises normally a plurality of structural devices 25 that are connected to respective external holding devices 52 such that the internal structures 27 of the structural devices 25 are rotatable relative to their respective holding devices 52 and relative to the double-skin 20 of the propulsive device 10 that the internal structures are located within.

Each attachment devices 44 of the structural devices 25 of a propulsive device 10 connect an internal structure 27, and thereby the propulsive device 10, to a holding device 52 which is located externally of the propulsive device 10.

In figure 10 the internal structure 27 is provided with an opening in the leading edge 28 region of the internal structure 27. The attachment device 44 comprises an electric motor 100 having a longitudinal axis that is the same as the rotational axis R of the internal structure 27 and an attachment member 45.

To enable the internal structure 27 to rotate, the electric motor 100 is fixed to the internal structure 27 and rotatably connected to the attachment member 45. An opposite side of the attachment member 45 is securely attached to an attachment element of the holding device 52.

The connection between the electric motor 100 and the attachment member 45 will allow the electrical motor 100 to rotate the internal structure 27 around the attachment member 45, i.e. around axis R. A skilled person in the art would know how the connection between the electric motor 100 and the attachment member 45 is to be designed in order to provide the rotation, whereby this is not described any further herein.

The attachment element 54 of the holding device 52 may be mounted to a holding unit 53 of the holding device 52 with a bolt element 55 rotatably about an axis T as indicated in figures 5 and 6. Alternatively, the attachment element 54 of the holding device 52 may be fixedly mounted to the holding unit 53 of the holding device 52.

The holding device 52 is attached to an external structure 12 which for example may be a framework or a mast of a vessel. The holding device 52 is preferably, but not necessarily, slidingly mounted to the external structure 12 along a guide device 13 in a well-known manner as indicated in figures 10 and 11.

It should be understood that a hydraulic or pneumatic motor may be used instead of the electric motor 100.

The embodiment of the attachment device 44 shown in figure 11 comprises an attachment member 45 that is passed through the opening in the leading edge region of the internal structure 27 and is securely attached to the internal structure 27. The internal structure 27 is therefore incapable of rotating relative to the attachment member 45 of the attachment device 44. The rotation of the internal structure 27 relative to the holding device 52, where the holding device 52 comprises an electric motor 100, and the double-skin 20 is obtained by attaching the attachment member 45 of the attachment device 44 to the attachment element 54 of the holding device 52, the attachment element 54 being connected to the electric motor 100, such that the attachment member 45 can be rotated by the electric motor 100 relative to the attachment element 54 about the rotational axis R and that substantially no axial movement along the axis R is allowed and that bending moments can be transferred from the attachment member 45 to the attachment element 54. A possible design is shown in figure 1 1 where the end portion of the attachment member 45 is provided with a cylindrically shaped head part 48 that is arranged within a correspondingly shaped but slightly larger housing part 49 of the attachment element 54. The head part 48 and the housing part 49 are shaped so that the head part 48 is capable of rotating within the housing part 49 about axis R and substantially no axial movement of the head part 48 in the axial direction along axis R is possible.

Furthermore, bending moments can be transferred from the attachment member 45 to the attachment element 44 and further into the external structure 12.

A person skilled in the art would know how the head part 48, the housing part 49 and the electrical motor 100 are to be designed in order to provide the rotation, whereby this is not described any further herein. It should be understood that a hydraulic or pneumatic motor may be used instead of the electric motor 100.

In a propulsion system according to the invention there is used conventional sheet material in the skin parts of the foil. Such sheet material may comprise of sailcloth or tightly woven or knitted sheet material. The material of the sheet or cloth may be selected from natural or artificial materials such as cotton, wool, nylon,

polyvinylchloride, polyethylene, Kevlar, etc. Due to considerations concerning structural stress or forces in or on the cloth or skin material, the skin may also comprise reinforced areas or sections. This relates e.g. to the areas where the mainly straight and rigid batten (2) penetrates the skin of the air- or hydrofoil, the areas being worn when rotating the internal structural devices according to the invention inside the double-skin of the foil, etc. In the embodiments wherein said external skins comprise clothing or soft material (soft meaning the material being able to fold back on itself), the internal structures of the air or hydro foil will preferably fit inside each other to be able to be stacked inside each other when the sail is reefed. When packing the airfoil according to the present invention, the entire airfoil structure will become stacked into a pile by stacking the internal structures onto each other and simultaneously folding the external skin material outside and/or inside the stack.

