Propulsion and steering arrangement

Abstract

 A propulsion and steering arrangement for a vessel comprises a screw propeller (2) and a turnable rudder (10) arranged behind the propeller (2). A fairing (6) at a tail end of the propeller (2) and a bulb-shaped body (20) provided on the rudder (10) form a streamlined body which is continuous except for a narrow gap between the fairing (6) and the bulb-shaped body (20). The rudder (10) has a twisted upper leading edge (12) extending from an upper end (17) of the rudder (10) to the bulb-shaped body (20) and a twisted lower leading edge (13) extending from a lower end (18) of the rudder (10) to the bulb-shaped body (20). At least one of the upper leading edge (12) and the lower leading edge (13) has a constant twist angle.

Description

FIELD OF THE PRESENT INVENTION

[0001] The present invention relates to a propulsion and steering arrangement for a vessel. The arrangement is of a kind that comprises a propeller, a rudder arranged behind the propeller, and a bulb-shaped body provided on the rudder.

BACKGROUND OF THE PRESENT INVENTION

[0002] The most common means for propelling a vessel is a screw propeller which has two or more propeller blades. To reduce fuel consumption and emissions, the propulsive efficiency of the propeller, which is defined as being the ratio between propulsion (also called effective) power and delivered power, should be as high as possible.

[0003] The prediction of the propulsive efficiency for a certain engine power is usually done through model scale tests. The prevailing opinion that was developed more than 100 years ago in the model testing practice of those days suggests that propeller and hull of a vessel can be viewed and assessed separately. In reality, however, the interaction between propeller and hull is a very important aspect. The propeller and the hull should be integrated and tuned to one another if optimal performance is to be achieved. This also holds true for the interaction between propeller and hull appendages such as a rudder.

[0004] In order to improve interaction between a screw propeller and a rudder, GB 762,445 teaches to arrange a bulb-shaped body behind the propeller in extension of the propeller axis. In order to overcome a contraction of the propeller slip stream, it is suggested to push a freely protruding head of the bulb-shaped body closely up to the trailing edge of the propeller blades so as to overlap the propeller hub. In one embodiment, a front part of the bulb-shaped body is supported by a rudder post of an unbalanced rudder, while a tail part, or aft part, of the bulb-shaped body is carried by a rudder blade, both parts of the bulb-shaped body being in articulated engagement. In another embodiment, the bulb-shaped body is supported by a balanced rudder and the propeller hub has a recess engaged by the protruding head of the bulb-shaped body to allow a swinging movement of the bulb-shaped body relative to the propeller hub when the rudder is turned.

[0005] EP 0 852 551 A discloses a propulsion and steering arrangement of a vessel, wherein a transition ring screwed on a hub of a screw propeller forms a continuous streamlined body with a bulb-shaped body supported by a rudder horn of a semi spade rudder behind the propeller. The streamlined body is broken only by a narrow rotation gap between the transition ring and the bulb-shaped body.

[0006] WO 2006/112787 A discloses a propulsion and steering arrangement of a vessel, wherein a fairing hubcap which is integral with a hub of a screw propeller forms a continuous streamlined body with a bulb-shaped body supported by a full spade rudder behind the propeller. The front end of the bulb-shaped body and the hubcap are designed to keep a narrow gap between the bulb-shaped body and the hubcap constant when the rudder is turned. Further, the rudder has a highly sophisticated design based on simulation and optimisation of the form of twisted leading edge that meets the swirling water propelled backwards by the propeller when the propeller drives the vessel in fore direction. The twist angle of the rudder is greatest in the area of the bulb-shaped body and decreases with the distance from the bulb-shaped body. The twisted leading edge profile of the rudder improves the propeller slip stream through the rudder area, thereby increasing propeller efficiency.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to improve the propulsion and steering arrangements disclosed in EP 0 852 551 A and WO 2006/112787 A.

[0008] According to a first aspect the present invention, there is provided a propulsion and steering arrangement for a vessel, the arrangement comprising a screw propeller and a turnable rudder arranged behind the propeller. A fairing at a tail end of the propeller and a bulb-shaped body provided on the rudder form a streamlined body which is continuous except for a narrow gap between the fairing and the bulb-shaped body. The rudder has a twisted upper leading edge extending from an upper end of the rudder to the bulb-shaped body and a twisted lower leading edge extending from a lower end of the rudder to the bulb-shaped body. The rudder is characterized in that at least one of the upper leading edge and the lower leading edge has a constant twist angle resulting much more rugged and easy to manufacture rudder than sophisticated solution described in WO 2006/112787.

[0009] The applicants found out that the fuel consumption of the propulsion and steering arrangement according to the present invention can be cut as compared with the conventional propulsion and steering arrangement of EP 0 852 551 A which has a leading edge profile without twist.

