Patent Description:
The invention also relates to an arrangement for sealing a propeller shaft located under water as defined in the preamble of independent claim <NUM>.

Publication <CIT> presents a sealing system, a method and a watercraft.

The object of the invention is to provide an improved method and an improved arrangement for sealing a propeller shaft located under water.

The method of the invention is characterized by the definitions of independent claim <NUM>.

Preferred embodiments of the method are defined in the dependent claims <NUM> to <NUM>.

The arrangement of the invention is correspondingly characterized by the definitions of independent claim <NUM>.

Preferred embodiments of the arrangement are defined in the dependent claims <NUM> to <NUM>.

In the following the invention will described in more detail by referring to the figures, of which.

First the method for sealing a propeller shaft <NUM> located under water and some embodiments and variants of the method will be described in greater detail.

In the method the propeller shaft <NUM> is arranged at a pod <NUM> that is suspended at a hull <NUM> of a ship and an air chamber <NUM> is provided circumferentially around the propeller shaft <NUM>. The pod <NUM> can be pivotable suspended at the hull <NUM> of a ship.

The method comprises supplying compressed air from a compressed air source <NUM> in an air supply line <NUM> to the air chamber <NUM>. Compressed air means in this context air, gas, or any mixture thereof.

The pressure in the air chamber <NUM> is provided circumferentially around the propeller shaft 1is preferably, but not necessarily, about <NUM> to about <NUM> bar higher than a pressure in a pod housing of the pod <NUM> such as in a pod housing limited by a shell structure (not marked with a reference number) of the pod <NUM>.

The pressure of the compressed air supplied from the compressed air source <NUM> to the air supply line can be in the range of about <NUM> to about <NUM> bar.

The method comprises discharging compressed air from the air chamber <NUM> in an air return line <NUM> and out of the air return line <NUM>.

The method comprises collecting liquid present in the compressed air discharged from the air chamber <NUM> in an intermediate leakage tank <NUM> that is provided in the air return line <NUM> within a pod housing of the pod <NUM>.

The method comprises closing the air return line <NUM> upstream of the intermediate leakage tank <NUM> and supplying compressed air to the intermediate leakage tank <NUM> effect flowing of liquid present in the intermediate leakage tank <NUM> in to a leakage tank <NUM>. The leakage tank <NUM> can be arranged within the hull <NUM> of the ship or within the pod housing of the pod <NUM>. The pressure of the compressed air that is supplied to the intermediate leakage tank <NUM> effect flowing of liquid present in the intermediate leakage tank <NUM> in to a leakage tank <NUM> is preferably, but not necessarily, in the range of about <NUM> bar to about <NUM> bar.

Said closing of the air return line <NUM> upstream of the intermediate leakage tank <NUM> can be done by closing a first valve <NUM> in the air return line <NUM> upstream of the intermediate leakage tank <NUM>.

Said supplying of compressed air to the intermediate leakage tank <NUM> can be done by supplying compressed air to the intermediate leakage tank <NUM> in a connecting air line <NUM> that is provided as a separate line, which sole function is to supply compressed air to the intermediate leakage tank <NUM> effect flowing of liquid present in the intermediate leakage tank <NUM> in to the leakage tank <NUM>.

Said closing of the air return line <NUM> upstream of the intermediate leakage tank <NUM> and said supplying of compressed air to the intermediate leakage tank <NUM> effect flowing of liquid present in the intermediate leakage tank <NUM> in to a leakage tank <NUM> is preferably, but not necessarily, performed in regular time intervals such as once every hour.

Alternatively can the connecting air line <NUM> be provided as a line that connects the air supply line <NUM>, that supplies compressed air from the compressed air source <NUM> to the air chamber <NUM> provided circumferentially around the propeller shaft <NUM>, and the air return line <NUM>, that discharges compressed air from the air chamber <NUM> provided circumferentially around the propeller shaft <NUM>, so that said supplying compressed air to the intermediate leakage tank <NUM> to effect flowing of liquid present in the intermediate leakage tank <NUM> in to a leakage tank <NUM>, is performed so that compressed air fed from the compressed air source <NUM> flows first partly in the air supply line <NUM>, thereafter flows in the connecting air line <NUM> and thereafter flows in the air return line <NUM> to the intermediate leakage tank <NUM> effect flowing of liquid present in the intermediate leakage tank <NUM> in to a leakage tank <NUM>.

