Technical field [0001] The present invention relates to an inboard demountable retractable thruster in accordance with the preamble of claim 1. The present invention relates also to a marine vessel in accordance with the preamble of claim 6.

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, a barge, a ferry etc. 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 thrusters have been developed further by making these units retractable i.e. the thruster may be kept within the hull but it may also be lowered below the hull i.e. below the baseline of the marine vessel. When the thruster is in lowered position it may be rotated round a vertical axis, and it may thus be used to generate thrust in any desired direction for steering purposes. Such thrusters are often used for dynamic positioning purposes and for maintaining the vessel in a fixed orientation with respect to prevailing wave and current directions. However, while sailing to a working location or while entering a harbor, the positioning thrusters are retracted flush with keel level of the vessel in order to decrease the water resistance and to not interfere with the sea bed in shallow waters. Such thrusters are normally, however, relatively difficult to inspect and maintain as such may be done only by using divers or by dry-docking the vessel. [0005] As an example of a prior art retractable thruster where the above mentioned problem is solved US 6,375,524 may be discussed. The US patent discusses a marine vessel provided with a vertical shaft in which the thruster is placed and where the thruster may be retracted from its operating position below the keel level of the vessel to two upper positions. The first, lower one is the position where the thruster is kept while sailing and the second, upper one is the position where the thruster may be inspected and maintained. To make this kind of operation function the marine vessel needs the vertical shaft or thruster well, and the thruster needs to be provided with such a frame that supports the thruster and its driving equipment and is connected to the well such that the thruster may be moved in vertical direction. In other words, the thruster may be installed in the thruster well from the deck of the marine vessel i.e. from above. Thus, there is no need for using divers or dry-docking the marine vessel in any installation or maintenance operation relating to the thruster.

[0006] The above US- patent shows how the thruster well is formed of two parts. A first part extends from the keel level of the marine vessel above a certain tween deck level. The first part of the thruster well has a first diameter, the diameter allowing the tubular thruster frame to be lowered therein with a small gap being left between the thruster well and the thruster frame. In certain positions along their length both the well and the frame are provided with seal rings, which, when facing one another, seal the gap. Above the tween deck the thruster well has a larger diameter such that the lifting equipment for the thruster may be arranged there and also leave room for the maintenance personnel. The tween deck is shown to be positioned below the water line so that if water is allowed to fill the thruster well the tween deck would also be flooded. To prevent such from taking place the first part of the thruster well is extended for such a vertical distance above the tween deck that the thruster well extends above the water line.

[0007] The above discussed thruster of the US patent fulfills all the basic requirements that are set to an inboard mountable retractable thruster. However, the thruster frame poses a problem as it is a tubular enclosure covering all the thruster components except for the thruster itself, i.e. the rotational drive unit is within the tubular frame, whereby the access to the drive unit is complicated. If the thruster is not so large that a man could fit into the tubular frame, the thruster has to be loosened from the frame to get access to the drive unit. Other downsides of the tubular frame are its size, weight and manufacture. [0008] An object of the present invention is to optimize the frame structure of the inboard demountable retractable thruster such that various thruster components are easily accessible without major disassembly operations.

[0009] Another object of the present invention is to reduce the weight and manufacturing costs of the thruster frame.

Disclosure of the Invention

[0010] The above and other objects of the invention are met by an inboard demountable retractable thruster for a marine vessel, the thruster comprising a propeller, a thruster body, means for driving and steering the propeller, means for moving the propeller in vertical direction between its top and bottom positions, means for guiding the vertical movement of the propeller, and a slide frame supporting the means for driving and steering the propeller, the slide frame being movable along the vertical movement guiding means, the vertical movement guiding means being fastened to a frame, the frame comprises an upper frame and a lower frame between which the vertical movement guiding means are arranged, wherein that the lower frame is a thruster basin, the thruster basin, when in operation, housing at least partially the slide frame and the means for driving and steering the propeller arranged in connection therewith.

[001 1] Other characteristic features of the inboard demountable retractable thruster and the marine vessel of the present invention will become apparent from the appended dependent claims.

[0012] 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 thruster can be lifted and demounted inboard for service purposes. This avoids the costs and risks associated with underwater demounting, or alternatively the need for a vessel to go to dry-dock,

• The construction of the thruster is less complicated and lighter, · The thruster components are easily accessible without a need to loosen the thruster from its frame. [0013] 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 The Drawings

[0014] In the following, the inboard demountable retractable thruster of the present invention is explained in more detail in reference to the accompanying Figures, of which

Figure 1 illustrates a partial vertical cross-sectional view along a longitudinal centreline of a marine vessel provided with the inboard demountable retractable thruster in accordance with a preferred embodiment of the present invention,

Figure 2 illustrates a vertical cross-sectional view of the inboard demountable retractable thruster of Figure 1 , the thruster being positioned in sailing position inside the hull of the marine vessel,

Figure 3 illustrates a vertical cross-sectional view of the inboard demountable retractable thruster of Figure 1 , the thruster being positioned in operating position below the keel level of the marine vessel, and

Figure 4 illustrates a vertical cross-sectional view of the inboard demountable retractable thruster of Figure 1 , the thruster being lifted above the sailing position thereof, i.e. in its maintenance, service, mounting or demounting position.

