NL2003813C2 - SEALING STRUCTURE. - Google Patents

Description

SEALING STRUCTURE

The invention relates to a sealing construction for sealing an axis rotatable underwater about an imaginary longitudinal axis, the construction comprising a structural part arranged transversely to the axis through which the axis can be guided or guided, at least two coaxial ring seals enclosing a pressure chamber sealing the shaft and the structural part with respect to each other, as well as pressure means for supplying a fluid into the pressure chamber under excess pressure, as well as a discharge for discharging the fluid.

An example of a seal construction for a ship is known from JP-A-11304005. This known seal construction forms part of the rear seal of a propeller shaft sleeve with a propeller shaft included therein. A continuous flow of fluid from the source must be generated in the seal structure. The excess fluid escapes under the outer ring seal (s). The supply of a fluid to the pressure chamber provides several advantages associated with an improved separation between the water outside the sealing structure and the space within it, in particular the lubricant-filled space between the propeller shaft and the propeller shaft tube. As a result of the back pressure generated by the fluid in the pressure chamber, first of all the load on the ring seals is considerably reduced, whereby the wear thereof decreases and the service life is extended. It can also thereby be prevented that the lubricant leaks out of the said space, and thus leads to environmental pollution.

A further sealing construction for driving a ship is known from the document EP 1 586 798 B1. The document describes a radial shaft seal which uses a number of adjacent pressure chambers and separated by sealing elements to seal said shaft relative to its environment. More specifically, the sealing elements are provided as radial elastomeric lip seals with which the shaft is sealed with respect to the environment. A radial shaft seal with elastomeric sealing elements only has the drawback that the pressure difference per sealing element is limited. After all, the maximum allowable pressure difference per element is low and a number of sealing elements must be placed in series. In addition, the pressure in the 2 pressure chambers between the sealing elements must be actively controlled. This has made it possible to enable the sealing structure to seal against higher pressures than is possible per individual sealing element. The liquid to be supplied to the pressure chambers is led through a fixed throttle, whereby pressure reduction takes place. The required liquid is withdrawn from the environment and flows out freely to the environment.

Because the required liquid again flows freely into the environment, the known sealing construction can only be used if there is no or only a limited back pressure. This is the case, for example, when the underwater seal construction 10 is situated reasonably close to the water surface and if the structural part is connected to the ambient pressure above the water surface. If this is not the case, for instance with completely submerged constructions or constructions that have to be used at larger depths, at which depths there are much higher pressures, the known sealing construction cannot be applied since a free outflow of the liquid is practically not. is possible.

Therefore, when structural parts have to be applied at greater depths than the depths usual for propeller shafts of a ship, other ways of sealing have always been used. For example, use can be made of special mechanical shaft seals to provide a seal. Such mechanical seals are, however, less attractive, in part due to their technical complexity and costs. In the case that the structural part forms part of, for example, a tidal turbine, it is known to pressurize the housing in which the turbine is arranged, for example by filling the housing with a gas, such as nitrogen or another suitable gas. Due to the increased pressure in the housing itself, the pressure difference over the shaft projecting through the housing is reduced and the seal quality of the shaft seal increases.

However, a drawback of bringing the (housing of the) structural part under pressure is that this is a technically complex operation, especially when the pressure has to be kept at a sufficiently high level for a longer period of time. In practical terms, this means that, for example, a supply line to the axle construction must be made. This is all the more objectionable because such constructions are often difficult to reach. Furthermore, the pressure within the structural part must be increased extremely to compensate for the pressure difference across the seal at very large water depths (for example more than 3 50 m, or even 100 m or more), which can lead to technical complications.

It is an object of the invention to provide a seal of the type mentioned in the preamble in which one or more of the above-mentioned drawbacks of the known shaft seals is obviated.

It is a further object of the invention to provide a sealing construction with which a rotatable shaft can be sealed to a structural part to relatively large depths.

According to an aspect of the invention at least one of the objects is achieved in a sealing construction for sealing an axis rotatable underwater about an imaginary longitudinal axis, the construction comprising a structural part arranged transversely to the axis through which the axis can be guided or guided, at least two coaxial ring seals enclosing each other with a pressure chamber for sealing the shaft and the structural part relative to each other, as well as pressure means for supplying a fluid under pressure to the pressure chamber, as well as a discharge for discharging the fluid, wherein the fluid discharge is connected to a discharge part which comprises a pump which is arranged for pumping discharged fluid further downstream.