Liquid can flow from the intermediate leakage tank <NUM> to the leakage tank <NUM> in a connecting liquid line <NUM>.

The method allows thus to drain the intermediate leakage tank <NUM> in a controller manner without a need to entering the pod <NUM>, provided that the leakage tank <NUM> is provided within the hull <NUM> of the ship. Alternatively, the leakage tank <NUM> can be provided within the pod housing of the pod <NUM> in a location that is easily accessible. Draining of the intermediate leakage tank <NUM> is preferably, but not necessarily, made while supplying compressed air from the compressed air source <NUM> to the air chamber <NUM> in the air supply line <NUM> so that a sufficient pressure against water surrounding the pod is maintained in the air chamber <NUM> circumferentially surrounding the propeller shaft <NUM>.

The method comprises preferably, but not necessarily, closing the air return line <NUM> downstream of the intermediate leakage tank <NUM> in connection with closing the air return line <NUM>. Such closing of the air return line <NUM> downstream of the intermediate leakage tank <NUM> prevents fluid from being discharged out of the air return line <NUM> when supplying pressurized air in the connecting air line <NUM> to the intermediate leakage tank <NUM>. Said closing of the air return line <NUM> downstream of the intermediate leakage tank <NUM> can be done by closing a second valve <NUM> in the air return line <NUM> downstream of the intermediate leakage tank <NUM>. The method comprises preferably, but not necessarily arranging, the possible second valve <NUM> of the air return line <NUM> outside the pod <NUM> and within the hull <NUM> of the ship.

If the method comprises closing a second valve <NUM> in the air return line <NUM> downstream of the intermediate leakage tank <NUM> in connection with closing the first valve <NUM> in the air return line <NUM>, the method comprises preferably, but not necessarily, supplying said compressed air in the connecting air line <NUM> to the intermediate leakage tank <NUM> by supplying compressed air to an upstream end <NUM> of the connecting air line <NUM> from the air supply line <NUM> supplying compressed air from the compressed air source <NUM> to the air chamber <NUM> provided circumferentially around the propeller shaft <NUM>, and by supplying compressed air from a downstream end <NUM> of the connecting air line <NUM> into the air return line <NUM> at a point of the air return line <NUM> downstream of the intermediate leakage tank <NUM> and upstream of the second valve <NUM>, and by supplying compressed air in the air return line <NUM> to the intermediate leakage tank <NUM> to effect said flowing of liquid present in the intermediate leakage tank <NUM> to the leakage tank <NUM> in the connecting liquid line <NUM>.

If the method comprises closing the second valve <NUM> in the air return line <NUM> downstream of the intermediate leakage tank <NUM> in connection with closing the first valve <NUM> in the air return line <NUM>, and if the method comprises supplying said compressed air in the connecting air line <NUM> to the intermediate leakage tank <NUM> by supplying compressed air to an upstream end <NUM> of the connecting air line <NUM> from the air supply line <NUM> supplying compressed air from the compressed air source <NUM> to the air chamber <NUM> provided circumferentially around the propeller shaft <NUM>, and by supplying compressed air from a downstream end <NUM> of the connecting air line <NUM> into the air return line <NUM> at a point of the air return line <NUM> downstream of the intermediate leakage tank <NUM> and upstream of the second valve <NUM>, and by supplying compressed air in the air return line <NUM> to the intermediate leakage tank <NUM> to effect said flowing of liquid present in the intermediate leakage tank <NUM> to the leakage tank <NUM> in the connecting liquid line <NUM>, the method comprises preferably, but not necessarily, supplying compressed air from the compressed air source <NUM> to the air chamber <NUM> through a first pressure regulator <NUM> in the air supply line <NUM> and supplying compressed air in the connecting air line <NUM> through a second pressure regulator <NUM> configured to provide a higher pressure than the first pressure regulator <NUM> in the air supply line <NUM>. In such embodiment of the method, the method comprises preferably, but not necessarily, arranging the first pressure regulator <NUM> of the air supply line <NUM> outside the pod <NUM> and within the hull <NUM> of the ship. In such embodiment of the method, the method comprises preferably, but not necessarily, arranging the second pressure regulator <NUM> in the connecting air line <NUM> outside the pod <NUM> and within the hull <NUM> of the ship.