According to this invention the said propulsion device is obtained by rigid or semi rigid and rotatable inner structural devices within a double-skin air- or hydrofoil, comprising an attachment device attached to a holding device. This particular embodiment of the object of invention includes several rigid or semi-rigid inner structures as disclosed supra constituting an inner framework forcing the skin of the foil to form a tight and flexible outer boundary on both sides, one side forming a curve, the other side forming a straight or straighter line, much like the shape of an aircraft wing.

The structural device of the said embodiment of the object of invention are produced by connecting two curved battens 1 to one straight or straighter batten 2. The curved battens 1 are held in place by spreaders 3, 6, 7, 8 which may be adjustable to create the wanted shape of the curve. The two curved battens 1 of this particular embodiment of the object of invention may be connected to a straighter batten 2 in a mirror symmetrical fashion at an angle of approximately 90 degrees. The said structural device is be connected to a holding device via an attachment device in the leading edge 4 and pocketed in a batten pocket or lifting rope or tension elements further back, hence making the whole structure rotatable around the axis R between the leading and trailing edge of the sail, e.g. the chord of the wing shaped structures. This embodiment of the structural device according to the present invention will be able to rotate freely about the axis (4,5) within the two skins constituting the outer boundaries of the airfoil. By rotating several inner structures simultaneously 90 degrees, the said airfoil will tack. In an embodiment wherein there are present several internal structures in the airfoil simultaneously (see figure 7), the internal structures may be interconnected to each other by providing connecting devices (e.g. ropes or wires) (9) between each structure. Such ropes or wires may be connected to each of the curved battens (1) to bring the batten paired curved structures (1) from a mainly horizontal (active) position to a mainly vertical position (inactive) by pulling one of the strings or wires (9) and releasing the opposite string or wire for rotating the structural devices inside the double-skin airfoil for alternating the side of the airfoil carrying the bulge of the airfoil.

One example of the embodiment of the invention is a double-skin airfoil with four internal rotating structural devices (figure 5) set to rotate in concert every time the boat comes about in the wind. The crewman loosens the outhaul on the boom and pulls one cord 9 designed to mirror or tack the airfoil when the boat tacks. The boat which had a perfect wing set up on starboard close hauled course now changes its shape to have a perfect wing setup on port side in just one pull of the tacking cord followed by a tightening of the outhaul.

The boat in the above example may be a 18ft catamaran that planes on the water surface. It has a standard rigging with a standard foresail, but with the above mentioned wing as a main sail. Due to its improved thrust, it is faster than its competitors with conventional sails. It can carry more sail before it is in danger of capsize due to less heeling force, and it has a sharper angle of attack and hence a faster Velocity Made Good (VMG). (VMG being the speed from a given point to another given point upwind, usually seen as an equation where angle of attack and boat speed being the major variables.)

When the above mentioned boat is beached, the sails are lowered and packed just like all the other catamarans in the race.

For some embodiments of the invention, two curved battens (1) may be connected to the straight or straighter batten (2) in a symmetrical or asymmetrical fashion at an angle of choice between 1 degree and 180 degrees.

On the above mentioned example, the boat (catamaran) designed for racing had curved battens at an angle of 90 degrees in all the four internal rotating structural devices. This is conceived as the most supportive design for the windward skin of the sail. The drawback is that the crewman has to loosen the outhaul on the boom for the inner structures to negotiate the 90 degrees’ rotations (ref. the above mentioned Pythagoras theorem.) A more cruising oriented sailor might want a set of inner structural devices with an angle of for example 55 degrees between the curved battens (1). This enables the inner structural devices to rotate without having to make more room within the tight skin (i.e. loosen the outhaul or the kick). Further, in one embodiment it may be possible that during the tacking of the wing sail on such a cruising sailboat the force created by the shift of the wind from one side to the other would be used to automatically rotate the structural devices. This can be done with for example the use of cog wheels or worm gear in the holding device transforming force from horizontal movement to rotational movement. The skippers would in this example only need to alter course, and the wing sail would tack itself just like any other single skin main sail. Another option is the use of electrical motors or hydraulics in the holding device or in the structural device to apply the force needed to turn the structural device. In such embodiments a hydraulic or electric motor may be attached to the structural device in such a way that the hydraulic or electric motor or an oscillating actuator rotates the internal structure relative the attachment device or the external holding device.

