PROPELLER FOR A MARINE VESSEL

Abstract

A propeller (20) for a marine vessel (10), the propeller (20) comprising a plurality of propeller blades (24, 26). The propeller blades comprise a leading edge (30), a trailing edge (32) and an outer edge (34) located between the leading edge and the trailing edge. A transition from the leading edge to the outer edge occurs at a first transition point (36) and a transition from the outer edge to the trailing edge occurs at a second transition point (38). A straight line from the first transition point to the second transition point coincides with the outer edge (34) or is located at least partially outside the propeller blade. A smallest distance (D.sub.2) from the second transition point to the axis of rotation (A) is smaller than a smallest distance (D.sub.\) from the first transition point to the axis of rotation.

Claims

1. A propeller combination comprising a forward propeller and an after propeller, said propellers being adapted to rotate in opposite directions around said axis of rotation, wherein each one of said forward propeller and said after propeller is a propeller according to the following: a propeller for a marine vessel, said propeller comprising a plurality of propeller blades, said propeller being adapted to be rotated around an axis of rotation, each one of said propeller blades comprising an edge that in turn comprises a leading edge, a trailing edge and an outer edge located between said leading edge and said trailing edge, as seen along said edge of said propeller blade, wherein a transition from said leading edge to said outer edge occurs at a first transition point and a transition from said outer edge to said trailing edge occurs at a second transition point, characterized in that as seen in a side plane view of said propeller blade in a plane that extends parallel to said axis of rotation, a straight line from said first transition point to said second transition point coincides with said outer edge or is located at least partially outside said propeller blade, wherein a smallest distance from said second transition point to said axis of rotation is smaller than a smallest distance from said first transition point to said axis of rotation, wherein, as seen in said side plane view of said propeller blade, a length of said outer edge along said axis of rotation is equal to or greater than 20% of the maximum length of the propeller blade along said axis of rotation, where each of the transition points is arranged at ends of the outer edge where the extension of the outer edge does not coincide with the straight line and where the edge bends off towards said axis of rotation forming one of said leading edge or said trailing edge, when seen in said plane, wherein said smallest distance from said first transition point to said axis of rotation for said after propeller is smaller than a smallest distance from said second transition point to said axis of rotation (A) for said forward propeller.

2. The propeller according to claim 1, wherein said first transition point is the outermost point, as seen in a radial direction from said axis of rotation, of said propeller blade.

3. The propeller according to claim 1, wherein the first and the second transition points are corners with a curvature radius smaller than 1/10 of a diameter of the propeller, or preferably smaller than 1/50 of a diameter of the propeller.

4. The propeller according to claim 1, wherein, as seen in said side plane view of said propeller blade, the length of said outer edge along said axis of rotation is equal to or less than 50% of the maximum length of the propeller blade along said axis of rotation.

5. The propeller according to claim 4, wherein, as seen in said side plane view of said propeller blade, the length of said outer edge along said axis of rotation is equal to or less than 40% of the maximum length of the propeller blade along said axis of rotation.

6. The propeller according to claim 1, wherein said smallest distance from said second transition point to said axis of rotation is equal to or less than 99% of said smallest distance from said first transition point to said axis of rotation.

7. The propeller according to claim 6, wherein said smallest distance from said second transition point to said axis of rotation is equal to or less than 95% of said smallest distance from said first transition point to said axis of rotation.

8. The propeller according to claim 1, wherein said smallest distance from said second transition point to said axis of rotation is equal to or greater than 70% of said smallest distance from said first transition point to said axis of rotation.

9. The propeller according to claim 8, wherein said smallest distance from said second transition point to said axis of rotation is equal to or greater than 75% of said smallest distance from said first transition point to said axis of rotation.

10. (canceled)

11. (Canceled)

12. (Canceled)

13. A marine vessel comprising a propeller combination according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

[0029] In the drawings:

[0030] FIG. 1 is a schematic perspective view of a marine vessel,

[0031] FIG. 2 is a schematic illustration of an embodiment of a propeller,

[0032] FIG. 3 is a schematic illustration of another embodiment of a propeller, and

[0033] FIG. 4 is a schematic illustration of an embodiment of a propeller combination.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0034] The invention will be described below for a marine vessel in the form of a boat 10 such as the boat illustrated in FIG. 1. The boat 10 should be seen as an example of a marine vessel which could comprise a propeller and/or propeller combination according to the present invention. However, the present invention may be implemented in a plurality of different types of marine vessels. Purely by way of example, the present invention could be implemented in a ship, a submarine or in a thruster intended for a semisubmersible unit.

[0035] The FIG. 1 boat 10 comprises a hull 12 and tractor-type drive 14. The drive 14 illustrated in FIG. 1 is configured to be mounted to the stern 16 of the hull 12 but it is also contemplated that other implementations of the drive may be configured to be mounted to other portions of a hull. The drive 14 includes at least one pulling (or tractor) propeller, which can be configured as a propeller combination, comprising a forward propeller 18 and an after propeller 20, mounted to a front end of a gear case 22. The forward and after propellers 18, 20 in the illustrated embodiment are a pair of counter-rotating propellers mounted on coaxially rotating shafts. However, it is also envisaged that the present invention can be applied for a single propeller. Furthermore, it is envisaged that the present invention can be applied for a pushing single propeller or a pushing propeller combination.

[0036] FIG. 2 illustrates an embodiment of a propeller 20 according to the first aspect of the present invention. Purely by way of example, the FIG. 2 propeller 20 may be adapted to form part of a pulling (or tractor) propeller or propeller combination, such as the FIG. 1 propeller combination, or a pushing propeller or propeller combination.