If the method comprises closing the second valve <NUM> in the air return line <NUM> downstream of the intermediate leakage tank <NUM> in connection with closing the first valve <NUM> in the air return line <NUM>, and if the method comprises supplying said compressed air in the connecting air line <NUM> to the intermediate leakage tank <NUM> by supplying compressed air to an upstream end <NUM> of the connecting air line <NUM> from the air supply line <NUM> supplying compressed air from the compressed air source <NUM> to the air chamber <NUM> provided circumferentially around the propeller shaft <NUM>, and by supplying compressed air from a downstream end <NUM> of the connecting air line <NUM> into the air return line <NUM> at a point of the air return line <NUM> downstream of the intermediate leakage tank <NUM> and upstream of the second valve <NUM>, and by supplying compressed air in the air return line <NUM> to the intermediate leakage tank <NUM> to effect said flowing of liquid present in the intermediate leakage tank <NUM> to the leakage tank <NUM> in the connecting liquid line <NUM>, the method comprises preferably, but not necessarily, supplying compressed air from the compressed air source <NUM> to the air chamber <NUM> through a first pressure regulator <NUM> in the air supply line <NUM> and supplying compressed air in the connecting air line <NUM> through a second pressure regulator <NUM> configured to provide a higher pressure than the first pressure regulator <NUM> in the air supply line <NUM> and providing a check valve as the first valve <NUM> in the air return line <NUM> upstream of the intermediate leakage tank <NUM>, wherein said closing of the first valve <NUM> in the return air line <NUM> upstream of the intermediate leakage tank <NUM> is effected by the difference between the pressure provided by the first pressure regulator <NUM> in the air supply line <NUM> and the pressure provided by the second pressure regulator <NUM> in the connecting air line <NUM>. In such embodiment of the method, the method comprises preferably, but not necessarily, arranging the first pressure regulator <NUM> of the air supply line <NUM> outside the pod <NUM> and within the hull <NUM> of the ship. In such embodiment of the method, the method comprises preferably, but not necessarily, arranging the second pressure regulator <NUM> in the connecting air line <NUM> outside the pod <NUM> and within the hull <NUM> of the ship.

If the method comprises closing the second valve <NUM> in the air return line <NUM> downstream of the intermediate leakage tank <NUM> in connection with closing the first valve <NUM> in the air return line <NUM>, and if the method comprises supplying said compressed air in the connecting air line <NUM> to the intermediate leakage tank <NUM> by supplying compressed air to an upstream end <NUM> of the connecting air line <NUM> from the air supply line <NUM> supplying compressed air from the compressed air source <NUM> to the air chamber <NUM> provided circumferentially around the propeller shaft <NUM>, and by supplying compressed air from a downstream end <NUM> of the connecting air line <NUM> into the air return line <NUM> at a point of the air return line <NUM> downstream of the intermediate leakage tank <NUM> and upstream of the second valve <NUM>, and by supplying compressed air in the air return line <NUM> to the intermediate leakage tank <NUM> to effect said flowing of liquid present in the intermediate leakage tank <NUM> to the leakage tank <NUM> in the connecting liquid line <NUM>, the method comprises preferably, but not necessarily, monitoring the pressure in the air supply line <NUM> with a pressure sensor <NUM>, and triggering an alarm and/or sending a signal from the pressure sensor <NUM> to a third valve <NUM> provided in the connecting air line <NUM> to close the third valve <NUM> provided in the connecting air line <NUM>, if the pressure in the air supply line <NUM> exceeds a predetermined threshold value when the third valve <NUM> provided in the connecting air line <NUM> is open as an indication that the first valve 20provided in air return line <NUM> upstream of the intermediate leakage tank <NUM> leaks and so as to prevent the pressure in the air chamber <NUM> circumferentially provided around the propeller shaft <NUM> to raise too much and so as to prevent damage of the air chamber <NUM>.

