Thrust Producing Assembly

Abstract

The present invention relates to a thrust-producing assembly for a marine vessel, comprising a rotatable device (201) configured to support a thrust-producing device configured to act on water supporting the vessel to generate thrust, the thrust-producing assembly comprising bearings (211, 212) for the rotatable device (201), the bearings (211, 212) comprising an enclosing portion (222) configured to be fixed to a portion of the vessel fixed relative to a rotation axis (R) of the rotatable device, the thrust-producing assembly comprising a liner (221) fixed to the rotatable device (201), the liner (221) being electrically insulated from the rotatable device (201).

Description

[Technical field]

[0001] The present invention relates to a thrust-producing assembly for a marine vessel, to a marine vessel equipped with such a thrust-producing assembly, and to a method of manufacturing a thrust-producing assembly for a marine vessel. [Background technology]

[0002] Bearings for rotatable devices, such as propeller shafts arranged to support thrust generating devices of a vessel, such as propellers, are known in various forms, examples being shown in U.S. Pat. No. 3,177,841 and German Patent Publication No. 3,030,141 A1, and it is desirable to avoid excessive wear of such bearings, as this can cause premature failure of the bearings. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 3,177,841 [Patent Document 2] German Patent Publication No. 3030141A1 Summary of the Invention [Problem to be solved by the invention]

[0004] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to reduce wear on the bearings of the rotatable equipment supporting the thrust generating equipment of a vessel. [Means for solving the problem]

[0005] This object is achieved by a thrust-producing assembly for a marine vessel, comprising a rotatable device configured to support a thrust-producing device configured to act on water supporting the vessel to generate thrust, said thrust-producing assembly comprising a bearing for said rotatable device, said bearing comprising an enclosing part configured to be fixed to a part of the marine vessel fixed relative to a rotation axis of said rotatable device, said bearing comprising a liner fixed to said rotatable device, said liner being electrically insulated from said rotatable device.

[0006] The rotatable device may be electrically conductive. The rotatable device may be made of a metallic material. The rotatable device may be made of metal. The metallic material of the rotatable device may be, for example, stainless steel, bronze, a bronze alloy or so-called Iconel.

[0007] A thrust generating device may be provided for propulsion of the vessel. Alternatively or additionally, a thrust generating device may be provided for controlling steering of the vessel, for example as part of a bow thruster.

[0008] The liner may be electrically conductive. The liner may be made of a metallic material. The liner may be metallic.

[0009] The liner may be cylindrical. The liner may be coaxial with the rotatable device. The liner may be fixed to the exterior of the rotatable device. The liner may surround the rotatable device. The liner may be fixed to the rotatable device by an interference fit. In some embodiments, the liner is fixed to the rotatable device in some other manner, for example, by adhesive.

[0010] The liner and the surrounding portion form part of the bearing.

[0011] The surrounding part is adapted to be fixed to a part of the vessel that is fixed relative to the axis of rotation of the rotatable device, which may for example be the hull of the vessel, a bracket or a post fixed to the hull, or the casing of a rotatable thruster mounted on the vessel, and therefore the surrounding part may not rotate.

[0012] The surround portion may be made of a plastic material and may or may not be reinforced with fiber or the like. For example, the surround portion may be made of fiber reinforced epoxy. In some embodiments, the surround portion is made of rubber or wood.

[0013] The surrounding portion and the liner may be at least partially cylindrical. The surrounding portion may surround the liner. The surrounding portion may thus surround the rotatable device. The bearing may thus be a radial bearing. Alternatively, the bearing may be an axial bearing. The liner and the surrounding portion may thus be distributed axially relative to the axis of rotation of the rotatable device.

[0014] The liner may be positioned to be exposed to the water supporting the vessel, sometimes referred to as overboard waters, and the rotatable device may be partially coated, such as with a plastic coating, to avoid exposure to the water, such as the ocean, supporting the vessel.

[0015] The invention is based on the realization that excessive wear of bearings for rotatable devices arranged to support a thrust generating device of a vessel can be caused by marine deposits on the bearings, the deposits being generated by currents in the water supporting the vessel. The marine deposits can be formed by lime deposits or calcareous coatings.

