Abstract:
The invention relates to a device for reducing the driving power requirement of a watercraft, comprising a flow guiding surface from which at least one first fin projects. A first end of said first fin is fixed to the flow guiding surface, and a second end of the first fin is embodied as a free end.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a device for reducing the drive power requirement of a watercraft, in particular a ship. The device according to the invention is in particular suitable for a drive system of a watercraft for improving the energy efficiency. 
       BACKGROUND OF THE INVENTION 
       [0002]    Devices for reducing the drive power requirement of a watercraft are known from the prior art. In EP 2 100 808 A1 such a device comprises, for example, a fore-nozzle. This fore-nozzle is in particular mounted at a short distance or directly upstream of the propeller when viewed in the direction of travel of the ship. Furthermore, fins, i.e. (guide) fins or hydrofoils, are provided in the fore-nozzle. The fore-nozzle substantially has the shape of a flat cone section, where both openings, both the water inlet and the water outlet opening, are configured as a substantially circular opening and the water inlet opening has a larger diameter than the water outlet opening. As a result, it is possible to improve the propeller inflow and to reduce the losses in the propeller jet by specific generation of pre-swirl by the fins installed in the fore-nozzle. A significant reduction in the drive power requirement and therefore a saving of fuel can be achieved by such a system. 
         [0003]    The previously known device described above, however, has a relatively large resistance for the propeller inflow so that the reduction in the drive power requirement in the relevant extent is primarily only established in slower or more heavily laden ships, so that the known device is usually only used in such ships. 
         [0004]    It is therefore the object of the present invention to provide a device for reducing the drive power requirement of a watercraft which can also be used particularly effectively in fast and very fast watercraft, for example ships having a speed of 20 knots or more or 25 knots and more. 
       SUMMARY OF THE INVENTION 
       [0005]    This object is solved whereby in a device for reducing the drive power requirement of a watercraft, comprising a flow-guiding device, at least a first fin projects from the flow-guiding device in such a manner that a first end of the first fin is fastened to the flow-guiding surface and a second end of the first fin is configured as a free end. 
         [0006]    The flow-guiding surface can be formed in one part or in one piece or be composed of several individual parts to form a flow-guiding surface, where the individual parts are preferably welded to one another or welded to the hull. 
         [0007]    The flow-guiding surface can in principle have all possible shapes. At the same time, the flow-guiding surface is disposed and configured in such a manner that the water flow can be guided by it at least partially onto a propeller. For example, the flow-guiding surface can have the shape of a square or rectangular plate. Furthermore, arcuate or curved configurations are feasible. In cross-section, an arcuately-configured flow-guiding surface can have a circular section, an elliptical section or an otherwise-curved shape. The flow-guiding surface has a length in the flow direction, for example, in the direction of travel of the watercraft. Furthermore, in a plate-shaped configuration, the flow-guiding surface has a width or in an arcuate configuration, it has an arc length. The thickness of the flow-guiding surface is hereinafter designated as profile thickness. Both the length and also the width or arc length and the profile thickness can be constant over the entire area of the flow-guiding surface or they can have different values. For example, the flow-guiding surface can also be profiled. In this case, for example, one edge of the flow-guiding surface could be configured to be rounded and have a thinner profile thickness than the central region of the flow-guiding surface. 
         [0008]    According to the invention, the first fin is connected at a first end in a suitable manner to the flow-guiding surface, or is fastened to the flow-guiding surface. For example, the first fin at its first end can be welded or flange-mounted to the flow-guiding surface. The second end of the first fin according to the invention is configured as a free end. Consequently, the first fin can project from the flow-guiding surface in any arbitrary direction, where the second end of the first fin is not connected to the flow-guiding surface or is otherwise fastened to the ships&#39; hull. The term “fin” is to be understood as any guide fin or a hydrofoil which is preferably arranged fixedly on the flow-guiding surface. At the same time, the term “fin” can be understood as any guide device which influences the propeller inflow, where the fin usually has a hydrofoil profile, i.e. a suction and a pressure side. Thus, fins in the present connection are flow guiding surfaces in the sense of stators which are arranged on the flow-guiding surface and influence the propeller inflow. In particular, it is preferred that the fins have an, in particular circular-arc-shaped, outwardly curved suction side and a substantially flat pressure side. 
         [0009]    The profile of the first fin can be uniform or different when observed over its length. In particular, the profile can be turned into itself, i.e. twisted, when viewed along the longitudinal direction of the first fin. Consequently, the first fin in addition to the flow-guiding surface also serves as a guiding surface for the water flow, where the flow-guiding surface and the first fin are arranged at an angle to one another and preferably the first fin is configured to be smaller than the flow-guiding surface. Length of the first fin is understood to be the distance between the first end and the second end of the first fin. Depth of the first fin is understood to be the depth of the fin in the longitudinal direction of the flow-guiding surface, that is in the direction of travel of the watercraft. The thickness of the fin is hereinafter designated as profile thickness. 
         [0010]    First fin in the sense of the present invention is to be understood as all fins which project from the flow-guiding surface and are connected with a first end to the flow-guiding surface and whose second end is configured as a free end. Preferably a plurality of such first fins can be provided. 
         [0011]    Preferably the flow-guiding surface is disposed upstream of a propeller. This means that the flow-guiding surface is disposed in the direction of travel of the watercraft, or the ship, upstream of a propeller of the watercraft. The designation “in the direction of travel” is to be understood here as the forwards direction of travel of a ship or a watercraft. 
         [0012]    In this case, it is further provided that the flow-guiding surface is located at a distance from the propeller. Furthermore, it is preferred that the flow-guiding surface is located at a distance from a shaft bearing, in particular a stern tube. A stern tube is used for mounting a propeller shaft of the propeller of the watercraft or the ship. For this purpose the flow-guiding surface can be arranged at least in sections above, below or also laterally of the propeller axis. Furthermore, the flow-guiding surface can at least partially enclose the propeller axis or the shaft bearing. Particularly preferably the flow-guiding surface is disposed in an arcuate shape above and at a distance from the propeller axis or the propeller shaft. In this case, the arcuately configured flow-guiding surface can also be configured to be closed in the circumferential direction. Preferably however, an arcuate flow-guiding surface has a cross-section of an eighth ring, a quarter ring. It is further preferred that the flow-guiding surface has a cross-section of a half ring, a two-thirds ring or a three-quarters ring. 
         [0013]    Furthermore, the flow-guiding surface can be configured to be arcuate and circumferentially open, where the flow-guiding surface does not have a circular cross-section but for example, has an elliptical cross-section. Preferably the flow-guiding surface is configured to be convex with respect to the propeller axis. 
         [0014]    In the case of an arcuate configuration of the flow-guiding surface, the arc length of the flow-guiding surface in a cross-sectional view is preferably less than 80%, particularly preferably less than 60%, quite particularly preferably less than 40% or 30% of the circumference of the conceptually circumferentially closed flow-guiding surface. 
