WO2018162064A1

WO2018162064A1 - A tunnel thruster for a marine vessel, a method of operating a tunnel thruster and a marine vessel

Info

Publication number: WO2018162064A1
Application number: PCT/EP2017/055545
Authority: WO
Inventors: Norbert BULTEN; Davor BILIC
Original assignee: Wärtsilä Netherlands B.V.
Priority date: 2017-03-09
Filing date: 2017-03-09
Publication date: 2018-09-13

Abstract

The tunnel thruster (10) of a marine vessel has a propeller (16) at the central part of the tunnel (12) and adjustable nozzles (28, 34) at both ends of the tunnel (12).

Description

A TUNNEL THRUSTER FOR A MARINE VESSEL, A METHOD OF OPERATING A TUNNEL THRUSTER AND A MARINE VESSEL

Technical field [0001 ] The present invention relates to a tunnel thruster in accordance with the preamble of claim 1 , a method of operating a tunnel thruster in accordance with the preamble of claim 13 and a marine vessel in accordance with claim 15.

Background art [0002] Marine vessels use various propulsion systems or units. The main propulsion unit or units is/are normally arranged in the aft part of the ship. The main propulsion unit may be either a fixed propeller arrangement creating a thrust force in the longitudinal direction of the marine vessel, or it may be a pod or a thruster, i.e. a propeller arrangement that may be rotated round a vertical axis.

[0003] The marine vessels have also other propulsion arrangements that are mainly used when manoeuvring a ship in a port, for instance. One type of such propulsion arrangements is a tunnel thruster, which may be used both at the bow and at the stern of a ship. The tunnel thruster is arranged in a horizontal tunnel running transverse to the longitudinal direction of the marine vessel through the hull of the marine vessel for assisting in moving the entire ship or one end of the ship sideways for instance for docking purposes.

[0004] The tunnel thrusters comprise several variations. Firstly, there are both fixed and retractable tunnel thruster. In the fixed tunnel thrusters the propeller of the thruster is arranged in a fixed tunnel running through the vessel hull. In retractable thrusters the tunnel and the propeller therewith are lowered below the keel of the vessel for operation. Secondly, the fixed tunnel thrusters may have a water inlet separate from the horizontal tunnel, or one end of the horizontal tunnel may function as the inlet opening and the opposite as the outlet opening.

[0005] SU-A1 -1740247 discusses the former construction, in which the bottom of the hull of the marine vessel is provided with a wide opening for the water to enter the thruster, and the sides of the marine vessel are provided with outlet openings for discharging the water from the thruster. The flow path from the inlet to the two outlets is T-shaped such that the upward channel from the inlet opening comprises an axial pump or propeller for advancing the water to horizontal parts of the flow path. The horizontal parts of the flow path have, upstream of the outlet opening a valve or closure member by means of which the water is prevented from entering the side of the vessel in the direction of which the vessel is desired to be moved. In other words, when the tunnel thruster is used, while powering the propeller one of the valves or closure members is closed such that the water flows from the inlet to either one of the outlets. The outlet openings have a reduced diameter compared to the earlier of upstream parts of the flow path, i.e. the outlet is nozzle-shaped, whereby the flow velocity is increased in the outlet.

[0006] The latter construction discussed in, for instance, US-A-5,522,335 is such that the tunnel has substantially the same diameter for the entire length thereof. The reason is, naturally, to keep the flow losses upstream of the propeller as well as downstream thereof as small as possible. However, it has been a long recognized fact that the manoeuvring effect of a water flow or thrust from a large outlet of a tunnel thruster, having a diameter substantially equal with the propeller diameter, is rather weak in such a case that the marine vessel is moving. For instance, it has been learned that if the marine vessel has a speed of 5 knots or above the tunnel thruster of the above US patent is quite ineffective.

[0007] It has also been known that reducing the diameter of the outlet opening or the nozzle of the tunnel thruster, by means of which the velocity of the water from the nozzle is increased, the manoeuvring capability of the marine vessel, even when it is moving, is significantly improved. However, such a design has not been possible for such tunnel thrusters that both ends of the tunnel act as both the inlet and the outlet passages of the thruster. In such a case the existence of a nozzle, i.e. reduced cross sectional flow area, upstream of the propeller, i.e. the nozzle defining the effective cross sectional flow are of the inlet passage, would cause a tremendous flow resistance.

