Background Stern tubes are used on large ships to enclose the propeller shaft which extends from a driving motor, through the ship hull and out to a propeller. The stern tube is intended to stabilise the propeller shaft, while establishing a seal between the rotating propeller shaft and the fixed wall of the ship. Conventional stern tubes are normally attached to a front and a rear fastening means by casting or the like. It is, however, difficult to adjust the stern tube to the propeller shaft, and in addition the stern tube is often somewhat deformed when being attached. As a result, after mounting of the stern tube, a great deal of adjustment work is normally re- quired before the propeller shaft can be positioned. In- sufficient adjustment leads to oblique and uneven wear on the sliding bearings in the propeller shaft and the sliding bearings have to be changed or repaired. Move- ments in the ship, the stern tube and/or the propeller shaft during use also make the bearings of the fixedly and rigidly mounted stern tube get worn faster than ex- pected. It is, for instance, common for propeller shafts

to become distorted so that they"beat"which results in uneven and heavy wear on the sliding bearings.

Object of the Invention Therefore, it is an object of the present invention to provide a stern tube which completely, or at least partly, solves the above-mentioned problems of prior-art stern tubes.

This object is achieved by means of the stern tube according to the appended claims.

Summary of the Invention The present invention relates to a stern tube for ships, for enclosing a propeller shaft, which extends between a propeller and a driving motor, comprising a tube having at least one interior bearing supporting the propeller shaft. The stern tube comprises a first fasten- ing means which is fixedly connected to a fixed part of the ship and arranged on a part facing the propeller, and a second fastening means which is spaced apart from the first fastening means and connected to a second fixed part of the ship. The invention is distinguished in that the second fastening means allows axial displacement of the stern tube relative to the fixed part, but prevents displacement of the stern tube in the radial direction.

Preferably, this can be provided by means of a holder part which has a sliding surface arranged against the tube wall. In this manner, the stern tube is allowed some degree of movability relative to the ship. As a result, strains in the stern tube, due to the attachment to the ship, are avoided and there is some degree of adjustment to the propeller shaft in question. By this construction, such adjustment can take place initially, during the mounting of the stern tube and the propeller shaft, as well as during subsequent use. Owing to this, uneven wear on the bearings is avoided, the wear thus being drasti- cally reduced and the strength increased. The mounting of

the stern tube and its adjustment to the propeller shaft is also facilitated.

Preferably, the second fastening means further allows pivoting of the stern tube relative to the fixed part of the ship. This is advantageously achieved by the second fastening means comprising a holder frame which is attached to the fixed part of the ship and has an inner curved surface and a holder part which is arranged on the tube and has an outer surface with a corresponding curva- ture. As a result, the possibilities of adjusting the stern tube are further increased, which further reduces the wear, thus increasing the strength. By this construc- tion, the stern tube can, among other things, adjust to beating movements of the propeller shaft, which often oc- cur and constitute an important reason for the wear on bearings and the like.

Brief Description of the Drawings Below, the invention will be described in more detail for the purpose of exemplification by means of embodiments and with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view of a stern tube according to the invention having a propeller shaft arranged therein; Fig. 2 is a view on a larger scale of the portion marked II in Fig. 1; Fig. 3 shows an alternative embodiment of a fasten- ing means according to the invention; and Fig. 4 shows a third embodiment of a fastening means according to the invention.

Description of Preferred Embodiments As shown in Fig. 1, a stern tube according to the invention comprises a hollow-circular tube 1 adapted to enclose a propeller shaft 2. The propeller shaft has an end 2a which is adapted to be connected to a propeller

and an opposite end 2b which is adapted to be connected to a driving motor. The tube may comprise several inter- connected tube segments la-lc, and it also comprises at least one interior bearing 3 with a bearing surface sup- porting the propeller shaft.

