WO2012085341A1

WO2012085341A1 - Marine vessel

Info

Publication number: WO2012085341A1
Application number: PCT/FI2011/051130
Authority: WO
Inventors: Oskar Levander; Aad Van Der Kam
Original assignee: Wärtsilä Finland Oy
Priority date: 2010-12-21
Filing date: 2011-12-19
Publication date: 2012-06-28
Also published as: FI20106361A; FI123164B; FI20106361A0

Abstract

The invention relates to a marine vessel (1 ) comprising a hull structure (2) with a bow (3), a stern (4), and a centre line skeg (5) extending along a longitudinal axis of the marine vessel. The marine vessel is provided with a counter rotating pro- peller (CRP) propulsion arrangement (6). In order to provide the marine vessel (1 ) with optimized steering capabilities, the marine vessel is provided with at least one additional steering means (9), which is arranged to be deployed between a raised position inside the hull structure (2) of the marine vessel (1 ) and a lowered position extending outside the hull structure (2) of the marine vessel (1 ).

Description

Marine vessel

Technical field

The present invention relates to a marine vessel comprising a hull structure with a bow, a stern, and a centre line skeg extending along a longitudinal axis of the marine vessel, which marine vessel is provided with a counter rotating propeller (CRP) propulsion arrangement, which comprises a fixed propulsion unit and a steerable propulsion unit according to the preamble of claim 1 .

Background art On marine vessels CRP propulsion arrangements have been used in order to lower power demand in comparison to twin shaft lines. Marine vessels with a CRP propulsion arrangement can be provided with a centre line skeg.

In solutions were the marine vessel is provided with a main shaft line and a steerable thruster the marine vessel is usually not equipped with a rudder. An ex- ample of such a CRP system can be found in WO 2004/056654 A1 . In this solution the main shaft line is a fixed, conventional engine, shaft, and propeller arrangement and the steerable thruster is an azimuthing pod propeller device.

Such arrangements have drawbacks in view of redundancy and lack of emergency steering. If the steerable thruster fails, no steering is available at all. Fur- thermore, such arrangements are not favourable for high speed operation of the marine vessel, particularly for course keeping. If, however, a rudder is used in connection with such an arrangement, the rudder will give rise to extra resistance.

Summary of invention

An object of the invention is to avoid the above mentioned drawbacks and to pro- vide a marine vessel with enhanced operational efficiency and safety. This object is attained by a marine vessel according to claim 1 . The basic idea of the invention is to provide the marine vessel, which comprises a CRP propulsion arrangement with a fixed propulsion unit and a steerable propulsion unit, with an additional steering facility which can be deployed only when steering is needed. This can be realized by means of at least one additional steering means arranged to be deployed between a raised position inside the hull structure of the marine vessel and a lowered position extending outside of the hull structure of the marine vessel. On a general basis this provides a low added resistance, as the steering means is mostly retracted into the hull structure.

The at least one additional steering means advantageously comprises a steering element arranged to be deployed between a raised position inside the hull structure of the marine vessel and a lowered position extending outside the hull structure of the marine vessel. Such a retractable arrangement can be adapted to the speed of the marine vessel in view of steering capacity.

Preferably the lowered position of the steering element extending outside the hull structure of the marine vessel is adjustable, whereby the steering element can be lowered only to the extent needed to turn the marine vessel. The steering force is adjusted by how deep the steering element is lowered.

In an advantageous embodiment, the steering element is arranged to be raised and lowered between said raised position and said lowered position in a vertical direction with respect to the longitudinal axis of the marine vessel, whereby such a retractable arrangement only occupies a limited space along the length (longitudinal axis) of the marine vessel when the steering element is in a retracted position inside the hull structure. It is to be understood that the arrangement does not have to be absolutely in said vertical direction, it may be inclined to some degree in either direction as well.

The steering element is arranged to be raised and lowered by means of a pair of hydraulic cylinders. Such a deployment mechanism provides a simple mechanical solution. In a further advantageous embodiment, the steering element is arranged to be pivoted between said raised position and said lowered position around a horizontal axis arranged inside the hull structure of the marine vessel. Such a retractable arrangement only requires a limited height inside the hull structure of the marine vessel when the steering element is in a retracted position.

The steering element is arranged to be pivoted by means of a hydraulic cylinder. Such a deployment mechanism provides a simple mechanical solution.

The at least one additional steering means is provided with a turning mechanism, whereby a desired steering angle can flexibly be provided. The at least one additional steering means is aligned with the centre line skeg and the longitudinal axis of the marine vessel. This provides for a streamlined arrangement. When the additional steering means comprises a single steering element, this means that the centre line skeg, the counter rotating propeller (CRP) propulsion arrangement, and the steering element are in line with each other along the longitudinal axis of the marine vessel.

Alternatively, the at least one additional steering means comprises a first steering element and a second steering element, which are arranged to be deployed between a raised position inside the hull structure of the marine vessel and a lowered position extending outside of the hull structure of the marine vessel. Such a retractable arrangement can be adapted to the speed of the marine vessel in view of steering capacity.