[0008] Thus, in view of the above discussed prior art, there are several problems that should be solved. Firstly, the construction discussed in the SU- patent application, requires three openings to be arranged in the vessel hull. The T-shaped flow path with its bend/s forms a considerable restriction to the water flow from the inlet to the outlets. And the positioning of the valve or closure members close to the outlet nozzle increases the flow restriction by increases the turbulence in the flow path. Secondly, the horizontal tunnel through the vessel hull is in a way an optimal construction, as it has only the necessary elements to make the thruster work. However, the wide tunnel, which is optimal in view of flow resistance in the suction side of the propeller, is not ideal in relation to the manoeuvrability of the marine vessel as discussed already above. The improved manoeuvrability of the marine vessel requires that the outlet from the tunnel is nozzle- shaped, i.e. tapering towards the outlet, but such a fixed construction would destroy the flow properties of the tunnel upstream of the propeller.

[0009] Therefore, an object of the present invention is to improve the manoeuvrability of a marine vessel using fixed tunnel thrusters, even at speed of 5 knots and above.

[0010] Another object of the present invention is to optimize the structure of the tunnel part for minimizing the flow resistance in the tunnel, and the power consumption of the tunnel thruster.

[001 1 ] Yet another object of the present invention is to design a novel tunnel thruster to have an open inlet to the tunnel and a nozzle- shaped tapering or converging outlet from the tunnel.

Disclosure of the Invention

[0012] The above and other objects of the invention are met by a tunnel thruster in a marine vessel, the tunnel thruster comprising a tunnel having an axis A, a tunnel wall, an inlet passage and an outlet passage provided at the opposite ends of the tunnel; a propeller being arranged to rotate about the axis A within the tunnel, wherein the inlet passage and the outlet passage are provided with adjustable nozzles having an adjustable cross-sectional flow area.

[0013] Other characteristic features of the tunnel thruster of the present invention will become apparent from the appended dependent claims.

[0014] The above and other objects of the invention are met by a method of operating the tunnel thruster such that, when manoeuvring a marine vessel in sideways direction is needed, the steps of

• starting the propeller to initiate a water flow from the inlet passage to the outlet passage and to generate a thrust force,

• throttling the cross sectional flow area of the adjustable nozzle in the outlet passage.

[0015] Other characteristic features of the method of operating a tunnel thruster of the present invention will become apparent from the appended dependent claims. [0016] The present invention, when solving at least one of the above-mentioned problems, also brings about a number of advantages, of which a few has been listed in the following:

• the manoeuvrability of the marine vessel using the tunnel thruster of the present invention is improved,

• the energy consumption of the tunnel thruster is minimized,

• the overall economy, including both the construction, installation, space requirements and the use of the tunnel thruster, is minimized.

[0017] However, it should be understood that the listed advantages are only optional, whereby it depends on the way the invention is put into practice if one or more of the advantages were obtained.

Brief Description of Drawing

[0018] In the following, the tunnel thruster of the present invention is explained in more detail in reference to the accompanying Figures, of which

Figure 1 illustrates a schematic vertical cross-sectional view of a tunnel thruster unit in accordance with a first preferred embodiment of the present invention taken along a plane running along the longitudinal centerline of the tunnel thruster,

Figure 2 illustrates a schematic end view of the tunnel thruster of Figure 1 as seen from the right,

Figure 3 illustrates a schematic end view of the tunnel thruster of Figure 1 as seen from the left,

Figure 4 illustrates a schematic vertical cross-sectional view of a tunnel thruster unit in accordance with a second preferred embodiment of the present invention taken along a plane running along the longitudinal centerline of the tunnel thruster,

Figure 5 illustrates a schematic end view of the tunnel thruster of Figure 4 as seen from the right,

Figure 6 illustrates a schematic end view of the tunnel thruster of Figure 4 as seen from the left, Figure 7 illustrates a schematic vertical cross-sectional view of a tunnel thruster unit in accordance with a third preferred embodiment of the present invention taken along a plane running along the longitudinal centerline of the tunnel thruster,

Figure 8 illustrates a schematic end view of the tunnel thruster of Figure 7 as seen from the right,

