EP3164330A1

EP3164330A1 - Marine vessel with a large propeller and gearbox

Info

Publication number: EP3164330A1
Application number: EP15814254.7A
Authority: EP
Inventors: Søren SCHNACK; Peter Teglman SCHIØLER
Original assignee: Odense Maritime Tech As; Odense Maritime Technology AS
Current assignee: Odense Maritime Tech As; Odense Maritime Technology AS
Priority date: 2014-07-01
Filing date: 2015-06-15
Publication date: 2017-05-10
Anticipated expiration: 2035-06-15
Also published as: WO2016000714A1; EP3164330B1; EP3164330A4; DK3164330T3; CN106536345A

Abstract

A marine vessel (1) driven by an engine (10, 50) with a very large first propeller (11) and a less large coaxial contra rotating second propeller (12). The marine vessel (1) comprises a hull (2) with a baseline (20) extending between the bow and the aft, an engine (10, 50) arranged inside the hull (2), a pair of coaxial contra-rotating propellers (11, 12) mounted in tandem on concentric shafts (32, 34) at or near the aft of the hull (2) and operably connected to the engine (10). The pair of coaxial contra-rotating propellers (11, 12) comprises a first propeller (11) with a first radius (R1) and a second propeller (12) with a second radius (R2) that is smaller than the first radius (R1). The axis (9) of the concentric shafts (32, 34) has a vertical distance (V) from the base line (20) that is at least equal to the second radius (R2) and smaller than the first radius (R1). Said first propeller (11) being arranged to be kept stationary in a specific angular position whilst the second propeller (12) is rotatable by the large internal combustion engine (10, 50).

Description

MARINE VESSEL WITH A LARGE PROPELLER AND GEARBOX TECHNICAL FIELD The present invention relates to a marine vessel with a large propeller, in particular to a marine vessel with a large propeller and a coaxial contra-rotating propeller (CCP) . BACKGROUND

Marine vessels, in particular cargo vessels have fuel costs as one of the major costs in their economy and therefore fuel consumption is one of the most important aspects of cargo ship design. The present trend of reduced speed (slow steaming) means that the potential for major improvements in the hull shape is very small, as the vast majority of the vessel's resistance depends mainly on the ships wetted surface area. The only items in the vessels propulsion system, with a significant loss, i.e. potential for saving, are the main engine and propeller. For a ship designer not involved in engine design, this leaves the propeller efficiency as the main field of interest. In order to minimize the kinetic energy lost in the propeller wash, the mass flow through the propeller disc, and thus the propeller diameter, has to be increased. The saving potential depends on the propeller load, which means that the saving potential is diminishing with increased diameter. Even considering the relatively large propellers presently being fitted, the potential is estimated to more than 10%.

The propeller diameter is generally limited by two factors, the engine RPM and the ships draught. As recent development in marine engines has provided engines capable of delivering a very large power at a relatively low RPM, the major constraint to propeller diameter is the ships draught. Cargo ship propellers normally have a small clearance above the ships baseline, and the propeller must be fully submerged even in a ballast condition .

For a cargo ship with some draught variation the largest propeller, which may be reasonably accommodated, has a diameter of abt . 75% of the design draught. By applying special aft body shapes like semi-ducts (i.e. concave hull sections above the propeller) , it is possible to keep larger propellers submerged, but the resulting increase in wetted surface has, so far, resulted in an increased resistance of a magnitude corresponding to the increase of the propeller efficiency. Several ships of this type have been built, but the design has not yet proved competitive. It should still, however, be considered as a potential source of power reduction in the design of cargo ships

SUMMARY On this background, it is a first aspect to provide a marine vessel with improved fuel efficiency.

This is achieved by providing a marine vessel driven by an engine, the marine vessel comprising a hull with a baseline extending between the bow and the aft, an engine arranged inside the hull a pair of coaxial contra- rotating propellers mounted in tandem on concentric shafts at or near the aft of the hull and operably connected to the engine, and the pair of coaxial contra- rotating propellers comprising a first propeller with a first radius and a second propeller with a second radius that is smaller than the first radius, the axis of the concentric shafts having a vertical distance (V) from the base line that is at least equal to the second radius and smaller than the first radius, and the first propeller being arranged to be kept stationary in a specific angular position whilst the second propeller is rotatable by the engine .