For larger sailboats, superyachts and commercial ships the use of electrical and/or hydraulic force is seen as favourable.

Furthermore, the present invention has applications outside the wind powered leisure craft industry. The invention can be used to help propel commercial vessels.

Such commercial vessels may be passenger ships, cruise ships, cargo ships etc. and may provide opportunity to save fuel on such ships and also to avoid exhaust emissions thus providing an efficient and environmentally friendly propulsion unit.

One embodiment of the object of invention to be used on, but not limited to, commercial vessels and mega sailing yachts constitutes of several single wing shaped rotatable inner structural devices (figure 3) with a leading and a trailing edge.

Several of these wing-shaped rotatable inner structures may be connected to a strong framework (12) either both in the front and in the back as depicted (figure 8) or only in the front. The skin of the foil is hoisted around both the inner wing shaped rotatable structures and the framework. When the wing shaped inner structures are rotated to a horizontal position the skin of the foil is wrapped tight. The inner wing shaped structures are rotatable 180 degrees in concert following the line between the leading and trailing edge of the sail, e.g. the chord (4,5) enabling the foil to tack, and the whole framework is rotatable vertically to enable adjusting and trimming of the foil. By rotating all the single wing shaped inner structures 90 degrees, the inner pressure is taken off the skin of the foil and the skin can be lowered partially (enabling reefing) or fully (to depower completely).

The material of the skin of the foil for this particular embodiment of the object of invention will have be made up of very heavy duty and reinforced soft cloth material. (Soft meaning that the material can be folded back on itself.) The material of the framework will have to be made of steel, carbon fiber, fiberglass aluminium, stainless steel, titanium and/or composite materials or combinations thereof to withstand the forces of the wind on the foil. Likewise, the inner wing shaped rotatable structural devices will have to be made of strong material like, but not limited to carbon fiber, fiberglass, stainless steel, aluminium, titanium and/or composite materials or combinations thereof.

To enable rotation of the inner wing shaped structures in concert to alter the shape of the structure and to tack the foil, worm drive, cogwheels, hydraulics or electrical devises may be used. This may be integrated into the holding device (fig 9) where the rotation of the attachment device can be made possible by electric or hydraulic power and with the use of cogwheels or worm drive. It is likewise possible to electrify or use hydraulics in the structural device itself when the attachment device is rotating within the structural device (fig 8).

Likewise, to rotate the whole foil around a vertical axis to trim and adjust the foil, the use of worm drive, cogwheels, hydraulics or electrical devises are advisory. It is also possible to hoist and lower the wing shaped structures within the rigid framework by use of worm drive, hydraulics, electrical devises or wires.

One example or application of the above technology would be to equip a 250 meter/ 13 000 DWT experimental ship much like the Wilhelmsen E/S Orcelle or the 130 meter/ 8000-ton EU supported Ecoliner with a set of proper packable, reefable and tackable wing sails. In the Ecoliner example the ships would be propelled by the above-mentioned wing sail technology instead of just square rig sails. This wing sail propulsion system would be working together with other power sources such as solar power, fuel cells or hydrocarbons. In this example the ship in question will achieve significantly reduced carbon footprint, together with a significant reduction in NOx.

Other applications of said invention are wind power plants and hydrofoil units like but not limited to the keel on a sailboat or the wings on submarines. It will also be possible to use one embodiment of this invention in hydropower plants such as tidal power units. For some embodiments of the invention it may be necessary to produce a structure with the two plate elements mentioned earlier

mirroring each other asymmetrically. This will change the leading/trailing edge every time the structures are rotated and hence the direction of the foil.

