A THRUST GENERATING ASSEMBLY

Abstract

The invention relates to a thrust generating assembly for a marine vessel, comprising a rotatable device (201) adapted to carry a thrust generating device adapted to generate a thrust by acting on water supporting the marine vessel, wherein the thrust generating assembly comprises a bearing (211, 212) for the rotatable device (201), wherein the bearing (211, 212) comprises an envelope (222) adapted to be fixed to a part of the vessel which is stationary in relation to a rotational axis (R) of the rotational device, wherein the thrust generating assembly comprises a liner (221) which is fixed to the rotatable device (201), wherein the liner (221) is electrically isolated from the rotatable device (201).

Claims

1-6. (canceled)

7. A marine vessel comprising an active cathodic anti-corrosion system and a thrust generating assembly, the thrust generating assembly comprising: a rotatable device adapted to carry a thrust generating device; the thrust generating device is adapted to generate a thrust by acting on water supporting the marine vessel; the rotatable device is electrically grounded; a water-lubricated bearing that allows the rotatable device to rotate about a rotational axis; the water-lubricated bearing comprises an envelope adapted to be fixed to a part of the vessel which is stationary in relation to the rotational axis of the rotatable device; the envelope comprises a plastic material; the water-lubricated bearing comprises a liner which is fixed to the rotatable device; and the liner is electrically isolated from the rotatable device.

8. The marine vessel according to claim 7, wherein the rotatable device is a propeller shaft.

9. The marine vessel according to claim 7, wherein the liner is fixed to the rotatable device by shrink fitting.

10. The marine vessel according to claim 7, wherein the electrical isolation of the liner from the rotatable device is provided by an electrically non-conductive layer between the liner and the rotatable device.

11. The marine vessel according to claim 10, wherein the electrically non-conductive layer is provided to the liner before the liner is fitted to the rotatable device.

12. The marine vessel according to claim 10, wherein the electrically non-conductive layer is provided to the rotatable device before the liner is fitted to the rotatable device.

13. A method of manufacturing a thrust generating assembly for a marine vessel comprising an active cathodic anti-corrosion system and a thrust generating assembly, the thrust generating assembly comprising: a rotatable device adapted to carry a thrust generating device; the thrust generating device is adapted to generate a thrust by acting on water supporting the marine vessel; the rotatable device is electrically grounded; a water-lubricated bearing that allows the rotatable device to rotate about a rotational axis; the water-lubricated bearing comprises an envelope adapted to be fixed to a part of the vessel which is stationary in relation to the rotational axis of the rotatable device; the envelope comprises a plastic material; the water-lubricated bearing comprises a liner which is fixed to the rotatable device; and the liner is electrically isolated from the rotatable device, the method comprising: providing the rotatable device comprising a metal material; providing the liner comprising a second metal material; applying an electrically non-conductive layer on a surface of the liner or on the rotatable device; and subsequently to applying the electrically non-conductive layer, fixing the liner to the rotatable device by shrink fitting, so that the electrically non-conductive layer is between the liner and the rotatable device.

14. The marine vessel according to claim 13, wherein the electrically non-conductive layer is applied to the liner before the liner is fitted to the rotatable device.

15. The marine vessel according to claim 13, wherein the electrically non-conductive layer is applied to the rotatable device before the liner is fitted to the rotatable device.

16. A method of manufacturing a thrust generating assembly for a marine vessel, comprising: providing a rotatable device comprising a metal material and adapted to carry a thrust generating device adapted to generate a thrust by acting on water supporting the marine vessel; providing a liner comprising a second metal material; applying an electrically non-conductive layer on a surface of the liner; and subsequently to applying the electrically non-conductive layer, fixing the liner to the rotatable device so that the surface to which the electrically non-conductive layer was applied faces the rotatable device.

Description

DESCRIPTION OF THE DRAWINGS

[0046] Below embodiments of the invention will be described with reference to the drawings in which,

[0047] FIG. 1 is a partially sectioned side view of a marine vessel, in the form of a cargo ship,

[0048] FIG. 2 is a partially sectioned side view of a part of the vessel in FIG. 1,

[0049] FIG. 3 is a sectioned side view of details in FIG. 2,

[0050] FIG. 4 depicts steps in a method according to an embodiment of the invention,

[0051] FIG. 5 is a partially sectioned side view of a part of a vessel according to an alternative embodiment of the invention,

[0052] FIG. 6 is a sectioned side view of details in FIG. 5,

[0053] FIG. 7 is a sectioned side view similar to the one in FIG. 6, of details of a further embodiment of the invention, and

[0054] FIG. 8 is a sectioned side view similar to the one in FIG. 6, of details of another embodiment of the invention.

DETAILED DESCRIPTION

[0055] FIG. 1 shows a marine vessel 1 comprising a hull 101. The vessel presents a bow 102, and a stern 103. A thrust generating assembly comprises a rotatable device, in the form of a propeller shaft 201, made in a metal material. The rotatable device presents a rotational axis R. The rotatable device carries a propeller 202. The rotatable device extends from a power providing device in the form of an engine or motor 203, through a structure of the hull 101, to the propeller 202. The vessel is provided with a rudder 104. The vessel also comprises a superstructure 105.

[0056] Reference is made also to FIG. 2. The thrust generating assembly comprises two water-lubricated bearings 211, 212 for the rotatable device 201. The bearings are provided in a stern tube 213, which is adapted to be fixed to, and extend through, the hull 101. The bearings 211, 212 are positioned at respective ends of the stern tube. Thereby, one of the bearings 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 extends. The space 214 is annular.

[0057] The vessel is provided with an active cathodic anti-corrosion system, such as an ICCP (Impressed Current Cathodic Protection) system. The active cathodic anti-corrosion system comprises a direct current electric power source 301, which provides a voltage between electric ground, provided e.g. by the vessel hull, and an anode 302. The anode is positioned so as to be exposed to the water supporting the vessel.