Figure 9 illustrates a schematic end view of the tunnel thruster of Figure 7 as seen from the left,

Figures 10a and 10b illustrate schematic cross sections of a tunnel thruster in accordance with a fourth preferred embodiment of the present invention taken along a plane running along the longitudinal centerline of the tunnel thrusters,

Figures 1 1 a illustrates a schematic cross section of a tunnel thruster in accordance with a fifth preferred embodiment of the present invention taken along a plane running along the longitudinal centerline of the tunnel thruster, and Figures 1 1 b and 1 1 c end views of the thruster of Figure 1 1 a as seen from the left and from the right, and

Figure 12 illustrates schematically a marine vessel provided with the tunnel thruster of the present invention.

Detailed Description of Drawing [0019] Figure 1 illustrates schematically a first preferred embodiment of the tunnel thruster of the present invention as a vertical cross section along the centreline of the tunnel thruster. Figure 2 shows an end view of the tunnel thruster of Figure 1 as seen from the right and Figure 3 a corresponding end view of Figure 1 as seen from the left. The tunnel thruster 10 of Figures 1 - 3 comprises a tunnel 12 having a cylindrical wall 14 and an axis A. The tunnel 12, when in use, is installed to run horizontally through the hull of a marine vessel in a direction perpendicular to the vertical longitudinal centreline plane of the marine vessel. The tunnel 12 houses a propeller 16 arranged rotatably about the axis A, the drive gear 18 and the support 20 by means of which the propeller 16 and the drive gear 18 are connected outside the tunnel to appropriate support and drive elements 22 within the hull of the marine vessel. The tunnel 12 is, at its both ends, provided with inlet/outlet passages 24 and 26, the passages, when in use, being in direct communication with the surrounding water. [0020] The tunnel 12 is provided with nozzles 28 and 34 positioned in the passages 24 and 26, i.e. between the openings in the vessel hull and the propeller 16. The nozzle 28 is formed of a first nozzle member 30 and a second nozzle member 32. The nozzle 34 is formed of a first nozzle member 36 and a second nozzle members 38. Preferably, but not necessarily, the first and second nozzle members are located one above the other, whereby they may, in this case, be called as the upper and the lower nozzle members. All nozzle members 30, 32, 36 and 38 have, in this embodiment of the present invention, a semi-cylindrical shape to follow the inner shape of the cylindrical tunnel wall 14. Preferably, but not necessarily, the nozzle members 30, 32, 36 and 38 are formed of plate material that is bent to have a semi-cylindrical cross section.

[0021 ] Each nozzle member 30, 32, 36 and 38 has, relating to its positioning in the tunnel, an inner edge 40, i.e. an edge facing the propeller, an outer edge 42, i.e. an edge facing the side of the marine vessel, and two side edges 44 extending, in an inclined manner, however, in the direction of the tunnel 12. The inner edge 40 of each nozzle member has a circumferential length corresponding to about Pi times the inner radius of the tunnel wall 14, i.e. has the semi-cylindrical shape. The inner edge 40 is, while the nozzle is fully open (see the right hand side nozzle 34 in Figure 1 ), preferably but not necessarily, positioned in a plane running at right angles to the axis A. The nozzle member has a desired width, the actual width being determined by the useable space and the desired convergence of the nozzle. Thus, each nozzle member 30, 32, 36 and 38 has, in this embodiment of the present invention, a basically semi-cylindrical shape, as shown in Figure 2, the shape, however, being modified by cutting basically triangular pieces away from the opposite side edges of the blanks of the nozzle members, as may be seen in the right hand side nozzles 36 and 38 of Figure 1 such that, when the nozzle members 30 and 32 are turned against one another as shown in the left hand side of Figure 1 , the side edges of the opposite nozzle members 30 and 32 meet one another for the entire length of the nozzle 28, whereby a convergent or tapered nozzle is formed. Like Figures 2 and 3 show, the cross sectional area of the outlet nozzle 28 of Figure 2 is less than half of that of the inlet nozzle 34 of Figure 3.

