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1. (WO2018139937) RUDDER DEVICE
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RUDDER DEVICE

The present invention relates to a rudder for a vessel. More specifically the invention relates to a rudder for a vessel where the rudder comprises a profile element provided at the leading edge of the rudder; a rudder body provided behind the profile element, where the rudder body is rotatable, by means of a rudder stock, relative to the profile element around a substantially vertical axis, and wherein the profile element is provided with ducts, connectable to a water supply, and adapted to discharge water rearwards along the surface of the rudder body. The invention also relates to a rudder system comprising such a rudder as well as a vessel provided with such a rudder system.

Generally, a rudder should be designed so as to produce minimum resistance and at the same time produce a maximum sideways lift in the intended lateral direction. These two properties have been difficult to optimize for the same rudder and a trade-off usually has to be made. Further, in order to secure a required steering effect, conventional rudders are very dependent upon high water velocity along the rudder surface, produced by means of a propeller rotating at high frequency and/or with a steep blade pitch angle. However, the high-efficiency propellers influence the propulsion of the vessel and makes it hard to manoeuvre at low speeds, which becomes particularly relevant when passing through narrow and/or highly trafficked waters and also for dynamically positioned vessels which aim at keeping a substantially fixed position, typically relative to the seabed.

In general, a ship rudder's effect/lift is dependent on the velocity of the fluid flow along the rudder surface. The force that turns a ship is dependent of the pressure difference between the two sides of the rudder. The pressure difference originates from a deflection of the water flow, where the deflection causes a change in the momentum of the flow, setting up a counterforce component on the rudder normal to the original direction of the water flow. Inherent in the deflection of the fluid flow is also a rotation of the fluid, leading to a pressure build up on the effected side of the rudder surface and thus significant rotational moment of the rudder. Further, frictional forces, so-called drag, acting in the direction of flow are also produced, where the total force vector on the rudder results from a combination of lift and drag.

WO 98/42565 relates to an arrangement for enhancing the steering effect of rudders comprising at least one passageway for supplying seawater from a pump to ducts in the rudder, and means communicating with the ducts and being adapted to discharge seawater supplied through these ducts at the rudder surface. Said means comprises a profile element extending vertically at the leading

edge of the rudder and being pivotable about a vertical axis to extreme positions at either side with respect to central plane of the rudder. There are provided distribution ducts which in association with the profile element are adjustable so that the profile element by opposite movement in relation to the angular rudder deflection causes seawater to be discharged along the rudder surface facing abaft at said angular deflection. The rudder according to WO 98/42565 is rotated by means of a motor or the like, while the profile element is rotated in a forced manner by means of a turning mechanism. It has been shown that the forced rotation of the profile element, opposite to the rotation of the rudder itself, has an unfortunate effect of the flow of water along the combined profile-rudder surface due to the deflection of the profile element from the direction of travel and due to the relative rotation between the profile element and the rudder body. The disrupted flow has a negative impact on the lifting force on the rudder, especially at large deflections, which will cause the rudder to stall, i.e. to lose its lifting capability. The distribution of water rearwards along the rudder body is regulated solely by the forced relative rotation of the rudder body and the profile element, where rotation causes the water supply ducts on the convex outer side to open and the ducts on the concave inner side to close/choke. However, at small to medium deflections it has been shown that there is a significant and undesirable leak of water also to the inner, concave side, where the leak negatively impacts the pressure build-up, and thus the efficiency of the rudder.

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art.

The object is achieved through features, which are specified in the description below and in the claims that follow.

The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

In a first aspect the invention relates to a rudder for a vessel, the rudder comprising;

- a profile element provided at the leading edge of the rudder,

- a rudder body provided behind the profile element, the rudder body being rotatable, by means of a rudder stock, relative to the profile element around a substantially vertical axis, wherein the profile element is provided with ducts, connectable to a water supply, and adapted to discharge water rearwards along the surface of the rudder body, and wherein the profile element is adapted to be rigidly connected to the hull of the vessel so that the profile element, in its longitudinal direction, is constantly pointing forward in the longitudinal direction of the hull.