[0016] For example, the vessel may be provided with an active cathodic protection system, such as an ICCP (impressed current cathodic protection) system. Furthermore, the rotatable equipment may be electrically grounded. The grounding of the rotatable equipment may be achieved, for example, by slip rings inside the hull. An active cathodic protection system may be provided to protect the propeller, e.g., the blades and / or the hub, by grounding.

[0017] Failure to electrically isolate the liner from the rotatable equipment can result in marine deposits forming on the bearing liner. Such deposits can be caused or enhanced by active cathodic protection systems. Deposition on the liner can also be influenced by the structure of the quay to which the vessel is docked. Shore power can also influence such deposits.

[0018] More specifically, when the liner is placed in such a way that it is exposed to the water supporting the vessel and the rotatable equipment is electrically grounded, if the liner is not electrically insulated from the rotatable equipment, current from the active cathodic protection system may flow from the water through the liner to the rotatable equipment. However, in accordance with the present invention, the liner is electrically insulated from the rotatable equipment, thereby preventing such current flow through the liner. This reduces or eliminates seawater deposits on the liner caused by such currents. This avoids excessive wear of the surrounding parts caused by such marine deposits. This avoids premature failure of the bearings.

[0019] The liner may be made of bronze, bronze alloy, stainless steel, copper alloy, titanium, or other non-corrosive metal or metal alloy, so that even if the liner is not protected by an active corrosion protection system as exemplified above due to electrical insulation from the rotatable device, it may be protected from corrosion due to the corrosion resistance of the material. Also, because the liner is made of a metallic material, it may be attached to the rotatable part with an interference fit, as exemplified above. Also, the metallic material of the liner provides a hard surface suitable for bearing for the rotatable device, especially when the surrounding part is made of a softer material, such as a plastic material as exemplified below. However, in some embodiments, the liner is made of graphite.

[0020] Preferably, the liner is electrically insulated from any parts that are in metallic contact with the rotatable device, and more generally, it is preferred that the liner be electrically insulated from any metallic parts.

[0021] The rotatable device may be a propeller shaft, and thus the thrust producing device may be a propeller. The shaft may extend from a power supply, such as an engine or electric motor, through the vessel's hull or propulsion pod to the propeller.

[0022] In some embodiments, the rotatable device may be a rotor on a thruster configured to be rotatably mounted to the vessel such that the direction of thrust provided by the thruster can be adjusted.

[0023] In some embodiments, the rotatable device may be a rudder stock of a vessel's rudder, and thus the bearing may be a rudder bearing.

[0024] In some embodiments, the bearing is a water-lubricated bearing. The bearing may thus be configured to provide a water film between the surrounding portion and the liner. The thickness of the water film may be, for example, 3 micrometers to 20 micrometers. Preferably, the thickness of the water film is 6 micrometers to 10 micrometers.

[0025] In some embodiments, where the rotatable device is a propeller shaft, the bearing is provided in a bridge structure arranged to hold the shaft away from the vessel's hull. The bridge structure may include one or more legs connecting the bearing to the vessel's hull. This may allow the water film to be provided directly from the surrounding water, where the bearing is a water-lubricated bearing.

[0026] Thus, in a water lubricated bearing, the liner may be positioned such that it is exposed to the water supporting the vessel through water introduced between the liner and the surrounding portion. This could allow current from an active cathodic protection system to flow from the water, through the liner, and into the rotatable equipment if the liner was not electrically insulated from the rotatable equipment. However, as suggested, in accordance with the present invention, such current flow through the liner is avoided because the liner is electrically insulated from the rotatable equipment. This reduces or eliminates marine deposits on the liner caused by such currents, thereby avoiding excessive wear of the surrounding portion caused by such marine deposits.

[0027] In some embodiments, the bearing is a friction bearing, and therefore the clearance between the liner and the surrounding portion may be substantially zero.

