Patent Description:
Marine vessels use various propulsion systems or units. The main propulsion unit or units is/are normally arranged in the aft part of the ship. In addition to such main propulsion units a marine vessel usually requires separate steering thrusters for facilitating safe and efficient port manoeuvring. Steering thrusters are generally of fixed or azimuthing type. Fixed thruster is arranged to a thruster duct running transversely from one side of the vessel hull to the opposite side. Thus the fixed thruster is capable of producing sideways force to the ship. Steerable azimuthing thruster is supported vertically rotatable in respect to the hull and is therefore capable of steering the vessel towards any selected direction.

Publication <CIT> discloses a transverse thruster which consists of a transverse-thrust passage, formed in the hull and consisting of a tunnel tube, and a transmission housing arranged in this transverse-thrust passage and having a propeller. <CIT> teaches to provide air-discharge openings formed in or at the wall of the tunnel tube at its both ends. An aim of the solution is to reduce noise during start-up. The air-discharge openings are connected to an air compressor via at least one air-supply tube and are of appropriate size for forming a finely distributed air flow.

<CIT> discloses an electric transverse tunnel thruster which is driven by motor arranged to rim of the propeller. The thruster comprises a cylindrical housing, which is open at both sides in its axial direction, a thruster body disposed inside the cylindrical housing and a pair of fairing ducts which are removably mounted to respective side surfaces of the thruster body inside the housing. The thruster body includes an annular stator, an annular rotor disposed inside the stator and a propeller blade provided on an inner peripheral surface of the rotor.

<CIT> discloses a thruster in which a nozzle duct is arranged around a propeller of the thruster. The nozzle duct is supported to hub of the thruster by means of vanes extending inwards in a duct. There is a rim drive electric motor used to drive the propeller. The rim drive electric motor comprises a rotor rim and a stator. The rotor rim is arranged on the outer perimeter of the propeller i.e. on the outer tips of the propeller blades. The rotor rim rotates in an annular groove extending radially outwards from an inner surface of the nozzle. Z Document <CIT> and <CIT> also disclose a thruster in which a nozzle duct is arranged around a propeller of the thruster.

Although these may be advantageous as such, there is still a need for improvements in operation of a propulsion assembly for a marine vessel. Particularly, it is an object of the invention to improve efficiency and reduce noise level of such assembly.

Objects of the invention can be met substantially as is disclosed in the independent claims and in the other claims describing more details of different embodiments of the invention.

A propulsion assembly for a marine vessel according to an embodiment of the invention comprises.

By means of the gas inlet, gas, preferably air is introduced such that a layer of air is maintained between the duct and the circular rim in the slot. The layer of air provides advantageous effects such as minimizing frictional resistance of the outer wall of the rim as well as noise dampening.

According to an embodiment of the invention a space is arranged radially between a bottom of the slot and outer surface of the rim, and that the at least one gas inlet is arranged to open into the space.

According to an embodiment of the invention one gas inlet is arranged to open into the space at its lowermost position.

According to an embodiment of the invention the slot is formed to the body as an indent from the level of the inner wall of the duct.

According to an embodiment of the invention the slot is formed to the body as a radially inward extending circumferential projections provided with the circumferential slot.

According to an embodiment of the invention the projection comprises a first fairing at a first side of the propeller and a second fairing at a second side of the propeller having the slot between the fairings.

According to an embodiment of the invention the projection comprises a first axial end and a second axial end. The outer diameter of the projection at the first end and at the second end is substantially the same, and equal to the inner diameter of the duct. The inner diameter of the projection is substantially equal to the inner diameter of the duct at the first axial end, and the inner diameter of the projection at its second axial end is less than outer diameter of the circular rim.

According to an embodiment of the invention the assembly comprises at least four gas inlets arranged to open into the slot.

According to an embodiment of the invention the assembly comprises <NUM> - <NUM> gas inlets arranged to open into the slot.

