WO2005047100A1

WO2005047100A1 - A propulsion system for marine vessels

Info

Publication number: WO2005047100A1
Application number: PCT/GB2004/004734
Authority: WO
Inventors: Brian Robert Harle
Original assignee: Brian Robert Harle
Priority date: 2003-11-11
Filing date: 2004-11-10
Publication date: 2005-05-26
Also published as: GB0326251D0

Abstract

A propulsion device (10) consisting of one or more hydrofoils (14) mounted on endless tracks (13) for movement non-rotationall through the water in a y direction orthogonal to the fore-and-aft axis -of the vessel. The hydrofoils (14) are presented to the water at an angle of attack (pi.tch) so as to provide thrust in the required direction of motion of the vessel.

Description

A Propulsion System For Marine Vessels

This invention relates to propulsion of water borne vessels by means of propulsive elements directly acting on water.

Ships are generally fitted with the largest propeller compatible with the stern sections of the vessel so that there is sufficient clearance between the tip of the propeller blades and the hull, and the propeller does not project below the keel of the vessel, which would both expose it to damage and effectively increase the draught of the vessel:

A simple simulation of marine power requirements such as SHIPDES, written by

Professor Molland of Southampton University, and used by marine engineering students, shows that if it were possible to fit a significantly larger propeller, dramatic improvements in efficiency would be achievable, reducing the power requirements for the same speed. This would reduce mass/space requirements for main engines and fuel bunkers and would increase cargo carrying capacity.

Take for example a 200m tanker of 50,000 tonnes dead weight with a beam of 32m, a draught of 11.7m and a design speed of 15 knots. If the largest screw propeller that can be installed has a diameter of 7m then, if this propeller turns at 87rpm, the propeller efficiency might be of the order of 0.48 and required power would be in the order of 14,000kw. If, on the other hand, a 13.35m propeller could be installed and turned at 26rpm, efficiency would be approximately 0.66 and the required power less than 10,000kw. If we assume a blade area ratio of unity and ignore the propeller boss, the 7m diameter propeller has an area of approximately 38.5sqm, with the blade tips moving through the water at approximately 31.9m per second. On the other hand, the 13.35m diameter propeller would have an area of approximately 140sqm and a tip speed of 18.2m per second. ^'

An object of the present invention is to replace conventional screw type propellers with a plurality of interconnected hydrofoils that move through the water along a predetermined linear path to generate thrust.

In the present invention a hydrofoil is distinguished from a flap or paddle in that the hydrofoil is presented to the water at an angle of attack such that there is a substantial laminar flow of water around the aerofoil shaped profile to generate a high pressure on the face of the foil and a lower pressure on the back surface. This laminar flow creates a force which can be resolved as a drag force opposing the movement of the hydrofoil and a lift force perpendicular to the drag force.

The hydrofoil is moved in a direction orthogonal to the required direction of thrust. A flap or paddle, on the other hand, is normally presented to the water at

an angle of attack of 90° so that only drag^' forces are present, and moves through the water along an axis parallel to the required direction of thrust. The cross- section of the hydrofoil is designed to reduce drag and increase lift, whereas the cross-sectional shape of flaps or paddles is largely irrelevant.

Propeller blades are a form of hydrofoil, and in the case of a conventional screw propeller orthogonal movement is achieved by rotating the propeller blades on a shaft that rotates about an axis substantially parallel to the propulsion direction. Other things being equal, the thrust developed by a screw propeller varies directly with the surface area. For a given propeller diameter, thrust can to some extent be enhanced by increasing the blade-area ratio, optimising other aspect of propeller geometry or adding a contra-rotating propeller to recover rotational energy given to the wake by the first propeller. Ultimately, however, limits on the diameter of the screw propeller limit the area and in turn the available thrust.

According to the present invention there is provided a marine propulsion system for a vessel comprising a plurality of variable pitch spaced hydrofoils mounted on one or more endless tracks so as to move in a direction transverse to an axis extending in a fore and aft direction of the vessel.

Preferably the direction extends across the beam of the vessel. The direction may extend substantially horizontally, or substantially vertically, or at an angle. On a multi-hull vessel said endless tracks may move between the hulls of the vessel. Preferably the hydrofoils are mounted at spaced positions around an endless loop that passes around two spaced end wheels and has two runs extending between the end wheels. Where loading on the hydrofoils is high, each end of the hydrofoils may be mounted on such endless loops.

A pitch change means is provided for changing the pitch angle of the hydrofoils where they pass around the end wheels.

