WO2024127049A1

WO2024127049A1 - Propeller for a watercraft and watercraft having such a propeller

Info

Publication number: WO2024127049A1
Application number: PCT/HU2023/050077
Authority: WO
Inventors: Attila Kovács
Original assignee: Kovacs Attila
Priority date: 2022-12-15
Filing date: 2023-11-08
Publication date: 2024-06-20
Also published as: HUP2200490A1

Abstract

The invention relates to a propeller (10) for a watercraft (100), comprising a shaft (12), a hub (14) concentrically arranged around the shaft (12), a plurality of blades (16) radially arranged about the shaft (12) and coupled to the wheel hub (14), said blades (16) having, in a mounted state of the propeller (10), a suction side (16a) towards the watercraft (100) and a thrust side (16b) opposite thereto, wherein, the hub (14) defines a central cavity (15) having, in a mounted state of the propeller (10), an open end (15a) towards the craft (100) and a closed end (15b) opposite thereto, and inside which blades (16) cavities (18) are formed, which have one or more elongated outlet openings (18a) formed on the thrust side (16b) of the blades (16) and extending along a longitudinal axis (13) of the blades (16), and are in fluid communication with the central cavity (15) through an inlet opening (18b). The invention also relates to a watercraft comprising a propeller according to the invention.

Description

Propeller for a watercraft and watercraft having such a propeller

The invention relates to a propeller for a watercraft.

The invention further relates to a watercraft comprising a propeller according to the invention.

Propellers are used to propel watercrafts such as boats or motorboats. The most commonly used type of propeller is the screw propeller, which consists of a hub concentrically arranged with a rotating shaft and blades (vanes) arranged in a regular pattern around it. The blades are fixed radially with respect to the shaft to the hub, usually in a fixed position, i.e. the angle of attack of the blades is constant. This can provide adequate thrust for vessels travelling at constant speed and load, but as the load increases or decreases or the speed changes, the propeller will enter a sub-optimal operating range. To avoid this, there are so-called variable pitch propellers, where the blades are fixed to the hub in a way that allows them to rotate around their longitudinal axis. In these propellers, the pitch angle of the blades can be varied according to the load or speed, thus achieving a better efficiency. Note that in this description both fixed pitch and variable pitch propellers will be referred to as propellers.

The propeller blades, which are at an oblique angle, describe a helical line as the propeller rotates when viewed from the side, so that the propeller moves in the water like a "screw". As the propeller blades move forward, they push the water backwards, creating a pressure differential between the suction side of the blades facing the watercraft and the thrust side opposite thereto, causing the hull to move forward. The blades usually have a wing profile with a leading edge facing the forward direction of rotation and a trailing edge opposite to the leading edge, thus further increasing the pressure differential created by the rotating propeller.

The biggest drawback of state-of-the-art propellers is that they operate at a relatively low efficiency of around 20%. Even to achieve this low efficiency, the propeller parameters (diameter, pitch, etc.) need to be chosen properly. We recognised that in propellers, the thrust generated is proportional to the mass of water moved by the propeller, and that this water volume can be increased by taking advantage of physical effects during propeller operation, such as centrifugal force or displacement during the circular motion of the blades.

We further recognised that the above effects can be exploited by the hollow design of the propeller blades and hub and the proper positioning of the inlet and outlet openings of the cavities, through which water can flow as the propeller rotates, allowing the propeller to move more water and generate more thrust for the same energy input. We also found that this increase in thrust occurs even at low propeller speeds (<1000 rpm). In other words, thrust can be generated with a higher efficiency compared to existing propellers, thus reducing the fuel consumption of the propulsion engine. As the propeller has to rotate more slowly to achieve the same thrust, cavitation can also be reduced or eliminated.

The invention aims to create a propeller that is free from the disadvantages of state-of-the-art solutions. In particular, it is an object of the invention to provide a propeller capable of producing thrust with greater efficiency than known propellers, even at lower rpm.

The problem according to the invention has been solved by a propeller having a shaft, a hub concentrically formed around the shaft, and a plurality of blades radially arranged around the shaft and coupled to the hub, the blades having a suction side facing the watercraft and a thrust side opposite the suction side when the propeller is mounted.