According to an embodiment of the invention the assembly comprises evenly distributed gas inlets, having an angle of <NUM> - <NUM> degrees between the gas inlets.

According to an embodiment of the invention the assembly comprises a circumferentially extending gas plenum in connection with the body provided with plurality of substantially evenly distributed gas inlets arranged to open into the slot.

According to an embodiment of the invention the gas plenum circumscribes the duct.

According to an embodiment of the invention the propeller shaft is a driven shaft. The propeller shaft may be driven by a bevel gear connection, or by an electric motor driving the shaft directly.

According to an embodiment of the invention the propeller shaft is a non-driven shaft.

According to an embodiment of the invention propeller is provided with a rim drive.

According to an embodiment of the invention propeller is provided with a mechanical rim drive.

According to an embodiment of the invention propeller is provided with an electric motor wherein the rim comprises a rotor part of the motor and the body of the duct is provided with a stator part of the motor.

According to an embodiment of the invention the propulsion assembly is a transverse tunnel thruster, wherein the duct of the propulsion assembly is a straight tube.

According to an embodiment of the invention the propulsion assembly is a shaft line propulsion system, wherein the body of the duct of the propulsion assembly is rigidly attached to a hull of a vessel and the shaft extends via a stern tube through the hull of the vessel.

According to an embodiment of the invention the propulsion assembly is a steerable azimuthing thruster wherein the body comprises a nozzle duct and the boss of the propeller is connected to the shaft in a support structure, the support structure extending radially from the boss for coupling the azimuthing thruster to a vessel in rotatably manner.

A transverse tunnel thruster for a marine vessel according to an embodiment of the invention comprises.

A steerable azimuthing thruster for a marine vessel according to an embodiment of the invention comprises.

By means of the invention the propeller can be designed to be highly loaded at tips of the blades, which improves efficiency of the propeller and can enable also smaller diameter of tunnel. This has positive impact on total cost and less vessel resistance, which in turn results in fuel savings.

The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims.

<FIG> depicts schematically a water submergible propulsion assembly <NUM> for a marine vessel <NUM> according to an embodiment of the invention. The propulsion assembly is a thruster assembly and it comprises a body <NUM>, which in turn comprises a duct <NUM> for water to flow through the body for generating thrust. The duct may be referred to as a tube or a tunnel. The duct <NUM> has a longitudinal axis L, and a first end <NUM> and a second end <NUM>. More precisely, the thruster assembly in the <FIG> is a transverse tunnel thruster, in which case the duct <NUM> is a straight tube having a first diameter D1. The duct <NUM> may also be referred to as a tunnel. The transverse tunnel thruster is installed rigidly to a hull of the vessel, typically inside the hull, such the first end <NUM> and the second end <NUM> open into the surrounding water at opposite sides of the hull, i.e. it is installed transversely to the longitudinal direction of the vessel. The thruster assembly <NUM> comprises a propeller <NUM> and a support structure <NUM> for the propeller <NUM>. The support structure comprises a propeller shaft <NUM> arranged at a centre line L of the duct, to which propeller shaft <NUM> the propeller <NUM> is attached to. The propeller shaft may be driven or non-driven depending on the actual practical solution.

The propeller <NUM> comprises at least three blades <NUM> and a boss <NUM> which is supported to the shaft <NUM>. The propeller further comprises a circular rim <NUM> attached the radial ends <NUM>' of the propeller blades <NUM>, and vice versa. The rim <NUM> is illustrated in the <FIG> as a cylindrical rim part having an axial length shorter than the propeller boss <NUM>. The rim has a radially outer surface which has a second diameter D2. The second diameter is less than the first diameter D1 such that the propeller with the rim <NUM> can be easily assembled to and disassembled from the shaft <NUM>. The rim is parallel to the boss <NUM> having equal radiuses at its axial ends. The rim reduces tip vortices created by the propeller, decreases noise generation and also improves efficiency of the thruster.