         [0015]    In principle however, other cross-sections are also feasible. For example, the flow-guiding surface can have an angled, for example, a rectangular cross-section. Furthermore a U-shaped configuration of the flow-guiding surface would be feasible. 
         [0016]    As a result of the arrangement of a first fin on the flow-guiding surface, where a first end of the first fin is fastened to the flow-guiding surface and a second end of the first fin is configured as a free end, it can be achieved that the dimensions, for example, the length or the width or the arc length and/or the profile thickness of the flow-guiding surface can be reduced considerably compared with the devices known from the prior art where nevertheless those regions in which the flow losses are particularly high and in which a swirl must be produced for efficient operation can still be reached by the first fin. 
         [0017]    In addition, it is preferred that the second end of the first fin starting from the flow-guiding surface is directed away from the propeller axis. That means that the distance from the first end of the first fin to the propeller axis is shorter than the distance from the second end (free end) of the first fin to the propeller axis. 
         [0018]    Consequently, the flow-guiding surface can be disposed at a distance from the propeller shaft, where the distance between propeller shaft and the flow-guiding surface is shorter compared to the prior art. Since the first fin protrudes from the flow-guiding surface in such a manner that its second end is directed away from the propeller axis, it is further ensured that the first fin extends sufficiently far from the propeller shaft (when viewed in the radial direction from the propeller shaft) and consequently can still positively influence the inflow onto the respectively associated propeller. 
         [0019]    By attaching a fin to the flow-guiding surface, the distance from the flow-guiding surface to the propeller shaft and also the profile thickness of the flow-guiding surface and therefore the resistance can thus be reduced so that the device can now also be used for fast and very fast ships where the positive effects for the reduction of the drive power requirement are still preserved or optionally even improved. Since the first fin projects outwards from the flow-guiding surface and possibly not from the propeller hub or the stern tube, this can extend relatively far outwards when viewed from the propeller axis and nevertheless still have sufficient strength, particularly in regard to bending stresses. 
         [0020]    Preferably the first fin has a greatest profile thickness, where this greatest profile thickness of the first fin is less than 50%, particularly preferably less than 25%, and quite particularly preferably less than 15% of the distance between the first end and the second end of the first fin. Thus, the profile thickness of the first fin at its thickest point is less than the length of the first fin between its first end and its second end. 
         [0021]    In principle, the flow-guiding surface can be disposed parallel to the propeller axis or parallel to the propeller shaft. This means that the distance between flow-guiding surface and propeller axis is substantially the same in each region. Preferably however the flow-guiding surface is disposed inclined with respect to the propeller axis towards the rear or towards the front. In this case, the flow-guiding surface is preferably configured to be profiled. The flow-guiding surface thus has a profile inlet edge which is directed away from the propeller and on which the water flow impinges in the direction of travel of the watercraft in the forwards direction of travel. The profile outlet edge of the flow-guiding surface is directed towards the propeller. The profile inlet edge and the profile outlet edge thus comprise the two front-side edges of the flow-guiding surface. In the case of a flow-guiding surface which is inclined with respect to the propeller axis towards the rear, the distance between propeller axis and flow-guiding surface is therefore greater in the region of the profile inlet edge than in the region of the profile outlet edge. As a result of such an arrangement of the flow-guiding surface, the inflow onto the propeller can be particularly advantageously influenced in certain regions. In the case of a flow-guiding surface arranged at an inclination to the propeller axis, the longitudinal axis of the flow-guiding surface thus does not run parallel to the propeller axis but at an angle and as a result is inclined in relation to the propeller axis. 
         [0022]    Preferably the shortest distance between flow-guiding surface and propeller axis is less than half the propeller diameter or less than the radius of the propeller. In the case of a flow-guiding surface arranged at an inclination to the propeller axis towards the rear, the distance between flow-guiding surface and propeller axis in the region of the profile outlet edge of the flow-guiding surface is therefore shorter than half the propeller diameter. 
         [0023]    Preferably at least one second fin is further provided which projects from the flow-guiding surface. In this case, the second fin is disposed with its first end on the flow-guiding surface or fastened to this and with its second end is disposed on a shaft bearing, in particular stern tube, or fastened to this. Consequently, the second fin starting from the flow-guiding surface is directed towards the propeller axis and in contrast to the first fin, has no free end but is connected to the hull or the shaft bearing. Consequently, the second fin runs between two fixed bearing points from the shaft bearing to the flow-guiding surface. Between the two ends, the second fin preferably has a pressure side, a suction side, a nose strip and an end strip. This configuration also applies similarly for the first fin which projects outwards with a free end from the flow-guiding surface. Depending on the configuration of the hull, the second fin can be mounted, instead of on a shaft bearing, directly on the hull or on the plating of the hull with its second end. 
         [0024]    “Second fin” is to be understood in the sense of the present invention as all fins which protrude from the flow-guiding surface and are connected with their first end to the flow-guiding surface and are connected with their second end to the shaft bearing or the hull. Preferably a plurality of such second fins can be provided. 
         [0025]    It is furthermore expedient that the first fin and/or the second fin are arranged substantially in the radial direction to the longitudinal axis of the flow-guiding surface or to the propeller axis of a drive propeller of a watercraft. Preferably both fins, the first and also the second fin, are arranged in the radial direction. In principle, the first fin and also the second fin are arranged at different angles to their respective tangents. The tangent for the first fin runs through a point on the outer wall surface of the flow-guiding surface whereas the tangent for the second fin runs through a point of the inner wall surface of the flow-guiding surface. Outer wall surface of the flow-guiding surface is to be understood as the wall surface directed away from the propeller axis or propeller shaft. On the other hand, inner wall surface is to be understood as the wall surface of the flow-guiding surface which is directed towards the propeller axis or the propeller shaft. 
         [0026]    It is further preferred that the extension of the individual fins (first fin and also second fin) in the longitudinal direction of the flow-guiding surface is smaller or shorter than the length of the flow-guiding surface. “Extension” is to be understood as the region or the length of the longitudinal profile of the flow-guiding surface over which the fins stretch in the longitudinal direction of the flow-guiding surface. Particularly preferably the extension of the individual fins in the longitudinal direction of the flow-guiding surface is less than 90%, quite particularly preferably less than 80% or even less than 60% of the length of the flow-guiding surface. The longitudinal direction substantially corresponds to the direction of flow. It is further preferred that the fins are disposed substantially in the rear region, that is in the region facing the propeller, of the flow-guiding surface. In principle however, a configuration of the fins over the entire extension of the flow-guiding surface in the longitudinal direction or even a central or front arrangement of the fins in relation to the direction of travel would also be possible. 