[0058] The rotatable device 201 is electrically grounded by means of a slip ring 303 connected to electric ground. Parts of the rotatable device 201 that are surrounded by water, have a coating to isolate the rotatable device from the water. Thereby, the active cathodic anti-corrosion system provides an electric circuit, extending through the anode, through the water supporting the vessel (as indicated by the broken line C in FIG. 2), through the propeller 202, and through the rotatable device 201. This circuit serves to protect any damages in the hull coating as well as the propeller 202 from corrosion.

[0059] Without any embodiment of the invention, the electric circuit provided by the active cathodic anti-corrosion system would also include a part, as indicated by the broken line D, extending through the water supporting the vessel, from the anode 302 to liners of the bearings 211, 212, which liners are described closer below. As explained herein, such a circuit part D is removed by embodiments of the invention.

[0060] Reference is made also to FIG. 3 which shows in detail the forward bearing 211. The rear bearing 212 is substantially identical in construction. Each bearing 211, 212 comprises a liner 221 which is fixed to the rotatable device 201. Each bearing further comprises an envelope 222 which is fixed to the stern tube 213. The envelope 222 and the liner 221 are cylindrical. The liner surrounds the rotating device. The envelope surrounds the liner. The liner is made in metal. The envelope is made in a plastic material.

[0061] During operation of the vessel, each bearing 211, 212 provides a water film in the annular space 224 between the envelope 222 and the liner 221. In FIG. 3, the thickness of this space is exaggerated for this presentation.

[0062] As illustrated in FIG. 2, water for the bearings 211, 212 is provided as follows: The inboard end of the stern tube 213 is sealed by a seal 231. Water, from outside of the vessel, is introduced, after being filtered, between the seal 231 and the forward bearing 211. Pumping of the water is provided by a pump arrangement 232. Filtering of the water may also be provided, e.g. by a filter in the pump arrangement 232. After being passed through the annular space 224 of the forward bearing 211, the water flows to the rearward bearing 212. The water is released rearwards of the rearward bearing 212, as illustrated by the arrow A in FIG. 2.

[0063] As can be seen in FIG. 3, and as understood from above, in the space 214 separating the bearings 211, 212, the rotatable device 201 is coated with a plastic coating 215, to avoid exposure to the water in the space 214.

[0064] As illustrated in FIG. 3, the liner 221 is electrically isolated from the rotatable device 201. The electrical isolation of the liner from the rotatable device is provided by an electrically non-conductive layer 223 between the liner and the rotatable device. Thereby, the liner is removed from the circuit provided by the active cathodic anti-corrosion system or any other external electrical current source. This will reduce or eliminate deposits on the liner, and excessive wear of the envelope 222 is thereby avoided.

[0065] In the example in FIG. 2, the propeller 202 is fixed to the rotatable device 201 with a flange connection, comprising a flange 228 on the rotatable device 201.

[0066] With reference to FIG. 4, a method of manufacturing the thrust generating assembly described above will be described. The method comprises the following steps: An electrically non-conductive layer is applied S1 on a surface of a liner. The layer may be formed by a layer of paint, e.g. a two component epoxy paint, or by thermal spraying. The liner is fixed S2, by shrink fitting, to a rotatable device, so that the surface to which the layer was applied faces the rotatable device.

[0067] Reference is made to FIG. 5, showing an alternative embodiment of the invention. The embodiment is similar to the one shown in FIG. 2 and FIG. 3, with the following difference: The rearward bearing 212 is provided in a bridging structure 241, arranged to hold the shaft 201 at a distance from the hull 101. The bridging structure comprises two legs forming a V-shape when seen in the longitudinal direction of the vessel. Such a bridging structure may also be referred to as an A-bracket. The legs of the bridging structure 241 connect the rearward bearing 212 with the hull 101. Alternatively, the bridging structure may comprise a single leg.

[0068] Reference is made also to FIG. 6. Similarly to what is shown in FIG. 3, the rearward bearing 212 comprises a liner 221 which is fixed to the shaft 201. The rearward bearing 212 comprises an envelope 222 which is fixed to a tube 242 of the bridging structure 241. Thereby, the water film between the liner and the envelope may be provided directly from the surrounding water.

[0069] As suggested above, without any embodiment of the invention, the electric circuit provided by the active cathodic anti-corrosion system would also include a part, as indicated by the broken line D in FIG. 5, extending through the water supporting the vessel, from the anode 302 to liners of the bearings 211, 212. As explained herein, such a circuit part D is removed by the liners 221 being electrically isolated from the shaft 201. As indicated in FIG. 6, in each bearing, the electrical isolation of the liner 221 from the shaft is provided by an electrically non-conductive layer 223 between the liner and the shaft. Thereby, the liner is removed from the circuit provided by the active cathodic anti-corrosion system or any other external electrical current source. This will reduce or eliminate deposits on the liner, and excessive wear of the envelope 222 is thereby avoided.

[0070] FIG. 7 shows a further embodiment, which is similar to the one shown in FIG. 5 and FIG. 6. Similarly to what is shown in FIG. 2, the rotatable device 201 comprises a flange 228 on the rotatable device 201. It should be noted that in this embodiment, a surface of the liner faces an axially facing surface of the flange of the rotatable device. Thereby, an electrically non-conductive layer 223 is provided between the liner 221 and the flange 228 on the rotatable device.

[0071] FIG. 8 shows another embodiment, which is similar to the one shown in FIG. 7, but differs therefrom as follows: A flange ring 229 connects the flange 228 of the rotatable device 201 to the liner 221. Thereby, an electrically non-conductive layer 223 is provided between the liner 221 and the flange ring 229.