For a ship spending most of its operational time in deep water, a very large propeller extending below the baseline offers a saving potential, but the problem of allowing the full draught in shallow water have meant that this potential has not been utilized so far. The present invention allows the use of a very large two or three bladed propeller, with a shaft height sufficient to provide clearance above the baseline, when kept stationary in a suitable angular position and a significant proportion of the diameter below the baseline and can thus still be fully submerged in ballast condition. A pair of coaxial contra rotating propellers, fitted in tandem on concentric shafts, has a higher hydrodynamic efficiency than a single propeller with the same diameter. The reason is that the tangential velocity component induced by the single propeller does not contribute to the thrust, whereas the tangential velocity component from the forward of the coaxial contra rotating propellers is eliminated by the second propeller, which deflects it aft wards, thereby contributing to the forward thrust. The second, i.e. aft most, propeller is normally somewhat smaller than the first propeller. This is partly due to the contraction of the flow, as it is accelerated through the propeller disc, and partly due to the reduced induction of tangential velocity at larger diameters, caused by the reduced pitch angle. A combination of a very large propeller with few blades, extending below the baseline during rotation, and a smaller concentric contra rotating propeller above the baseline, offers most of the reduction in propulsive power of both the very large propeller, and the counter- rotating propellers, while maintaining propulsion in shallow waters.

In a first possible implementation of the first aspect the first propeller has a plurality of blades and the second propeller has a plurality of blades, at least the tips of the blades of the first propeller protrude below the baseline during rotation of the first propeller and wherein the specific rotational position is an inactive position wherein the blades of the first propeller do not protrude below the baseline. In a first possible implementation of the first aspect the marine vessel further comprises a gearbox operably connecting the concentric shafts to the engine, the gearbox having at least two positions: a first position wherein the first propeller and the second propeller are operably connected to the engine for contra-rotation when the engine is running, and a second position wherein the first propeller is kept stationary in the specific angular position and the second propeller is operably connected for rotation when the engine is running.

In order to work, however, such a contra rotating propeller requires a drive system allowing the large propeller to be kept stationary in a predetermined angular position, while the smaller propeller keeps propelling the ship at a reduced speed. The diameter of the large propeller may be of the same magnitude as the ships design draft, which for a large container vessel could be 14m or more.

In a third possible implementation of the first aspect the first propeller is fully submerged in a ballast condition of the marine vessel. In a fourth possible implementation of the first aspect the first propeller is two bladed or three bladed.

On this background, it is a second aspect to provide a gear for driving a pair of contra rotating propellers mounted in tandem on concentric shafts with a single engine .

This is achieved by providing a gear comprising: an input shaft with a first gearwheel of a first gear permanently mounted on the input shaft and a second gearwheel of a second gear mounted on the input shaft via a clutch with the clutch being configured to selectively engage the second gearwheel with the input shaft, a break operably connected to the second gearwheel, a concentric output shaft with an inner shaft and an outer shaft, a third gearwheel permanently secured to the outer shaft, the third gearwheel meshing with the second gearwheel, a fourth gearwheel permanently secured to the inner shaft, and a fifth gearwheel rotatable about a further rotation axis, the fifth gearwheel meshing with the first gearwheel and with the fourth gearwheel.

In a first possible implementation of the second aspect the clutch is hydraulically and/or electronically controllable and/or wherein the break is hydraulically and/or electronically controllable.

In a second possible implementation of the second aspect the outer shaft or the third gearwheel is provided with a thrust bearing capable of handling trust in one axial direction and the fourth gearwheel is provided with a thrust bearing capable of handling trust in two opposite axial directions.