The essence of the invention is that the hub defines a central cavity having an open end, which is, when the propeller is mounted, facing the craft and a closed end opposite thereto, and which blades have cavities formed in the interior thereof with one or more elongated outlet openings on the pressure side of the blades and extending along the longitudinal axis of the blades, and in fluid communication with the central cavity via an inlet opening. As the propeller rotates, the water entering the central cavity through the open end is forced by centrifugal force into the blade cavities. The water in the cavities of the blades, due to centrifugal force and the movement of the blades during rotation, is discharged from the cavities through the outlet ports towards the thrust side, thereby increasing the thrust of the propeller.

Some preferred embodiments of the invention are defined in the dependent claims.

Further details of the invention will be explained with the help of a drawing using examples. It is in the drawing

Figure 1 a is a schematic view of an exemplary embodiment of a propeller according to the invention, viewed from the thrust side of the blades;

Figure 1 b is a schematic view of the propeller shown in Figure 1 a, viewed from the suction side of the blades;

Figure 1 c is a schematic side view of the propeller shown in Figure 1 a;

Figure 2 is a schematic side sectional view of the propeller shown in Figure 1 a, represented by a single blade;

Figure 3 is a schematic A-A sectional view of the propeller blade shown in Figure 1 a;

Figure 4 is a schematic perspective view of an exemplary embodiment of a helical shape baffle according to the invention;

Figure 5a is a cross-sectional view illustrating a possible embodiment of the external and internal baffles according to the invention;

Figure 5b is a cross-sectional view illustrating another possible embodiment of the external and internal baffles according to the invention;

Figure 5c is a cross-sectional view illustrating a third possible embodiment of the external and internal baffles according to the invention;

Figure 5d is a sectional view illustrating a fourth possible embodiment of the external and internal baffles according to the invention;

Figure 5e is a cross-sectional view illustrating a fifth possible embodiment of the external and internal baffles according to the invention;

Figure 5f is a cross-sectional view illustrating a sixth possible embodiment of the external and internal baffles according to the invention.

Figures 1 a to 1 c show an exemplary embodiment of a propeller 10 according to the invention for propelling watercraft 100, for example a boat, a motorboat, etc. The propeller 10 has a shaft 12, a hub 14 concentrically formed about the shaft 12, and a plurality of blades 16 radially arranged about the shaft 12 and coupled to the wheel hub 14. The propeller 10 is pivotally mounted to the watercraft 100 for rotation about the shaft 12 and is rotated about the shaft 12 during operation. Note that the shaft 12 may be imaginary or physical, in the latter case for example a metal rod. The shaft 12 is concentrically surrounded by the hub 14, which can be made of, for example, metal, composite material, etc. In a preferred embodiment, the hub 14 is cylindrical in shape with its axis of symmetry coincident with the shaft 12, as can be observed, for example, in Figures 1 c and 2. The function of the hub 14 is, inter alia, to provide a connection between the shaft 12 and the blades 16 and to provide a mounting surface for the blades 16.