[0028] In some embodiments, when the rotatable device is a propeller shaft, the bearing is provided in a stern tube configured to be fixed to and extend through the hull of the vessel, whereby the stern tube may form a housing for the bearing, and the surrounding portion and the liner may then be disposed in the annular cylindrical space between the rotatable device and the stern tube.

[0029] In some embodiments, preferably, two bearings, each as exemplified above, may be located at or near each end of the stern tube, such that one bearing may be closer to the bow of the vessel than the other bearing, and thus one bearing is forward of the other bearing when viewed in the direction of the vessel's forward motion. The bearings may be spaced apart in the stern tube through which the propeller shaft passes, leaving a gap between the bearings.

[0030] The inner end of the stern tube may be provided with a seal. Water from outside the vessel may be introduced between the seal and the forward bearing, preferably after being filtered. The water may be introduced by a pump. The water flows through the forward bearing before flowing to the aft bearing. If there is a space separating the bearings, the surface of the propeller shaft may be provided with a coating, such as a plastic coating, to prevent exposure of the surface to water.

[0031] Preferably, electrical insulation of the liner from the rotatable device is provided by a non-conductive layer between the liner and the rotatable device. This layer may be formed by a layer of paint of any suitable non-conductive composition. In some embodiments, this layer is formed by a two-component epoxy paint. In some embodiments, thermal spraying using a high temperature jet is used to form this layer.

[0032] The surface of the liner for fastening the liner to the rotatable device may face a radially facing surface of the rotatable device. Alternatively or additionally, the surface of the liner may face an axially facing surface of the rotatable device, such as a surface of a flange of the rotatable device, whereby a non-conductive layer may be provided between the liner and the axially facing surface of the rotatable device to electrically insulate the liner from the rotatable device.

[0033] In accordance with embodiments of the manufacturing method described below, where the liner is secured to the rotatable device by an interference fit, this layer may be applied to the liner before the liner is attached to the rotatable device. This layer is preferably configured to withstand temperatures in excess of 200 degrees Celsius, such that the layer can withstand the heating of the liner required to effect the interference fit.

[0034] Alternatively, this layer may be applied to the rotatable device before the liner is attached to the rotatable device.

[0035] The object is also achieved by a vessel comprising a thrust producing assembly as claimed in any one of the claims and by embodiments thereof.

[0036] The object is also achieved by a method for manufacturing a thrust-producing assembly for a marine vessel, comprising: providing a rotatable device made of a metallic material and configured to support a thrust-producing device configured to act on the water supporting the vessel to generate a thrust; providing a liner made of a metallic material; applying a non-conductive layer to a surface of the liner; and, after applying the non-conductive layer, fixing the liner to the rotatable device such that the surface to which the layer is applied faces the rotatable device, whereby the non-conductive layer is provided on the liner rather than on the rotatable device before the liner is fixed to the rotatable device. This is advantageous because the liner may be significantly smaller and lighter than the rotatable device and therefore easier to handle when applying the layer. [Brief description of the drawings]

[0037] [Figure 1] FIG. 1 is a partial cross-sectional side view of a vessel in the form of a cargo ship. [Diagram 2] FIG. 2 is a partial cross-sectional side view of a portion of the vessel of FIG. [Diagram 3] FIG. 3 is a cross-sectional side view of a detail of FIG. 2. [Figure 4] FIG. 2 illustrates the steps of a method according to one embodiment of the present invention. [Diagram 5] FIG. 2 is a partial cross-sectional side view of a portion of a marine vessel according to another embodiment of the present invention. [Figure 6] FIG. 6 is a cross-sectional side view of a detail of FIG. 5. [Figure 7] FIG. 7 is a cross-sectional side view similar to FIG. 6, showing details of another embodiment of the invention. [Figure 8] FIG. 7 is a cross-sectional side view similar to FIG. 6 showing details of another embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0039] Fig. 1 shows a vessel 1 comprising a hull 101. The vessel has a bow 102 and a stern 103. The thrust producing assembly comprises a rotatable device in the form of a propeller shaft 201 made of a metallic material. The rotatable device has an axis of rotation R. The rotatable device comprises a propeller 202. The rotatable device extends from a power supply in the form of an engine or motor 203 through the structure of the hull 101 to the propeller 202. The vessel is provided with a rudder 104. The vessel also comprises a superstructure 105.