The stern tube is connected with the aid of fasten- ing means 5,6 to fixed parts 4 of the ship, such as the hull, bulkheads or the like. The stern tube comprises at least two fastening means which are spaced apart in the longitudinal direction of the tube, a first fastening means 5 being fixedly connected to a first fixed part 4a of the ship and arranged on a part facing the propeller, and a second fastening means 6 being spaced apart from the first fastening means 5 and connected to a second fixed part 4b of the ship. The first fastening means 5 is a fixed connection between the stern tube and the fixed part of the ship, and may, for instance, be pro- vided with the aid of mechanical fastening means, such as bolt joints 7, curing joining materials 8, such as epoxy, or preferably a combination thereof. Other ways of pro- viding a rigid connection are, however, possible, which is obvious to the one skilled in the art.

The second fastening means 6 allows axial displace- ment of the stern tube relative to the fixed part 4b, but prevents displacement of the stern tube in the radial di- rection. This is preferably achieved by the second fas- tening means comprising a holder part 9 which is ar- ranged on the fixed part 4b of the ship and which, with a sliding surface, is arranged about and abuts against the tube lc. Moreover, it is an advantage if the stern tube has an even and smooth outer surface in the area of the abutment of the holder part against the same. As a result, the stern tube is allowed to slide relative to the holder part in the longitudinal direction of the tube, while being locked in the other directions. Advan- tageously, the holder part also comprises, on its surface

facing the tube, at least one indentation 10 in the form of a groove and a seal 11 arranged therein.

Preferably, the stern tube, in the area of the abut- ment of the holder part 9 against the same, further has a preferably circular cross-section which is constant in the longitudinal direction of the propeller shaft. Be- sides a movement in the axial direction of the tube rela- tive to the holder, a turning movement between these parts is also allowed about the longitudinal axis, which further enhances the adjustability and reduces the wear on the bearings.

In a first embodiment of the invention, which is shown in Fig. 2, the holder part 9 is attached to the fixed part 4b of the ship by means of, on the one hand, a bolt joint 12 and, on the other hand, a curing mate- rial 13, such as an epoxy. Here, this material is ar- ranged between parallel plane surfaces of the holder part and the fixed part, respectively. It is, however, also possible within the scope of the invention to use other ways of providing a fixed connection.

In a second embodiment, which is shown in Fig. 3, the holder part 9 and the fixed part 4b are connected to each other in a similar manner, but in this embodi- ment the curing material is arranged between surfaces which in cross-section have at least one and preferably two angles, preferably right angles. As a result, the connection will be more stable and firm. In this embodi- ment, the holder part also has a larger abutment surface facing the tube wall as well as two sealing rings 11.

In a third and most preferred embodiment, the holder part 9 is connected to the fixed part 4b in a way similar to that in the second embodiment. However, this embodi- ment differs from the second embodiment in that the holder part 9 in this embodiment comprises two parts: a holder frame 9a which is attached to the fixed part of the ship and which has an inner curved surface and a holder part 9b which abuts against the tube and which has

an outer surface facing the holder frame and having a corresponding curvature. The holder part 9b is adapted to be able to be arranged in the holder frame 9a, and the curvature is adapted to allow at least some degree of pivoting of the holder part 9a relative to the holder frame 9b but prevent displacement of the same in the longitudinal direction of the tube. Most preferably, the curved surfaces have a spherical curvature. Owing to this, the second fastening means, in this embodiment, also allows pivoting of the stern tube relative to the fixed part of the ship.

By means of the stern tube according to the inven- tion, a fixed attachment is provided in the aft position, which results in a completely fixed point and a forward point that is to some extent flexible. Owing to this, the mounting of the stern tube and the propeller shaft therein will be easier and more flexible. The stern tube according to the invention adjusts to the shaft, on the one hand, initially when being mounted and, on the other hand, afterwards during operation. This results in better ad- justment of the bearing load and thus enhanced strength of the bearing. Since the stern tube is not radially movable in the front fastening means either, relative to the fixed part of the ship, a satisfactory support is still provided for the propeller shaft.

The invention has now been described by means of an embodiment. It will, however, be appreciated that many variants of the invention are possible. It is, for in- stance, possible to provide the limited movability of the second fastening means in other ways. It is also possible to use the fastening means according to the invention in different types of stern tubes. Such variants as well as other obvious variants must be considered to fall within the scope of the invention such as delimited by the ap- pended claims.