The blades 16 of the propeller 10 according to the invention are arranged radially around the shaft 12 and are fixed to the hub 14, similar to conventional propellers. In the context of the present invention, the attachment of the blades 16 to the hub 14 includes, mutatis mutandis, the case where the blades 16 are permanently attached to the hub 14, for example by welding, and the case where the blades 16 are rotatably attached to the hub 14 about their longitudinal axes 17, as described previously in relation to variable pitch propellers. The blades 16 having a suction side 16a which faces the watercraft 100 in a mounted state of the propeller 10, and a thrust side 16b opposite thereto, as can be seen in Figures 1 b and 1 a respectively. Note that the blades 16 are angled with the plane perpendicular to the shaft 12, due to the general principle of operation of propellers (see Figure 1 c), so that the suction sides 16a are angled with the line of travel and do not face exactly towards the watercraft 100. The suction side 16a and the thrust side 16b may have an unplanar surface, such as a curved surface, as is known to the skilled person. The blades 16 have a leading edge 17b, which is closer to the watercraft 100 along the shaft 12 when the propeller 10 is installed, and a trailing edge 17a which is further from the watercraft 100 along the shaft 12. In other words, the propeller 10 rotates in the advancing state of the watercraft 100 from the trailing edges 17a towards the leading edges 17b. The trailing edge 17a and the leading edge 17b, respectively, have a purposefully curved configuration, as can be observed in Figures 1a and 1 b and as is known to the skilled person. In a possible embodiment, the blades 16 are drop or wing shaped tapering at their trailing edge 17a, i.e. the cross-section of the blades 16 in a plane parallel to the shaft 12 is a drop or wing shaped cross-section. In the preferred embodiments shown in Figures 1 a to 1 c, the propeller 10 is provided with four blades 16, but of course, embodiments in which the propeller 10 comprises fewer than four or more than four blades 16 are also conceivable. The hub 14 of the propeller 10 according to the invention defines a central cavity 15 having, when the propeller 10 is mounted, an open end 15a facing the watercraft 100 and a closed end 15b opposite the open end 15a, as can be seen, for example, in Figure 2. That is, during the operation of the propeller 10 and the forward movement of the watercraft 100, water can flow into the cavity 15 through the open end 15a, but cannot leave the cavity 15 through the closed end 15b. The water will normally enter the cavity 15 due to the torque pressure generated during the forward motion of the watercraft 100. In order to increase the amount of water flowing into the cavity 15, in a preferred embodiment, the hub 14 comprises a turbine 20 concentrically arranged with the shaft 12 at the open end 15a and fixed to the hub 14. The blades of the turbine 20 rotate as a rigid body together with the propeller 10 and the hub 14, thereby guiding the water in the vicinity of the open end 15a into the central cavity 15. In a further preferred embodiment, the hub 14 comprises a baffle 22 having a helical surface arranged in the central cavity 15 along the shaft 12 and having an axis coincident with the shaft 12. A possible embodiment of the baffle 22 is shown in Figure 4. The baffle 22 is fixed to the hub 14, so that it rotates as a rigid body together with the propeller 10 and the hub 14. Note that a helical surface is understood to be a surface swept by a straight line, which straight line is perpendicular to the axis and travels at a uniform speed along a straight axis and simultaneously rotates about the axis at a uniform angular velocity, as is known to the person skilled in the art. As the propeller 10 rotates, the baffle 22 will rotate the water in the cavity 15, which will be subjected to a centrifugal force in a direction perpendicular to the shaft 12. The purpose of this is explained in more detail below.

The blades 16 according to the invention are hollow, inside which blades 16 cavities 18 are formed, which have one or more elongated outlet openings 18a formed on the thrust side 16b of the blades 16 and extending along a longitudinal axis 13 of the blades 16, and are in fluid communication with the central cavity 15 through an inlet opening 18b. In other words, the cavities 18 of the blades 16 are in fluid communication with the central cavity 15 via the inlet openings 18b. The water in the cavity 15 is normally forced through the openings 18b into the cavities 18 by the torque pressure generated during the forward motion of the watercraft 100 and by the centrifugal force generated during the rotation of the blades 16. In embodiments including baffle 22, the centrifugal force generated by the rotating baffle 22 also assists the water in the central cavity 15 to enter the cavities 18.

The openings 18a are arranged along the longitudinal axes 13 perpendicular to the shaft 12, i.e. parallel to or at a small angle to them, as can be observed, for example, in Figure 1 a. The blades 16 preferably comprise at least two and up to five output openings 18a, for example four output openings 18a per blade 16. The openings 18a have an elongated configuration, i.e., their extent (length) along the longitudinal axis 13 is greater than their extent (width) perpendicular to the longitudinal axis 13. Note that the openings 18a on a given blade 16 are not necessarily parallel to each other, nor are the openings 18a necessarily straight, as can be seen in Figure 1 a. For example, the shape of the openings 18a may follow the shape of the trailing edge 17a or the leading edge 17b. In a preferred embodiment, the length of the outlet openings 18a is at least 50% of the length of the blades 16 along the longitudinal axis 13. Note that the length of the blades 16 is understood to be the length from the hub 14 to the tip of the blade 16, i.e., the distance from the hub 14 to the circle that can be drawn around the propeller 10. The openings 18a may be formed, for example, by notches made on the pressure side 16b. A sectional view of the openings 18a of this exemplary embodiment is shown in Figure 3.