The method comprises preferably, but not necessarily, discharging compressed air out of the air return line <NUM> through a throttle valve <NUM>. In such case, the method comprises preferably, but not necessarily, arranging the throttle valve <NUM> of the air return line <NUM> outside the pod <NUM> and within the hull <NUM> of the ship.

The method comprises preferably, but not necessarily, monitoring the liquid level in the leakage tank <NUM> with a level monitor <NUM>, and giving a signal to a drainage valve <NUM> arranged in fluid connection with the leakage tank <NUM> to effect opening of the drainage valve <NUM> if a predetermined threshold liquid level in the leakage tank <NUM> is exceeded.

The method comprises preferably, but not necessarily, providing a fourth valve <NUM> in the air supply line <NUM>. In such case, the method comprises preferably, but not necessarily, arranging the fourth valve <NUM> of the air supply line <NUM> outside the pod <NUM> and within the hull <NUM> of the ship.

In the method, the air chamber <NUM> is preferably, but not necessarily, provided between a face seal <NUM> that is provided circumferentially around the propeller shaft <NUM> and a first seal ring <NUM> that is provided circumferentially around the propeller shaft <NUM>. The face seal <NUM> is preferably, but not necessarily, configured separate the air chamber <NUM> from water surrounding the pod <NUM>. In the method a lubricant chamber <NUM> can be provided between the first seal ring <NUM> that is provided circumferentially around the propeller shaft <NUM> and a second seal ring <NUM> that is provided circumferentially around the propeller shaft <NUM> so that the lubricant chamber <NUM> is provided circumferentially around the propeller shaft <NUM>. If a lubricant chamber <NUM> is provided circumferentially around the propeller shaft <NUM>, the method can comprise supplying lubricant in a lubricant supply line <NUM>, preferably, but not necessarily, by means of gravity, from a lubricant tank <NUM> to the lubricant chamber <NUM> and supplying lubricant in a lubricant return line <NUM> from the lubricant chamber <NUM> to the lubricant tank <NUM>. If the method comprises providing a lubricant tank <NUM> as described, the method can comprise monitoring the level of lubricant in the lubricant tank <NUM> by means of a first level sensor <NUM> and a second level sensor <NUM>. If the method comprises providing a lubricant tank <NUM> and sensors <NUM> and <NUM>, as described, the method can comprise providing the first level sensor <NUM> and the second level sensor <NUM> and the lubricant tank <NUM> within the pod housing of the pod <NUM>. If such lubricant chamber <NUM> is provided circumferentially around the propeller shaft <NUM>, the pressure in the lubricant chamber <NUM> is preferably, but not necessarily, <NUM> to <NUM> bar higher than a pressure in a pod housing of the pod <NUM> such as in a pod housing limited by a shell structure (not marked with a reference number) of the pod <NUM>. If such lubricant chamber <NUM> is provided circumferentially around the propeller shaft <NUM>, the pressure in the air chamber <NUM> is preferably, but not necessarily, <NUM> to <NUM> bar higher than the pressure in the lubricant chamber <NUM> is provided circumferentially around the propeller shaft <NUM>.

The method comprises preferably, but not necessarily, providing the first valve <NUM> in the air return line <NUM> within the pod housing of the pod <NUM>.

The method comprises preferably, but not necessarily maintaining essentially the same pressure within the pod <NUM> and within the hull <NUM> of the ship.

The method comprises preferably, but not necessarily, arranging the compressed air source <NUM> outside the pod <NUM> and within the hull <NUM> of the ship.

Next the arrangement for sealing a propeller shaft <NUM> located under water and some embodiments and variants of the arrangement will be described in greater detail.

In the arrangement, the propeller shaft <NUM> is arranged at a pod <NUM> that is suspended at a hull <NUM> of a ship. The pod <NUM> can be pivotable suspended at the hull <NUM> of a ship.

