STERN TUBE

Abstract: The present invention relates to a stern tube (1) for ships, for enclosing a propeller shaft (2) which extends between a propeller and a driving motor. More specifically, the invention relates to a stern tube comprising a tube having at least one interior bearing (3) supporting the propeller shaft, a first fastening means (5) which is fixedly connected to a fixed part (4a) of the ship and arranged on a part facing the propeller, and a second fastening means (6) which is spaced apart from the first fastening means and connected to a second fixed part of the ship. According to the invention, the second fastening means (6) allows axial displacement of the stern tube (1) relative to the fixed part (4b), but prevents displacement of the stern tube (1) in the radial direction.

Description: STERN TUBE Technical Field The present invention relates to a stern tube for ships, for enclosing a propeller shaft which extends between a propeller and a driving motor. More specif1- cally, the invention relates to a stern tube comprising a tube having at least one interior bearing supporting the propeller shaft, a first fastening 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. 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 ad ustment work is normally required before the propeller shaft can be positioned. Insufficient adjustment leads to oblique and uneven wear on the sliding bearings m the propeller shaft and the sliding bearings have to be changed or repaired. Movements m 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 expected. It is, for instance, common for propeller shafts to become distorted so that they "beat" which results m uneven and heavy wear on the sliding bearings. Obiect 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 fastening 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 m that the second fastening means allows axial displacement of the stern tube relative to the fixed part, but prevents displacement of the stern tube m 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 m the stern tube, due to the attachment to the ship, are avoided and there is some degree of adjustment to the propeller shaft m 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 drastically 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 construction, 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 m more detail for the purpose of exemplification by means of embodiments and with reference to the accompanying drawings, m 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 m Fig. 1 ; Fig. 3 shows an alternative embodiment of a fastening 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 m 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 interconnected 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 fastening 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 m 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 provided 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 providing a rigid connection are, however, possible, which is obvious to the one skilled m the art. The second fastening means 6 allows axial displacement of the stern tube relative to the fixed part 4b, but prevents displacement of the stern tube m the radial direction. This is preferably achieved by the second fastening means comprising a holder part 9 which is arranged 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 m 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 m the longitudinal direction of the tube, while being locked m the other directions. Advantageously, the holder part also comprises, on its surface facing the tube, at least one indentation 10 m the form of a groove and a seal 11 arranged therein. Preferably, the stern tube, m the area of the abutment of the holder part 9 against the same, further has a preferably circular cross-section which s constant m the longitudinal direction of the propeller shaft. Besides a movement m the axial direction of the tube relative 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 m 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 material 13, such as an epoxy. Here, this material is arranged 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 m Fig. 3, the holder part 9 and the fixed part 4b are connected to each other m a similar manner, but m this embodiment the curing material is arranged between surfaces which m 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 embodiment, 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 m a way similar to that m the second embodiment. However, this embodiment differs from the second embodiment m that the holder part 9 m 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 m 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 m the longitudinal direction of the tube. Most preferably, the curved surfaces have a spherical curvature. Owing to this, the second fastening means, m 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 invention, a fixed attachment is provided m the aft position, which results m 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 m better adjustment of the bearing load and thus enhanced strength of the bearing. Since the stern tube is not radially movable m 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 instance, possible to provide the limited movability of the second fastening means m other ways. It is also possible to use the fastening means according to the invention m 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.

Claims: CLAIMS 1. A stern tube (1) for ships, for enclosing a pro- peller shaft (2) , which extends between a propeller and a driving motor, comprising a tube having at least one interior bearing (3) supporting the propeller shaft (2 ) , a first fastening means (5) which is fixedly connected to a fixed part (4a) of the ship and arranged on a part facing the propeller, and a second fastening means (6) which is spaced apart from the first fastening means (5) and connected to a second fixed part (4b) of the ship, c h a r a c t e r i s e d m that the second fastening means (6) allows axial displacement of the stern tube (1) relative to the fixed part (4b), but prevents displacement of the stern tube (1) in the radial direction. 2. A stern tube as claimed m claim 1 , wherein the second fastening means (6) comprises a holder part (9) which is arranged on the fixed part of the ship and which, with a sliding surface, is arranged about and abuts against the tube (1) . 3. A stern tube as claimed m claim 2 , wherein the holder part (9) further comprises, on its surface facing the tube, an indentation (10) and a seal (11) arranged therein. 4. A stern tube as claimed m claim 2 or 3, wherein the stern tube, m the area of the abutment of the holder part against the same, has a preferably circular cross - section which is constant m the longitudinal direction of the propeller shaft. 5. A stern tube as claimed m any one of claims 2-4, wherein the stern tube, m the area of the abutment of the holder part (9) against the same, has an even and smooth outer surface . 6. A stern tube as claimed m any one of the preceding claims, wherein the second fastening means (6) further allows pivoting of the stern tube relative to the fixed part of the ship. 7. A stern tube as claimed m claim 6 , wherein the second fastening means comprises a holder frame (9a) which is attached to the fixed part of the ship and has an inner curved surface and a holder part (9b) which is arranged on the tube and has an outer surface with a corresponding curvature, the holder part (9b) being adapted to be arranged m the holder frame (9a) , and the curva- ture being adapted to allow at least some degree of pivoting of the holder part relative to the holder frame but prevent displacement of the same m the longitudinal direction of the tube (1) . 8. A stern tube as claimed m claim 7 , wherein the curved surfaces have a spherical curvature .

Inventors: BOKEDAL NILS, BOKEDAL, NILS
Applicants: BOKEDAL NILS, SVENSKA BEARING AB, BOKEDAL, NILS
Application year: 2000
Main classification: B63H23
IPC codes: B63H23, F16C35