[0040] Referring also to Figure 2, the thrust producing assembly includes two water lubricated bearings 211, 212 for the rotatable device 201. The bearings are mounted in a stern tube 213 and are arranged to be fixed to and extend through the hull 101. The bearings 211, 212 are located at each end of the stern tube, such that one bearing 211 is closer to the bow of the vessel than the other bearing 212. The bearings are separated by a space 214 in the stern tube 213 through which the propeller shaft 201 passes. This space 214 is annular.

[0041] The ship is provided with an active cathodic protection system, such as an ICCP (impressed current cathodic protection) system. The active cathodic protection system includes a DC power supply 301 that provides a voltage between an electrical ground, for example provided by the ship's hull, and an anode 302. The anode is positioned so that it is exposed to the water supporting the ship.

[0042] The rotatable device 201 is electrically grounded by slip ring 303 which is connected to electrical ground. The portion of the rotatable device 201 surrounded by water has a coating to insulate the rotatable device from the water. An active cathodic protection system is thereby provided with an electrical circuit that runs through the anode, through the water supporting the vessel (shown by dashed line C in FIG. 2), through the propeller 202, and through the rotatable device 201. This circuit serves to protect the propeller 202 from corrosion and to protect the vessel's hull coating from damage.

[0043] If the present invention were not implemented at all, the electrical circuit provided by the active cathodic protection system would also include a portion extending from the anode 302, through the water supporting the vessel, to the liners of the bearings 211, 212, as shown by dashed line D, which will be described in more detail below. As described herein, embodiments of the present invention exclude such circuit portion D.

[0044] Reference is also made to Figure 3, which shows the forward bearing 211 in detail. The aft bearing 212 is substantially similar in construction. Each bearing 211, 212 includes a liner 221 fixed to the rotatable device 201. Each bearing further includes an enclosing portion 222 fixed to the stern tube 213. The enclosing portion 222 and the liner 221 are cylindrical. The liner surrounds the rotatable device. The enclosing portion surrounds the liner. The liner is made of metal. The enclosing portion is made of a plastic material.

[0045] During operation of the vessel, each bearing 211, 212 provides a film of water in the annular space 224 between the surrounding portion 222 and the liner 221. In Figure 3, the thickness of this space has been exaggerated for the purposes of this illustration.

[0046] As shown in Figure 2, water for the bearings 211, 212 is supplied as follows: The inboard end of the stern tube 213 is sealed by a seal 231. Water from outside the vessel is introduced between the seal 231 and the forward bearing 211 after being filtered. The flow of water is achieved by a pumping device 232. The water may also be filtered, for example by a filter in the pumping device 232. After passing through the annular space 224 of the forward bearing 211, the water flows to the aft bearing 212. As shown by the arrow A in Figure 2, the water is discharged aft of the aft bearing 212.

[0047] As can be seen in FIG. 3 and understood from the above description, in the space 214 separating the bearings 211, 212, the rotatable device 201 is coated with a plastic coating 215 to avoid exposure to water within the space 214.

[0048] As shown in Figure 3, the liner 221 is electrically isolated from the rotatable device 201. Electrical isolation of the liner from the rotatable device is provided by a non-conductive layer 223 between the liner and the rotatable device, which removes the liner from the circuit provided by an active cathodic protection system or any other external current source. This reduces or eliminates deposits on the liner, thereby avoiding excessive wear of the surrounding portion 222.

[0049] In the example of FIG. 2, the propeller 202 is secured to the rotatable device 201 by a flange connection that includes a flange 228 on the rotatable device 201 .

[0050] With reference to Figure 4, a method for manufacturing the thrust producing assembly as described above is described. This method comprises the following steps: A non-conductive layer is applied to the surface of the liner (S1). This layer may be formed by a layer of paint, for example a two-component epoxy paint, or by thermal spraying. The liner is fixed to the rotatable device by a shrink fitting (S2), such that the surface provided with the layer faces the rotatable device.