According to an embodiment of the invention, the fluid flowing out of the pressure chamber 20 is forcibly discharged to the environment or recirculated towards the pressure chamber. The forced discharge takes place under the influence of one or more pumps. These can sufficiently increase the pressure in the outflowed fluid from the relatively low pressure that prevails in the structural part to the relatively high ambient pressure (caused by the water column and therefore dependent on the depth to which the structural part is submerged).

As already mentioned above, in certain embodiments, the fluid is returned to the pressure chamber (s). To this end, the sealing structure may have a discharge part connected to the pressure chamber for returning discharged fluid to the pressure chamber. More in particular, the discharge part 30 can be arranged such that already discharged fluid is circulated via the pressure means to the pressure chamber. An advantage of this embodiment is that the quality of the circulating fluid can be well controlled. When the fluid is recirculated in a closed system, the chance of contamination of the seal, for example as a result of entering biological organisms or substances in the fluid, is relatively small. Moreover, no fluid needs to end up in the environment, so that an environmentally friendly seal can be obtained.

In other embodiments, when at least the seal is in use, the discharge part is adapted to open into the underwater environment for supplying discharged fluid thereto. This embodiment can be carried out in a simple construction.

According to an embodiment the discharge part has a reservoir for temporarily storing discharged fluid. The reservoir can be connected to the pump for further draining of fluid.

In a further embodiment the discharge part comprises a heat exchanger for cooling the discharged fluid. The fluid can provide local cooling at the location of the connection of the structural part to the shaft. The connection can become hot as a result of the rotation of the shaft, which may in time lead to damage to the structure and / or shaft. Certainly (but not only) in the case that the fluid is recirculated, the fluid can be heated, for example in the pressure chamber, so that its cooling effect diminishes. By passing the fluid along a heat exchanger, the fluid can be given the desired (low) temperature.

In a further embodiment, the sealing structure comprises three, four or more consecutive coaxial ring seals, two adjacent ring seals of which each bound a pressure chamber. By realizing a number of adjacent pressure chambers in this way, a higher pressure difference can be absorbed than can be achieved with a single pressure chamber. The pressure means are herein preferably such that, viewed from the side with the highest pressure (e.g. the side adjacent to the underwater environment) to the side with the lowest pressure (e.g. the inner space of the structural part), in the successive pressure chambers generate a cascading pressure. The pressure chambers work together in this embodiment to gradually absorb the overpressure in the longitudinal direction of the shaft.

In a further embodiment, the pressures in the successive pressure chambers are reduced stepwise in substantially the same steps, so that the different seals are loaded in almost the same way, which considerably improves the service life of the seal. Nevertheless, if desired, the pressure can also be adjusted (usually reduced) in various printing steps.

In a further embodiment, the pressure chambers are connected in series, so that the seal can still be operational in the event of damage to one or more of them.

The sealing elements, more in particular the ring seals, of the sealing construction can take numerous forms, such as for example slip ring seals, depending on the situation and the desired sealing properties. In an advantageous embodiment, the ring seals comprise lip seals whose lip faces the relatively high pressure side.

As explained earlier, in the field of tidal turbines, unlike the field of ship drives, no sealing constructions with ring seals and pressure chambers are currently used. With tidal turbines, mechanical or similar seals are currently mainly used, whereby the nacelle of the turbine may or may not be brought under excess pressure (relative to an atmospheric pressure) to reduce the pressure difference across the seal. However, there are drawbacks to the use of such seals and to pressurize the tide turbine nacelle with gas such as nitrogen, certainly when they are at considerable depth, for example - but not limited to - depths of 20 m or more. Disadvantages include that pressurizing the nacelle is a technically complex operation, especially when the pressure has to be kept at a sufficiently high level for a longer period of time. The nacelle is then connected via a gas supply line to a gas source above the water surface.

It is therefore a further object of the invention to provide a nacelle provided with a simple and durable sealing construction that is suitable for applying the nacelle to large water depths.

According to a further aspect of the invention this object is achieved in a nacelle of an underwater turbine comprising an axis rotatable about an imaginary longitudinal axis, a structural part of the housing arranged transversely to the axis through which the axis 30 is guided, at least two coaxial, mutually pressure chamber including ring seals for sealing the shaft and the structural part with respect to each other, as well as pressure means for supplying a fluid under pressure to the pressure chamber, as well as a discharge for discharging the fluid, the discharge 6 being connected to a discharge part which comprises a pump which is adapted for pumping discharged fluid further downstream.