The pitch change means is operable to set the pitch angle of the hydrofoils along one run of the track at a first angle of attack and to set the pitch angle of the hydrofoils along a second run of the track in the opposite direction to the first angle so that the hydrofoils generate lift in a common direction.

The pitch change means may be operable to change the pitch angles of those hydrofoils on the port side of the vessel at a first angle and those hydrofoils on a starboard side of the vessel at an opposite angle to the first angle so as to steer the vessel.

If desired, the pitch change means may be used to set the pitch angle of the hydrofoils on a first run of the track to an angle transverse to the run of the track and those on the second run of the track to an angle substantially parallel to a second run of the track whereby the hydrofoils on the first run act as paddles to move the stern of the vessel sideways. In one embodiment, the pitch change means comprises:

two concentric discs mounted at one or both ends of each hydrofoil, an inner one of the discs being secured in a fixed relationship to the endless track while an outer one of the discs is secured to the hydrofoil, locking means for selectively locking the inner and outer discs together, said locking means being operable when it is desired to change the pitch of a hydrofoil, to release the lock between the inner and outer discs,

- coil springs between the two discs to urge the hydrofoil to a zero pitch position when the lock between the discs is released, and

- pins that project from the outer disc dimensioned and positioned so as to engage a pitch change lever that is positioned adjacent the endless track, said lever being operable to engage selected pins and, when the lock between the discs is released, move the outer disc and an attached hydrofoil against the action of the springs until the hydrofoil assumes a desired pitch angle, whereupon the lock between the two discs is then re-engaged.

Preferably the two discs are normally locked together, and possible means of effecting this include a positive or friction clutch between the two discs, or a pin mounted in the outer disc which engages with a toothed wheel on the inner disc.

In an alternative embodiment of a pitch change mechanism each hydrofoil is pivotally mounted on at least one of the tracks and is provided with a cranked lever that has a guide pin at one end, said pitch change means comprises a pair of spaced guide rails alongside each run of the track, said guide rails being positioned and arranged relative to the track and the guide pins so as to receive the guide pins between the rails and thereby rotate the hydrofoils about their pivotal attachment to the track to predetermined pitch angles.

The guide rails may be fixed relative to the path of movement of the track so as to set predetermined fixed pitch angles or the guide rails may be selectively moveable relative to the path of movement of the track so as to vary selectively the pitch angle of the hydrofoils.

If desired, the guide rails may extend at an angle to the path of movement of the track so as to change the pitch angle of the hydrofoils to and from, a first angle of pitch, to and from, a second angle of pitch that is greater than, less than, or the reverse of, the first angle so as to steer the vessel.

The present invention will now be described by way of examples, with reference to the accompanying drawings in which:-

Figure 1 shows typical prior known propulsion systems of a tanker as discussed above, viewed from astern, showing the ship's hull and a 7m diameter propeller; Figure 2 shows the vessel of figure 1 with a notional 13.35m diameter propeller, which in practice could not be fitted;

Figure 3 shows the vessel of Figure 1 with a propulsion system constructed in accordance with the present invention with a hydrofoil area equivalent to a

13.35m diameter propeller;

Figure 4 shows one embodiment of the proposed propulsion system of Figure 3 viewed from above;

Figure 5 shows the propulsion system of Figures 3 or 4 equipped with additional pitch controllers equidistant from the two drive wheels;

Figure 6 shows a possible means of changing the pitch of the hydrofoils of the propulsion system shown in Figures 3 to 5;

Figure 7 shows component parts of the pitch change mechanism shown in Figure 6.

Figure 8 shows a second embodiment of a pitch change mechanism suitable for use with the propulsion system shown in Figure 3; and Figure 9 shows the provision of additional stabilising means for the propulsion system of Figures 3 to 8.

Referring to Figure 1, there is shown a prior known marine propulsion system in which a vessel 10 is fitted with a rotary screw propeller 11. The propeller 11 is typically 7.0m in diameter. Such a propulsion system would typically be used to propel a 50,000 tonnes dead weight tanker of 200m length having a beam of 32m and a draught of 11.7m. As explained above, the required power would be of the order of 14,000kw. If the propeller 11 could be replaced by one of 13.35m diameter as shown in Figure 2, then, as explained above, the required power would be of the order of less than 10,000kw.

Referring to Figure 3 there is shown a marine propulsion system 12 for a vessel 10 constructed in accordance with the present invention. The system 12 comprises basically an endless track 13 in the form of a pair of spaced endless metal or reinforced fabric belts, or chains, on which are mounted a plurality of spaced hydrofoils 14. The endless tracks 13 are constrained to run around end wheels 15 that are driven by motors 16.

