The present invention relates to a propelling unit for propelling a vessel through water, such as a boat or a ship. Such a vessel may have two or more ways of forward or backwards motion, such as boats having both a sail and a propeller for ensuring forward motion. A problem associated with such multiple propulsion system is that it creates drag, i.e. flow resistance, when not in use, for instance the propeller of the ship will cause significant drag when sailing by sail. A number of solutions addressing this problem are known, e.g. the rear mounted motor/propeller units that enable the propeller to be lifted out of the water when travelling by sail. This is a satisfactory solution for in particular smaller boats, such as very small sail boats, where the engine can be handled somewhat easy by hand. Another solution in relation to the development is a collapsible propelling unit, to minimize the effect of the drag on the propulsion of the vessel. Hereby the

hydrodynamic drag is minimized by the use of folding or collapsing propellers or propelling units. Such propelling units are well known in marine applications. When dragging a propeller in a stationary position through the water, a large amount of turbulence will form around the propeller. This will introduce a large amount of drag on the vessel, which requires more power from alternative power sources, such as sails, to overcome this drag.

The known collapsible propelling units include foldable boat propellers, which fold their blades about axes perpendicular to the propeller shaft axis and propellers with adjustable pitch and feathering ability (CP propellers).

Also retractable devices are seen, which can be retracted into the main ship hull. They are often seen used for generation of transverse thrust in connection with

maneuvering, but can also be used for forward thrust.

Accordingly, in CA2139204 a boat propeller is disclosed, which rotates the blades around axes parallel to the propeller shaft axis. This propeller however aims at varying the diameter of the propeller disc (The area where the propeller is active), optimizing the output of the propeller rather than reducing the resistance, and the mechanism can be seen more as a load controlling mechanism.

Another solution is a propeller known from DE 41 19810 A1. Herein is described an aircraft propeller with foldable blades, which has a variable adjustable pitch angle with a link between outer linkage positions and propeller drive shaft. The two bladed propeller is designed for powered gliders. The two blades are connected via a mechanism that folds away the blades when not in use. The blades are covered by a shell also when not in use, though the solution is not aerodynamically optimized as the shell and the fuselage of the glider is not closed, introducing drag on the glider when the propeller is in use, as the shell and the fuselage has a gap with the propeller extruding. The mechanism of said propeller unfolds the blades by the centrifugal forces, which requires a higher minimum output from the propulsion system to function than if it was driving a normal propeller, minimizing the flexibility of the solution. The solution is mainly intended to accelerate and lift a glider into the comfort zone of the gliding abilities, which reduces the influence of the less efficiency of the propulsion system.

A different solution is known from US 5, 183,384. Herein is disclosed a foldable propeller assembly which attempts to deal with the introduced force by having blades mounted so that they unfold when thrust is applied, using the centrifugal force caused by the rotation and the forces introduced by the water. The use of centrifugal force for engaging the mechanism requires a higher minimum input of torque from the propulsion system, lowering flexibility of the implementation.

Yet other solutions are described in US 6,371 ,726, NZ 277760, CA1172521 and GB 1 453 317. All of these solutions are different solutions for minimizing the hydrodynamic effects of dragging the propeller through the water by folding it away from the swept area, however, being mounted orthogonally to the drive shaft and folding in to being parallel with the driveshaft, using different mechanisms and systems. These solutions do minimize the introduced effects, but still drag the propeller through the water, even though being folded, and therefore never remove the drag entirely.

All of the known solutions, apart from those that are retracted fully when not in use, do not completely eliminate the resistance from the blades. The foldable propellers lack a mechanism that fully controls the folding/unfolding procedure, as they utilize the centrifugal force generated when rotating the propeller.

A problem associated with the above-mentioned solutions is that some of these solutions are either unsuitable or impossible to use on larger vessels and/or only reduce the introduced hydrodynamic effects of dragging a propeller to some extent.