[0010] What was not expected by the applicants was that the propulsion and steering arrangement according to the present invention can achieve the same fuel savings as the conventional propulsion and steering arrangement of WO 2006/112787 A in which the twist of the rudder decreases from the area of the bulb-shaped body towards the upper or lower end of the rudder. Although the theoretical propulsion efficiency tends to be higher for the propulsion and steering arrangement of WO 2006/112787 A when the rudder is parallel to the axis of rotation of the propeller, propulsion efficiency tends to be higher for the propulsion and steering arrangement according to the present invention when the rudder is turned to steer the vessel. Considering that the rudder of a vessel is often actuated at sea to fight cross wind and current, overall propulsion efficiency and fuel consumption will be in practice substantially the same for both propulsion and steering arrangements. In case there is much manoeuvring, overall propulsion efficiency and fuel consumption will be even better for the propulsion and steering arrangement according to the present invention.

[0011] The propulsion and steering arrangement according to the present invention has an additional benefit as the manufacturing costs for the rudder having the constant twist angle are less than those for the rudder of WO 2006/112787 A.

[0012] Preferably, both the upper leading edge and the lower leading edge have a constant twist angle.

[0013] The at least one twist angle is preferably less than 15°, more preferably less than 10°, and most preferably between 5° and 10°.

[0014] The at least one twist angle decreases in aft direction to 0° within a range defined by the respective leading edge and the pivot axis of the rudder.

[0015] The bulb-shaped body is preferably provided on a rudder blade of the rudder to allow a swinging movement of the bulb-shaped body relative to the fairing when the rudder is turned. The rudder may be either a full spade rudder or a semi spade rudder.

[0016] The propulsion efficiency and fuel savings of the propulsion and steering arrangement according to the present invention are the more remarkable the farer the pivot axis of the rudder is disposed from the leading edge of the rudder, or the more the upper and lower leading edges of the rudder are displaced from the axis of rotation of the propeller for a given turning angle of the rudder. For this reason, the pivot axis of the rudder is preferably located at 30 to 50% of the maximum rudder length from the upper or lower leading edge in aft direction, more preferably at 35 to 50% of the maximum rudder length, and most preferably at 40 to 50% of the maximum rudder length.

[0017] According to a second aspect the present invention, there is provided a vessel having the afore-mentioned propulsion and steering arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 

Fig. 1 shows a propulsion and steering arrangement according to a first embodiment of the present invention.

Fig. 2 shows the rudder of Fig. 1 with upper and lower cross sections.

Fig. 3 shows the upper cross section of Fig. 2.

Fig. 4 shows the lower cross section of Fig. 2.

Fig. 5 shows a propulsion and steering arrangement according to a second embodiment of the present invention mounted on the stern of a vessel.

DETAILED DISCLOSURE OF THE INVENTION

[0019] The invention is now explained in greater detail with reference to Figs. 1 to 6 which illustrate preferred embodiments of the present invention.

First Embodiment

[0020] Figs. 1 to 4 show a propulsion and steering arrangement according to a first embodiment of the present invention. The propulsion and steering arrangement is to be mounted on the stern of a vessel. The vessel may be equipped with one or more of the propulsion and steering arrangements.

[0021] As illustrated in Fig. 1, the propulsion and steering arrangement according to the first embodiment comprises a screw propeller to be mounted on a drive shaft (not shown) of the vessel, and a full spade rudder 10 to be mounted at a pivot axis P to a rudder stock (not shown) of the vessel behind the propeller 2. In this context, the term "behind" refers to the fore direction of the vessel as indicated by arrow F.

[0022] When the propeller 2 is driven by the drive shaft, the propeller 2 propels the vessel in either the fore direction F or in the opposite aft direction. When the vessel is propelled in the fore direction F by the propeller 2, water that has passed the propeller 2 forms a slip stream of swirling water which travels towards the rudder 10.

[0023] The propeller 2 has a hub 4 on which three propeller blades 8 are mounted. It can also have less or more blades. The propeller 2 is shown as a variable pitch propeller, but may also have a fixed pitch.

[0024] The tail end of the propeller 2 is defined by a fairing hubcap 6 which has been screwed on or shrunk on the propeller hub 4 to be integral with the hub 4. The illustrated outer contour of the propeller hub 4 can also be cast in a single piece. The fairing hubcap 6 has a recess. The recess is engaged by a front end 22 of a bulb-shaped body 20 which has been attached to a rudder blade 10a of the rudder 10 by means of a flange connection to be integral with the rudder blade 10a.