Preferably, the lowered position of the first steering element outside the hull structure of the marine vessel and the lowered position of the second steering element outside the hull structure of the marine vessel are adjustable, whereby the steer- ing elements can be lowered only to the extent needed to turn the marine vessel. The steering force is adjusted by how deep the steering elements are lowered. Advantageously, the first steering element and the second steering element are arranged to be deployed independently of each other, whereby course correction and steering direction can be easily achieved with minimum resistance.

In an advantageous embodiment, the first steering element and the second steer- ing element are arranged to be raised and lowered between said raised positions and said lowered positions in a vertical direction with respect to the longitudinal direction of the marine vessel, whereby such a retractable arrangement only occupies a limited space along the length (longitudinal axis) of the marine vessel when the steering elements are in a retracted position inside the hull structure. It is to be understood that the arrangement does not have to be absolutely in said vertical direction, it may be inclined to some degree in either direction as well.

Advantageously, the first steering element and the second steering element are arranged to be raised and lowered by means of a respective pair of hydraulic cylinders. Such a deployment mechanism provides a simple mechanical solution. In a further advantageous embodiment, the first steering element and the second steering element are arranged to be pivoted between said raised positions and said lowered positions around a horizontal axis arranged inside the hull structure of the marine vessel. Such a retractable arrangement only requires a limited height inside the hull structure of the marine vessel when the steering elements are in a retracted position.

Advantageously, the first steering element and the second steering element are arranged to be pivoted by means of a respective hydraulic cylinder. Such a deployment mechanism provides a simple mechanical solution.

Furthermore, it is advantageous that the first steering element and the second steering element are arranged with opposite preset steering angles, whereby turning of the steering elements is not necessary.

Preferably, the first steering element and the second steering element are arranged in parallel on opposite sides of the centre line skeg. This means that the first steering element and the second steering element are arranged in parallel with the centre line skeg, the counter rotating propeller (CRP) propulsion arrangement, and thus also in parallel with the longitudinal axis of the marine vessel. Advantageously, the at least one additional steering means is arranged aft of the CRP propulsion arrangement in order to benefit from the CRP propulsion arrangement propeller flow.

The CRP propulsion arrangement advantageously comprises a main shaft line provided with a first propeller device, forming the fixed propulsion unit, and a steerable thruster apparatus provided with a second propeller device, forming the steerable propulsion unit. Thus, the CRP propulsion arrangement can be aligned with the centre line skeg so that the main shaft line and the steerable thrusters are arranged along the centre line skeg and thus along the longitudinal axis of the marine vessel. The main shaft line forms a fixed propulsion unit with a conven- tional engine, shaft and propeller arrangement. The steerable thruster forms a steerable propulsion unit, which can be in the form of a so-called L-drive, Z-drive or an azimuthing propeller pod device.

Advantageous features of the invention are given in claims 2-20.

Brief description of drawings In the following the invention will be described, by way of example only, with reference to the accompanying schematic drawings, in which

Figures 1 -5 illustrate a first embodiment of the invention,

Figures 6-10 illustrate a second embodiment of the invention,

Figure 1 1 illustrates a third embodiment of the invention, Figures 12-16 illustrate a fourth embodiment of the invention,

Figures 17-21 illustrate a fifth embodiment of the invention, and Figure 22 illustrates a sixth embodiment of the invention. Detailed description

Figures 1 -5 illustrate a first embodiment of the invention. A marine vessel is generally indicated with reference numeral 1 . The marine vessel 1 comprises a hull structure 2 with a bow 3, a stern 4, and a centre line skeg 5 extending along a longitudinal axis of the marine vessel 1 . Terms like "front", "forward" and "in front of relate to the bow end of the marine vessel, i.e. a normal direction of operation. Terms like "aft", "backward" and "behind" relate to the stern end of the marine vessel, i.e. to a direction opposite the normal direction of operation of the marine vessel.

The marine vessel 1 is provided with a counter rotating propeller (CRP) propulsion arrangement 6 (Figures 2-5) comprising a fixed propulsion unit and a steer- able propulsion unit. In this embodiment the CRP propulsion arrangement 6 comprises a main engine (not shown) connected to a main shaft line 71 provided with a first propeller device 72, which form the fixed propulsion unit, and a steerable thruster apparatus 8 provided with an electric motor 81 and a second propeller device 82, which form the steerable propulsion unit. The main shaft line 71 is arranged along the centre line skeg 5. The main shaft line 71 and the steerable thruster apparatus 8 are aligned with the longitudinal axis of the marine vessel 1 . In the embodiment shown, the steerable thruster apparatus is a so-called L-drive. The steerable thruster apparatus could also e.g. be in the form of a Z-drive. An alternative steerable thruster apparatus would be an azimuthing propeller pod device with an electric motor arranged in the submerged pod itself.

CRP propulsion arrangements like this are well known to a person skilled in the art and are therefore not discussed in any greater detail in this connection.

There are some drawbacks to such thruster/pod CRP propulsion systems. There is only one steering device, i.e. the thruster/pod apparatus, whereby there is a lack of redundancy and emergency steering facilities. Further, such a thruster/pod apparatus is not ideal for course keeping at high speeds. Steering with the appa- ratus will result in a speed loss, since turning the apparatus will change the water flow into the propeller and will direct the thrust vector to the side and reduce the component pushing the marine vessel forward.