The present invention addresses this problem by providing a propelling unit for propelling a vessel through water, said propelling unit comprising a rotor comprising a plurality, preferably two or more, foldable hydrodynamic blades, said rotor being mounted on a drive shaft connected to drive means for propelling said vessel by rotating said rotor around an axis, a shielding shield shiftable between a first and second position, wherein the shielding shield in said first position is adapted to cover and to accommodate the rotor with the blades in their retracted position, and wherein the shielding shield in the second position allows for the blades to be extracted, wherein an extraction mechanism is provided for performing said shifting between the first and second positions.

Hereby, there is provided a collapsible propeller mechanism that has the feature that, when collapsed, it is completely encased in a shell of a vessel in a flush manner without more than the absolute minimum gap between rotating body and non-rotating body, allowing minimal drag and other undesired aero- and/or hydrodynamic forces on a second propulsion system. The propelling unit preferably comprises a shell, a set of collapsible or foldable blades fitting inside said shell in a flush manner when collapsed, a mechanism for collapsing or retracting and extracting the blades that includes the functionality of extending the shielding shell and turning the blades out to form the rotor, i.e. a propeller. When retracting the rotor, the shielding shell is again extended and the mechanism is adapted to retract (fold back) the blades of the rotor and then withdraw the shielding shell to cover the retracted rotor and also form a uniform, flush surface around the rotor. This functionality is preferably integrated with the drive means for driving the rotor when unfolded. The shielding shell fits over the blades in a flush manner with the housing to achieve a minimal hydrodynamic drag. This collapsible propelling unit according to the invention can be used for many purposes. In a preferred embodiment, the propelling unit is provided on the keel of a sail boat in order to reduce hydrodynamic drag of the propelling unit when going under sail. The propelling unit can preferably be built into a bulbous keel, where it makes a positive contribution to the keel weight, and potentially even with an engine built into the keel also. The blades are preferably specially designed for their position, in the front, the middle or the back of the torpedo shaped hull or bulbous keel. The blades of the rotor may be designed to rotate in either a clockwise or counter-clockwise direction. The special shape of the blades, and not least the designed propeller rake (leaning in axial direction), allows for the blades to fold perfectly in, overlapping each other. With more than one propeller working together on the same hull/body, the special efficiency gain from more propellers working together in counteracting directions can be attained. The actual turning mechanism for folding and unfolding the propelling unit can be done in numerous ways and can use various technologies.

In the following the invention is described in more detail with reference to the accompanying drawings, in which:

Fig. 1 is a schematic perspective view of a bulbous keel with a propeller unit according to an embodiment of the invention;

Fig. 2 is a side view of same;

Figs. 3 and 4 are schematic top views of the bulbous keel with the propeller unit

according the embodiment with the propeller rotors retracted and extracted, respectively;

Fig. 5 is a detailed side view of the propeller unit according to an embodiment of the invention;

Figs. 6 and 7 are a cross-sectional side view of same;

Figs. 8 and 9 are cross-section views of the sections A-A and B-B, respectively, in fig.

7;

Fig. 10 is a view of the propeller rotor with the blades extended; and

Fig. 11 is a schematic exploded perspective view of a blade of the propeller rotor according to an embodiment of the invention. With reference to figures 1 to 4, an embodiment of the invention is shown, where a bulbous keel 20 of a boat 22, such as a sailing boat, is fitted with a propelling unit engaged for propulsion. The bulbous keel has a bulbous housing 4 and in the figures various embodiments are shown, where a propulsion unit may be fitted at one end, i.e. either the front or the rear end of the bulbous keel or at both ends, i.e. the propeller unit can be installed in either end of the bulbous keel. If installed behind it is referred to as a pushing propeller and if installed in front as a pulling propeller.

The Propeller unit comprises foldable blades 1 , 1 ' and the blades 1 are covered by a shielding shell 2, when the propeller blades V are collapsed (as shown in fig. 8). When the propeller blades are collapsed (or folded in), the blade foot 3 (see fig. 11) is turned into position forming a completely smooth outer body together with the torpedo shaped hull 4 and the shielding shell 2. The blades 1 , 1 ' are mounted in a rotor configuration on an extraction mechanism 5, which is mounted on the propeller drive shaft 6.