[0025] The front end 22 of the bulb-shaped body 20 projects into the recess of the hubcap 6 without contacting the recess. The recess of the hubcap 6 and the front end 22 of bulb-shaped body 20 are curved to keep a narrow gap between the recess of the hubcap 6 and the front end 22 of the bulb-shaped body 20 constant when the rudder 10 is turned. The bulb-shaped body 20 and the hubcap 6 form a continuous streamlined body which is broken only by the narrow gap. The streamlined body prevents a contraction of the propeller slip stream, thereby increasing propeller efficiency.

[0026] The design of the rudder 10 is now explained in more detail with reference to Figs. 2 to 4. Fig. 2 shows the full spade rudder 10 of Fig. 1 together with an upper cross section at an upper end 17 of the rudder 10 and a lower cross section at a lower end 18 of the rudder 10. Figs. 3 and 4 show the upper and lower cross sections in more detail.

[0027] As shown in Figs. 2 to 4, the rudder 10 has a streamlined profile with an upper leading edge 12 extending from the upper end 17 of the rudder 10 to the bulb-shaped body 20, a lower leading edge 13 extending from the lower end 18 of the rudder 10 to the bulb-shaped body 20, and a trailing edge 15 extending behind the bulb-shaped body 20 from the upper end 17 to the lower end 18 of the rudder 10. The upper leading edge 12 has a constant first twist angle a of 8° with respect to a centreline C of the rudder 10 in port-side direction, while the lower leading edge 13 has a constant twist angle β of 6° with respect to the centreline C of the rudder 10 in starboard direction. The twist angles α, β can have different values, but are preferably less than 15° in each direction.

[0028] The twists of the illustrated upper and lower leading edges 12, 13 decrease in aft direction to 0° within a range defined by the respective leading edge 12, 13 and the pivot axis P of the rudder 10, so that the trailing edge 15 is not twisted and extends in a straight line. The twists can also decrease to 0° within a range defined by the pivot axis P and the trailing edge 15, or the twists can continue up to the trailing edge 15 so that a fishtail rudder is formed.

[0029] When the propeller 2 drives the vessel in the fore direction F, the twisted leading edges 12, 13 meet the swirling water propelled backwards by the propeller 2. The twisted leading edge profile of the rudder 10 improves the propeller slip stream through the rudder area, thereby increasing propeller efficiency.

[0030] As best shown in Fig. 1, the pivot axis P of the illustrated rudder 10 is located at about 45% of a maximum rudder length L from the upper leading edge 12 in aft direction. The pivot axis P can also be located at a different position, but preferably at 35 to 50% of the maximum rudder length L to achieve a good balance of the rudder 10.

[0031] If the pivot axis P of the illustrated rudder 10 is located within the above-mentioned range of the maximum rudder length L, the displacement of the leading edges 12, 13 of the rudder 10 from the axis of rotation of the propeller 2 is large for a small turning angle of the rudder 10. Under such a large displacement, the constant twist angles α, β increase propeller efficiency as compared with the conventional leading edge profile of WO 2006/112787 A, which has large twist angles close to the bulb-shaped body and small twist angles close to the upper and lower ends of the rudder.

[0032] Furthermore, the manufacturing costs for the rudder 10 having the constant twist angles α, β is less than those for the rudder of WO 2006/112787 A which has changing twist angles.

Second Embodiment

[0033] Fig. 5 shows a propulsion and steering arrangement according to a second embodiment of the present invention mounted on the stern of a vessel.

[0034] As illustrated in Fig. 5, the propulsion and steering arrangement according to the second embodiment comprises a screw propeller 2 mounted on a drive shaft 30 of the vessel, and a semi spade rudder 10' mounted behind the propeller 2 to the hull of the vessel. The semi spade rudder 10' comprises a leading head 10d which is fixed to the hull, and a turnable rudder blade 10a on which a bulb-shaped body 20 is flanged into place.

[0035] The leading head 10d is provided with a lower main bearing 10e. The lower main bearing 10e supports a rudder stock 32 to which the rudder blade 10a is mounted.

[0036] The propeller 2 has a hub 4 on which four propeller blades 8 are mounted. It can also have less or more blades. The propeller 2 is shown as a variable pitch propeller, but may also have a fixed pitch.

[0037] The propeller hub 4 has been cast in a single piece to have the shape of a fairing. Alternatively, the fairing can be a hubcap which has been screwed on or shrunk on the propeller hub. The hub 4 has a recess which is engaged by a front end of the bulb-shaped body 20 without contacting the recess. The bulb-shaped body 20 and the hub 4 form a continuous streamlined body which is broken only by a narrow gap to allow a swinging movement of the bulb-shaped body 20 relative to the hub 4 when the rudder blade 10a is turned. The streamlined body prevents a contraction of the propeller slip stream, thereby increasing propeller efficiency. The recess of the hub 4 and the front end of bulb-shaped body 20 are curved to keep the narrow gap constant when the rudder blade 10a is turned.