At the open end 15a, the water flowing into the central cavity 15 through the inlet openings 18b of the blades 16 can leave the central cavity 15 in the direction of the blades 16, from where the water is discharged by centrifugal force through the outlet openings 18a towards the thrust side 16b of the blades 16, thus increasing the thrust. In a particularly preferred embodiment, external baffles 30 extending towards the trailing edge 17a of the blades 16 are arranged on the outer side 19a of the outlet openings 18a, at the edge of the outlet openings 18a near the leading edge 17b of the blade 16. The external baffles 30 are attached to the thrust side 16b at the leading edge 17b of the openings 18a, as can be seen in Figures 5a-df. The external baffles 30 are positioned on the outer side 19a above the openings 18a in such a way that the openings 18a are left free and not closed. In other words, the baffles 30 protrude from the openings 18a and overlap the openings 18a when viewed from the direction of the thrust side 16b. The baffles 30 direct the water exiting the openings 18a towards the trailing edges 17a of the blades 16, thereby assisting the rotation of the propeller 10. In other words, the water exiting the opening 18a strikes the external baffle 30, causing it to travel in a direction having a velocity component towards the trailing edge 17a.

In a preferred embodiment, the outlet aperture 18a comprises internal baffles 31 disposed on the inner side 19b of the outlet aperture 18a above the cavity 18, near the edge of the outlet aperture 18a at the trailing edge 17a of the blade 16. The internal baffles 31 are attached to the inner part of the blade 16 above the cavity 18 at the edge of the openings 18a near the trailing edge 17a. The internal baffles 31 are positioned on the inner side 19b, below the openings 18a, such that the openings 18a are left unobstructed and not closed, as can be seen in Figures 5a- 5e. In other words, the internal baffles 31 protrude from the plane of the openings 18a and overlap the openings 18a when viewed from the direction of the cavity 18. The internal baffle 31 baffles the water in the cavity 18 towards the opening 18a such that, during the rotation of the propeller 10, the baffle 31 collides with the water in the cavity 18, which is inert relative to the blades 16, forcing the water towards the opening 18a. The internal baffles 31 are preferably configured to be extended towards the leading edges 17b of the blades 16 (see Figures 5a-5e), i.e. , to face the direction of rotation of the propeller 10 during the forward motion of the watercraft 100. In the embodiment illustrated in Figure 5f, the internal baffles 31 are configured to internally connect the suction side 16a and the thrust side 16b of the blades 16 in the cavity 18, i.e., the internal baffles 31 in this embodiment divide the cavity 18 into a plurality of smaller portions.

In a particularly preferred embodiment, the blades 16 comprise both baffles 30 and 31 which together assist the flow of water in the cavities 18 towards the trailing edges 17a. The baffles 30 and 31 preferably extend along the entire length of the openings 18a. In one possible embodiment, the external and/or internal baffles 30, 31 may have a convex shape, such as an arc shape, when viewed from the outlet opening 18a, as shown in Figures 5a and 5b. In the embodiments illustrated in Figures 5c to 5f, the external and/or internal baffles 30, 31 are formed as flat plates. Note that the external and/or internal baffles 30, 31 are also formed from the material of the blade 16 by notching and folding out or folding in the portions adjacent to the notch, as can be seen in Figures 5b and 5d.

The invention also relates to a watercraft 100 comprising a propeller 10 according to the invention. The watercraft 100 may be, for example, a ship, a boat, etc.

In order to illustrate the surprising technical advantage of the propeller 10 according to the invention, comparative measurements were made to determine the thrust forces generated by a state-of-the-art propeller and by different embodiments of the propeller 10 according to the invention, at the same size and rpm. Each of the propellers 10 used for the test and the state-of-the-art propeller contained four blades 16 with a pitch (rise) of 2.8 inches. The propeller diameter was selected to be 135 mm and the rotational speed was 300 rpm. The prior art propeller had solid blades and hub, but the shape of the blades and hub were the same as the blades 16 and hub 14 of the propeller 10 according to the invention. Variants of the propellers 10 of the invention were made according to six embodiments, which were as follows:

Embodiment 1 : comprising a hub 14 of hollow construction according to the invention, having an open end 15a and a closed end 15b, with baffles 22, and comprising four hollow blades 16 each having four openings 18a.

Embodiment 2: differs from embodiment 1 in that the openings 18a have external baffles 30.

Embodiment 3: differs from embodiment 1 in that the openings 18a have internal baffles 31 .

Embodiment 4: differs from embodiment 2 in that there are also internal baffles 31 at the openings 18a.

Embodiment 5: differs from embodiment 1 in that the hub 14 is fitted with a turbine 20.

Embodiment 6: differs from embodiment 4 in that the hub 14 is fitted with a turbine 20.