The inventors have come to the surprising insight that a nacelle for a tidal turbine operating at relatively great depth can indeed be properly sealed with a sealing construction of the type mentioned in the preamble that is used in shipping for sealing the propeller shaft of a ship. If the discharge of such a sealing structure is connected to a discharge part with a pump for pumping the fluid discharged from the pressure chamber, the pressure in the fluid can be increased such that it can be recirculated or in the vicinity of the nacelle (where high water pressure) can be discharged. The sealing construction can further be arranged such that local changes in water pressure can be followed automatically, without the need for active pressure regulation of the pressure (s) in the pressure chamber (s). Local changes in water pressure may, for example, be the result of tidal changes or weather conditions at the water surface.

If the seal construction has a sufficient number of consecutive ring seals and associated pressure chambers, the pressure difference collected by the seal can be so great that even when the nacelle is placed at a great depth (for example more than 50 m or even more than 80 m), in the inside of the nacelle can have a low pressure, for example a pressure of about 1 atmosphere.

The fluid can in principle consist of any suitable liquid and / or gas composition. In a further embodiment, however, the fluid is water (e.g., seawater) that has been withdrawn from the underwater environment. An environmentally friendly seal can be obtained by the correct choice of the fluid 25 (for example water). In order to ensure a supply of fluid, in a further embodiment the nacelle can be provided with a fluid input element for introducing fluid, in this case water from the underwater environment.

In many cases, the shaft will have to be lubricated in order to allow a rotation of the shaft relative to the nacelle for longer periods and without damage. It is known to lubricate the shaft by applying lubricant between the shaft and the nacelle or at least a structural part therein via a lubricating element. Lubricant can for instance be provided in a lubricant chamber connecting to the shaft. Under certain circumstances this lubricant can flow away and end up in the environment. This not only has a polluting effect on the environment, but often also means that the supply of lubricants must be replenished periodically in order to be able to lubricate the shaft sufficiently. According to a further preferred embodiment of the invention, however, the lubricating element and the lubricating means are formed by the one or more pressure chambers and the fluid flowing therein, in particular the water extracted from the environment, respectively. In this embodiment, therefore, no separate lubrication is required, so that there is no risk of contamination of the underwater environment with lubricants. Furthermore, the fluid remains relatively cool with respect to the usual lubricants, so that heating of the shaft with all its negative consequences occurs less easily.

Further advantages, features and details of the present invention will be elucidated in the following description of some embodiments thereof. Reference is made in the description to the accompanying figures.

Figure 1 shows an axial section of a propeller shaft construction with a first embodiment of the sealing construction according to the invention.

Figure 2 shows an alternative embodiment of the seal structure for the propeller shaft structure of Figure 1.

Figure 3 shows a schematic diagram of a further embodiment of the sealing construction in which the fluid is collected and recirculated;

Figure 4 shows a schematic diagram of a still further embodiment of the sealing construction in which the fluid is collected and discharged into the environment; and

Figure 5 shows the desired Q-H curve for a pump in an embodiment of the sealing construction according to the invention.

An example of the application of an embodiment of a sealing construction according to the invention to a propeller shaft construction is shown in figure 1. Figure 1 first of all shows a propeller shaft 1 as well as a propeller shaft sleeve 2 indicated in its entirety by 2, the propeller shaft sleeve 2. This propeller shaft sleeve 2 comprises a box section 3, a rear construction part 4 which is guided outwards through the ship's skin 5, and a front construction part 6. The rear construction part 4 supports the rear bearing 7, the front construction part 6, the 8 front bearing 8. In these bearings 7, 8 the propeller shaft 1 is rotatably received about its axis 9.

In connection with the sealing of the propeller shaft 1 with respect to the rear construction part 4, the rear seal designated in its entirety by 10 is provided.

For the front construction part 6, furthermore, the pre-sealing designated in its entirety by 11 is provided. In the space 12 bounded by the propeller shaft 1, the propeller shaft case 2 and the seals 10, 11 an amount of liquid lubricating oil is provided, the hydrostatic pressure of which is determined inter alia by the height of the lubricating oil column determined by the lubricating oil level 14 of the amount of lubricating oil 15 in the lubricating oil container 16, as well as the difference in height of the line 13 with which this lubricating oil container 16 is connected to the space 12.