The arrangement comprises an air chamber <NUM> that is provided circumferentially around the propeller shaft <NUM>, an air supply line <NUM> configured to supply compressed air from a compressed air source <NUM> to the air chamber <NUM>, and an air return line <NUM> configured to discharge compressed air from the air chamber <NUM> and out of the air return line <NUM>. Compressed air means in this context air, gas, or any mixture thereof.

The arrangement comprises an intermediate leakage tank <NUM> that is in fluid connection with the air return line <NUM> and that is configured to collect liquid present in the compressed air in the air return line <NUM>. The intermediate leakage tank <NUM> is provided within a pod housing of the pod <NUM>.

The arrangement comprises a drainage arrangement comprising a first valve <NUM> in the air return line <NUM> upstream of the intermediate leakage tank <NUM>, a leakage tank <NUM> that can be provided within the hull <NUM> of the ship and that is in fluid connection with the intermediate leakage tank <NUM> by means of a connecting liquid line <NUM>, and a connecting air line <NUM> in fluid connection with the intermediate leakage tank <NUM>. The drainage arrangement is configured to close the first valve <NUM> that is provided in the air return line <NUM> upstream of the intermediate leakage tank <NUM>, and to supply compressed air to the connecting air line <NUM> to effect flowing of liquid present in the intermediate leakage tank <NUM> to the leakage tank <NUM> in the connecting liquid line <NUM>. The pressure of the compressed air that is supplied to the intermediate leakage tank <NUM> effect flowing of liquid present in the intermediate leakage tank <NUM> in to a leakage tank <NUM> is preferably, but not necessarily, in the range of about <NUM> bar to about <NUM> bar. The arrangement allows thus to drain the intermediate leakage tank <NUM> in a controller manner without a need to entering the pod <NUM>, provided that the leakage tank <NUM> is provided within the hull <NUM> of the ship. Alternatively, the leakage tank <NUM> can be provided within the pod housing of the pod <NUM> in a location that is easily accessible. The arrangement for sealing the propeller shaft is preferably, but not necessarily, configured to supply compressed air from the compressed air source <NUM> to the air chamber <NUM> in the air supply line <NUM> so that a sufficient pressure against water surrounding the pod is maintained in the air chamber <NUM> circumferentially surrounding the propeller shaft <NUM> during the described function of the drainage arrangement. The drainage arrangement is preferably, but not necessarily, configured to close the first valve <NUM> that is provided in the air return line <NUM> upstream of the intermediate leakage tank <NUM>, and to supply compressed air to the connecting air line <NUM> to effect flowing of liquid present in the intermediate leakage tank <NUM> to the leakage tank <NUM> in the connecting liquid line <NUM>, in regular time intervals such as once every hour.

The drainage arrangement comprises preferably, but not necessarily, as illustrated in <FIG>, a second valve <NUM> in the air return line <NUM> downstream of the intermediate leakage tank <NUM> and the drainage arrangement preferably, but not necessarily, is configured to close the second valve <NUM> in the air return line <NUM> in connection with the closing of the first valve <NUM> in the air return line <NUM>. Such second valve <NUM> prevents fluid from being discharged out of the air return line <NUM> when supplying pressurized air in the connecting air line <NUM> to the intermediate leakage tank <NUM>.