These and other aspects of the invention will be apparent from and the example embodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following portion of the present description, the invention will be explained in more detail with reference to the example embodiments shown in the drawings, in which :

Fig. 1 is a diagrammatic rear view of a marine vessel according to an example embodiment showing the propeller arrangement,

Fig. 2 is a diagrammatic sectional view of the aft of the marine vessel according to Fig. 1,

Fig. 3 is view in detail of the aft portion of the marine vessel according to Fig. 1 showing the rudder and the propellers ,

Fig. 4 is a diagrammatic rear view of the marine vessel according to Fig. 1, showing an inactive or locked position of one of the propellers of a pair of coaxial contra-rotating propellers, Figs. 5 and 6 are different sectional views of a gearbox that is used in a variation of the example embodiment marine vessel according to Fig. 1,

Fig. 7 is a sectional view of the propellers and propeller shaft according to an embodiment,

Fig. 8 is the sectional view of the aft part of another example embodiment marine vessel according to Fig. 1, Fig. 9 is sectional view in greater detail of the example embodiment marine vessel shown in Fig. 8, showing twin engines and a corresponding gearbox,

Fig. 10 is a sectional view of a marine vessel according to an example embodiment, and

Fig. 11 is a sectional view of the propellers and propeller shaft and pod drive according to another embodiment .

DETAILED DESCRIPTION

In the following detailed description, the marine vessel will be described by the example embodiments. Fig. 1, 2 and 3 diagrammatically show the aft section of a marine vessel. The marine vessel 1 comprises a hull 2 and a superstructure 3 (shown in Fig. 10) . In an embodiment the marine vessel 1 is a cargo vessel. The marine vessel 1 is designed with a predetermined draught that is chosen such that draught of the marine vessel 1 does not exceed the water depth of the ports of call. The draught is determined as the depth of the baseline 20 of the hull 2 when the marine vessel one is fully loaded. The baseline roughly extends between the bow and the aft of the hull 2. The water line 15 of the marine vessel 1 in a ballast condition is also shown. An internal combustion engine 10 is located inside the hull 2. In an embodiment the combustion engine 10 is a large slow running two-stroke self-igniting internal combustion engine. The large two-stroke internal combustion engine 10 is provided with a gearbox 14 which in turn is connected to a driveshaft 13. The driveshaft 13 comprises two concentric shafts that are described in greater detail further below. A pair of coaxial contra- rotating propellers is fitted in tandem on the concentric shafts. The pair of coaxial contra-rotating propellers includes a first propeller 11 and a second propeller 12. The first propeller 11 has a radius Rl and the second propeller 12 has a radius R2. The radius R2 of the second propeller 12 is smaller than the radius Rl of the first propeller 11.

The drive shaft 13 comprising the two concentric shafts has an axis 9 that extends substantially horizontally from the gearbox 14 to the pair of counter-rotating propellers. The axis 9 is positioned at horizontal distance V from the baseline 20. The radius R2 is equal or smaller than the horizontal distance V, so that the blades 22 of the second propeller 12 do not protrude below the baseline 20 when the second propeller 12 is rotating. The radius Rl is larger than the horizontal distance V so that the blades 21 of the first propeller 11 protrude below the baseline 20 when the first propeller 11 is rotating. The horizontal distance B between the axis 9 of the propeller shaft 13 and the waterline 15 in ballast operation is larger than the radius Rl, so that it is ensured that the first propeller 11 is fully submerged, also during ballast operation. A rudder 17 is placed just behind the pair of counter- rotating propellers and the rudder 17 can pivot about an axis 7 in order to control the direction of the marine vessel 1.

Fig. 4 shows the first propeller 11 in a specific angular position, a non-active position, in which the propeller is locked when the marine vessel 1 sails in shallow waters, e.g. in a harbor or channel. In this specific angular position (non-active position) the blades 21 of the first propeller 11 does not protrude below the baseline 20. In the shallow water operation the second propeller 12 is rotated for either forward or reverse propulsion of the marine vessel 1, with the second propeller 12 being rotated by the large internal combustion engine 10 in the suitable of the two rotational directions (the engine is in an embodiment reversible) . Due to the fact that the radius R2 of the second propeller 12 is less than the horizontal distance B, the propeller blades 22 of the second propeller 12 do not protrude below the baseline 20 and do therefore not increase the effective draught of the marine vessel 1.