The assembly <NUM> is provided with a circumferential slot <NUM> at its inner surface such that the circular rim <NUM> extends at least partly into the slot <NUM> in radial direction. The circumferential slot <NUM> opens inside the duct <NUM> between the first <NUM> end and the second end <NUM> of the duct. The slot <NUM> has substantially radially extending side walls <NUM>'. Respectively, the circular rim <NUM> has substantially radially extending side walls <NUM>', the side walls of the slot and the rim being at least part radially overlapping. This way the radially extending side walls <NUM>',<NUM>' form a radial gap between the slot <NUM> and the circular rim <NUM>.

There is at least one gas inlet <NUM> arranged to open into the slot <NUM>. There is a space is arranged radially between a bottom of the slot and outer surface of the rim, and that the at least one gas inlet is arranged to open into the space. By means of the gas inlet, gas, preferably air is introduced such that a layer of air is maintained between the duct <NUM> and the circular rim <NUM> in the slot <NUM>. The layer of air provides advantageous effects such as noise dampening as well as minimizing frictional resistance of the outer wall of the rim <NUM>.

There is a space arranged radially between a bottom of the slot <NUM> and radially outer surface of the rim <NUM>, wherein the at least one gas inlet <NUM> is arranged to open into the thus formed space. The gas inlet may be arranged to a bottom wall of the slot <NUM>.

In the embodiment shown in the <FIG> the slot <NUM> is formed to the duct <NUM> by means of two radially inward extending circumferential projections <NUM>, which are arranged such that first one of the projections <NUM> is axially on a first side of the rim <NUM> and the second one of the projections <NUM> is arranged axially on a second side of the rim <NUM>. The projections are ring-like parts, optionally formed of several segments. The projections <NUM> are releasably assembled to the duct <NUM> so that the propeller with the rim <NUM> can be easily assembled to and disassembled from the shaft <NUM>. The propeller and the projections are installed so that firstly the projection <NUM> behind (as seen from the first end <NUM>. of the duct, or on the side of the support structure <NUM>) the propeller is installed and attached to the duct <NUM>, next the propeller is attached to the shaft <NUM> and after that the projection <NUM> in front of the propeller <NUM>, seen from the first end <NUM> of the duct. The projection <NUM> is a circular part, or an assembly of circular segments having a cylindrical outer surface. Its radially inner surface provides smooth change of inner diameter between the first axial end and second axial end of the projection <NUM>.

The projections are formed so as to provide a first fairing at a first side of the propeller <NUM> and a second fairing at a second side of the propeller <NUM>. This way, even if the outer diameter, the second diameter D2, of the rim is smaller than the inner diameter of the duct <NUM>, the first diameter D1, efficiency of the propeller is maintained at good level thanks to the radial projections <NUM> on both sides of the rim <NUM>. When the slot is arranged between the projection parts having fairings on a side in contact with the water flow when in use, the hydrodynamical efficiency is improved. The fairing smoothly bridges the radial gap/step between the duct inner surface and the rim inner surface that has smaller diameter. The projection <NUM> has a first axial end and a second axial end. Its inner diameter is substantially equal to the first diameter D1 at the first axial end. The outer diameter of the projection <NUM> is substantially equal at its first and second ends. Inner diameter of the projection <NUM> at its second axial end is less than the second diameter D2.

The projections are made as a removable assembly of at least two parts to enable installation and removal of the propeller.

As it becomes clear from the <FIG>, which shows an embodiment of the sectional view II-II of the <FIG>, the assembly comprises multiple gas inlets <NUM> in the wall of the duct <NUM> opening into the slot <NUM>. The assembly <NUM> comprises evenly distributed gas inlets <NUM> in the duct <NUM>, having an angle A of <NUM> - <NUM> degrees between two adjacent gas inlets <NUM>. The assembly <NUM> comprises a circumferentially extending gas plenum <NUM> in connection with the body <NUM> which is provided with plurality of substantially evenly distributed gas inlets <NUM> arranged to open into the slot <NUM> inside the duct <NUM>. As is depicted in the <FIG> the gas plenum advantageously circumscribes the body <NUM> outside the duct <NUM>. The plenum <NUM> and the gas inlets <NUM> are connected to a source of pressurized air <NUM> by means of a pipe <NUM> and a control valve system <NUM> arranged between the source of pressurized air <NUM> and the plenum <NUM>.