In one embodiment the invention consists of a specific structural device to be used in numbers within double-skin air- or hydrofoils. The said framework is made up of rigid and/or semi rigid battens and rigid or adjustable spreaders connected to each other in the following way:

Two curved battens (1) are connected to one straight or straighter batten (2) at an angle. The curved battens are connected to the straight or straighter batten with spreaders (3) to ensure the wanted curve of the curved battens and to provide strength to the entire structure. There may or may not be spreaders between the curved battens. In the leading edge of the structure there will be an attachment device in the shape of a rod (4) t. In the back of the structure (trailing edge) there may be a rod (5) On all the curved battens there will be attached a rope at around max camber. The rope will work both as a support device and as an adjustment system turning the structural devices in consert. The curved battens may be constructed of semi flexible or bendable material such as, but not limited to, wood, fiberglass or carbon fiber. The spreaders connecting the curved battens with the straight or straighter batten may be adjustable by tension elements (6). One can either adjust the length of the spreaders, or one can adjust the angle between the spreaders and the straight or straighter batten (8). One can also move the spreaders longitudinal to make more or less camber. This provides opportunity to change the curve of the batten and therefore to trim the foil. The tension elements (6) may be - but are not limited to - ropes, hydraulic devices, electronic or electromagnetic devices, worm drive or other mechanical devices.

The device may be constructed entirely or partially of material like, but not limited to, carbon fiber, fiberglass, aluminium, titanium and stainless steel and/or composite materials, wood, glue wood, etc. One of the advantages with internal structures according to the present invention is that they make the entire airfoil structure manually and/or automatically (e.g. electrically or hydraulically) adjustable and manageable with a limited weight depending on the weight of the materials of the inner structures and the size of such structures (light metal or metal alloy, wood, glass fiber rods or battens, etc.) and the material of the airfoil (sail clothing, cotton vs. artificial polymer materials, reinforcement structures etc.).

For one particular embodiment of the invention which provides trimmable semi rigid structural device the battens and spreaders are made of carbon fiber strengthened by stainless steel and composite material at the moving parts of the structure.

The above embodiment of the invention is connected with the attachment device to a batten car at the leading edge in a way that allows for rotation of the structure.. The batten car may be connected to a mast luff groove on a sailboat making it possible to hoist and lower the structural device within a double-skin sail much like one would hoist and lower a single skin mainsail. If a similar embodiment of invention is to be used as a headsail on a sailboat it may be connected to a headsail hank instead of a batten car enabling it to be hoisted and lowered on the forestay much like any other headsail. The trailing edge of the structure may end in a longer rod (5) following the same axis as the attachment device. If this is enveloped within a thin rope connected to the top of the mast or in a batten pocket in the sailcloth of the double-skin airfoil at the trailing edge, it ensures support aft for rotation.

This said embodiment of the invention is rotatable on the axis (4,5) constituting the chord of the wing shaped structures. It is trimmable by adjusting the angle of the spreaders. By applying tension with a thin rope (6) on the spreader of choice, the angle of the spreaders will be wide or sharp, creating the wanted shape of the flexible batten.

The said structural device may be used in numbers within a double-skin air- or hydrofoil. For one airfoil embodiment of the present invention, the outer skin can be sailcloth made of nylon, polyester, spectra, dynema, aramid, carbon fiber or any other material suitable for making a soft reefable and packable sail. The outer skin of the airfoil may or may not have stretch material or tension elements laminated or sewn into the foil at designated places. At certain areas the soft sailcloth will have to be reinforced to withstand tear and wear associated with the rotatable inner structures. The cloth may also be reinforced at certain areas with material designed to reduce friction both to reduce wear, and to reduce the force necessary for rotating the inner structures.

At the leading edge of the foil there may be a slot in the sailcloth for each structural device. For this particular embodiment of the present invention the sailcloth is not connected to the inner rotatable structure at the leading edge, thus enabling the structure to rotate freely within the double-skin air foil. If the angle between the two wing shaped structures are wider than 60 degrees there may be a slot in the trailing edge of the sailcloth as well. When tacking, the sailor may loosen the kick or the outhaul, tack the airfoil and tighten the outer skin again by reversing the previous operation. If the angle is 60 degrees or less, there is no need for this operation.

Concerning the internal structural device of the foil according to the present embodiment of invention, each structure may individually or in concert be rotated following the axis of the attachment device. Such a rotation will alternate the curved surface side of the airfoil and the flat surface side of the airfoil. Used in numbers within a double-skin airfoil it enables a fully trimmable, tackable double skinned airfoil that can be hoisted on almost any sailboat. It can be reefed and packed like any other fully battened sail.