The hydrofoils 14 are of variable pitch design and of symmetrical profile, and as will be seen in Figure 4 pitch change mechanisms 17 are provided for altering the pitch of the hydrofoils. Assuming the tracks 13 are rotating in an anti-clockwise direction as viewed from above, the pitch change mechanisms 17 operate to ensure that the hydrofoils along one run of the track (shown in the top portion of Figure 4) have an angle of attack that generates lift in the direction of the arrow L, whereas those hydrofoils along a second run of the track (on the lower portion of Figure 4) have an angle of attack that is the reverse of those on the first run. In this way the second surfaces of the hydrofoils also produce lift in the direction of the arrow L. The pitch angle of the hydrofoils are altered by the pitch change mechanisms 17 so that they assume positions almost tangential to the perimeter of the end wheels 15 when the hydrofoils 14 pass around the end wheels 15. The details of some possible pitch change mechanisms will be described in relation to Figures 6 to 8.

Referring to Figure 5 the propulsion system of Figure 4 is provided with two additional pitch change mechanisms 17 equispaced between the end wheels 15 to effect steering of the vessel. Again, the exact detail of these will be described in relation to Figures 6 to 8. Referring to Figure 5 the endless track is rotating in an anti-clockwise direction when viewed from above, and the pitch of the hydrofoils 14 is selectively changed so as to be able to provide steering of the vessel. The hydrofoils 14 in both runs of the loop of the endless track 13 on the port side are set to have an angle of attack that produces lift in the direction of the arrows L2, whereas those hydrofoils on the starboard side of the vessel have their angles of attack altered so that thrust is produced in the opposite direction as shown by the arrows L3. Figure 6 shows details of the pitch change mechanism 17 adjacent to the starboard end wheel 15 on figures 4 and 5. Referring to Figure 6 each of the hydrofoils 14 is mounted on a two-part disc assembly 19 (shown in more detail in Figure 7) to allow each of the hydrofoils to pivot about its centroid and to be held at predetermined selected positive or negative pitch angles. The two part disc assembly 19 comprises an inner disc 22 and a second co-axial concentric outer disc 20. The outer disc 20 is secured in a fixed relationship to the hydrofoil 14, while the inner disc 22 is similarly secured to the endless track 13. The discs 22 are spaced at fixed intervals along the length of the track 13.

It is preferred to mount a disc 22 on each track 13 at positions corresponding to the ends of the hydrofoils. However, it may be possible to provide the discs 20, 22 on only one of the tracks 13 (ie. at only one end of the hydrofoils 14) and to mount the other end of the hydrofoils in simple journal bearings or bushes on the respective track 13.

Attached to the outer disc 20 are pitch change studs 26. The pitch change studs are dimensioned and positioned so as to engage a pitch change lever 24 as will be explained below. Passing through the outer disc 20 are locking pins 23. The discs 20 and 22 may be locked together by an extension 23c of the locking pins 23 (as shown on figure 7) or by a positive or friction clutch between the two parts of the disc assembly (not shown). The locking pins 23 are spring mounted (not shown) such that they will adopt only a fully raised or fully lowered position and are interconnected such that depressing or raising one locking pin will in turn depress or raise the other (mechanism not shown).

When it is required to change the pitch of a hydrofoil, for example when the hydrofoil passes round the end wheel 15, a locking plate 28a is positioned adjacent the endless track in the region where the hydrofoils approach the end wheel 15. When the hydrofoil assembly is moved past the said locking plate 28a a locking pin 23 will be depressed (from position 23a to position 23b in figure 7). Two such locking pins 23 are provided on each pair of discs such that one of the pins 23 will be depressed by a locking plate 28a whatever the original orientation of the hydrofoil.

Depressing a locking pin 23 releases the lock between the two discs, either by disengaging the locking pin extensions 23c from a toothed wheel 29 (see figure 7) or by the alternative arrangement of disengaging a clutch between the two discs.

Coil springs 25 between the discs 20 and 22 then move the hydrofoil and disc 20 to a zero pitch orientation.

If a positive pitch is to be given to the hydrofoil (as shown in figure 6) then a consequence of this zero pitch orientation is that the pitch control studs 26 are oriented such that the right hand stud will engage with pitch control lever 24. The pitch control lever 24 acting on the pitch control stud 26 rotates the outer disc 20 and hence the attached hydrofoil against the action of the coil springs. By setting pitch control lever 24 to an appropriate angle, the pitch angle to which the hydrofoil is turned can be controlled. Once the hydrofoil is set to the required pitch, a locking pin 23 is raised by the locking plate 28b (from position 23b to position 23a on figure 7), and the hydrofoil assembly locked in its new pitch angle.