[0038] Similar to the full spade rudder 10 according to the first embodiment, the semi spade rudder 10' according to the second embodiment has a streamlined profile with a twisted upper leading edge 12, a twisted lower leading edge 13, and a trailing edge 15 which is not twisted and extends in a straight line. The upper leading edge 12 extends from an upper end of the leading head 10d to a lower end of the leading head 10d. The lower leading edge 13 extends from a lower end 18 of the rudder blade 10a to the bulb-shaped body 20. The upper leading edge 12 has a constant first twist angle with respect to a centreline of the rudder 10' in starboard direction, while the lower leading edge 13 has a constant twist angle with respect to the centreline in port-side direction. The twist angles have values less than 15° in each direction, more preferably less than 10°, and most preferably between 5° and 10°. The twist of the upper leading edge 12 decreases to 0° in aft direction towards the rudder stock 32. The twist of the lower leading edge 13 decreases to 0° in aft direction within a range defined by the lower leading edge 13 and the pivot axis P of the rudder blade 10a. The range between the pivot axis P and the trailing edge 15 can also be twisted.

[0039] When the propeller 2 drives the vessel in the fore direction, the twisted leading edges 12, 13 meet the swirling water propelled backwards by the propeller 2. The twisted leading edge profile of the rudder 10' improves the propeller slip stream through the rudder area, thereby increasing propeller efficiency.

[0040] The illustrated rudder 10' has a constant rudder length in fore and aft direction. The pivot axis P of the rudder blade 10a is located at about 41% of the rudder length from the upper or lower leading edge 12, 13 in aft direction. The pivot axis P can also be located at a different position, but preferably at 35 to 50% of the rudder length to achieve a good balance of the rudder 10'.

[0041] If the pivot axis P of the illustrated rudder 10' is located within the above-mentioned range of the maximum rudder length, the displacement of the lower leading edge 13 of the rudder blade 10a from the axis of rotation of the propeller 2 is large for a small turning angle of the rudder 10'. Under such a large displacement, the constant twist angle of the lower leading edge 13 increases propeller efficiency as compared with a lower leading edge which has a large twist angle close to the notch and a small twist angle close to the lower end of the rudder blade.

[0042] Furthermore, the manufacturing costs for the semi spade rudder 10' having the constant twist angles is less than those for a semi spade rudder which has changing twist angles.

Claims

1. A propulsion and steering arrangement for a vessel, the arrangement comprising a screw propeller (2) and a turnable rudder (10; 10'; 10') arranged behind the propeller (2), wherein
a fairing (4; 6) at a tail end of the propeller (2) and a bulb-shaped body (20) provided on the rudder (10; 10') form a streamlined body which is continuous except for a narrow gap between the fairing and the bulb-shaped body (20), and
the rudder (10; 10') has a twisted upper leading edge (12) extending from an upper end (17) of the rudder (10; 10') to the bulb-shaped body (20) and a twisted lower leading edge (13) extending from a lower end (18) of the rudder (10; 10') to the bulb-shaped body (20),
characterized in that
at least one of the upper leading edge (12) and the lower leading edge (13) has a constant twist angle (α, β).

2. A propulsion and steering arrangement according to claim 1, wherein both the upper leading edge (12) and the twisted lower leading edge (13) have a constant twist angle (α, β).

3. A propulsion and steering arrangement according to claim 1 or 2, wherein the at least one twist angle (α, β) is less than 15°, preferably less than 10°, and more preferably between 5° and 10°.

4. A propulsion and steering arrangement according to any one of the preceding claims, wherein the at least one twist angle (α, β) decreases in aft direction to 0° within a range defined by the respective leading edge (12, 13) and the pivot axis (P) of the rudder (10; 10').

5. A propulsion and steering arrangement according to any one of the preceding claims, wherein the bulb-shaped body (20) is provided on a rudder blade (10a) of the rudder (10; 10') to allow a swinging movement of the bulb-shaped body (20) relative to the fairing (6) when the rudder blade (10a) is turned.

6. A propulsion and steering arrangement according to claim 5, wherein the rudder (10) is a full spade rudder.

7. A propulsion and steering arrangement according to claim 5, wherein the rudder (10') is a semi spade rudder.

8. A propulsion and steering arrangement according to any one of the preceding claims, wherein the pivot axis (P) of the rudder (10; 10') is located at 30 to 50% of the maximum rudder length (L) from the upper or lower leading edge (12, 13) in aft direction, preferably at 35 to 50% of the maximum rudder length (L), and more preferably at 40 to 50% of the maximum rudder length (L).

9. A vessel having a propulsion and steering arrangement according to any one of the preceding claims.

Drawing