         [0027]    The respective two first ends of the first and the second fin are fastened on the flow-guiding surface. Advantageously, the first end of the first fin can either be fastened on the outer wall surface of the flow-guiding surface, for example, by flange-mounting or also guided into the flow-guiding surface profile, that is the wall of the flow-guiding surface. Alternatively it is also possible to guide the first fin through the guiding surface profile or the flow guiding surface. The first end of the first fin thus forms the root of the first fin and the second end forms the tip of the first fin. 
         [0028]    All the possible configurations described for the first fin can also be transferred similarly to the configuration of the second fin and conversely or can be applied there. 
         [0029]    The flow-guiding surface can preferably be connected via the second fin to the hull. Additionally or alternatively, the flow-guiding surface can also be connected to the hull via further connecting means, for example “brackets” or retaining clips or shaft bracket arms located for example below or above the flow-guiding surface. The shaft bracket arms could also be configured as fins at least in certain areas. 
         [0030]    In a preferred embodiment, a plurality of first and second fins are provided. This means that a plurality of fins are provided which protrude from the flow-guiding surface outwards in such a manner that they are connected to the flow-guiding surface with their respective first end and are arranged to be free-standing with their respective second end. Furthermore, a plurality of fins are provided which are connected with their first end to the flow-guiding surface and are connected with their second end to the hull or the propeller shaft. In particular, it is preferred that a same number of first fins and second fins is provided. In principle, however it would also be possible to provide an unequal number of first and second fins. 
         [0031]    It is particularly preferred that the device has at least three first fins and/or at least three second fins, preferably three to seven first fins and/or three to seven second fins. In a preferred embodiment, an odd number of first fins and/or second fins can be provided. 
         [0032]    It is further preferred that more first fins are provided on the propeller upwards-beating side of the flow-guiding surface than on the propeller downwards-beating side of the flow-guiding surface and/or that more second fins are provided on the propeller upwards-beating side of the flow-guiding surface than on the propeller downwards-beating side of the flow-guiding surface. The term “propeller upwards-beating side of the flow-guiding surface” is understood as that side of the flow-guiding surface on which the propeller arranged downstream of the flow-guiding surface in a frontal view of the flow-guiding surface turns from bottom to top when travelling forwards. Accordingly on the propeller downwards-beating side the propeller turns from top to bottom. The embodiment described in the present case can therefore be used particularly expediently in flow-guiding surfaces whose central longitudinal axis of rotation is not displaced laterally with respect to the propeller axis but rather lies in a plane standing vertically on the propeller axis so that with an imaginary division of the flow-guiding surface by a central vertical axis one half of the flow-guiding surface lies on the propeller upwards-beating side and the other half lies on the propeller downwards-beating side. 
         [0033]    In order to minimise the rotational losses at the propeller and to reduce twisting in the propeller backwash induced by the propeller inflow perturbed by the hull of the ship, a (pre-)swirl is produced by the fins (first fins or second fins) disposed on the flow-guiding surface which is aligned in such a manner that a smaller twisting of the flow is established downstream of the propeller in the propeller backwash region compared to a propeller without a flow-guiding surface with fins placed in front. The twisting of the propeller backwash is now particularly small if at least one first fin and/or one second fin more is disposed on the propeller upwards-beating side than on the propeller downwards-beating side. 
         [0034]    Alternatively or additionally to the distribution of the first fins and/or second fins on the propeller upwards-beating side and propeller downwards-beating side, the first fins and/or the second fins can form an asymmetric first fin system or an asymmetric second fin system. Here, an asymmetry relates, for example, to an angular arrangement of the fins with respect to the propeller axis and/or their dimensioning such as profile length, profile cross-section or another quantity. In the case of an asymmetry in relation to the angular arrangement directed onto the propeller axis, an unequal angular distribution is established between the axes of the individual first fins and/or second fins when viewed in the radial direction from the propeller axis. An asymmetric arrangement can also be present if the vertical central axis of the flow-guiding surface is used as the axis of symmetry. This axis of symmetry usually at the same time divides the upwards-beating and downwards-beating side of the flow-guiding surface. This results in a particularly effective first fin system or second fin system in a manner which is easy to configure and arrange. 
         [0035]    In a further preferred embodiment, the at least one first fin is arranged in extension of the at least one second fin so that both together form a complete fin. Thus, for example, the longitudinal axes of the first fin and the second fin can substantially stand on one another and/or the first fin and the second fin are disposed on a common radial axis. Preferably the first end of the second fin, which is expediently disposed on the inner wall surface of the flow-guiding surface is located opposite the first end of the first fin which is disposed on the outer wall surface of the flow-guiding surface so that only the flow-guiding surface lies between the two fins. In principle, both end regions could each be introduced into the profile of the flow-guiding surface or into the flow-guiding surface so that these then possibly abut against one another or are only slightly spaced apart from one another. It is also possible to use a continuous fin which is guided through a recess in the flow-guiding surface and of which one subsection forms a first fin and another subsection forms a second fin. As a result of this preferred arrangement of the two fins, fluidically a single fin is obtained which expediently runs from the shaft bearing to the free end of the first fin. If a plurality of first fins and second fins, in particular the same number of first fins and second fins are provided, these are each advantageously arranged in fin pairs which then each form complete fins. Thus, for example, three first fins and three second fins could together form three complete fins. 
         [0036]    Compared to the pure stator arrangements known from the prior art or arrangements with fins without flow-guiding surface, projecting radially from the stern tube, a significantly increased strength of the entire arrangement is obtained through the provision of the flow-guiding surface. As a result, the complete fins can be designed to be sufficiently long with an ensured fatigue strength in order to optimally influence the inflow onto the propeller or achieve the best possible efficiency. In the arrangements known from the prior art with long fins without flow-guiding surface, a fatigue strength is frequently not achieved. 
         [0037]    The length of the complete fin can generally be larger or smaller than the radius of a propeller of the watercraft. The length of the complete fin is measured from the propeller axis to the outermost (free) end of the first fin, where optionally the flow-guiding surface disposed between the two fins (first and second fin) is also included. Preferably the length of the complete fin is a maximum of 90% of the radius of the propeller, particularly preferably a maximum of only 75%. However, a sufficient strength of the device is thereby achieved. 
         [0038]    In a further preferred embodiment, the first fin and/or the second fin are disposed at an angle of attack radially to the propeller axis. In particular, the first fin and the second fin can have different angles of attack. If a plurality of first fins and/or second fins are provided, these can also have different angles of attack amongst one another. By setting the different angles of attack, it is possible to optimise a pre-swirl. The angle of adjustment is, for example, enclosed by a chord running from the nose strip to the end strip of the respective fin or also the longitudinal axis of the fin in cross-sectional view and the propeller axis. 