In some embodiments of the arrangement the connecting air line <NUM> is, as illustrated in the <FIG> and <FIG>, in fluid connection with the intermediate leakage tank <NUM> so that an upstream end <NUM> of the connecting air line <NUM> is in fluid connection with the air supply line <NUM> that is configured to supply compressed air from the compressed air source <NUM> to the air chamber <NUM> that is provided circumferentially around the propeller shaft <NUM> and so that a downstream end <NUM> of the connection air line <NUM> is in fluid connection with the air return line <NUM> at a point downstream of the intermediate leakage tank <NUM> provided in the air return line <NUM> and upstream of a second valve <NUM> provided in the air return line <NUM> such that the drainage arrangement is configured to supply said compressed air to the upstream end <NUM> of the connecting air line <NUM> from the compressed air source <NUM>, and from the downstream end <NUM> of the connecting air line <NUM> to the air return line <NUM> and in the air return line <NUM> to the intermediate leakage tank <NUM> leakage to effect said flowing of liquid present in the intermediate leakage tank <NUM> to the leakage tank <NUM> in the connecting liquid line <NUM>. In such embodiments of the arrangement, the connecting air line <NUM> can be provided with a valve <NUM> for opening and closing the flow in the connecting air line <NUM>. In such embodiments of the arrangement, a first pressure regulator <NUM> can be provided in the air supply line <NUM>, the connecting air line <NUM> can be provided with a valve <NUM> and with a second pressure regulator <NUM> configured to provide a higher pressure than the first pressure regulator <NUM> that is provided in the air supply line <NUM>, and the first valve <NUM> in the air return line <NUM> upstream of the intermediate leakage tank <NUM> can be in the form of a check valve, wherein the drainage arrangement is configured to open the third valve <NUM> provided in the connecting air line <NUM> to supply compressed air through the second pressure regulator <NUM> in the connecting air line <NUM> and in the air return line <NUM> into the intermediate leakage tank <NUM> to effect closing of the first valve <NUM> provided in the air return line <NUM> and to effect flowing of liquid present in the intermediate leakage tank <NUM> to the leakage tank <NUM> in the connecting liquid line <NUM>. <FIG> and <FIG> illustrates such embodiments. The possible first pressure regulator <NUM> in the air supply line <NUM> is preferably, but not necessarily, arranged outside the pod <NUM> and within the hull <NUM> of the ship. The possible second pressure regulator <NUM> and/or the possible third valve <NUM> are preferably, but not necessarily, arranged outside the pod <NUM> and within the hull <NUM> of the ship. If the connecting air line <NUM> is provided with a valve <NUM> for opening and closing the flow in the connecting air line <NUM>, the arrangement comprises preferably, but not necessarily, a pressure sensor <NUM> connected to the air supply line <NUM>, whereby the arrangement is configures to send a signal from the pressure sensor <NUM> to the third valve <NUM> provided in the connecting air line <NUM> of the drainage circuit arrangement and triggering an alarm and closing the third valve <NUM> provided in the connecting air line <NUM> of the drainage arrangement if the pressure in the air supply line <NUM> exceeds a predetermined threshold value when the third valve <NUM> provided in the connecting air line <NUM> of the drainage arrangement is open as an indication that the first valve <NUM> leaks so as to prevent the pressure in the air chamber <NUM> circumferentially provided around the propeller shaft <NUM> to raise too much and so as to prevent damage of the air chamber <NUM>.

The face seal <NUM> is preferably, but not necessarily, configured separate the air chamber <NUM> from water surrounding the pod.

The air return line <NUM> is preferably, but not necessarily, configured to discharge compressed air out of through a throttle valve <NUM>. The throttle valve <NUM> of the air return line <NUM> is preferably, but not necessarily, arranged outside the pod <NUM> and within the hull <NUM> of the ship.

The arrangement comprises preferably, but not necessarily, a level monitor <NUM> configured to monitor the liquid level in the leakage tank <NUM>, wherein the level monitor is configured to give a signal to a drainage valve <NUM> to effect opening of a drainage valve <NUM> of the leakage tank <NUM> if a predetermined threshold liquid level in the leakage tank <NUM> is exceeded.

The arrangement comprises preferably, but not necessarily, a fourth valve <NUM> in the air supply line <NUM>. The fourth valve <NUM> of the air supply line <NUM> is preferably, but not necessarily, arranged outside the pod <NUM> and within the hull <NUM> of the ship. If the arrangement comprises a fourth valve <NUM> of the air supply line <NUM>, the arrangement can comprise a flushing circuit arrangement configured to feed water into the air supply line <NUM> downstream of the fourth valve <NUM> into the air supply line <NUM>, wherein the flushing circuit arrangement comprises a water source <NUM>, a valve <NUM> downstream of the water source <NUM> and upstream of the air supply line <NUM>, and wherein the flushing circuit arrangement being configured to close the fourth valve <NUM> of the air supply line <NUM> and to open the valve <NUM> so as to feed water into the air supply line <NUM> and via the air chamber <NUM> that circumferentially surrounds the propeller shaft <NUM> int the air return line <NUM>. <FIG> illustrates a such embodiment. The water source and the valve <NUM> are preferably, but not necessarily, provided outside the pod <NUM> and within the hull <NUM> of the ship.