In isometric view of figure 1 , an embodiment of the invention is shown where a bulbous keel 20 of a boat 22, such as a sailing boat, is fitted with a propelling unit engaged for propulsion at one end and where the shielding shell 2 is provided with indentations 2' that interlocks with the foot 3 of the blades 1 ' in a flush manner, minimizing undesired hydrodynamic resistance and turbulence when the rotor is extracted. In fig. 2, an embodiment is shown where a propelling unit at both ends is provided and in the situation where both units are closed in their inactive positions. The indentations 2' at the rim of the shielding shells 2 are also shown.

In an embodiment shown in fig. 4, at one end, the rotor is extracted and at the other end two rotors in series are provided and shown in their retracted configuration. It is by the invention realized that a two rotor configuration may be provided at a given end of the bulbous keel independent of what kind of propulsion system that may or may not be provided at the other end.

In figure 5 a detailed side view is shown and in figures 6 and 7 the same is shown as cross-sections of the mechanism. In figures 8, 9 and 10 end views, in a simplified manner, are shown. Wth reference to in particular in figs. 9 and 10 there is shown the bell shaped parts 10 of the mechanism 7 allowing for folding the blades 1 , 1 ' of the propelling unit in and out and thereby engaging or disengaging the propulsion.

In the figures 5-10 there is shown an embodiment of the invention where a gearing mechanism similar to a planetary gear is provided using the bell shaped parts 10 at the bottom 3 of the blade parts 1 to rotate the blades into or out from the shielding shell, by rotating a center cog, mounted in the centre of the mechanical box 5, on the inner shaft 6', that extends out of the outer shaft 6, which is mounted on the mechanical box 5. The inner axle 6' is also used to engage and disengage the shielding shell 2 to allow for said rotating movement of the blades.

The functionality of retracting the shell/hub and turning the blades are done by pushing and turning the inner shaft/"push-pull-rod" that runs inside the hollow propeller shaft respectively. The hollow (main) shaft 6 transfers the rotational (propulsive) power when the rotor is extracted. Folding the blades in or out when the shielding shell is open requires a relative translating/turning movement of the push/pull rod relative to the main shaft or vice versa, for this reason the extraction of the blades can also be done by holding still the push/pull rod and turning the shaft slightly. With reference to fig. 6, the inner shaft 67"push-pull-rod" is only constrained to the inner/centre cog in the radial direction, as the inner shaft, in the part that can slide through the inner cog, is square (or similar "lock-and-key-fitting shape, i.e. not round, but square in the shown embodiment), and can transfer radial movement to the inner/centre cog that has an equal (square) shaped opening, with a tolerance that allows for the inner shaft 6' to slide through the opening in the inner/centre cog also. The ability for the inner shaft to slide through the centre cog allows for a longitudinal movement of the inner shaft that can control the position of the shielding shell. This is done through the connection (position 1 1 (see fig. 6)), which is only able to transfer axial movement/force (a bearing) and not radial movement/force. The shielding shell 2 and the mechanical box 5 are aligned by means of the inner tube fitted to the mechanical box 5 and the outer tube inside the shielding shell. These tubes/cylinders are also locked against rotation with tracks on the opponent faces (position 12).

Alternatively, the connection (Position 1 1) is locked in order to transfer rotation to the shielded shell 2, and the guiding tracks in position (12) are turned/shaped in a way that forces the right relative turning of the inner shaft 6' and hence the folding in/out of the blades.

Inside the propeller head, a piston 13 may be provided fixed to the inner shaft 6' whereby the piston 13 functions as a part of hydraulic drive means so that the propeller head, i.e. shielding shell 2, can be axially displaced by controlling the pressure of and/or the amount of hydraulic fluid on either sides of the piston 13.

In summary, the extraction mechanism can be operated either by the push/pull rod or by the cylinder build in to the propeller head.