New "safe return to port" rules will come into force, which in practice necessitate two propulsion devices and two steering devices. A CRP system has two propulsion devices, but only one steering device. An additional rudder or steerable thruster apparatus could be an alternative, but they e.g. cause additional resistance and require additional space.

According to the present invention, the marine vessel 1 is provided with at least one additional steering means 9, which comprises a steering element 90. The additional steering means 9 is located aft of the steerable thruster apparatus 8. Figures 2-5 show the marine vessel 1 from the side. The steering element 90 is arranged to be deployed between a raised position (Figure 2) inside the hull structure 2 of the marine vessel 1 and a lowered position (Figures 3-5) extending outside the hull structure 2 of the marine vessel 1 .

In this embodiment, the steering element 90 is arranged to be raised and lowered in a vertical direction with respect to the longitudinal axis of the marine vessel, whereby such a retractable arrangement only occupies a limited space along the length (longitudinal axis) of the marine vessel. The space required for such a steering means compartment 15 thus mainly extends in a substantially vertical direction for receiving the steering element in a retracted position inside the hull structure. It is to be understood that such an arrangement does not have to be absolutely in said vertical direction, it may be inclined to some degree in either direction as well. The steering element 90 has a plate like shape. The steering element 90 is arranged to be raised and lowered by means of a deployment mechanism supported on a steering housing 95 arranged within the hull structure 2 of the marine vessel 1 . The deployment mechanism of the steering housing 95 comprises a pair of hydraulic cylinders 12, which at a lower end 121 are fastened to the steer- ing element 90 and at an upper end 122 to a fixed support 13 of the steering housing 95. This ensures a controlled and stabilized movement, i.e. raising and lowering of the steering element 90 by means of the hydraulic cylinders 12.

Such a retractable steering means in its retracted position only requires a space with a limited length along the longitudinal axis of the marine vessel 1 within the hull structure 2 of the marine vessel 1 .

In Figure 2 the additional steering means 9 comprising the steering element 90 is shown in a retracted position inside the hull structure 2 of the marine vessel 1 . Thus, there is practically no added resistance when the steering element is in this position. This position would be used in normal operating conditions.

The lowered position of the steering element 90 is adjustable.

Figure 3 shows the steering element 90 lowered out of the hull structure 2 to some extent. A position like this would be used mainly for course keeping when the marine vessel 1 operates a high speeds. Figure 4 shows the steering element 90 lowered out of the hull structure 2 to a greater degree than in Figure 3. A position like this would be used mainly for steering in emergency situations. Figure 5 shows the steering element 90 being fully lowered from the hull structure 2. A position like this would also be used mainly for steering in emergency situations. A typical emergency situation would be a so-called "take me home" operation when the steerable thruster apparatus 8 would be damaged or un-operational.

The additional steering means 9 with the steering element 90 would have to be efficiently sealed with respect to the hull structure 2. The additional steering means 9 is supported on the steering housing 95. The steering housing 95 has to have a slot in order to provide for the raising and lowering of the steering element 90. A seal system can be provided for sealing purposes between the slot in the steering housing 95 and the steering element 90. The seal system would also have to be adapted to the configuration of the steering element as well as to the retracted position of the steering element and the various lowered positions of the steering element in order to effectively seal in all modes of operation of the additional steering means 9. The steering means compartment 15 is mainly above the water line, whereby it has to be sealed mainly from splashing and does not have to be watertight.

As shown in a top section view in Figure 1 , the additional steering means 9 is provided with a turning mechanism 93 comprising an electric motor 94 and a pinion and rack for turning the steering housing 95. The turning mechanism 93 is used to provide a required steering angle for the steering element 90, which is illustrated by the two curved black arrows. The turning mechanism 93 would have to be sealed with respect to the hull structure 2 of the marine vessel 1 .

The steering force would be adjusted by how deep the steering element would be lowered. Advantageously, the steering element should normally be lowered slowly and smoothly and only to a small extent as possible. When a fast response is desired, quick lowering is advantageous for steering and course keeping.

As the additional steering means 9 is located aft of the CRP propulsion arrangement, more particularly behind the steerable thruster apparatus 8, already a small steering element area would give sufficient steering force at high speeds. Manoeuvring and steering at low speeds in normal conditions would be handled by the steerable thruster apparatus. The centre line skeg 5 would provide for course stability as such.

The additional steering means can advantageously be provided with a lifting mechanism for raising the steering element into the steering means compartment 15 in case of failure of the hydraulic cylinder arrangement. In this way the addi- tional steering means in an inoperable state would not extend outside the marine vessel providing undesired resistance to the movement of the marine vessel.

The marine vessel 1 is not provided with a rudder, neither a fixed rudder nor a turnable rudder. Figures 6-10 illustrate a second embodiment of the invention. A marine vessel is generally indicated with reference numeral 1 . The marine vessel 1 comprises a hull structure 2 with a bow 3, a stern 4, and a centre line skeg 5 extending along a longitudinal axis of the marine vessel 1 . Terms like "front", "forward" and "in front of relate to the bow end of the marine vessel, i.e. a normal direction of operation of the marine vessel. Terms like "aft", "backward" and "behind" relate to the stern end of the marine vessel, i.e. to a direction opposite the normal direction of operation of the marine vessel.