Detailed Description of Drawing

[0015] Figure 1 illustrates a partial vertical cross-sectional view along a longitudinal centreline of a marine vessel 2 provided with the inboard demountable retractable thruster 8 in accordance with a preferred embodiment of the present invention. The embodiment shows an inboard demountable retractable thruster 8 arranged at the bow of a marine vessel. However, retractable thrusters may, in practice, be applied in any longitudinal position along the length of the hull thereof. The Figure shows the thruster 8 positioned in a vertical thruster well which is formed of a lower thruster well 10’ and an upper thruster well 10”, which extend from the deck 4 of the marine vessel 2 all the way to the keel level KL thereof. The inboard demountable retractable thruster 8 is shown in its operating position below the keel level KL of the marine vessel 2. The thruster well is, in principle, formed of two parts. A lower thruster well 10’ positioned mainly below the waterline WL and starting from the keel level KL, i.e. at the bottom of the marine vessel 2 and extending above the waterline WL. The upper thruster well may, depending on the marine vessel, be either a series of closable openings one above the other in the decks of the vessel or a tubular well arranged in vertical direction through the decks of the vessel. There may be a cavity between the upper and lower thruster wells, the cavity being applicable, for instance, for servicing and maintaining the thruster.

[0016] Figure 2 illustrates a vertical cross-sectional view of the inboard demountable retractable thruster of Figure 1 , the thruster being positioned in sailing position inside the lower thruster well 10’ inside the hull of the marine vessel. The retractable thruster 8 is mainly formed of a thruster propeller 12, its right angle gear arranged within the thruster body 14 of the propeller 12, a nozzle ring 16 surrounding the propeller 12 and connected to the thruster body 14, a drive shaft 18 surrounded by a steering pipe 20, electric drive motor 22, which is, in this illustrated embodiment, arranged at the upper end of the drive shaft 18, means (not shown) for moving the thruster 8 between its top and bottom positions and upper and lower guide arrangements 24 and 26 for supporting the inboard demountable retractable thruster as it is moved in vertical direction. Already at this stage, it should, however, be understood that the drive shaft and the electric motor may be replaced with an electric or hydraulic drive unit arranged on the same axis with the thruster propeller 12 in connection with the thruster body 14. In such a case only necessary electric wiring and/or hydraulic tubing need to be brought down to the thruster body 14. [0017] The retractable thruster 8 is fastened at its upper end to a tween deck 6, or more generally, to supporting hull structures (these cover all beams, walls, decks, reinforcements, etc. arranged in the hull of a marine vessel) by means of an upper frame 28. At least two vertical guide bars 24 are fastened at their upper ends to the upper frame 28 and at their lower ends to a lower frame, i.e. a thruster basin 30. A slide frame 32 is arranged in connection with the guide bars 24 such that the slide frame 32 is able to slide vertically along the guide bars 24. The slide frame 32 supports the drive motor 22 and is connected by means of the steering pipe 20 to a thrust beam 34 located below the thruster basin 30. The drive shaft 18 runs through the steering pipe 20 down to the thruster body 14. The thrust beam 34 is arranged rotatably to the lower end of the steering pipe 20. The steering pipe 20 is at its upper end rotatably supported to the slide frame 32 and attached at it lower end to the thruster body 14. Rotation of the steering pipe 20, and subsequently steering the propeller 12 is done by rotation gear 54 (Fig. 3). The thrust beam 34 extends substantially horizontally towards the wall 36 of the lower thruster well 10’. The wall 36 is provided with vertical guide rails 26 with which the ends of the thrust beam 34 are arranged in sliding communication. In other words, the vertical movement of the thruster is ensured by the guide bars 24 at the upper end of the thruster 8 and by the guide rails 26 at the lower end of the thruster 8. The thrust beam 34 and guide rails 26 transfer the thrust force of the propeller first to the wall of the lower thruster well 10’ and then further to the hull of the marine vessel.