On board the vessel of which the propeller shaft construction in question forms a part, there is a fluid source 17 for supplying a fluid (i.e. a gas, a liquid or a mixture of both). The fluid can be compressed air, whereby the compressed air can be supplied by the on-board network. Such compressed air has a pressure that is typically between about 7.5 and 8.5 bar. However, the fluid can also be water, for example seawater that comes from the environment of the vessel.

The fluid is connected via a fixed throttling device 18 with a single, fixed passage, as will be explained later, to the space 19 above the lubricating oil level 14 in the lubricating oil container 16. The throttling device 18 has such a passage that a fluid flow of, for example, approximately 25 is normally issued per minute. A line 20 runs from the lubricating oil container 16 to the rear seal 10. The line 20 is connected there to a pressure chamber 21, which is defined between the lip seals 22,23. The lip of the front lip seal 23 faces forward to the space 12, while the lip of the other lip seal 22 faces backwards. The further lip seal 24 is also directed rearwards.

As shown in Figure 1, the conduit 20 is further connected to the discharge valve 25. The throttle device 18 is selected such that any fluid 30 continuously escapes via the discharge valve 25. This means that the pressure in the pressure chamber 21 is equal to the liquid column which is located between the discharge valve 25 and the water level 26 in which the relevant vessel is located. Because the pipe 20 is connected both to the pressure chamber 21 and to the discharge valve 25, it is not necessary to lay a second pipe which runs separately to the discharge valve 25.

The fluid with any leaked liquid can be discharged from the pressure chamber 21 by means of a first discharge line 50, which leads to the collecting reservoir 51. The collecting reservoir is provided with an air vent 52. The reservoir 52 is connected via a second discharge line 53 to the aforementioned line 20 which leads to the pressure chamber 21. In the second discharge line 53, a phiheid pump 54, for example a centiphigital pump or similar pump, is arranged to pump the fluid discharged via the first line 50 towards the line 20.

Similarly, a further pressure chamber 31 located between the lip seals 32 and 33 is pressurized. These lip seals have a lip which is rearwardly directed to the space 12 in which the lubricating oil is located. Connected to this pressure chamber 31 is a fluid container 34, for example a container for oil, to which a pressure can be supplied via line 35 and throttling device 36. This pressure is related to the pressure as set and measured by the valve 25. This means that the pressure in the pressure chamber 31 fluctuates together with the water column up to the water level 26. Therefore, as soon as the pressure of the lubricating oil in the space 12 should As a result of an increasing draft or a high wave, the pressure in the pressure chamber 31 is also increased. The lip seal 32 is therefore not additionally loaded with increasing pressure of the lubricating oil in the space 12 since the higher lubricating oil pressure is counteracted by the pressure of the fluid (oil) in the pressure chamber 31. The service life of the lip seal 32 is thereby increased.

A second throttle device 37 is coupled in series with the fixed throttle device 36. This second throttle device flows into the environment. The branch line 38 leading to the lubricating oil container 34 is therefore loaded with a pressure that is approximately half the pressure in the line 35 if the throttling devices 36 and 37 are identical.

The fluid with any leaked liquid can be discharged from the pressure chamber 31 by means of a first discharge line 55, which leads to the collecting reservoir 57. The reservoir 57 is connected via a second discharge line 58 to the aforementioned fluid container 34 (lubricating oil container). In the second discharge line 58, a second fluid pump 56, for example a centigital pump or similar pump, is arranged to pump the fluid discharged via the first conduit 55 towards the fluid container 34 to allow a recirculation thereof in the direction of the pressure chamber 32.

The pre-sealing is not limited to an embodiment with a single pressure chamber. In other embodiments, more pressure chambers are present, for example three pressure chambers 31, 39, 40 which are formed between four lip seals 32, 33, 41 and 42. The pipe 35 is now connected to three series-connected throttling devices 36, 37, 43. , the latter of which flows into the ambient atmosphere. This may in each case be a piece of pipe with a small internal diameter. The lubricating oil containers 34, 35 are loaded via cascading pressure lines, such that the pressure chambers 31, 39 also have a cascading pressure. The pressure in the front pressure chamber 40 is the lowest since it is only exposed to the lubricating oil column of the lubricating oil in the associated lubricating container 47, which is in communication with the atmosphere via the line 48. Via discharge lines 49a, 49b and 49c can be used from a number of pumps 70a, 70b and 70c the fluid introduced into the respective pressure chambers 31, 39 and 40 are discharged to the respective lubricating oil containers 34, 45 and 47.