[0022] The nozzle members 30 and 32, as well as nozzle members 36 and 38 are, in pairs, pivoted to one another and to the tunnel wall 14 at the ends of the inner edges 40 of the nozzle members. The pivot axis B, preferably but not necessarily, intersects the axis A of the tunnel 12. A preferred but not necessary way of performing the pivoting is to provide the ends of the inner edges of a first nozzle member with mechanical connections, for instance shafts, extending radially outwardly from the first nozzle member and the ends of the inner edges of a second nozzle member with other mechanical connections, for instance sleeves, extending radially outwardly from the second nozzle member such that the shafts of the first nozzle member run through the sleeves of the second nozzle member, the shafts being rotatable within the sleeves. The centres of both the shafts and the sleeves are preferably located in the same plane running along the inner edges. Both the shafts and the sleeves are taken outside the tunnel 12 through the tunnel wall 14. The ends of the shaft and the sleeve need to be provided, at least at one side of the tunnel, preferably at both sides thereof, an arrangement for operating the nozzle members. Such an arrangement may include a further device for forcibly moving the nozzle members in a synchronized fashion to ensure that the movement of the opposite nozzle members is symmetrical on both sides of the tunnel. A device for operating the nozzle members may, for instance, be a hydraulic cylinder coupled by means of an arm to the end of one of the shaft and the sleeve or to the ends of them both. Another way to arrange the pivoting is to provide both nozzle members with shafts close to the ends of the inner edges, take the shafts side by side out through the tunnel wall, and provide the shafts with means for turning the nozzle members, preferably, in synchronized manner.

[0023] The tunnel thruster of the present invention is operated such that when the bow or aft of a marine vessel or the entire marine vessel needs to be moved sideways, the propeller in the tunnel thruster is started to rotate in a desired direction for initiating a water flow from the inlet passage to the outlet passage to generate a thrust force. If it is decided that a stronger steering impulse than available when both nozzles are fully open is needed, the nozzle at the pressure or thrust side of the propeller, i.e. the nozzle acting as the outlet nozzle, is throttled. In other words, its cross sectional area is adjusted or reduced by turning the first and second nozzle members towards one another. The nozzle members may be turned until their side edges rest against one another and the cross sectional flow area of the nozzle is at its smallest. The nozzle members are preferably turned to such an angular position in relation to the wall of the tunnel that the flow direction of the water jet exiting the nozzle is horizontal, maximizing the effect of the water jet. If the nozzle members are identical, their angular position in relation to the wall of the tunnel is also the same. And, if the nozzle members, like those in Figures 1 - 3, are not identical, the nozzle member extending for a shorter distance in the axial direction of the tunnel should be turned somewhat more than the opposite nozzle member to result, in operation, a horizontal water jet. Naturally, the nozzle at the inlet passage or suction side of the propeller is kept fully open. [0024] In a specific variation of the first embodiment the nozzle is formed with a single nozzle member, whereby the nozzle member forms the nozzle together with the opposite wall of the tunnel.

[0025] Figure 4 illustrates schematically a second preferred embodiment of the tunnel thruster of the present invention as a vertical cross section along the centreline of the tunnel thruster. Figure 5 shows an end view of the tunnel thruster of Figure 4 as seen from the right and Figure 6 a corresponding end view of Figure 4 as seen from the left. The tunnel thruster 50 of Figures 4 - 6 comprises a tunnel 52 having an axis A and, at the central part thereof, a cylindrical central wall 54. The tunnel 52 is installed to run horizontally through the hull of a marine vessel, i.e. its axis A running in a direction perpendicular to the vertical longitudinal centreline plane of the marine vessel. The cylindrical central wall 54 houses a propeller 56, the propeller gear 58 and the support 60 by means of which the propeller 56 and the propeller gear 58 are connected to the appropriate support and drive elements 62 in the hull of the marine vessel.