[0018] The wall 36 of the lower thruster well 10’ forms a cavity in which the propeller

12, the thruster body 14 and the nozzle ring 16 (if in use) are housed when they are not in operation. The height of the wall is, normally, somewhat more than the diameter of the propeller 12 or the nozzle ring (if in use). In such a case that the waterline WL of the marine vessel extends higher than the wall 36 of the lower thruster well 10’, the wall 36 is provided with a substantially vertical wall extension 38 to raise the height of the wall above waterline WL. The wall extension 38 extending from the deck 40 (normally the lowermost deck, but sometimes the deck or the second deck above the lowermost one) upwards may be a unitary part of the wall 36, to which the guide rails 26 are fastened, or as a separate wall member fastened in a water-tight manner to the wall 36 or to the deck 40. The thruster basin 30 is located inside the wall extension 38 when the thruster is mounted in the lower thruster well 10”. The thruster basin 30 is formed of a basin bottom 42, i.e. foundation plate, a basin wall 44 and the basin flange 46. The basin wall 44 extends upwards from (preferably, but not necessarily, vertically and at right angles to) the basin bottom 42. The basin flange extends outwards from the basin wall 44. The basin flange 46 is positioned preferably, but not necessarily, to the upper rim of the basin wall 44 and extends preferably, but not necessarily radially outwards therefrom. The horizontal cross section of the thruster basin 30 is preferably, but not necessarily, round, though also square, rectangular and alike shapes may come into question, if desired. In a similar manner, the horizontal cross section of the lower thruster well 10’ is preferably, but not necessarily, round, though also square, rectangular and alike shapes may come into question, if desired. The basin flange 46 is arranged to rest on the upper rim 48 of the wall extension 38. A seal is provided between the basin flange 46 and the rim 48 of the wall extension 38. The basin bottom 42 is provided with an opening 50 for the steering pipe 20. The opening 50 is provided with a seal 52 for preventing water from entering the interior of the basin 30. [0019] Figure 3 illustrates a vertical cross-sectional view of the inboard demountable retractable thruster of Figures 1 and 2, the thruster being positioned in operating position with its propeller and thruster body below the keel level KL of the marine vessel. Figure 3 reveals why the thruster basin 30 is needed. Now the presence of the thruster basin 30 sealed in a water-tight manner in relation to both the steering pipe 20 and the wall extension 38 of the lower thruster well 10’ makes it possible to bring the slide frame 32 with all its equipment, like for instance the rotation gear 54 turning the thruster body, at the waterline WL, or even below the waterline. Thus the slide frame 32 and the thruster basin 30 are dimensioned such that the slide frame 32 fits within the interior dimensions of the thruster basin 30. Without the thruster basin 30 all such equipment that should not get into contact with seawater should be arranged at a higher level, which would mean increase in the length of the drive shaft and the steering pipe. Such would also mean increase in the weight of the thruster, and, naturally, also more space occupied by the thruster.

[0020] The required height of the basin wall 44 depends on the dimensions of the thruster in relation to the difference between the keel level KL and the water line WL. At its minimum the thruster body 14, the propeller 12 and the nozzle ring 16 need space in vertical direction somewhat more than the diameter of the propeller or nozzle ring, when the thruster is in its rest position, i.e. immobile, inside the thruster well 10’ in the hull of the marine vessel.

[0021] Figure 4 illustrates a vertical cross-sectional view of the inboard demountable retractable thruster of Figure 1 , the thruster being lifted above the sailing position thereof, i.e. in either its service and maintenance position or its total mounting or demounting position. The Figure also shows the importance of the wall extension 38, i.e. even though there is nothing to prevent the seawater from entering the lower thruster well 10’ the seawater does not occupy the deck 40 as the wall extension extends higher than the water line WL. The wall extension 36 offers also a possibility to mount a cover 56 on the rim of the wall extension 38 and the seal thereon such that the lower thruster well 10’ is again covered, and the cover 56 may be used as a supporting surface for servicing the thruster propeller or the thruster body.

[0022] Figure 4 also shows a preferred dimensioning of the extension wall as follows: In accordance with a preferred embodiment of the present invention the required height of the thruster well 10’, i.e. the height of the wall 36 is of the order of 1.1 - 1.5 times the propeller or the nozzle ring diameter. If the water line WL extends higher, a wall extension 38 to the wall 36 of the lower thruster well 10’ is needed, as shown in the Figures. For instance, if the waterline WL has a height H1 from the keel level KL and the deck 40 has a height H2 from the keel level KL, the wall extension 38 has a height h, the height h being greater than H1 - H2, preferably of the order of at least 1 .2 times H1 - H2, more preferably of the order of at least 1.5 times H1 - H2.

[0023] It should be understood that the above is only an exemplary description of a novel and inventive inboard demountable retractable thruster. It should be understood that though the specification above discusses a certain type of a retractable thruster, the type of the retractable 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, a hydraulic motor arranged down in the thruster body, or a diesel motor in Z-drive configuration. Also, it is clear that the shape of the nozzle ring does not limit the invention, whereby the rings may be either cylindrical or conical. 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 shown in the description or in the drawings.