The rudder according to the first aspect of the invention solves one of the major drawbacks of the prior art, namely that the profile element is no longer rotatable, but adapted to be fixed to the hull of the vessel, which leads to a more stable and non-disrupted flow of water around the rudder, in particular at medium to large deflections.

The rudder according to the first aspect of the invention provides a slim rudder having a relatively low coefficient of resistance together with optimized sidewise lifting properties, such optimization being possible due to the use of the artificially induced water flow over the relevant rudder surfaces. In one embodiment, the rudder body may be formed with a NACA (National Advisory Committee for Aeronautics) profile that is substantially symmetrical along a central longitudinal axis of the profile. In its neutral position, when the rudder body is non-rotated relative to the profile element, the whole rudder, i.e. the combined leading edge profile and rudder body, may be formed with a NACA profile. The applicant has performed particularly successful tests with a NACA64(3)-18 profile. The profile element may, in one embodiment, constitute in the order of 10-30% of the total length of the rudder, and even more preferably around 15% of the length of the rudder, which has been shown to be particularly useful for optimizing the lift of the rudder.

In a second aspect, the invention relates to a rudder system comprising a rudder according to the first aspect of the invention, the rudder system further comprising:

- a steering system for rotating the rudder body relative to the profile element;

- a water supply; and

- a water distribution system for distributing water from the water supply to the rudder.

The rudder system according to the second aspect of invention may secure that the pressurized water, that is discharged rewards tangentially to port or starboard sides of the rudder body, only will flow along one of the surfaces of the rudder, avoiding any leak flow along the opposite rudder surface. Hence, no detrimental opposing effects on the opposite surface of the rudder will occur, thereby enhancing the steering effect.

The flow of water rearwards along the rudder body will, due to its high speed and thereby the Coanda effect, cling to the rudder surface, preventing the formation of stagnant water at the rudder surface, which would normally initiate an early stall effect on the propeller-induced water flow over the rudder surface.

The rudder according to the present invention is particularly effective when an "S"-manoeuvring course is required, such as when manoeuvring in narrow waters, since a high water speed is maintained over the rudder due to the water jet, even when the speed of vessel is slow, the propeller rotation is low and rudder deflection is large.

It should be appreciated that the rudder according to the invention is particularly effective when the deflection of the rudder body exceeds 20-30 degrees relative to the neutral position, and even larger than 45 degrees. However, the beneficial effect of the rudder and rudder system according to the invention is noticeable even at smaller deflections.

In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein :

Fig. 1 shows schematically the aft part of a vessel provided with a rudder and rudder system according to the present invention;

Figs. 2a-d show schematically a proposed fitting and control valve used for feeding water to the rudder surfaces;

Figs. 3 shows, as seen from above, one embodiment of a rudder according to the first aspect of the invention in a neutral position ;

Fig. 4 shows, as seen from above, the rudder from Fig. 3 initiating a starboard and port turn of the vessel, respectively;

Fig. 5 shows, as seen from above, the rudder from Fig. 3 with a typical flow of water from different water sources along the rudder surface;

Fig. 6 shows, in a schematic side view, a rudder according to the first aspect of the invention;

Fig. 7 shows, in a schematic top view and side view, the flow of water into a rudder according to the present invention; and

Fig. 8 shows schematically in vertical and horizontal cross-sections through the rudder body, the water ducts in the rudder body.

In the following, the reference numeral 1 will indicate a rudder according to the first aspect of the invention, while the reference numerals 10 and 100 indicate a rudder system and a vessel according to the second and third aspects of the invention, respectively. The figures are shown simplified and schematically and the various features therein are not necessarily drawn to scale. Identical reference numerals refer to identical or similar features in the drawings.