The rear smaller propeller 12 operates in the shadow of the forward first propeller 11 when the latter is locked, causing a somewhat uneven wake field. This is not considered a substantial drawback because the rear smaller second propeller 12 is only used with the forward large first propeller 11 in the locked position for a minor part of the propulsion of the marine vessel 1, i.e. in shallow water. During deepwater operation both the first propeller 11 and the second propeller 12 are rotated by the large internal combustion engine 10 for creating forward trust, with the first propeller 11 and the second propeller 12 contra-rotating and the blades 21 of the first propeller 11 protruding below the baseline 20.

In order to establish a pair of coaxial contra rotating propellers, mechanically driven by a single engine 10, with the possibility to keep the first propeller 11 stationary, a gearbox 14 is provided, which includes a clutch 43 and a brake 42, shown in Figs. 5 and 6. The gearbox 14 has been split in two gears, one for each propeller 11, 12, and both driven by the same input shaft 31. The input shaft 31 is located above the two concentric output shafts 32, 34 at the bottom of the gearbox 14.

A large gear can be made with an efficiency of more than 98% per stage, and the drive for the large first propeller 11, which is installed on the external shaft 34 (aft gear 33, 38) has only one stage. The very large first propeller 11 may require a rotational speed lower than suitable for the engine 10, and the aft gear is consequently shown as a reduction gear, but it should be understood that the aft gear 33,38 could also have a 1:1 ratio. In order to obtain counter-rotation, the drive for the second propeller 12, which is fitted on the internal shaft 32 (forward gear 35, 39, 40) has to have two stages. This drive is always engaged, and the second propeller 12 stops and starts together with the engine 10.

Thrust bearings 34,36,37 in the form of thrust-cams and Mitchell-blocks are integrated in the gearbox 14. The gear wheels 33, 35 on the output shafts 32, 24 may in an embodiment double as thrust-cams. The blocks 34,36,37 are shown on both sides of the inner-shaft gearwheel 35, but only on the fore side of the outer-shaft gearwheel 33. This reflects a system where the first propeller 11 is not used to deliver any backwards thrust.

The gear box 14 is divided into two separate spaces 47,48, and in an embodiment the lubrication system of the two drives is separate, in order to ensure a certain redundancy, in case of gear breakdown. The first gearwheel 38 for the first propeller 11 is free to rotate relative to the input shaft 31, and the torque must be transmitted via the multi-disc frictional clutch 43 fitted to the aft end of the input shaft 31. Every second disc in the clutch 43 has a toothed center cut-out, and is connected to the input shaft 31 which has got external splines, and every second disc has a toothed periphery, and is connected to the housing, which has got internal splines. When the discs are forced together by a hydraulic actuator, the housing which is integrated with the gear wheel 38, are locked to the input shaft 31, thereby engaging the first propeller drive. When the marine vessel 1 approaches shallow water, the first propeller 11 drive may be disengaged without stopping the engine 10. A brake 42 similar to the clutch 43, but fitted on forward of the clutch 40, on the outside of the rotating housing, will then lock the housing to the static part of the gearbox 14, thereby keeping the first propeller 11 stationary in an appropriate (inactive) angular position. As the clutch 43 and brake 42 are both hydraulically operated the disengaging and braking are well suited for connection to a control system for automatic control of the operation of the first propeller 11. In an embodiment the control system receives input from an echo sounder and other navigational systems.

Whether or not, it is required to stop the engine 10 while the drive for the large propeller is being engaged, depends on the clutch's ability to absorb sufficient dissipated energy, without excessive temperature rises. The engagement is practicable either way.