The marine vessel 1 is provided with a counter rotating propeller (CRP) propul- sion arrangement 6 (Figures 7-10) comprising a fixed propulsion unit and a steer- able propulsion unit. In this embodiment the CRP propulsion arrangement 6 comprises a main engine (not shown) connected to a main shaft line 71 provided with a first propeller device 72, which form the fixed propulsion unit, and a steerable thruster apparatus 8 provided with an electric motor 81 and a second propeller device 82, which form the steerable propulsion unit. The main shaft line 71 is arranged along the centre line skeg 5. The main shaft line 71 and the steerable thruster apparatus 8 are aligned with the longitudinal axis of the marine vessel 1 . In the embodiment shown, the steerable thruster apparatus is a so-called L-drive. The steerable thruster apparatus could also e.g. be in the form of a Z-drive. An alternative steerable thruster apparatus would be an azimuthing propeller pod device with an electric motor arranged in the submerged pod itself.

There are some drawbacks to such thruster/pod CRP propulsion systems. There is only one steering device, i.e. the thruster/pod apparatus, whereby there is a lack of redundancy and emergency steering facilities. Further, such a thrust- ers/pod apparatus is not ideal for course keeping at high speeds. Steering with the apparatus will result in a speed loss, since turning the apparatus will change the water flow into the propeller and will direct the thrust vector to the side and reduce the component pushing the marine vessel forward. New "safe return to port" rules will come into force, which in practice necessitate two propulsion devices and two steering devices. A CRP system has two propulsion devices, but only one steering device. An additional rudder or steerable thruster apparatus could be an alternative, but they e.g. cause additional resis- tance and require additional space.

According to the present invention, the marine vessel 1 is provided with at least one additional steering means 9, which comprises a first steering element 91 and a second steering element 92. The additional steering means 9 is located aft of the steerable thruster apparatus 8. Figures 7-10 show the marine vessel 1 from the side, whereby only one of the steering elements, i.e. the second steering element 92 on the starboard side of the marine vessel 1 , is shown. The first steering element 91 and the second steering element 92 are arranged to be deployed between a raised position (Figure 7) inside the hull structure 2 of the marine vessel 1 and a lowered position (Figures 8-10) extending outside the hull structure 2 of the marine vessel 1 .

In this embodiment, the first steering element 91 and the second steering element 92 are arranged to be raised and lowered in a vertical direction with respect to the longitudinal axis of the marine vessel, whereby such a retractable arrangement only occupies a limited space along the length (longitudinal axis) of the marine vessel. The space required for such a steering means compartment 15 thus mainly extends in a substantially vertical direction for receiving the steering elements in a retracted position inside the hull structure. It is to be understood that the arrangement does not have to be absolutely in said vertical direction, it may be inclined to some degree in either direction as well. The first steering element 91 and the second steering element 92 are identical in configuration and have a plate like shape. The first steering element 91 and the second steering element 92 are arranged to be raised and lowered by means of a deployment mechanism comprising a respective pair of hydraulic cylinders 12, which at a lower end 121 are fastened to a steering element (the second steering element 92 as shown in Figures 7-10) and at an upper end 122 to a respective support 13 arranged inside the hull structure 2 of the marine vessel 1 . This ensures a controlled and stabilized movement, i.e. raising and lowering of the first steering element 91 and the second steering element 92 by means of the respective pair of hydraulic cylinders 12. Figures 6, 7 and 1 1 show the steering elements retracted into the hull structure 2 of the marine vessel 1 . The first steering element 91 and the second steering element 92 are arranged in an identical and symmetrical manner as can be seen from Figures 6 and 1 1 . The first steering element 91 and the second steering element 92 are both set with a fixed steering angle a symmetrically on opposite sides of the centre line skeg 5 along the longi- tudinal axis of the marine vessel 1 .

Such a retractable steering means arranged along the longitudinal axis of the marine vessel 1 in the retracted position only requires a space with a limited length along the longitudinal axis of the marine vessel 1 within the hull structure 2 of the marine vessel 1 . In Figure 7 the additional steering means 9 comprising the first steering element 91 and the second steering element 92 is shown in a retracted position inside the hull structure 2 of the marine vessel 1 . Figure 7 only shows the second steering element 92, which is on the starboard side of the marine vessel 1 . Thus, there is practically no added resistance when the steering elements are in this position. This position would be used in normal operating conditions.

The lowered position of the first steering element 91 and the lowered position of the second steering element 92 are adjustable. The first steering element 91 and the second steering element 92 are arranged to be deployed independently of each other. Figure 8 shows a steering element (the second steering element 92) lowered out of the hull structure 2 to some extent. A position like this would be used mainly for course keeping when the marine vessel 1 operates a high speeds.

Figure 9 shows a steering element (the second steering element 92) lowered out of the hull structure 2 to a greater degree than in Figure 8. A position like this would be used mainly for steering in emergency situations. Figure 10 shows a steering element (second steering element 92) being fully lowered from the hull structure 2. A position like this would also be used mainly for steering in emergency situations. A typical emergency situation would be a so-called "take me home" operation when the steerable thruster apparatus 8 would be damaged or un-operational.