[0026] The tunnel 52 is, in this embodiment of the present invention, at its both ends, i.e. at its inlet and outlet passages, provided with outer tunnel walls 64 and 66 having, in general a polygonal cross section, here a rectangular, preferably square, cross-section, the outer tunnel walls 64 and 66 being joined to the cylindrical central wall 54 with a transitional tunnel sections 68, preferably such that the cross sectional flow area in both cylindrical and polygonal parts remains substantially the same. Both ends of the tunnel 52 is, inside the outer tunnel walls 64 and 66, provided with nozzles 70 and 72. The nozzle 70 is formed of a first nozzle member 74 and a second nozzle member 76. The nozzle 72 is formed of a first nozzle member 78 and a second nozzle member 80. All nozzle members 74, 76, 78 and 80 are formed, in this embodiment, preferably, but not necessarily of plate material that is bent to have a semi-rectangular (preferably, semi- square) cross section to follow the shape of the rectangular outer tunnel walls 64 and 66. Thus, each semi-rectangular nozzle member may be considered to be formed of a base plate extending substantially to the entire width of the rectangular tunnel, and two side plates extending at most for the half of the width or height of the rectangular tunnel. A preferred, but not necessary, option in the production of the nozzle members 74, 76, 78 and 80 is to start with a rectangular plate blank having a length corresponding substantially to one half of the circumferential length of the outer tunnel walls 64 and 66, and a desired width, the actual width being determined by the useable space and the desired convergence of the nozzle. Thus, each nozzle member 74, 76, 78 and 80 has, in this embodiment of the present invention, a basically semi-rectangular shape, as shown in Figure 5, which is, however, modified by cutting basically triangular pieces away from the opposite side edges of the blanks of the nozzle members, as may be seen in the right hand side nozzle 72 of Figure 4 such that, when the nozzle members 74 and 76 are turned against one another as shown in the left hand side of Figure 4, the side edges of the opposite nozzle members 74 and 76 meet one another for the entire length of the nozzle 70. Thus, like Figures 5 and 6 show, the cross sectional area of the outlet nozzle 70 of Figure 5 is, for instance, less than half (about one third) of that of the inlet nozzle 72 of Figure 6.

[0027] The nozzle members 74 and 76, as well as nozzle members 78 and 80 may be, in pairs, pivoted to one another and to the tunnel wall in a similar manner as discussed in connection with the first embodiment of Figures 1 - 3. Another option is to use hinges to pivot the nozzle members to the tunnel walls. In a similar fashion the operation of the tunnel thruster of Figures 4 - 6 as well as the orientation of the nozzle members is basically identical to that discussed above in connection with the first embodiment of the present invention.

[0028] A variation to the second embodiment is to arrange the above mentioned side plates to have a triangular shape such that when the opposite nozzle members are turned to have their side edges one against the other, the nozzle is closed. Naturally, in such a case, when effective thrust is desired the above mentioned side edges are left at a distance from one another.

[0029] Figure 7 illustrates schematically a third preferred embodiment of the tunnel thruster of the present invention as a vertical cross section along the centreline of the tunnel thruster. Figure 8 shows an end view of the tunnel thruster of Figure 7 as seen from the right and Figure 9 a corresponding end view of Figure 7 as seen from the left. The tunnel thruster 50' of Figures 7 - 9 utilizes the same basic tunnel construction as the embodiment of Figure 4, whereby the same reference numerals are used, i.e. the tunnel 52 having an axis A and, at the central part thereof, a cylindrical central wall 54. The tunnel 52 is installed to run horizontally through the hull of a marine vessel in a direction perpendicular to the vertical longitudinal centreline plane of the marine vessel. The cylindrical central wall 54 houses a propeller 56, the propeller gear 58 and the support 60 by means of which the propeller 56 and the propeller gear 58 are connected to the appropriate support and drive elements 62 in the hull of the marine vessel.

[0030] The tunnel 52 is, in this embodiment of the present invention, at its both ends, i.e. at its inlet and outlet passages, provided with outer tunnel walls 64 and 66 having a polygonal cross section, preferably a rectangular cross-section, more preferably a square cross-section, the outer tunnel walls 64 and 66 being joined to the cylindrical central wall 54 with a transitional tunnel sections 68, preferably such that the cross sectional flow area remains substantially the same. The outer tunnel walls 64 and 66 are housing nozzles 82 and 84. The nozzles 82 and 84 are formed of four nozzle members 86, 88, 90 and 92, and nozzle members, 86', 88', 90' and 92', respectively, one for each side of the rectangular tunnel part. All nozzle members 86, 88, 90 and 92, and nozzle members, 86', 88', 90' and 92', are formed, in this embodiment, preferably, but not necessarily, of plate material that is cut to a shape of a trapezoid, preferably an isosceles trapezoid, the long base having a length corresponding to a corresponding width of the rectangular tunnel part it is to be installed on, and the short base corresponding to the desired width of the outlet nozzle. Thus, the isosceles trapezoid shape of the nozzle members ensures that, when the nozzle members 86, 88, 90 and 92 are turned against one another as shown in the left hand side of Figure 8, the side edges of the adjacent nozzle members meat one another for the entire length of the nozzle 82.