The alternative pitch control lever 24a is displaced so that it cannot engage with the left hand pitch control stud 23 and the locking plate 28c is displaced such that it cannot interfere with the movement of the hydrofoil.

Alternatively, if a negative pitch is to be given to the hydrofoil 14, pitch control lever 24a is set to the required negative pitch, and is moved such that it will engage with the left hand stud 23. Pitch control lever 24a pushes the hydrofoil assembly to the required negative pitch. Locking plate 28c is moved to a position where it can engage with a locking pin 23 and a locking pin 23 is then raised by locking plate 28c (from position 23b to position 23a on figure 7) to lock the hydrofoil assembly at this pitch angle. In this case, pitch control lever 24 is displaced so that it cannot engage with the right hand pitch control stud and the locking plate 28b is displaced such that it cannot interfere with the movement of the hydrofoil.

The operation of the pitch change mechanism is further illustrated in figure 7 wherein figure 7a depicts the outer disc 20 and inner disc 22 showing the hydrofoil 14 and preferred positions of the locking pins 23 and pitch control studs 26. Figure 7b is a cross-section along AA wherein the hydrofoil assembly is moving from left to right such that the raised locking pin 23a is about to be depressed by the locking plates 28a to allow the pitch angle of the hydrofoil to be changed. Figure 7c is a cross-section along BB showing the locking pins 23a engaged with the toothed wheel 29. Figure 7d is a cross-section along AA wherein the hydrofoil assembly is moving from left to right such that the lowered locking pin 23b is about to be lifted by the locking plates 28b locking the hydrofoil at a new pitch angle, and Figure 7d shows a cross-section along BB of the same situation, wherein the locking pins 23b are not engaged with the toothed wheel 29. Figure 7f shows further details of the said locking pin and toothed wheel.

Figure 8 shows a hydrofoil 14 attached to a track 13 moving in an anticlockwise direction around end wheels 15 where the hydrofoil 14 has just passed round the starboard end wheel 15. Referring to Figure 8 there is shown an alternative pitch change mechanism. In this mechanism (see Figure 8a) the hydrofoils 14 are provided with a cranked lever 30 that has a guide pin 31 at one end. The hydrofoils 14 are pivotally mounted at the pivot region 32 of the cranked lever 30 in journal bearings 34 in one of the tracks 13. If desired, the hydrofoil could have a similar cranked lever mounted at its other end. In this latter case the other end of the hydrofoil would be mounted in journal bearings in the other track 13 (only one such mechanism will be described for simplicity). The pitch change mechanism further comprises two fixed guide rails 33 that run alongside each run of the respective track 13 (only one such pair of rails 33 is shown in Figure 8a). The distance of the rails 33 from the track 13 and the angle that the guide rails make to the run of the track 13 is set to achieve the desired pitch angle. If the guide rails run parallel to the run of the track 13 and the guide rails are close to the track 13 as shown in Figure 8b then the pitch angle will be shallow. If the guide rails 33 are parallel to the track 13 and spaced further away from the track 13 (as shown in Figure 8c) the pitch of the hydrofoils 14 is increased.

If the guide rails 33 are placed below the top run of the track 13 as shown in Figures 8a, 8b and 8c then the hydrofoils 14 are set to have a positive pitch angle. Whereas, if the guide rails are placed above the top run of the track 13 as shown in Figure 8d the pitch angle will be set negative (or the reverse of that shown in

Figures 8a, 8b or 8c).

If the guide rails 33 pass from one side of the tracks 13 to the other side as shown in Figure 8e then the pitch of the hydrofoils changes from positive to zero and then to negative angles.

Although the guide rails 33 are installed in fixed positions relative to the tracks 13 to produce predetermined pitch angles, if desired they could be moved bodily relative to the track 13 in a controlled manner to vary the angle of attack collectively. In this way it would be possible to achieve, selectively, the different pitch angles as shown in any of Figures 8a to 8e.

In operation of the guide rails 33 the guide pin 31 engages the lead-in angled ends

33a of the rails 33 and rotates the hydrofoil about the bearing 34 in the tracks 13.

Referring now to Figure 9 there is shown schematically a rotatable support 36 that is positioned alongside long runs of the track 13. The support 36 is fixed relative to the track run and rotates about its longitudinal axis 37. The perimeter of the support engages the sides of the track 13 to prevent the track 13 being deflected too far away from the path 38 of a non-loaded track 13 (shown dotted) by the thrust generated on the hydrofoils 14. The support 36 may also be a means of transferring thrust from the hydrofoils to the vessel.