The additional steering means 9 with the first steering element 91 and the second steering element 92 would have to be efficiently sealed with respect to the hull structure 2. The hull structure 2 has to have slots in order to provide for the raising and lowering of the steering elements. A seal system can be provided for sealing purposes between the slots in the hull structure 2 and the respective steering elements. The seal system would also have to be adapted to the configuration of the steering elements as well as to the retracted position of the steering elements and the various lowered positions of the steering elements in order to effectively seal in all modes of operation of the additional steering means 9. The steering means compartment 15 is mainly above the water line, whereby it has to be sealed mainly from splashing and does not have to be watertight.

As shown in a top section cut view in Figure 6, the first steering element 91 and the second steering element 92 are both set with a fixed steering angle a with re- spect to the longitudinal axis of the marine vessel 1 and the centre line skeg 5. The respective steering angles (a) are the same, opposite and preset. In this embodiment the first steering element 91 and the second steering element 92 converge towards the bow 3 of the marine vessel 1 .

Figure 1 1 shows a top section cut view of the at least one additional steering means 9 according to a third embodiment of the invention. The first steering means 91 and the second steering means 92 are both set with a fixed steering angle a with respect to the longitudinal axis of the marine vessel 1 and the centre line skeg 5. The respective steering angles (a) are the same, opposite and preset. In this embodiment the first steering means 91 and the second steering means 92 converge towards the stern 3 of the marine vessel 1 . To any other extent, the disclosure relating to Figures 6-10 apply for this embodiment as well.

The preset steering angles provide an alternative arrangement by which a turning of the rudders can be avoided, which would necessitate a turning mechanism and corresponding sealing arrangements. A typical steering angle a could be about 5 degrees, i.e. preferably 3-10 degrees, or more preferably 4-7 degrees.

For course correction it would be sufficient only to lower one of the steering elements to some extent. This would then be the first steering element 91 or the second steering element 92 depending on the desired course correction. The steering direction would be selected by choosing which one of the steering elements would be lowered, i.e. the first steering element 91 or the second steering element 92. The steering force would be adjusted by how deep the respective steering elements would be lowered. Advantageously, the steering elements should normally be lowered slowly and smoothly and only to a small extent as possible. Emergency breaking can be assisted by lowering both steering elements simultaneously. When a fast response is desired, quick lowering is advantageous for steering and course keeping.

The additional steering means can advantageously be provided with a lifting mechanism for raising the steering elements into the steering means compartment 15 in case of failure of the hydraulic cylinder arrangement. In this way the additional steering means in an inoperable state would not extend outside the marine vessel providing undesired resistance to the movement of the marine vessel. The marine vessel 1 is not provided with a rudder, neither a fixed rudder nor a turnable rudder.

Figures 12-16 illustrate a fourth embodiment of the invention. A marine vessel is generally indicated with reference numeral 1 . The marine vessel 1 comprises a hull structure 2 with a bow 3, a stern 4, and a centre line skeg 5 extending along a longitudinal axis of the marine vessel 1 . Terms like "front", "forward" and "in front of relate to the bow end of the marine vessel, i.e. a normal direction of operation of the marine vessel. Terms like "aft", "backward" and "behind" relate to the stern end of the marine vessel, i.e. to a direction opposite the normal direction of operation of the marine vessel .

The marine vessel 1 is provided with a counter rotating propeller (CRP) propulsion arrangement 6 (Figures 13-16) comprising a fixed propulsion unit and a steerable propulsion unit. In this embodiment the CRP propulsion arrangement 6 comprises a main engine (not shown) connected to a main shaft line 71 provided with a first propeller device 72, which form the fixed propulsion unit, and a steer- able thruster apparatus 8 provided with an electric motor 81 and a second propeller device 82, which form the steerable propulsion unit. The main shaft line 71 is arranged along the centre line skeg 5. The main shaft line 71 and the steerable thruster apparatus 8 are aligned with the longitudinal axis of the marine vessel 1 . In the embodiment shown, the steerable thruster apparatus is a so-called L-drive. The steerable thruster apparatus could also e.g. be in the form of a Z-drive. An alternative steerable thruster apparatus would be an azimuthing propeller pod device with an electric motor arranged in the submerged pod itself.

There are some drawbacks to such thruster/pod CRP propulsion systems. There is only one steering device, i.e. the thruster/pod apparatus, whereby there is a lack of redundancy and emergency steering facilities. Further, such a thrust- ers/pod apparatus is not ideal for course keeping at high speeds. Steering with the apparatus will result in a speed loss, since turning the apparatus will change the water flow into the propeller and will direct the thrust vector to the side and reduce the component pushing the marine vessel forward.

According to the present invention, the marine vessel 1 is provided with at least one additional steering means 9, which comprises a steering element 90. The additional steering means 9 is located aft of the steerable thruster apparatus 8. Figures 13-16 show the marine vessel 1 from the side. The steering element 90 is arranged to be deployed between a raised position (Figure 13) inside the hull structure 2 of the marine vessel 1 and a lowered position (Figures 14-16) extend- ing outside the hull structure 2 of the marine vessel 1 .