[0031 ] Each nozzle member is pivoted at its long base to the tunnel wall the long base being closer to the propeller than the shorter base. The pivoting may be performed as discussed in connection with the first preferred embodiment or by using hinges to pivot the nozzle members to the tunnel walls. The way of operating the nozzles discussed in connection with the first embodiment may be applied here in this embodiment, too.

[0032] The third embodiment has a variation where only three nozzle members are used. In other words, the nozzle is, then, formed of three nozzle members and, at one side of the nozzle, the tunnel wall. In such a case, one of the nozzle members, i.e. the one positioned opposite the tunnel wall, i.e. the base plate, has the shape of an isosceles trapezoid. The two nozzle members, i.e. the side plates, at the sides of the isosceles trapezoid, have the shape of an irregular quadrilateral polygon having at least one right angle. If it is assumed that the base plate is hinged to the top wall of the rectangular tunnel, the side plates are hinged to the same circumference, i.e. the hinges of all three plates are positioned in the same plane running at right angles to the tunnel axis, on the side walls of the tunnel. The side plates are installed such that the right angle of the side plate is positioned at the corner between the side wall and the bottom of the tunnel, whereby when turning the side plate or nozzle member the side plate slides along the bottom of the tunnel. A nozzle is formed when the side plates are turned inwards until they meet the side edges of the top plate, i.e. the isosceles trapezoid. Thus, the side plates may have a shape of a square, a rectangle, a right trapezoid, etc. just to name a few alternatives without any intention of limiting the scope of the invention to the listed variants.

[0033] Figures 10a and 10b illustrate schematic cross sections of a tunnel thruster 100 in accordance with a fourth preferred embodiment of the present invention taken along a plane running along the longitudinal centerline of the tunnel thruster. The tunnel thruster 100 of the Figures has a similar polygonal tunnel 102, at its end parts housing the adjustable nozzles, as in the third embodiment. The difference may be seen in the nozzle members 104 and 106, which are now formed as rectangular plates pivoted or hinged to the opposite walls of the tunnel 102. The nozzle members 104 and 106 are designed to be, when in their rest position, either against the walls of the tunnel 102 as shown on the right hand side of the Figures or closing the tunnel as shown on the left hand side of Figure 10a. When in operation, the nozzle members 104 and 106 are turned such that they form a nozzle as shown on the left hand side of Figure 10b. Naturally, the cross section of the tunnel 102 is, in this embodiment, rectangular, preferably square.

[0034] Figures 1 1 a, 1 1 b and 1 1 c illustrate a fifth preferred embodiment of the present invention. This is a simplified embodiment of the fourth embodiment as now the tunnel thruster 100' is provided with only one nozzle member 108, which may be turned to form a nozzle as shown in the drawings or to close the entire tunnel 102 if such is desired. Naturally, the cross section of the tunnel 102 is, in this embodiment, rectangular preferably square.

[0035] Figure 12 illustrates very schematically a marine vessel 2 having a tunnel thruster 10 at the bow thereof. The tunnel thruster could also be positioned at the aft of the vessel, too.

[0036] In view of the above, it is clear that, basically in the manner discussed in the third embodiment, a nozzle may be formed of three, or five, six or any number of nozzle members, which, then, require that the non-cylindrical part of the tunnel has as many side walls as there are members in the nozzle.

[0037] It should be understood that in the above only five exemplary preferred embodiments of a novel and inventive tunnel thruster are discussed. It should be understood that though the specification above discusses a certain type of a tunnel thruster, the type of the tunnel thruster does not limit the invention to the types discussed. Thus it is clear that the drive of the propeller may be arranged by means of an electric or a hydraulic motor arranged down in the thruster body, i.e. in connection with or in place of the drive gear shown in the drawings. The above explanation should not be understood as limiting the invention by any means but the entire scope of the invention is defined by the appended claims only. From the above description it should be understood that separate features of the invention may be used in connection with other separate features even if such a combination has not been specifically discussed in the description or illustrated in the drawings.