Claims

1. A marine propulsion system for a vessel comprising a plurality of variable pitch spaced hydrofoils mounted on an endless track for movement bodily in a direction transverse to an axis extending in a fore and aft direction of the vessel.

2. A propulsion system according to claim 1 wherein the direction extends across the beam of the vessel.

3. A propulsion system according to claim 2 wherein the direction extends substantially horizontally.

4. A propulsion system according to claim 1 wherein the direction extends substantially vertically.

5. A propulsion system according to any one of the preceding claims wherein the hydrofoils are mounted at spaced positions around an endless track that passes around two spaced end wheels and has two runs extending between the end wheels.

6. A propulsion system according to claim 5 wherein said end wheels are turned by motors to propel the endless track.

7. A propulsion system according to claim 5 or 6 wherein a pitch change means is provided for changing the pitch angle of the hydrofoils as they pass around the end wheels.

8. A propulsion system according to claim 7 wherein the pitch change means is operable to set the pitch angle of the hydrofoils along one run of the loop at a first angle of attack and to set the pitch angle of the hydrofoils along a second run of the track in the opposite direction to the first angle so that the hydrofoils generate lift in a common direction.

9. A propulsion system according to claim 7 or claim 8 where the pitch change means is operable to change the pitch angles of those hydrofoils on the port side of the vessel at a first angle and those hydrofoils on a starboard side of the vessel at an opposite angle to the first angle so as to be able to steer the vessel.

10. A propulsion system according to any one of claims 7 to 9 wherein the pitch angle of the hydrofoils on a first run of the track are set to an angle transverse to the run of the track and those on the second run of the track are set to an angle substantially parallel to a second run of the track whereby the hydrofoils on the first run act as paddles to move the stern of the vessel sideways.

1 1. A propulsion system according to any one of claims 7 to 10 wherein the pitch change means comprises: two concentric discs mounted at one or both ends of each hydrofoil, an inner one of the discs being secured in a fixed relationship to the endless track while an outer one of the discs is secured to the hydrofoil, locking means for selectively locking the inner and outer discs together, said locking means being operable when it is desired to change the pitch of a hydrofoil, to release the lock between the inner and outer discs, - coil springs between the two discs to urge the hydrofoil to a zero pitch position when the lock between the discs is released, and - pins that project from the outer disc dimensioned and positioned so as to engage a pitch change lever that is positioned adjacent the endless track, said lever being operable to engage selected pins and, when the lock between the discs is released, move the outer disc and an attached hydrofoil against the action of the springs until the hydrofoil assumes a desired pitch angle, whereupon the lock between the two discs is then re-engaged.

12. A propulsion system according to claim 11 wherein the inner and outer discs are locked together by a releasable clutch such as a friction clutch.

13. A propulsion system according to claim 11 wherein the inner and outer part of the two-part disc are locked together by means of spring loaded studs mounted in one of the discs that engage a toothed wheel mounted on the other of the discs.

14. A propulsion system according to any one of claims 7 to 10 wherein each hydrofoil is pivotally mounted on at least one of the tracks and is provided with a cranked lever that has a guide pin at one end, said pitch change means comprises a pair of spaced guide rails alongside each run of the track, said guide rails being positioned and arranged relative to the track and the guide pins so as to receive the guide pins between the rails and thereby rotate the hydrofoils about their pivotal attachment to the track to predetermined pitch angles.

15. A propulsion system according to claim 14 wherein the guide rails are fixed relative to the path of movement of the track so as to set predetermined fixed pitch angles.

16. A propulsion system according to claim 14 wherein the guide rails are selectively moveable relative to the path of movement of the track so as to vary selectively the pitch angle of the hydrofoils.

17. A propulsion system according to any one of claims 14 to 16 wherein the guide rails extend at an angle to the path of movement of the track so as to change the pitch angle of the hydrofoils to and from, a first angle of pitch, to and from, a second angle of pitch that is the reverse of the first angle.

18. A propulsion system according to claim 5 wherein a rotatable support is positioned alongside the endless track so as to reduce the deflection of said track.

19. A propulsion system according to claim 18 wherein said rotatable support is a means of transferring thrust from the hydrofoils, via the endless track to the vessel.

20. A propulsion system according to claim 18 or 19 wherein the endless track is propelled by said rotatable support, which is provided with a drive motor to augment or replace the drive motors propelling the end wheels.