In this embodiment, the steering element 90 is arranged to be pivoted around a horizontal axis 10 arranged and supported inside the hull structure 2 of the marine vessel 1 . The horizontal axis 10 is supported on a steering housing 95 arranged within the hull structure 2 of the marine vessel 1 . Such a retractable ar- rangement only requires a limited height inside the hull structure of the marine vessel when the steering element is in a retracted position. The space required for such a steering means compartment 15 thus mainly extends in a substantially horizontal direction along the length (longitudinal axis) of the marine vessel for receiving the steering element in a retracted, swung-up position inside the hull structure.

The steering element 90 has an elongated plate like shape. A front end of the steering element 90 is hinged to the horizontal axis 10. Figure 13 shows the steering element retracted into the hull structure 2 of the marine vessel 1 . The movement the steering element 90, i.e. the pivoting of the steering element be- tween a raised position and a lowered position, is achieved by a hydraulic cylinder 1 1 which at a first end 1 1 1 is hinged to a front end of the steering element 90 and which at a second end 1 12 is hinged to a fastening point 14 on an extension 96 of the steering housing 95. Such a retractable steering means with the elon- gated steering element configuration arranged along the longitudinal axis of the marine vessel 1 in the retracted position only requires a space with a limited height within the hull structure 2 of the marine vessel 1 .

In Figure 13 the additional steering means 9 comprising the steering element 90 is shown in a swung up position inside the hull structure 2 of the marine vessel 1 . Thus, there is practically no added resistance when the steering element is in this position. This position would be used in normal operating conditions.

The lowered position of the steering element 90 is adjustable.

Figure 14 shows the steering element 90 lowered out of the hull structure 2 to some extent. A position like this would be used mainly for course keeping when the marine vessel 1 operates at high speeds.

Figure 15 shows the steering element 90 lowered out of the hull structure 2 to a greater degree than in Figure 14. A position like this would be used mainly for steering in emergency situations. Figure 16 shows the steering element 90 fully swung down, i.e. the rudder being fully lowered from the hull structure 2. A posi- tion like this would also be used mainly for steering in emergency situations. A typical emergency situation would be a so-called "take me home" operation when the steerable thruster apparatus 8 would be damaged or un-operational.

As shown in a top section view in Figure 12, the additional steering means 9 is provided with a turning mechanism 93 comprising an electric motor 94 and a pinion and rack for turning the steering housing 95. The turning mechanism is used to provide a required steering angle for the steering element 90, which is illus- trated by the two curved black arrows. The turning mechanism 93 would have to be sealed with respect to the hull structure 2 of the marine vessel 1 .

The marine vessel 1 is not provided with any other rudder, neither a fixed rudder nor a turnable rudder. Figures 17-21 illustrate a fifth embodiment of the invention. A marine vessel is generally indicated with reference numeral 1 . The marine vessel 1 comprises a hull structure 2 with a bow 3, a stern 4, and a centre line skeg 5 extending along a longitudinal axis of the marine vessel 1 . Terms like "front", "forward" and "in front of relate to the bow end of the marine vessel, i.e. a normal direction of operation of the marine vessel. Terms like "aft", "backward" and "behind" relate to the stern end of the marine vessel, i.e. to a direction opposite the normal direction of operation of the marine vessel.

The marine vessel 1 is provided with a counter rotating propeller (CRP) propul- sion arrangement 6 (Figures 18-21 ) comprising a fixed propulsion unit and a steerable propulsion unit. In this embodiment the CRP propulsion arrangement 6 comprises a main engine (not shown) connected to a main shaft line 71 provided with a first propeller device 72, which form the fixed propulsion unit, and a steer- able thruster apparatus 8 provided with an electric motor 81 and a second propel- ler device 82, which form the steerable propulsion unit. The main shaft line 71 is arranged along the centre line skeg 5. The main shaft line 71 and the steerable thruster apparatus 8 are aligned with the longitudinal axis of the marine vessel 1 . In the embodiment shown, the steerable thruster apparatus is a so-called L-drive. The steerable thruster apparatus could also e.g. be in the form of a Z-drive. An alternative steerable thruster apparatus would be an azimuthing propeller pod device with an electric motor arranged in the submerged pod itself.

According to the present invention, the marine vessel 1 is provided with at least one additional steering means 9, which comprises a first steering element 91 and a second steering element 92. The additional steering means 9 is located aft of the steerable thruster apparatus 8. Figures 18-21 show the marine vessel 1 from the side, whereby only one of the steering elements, i.e. the second steering element 92 on the starboard side of the marine vessel 1 , is shown. The first steering element 91 and the second steering element 92 are arranged to be deployed between a raised position (Figure 18) inside the hull structure 2 of the marine vessel 1 and a lowered position (Figures 19-21 ) extending outside the hull struc- ture 2 of the marine vessel 1 .

In this embodiment, the first steering element 91 and the second steering element 92 are arranged to be pivoted around a respective horizontal axis 10 arranged and supported inside the hull structure 2 of the marine vessel. The horizontal axis 10 is generally arranged in a right angle with respect to a fixed steering angle a (Figures 17 and 22). Such a retractable arrangement only requires a limited height inside the hull structure of the marine vessel when the steering elements are in a retracted position. The space required for such a steering means compartment 15 thus mainly extends in a substantially horizontal direction for receiving the steering elements in a retracted, swung-up position inside the hull struc- ture.