         [0039]    In a further preferred embodiment the first fin has a free end which forms the region of the first fin most remote from the flow-guiding surface. At this free end region a fin end piece protrudes from the first fin. Thus, for example, a longitudinal axis of this fin end piece can be located at an angle to the longitudinal axis of the first fin. The term “protruding fin end piece” in the present case generally means all the components disposed in the region of the free end of the first fin which are not disposed precisely in the extension of the first fin but protrude obliquely from the first fin or at a specific angle from the first fin or deviate from the fictitiously extended profile contour of the first fin. The fin end piece therefore protrudes from the fin plane. Such a protruding fin end piece acts similar to the “winglets” known from aircraft aerofoils and reduces the probability of vortices becoming detached in the end region of the first fin and of cavitation occurring in the same. 
         [0040]    The fin end piece can go over into the free end region of the first fin at a radius. Alternatively the fin end piece can be mounted at an angle on the free end of the first fin so that the fin end piece plane and the plane over which the first fin extends are at this angle. 
         [0041]    In principle, the fin end piece can protrude on both sides, i.e. both on the pressure side and on the suction side, of the first fin from this or only on one of the two sides. In the last embodiment it is preferred that the fin end pieces only protrude towards the suction side of the first fin since as a result greater hydrodynamic effects in relation to the reduction of vortex formation can be achieved. For the embodiment in which the fin end piece protrudes or projects on both sides of the first fin, two separate fin end pieces can also be provided which then each protrude on one side. In principle, however in this embodiment a one-piece design of the fin end piece is possible. 
         [0042]    It is further preferred that in the presence of at least one first fin and one second fin, the first fin has a larger length than the second fin. In particular, the length of the first fin can be at least one and a half times, preferably at least twice as large as the length of the second fin. As a result of this embodiment, an improved effect in relation to the drive power requirement and in relation to the stability of the device is achieved. As a result of the length distribution in this preferred embodiment, the flow-guiding surface is disposed relatively close to the shaft bearing of the propeller shaft so that the device has a relatively low resistance and can also be used for very fast ships. Generally, however, any design is possible in which the second fin has a greater length than the first fin, e.g. at least one and a half times or at least twice the length or in which both fins have approximately the same length. 
         [0043]    In order to ensure a sufficiently low resistance of the device, according to a further embodiment it can be provided that the profile thickness of the flow-guiding surface is no more than 10%, preferably no more than 7.5%, particularly preferably no more than 6% of the length of the flow-guiding surface. Here the maximum profile thickness and the maximum extension in the longitudinal direction, i.e. from the profile inlet edge to the profile outlet edge of the flow-guiding surface, should be used. By this means, the resistance of the device is also further reduced. 
         [0044]    In a further preferred embodiment, a stabilizing strut is further provided which is disposed between shaft bearing and inner side of the flow-guiding surface and is fastened both on the shaft bearing and on the flow-guiding surface. Such a stabilizing strut can be provided if according to local conditions or particular configuration of the device, an additional stabilization or retaining of the device or the flow-guiding surface is desired. The strut can generally be configured as a normal compression or tension rod without flow-guiding properties. Alternatively, the stabilizing strut itself can also have a fin profile, i.e. a hydrofoil profile or similar for specific influencing of the propeller inflow, for example, to produce pre-swirl. 
         [0045]    The first fin and/or the second fin can further be configured to be swept. The term “swept” familiar, inter alia, from air travel, is to be understood in the present context as an angular deviation of the first fin and/or the second fin in relation to an orthogonal of the longitudinal axis of the flow-guiding surface. In this case, the leading edge and/or trailing edge of the fin (first fin and/or second fin), when viewed in the direction of flow, can be inclined at an angle with respect to the orthogonal (these states are known as leading-edge sweep or trailing-edge sweep). 
         [0046]    In a preferred embodiment only the leading edge of the first fin and/or the second fin is inclined with respect to the orthogonal or located at an angle to the orthogonal and the trailing edge is aligned approximately parallel to the orthogonal. There can also be embodiments in which only the first fin is configured to be swept but not the second fin. 
         [0047]    In a further preferred embodiment, both the first fin and the second fin are configured to be swept. This can in particular be preferred when the flow-guiding surface comprises at least one complete fin where the complete fin is then particularly preferably configured to be continuously swept, i.e. with the same angular deviations of the leading edges and/or the trailing edges of the first fin and the second fin to the orthogonal of the longitudinal axis of the flow-guiding surface. 
         [0048]    It is further preferred that the flow-guiding surface is configured as a nozzle and particularly preferably as a fore-nozzle. For this purpose, the flow-guiding surface is shaped in such a manner that it not only has the property to guide the flow specifically onto the propeller but additionally is also shaped in such a manner that the inflow velocity is increased at least in sections. This can be provided, for example, with an arcuately configured flow-guiding surface in which the radius of the ring (in a cross-sectional view) in the longitudinal direction of the flow-guiding surface decreases from front to back towards the propeller. 
         [0049]    Fore-nozzle is to be understood as a nozzle which is disposed upstream of the propeller of the watercraft in the direction of travel of the ship or watercraft. 
         [0050]    In a preferred embodiment wherein the flow-guiding surface is configured as a nozzle or fore-nozzle, no propeller is disposed inside the nozzle or fore-nozzle, other than for example in Kort nozzles or rudder propellers. Furthermore, the nozzle or fore-nozzle and also the flow-guiding surface not configured as a nozzle is disposed at a distance from the propeller. The nozzle or fore-nozzle is configured in such a manner that the through-flowing water flow is guided at least partially onto the propeller located thereafter. Usually the nozzle or fore-nozzle will have a tubular shape. However, any other cross-sectional shape, for example, an angled cross-sectional shape is also feasible. 
         [0051]    The nozzle or fore-nozzle can be configured in one part or one piece or be composed of several individual parts to form a nozzle or fore-nozzle, wherein the individual parts are preferably welded to one another or to the hull. Preferably at least one partial region of the nozzle or fore-nozzle is located underneath the propeller shaft of the ships&#39; propeller. 
         [0052]    Generally it is possible that the nozzle or fore-nozzle only comprises a partial section of a nozzle or a nozzle ring (for example, a quarter nozzle ring, a third nozzle ring, a half nozzle ring, etc.). In such an embodiment the nozzle or fore-nozzle is configured to be open when viewed over the circumference. 
         [0053]    Preferably however the nozzle or fore-nozzle is configured to be closed in the circumferential direction. For this purpose the nozzle or fore-nozzle can be configured to be continuous about 360 degrees in the circumferential direction. In the case of a nozzle or fore-nozzle configured to be multipart, furthermore, in particular with a closed nozzle circumference, the individual parts of the nozzle or fore-nozzle can be connected to the hull and/or the stern tube so that the hull and/or the stern tube then form a part of the nozzle circumference. 
         [0054]    In all the aforesaid embodiments of the device, the flow-guiding surface can be configured as a nozzle or fore-nozzle. In such a configuration, the first fins are arranged projecting outwards from the nozzle or fore-nozzle. Therefore in such an embodiment the first fins are also called outer fins. On the other hand, when a flow-guiding surface is provided as a nozzle or fore-nozzle, the second fins are arranged inside the nozzle or fore-nozzle. These second fins are accordingly also called inner fins. 