Depending on the case the propeller shaft maybe a driven shaft, which means that the shaft is attached to the propeller such that torque and axial thrust can be transmitted from the propeller to the shaft. Also, the shaft is also coupled to a prime mover, such as an electric or hydraulic motor.

The propeller shaft may be a non-driven, which means that the shaft is attached to the propeller such that axial thrust can be transmitted from the propeller to the shaft. In such a case the propeller may be provided with a rim drive and be rim driven e.g. driven by an electric motor <NUM>, having a rotor part arranged to the rim and a stator part to the body. This particular feature is depicted in the <FIG> which schematically shows a detail where the rotor part <NUM> is in connection with the rim <NUM> and the stator part <NUM> in connection with the body <NUM>. The propeller may also be mechanically drive by suitable gear system or a belt or a chain drive. Also hydraulic or pneumatic force transmission via the rim of the propeller is feasible alternative to operate the thruster.

<FIG> depicts schematically a water submergible thruster assembly <NUM> for a marine vessel according to an embodiment of the invention. The thruster assembly comprises a body <NUM>, which in turn comprises a duct <NUM> for water to flow through the body for generating thrust. The duct <NUM> has a longitudinal axis, and a first end <NUM> and a second end <NUM>. More precisely, the thruster assembly in the <FIG> is a steerable azimuthing thruster, in which case the duct <NUM> is a nozzle duct. The boss <NUM> of the propeller is connected to a support structure <NUM> extending radially from boss for coupling the steerable azimuthing thruster to a vessel <NUM> in manner rotatably around a vertical axis as depicted by the arrow A. The thruster assembly <NUM> comprises a propeller <NUM> and a support structure <NUM> for the propeller <NUM>.

In the <FIG> the slot is formed to the body as an indent from the general level of the inner wall of the duct. In other words, in this embodiment the radially inner wall of the rim is substantially flush with the wall of the duct <NUM>. The plenum <NUM> and the gas inlets <NUM> are connected to a source of pressurized air <NUM> by means of a pipe <NUM> and a control valve system <NUM> arranged between the source of pressurized air <NUM> and the plenum <NUM>. Practically the functionalities of the introduction of gas in the embodiment of the <FIG> correspond to that of the <FIG> and at least their main features are totally interchangeable.

<FIG> discloses an embodiment of the invention as a sectional view at the location of the section II-II in the <FIG>. The assembly <NUM> comprises one gas inlet <NUM> in the duct <NUM>, which is positioned to open into the slot <NUM> at its lowermost position. The gas inlet <NUM> is connected to a source of pressurized air <NUM> by means of a pipe <NUM> and a control valve system <NUM> arranged between the source of pressurized air <NUM> and the inlet <NUM>. This is the most straightforward manner of realizing the introduction of the pressurized air into the slot.

<FIG> discloses an embodiment of the invention as a sectional view at the location of the section II-II in the <FIG>. The assembly <NUM> comprises three gas inlets <NUM> in the duct <NUM>, one of which is positioned to open into the slot <NUM> at its lowermost position and to other equally distributed to the rim of the duct. The gas inlets <NUM> are each connected to a common source of pressurized air <NUM> by means of a pipe <NUM> and a control valve system <NUM> arranged between the source of pressurized air <NUM> and inlet. This is the most straightforward manner of realizing the introduction of the pressurized air into the slot with improved distribution of gas introduction compared to the embodiment of the <FIG>.