The first steering element 91 and the second steering element 92 are identical in configuration and have an elongated plate like shape. A front end of the first steering element 91 and a front end of the second steering element 92 are hinged to the respective horizontal axis 10. Figures 17, 18 and 22 show the steering elements retracted into the hull structure 2 of the marine vessel 1 . The movement the steering elements, i,e. the pivoting of the steering elements between a raised position and a lowered position, is achieved by respective hydraulic cylinders 1 1 which at a first end 1 1 1 are hinged to a front end of the respective steering element and which at a second end 1 12 are hinged to respective fastening points 14 in the hull structure 2. The first steering element 91 and the second steering element 92 are arranged in an identical and symmetrical manner as can be seen from Figures 17 and 22. The first steering element 91 and the second steering element 92 are both set with a fixed steering angle a symmetrically on each side of the centre line skeg 5 along the longitudinal axis of the marine vessel 1 . Such a retractable steering means with the elongated steering element configuration arranged along the longitudinal axis of the marine vessel 1 in the retracted position only requires a space with a limited height within the hull structure 2 of the marine vessel 1 .

In Figure 18 the additional steering means 9 comprising the first steering element 91 and the second steering element 92 is shown in a swung up position inside the hull structure 2 of the marine vessel 1 . Figure 18 only shows the second steering element 92, which is on the starboard side of the marine vessel 1 . Thus, there is practically no added resistance when the steering elements are in this position. This position would be used in normal operating conditions. The lowered position of the first steering element 91 and the lowered position of the second steering element 92 are adjustable. The first steering element 91 and the second element 92 are arranged to be deployed independently of each other.

Figure 19 shows a steering element (the second steering element 92) lowered out of the hull structure 2 to some extent. A position like this would be used mainly for course keeping when the marine vessel 1 operates at high speeds.

Figure 20 shows a steering element (the second steering element 92) lowered out of the hull structure 2 to a greater degree than in Figure 19. A position like this would be used mainly for steering in emergency situations. Figure 21 shows a steering element (the second steering element 92) fully swung down, i.e. the steering element being fully lowered from the hull structure 2. A position like this would also be used mainly for steering in emergency situations. A typical emergency situation would be a so-called "take me home" operation when the steer- able thruster apparatus 8 would be damaged or un-operational. The additional steering means 9 with the first steering element 91 and the second steering element 92 would have to be efficiently sealed with respect to the hull structure 2. The hull structure 2 has to have slots in order to provide for the raising and lowering of the steering elements. A seal system can be provided for sealing purposes between the slots in the hull structure 2 and the respective steering elements. The seal system would also have to be adapted to the configuration of the steering elements as well as to the retracted position of the steering elements and the various lowered positions of the steering elements in order to effectively seal in all modes of operation of the additional steering means 9. The steering means compartment 15 is mainly above the water line, whereby it has to be sealed mainly from splashing and does not have to be watertight.

Figure 17 shows a top section cut view of the additional steering means 9 according to the fifth embodiment of the invention. The first steering element 91 and the second steering element 92 are both set with a fixed steering angle a with respect to the longitudinal axis of the marine vessel 1 and the centre line skeg 5. The respective steering angles (a) are the same, opposite and preset. In this embodiment the first steering element 91 and the second steering element 92 converge towards the bow 3 of the marine vessel 1 .

Figure 22 shows a top section cut view of the at least one additional steering means 9 according to a sixth embodiment of the invention. The first steering ele- ment 91 and the second steering element 92 are both set with a fixed steering angle a with respect to the longitudinal axis of the marine vessel 1 and the centre line skeg 5. The respective steering angles (a) are the same, opposite and preset. In this embodiment the first steering element 91 and the second steering element 92 converge towards the stern 4 of the marine vessel 1 . To any other ex- tent, the disclosure relating to Figures 17-21 apply for this embodiment as well. The preset steering angles provide an alternative arrangement by which a turning of the steering elements can be avoided, which would necessitate a turning mechanism and corresponding sealing arrangements. A typical steering angle a could be about 5 degrees, i.e. preferably 3-10 degrees, or more preferably 4-7 degrees.

For course correction it would be sufficient only to lower one of the steering elements to some extent. This would then be the first steering element 91 or the second steering element 92 depending on the desired course correction. The steering direction would be selected by choosing which one of the steering elements would be lowered, i.e. the first steering element 91 or the second steering element 92. The steering force would be adjusted by how deep the respective steering element would be lowered. Advantageously, the steering elements should normally be lowered slowly and smoothly and only to a small extent as possible. Emergency breaking can be assisted by lowering both steering elements simultaneously. When a fast response is desired, quick lowering is advantageous for steering and course keeping.

As the additional steering means 9 is located aft of the CRP propulsion arrangement, more particularly behind the steerable thruster apparatus 8, already a small steering element area would give sufficient steering force at high speeds. Ma- noeuvring and steering at low speeds in normal conditions would be handled by the steerable thruster apparatus. The centre line skeg 5 would provide for course stability as such.