[0051] Please refer to Figure 5 which shows another embodiment of the present invention. This embodiment is similar to the embodiment shown in Figures 2 and 3 with the following differences: The aft bearing 212 is provided in a bridge structure 241 and is arranged to hold the shaft 201 away from the hull 101. The bridge structure includes two legs which form a V-shape when viewed in the longitudinal direction of the vessel. Such a bridge structure can also be called an A-bracket. The legs of the bridge structure 241 connect the aft bearing 212 to the hull 101. Alternatively, the bridge structure may include a single leg.

[0052] See also Figure 6. Similar to that shown in Figure 3, the rear bearing 212 comprises a liner 221 fixed to the shaft 201. The rear bearing 212 comprises an encasement part 222 fixed to a tube 242 of a bridge structure 241. Thereby, the water film between the liner and the encasement part can be supplied directly from the surrounding water.

[0053] As alluded to above, if the present invention is not implemented at all, the electrical circuit provided by the active cathodic protection system would also include a portion extending from the anode 302 through the water supporting the vessel to the liners of the bearings 211, 212, as shown by dashed line D in FIG. 5. As explained herein, such circuit portion D is eliminated by electrically insulating the liner 221 from the shaft 201. As shown in FIG. 6, for each bearing, electrical insulation of the liner 221 from the shaft is provided by a non-conductive layer 223 between the liner and the shaft. This excludes the liner from the circuit provided by the active cathodic protection system or other external current source. This reduces or eliminates deposits on the liner, thereby avoiding excessive wear of the surrounding portion 222.

[0054] Figure 7 shows another embodiment similar to that shown in Figures 5 and 6. Similar to that shown in Figure 2, the rotatable device 201 includes a flange 228 on the rotatable device 201. It should be noted that in this embodiment, the surface of the liner faces the axially oriented surface of the flange of the rotatable device. This provides a non-conductive layer 223 between the liner 221 and the flange 228 on the rotatable device.

[0055] Figure 8 shows another embodiment similar to that shown in Figure 7, but with the following differences: A flange ring 229 connects the flange 228 of the rotatable device 201 to the liner 221. This provides a non-conductive layer 223 between the liner 221 and the flange ring 229.

Claims

1. A vessel (1) including an active cathodic protection system and a thrust producing assembly, the thrust producing assembly includes a rotatable device (201) configured to support a thrust producing device configured to act on water supporting the vessel to generate thrust; the rotatable device is electrically grounded; the thrust producing assembly includes bearings (211, 212) for the rotatable device (201); the bearing is a water-lubricated bearing; the bearings (211, 212) comprise an enclosing portion (222) configured to be fixed to a portion of the vessel that is fixed relative to the axis of rotation (R) of the rotatable device; the surrounding portion is made of a plastic material; the bearing includes a liner (221) fixed to the rotatable device (201); The liner (221) is electrically insulated from the rotatable device (201).

2. 2. The watercraft of claim 1, wherein the rotatable device (201) is a propeller shaft.

3. A vessel as described in claim 1, wherein the liner is fixed to the rotatable device by an interference fit.

4. 2. The vessel of claim 1, wherein electrical insulation of the liner (221) from the rotatable device (201) is provided by a non-conductive layer between the liner (221) and the rotatable device (201).

5. The liner is secured to the rotatable device by an interference fit; 5. The marine vessel of claim 4, wherein the non-conductive layer is provided on the liner before the liner is attached to the rotatable device, or the non-conductive layer is provided on the rotatable device before the liner is attached to the rotatable device.

6. A method for manufacturing a thrust generating assembly for a vessel as described in claim 1, comprising: providing a rotatable device (201) made of a metallic material and configured to support a thrust generating device configured to act on water supporting the vessel to generate thrust; A liner (221) made of a metal material is provided; Applying a non-conductive layer to the surface of the liner (221) or the rotatable device (S1); and after applying the non-conductive layer, fixing (S2) the liner (221) to the rotatable device (201) by an interference fit so that the non-conductive layer is between the liner (221) and the rotatable device (201).

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