Another embodiment of the invention is shown in Figure 3. In the embodiment of Figure 3, in a cannula 106 (shown schematically with dotted lines) of a sea turbine for generating electric power, a rotating pipe seal is provided, for example of a similar type as described in EP 1 586 798 BI. The pressure (Po) in the cannula is relatively low, for example equal to 1 bar. The rotating pipe seal comprises a fixed housing 60 and a runner sleeve 59. The housing is attached to a fixed pipe, the runner sleeve to a pipe rotatable about the center line. Various lip seals form part of the housing (in the embodiment shown the lip seals 61 to 66, but a larger or smaller number of seals is of course also possible). Between each pair of this lip seal, a pressure chamber 71 to 75 is provided, as well as annular throttling devices 81 to 84.

With reference to Fig. 3, a fluid under pressure (Pj), for example (sea) water originating from a fluid supply element 102, is supplied (with a volume flow Qv4) and fed via a line 76 to the first pressure chamber 71. The fluid flows into the first pressure chamber 71. The fluid can leave the first pressure chamber via a line 77 and can be passed on to the second pressure chamber 72. The fluid then first enters the first throttle device 81. Downstream of the first throttle device 81, the fluid flows via line 78 into the second pressure chamber 72 and via line 79 into the second throttle device 82. The pressure in the second pressure chamber 72 is lower than the pressure in the first pressure chamber 71.

In this way the fluid is directed to each of the following pressure chambers 73-75. As a result of this successive and alternating throttling device 81-84 and pressure chambers 71-75, the pressure (P1, P2, P3, P4, P0) gradually decreases with regular steps, so that all lip seals are only loaded to a very limited extent.

The fluid therefore flows from the supply line 76 via the different pressure chambers to the discharge line 103. Via discharge line 103 the fluid (volume flow Qvi) is led to a reservoir 104 present in the cannula. The reservoir 104 is connected to an automatic air vent valve 105 and to a pump module 107 placed in the cannula 106. The pump module 107 includes, inter alia, a pump 108 with which the fluid (with a volume flow QV2) can be pumped. The pump 108 returns the fluid (volume flow QV3, where in principle it holds that Qvi = QV3 + Qv4) back in the direction of the supply line 76 of the first pressure chamber 71.

Figure 4 shows an alternative embodiment of the invention. Instead of being recirculated, the fluid is discharged into the environment after it has passed through the pressure chambers 20. The fluid supplied via supply part 102, i.e. the sea water from outside the nacelle 106, has a high pressure (Pi) and is led to the pressure chambers under this pressure. However, the pressure (Po) of the fluid leaving the last pressure chamber is much lower. In order to still be able to discharge the fluid, for example via the discharge element 109, the fluid pressure must be increased to Pi or higher. This pressure increase is accomplished by a pump 110 connected to the line 111.

With reference to Figure 3, to map the system behavior of the circulation system, the pressures and volume flows in the seal structure can be mapped under different operating conditions. For example, if it is assumed that the water pressure Pi may vary within a bandwidth of ± 1 bar as a result of, for example, tidal movements, the nominal water pressure is 5 bar (corresponding to a depth of approximately 50 m) and the pressure Po in the (turbine) housing or cannula is assumed to be atmospheric (Po = 0 12 bar) and if it is assumed for the volume flows that Qvi = QV3 + Qv4, the pressures in the different pressure chambers and the corresponding volume flows can be calculated. The minimum volume flow required in the pressure chambers will depend, among other things, on the heat development in the seal. This again depends on speed and pressure. Based on a volume flow Qvi through the throttling, the values shown in Table 1 below are calculated.