The additional steering means can advantageously be provided with a lifting mechanism for raising the steering elements into the steering means compart- ment 15 in case of failure of the hydraulic cylinder arrangement. In this way the additional steering means in an inoperable state would not extend outside the marine vessel providing undesired resistance to the movement of the marine vessel. The marine vessel 1 is not provided with any other rudder, neither a fixed rudder nor a turnable rudder.

As an alternative to the above discussed embodiments, the additional steering means may be provided with a flap mechanism, whereby only a part of the steer- ing element, i.e. a flap, would be turned in order to provide for a desired steering force. Furthermore, the number of hydraulic cylinders employed for the raising and lowering of the steering elements may vary.

The description and the thereto related drawings are only intended to clarify the basic idea of the invention. The invention may vary within the scope of the ensuing claims.

Claims

1 . Marine vessel comprising a hull structure (2) with a bow (3), a stern (4), and a centre line skeg (5) extending along a longitudinal axis of the marine vessel (1 ), which marine vessel is provided with a counter rotating propeller (CRP) pro- pulsion arrangement (6), which comprises a fixed propulsion unit (71 ,72) and a steerable propulsion unit (8,81 ,82), characterised in that the marine vessel (1 ) is provided with at least one additional steering means (9) arranged to be deployed between a raised position inside the hull structure (2) of the marine vessel (1 ) and a lowered position extending outside the hull structure (2) of the marine vessel (1 ).

2. Marine vessel according to claim 1 , characterised in that the at least one additional steering means (9) comprises a steering element (90) and in that the steering element (90) is arranged to be deployed between a raised position inside the hull structure (2) of the marine vessel (1 ) and a lowered position extending outside the hull structure (2) of the marine vessel (1 ).

3. Marine vessel according to claim 2, characterised in that the lowered position of the steering element (90) extending outside the hull structure (2) of the marine vessel (1 ) is adjustable.

4. Marine vessel according to claim 2, characterised in that the steering element (90) is arranged to be raised and lowered between said raised position and said lowered position in a vertical direction with respect to the longitudinal axis of the marine vessel (1 ).

5. Marine vessel according to claim 4, characterised in that the steering element (90) is arranged to be raised and lowered by means of a pair of hydraulic cylinders (12).

6. Marine vessel according to claim 2, characterised in that the steering element (90) is arranged to be pivoted between said raised position and said lowered position around a horizontal axis (10) arranged within the hull structure (2) of the marine vessel (1 ).

7. Marine vessel according to claim 6, characterised in that the steering element (90) is arranged to be pivoted between a raised position and a lowered position by means of a hydraulic cylinder (1 1 ).

8. Marine vessel according to claim 1 , characterised in that the at least one additional steering means (9) is provided with a turning mechanism (93).

9. Marine vessel according to claim 1 , characterised in that the at least one additional steering means (9) is aligned with the centre line skeg (5) and the lon- gitudinal axis of the marine vessel (1 ).

10. Marine vessel according to claim 1 , characterised in that the at least one additional steering means comprises a first steering element (91 ) and a second steering element (92), and in that the first steering element (91 ) and the second steering element (92) are arranged to be deployed between a raised position in- side the hull structure (2) of the marine vessel (1 ) and a lowered position extending outside the hull structure (2) of the marine vessel (1 ).

1 1 . Marine vessel according to claim 10, characterised in that the lowered position of the first steering element (91 ) extending outside the hull structure (2) of the marine vessel (1 ) and the lowered position of the second steering element (92) extending outside the hull structure (2) of the marine vessel (1 ) are adjustable.

12. Marine vessel according to claim 10, characterised in that the first steering element (91 ) and the second steering element (92) are arranged to be deployed independently of each other.

13. Marine vessel according to claim 10, characterised in that the first steering element (91 ) and the second steering element (92) are arranged to be raised and lowered between said raised position and said lowered position in a vertical direction with respect to the longitudinal axis of the marine vessel (1 ).

14. Marine vessel according to claim 13, characterised in that the first steering element (91 ) and the second steering element (92) are arranged to be raised and lowered by means of a pair of hydraulic cylinders (12).

15. Marine vessel according to claim 10, characterised in that the first steer- ing element (91 ) and the second steering element (92) are arranged to be pivoted between said raised position and said lowered position around a horizontal axis (10) arranged within the hull structure (2) of the marine vessel (1 ).

16. Marine vessel according to claim 15, characterised in that the first steering element (91 ) and the second steering element (92) are arranged to be pivoted between a raised position and a lowered position by means of respective hydraulic cylinders (1 1 ).

17. Marine vessel according to claim 10, characterised in that the first steering element (91 ) and the second steering element (92) are arranged with opposite fixed steering angles (a).

18. Marine vessel according to claim 10, characterised in that the first steering element (91 ) and the second steering element (92) are arranged in parallel on opposite sides of the centre line skeg (5).

19. Marine vessel according to claim 1 , characterised in that the at least one additional steering means (9) is arranged aft of the CRP propulsion arrangement (6).

20. Marine vessel according to claim 1 , characterised in that the CRP propulsion arrangement (6) comprises a main shaft line (71 ) provided with a first propeller device (72), which form the fixed propulsion unit, and a steerable thruster apparatus (8) provided with a second propeller device (82), which form the steer- able propulsion unit.