In order to minimize the loss due to viscous friction between the plates in the clutch 43 or brake 42, when disengaged, submersion of the plates in the gear oil is avoided in an embodiment. The clutch and brakes may either be ry' or partially submerged, i.e. working in a sparse amount of lubricating oil. Disc springs fitted between the plates may be one way to prevent these from being in close contact while disengaged.

In an embodiment, Fig. 7, the first propeller 11 is provided with feathering propeller blades 21. When the marine vessel 1 is operated for extended periods on the smaller second propeller 12 only, and/or at any significant speed, the blades 21 of the large first propeller 11 may have to be feathered (i.e. aligned with the flow) , in order to avoid excessive resistance and torque on the brake system. This means the blades 21 must be able to rotate about a radial axis (pitch axis) .

Due to the concentric shafts 32,34, a conventional controllable pitch system is impractical, but by locating the blade's center of effort sufficiently aft of the pitch axis (towards the trailing edge) , the blades 21 will automatically turn into a feathered position when the first propeller 11 is stopped while the marine vessel 1 moves forward. This will work well with a highly skewed blade design. When the first propeller 11 starts turning, the thrust acting on the blades 21 will increase the pitch (i.e. rotate the blade about the pitch axis) until the blades 21 meet a stopping device in a predetermined position. With a feathering system according to this embodiment the large propeller 11 cannot provide any astern thrust, and all astern manoeuvers must be executed using the smaller second propeller 12 only. The concentric propeller shafts 32,34 and hubs are shown in principle in Fig. 7. The stopping device can be made in various ways, and has not been shown. One way would be to cut away part of the blade foot, and locate a stop block, which may be integral with the inside of the hub, such that it fills part of the cut-away. In connection with this device, a liquid ^xtrap' (i.e. a kind of cavity, filled with lubricant) , should be considered as a pitch damping device. As the rotating blade foot approaches the stop, the cavity volume must be reduced, forcing the liquid through one or more small openings, thus ensuring a soft stop, as well as preventing possible vibrations. Figs. 8 and 9 illustrate another embodiment of the marine vessel 1 with a twin engine drive, comprising a large internal combustion engine 10 and a less large internal combustion engine 50. A gearbox 54 operatively connects the large internal combustion engine 10 to the first propeller 11 and connects the less large internal combustion engine 50 to the second propeller 12. The gearbox 15 includes two separate sets of gears with a housing compartment for each of them. The gear that connects the large internal combustion engine 10 to the first propeller 11 is located in the aft section of the gearbox 54 and includes a gearwheel 53 mounted on an input shaft 52 that is directly coupled to the crankshaft of the large internal combustion engine 10. The gearwheel 53 meshes with the gearwheel 55 that is mounted on the outer concentric shaft 34 which is in turn connected to the large first propeller 11. The gear that connects the less large internal combustion engine 50 to the second propeller 12 is located in the forward section of the gearbox 54 and includes a gearwheel 58 that meshes with the gearwheel 56 that is mounted on the inner concentric shaft 32 which is in turn connected to the second less large propeller 12. During Deepwater operation where the first propeller 11 and the second propeller 12 are counter-rotating the less large internal combustion engine 50 rotates in opposite direction relative to the rotation direction of the large internal combustion engine 10. In shallow water operation the large internal combustion engine 10 is stopped and due to the permanent connection between the large internal combustion engine 10 and the first propeller 11 the latter is thereby also stopped. In an embodiment the large internal combustion engine 10 can be provided with means to stop the engine in particular angular position, so that the large first propeller 11 stops in the inactive position with the blades 21 of the first propeller 11 not protruding below the baseline 20 of the hull 2. Astern manoeuvers carried out with the large internal combustion engine 10 stopped and the less large internal combustion engine 50 reversing.

Fig. 11 shows an embodiment using a pod drive. The drive system uses an electrically driven second propeller 12 (pod drive 57) that is fitted aft of the very large conventionally driven first propeller 11 (the first propeller 11 is driven by a combustion engine via a simple driveshaft) . Electric power for the pod drive can be provided by generator sets (not shown) in the marine vessel 1. The point drive is rotatable about an axis 7 so as to assist in controlling the direction of the marine vessel 1.