During the measurements, we found that the current consumption of both the state-of-the-art propeller and the propellers 10 of embodiments 1 to 6 was 5.5 Amps, i.e. the same energy input was required to operate each of the tested propellers. The thrust generated by the state-of-the-art propeller was 410 grams. In contrast, the thrusts generated by the propellers 10 of embodiments 1 to 6 were 435 grams, 450 grams, 440 grams, 480 grams, 445 grams and 505 grams, respectively, which represented thrust increases of 6%, 9.7%, 7.3%, 17%, 8.5% and 23% over the thrust of the state-of-the-art propeller. From the above values, it can also be concluded that a strong synergism is observed when using the different elements (baffles 30, 31 and turbine 20) together. For example, the use of the baffle 30 or 31 alone resulted in an increase in thrust of only 3.7% and 1 .3% respectively compared to embodiment 1 , whereas the use of both baffles 30, 31 together resulted in an increase in thrust of 11 %, which is 6% more than the sum of the partial percentages.

Various modifications to the above disclosed embodiments will be apparent to a person skilled in the art without departing from the scope of protection determined by the attached claims.

Claims

1. A propeller (10) for a watercraft (100), comprising a shaft (12), a hub (14) concentrically arranged around the shaft (12), a plurality of blades (16) radially arranged about the shaft (12) and coupled to the wheel hub (14), said blades (16) having a suction side (16a) which faces the watercraft (100) in a mounted state of the propeller (10), and a thrust side (16b) opposite thereto, characterized in that, the hub (14) defines a central cavity (15) having, in a mounted state of the propeller (10), an open end (15a) towards the craft (100) and a closed end (15b) opposite thereto, and inside which blades (16) cavities (18) are formed, which have one or more elongated outlet openings (18a) formed on the thrust side (16b) of the blades (16) and extending along a longitudinal axis (13) of the blades (16), and are in fluid communication with the central cavity (15) through an inlet opening (18b).

2. The propeller (10) according to claim 1 , characterized in that the hub (14) comprises a baffle (22) in the form of a helical surface arranged in the centre cavity (15) along the shaft (12) and having an axis coincident with the shaft (12).

3. The propeller (10) according to claim 1 or 2, characterized in that it comprises a turbine (20) concentrically arranged with the shaft (12) at the open end (15a) of the hub (14).

4. The propeller (10) according to any one of claims 1 to 3, characterized in that it comprises external baffles (30) arranged on an outer side (19a) of the outlet openings (18a) at the thrust side (16b), near a leading edge (17b) of the blade (16), the external baffles (30) extending towards a trailing edge (17a) of the blade (16).

5. The propeller (10) according to any one of claims 1 to 4, characterized in that it comprises internal baffles (31 ) arranged on an inner side (19b) of the outlet openings (18a) facing the cavity (18), at the edge of the outlet opening (18a) near the trailing edge (17a) of the blade (16).

6. The propeller (10) according to claim 5, characterized in that the internal baffles (31 ) extend towards the leading edge (17b) of the blade (16).

7. The propeller (10) according to claim 5 or 6, characterized in that the internal baffles (31 ) in the cavity (18) internally connect the suction and thrust sides (16a, 16b) of the blade (16).

8. The propeller (10) according to any one of claims 4 to 7, characterized in that the external and/or internal baffles (30, 31 ) have a convex shape viewed from the outlet opening (18a).

9. The propeller (10) according to any one of claims 4 to 7, characterized in that the external and/or internal baffles (30, 31 ) are flat plates.

10. The propeller (10) according to any one of claims 4 to 9, characterized in that the external and/or internal baffles (30, 31 ) are formed from the material of the blade (16).

11 . The propeller (10) according to any one of claims 1 to 10, characterized in that each of the blades (16) comprises at least two and up to five outlet openings (18a).

12. The propeller (10) according to any one of claims 1 to 11 , characterized in that the length of the outlet openings (18a) is at least 50% of the length of the blades (16) along the longitudinal axis (13).

13. The propeller (10) according to any one of claims 1 to 12, characterized in that the blades (16) have drop or wing shaped profiles tapering at their trailing edge (17a).

14. The propeller (10) according to any one of claims 1 to 13, characterized in that the blades (16) are pivotably coupled to the hub (14) about their longitudinal axes (13).

15. A watercraft (100) characterized in that it comprises a propeller (10) according to any one of claims 1 to 14.