The chamber <NUM> is preferably, but not necessarily, provided between a face seal <NUM> that is provided circumferentially around the propeller shaft <NUM> and a first seal ring <NUM> that is provided circumferentially around the propeller shaft <NUM>. The arrangement comprises preferably, but not necessarily, a lubricant chamber <NUM> provided between the first seal ring <NUM> that is provided circumferentially around the propeller shaft <NUM> and a second seal ring <NUM> that is provided circumferentially around the propeller shaft <NUM>, wherein the lubricant chamber <NUM> is provided circumferentially around the propeller shaft <NUM>. The arrangement comprises preferably, but not necessarily, a lubricant supply line <NUM> configured to supply lubricant, preferably, but not necessarily by means of gravity, from a lubricant tank <NUM> to the lubricant chamber <NUM> and a lubricant return line <NUM> configured to supply lubricant from the lubricant chamber <NUM> to the lubricant tank <NUM>. <FIG> illustrates a embodiment. A first level sensor <NUM> and a second level sensor <NUM> are preferably, but not necessarily, configured to monitor the level of lubricant in the lubricant tank <NUM>. The possible first level sensor <NUM> and the possible second level sensor <NUM> and the possible lubricant tank <NUM> are preferably, but not necessarily, provided within the pod housing of the pod <NUM>. If such lubricant chamber <NUM> is provided circumferentially around the propeller shaft <NUM>, the pressure in the lubricant chamber <NUM> is preferably, but not necessarily, <NUM> to <NUM> bar higher than a pressure in a pod housing of the pod <NUM> such as in a pod housing limited by a shell structure (not marked with a reference number) of the pod <NUM>. If such lubricant chamber <NUM> is provided circumferentially around the propeller shaft <NUM>, the pressure in the air chamber <NUM> is preferably, but not necessarily, <NUM> to <NUM> bar higher than the pressure in the lubricant chamber <NUM> is provided circumferentially around the propeller shaft <NUM>.

The first valve <NUM> in the return air line <NUM> is preferably, but not necessarily, provided within the pod <NUM> housing of the pod <NUM>.

The arrangement is preferably, but not necessarily, configured to maintain essentially the same pressure within the pod <NUM> and within the hull <NUM> of the ship.

The compressed air source <NUM> is preferably, but not necessarily, arranged outside the pod <NUM> and within the hull <NUM> of the ship.

The possible second valve <NUM> in the air return line <NUM> downstream of the intermediate leakage tank <NUM> is preferably, but not necessarily, arranged outside the pod <NUM> and within the hull <NUM> of the ship.

Claim 1:
A method for sealing a propeller shaft (<NUM>) located under water, wherein the propeller shaft (<NUM>) is arranged at a pod (<NUM>) that is suspended at a hull (<NUM>) of a ship and wherein an air chamber (<NUM>) is provided circumferentially around the propeller shaft (<NUM>), wherein the method comprising
supplying compressed air from a compressed air source (<NUM>) in an air supply line (<NUM>) to the air chamber (<NUM>),
discharging compressed air from the air chamber (<NUM>) in an air return line (<NUM>) and out of the air return line (<NUM>), and
colleting liquid present in the compressed air discharged from the air chamber (<NUM>) in an intermediate leakage tank (<NUM>) that is provided in the air return line (<NUM>) within a pod housing of the pod (<NUM>),
characterized
by closing the air return line (<NUM>) upstream of the intermediate leakage tank (<NUM>), and
by supplying compressed air to the intermediate leakage tank (<NUM>) to effect flowing of liquid present in the intermediate leakage tank (<NUM>) to a leakage tank (<NUM>).