Fig. 1 shows schematically the aft end of a large vessel 1 00 provided with a rudder 1 and rudder system 10 according to the present invention. The rudder system 10 comprises a rudder 1 arranged downstream of a propeller 2. The rudder system 10 further comprises a water supply 4 and a water distribution system 5. The rudder 1 includes a profile element 1 1 at the leading edge thereof and a rudder body 6 behind the profile element 1 1 . The rudder body 6 is rotatable by means of a steering system 3 which is remotely activatable, typically from the bridge of the vessel 100. The steering system 3 comprises a control unit 8 including an impulse generator. Further, the water distribution system 5 comprises an electric motor 12, connected to the control unit 8, for operating the water distribution system 5. The water supply 4 comprises a pump 14 for supplying water to the rudder 1 through a pipe system 16 via the water distribution system 5. In the shown embodiment, the pump 14 is a ballast water pump arranged in a well 18 of the hull 20 of the vessel 100, pumping water from a sea chest 19 through a first pipe inlet 21 . In the shown embodiment, the rudder system 10 further comprises a second pipe inlet 22 enabling direct fluid communication between the surrounding sea and the pipe system 16 without the need of a pump when the vessel 100 is at speed. The second pipe inlet 22 comprises a 24 valve and a hatch 26, both of which may be used to shut off the water supply to the pipe system 16 and further to the rudder 1 , via the second pipe inlet 22. Both the valve 24 and the hatch 26 of the second pipe inlet 22 may be remotely operateable, typically from the bridge. According to the present invention, water may be pumped from the sea by means of the pump 14 through the first pipe inlet 21 , or discharged directly from the sea through the second pipe inlet 22 when the vessel is in transit, and supplied to the rudder 1 through the pipe system 16, via the water distribution system 5, and further through into a pipe system/ducts in the rudder 1 and out rearwards along the sides of the rudder 1 as will be described in more detail below with reference to the following figures. Rotation of the rudder body 6, by means of the steering system 3, generates an impulse in an electrical impulse generator in the control unit 8, the generated impulse being used to regulate the flow of water through the water distribution system 5 supplying water to the required surface of the rudder 1 , by means of the electric motor 12 and valve as will be explained below, thereby forcing an increased and controlled water flow along the required rudder surface of the rudder body 6.

Fig. 2 shows schematically one embodiment of a water distribution system 5 in a rudder system 10 according to the second aspect of the invention. A Y-junction 28 has an inlet 30 in fluid communication with the pipe system 16 from the water supply 4, as indicated in Fig. 1 . The water distribution member further comprises a water distribution member, here in the form of a valve 32 in an intermediate housing 34. The valve 32, which may typically be a ball valve or the like, is configured in such a manner that by turning it approximately 60°, as indicated in Fig. 2b, the direction of flow of water from the inlet may change from one outlet 36 to the other outlet 38, the two outlets 36, 38 being connected to the ducts on each side of the rudder 1 as will be explained below. The arrows in Figs. 2a, c and d indicate the direction of flow through the valve 32. As described in more detail below, the pumped water is further directed through the ducts/channels in the profile element 1 1 and out in through vertical slits in the ducts rearwards along the rudder body 6. The direction of the valve 32, and thereby the direction of the flow of water along the rudder body 6, is controlled by means of the electric motor 12, and based on input on the deflection of the rudder body 6 from the control unit 8 of the steering system 3, as indicated in Fig. 1 In Fig. 2a the water flow/jet passes along the starboard surface 40 of the rudder 1 , while in Fig. 2c the water flows along the port side 42 surface of the rudder 1 , see Fig. 3. In Fig. 2d the valve is in a neutral position, where an equal amount of water flows into each of the two outlets 36, 38. The valve 32 will typically be in its neutral position when the rudder body 6 is in its neutral position, as will be explained below and shown in Fig. 3

Fig. 3 shows an embodiment of a rudder 1 according to the first aspect of the invention as seen from above. The rudder 1 , which is formed with a NACA profile, is in its neutral position, indicating that the rudder body 6 is non-rotated/non-deflected relative to the profile element 1 1 . Neutral