The housing 5 contains a mechanism 7 that folds and unfolds the blades 1 , 1 ' around axles 3' around which the bell-shaped cogs 10 are rotating and which axles 3' are parallel to the propeller drive shaft 6. The blades 1 , 1 ' folds and unfolds by turning the sun cog 8 that turns the moon cogs 9 that again turns the special bell shaped outer moon layer cogs 10 connected to the blades 1 at the blade foot 3 (see figures 9-1 1). When the propeller is folded in, the shielding shell 2 covers the blades 1 ' and locks them in position. In the shown embodiments of the invention an extraction mechanism based on a planetary gear is shown, but it is realized that other types of actuation may be provided.

In the solution shown in the figures, the mechanism of the propeller unit is provided with a hollow outer shaft 6 with a thinner shaft 6' inside. The inner shaft 6' pushes the shielding cap 2 away from the propeller by moving it away in the longitudinal direction. When the shielding cap 2 is pushed out, the blade feet 3 are unlocked, allowing the folding out of the blades 1 by turning the inner shaft 6' relatively to the outer shaft 6. Once the blades 1 are in the desired position (open or closed) the propeller hub 2 is pulled back, and every individual blade foot 3 is locked.

With reference to fig. 9, the folding/unfolding mechanism of the propelling unit comprises a sun cog (centre cog) 8, driving the intermediate layer of planetary cogs (moons) 9, which again drive the special bell-like shaped toothed parts 10, which can be seen/described as the outer moon layer if compared with a planetary gear. This mechanism is unique because the planetary gear comprises two layers of "moons" where the cogs in the outer layer (second moon layer) are basically only a part of a moon-wheel. The special way in which the turning sequence is made, every individual bell-shaped moon wheel 10 is being pushed/turned, first by one of the intermediate moons 9 and later in the sequence by the another. The benefit from this mechanism is that the shafts 3' extending out of the housing 5, can be very close to the outer edge. It enables a very compact solution, and allows the shaft 3' to be relatively thick and for the gearing of the outer moon to have a reasonable diameter that makes a good gearing with the intermediate moon gear layer and the sun cog wheel in comparison with a solution with only one layer of moon cog wheels. The gearing could also be driven by e.g. a similar mechanism based on linear or rotational hydraulic or electrical actuation, mechanisms using belt drive or chain drive inside the housing.

The blades 1 of the propeller unit are mounted on blade roots 3 with a characteristic shape, ensuring a clean/flush surface of the roots 3 against the shell 2 both in the folded and unfolded position, and the propeller can have any number of blades from two or more, such as five as shown in fig. 10. The geometry of the mechanism and the number of teeth on the gears is developed and tailored to fit the number of blades and the required angular motion of the blades. Furthermore, the blades are designed to fit the requirements for the vessel propulsion system and desired location or area of use. The sun wheel in the mechanism can be customized to be driven mechanically, electrically or hydraulically, depending on the available power source on a relevant vessel, as well as the linear motion of the inner shaft 6', and the rotation of the propeller unit when unfolded. The propeller unit ensures minimum hydrodynamic resistance in the folded mode when not in use, as well as when the propeller unit is unfolded. This means that when the propeller is used on a sailing vessel, it will increase performance of the sailing vessel and optimize comfort and aerodynamic efficiency of the sails, which could lead to smaller sails and/or higher speeds, when sailing by wind.

Furthermore the blades are protected by the shell in the folded mode, reducing the risk of damage of the blades due to grounding or encounter with objects in the water, which will also minimize damage to surrounding animal and plant life, when travelling through the water. Above the invention is explained with reference to some preferred embodiments. However, it is realized that other variants of the propelling unit according to the invention may be provided without departing from the invention as defined in the accompanying claims. For instance, above the invention is described with reference to a sea-going vessel providing propeller propulsion through the water. However, it is realized that the invention may also find use as a propeller propulsion system for an aircraft, such as a powered sailplane, where the medium in which the propeller is operating is air. Further, it is realized by the invention that the invention may be used for a vessel that is fully submerged in the water, such as a torpedo or a submarine vessel.