The invention has been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. The reference signs used in the claims shall not be construed as limiting the scope.

Claims

CLAIMS :

1. A marine vessel (1) driven by an engine (10,50), said marine vessel (1) comprising:

a hull (2) with a baseline (20) extending between the bow and the aft,

an engine (10,50) arranged inside said hull (2), a pair of coaxial contra-rotating propellers (11,12) mounted in tandem on concentric shafts (32,34) at or near the aft of said hull (2) and operably connected to said engine (10), and

said pair of coaxial contra-rotating propellers (11,12) comprising a first propeller (11) with a first radius (Rl) and a second propeller (12) with a second radius (R2) that is smaller than said first radius (Rl), the axis (9) of said concentric shafts (32,34) having a vertical distance (V) from said base line (20) that is at least equal to said second radius (R2) and smaller than said first radius (Rl), and

said first propeller (11) being arranged to be kept stationary in a specific angular position whilst said second propeller (12) is rotatable by said engine (10, 50) .

2. A marine vessel (1) according to claim 1, wherein said first propeller (11) has a plurality of blades (21) and said second propeller has a plurality of blades (22), at least the tips of the blades (21) of said first propeller (11) protrude below said baseline during rotation of said first propeller (11) and wherein said specific angular position is an inactive position wherein the blades (21) of said first propeller (11) do not protrude below said baseline (20.

3. A marine vessel (1) according to claim 1 or 2, further comprising a gearbox (14) operably connecting said concentric shafts (32,34) to said engine (10), said gearbox having at least two positions:

a first position wherein said first propeller (11) and said second propeller (12) are operably connected to said engine for counter-rotation when said engine is running, and

a second position wherein said first propeller (11) is kept stationary in said specific rotational position and said second propeller (12) is operably connected for rotation when said engine (10) is running.

4. A marine vessel (1) according to claim 1 or 2, further comprising a gearbox (54) operably connecting said concentric shafts (32,34) to said engine (10) and to another engine, said gearbox (54) operably connecting said first propeller (11) to said engine (20) and said gearbox (54) operably connecting said second propeller (12) said internal combustion engine (50) .

5. A marine vessel (1) according to any one of claims 1 to 4, wherein said first propeller (11) is fully submerged in a ballast condition of said marine vessel ( 1 ) .

6. A marine vessel (1) according to any one of claims 1 to 5, wherein said first propeller (11) is two bladed or three bladed.

7. A marine vessel (1) according to any one of claims 1 to 6, wherein said first propeller (11) is provided with feathering propeller blades (21) .

8. A gear for driving a pair of contra-rotating coaxial propellers (11,12) mounted in tandem on concentric shafts (32,34) with a single engine, said gear comprising: an input shaft (31) with a first gearwheel (39) of a first gear permanently mounted on said input shaft and a second gearwheel (38) of a second gear mounted on said input shaft (31) via a clutch (43) with said clutch being configured to selectively engage said second gearwheel (38) with said input shaft (31), a break (42) operably connected to said second gearwheel ( 38 ) , a concentric output shaft with an inner shaft (32) and an outer shaft (43), a third gearwheel (33) permanently secured to said outer shaft (34), said third gearwheel (33) meshing with said second gearwheel (38) to form said second gear, a fourth gearwheel (35) permanently secured to said inner shaft (32), and a fifth gearwheel (40) rotatable about a further rotation axis, said fifth gearwheel (40) meshing with said first gearwheel (39) and with said fourth gearwheel (35) to form said first gear.

9. A gearbox according to claim 8, wherein said clutch (43) is hydraulically and/or electronically controllable and/or wherein said break (42) is hydraulically and/or electronically controllable.

10. A gearbox according to claim 8 or 9, wherein said outer shaft or said third gearwheel (33) is provided with a thrust bearing (34) capable of handling trust in one axial direction and said fourth gearwheel (35) is provided with a thrust bearing (34) capable of handling trust in two opposite axial directions.