         [0055]    As a result of the preferred circumferentially closed profile of the nozzle or fore-nozzle, these have an inner region which is enclosed by the nozzle jacket of a nozzle or fore-nozzle which is conceptually closed at both openings (water inlet and water outlet opening). The at least one outer fin is now preferably arranged outside this inner region and rather protrudes outwards when viewed from the fore-nozzle or nozzle. In particular, the at least one outer fin can project from the outer side of the nozzle or fore-nozzle. 
         [0056]    In contrast to the prior art, a fin pertaining to the nozzle or fore-nozzle, the at least one outer fin, is now provided outside the nozzle or fore-nozzle. Expediently at least one end region of the outer fin is disposed on the outer wall surface of the nozzle or fore-nozzle and projects outwards from this. That is, the remaining region of the at least one outer fin is located at a distance from the nozzle or fore-nozzle. As a result of providing a fin outside on a nozzle or fore-nozzle for the first time, it is now achieved that the diameter and/or profile thickness of the nozzle or fore-nozzle can be reduced significantly compared with the devices known from the prior art and the at least one outer fin nevertheless reaches those regions in which the flow losses are particularly high and in which a swirl must be produced for efficient operation. If the diameter in the devices known from the prior art were to be simply reduced, the fins would in contrast to the present invention not extend sufficiently far from the propeller hub (when viewed in the radial direction from the propeller hub) and thus would no longer or only to a small extent have a positive influence on the inflow to the propeller assigned in each case. 
         [0057]    By attaching one or more outer fins to the outer side of the fore-nozzle or nozzle, the diameter of the nozzle or fore-nozzle and therefore the resistance thereof can be reduced so that the device can now also be used for fast and very fast ships where the positive effects on the reduction of the drive power requirement are maintained or optionally even improved. Since the outer fin projects outwards from the nozzle or fore-nozzle and possibly not from the propeller hub or the stern tube, this can extend relatively far outwards when viewed from the propeller axis and nevertheless still have sufficient strength, in particular in relation to bending stresses. 
         [0058]    The nozzle or fore-nozzle can be configured to be rotationally symmetrical or rotationally asymmetrical. Furthermore, the nozzle or fore-nozzle can be disposed concentrically with the propeller axis or eccentrically thereto. In particular, the axis of rotation and/or the longitudinal axis of the nozzle or fore-nozzle can be arranged upwardly and/or laterally offset with respect to the propeller axis. Furthermore, the nozzle or fore-nozzle can be arranged in such a manner that its axis of rotation or its longitudinal axis runs parallel to the propeller axis or runs at an angle to the propeller axis and consequently is inclined in relation to the propeller axis. The nozzle or fore-nozzle is furthermore preferably aligned centrally in the horizontal direction, relative to the propeller axis. As a result, the axis of rotation of the nozzle or fore-nozzle and the propeller axis lie in a vertical plane. Generally however a twisted arrangement of the nozzle or fore-nozzle with respect to a vertical running through the propeller axis or a parallel thereto is also possible. 
         [0059]    The displacement of the nozzle or fore-nozzle with respect to the propeller axis upwards and/or to the side can be advantageous particularly because the water speed is usually faster in the lower region of the fore-nozzle or the propeller than in the upper region as a result of the shape of the ship or the configuration of the hull. As a result of the displacement of the fore-nozzle with respect to the propeller axis, adapted to the particular configuration of the hull, a homogenisation of the propeller inflow and therefore a better efficiency can possibly be achieved. 
         [0060]    Expediently the fore-nozzle consists of a continuous and/or one-piece annular body or nozzle ring. The preferred embodiment can also be used in multi-propeller ships where a nozzle or fore-nozzle is then expediently to be assigned to each propeller. The propellers assigned to the device are usually installed fixed or in a fixed position on the hull. The fore-nozzle or nozzle together with the propeller of the watercraft forms a drive system. 
         [0061]    Furthermore, it is advantageous if the diameter of the nozzle or fore-nozzle is no more than 85%, preferably no more than 70%, particularly preferably no more than 50% or no more than 35% of that diameter of the propeller to which the nozzle or fore-nozzle is assigned. This also ensures that the nozzle profile or the nozzle ring overall is not too large and therefore the resistance of the nozzle or fore-nozzle is so low that it is possible to also use the device in fast and very fast ships. If the nozzle or fore-nozzle should not be rotationally symmetrical or cylindrical or conical, instead of the diameter, the greatest extension of the nozzle or fore-nozzle in height or width can be related to the propeller diameter. Furthermore, the outside diameter of the fore-nozzle should expediently be used. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0062]    The invention is explained in further detail hereinafter by means of the exemplary embodiments shown in the drawings. In the figures shown schematically: 
           [0063]      FIG. 1  shows a rear view of a lower region of a hull with a flow-guiding surface configured in a plate shape, arranged upstream of the propeller; 
           [0064]      FIG. 2 : shows a rear view of a lower region of a hull with a flow-guiding surface configured in an arcuate shape, arranged upstream of the propeller; 
           [0065]      FIG. 3 : shows a side view of a flow-guiding surface with a first fin; 
           [0066]      FIG. 4 : shows a perspective view of a further embodiment with arcuately configured flow-guiding surface; 
           [0067]      FIG. 5 : shows a sectional view of a fin; 
           [0068]      FIG. 6 : shows a rear view of a lower region of a hull with fore-nozzle arranged coaxially with the propeller; 
           [0069]      FIG. 7 : shows a rear view of a lower part of a hull with fore-nozzle shifted upwards with respect to the propeller axis; 
           [0070]      FIG. 8 : shows a side view of a fore-nozzle with outer fin which is inclined with respect to the propeller axis; 
           [0071]      FIG. 9 : shows a perspective view of a further embodiment of the device; 
           [0072]      FIG. 10 : shows a side view of the device from  FIG. 9 ; and 
           [0073]      FIG. 11 : shows a perspective view of a further embodiment of the device installed on a hull. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0074]    In the various embodiments shown in the following, the same components are provided with the same reference numbers. 
         [0075]      FIG. 1  shows a rear view of the rear lower region of a hull  30 . A shaft bearing  31  configured as a stern tube projects from the hull  30  from the stern approximately in the horizontal direction. In the diagram in  FIG. 1 , the shaft bearing  31  runs out from the plane of the drawing or into this. A propeller shaft (not shown here) which runs along the propeller axis  32 , is mounted in this shaft bearing  31 . In the diagram from  FIG. 1  the propeller axis  32  also leads out from the plane of the drawing or into this. The propeller  33  is only indicated schematically as a propeller circle since this lies downstream of the flow-guiding surface  50  in the direction of travel and therefore outside the plane of the drawing. The present ship is a so-called single-propeller ship and therefore only has one propeller  33 . 