Another particular embodiment of the invention is made up of plate elements with or without cut-outs (Fig. 2). Two plate elements may be connected to each other in a mirror fashion at an angle of approximately 60 degrees. Made of carbon fiber strengthen by stainless steel and composite material wing shaped plate elements provides more strength to the structure, but less flexibility. The said structural device may be used in numbers within a double-skin air- or hydrofoil and is rotatable around the axis (4,5). Constituting the chord of the wing shaped structures. (The chord being the direct imaginary line from the leading edge to the trailing edge) The said rotatable structural devices may be connected at the leading edge to batten cars in a mast luff groove, headsail hanks to a forestay and to a rope or pocket in the sailcloth at the trailing edge. The soft skin of the wing may wrap around the mast or around the said rotatable structures as explained above. With an angle of 60 degrees or less there will not be necessary to adjust the tightness of the outer skin every time the foil tacks.

All the above embodiments of the object of inventions may be connected to a rigid framework (12) both at the leading and trailing edge with the use of pins, bearings, worm drive, rings, hydraulic devices or any other devices providing both strength and rotational ability. When a rigid framework is used for support, the soft skin of the foil may be wrapped around both the propulsive system and the entire rigid framework.

The invention has now been explained with reference to a non-limiting example. A person skilled in the art will, however, appreciate that modifications and changes may be made to this embodiment which will be within the scope of the invention as defined in the following claims.

Claims

1. A propulsive device (10) having a double-skin (20) and an external shape of an airfoil or a hydrofoil, the propulsive device (20) comprising a plurality of structural devices (25) comprising respective internal structures (27) that are placed within the double-skin (20) for adjustment of an external shape of the double-skin (20), characterized in that each internal structure (27) having a leading edge and a trailing edge, wherein each structural device (25) comprises an attachment device (44) that is attached to the leading edge of the structural device (25) and extend outwards from the structural device (25) and through the double- skin (20) for attachment to a respective holding device (52) that is located externally of the propulsive device (10) and support the propulsive device (10), each internal structure (27) further being rotatable relative to the double-skin (20), whereby the external shape of the double-skin (20) is adjustable.

2. Propulsive device (10) according to claim 1,

wherein each attachment device (44) is:

- rotatably attached to its respective internal structure (27), and/or

- fixedly attached to its respective internal structure (27) and adapted to be rotatably attached to their respective holding devices (52), and/or

- provided with internal rotatability such that the internal structure (27) can be rotated relative to respective holding devices (52) when the attachment devices (44) are attached to the holding devices (52).

3. Propulsive device (10) according to claim 1 or 2,

wherein the propulsive device (10) is provided with an adjustment system for rotation of one or some or all the structural devices (25).

4. Propulsive device (10) according to any preceding claims 1-3,

wherein the structural device (25) is rotatable about a rotational axis that is co axial with a longitudinal axis of the attachment device (44).

5. Propulsive device (10) according to one of the claims 1-4,

wherein the attachment device (44) is bolt-shaped with a longitudinal axis that is co-axial with the rotational axis of the attachment device (44).

6 Propulsive device (10) according to one of the claims 1-5,

wherein the internal structure (27) is provided with a support device (39) attached to the internal structure (27) for additional support of the structural device (25).

7. Propulsive device (10) according to one of the claims 1-6, wherein the structural device (25) comprises a first section (31) and a second section (32) that are attached to each other forming an internal angle larger than 0° and smaller than 180° between the first section and the second section (31, 32).

8. Propulsive device (10) according to one of the claims 1-7,

wherein the internal structure (27) is substantially flat-shaped.

9. A propulsive system comprising a propulsive device (10) according to any one of the preceding claims 1-8, and a plurality of holding devices (52), the attachment devices (44) being attached to the leading edge of respective internal structures (27) and extend outwards from the structural devices (25) and through the double-skin (20) for attachment to respective holding devices (52) that are located externally of the propulsive device (10), the internal structures (27) being rotatable relative to the respective holding devices (52) and the double-skin (20) whereby the external shape of the double-skin (20) is adjustable, the holding devices (52) being adapted for movable or fixed connection to an external structure.

10. A propulsive system according to claim 9,

wherein the holding devices (52) are adapted to be movably mounted to an external structure (12).

1 1. A propulsive system according to claim 9,

wherein the holding devices (52) are adapted to be movable relative to each other.