Pi P2 P3 P4 Po AP per lip Qvi [bar] [bar] [bar] [bar] [bar] 1 / hour 4.00 pÖ pö pö ÖjÖÖ pö 134.16 4.20 3J5 2JÖ p5 ÖjÖÖ ÜÖ5 137 , 48 ~ MÖ pÖ pö ÜÖ ÖjÖÖ UÖ 140.71 ~ 4p p5 pÖ ljÏ5 ÖjÖÖ U5 143.87 ~ 4p 3p pÖ UÖ ÖjÖÖ UÖ 146.97 ~ pÖ 3/75 2 ^ 0 U5 ÖjÖÖ p5 150.00 ~ PÖ pÖ pÖ pÖ ÖiÖÖ Ï3Ö 152.97 ~ PÖ p5 PÖ p5 ÖjÖÖ Ï35 155.88 5.60 pÖ pÖ MÖ ÖjÖÖ lp 158.75 ~ PÖ 4 ~ 35 UÖ M5 ÖjÖÖ M5 161.55 ~ PÖ 4p pÖ ÜÖ ÖiÖÖ pÖ 164.32 10

Ideally, the following should apply: Qvi = QV2 = Qv3 and QV4 = 0, but in practice QV2, Qv3 and Qv4 are still dependent on the pump solution. Figure 5 shows the corresponding desired Q-H curve for the pump.

The present invention is not limited to the embodiments thereof described herein. The requested rights are partly determined by the appended claims, within the scope of which many modifications and adjustments are conceivable.

Claims (16)

Sealing structure for sealing an axis (1) rotatable underwater around an imaginary longitudinal axis, the structure comprising a structural part (4, 5) arranged transversely to the axis 5 (1) through which the axis (1) can be guided or guided , at least two coaxial ring seals (22, 23; 32,33,41,42) enclosing a pressure chamber (21) for sealing the shaft (1) and the structural part (4, 5) with respect to each other, as well as pressure means (17-20; 34.45.47) for supplying a fluid under pressure to the pressure chamber (21; 31.39.40), and a discharge (50) for discharging the fluid, the discharge being connected is on a discharge part (53; 49a-49c) which comprises a pump (54; 70a-70c) which is adapted to pump discharged fluid further downstream. 2. Sealing structure according to claim 1, wherein the discharge part is connected to the pressure chamber (21) for returning discharged fluid to the pressure chamber (21). 3. Sealing construction according to claim 2, wherein the discharge part is arranged to circulate already discharged fluid via the pressure means to the pressure chamber. A sealing structure as claimed in any one of claims 1-3, wherein the discharge part is adapted to open out into use in the underwater environment for supplying discharged fluid thereto. 25 A sealing structure according to any one of the preceding claims, wherein the pump is adapted to increase the pressure of the fluid in the discharge part to a pressure equal to or higher than the water pressure in the underwater environment. A sealing structure according to any one of the preceding claims, wherein the discharge part has a reservoir for temporarily storing discharged fluid. A sealing structure according to claim 6, wherein the reservoir is connected to the pump for further draining fluid. 8. A sealing construction according to any one of the preceding claims, wherein the discharge part comprises a heat exchanger for cooling the discharged fluid. Sealing structure according to one of the preceding claims, comprising at least three consecutive coaxial ring seals, two of which are adjacent ring seals, each bounding a pressure chamber. 10 A sealing construction according to claim 9, wherein the pressure means are adapted to generate a cascading pressure, viewed from the side with the highest pressure to the side with the lowest pressure, in the successive pressure chambers. A sealing structure according to claim 10, wherein the pressure chambers are connected in series. 12. A sealing structure according to any one of the preceding claims, wherein the ring seals comprise lip seals whose lip faces the relatively high pressure side. A nacelle of an underwater turbine comprising an axis (1) rotatable about an imaginary longitudinal axis, a structural part (4, 5) of the nacelle through which the axis (1) is guided, at least two coaxial ones, arranged transversely to the axis (1) ring seals (22, 23) including mutually a pressure chamber (21) for sealing the shaft (1) and the structural part (4, 5) relative to each other, as well as pressure means (17-20) for supplying an overpressure fluid in the pressure chamber (21), as well as a discharge (50) for discharging the fluid, the discharge (50) being connected to a discharge part which comprises a pump adapted for pumping discharged fluid further downstream. The nacelle of claim 13, wherein the fluid is water withdrawn from the underwater environment and wherein the nacelle comprises a fluid input element for introducing water from the underwater environment. A nacelle according to claim 13 or 14, wherein a pressure lower than the water pressure of the underwater environment, in particular an atmospheric pressure, prevails in the nacelle. 16. Nacelle according to one of claims 13-15, comprising a lubricating element 10 for applying lubricants between the shaft and the construction part for lubricating the rotation of the shaft relative to the construction part, wherein the lubricating element and the lubricating means are formed through the pressure chamber and the fluid, in particular the water withdrawn from the environment.