         [0076]    The flow-guiding surface  50  is located at a distance from the propeller upstream of the propeller  33 . Furthermore, the flow-guiding surface  50  is configured to be plate-shaped and thus extends on a plane parallel to the propeller axis  32 . The flow-guiding surface  50 , as shown in  FIG. 1 , is located at a constant distance  54  from the propeller axis  32 . 
         [0077]    The device  100  shown in  FIG. 1  has two first fins  50   a  projecting outwards from the flow-guiding surface  50 . Each of these two first fins  50   a  is connected with its first end  501  to the flow-guiding surface  50 . The respective second end  502  of the first fin  50   a  is configured as a free-standing end. Furthermore, the device shown in  FIG. 1  has a second fin  51   a . This second fin  51   a  is connected with its first end  503  to the flow-guiding surface  50 . With its second end  504  the second fin  51   a  is connected to the shaft bearing  31 . 
         [0078]      FIG. 2  shows a rear view of the rear region of a hull  30 . The device according to  FIG. 2  differs from the device according to  FIG. 1  only in that the flow-guiding surface  50  is configured to be arcuate. 
         [0079]      FIG. 3  shows a side view of the lower stern section of a ship. Projecting approximately horizontally from the stern of a hull  30  is a shaft bearing  31  configured as a stern tube in which a propeller shaft (not shown here) is located. The propeller shaft runs along a propeller axis  32 . A propeller  33  is provided at the end of the shaft bearing  31 . Further, in the direction of travel upstream of the propeller  33  a flow-guiding surface  50  is shown at a distance from the propeller  33  and upstream of the propeller  33 . Furthermore, a first fin  50   a  projecting outwards or upwards is located on the flow-guiding surface  50 . The first fin  50   a  is connected with its first end  501  to the flow-guiding surface in the upper region of said arcuately configured flow-guiding surface  50  whilst its second end  502  is configured as a free-standing end. 
         [0080]      FIG. 4  shows a perspective view of a further embodiment of the device  100 . This device  100  also comprises a fore-nozzle  10  configured to be open in the circumferential direction and four outer fins  20   a  to  20   d  as well as four inner fins  21   a  to  21   d , where in each case a fin pair  20   a ,  21   a ;  20   b ,  21   b ;  20   c ,  21   c ;  20   d ,  21   d  forms a complete fin. Thus, according to  FIG. 4 , the flow-guiding surface  50  is configured as an open nozzle ring. The open nozzle ring corresponds approximately to a so-called two-thirds nozzle since this nozzle ring corresponds to approximately two thirds of a circumferentially closed nozzle. Furthermore, reference is made to the explanations to  FIG. 9 .  FIG. 9  shows a similar embodiment where however, in contrast to the embodiment shown in  FIG. 4 , the device  100  in  FIG. 9  shows a fore-nozzle  10  which is configured to be closed in the circumferential direction. 
         [0081]      FIG. 5  shows a cross-sectional view of an example of a fin. The fin shown can in principle be the cross-section of a first fin  50   a  or second fin  51   a . In the example shown in  FIG. 5 , the fin shown is the first fin  50   a . The fin  50   a  has a curved suction side  203  arranged at the top in the drawing of  FIG. 5  and an oppositely arranged, substantially flat pressure side  204 . The rounded front face  205  which forms a part of the leading edge of the fin  50   a  would be placed in the flow in a state installed in the fore-nozzle  10 , i.e. disposed upstream. To that effect, the approximately pointed rear face  206  (i.e. the profile end) which forms a part of the trailing edge of the fin  50   a  would be located downstream of the propeller flow in the state installed in a fore-nozzle  10 . 
         [0082]      FIG. 6  shows a rear view of the rear lower region of a hull  30 . A shaft bearing  31  configured as a stern tube projects from the hull  30  from the stern approximately in the horizontal direction. In the diagram in  FIG. 6 , the shaft bearing  31  runs out from the plane of the drawing or into this. A propeller shaft (not shown here) which runs along the propeller axis  32 , is mounted in the shaft bearing  31 . In the diagram from  FIG. 6  the propeller axis  32  also leads out from the plane of the drawing or into this. The propeller axis  32  at the same time forms the longitudinal axis of a fore-nozzle  10  arranged concentrically about the propeller axis  32 . Since the fore-nozzle  10  in the present exemplary embodiment is shown as a rotationally symmetrical body, the propeller axis  32  at the same time also forms the axis of rotation of the fore-nozzle  10 . The propeller  33  is only indicated schematically as a propeller circle since this lies downstream of the fore-nozzle  10  in the direction of travel and therefore outside the plane of the drawing. The present ship is a so-called single-propeller ship and therefore only has one propeller  33 . 
         [0083]    The fore-nozzle  10  has a circumferentially closed nozzle wall  11  which in turn comprises an inner wall surface  12  and an outer nozzle wall surface  13 . A vertical central line  34  and a horizontal central line  35  is drawn through the propeller  33 . Since the fore-nozzle  10  is arranged concentrically to the propeller  33 , the central lines  34 ,  35  are also central lines for the fore-nozzle  10 . The propeller axis  32  lies at the point of intersection of the two central lines  34 ,  35 . In an imaginary division of the fore-nozzle  10  by the vertical central line  34 , the left fore-nozzle half is the propeller upwards-beating side  14  of the fore-nozzle  10  and the right fore-nozzle half is the propeller downwards-beating side  15  of the fore-nozzle  10 . 
         [0084]    Inner fins  21   a ,  21   b ,  21   c  each arranged to run between the shaft bearing  31  and the inner side  12  of the fore-nozzle wall  11  are provided on the propeller upwards-beating side  14  of the fore-nozzle  10  (in relation to a right-handed propeller). Another inner fin  21   d  which also runs between shaft bearing  31  and fore-nozzle wall  11  is mounted on the propeller downwards-beating side  15  and specifically above the horizontal central line  35 . The inner fins  21   a ,  21   b ,  21   c ,  21   d  are each fastened on the shaft bearing  31  and on the fore-nozzle  10 . From the outer fore-nozzle wall surface  13 , four outer fins  20   a ,  20   b ,  20   c ,  20   d  project outwards from the fore-nozzle  10 . The outer fins  20   a ,  20   b ,  20   c ,  20   d  are each arranged in extension of the inner fins  21   a ,  21   b ,  21   c ,  21   d . The outer fins  20   a ,  20   b ,  20   c ,  20   d  and also the inner fins  21   a ,  21   b ,  21   c ,  21   d  are all arranged radially to the propeller axis  32  or the axis of rotation of the fore-nozzle and run accordingly in the radial direction to the propeller axis  32 . The longitudinal axis of the inner fins  21   a ,  21   b ,  21   c ,  21   d  approximately corresponds to the longitudinal axis of the outer fins  20   a ,  20   b ,  20   c ,  20   d  in an imaginary extension. Therefore the individual fin pairs  20   a ,  21   a ;  20   b ,  21   b ;  20   c ,  21   c ;  20   d ,  21   d ; each form a complete fin. That is, they act fluidically approximately as a continuous fin but are de facto interrupted by the fore-nozzle  10  and each fastened thereon (for example, by welding or by welding to the fore-nozzle). The device  100  thereby acquires a high stability with a relatively large length of the complete fin. 