position corresponds to 0° rotation relative to the longitudinal direction L of the profile element 1 1 , which coincides with the travelling direction of the vessel, the vessel not being shown in this figure. The profile element 1 1 is provided with ducts 44, 46 which is in fluid communication with the outlets 36, 38 of the Y-junction, respectively, as shown in Fig. 2. The ducts 44, 46 extend vertically along substantially the full height of the profile element 1 1 as will be shown in the following figures, and water is discharged at high pressure through not shown narrow slits along the height of the ducts 44, 46, thereby being discharged tangentially along the rudder body 6 over substantially the full height of the rudder body 6. The profile element 1 1 is further provided with guiding means 48, here in the form of flexible guide flaps extending rearwardly and vertically along the height of the slits in the ducts 44, 46, spanning the gap between the profile element 1 1 and the rudder body 6 and leading the water tangentially along the sides of the rudder 6 for optimized performance. In alternative not shown embodiment, the guiding means 48 may be provided as a plurality of nozzles directing the flow of water rearwards along the sides 40, 42 of the rudder body 6. In the shown embodiment, the rudder body 6 is also provided with ducts 50, 52 extending vertically and longitudinally through the rudder body 6 for water to be discharged rearwards towards aft end 54 of the rudder body 6 through openings 56, 58 on the sides 40, 42 of the rudder body 6. The ducts 50, 52 in the rudder body 6 are also connected to the outlets 36, 38 of the Y-junction/Y-slot as will be described in further detail below. The ducts 50, 52 extend vertically through the rudder stock 60, the rudder stock 60 being connected to the steering system 3 as will be understood by a person skilled in the art and not discussed in further detail herein. In the neutral position of the rudder body 6 shown in Fig. 3, an equal amount of water flows along both sides of the rudder 1 , reducing the frictional drag from the surrounding water on the rudder body 6. The neutral position of the rudder body 6 corresponds to the neutral position of the valve 32 as indicated in Fig. 2d.

Fig. 4 shows the rudder 1 from Fig. 3 in two different positions. At the upper part of the figure, the rudder body 6 is rotated 20° towards the port side 42 with the aft end 54 of the rudder body 6 swung out towards the starboard side. In the lower part of the figure, the rudder body 6 is rotated 20° to the starboard side 40 with the aft end 54 of the rudder body 6 swung out to the port side. In the upper part of the figure, the flow of water around the rudder 1 is deflected by rotation of the rudder body 6 relative to the profile element 1 1 . The rotation of the rudder body 6 relative to the profile element 1 1 alters the flow of water past the rudder 1 , which creates a pressure difference between the two sides 40, 42 of the rudder 1 . The deflection of water from the rotated rudder body 6 creates a counterforce acting on the rudder 1 normal to the directional change of the water flow, thus creating a lift. The pressure is increased on the inner, concave starboard side 40 of the rudder body 6, while the pressure is reduced on the outer, convex port side 42 of the rudder body 6. Via control of the water distribution system 5, water is only discharged rewards along the port side 42 of the rudder body 6, thus adding momentum to the water flow on the port side 42 and also, due to the Coanda effect, improving the flowing water's attachment to the convex, port side surface 42 of the rudder 1 . In order to improve the lifting force even further, water is also discharged rearwards as a jet from the opening 58 in the rudder body 6, further adding momentum to the flow of water towards

the aft end 54 of the rudder body 6. The water discharged tangentially to the rudder body 6 has been shown to improve the generated lift on the rudder 1 significantly, particularly at medium to large deflections. On the rudder 1 shown in the upper part of the figure, the lifting force will act in the port direction on the rudder 1 implying that the ship will turn towards starboard side, whereas on the rudder 1 shown in the lower part of the figure, the opposite effects take place, and the lift acts in the starboard direction turning the ship towards the port side.