Claims

1 . A tunnel thruster in a marine vessel, the tunnel thruster (10, 50, 50', 100, 100') comprising a tunnel (12, 52 102) having an axis A, a tunnel wall (14, 64, 66), an inlet passage (26) and an outlet passage (24) provided at the opposite ends of the tunnel (12, 52 102); a propeller (16) being arranged to rotate about the axis A within the tunnel (12, 52, 102), characterized in the inlet passage (26) and the outlet passage (24) being provided with adjustable nozzles (34, 28; 70, 72; 82, 84) having an adjustable cross- sectional flow area.

2. The tunnel thruster as recited in claim 1 , characterized in that the adjustable nozzle (34, 28; 70, 72; 82, 84) is formed of at least one pivoted nozzle member (30, 32; 36, 38; 74, 76; 78, 80; 86, 88, 90, 92; 86', 88', 90', 92'; 104, 106; 108).

3. The tunnel thruster as recited in claim 1 or 2, characterized in that the tunnel (12) has a cylindrical wall (14) for an entire length thereof.

4. The tunnel thruster as recited in claim 3, characterized in that the adjustable nozzle (28; 34) is formed of at least one pivoted nozzle member (30, 32; 36, 38).

5. The tunnel thruster as recited in claim 4, characterized in that the at least one pivoted nozzle member (30, 32; 36, 38) has a semi-cylindrical cross section with an inner edge (40), an outer edge (42) and two side edges (44).

6. The tunnel thruster as recited in claim 5, characterized in that the inner edge (40) has opposite ends, the ends being provided with mechanical connections outside the tunnel (12), at least one of the mechanical connections connecting the nozzle member (30, 32; 36, 38) with a device for turning the nozzle member (30, 32; 36, 38).

7. The tunnel thruster as recited in claim 1 or 2, characterized in that the tunnel thruster (50, 50'; 100, 100') has a cylindrical central wall (54) and, at the ends thereof, outer walls (64, 66) having a polygonal cross section.

8. The tunnel thruster as recited in claim 2 and 7, characterized in that the at least one pivoted nozzle member is a planar plate (86, 88, 90, 92; 86', 88', 90', 92'; 104, 106; 108).

9. The tunnel thruster as recited in claim 2, characterized in that the at least one pivoted nozzle member (74, 76; 78, 80) has a semi-rectangular cross section or a semi- square cross section.

10. The tunnel thruster as recited in claim 2, characterized in that the adjustable nozzle (82, 84) is formed of at least four pivoted nozzle members (86, 88, 90, 92; 86', 88', 90', 92'; 104, 106; 108), the at least four pivoted nozzle members (86, 88, 90, 92; 86', 88', 90', 92') being formed of plate material and having a trapezoid shape.

1 1 . The tunnel thruster as recited in claim 2, characterized in that each nozzle member (30, 32; 36, 38; 74, 76; 78, 80; 86, 88, 90, 92; 86', 88', 90', 92'; 104, 106; 108) is pivoted or hinged to the wall (64, 66) of the tunnel (52, 102).

12. The tunnel thruster as recited in claim 2, characterized in that the at least one pivoted nozzle member (74, 76; 78, 80; 104, 106; 108) is capable of closing the tunnel (52, 102).

13. A method of operating the tunnel thruster as recited in any one of the claims 1 - 12, characterized by, when manoeuvring a marine vessel in sideways direction is needed, the steps of

a) starting the propeller to initiate a water flow from the inlet passage (26) to the outlet passage (24) and to generate a thrust force,

b) throttling the cross sectional flow area of the adjustable nozzle (28, 82) in the outlet passage (24).

14. The method of operating the tunnel thruster as recited in claim 13, characterized by maintaining the adjustable nozzle (34, 84) in the inlet passage (26) fully open.

15. A marine vessel comprising the tunnel thruster as recited in any one of the claims 1 - 12.

16. The marine vessel as recited in claim 15, characterized in that the marine vessel (2) has a longitudinal centreline plane, and that the axis of the tunnel (12) is at right angles to the centreline plane.