         [0085]    Overall three complete fins are arranged on the propeller upwards-beating side  14  and one complete fin on the propeller downwards-beating side  15 . On the propeller downwards-beating side  15  and specifically below the horizontal central line  35 , there is further provided a stabilizing strut  22  which runs between shaft bearing  31  and fore-nozzle  10  and is connected to both. This stabilizing strut  22  is configured in such a manner that it acts as a compression or tension rod and fastens the fore-nozzle  10  to the hull and stabilizes this. The stabilizing strut  22  is not configured as a fin, i.e. it does not have a hydrofoil profile or the like but is configured in such a manner that it influences the flow as little as possible. The stabilizing strut  22  has a greater profile width compared with the fins  20   a ,  20   b ,  20   c ,  20   d ,  21   a ,  21   b ,  21   c ,  21   d.    
         [0086]    The outer fins  20   a ,  20   b ,  20   c ,  20   d  each have a first end  201  which is disposed on the outer wall surface  13  of the fore-nozzle  10  and is connected to the fore-nozzle  10 . The outer fins also have a second end  202  opposite the first end  201  which is configured as a free end. Fin end pieces  23  project laterally from the second end  202 . In the diagram in  FIG. 6 , the fin end pieces  23  each point towards the lower side of the outer fins  20   a ,  20   b ,  20   c , which forms the suction side. At the outer fin  20   d , two fin end pieces  23  which are arranged symmetrically to one another are provided on the free end  202 . One fin end piece  23  protrudes towards the upper side and one towards the lower side of the outer fin  20   d . The fin end pieces  23  act as “winglets” and reduce the occurrence of so-called detachment turbulence and cavitation in the region of the free ends  202  of the outer fins  20   a ,  20   b ,  20   c ,  20   d . The fin end pieces  23  each go over into the respective outer fin  20   a ,  20   b ,  20   c ,  20   d  at a radius. 
         [0087]      FIG. 7  shows a similar view to  FIG. 6 . In the embodiment according to  FIG. 7 , unlike  FIG. 6 , the fore-nozzle  10  with its axis of rotation  16 , which at the same time also forms the longitudinal axis of the fore-nozzle  10 , is shifted upwards with respect to the propeller axis  32 . Accordingly, the inner fins  21   a ,  21   b ,  21   c ,  21   d  have different lengths whereas in the diagram from  FIG. 6  the inner fins  21   a ,  21   b ,  21   c ,  21   d  all have the same length. The stabilizing strut  22  is also shortened compared with the embodiment from  FIG. 6 . In the diagram from  FIG. 7 , the outer fins  20   a ,  20   b ,  20   c ,  20   d  furthermore also have different lengths whereas in the diagram from  FIG. 6  the outer fins  20   a ,  20   b ,  20   c ,  20   d  each have the same length. Both in the embodiment from  FIG. 6  and in the embodiment from  FIG. 7 , the radius of the propeller  33  is in each case greater than the length of the (longest) complete fin. In the embodiment from  FIG. 7  the length of the longest complete fin (for example, composed of outer fin  20   c  and inner fin  21   c ) is longer than the complete fin from  FIG. 6 . 
         [0088]      FIG. 8  shows a side view of the lower stern section of a ship. A shaft bearing  31 , configured as a stern tube in which a propeller shaft (not shown here) is arranged, projects approximately horizontally from the stern of a hull  30 . The propeller shaft runs along a propeller axis  32 . A propeller  33  is provided at the end of the shaft bearing  31 . A fore-nozzle  10  is further provided in the direction of travel ahead of the propeller  33 . The axis of rotation or longitudinal axis  16  runs centrally through the rotationally symmetrical fore-nozzle  10 . The fore-nozzle  10  is shifted upwards with its axis of rotation  16  with respect to the propeller axis  32 . Furthermore, the axis of rotation  16  is inclined at an angle α with respect to the propeller axis  32 . That is, the fore-nozzle  10  is aligned or arranged with its leading upper edge region, when viewed in the direction of travel, inclined or tilted forwards and downwards with respect to the propeller axis  32 . In the upper region of the fore-nozzle  10 , an outer fin  20  projects upwards from the fore-nozzle  10 . The outer fin  20  is located in the trailing region of the fore-nozzle  10  facing the propeller  33  when viewed in the direction of travel. A rudder  36  for manoeuvring the ship is provided downstream of the propeller  33  in the direction of travel. 
         [0089]      FIG. 9  shows a perspective view of another embodiment of the device  100  according to the invention. This device  100  also comprises a nozzle ring closed into itself in the circumferential direction or a fore-nozzle  10  and four outer fins  20   a  to  20   d  and four inner fins  21   a  to  21   d , where respectively one pair of fins  20   a ,  21   a ;  20   b ,  21   b ;  20   c ,  21   c ;  20   d ,  21   d  forms a complete fin. The individual fins  20   a  to  20   d ;  21   a  to  21   d  each have a cross-sectional profile in the manner as shown in  FIG. 5 . In particular, each of the fins  20   a  to  20   d ;  21   a  to  21   d  comprises a suction side  203  and a pressure side  204 . The fins  20   a  to  20   d ;  21   a  to  21   d  are each disposed in the rear region of the fore-nozzle  10 . The diagram in  FIG. 9  shows a type of exploded view so that the individual fins  20   a  to  20   d ;  21   a  to  21   d  are not shown continuously in their state connected to the fore-nozzle  10 . Both the outer fins  20   a  to  20   d  and the inner fins  21   a  to  21   d  are disposed in the rear region of the fore-nozzle  10  when viewed in the direction of travel  37 . In particular, the rear region is no longer than 70%, preferably 55%, of the total length of the fore-nozzle  10  when viewed in the direction of travel. The fore-nozzle  10  is shown transparent in  FIG. 9  so that for reasons of clarity the outer fins  20   a  to  20   d  and the inner fins  21   a  to  21   d  are each completely identifiable. 