Fig. 5 shows a rudder 1 rotated 45° in the starboard direction, meaning that the rudder body 6 is rotated 45° towards starboard around the rudder stock, implying that aft end swings out to the port side. In the figure, the flow of water originating from different water sources is also indicated. Water from the water supply 4, as indicated in Fig. 1 , is discharged tangentially to the surface of the rudder body 6 on the outer, convex side of the rudder body 6 through the duct 46 on the starboard side 40 of the profile element 1 1 and through the duct 52 on the starboard surface/side 40 of the rudder body 6. The water jetted/discharged rearwardly from the water supply 4, via the ducts 46, 52, clings to the surface of the rudder body 6 due to the Coanda effect. This reduces the frictional drag on the rudder body 6, adds momentum to the flowing water, hinders water stagnation and thus generally improves the lift on the rudder 1 due to improved circulation of water on the outer, convex side of the rudder 1 . In practise, this enables lift also at medium to large deflections without stalling. The water from the water supply 4, in the shown embodiment including a ballast pump 14 as indicated in Fig. 1 , is denoted W and clings to the convex outer starboard surface 40 closest to the rudder body 6. Further, the flow of water from the vessel's propeller 2, see Fig. 1 , is split by the profile element 1 1 at the leading edge of the rudder 1 to flow along each side if the rudder body 6 and it is denote P. Finally, the flow of water from the surrounding sea is denoted S in the figure. In total, the flow of water from the different sources is part of a complex flow pattern around the rudder 1 . The form of the rudder 1 , its deflection and also the water discharged along the convex, starboard side 42 of the rudder 6, affects the water flow around the rudder 1 . The result is a deflected water flow with different flow velocities on the port and starboard sides of the rudder 1 , and finally a pressure difference across the rudder resulting in the desired lift.

Fig. 6 shows a schematic, enlarged side view of a rudder 1 according to the first aspect of the invention. The profile element 1 1 extends vertically down to a fundament 59 to which it is rigidly and non-rotatably connected. The vertical height of the profile element 1 1 substantially coincides with the height of the rudder body 6. The fundament 59 is an integrated part of or rigidly connected to the hull 20 which is not shown in this figure. The two ducts 44, 46, which connect to the outlets 36, 38 of the water distribution system 5, see Fig. 2, extend vertically substantially along the full height of the profile element 1 1 . The rudder stock 60, together with which the rudder body 6 may rotate, is rotatably connected to the fundament 59 via a not shown bearing arrangement. The water ducts 50, 52 in the rudder body 6, of which only one is visible in the figure, extend vertically inside the rudder stock 60 and further longitudinally through the rudder body 6 towards the openings 56, 58, of which only one is visible in the figure, in the rudder body 6. As can be seen from the figure, the opening 56 extend vertically along the full height of the rudder body 6, thus jetting water rearwards along the full height of the rudder body 6 for maximum effect.

Fig. 7 shows the rudder 1 from Fig. 6 together with a portion of the water distribution system 5. The water distribution system 5 is shown in a top view in the upper part of the figure, while the water distribution system 5 is shown connected to the rudder 1 in a side view in the lower part of the figure. The Y-junction 28 and valve 32 are shown simplified and schematically. The water from the inlet 30 is distributed to either of the two outlets 36, 38. The first outlet 36 is connected to and supplies water to the ducts 44, 50 on the port side 42 of the rudder 1 , while second outlet 38 is connected to and supplies water to the ducts 46, 52 on the starboard side 40 of the rudder 1 . The supplied water will be distributed substantially equally between the ducts 44, 46 in the profile element 1 1 and the ducts in the rudder 50, 52 body 6 as indicated in the lower part of the figure. When the rudder body is in its neutral position, corresponding to 0°, the water may be distributed equally on the port 42 and starboard sides 40, while when the rudder body 6 is deflected, the water will be equally distributed between the ducts 44, 46 in the profile element 1 1 and the ducts in the rudder 50, 52 on the port or starboard side, depending on the direction of the deflection, as mentioned above. In order to simplify to the removal of bio-/maritime fouling in the ducts 44, 46 in the profile element, and optionally also the ducts 50, 52 in the rudder body 6, the ducts 44, 46 (50, 52) may be lined with not shown, removable liners. The liners will typically be provided in glass-reinforced plastic (GRP) or similar, and they may be removable from the vessel's engine room. For easy removal the liners may be articulate. The liners may be removed for cleaning while the ship/vessel is in dock

Fig. 8 shows a schematic vertical cross-section through the rudder stock 60 to the left, and a horizontal cross-section through the rudder body 6 to the right. Both cross-sections clearly indicate the two separate ducts 50, 52 extending through the rudder body 6 with openings 56, 58. The openings 56, 58 are formed as vertical, narrow slits in the ducts 50, 52 ensuring a high-pressure, tangential discharge of water towards the aft end 54 of the rudder body 6.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.