<FIG> discloses an embodiment of the invention as a sectional view at the location of the section II-II in the <FIG>. The assembly <NUM> comprises four gas inlets <NUM> in the duct <NUM>, one of which is positioned to open into the slot <NUM> at its lowermost position and to other equally distributed to the rim of the duct. The gas inlets <NUM> are each connected to a common source of pressurized air <NUM> by means of a pipe <NUM> and a control valve system <NUM> arranged between the source of pressurized air <NUM> and inlet. This is the most straightforward manner of realizing the introduction of the pressurized air into the slot with improved distribution of gas introduction compared to the embodiment of the <FIG>. Should the practical application need more than four gas inlets <NUM>, the embodiment shown in the <FIG> is believed to be the most feasible way of obtaining the air distribution into the slot.

<FIG> depicts schematically a water submersible thruster assembly <NUM> for a marine vessel <NUM> according to an embodiment of the invention. The thruster assembly comprises a duct <NUM> for water to flow through the body for generating thrust. The duct <NUM> has a longitudinal axis L, and a first end <NUM> and a second end <NUM>. The duct <NUM> is a straight tube having a first diameter D1 at its second end <NUM>, while the first end of the duct has smaller diameter than the first diameter. The rim <NUM> is illustrated in the <FIG> as a cylinder having an axial length shorter than the propeller boss <NUM>. The rim has a radially outer surface which has a second diameter D2. The second diameter is less than the first diameter D1 such that the propeller with the rim <NUM> can be easily assembled to and disassembled from the shaft <NUM> via the second end of the duct <NUM>.

In the embodiment shown in the <FIG> the slot <NUM> is formed to the duct <NUM> by means of two radially inward extending circumferential projections <NUM>, which are arranged such that first one of the projections <NUM> is axially on a first side of the rim <NUM> and the second one of the projections <NUM> is arranged axially on a second side of the rim <NUM>.

It is notable that due to decreasing of the diameter of the duct in front of the propeller <NUM> the projection <NUM> is flush with the inner wall of the duct, at the axial end of the projection farthest from the propeller. The projections are made as a removable assembly of at least two parts to enable installation and removal of the propeller. In other respect the embodiment of the <FIG> corresponds to the embodiment of the <FIG>.

<FIG> depicts schematically a propulsion assembly <NUM> for a marine vessel according to an embodiment of the invention. The propulsion assembly <NUM> is a shaft line propulsion system, wherein the body <NUM> of the duct <NUM> of the propulsion assembly is rigidly attached to a hull of a vessel <NUM> and the shaft <NUM> extends via a stern tube through the hull of the vessel <NUM>. The operation and features relating to the duct <NUM>, the slot <NUM> and the gas inlets <NUM> may be adopted from anyone of the embodiments shown in the <FIG>. There is a rudder <NUM> arranged in co-operation with the duct <NUM> and the propeller <NUM> for obtaining steering effect of propulsion for the vessel.

Claim 1:
A propulsion assembly (<NUM>) for a marine vessel (<NUM>) comprising
- a body (<NUM>) comprising a duct (<NUM>) having a longitudinal axis (L), and a first end (<NUM>) and a second end (<NUM>),
- a support structure (<NUM>) for a propeller (<NUM>) comprising a propeller shaft (<NUM>) at a centre line of the duct (<NUM>),
- a propeller (<NUM>), positioned into the duct (<NUM>) and being attached to the propeller shaft (<NUM>), wherein the propeller (<NUM>) comprising at least three blades (<NUM>) and a boss (<NUM>) which is supported to the shaft (<NUM>), and further a circular rim (<NUM>) to which radial ends (<NUM>') of the propeller blades are attached, characterized in that
- a circumferential slot (<NUM>) is provided, opening inside the duct between the first end (<NUM>) and the second end (<NUM>), into which slot the circular rim (<NUM>) is arranged to extend radially, and in that the assembly further comprising
- at least one gas inlet (<NUM>) arranged to open into the slot (<NUM>).