         [0090]    The fin end pieces  23  which are attached to each of the second ends  202  of the outer fins  20   a  to  20   d  are configured in the manner of plates and project laterally on one side from the outer fins  20   a  to  20   d . The edge  231  of the fin end pieces  23  configured as plates, facing the leading edge or the front face  205  of the outer fins  20   a - 20   d  runs laterally to the main inflow direction  18  of the fore-nozzle  10  and slightly obliquely rearwards. The two lateral edges  232  of the fin end pieces  23  are aligned approximately parallel to the main inflow direction  18  whilst the trailing edge  233  of the fin end pieces  23  runs substantially orthogonally to the main inflow direction  18 . In relation to the longitudinal direction of the outer fins  20   a  to  20   d , the fin end pieces  23  protrude outwards at an angle of 90° to 120° where the fin end pieces  23  in the case of a right-handed propeller protrude laterally from the outer fins  20   a  to  20   d  in the direction of rotation of the propeller. In the device  100  from  FIG. 9 , the inner fins  21   a  to  21   d  each have a greater length than the outer fins  20   a  to  20   d . Furthermore all the outer fins  20   a  to  20   d  have the same dimensions in relation to their length, width and depth, and also profile shape. The same applies similarly for the inner fins  21   a  to  21   d . Since the inner fins  21   a  to  21   d  have the same length, the axis of rotation or longitudinal axis of the fore-nozzle  10  is arranged coaxially with the propeller axis, that is the two axes lie one upon the other. 
         [0091]    The outer fins  20   a  to  20   d  are configured to be swept whereas the inner fins  21   a  to  21   d  are configured to be non-swept. This can be seen in detail in the diagram in  FIG. 10  which shows the device  100  from  FIG. 9  in a side view. The axis of rotation or longitudinal axis  16  of the fore-nozzle  10  is indicated in the diagram in  FIG. 10 . A first upwardly-projecting orthogonal  17   a  and a second downwardly-projecting orthogonal  17   b  to the axis of rotation  16  is indicated. The fore-nozzle  10  is shown transparent in  FIG. 10  so that for reasons of clarity the interior inner fins  21   b  to  21   d  can be identified. It can further be identified that the leading edge  205  of the inner fin  21   b  is disposed substantially parallel to the orthogonal  17   a . It can also be identified that the trailing edge  206  of the inner fin  21   d  is disposed substantially parallel to the orthogonal  17   b . Since the inner fins  21   b  to  21   d  have the same configuration, these parallel arrangements apply similarly for all inner fins  21   b  to  21   d . In other words, the depth of the inner fins  21   b  to  21   d  when viewed in the main inflow direction  18  or when viewed in the direction of travel  37  is substantially constant over the length of the inner fins  21   b  to  21   d . The inner fins  21   b  to  21   d  are accordingly configured to be non-swept. 
         [0092]    In contrast to this, the outer fins  20   b  to  20   d  are configured to be swept and specifically having a leading-edge sweep. Accordingly, the leading edge  205  of the outer fin  20   b  is aligned at a sweep angle  13  to the orthogonal  17   a . This applies similarly for the remaining outer fins as a result of the same configuration. The trailing edges  206  of the outer fins  20   b  to  20   d  are again aligned substantially parallel to the orthogonals  17   a ,  17   b  so that the trailing edge of the outer fins  20   b  to  20   d  is not swept, that is, not inclined at an angle to the orthogonals. Accordingly the depth of the outer fins  20   b  to  20   d  decreases when viewed in the direction of travel  37  from the first end  201  to the second end  202 . Since the leading edge  205  is rectilinear, the decrease from one end  201  to the other end  202  is continuous. The outer fin  20   a  and inner fin  21   a  not shown in  FIG. 10  are configured similarly to the other inner fins  21   b  to  21   d  and outer fins  20   b  to  20   d.    
         [0093]    It can be further identified in  FIG. 10  that the outside diameter of the fore-nozzle  10  decreases continuously in the main inflow direction  18 . Likewise, the inside diameter of the fore-nozzle  10  decreases in the main inflow direction  18  but not continuously as a result of the arcuate configuration of the inner fore-nozzle wall surface  11  in profile view. 
         [0094]      FIG. 11  shows another embodiment of a device  100  according to the invention which is configured similarly to that from  FIGS. 9 and 10 . In particular this device  100  also comprises four outer fins  20   a  to  20   d  and four inner fins  21   a  to  21   d  where respectively one fin pair forms a complete fin. Both in the embodiment from  FIG. 11  and also in the embodiment from  FIGS. 9 and 10 , and  1  and  2 , the complete fins are arranged asymmetrically inside the fore-nozzle  10 . 
         [0095]    In contrast to the embodiment according to  FIGS. 9 and 10 , in the embodiment from  FIG. 11  the second end  203  of the outer fins  20   a  to  20   d  does not go over into the fin end pieces  23  at an angle, but with a transition  23   a  having a radius. Furthermore, in  FIG. 11  the complete fins run through the fore-nozzles  10 , that is, the complete fins are formed in one piece whereas in the embodiment from  FIGS. 9 and 10  the complete fins are each formed in two pieces and the inner fins and outer fins are each fastened separately to the fore-nozzle  10 . Another difference in the embodiment according to  FIG. 11  with respect to the embodiment according to  FIGS. 9 and 10  consists in that both the inner fins  21   a  to  21   d  and also the outer fins  20   a  to  20   d  are configured to be swept. Here also only the leading edge of the fin is configured to be swept in each case, but not the trailing edge. The sweep of the leading edges of the inner fins  21   a  to  21   d  is accomplished at the same angle with respect to an orthogonal to the axis of rotation as for the outer fins  20   a  to  20   d  so that a continuous leading-edge sweep with a constant angle is obtained. 
         [0096]    It can further be identified in  FIG. 11  that the device  100  is mounted on the hull  30  and specifically in the direction of travel  37  at the rear end of the hull  30 . 
       REFERENCE LIST 
       [0000]    
       
           100  Device 
           10  Fore-nozzle 
           11  Fore-nozzle wall 
           12  Inner fore-nozzle wall surface 
           13  Outer fore-nozzle wall surface 
           14  Propeller upwards-beating side 
           15  Propeller downwards-beating side 
           16  Axis of rotation of the fore-nozzle 
           17  Orthogonal to the axis of rotation 
           18  Main inflow direction 
           20 ,  20   a ,  20   b,    
           20   c ,  20   d  Outer fins 
           201  First end of outer fin 
           202  Second end of outer fin 
           203  Suction side 
           204  Pressure side 
           205  Front face 
           206  Rearward face 
           21   a ,  21   b,    
           21   c ,  21   d  Inner fins 
           22  Stabilizing strut 
           23  Fin end piece 
           23   a  Transition 
           30  Ship&#39;s hull 
           31  Shaft bearing 
           32  Propeller axis 
           33  Propeller 
           34  Vertical central line 
           35  Horizontal central line 
           36  Rudder 
           37  Direction of travel 
           50  Flow-guiding surface 
           50   a  First fin 
           51  Profile thickness of flow-guiding surface 
           51   a  Second fin 
           52  Profile inlet edge 
           53  Profile outlet edge 
           54  Distance between flow-guiding surface and propeller axis 
           55  Propeller diameter 
           501  First end of first fin 
           502  Second end of first fin 
           503  First end of second fin 
           504  Second end of second fin 
         α Angle of intersection between axis of rotation and propeller axis 
         β Sweep angle