[0037] Irrespective of the intended use of the propeller 20, the propeller 20 comprises a plurality of propeller blades 24, 26. In the FIG. 2 view, two propeller blades are visible but it is contemplated that embodiments of the propeller may comprise at least three propeller blades. The propeller 20 is adapted to be rotated around an axis of rotation A.

[0038] With reference to one 24 of the FIG. 2 propeller blades 24, 26, each one of the propeller blades 24, 26 comprises an edge 28 that in turn comprises a leading edge 30, a trailing edge 32 and an outer edge 34 located between the leading edge 30 and the trailing edge 32, as seen along the edge 28 of the propeller blade 24. A transition from the leading edge 30 to the outer edge 34 occurs at a first transition point 36 and a transition from the outer edge 34 to the trailing edge 32 occurs at a second transition point 38.

[0039] Moreover, as indicated in FIG. 2, as seen in a side plane view of the propeller blade 24 in a plane P that extends parallel to the axis of rotation A, a straight line from the first transition point 36 to the second transition point 38 coincides with the outer edge 34 or is located at least partially outside the propeller blade 24. In the FIG. 2 embodiment of the propeller 20, the outer edge 34 follows a substantially straight line. This means that when the outer edge follows the straight line this would result in that the outer edge follows a section of an envelope of an imaginary cone when the propeller rotates. FIG. 3 illustrates another embodiment of the propeller wherein the outer edge 24 has a parabolic shape, as seen in the plane P that extends parallel to the axis of rotation A.

[0040] Furthermore, a smallest distance D.sub.2 from the second transition point 38 to the axis of rotation A is smaller than a smallest distance D.sub.1 from the first transition point 36 to the axis of rotation A. As indicated in FIG. 2, the smallest distances may be the distance from the axis of rotation A to the first transition point 36 and the second transition point 38, respectively, in a direction being parallel to a radial axis R.

[0041] Each of the transition points 36, 38 is arranged at ends of the outer edge 34 where the extension of the outer edge does not coincide with the straight line and where the edge bends off towards said axis of rotation A, thus the edge now forming one of said leading edge 30 or said trailing edge 32, when seen in said plane P.

[0042] Furthermore, in the FIG. 2 embodiment, the first transition point 36 is the outermost point, as seen in a radial direction from the axis of rotation, of the propeller blade 24. Put differently, the smallest distance D.sub.1 from the first transition point 36 to the axis of rotation A is larger than the smallest distance from any other point on the edge 28 of the propeller blade 24 to the axis of rotation A.

[0043] Further, the first and the second transition points are corners with a curvature radius smaller than 1/10 of a diameter of the propeller, or preferably smaller than 1/50 of a diameter of the propeller. Thus, two relatively sharp transition points are preferably arranged. This provides an outer edge that is clearly distinct from the leading edge and the trailing edge through respective first and second transition points. Arranging clear transition points will provide a more pure function according to the invention to the outer edge, which is to be able to reduce the risk of cavitation issues.

[0044] As a non-limiting example, as seen in the side plane view of the propeller blade, the length L.sub.1 of the outer edge 34 along the axis of rotation A may be equal to or greater than 5%, preferably equal to or greater than 20%, of the maximum length L.sub.tot of the propeller blade 24 along the axis of rotation A.

[0045] Furthermore, though purely by way of example, as seen in the side plane view of the propeller blade, the length L.sub.1 of the outer edge 34 along the axis of rotation A is equal to or less than 50%, preferably equal to or less than 40%, of the maximum length L.sub.tot of the propeller blade 24 along the axis of rotation A.

[0046] As another non-limiting example, the smallest distance D.sub.2 from the second transition point 38 to the axis of rotation A may be equal to or less than 99% , preferably equal to or less than 95%, of the smallest distance D.sub.1 from the first transition point 36 to the axis of rotation A.

[0047] Further, though purely by way of example, the smallest distance D.sub.2 from the second transition point to the axis of rotation may be equal to or greater than 70%, preferably equal to or greater than 75%, of the smallest distance from the first transition point to the axis of rotation.

[0048] The ratio between the distances D.sub.1, D.sub.2 as well as the length L.sub.1 of the outer edge 34 may be selected on the basis of a predicted slip stream shape generated by the propeller itself or by another component, such as another propeller, located upstream of the propeller. Purely by way of example, the distances D.sub.1, D.sub.2 and possibly also the length L.sub.1 may be such that the outer edge 34 is within the predicted slip stream, thereby reducing the risk for cavitation associated disturbances, but close to the slip stream to thereby obtain a large propeller area.

[0049] FIG. 4 illustrates an embodiment of a propeller combination 40 comprising a forward propeller 18 and an after propeller 20. The propellers 18, 20 are adapted to rotate in opposite directions around the axis of rotation A. At least one of the forward propeller 18 and the after propeller 20 is a propeller according to the first aspect of the present invention, for instance as exemplified above with reference to FIG. 2 or FIG. 3. In the FIG. 4 embodiment, each one of the forward propeller 18 and the after propeller 20 is a propeller according to the first aspect of the present invention.

[0050] Further, as indicated in the FIG. 4 embodiment, the smallest distance D.sub.1 from the first transition point to the axis of rotation A for the after propeller 20 is smaller than a smallest distance from the second transition point D.sub.2 to the axis of rotation A for the forward propeller 18.

[0051] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.