WO2007072185A2

WO2007072185A2 - A propulsion system for a watercraft

Info

Publication number: WO2007072185A2
Application number: PCT/IB2006/003712
Authority: WO
Inventors: Andrew Bruce Taylor
Original assignee: Cape Advanced Engineering (Proprietary) Limited
Priority date: 2005-12-20
Filing date: 2006-12-20
Publication date: 2007-06-28
Also published as: WO2007072185B1; WO2007072185A3

Abstract

A propulsion system (10) for a watercraft comprises a propeller (12), a drive (14) for driving the propeller, a mounting arrangement for mounting the propeller to the stern of the watercraft and a trim hydrofoil 18 which is disposed at a level lower than the propeller. The system (10) includes a steering sub-system (22) which includes a pair of spaced opposed rudders (24.1 and 24.2) which are located at opposite sides of the propeller (12). The sub-system includes a shroud (26) which extends over the propeller (12) between the rudders. The shroud is pivotally mounted to a mounting plate (19) forming part of the mounting arrangement, in an arrangement permitting pivoting of the steering sub-system and thereby the rudders about a vertical pivot axis to facilitate steering and also tilting forward Iy and rearward Iy to thereby alter the angle of attack of the hydrofoil (18).

Description

A PROPULSION SYSTEM FOR A WATERCRAFT

FIELD OF INVENTION

This invention relates to a propulsion system for a watercraft. It relates also to watercraft having the propulsion system mounted thereto.

SUMMARY OF INVENTION

According to a first aspect of the invention there is provided a propulsion system for a watercraft, including:

propulsion means having an upper side and a lower side, which is operable to propel the watercraft along a body of water;

drive means for driving the propulsion means; propulsion mounting means for mounting the propulsion means at the stern of the watercraft; and

a trim hydrofoil which is disposed at a level operatively lower than the upperside of the propulsion means.

The trim hydrofoil may be disposed aft of the propulsion means.

In another embodiment of the invention, the trim hydrofoil may be disposed fore of the propulsion means.

In yet another embodiment of the invention, the trim hydrofoil may be disposed below the propulsion means.

In a particular embodiment , the propulsion means may be in the form of a jet nozzle having an upper side and a lower side and the drive means may be in the form of a jet drive, the trim hydrofoil being disposed at a level operatively lower than the upper side of the nozzle.

In another embodiment , the propulsion means may be in the form of a propeller defining an axis of rotation, the trim hydrofoil being disposed at a level operatively lower than the tips of propeller blades of the propeller, at their highest point of travel. The trim hydrofoil may be disposed below the axis of rotation of the propeller.

The propeller may be in the form of a surface-piercing propeller.

The propulsion system may include at least one auxiliary trim hydrofoil which is disposed aft of the propeller operatively above the axis of rotation of the propeller.

The auxiliary trim hydrofoil may be disposed at a height between the axis of rotation of the propeller and an upper tip of the propeller.

The propulsion system may include a steering sub-system including steering means which is mountable to the propulsion mounting means and which is operable to interfere with water moving relative to the watercraft, in use, thereby to alter the direction of travel of the watercraft.

The steering means may include at least one rudder and steering mounting means for mounting the rudder to the propulsion mounting means; and rudder control means for controlling the movement of the rudder.

The steering means may include a pair of spaced, opposed rudders which are each located at a different one of the opposite sides of the propeller.

The trim hydrofoil may be mounted to and extend between the rudders. The auxiliary trim hydrofoil may be mounted to and extend between the rudders.

The propulsion system may include at least one additional auxiliary trim hydrofoil which extends laterally outwardly from one of the rudders.

The propulsion system may include two additional auxiliary trim hydrofoils wherein each additional auxiliary trim hydrofoil extends laterally outwardly from a different one of the rudders.

The steering sub-system may include a shroud which is disposed above the propeller and which extends between the rudders.

The shroud may be is in the form of a convexly curved panel.

The steering mounting means may be hingedly mounted to the shroud, thereby permitting hinged displacement of the shroud and thereby the rudders relative to the watercraft.

The steering mounting means may be pivotally connected to the shroud in an arrangement permitting pivotal displacement of the shroud about a pivot axis, the control means being operable to control pivotal displacement of the shroud and thereby the rudders, in use According to a second aspect of the invention there is provided a watercraft having the propulsion system defined hereinabove, mounted to the stern thereof.

According to a third aspect of the invention there is provided a watercraft having a pair of the propulsion systems defined hereinabove, mounted to the stern thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention are described hereinafter by way of a non- limiting example of the invention, with reference to and as illustrated in the accompanying diagrammatic drawings. In the drawings:

Figure 1 show a schematic perspective view of a propulsion system for a watercraft, in accordance with the invention, with its covers removed;

Figure 2 show a schematic perspective view of the propulsion system of Figure 1 , with the covers in place;

Figures 3 A - C, show schematic perspective views of the propulsion system of Figure 1 , showing the manner in which the steering system of the propulsion system is operable to effect steering of a watercraft to which the propulsion system is mounted; Figure 4 shows a monohull watercraft in accordance with the invention, having the propulsion system of Figure 1 , mounted to the stern thereof;

Figure 5 shows another embodiment of a monohull watercraft in accordance with the invention, having a pair of the propulsion systems of Figure 1 , mounted to the stern thereof;

Figures 6 A - C show schematic longitudinal sections through the propulsion system in accordance with the invention, showing three different operating positions of the steering sub-system of propulsion system of Figure 1 , providing for the angle of attack of the trim hydrofoil to be altered, while in use;

Figures 7 A - C show schematic longitudinal sections through the propulsion system in accordance with the invention, showing three different embodiments of the propulsion system of Figure 1 wherein three different spatial relationships between the propeller and the steering sub-system are illustrated;

Figure 8 shows another embodiment of a propulsion system for a watercraft, in accordance with the invention;

Figure 9 shows yet another embodiment of a propulsion system for a watercraft, in accordance with the invention; Figures 10 A - C show three different positions of the steering sub-system of the propulsion system of Figure 9, providing for the angle of attack of the trim hydrofoil to be altered; and

Figure 11 shows a schematic rear end view of the propulsion system of Figure 9.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to the drawings, a propulsion system for a watercraft, in accordance with the invention, is designated generally by the reference numeral 10. The propulsion system 10 comprises, broadly, propulsion means in the form of a surface-piercing propeller 12, drive means in the form of a drive designated generally by the reference numeral 14 for driving the propeller, propulsion mounting means in the form of a mounting arrangement designated generally by the reference numeral 16 for mounting the propeller 12 to the stern of a watercraft and a trim hydrofoil 18.

The drive 14 includes a motor (not shown) and a propeller shaft 20 which is driven by the motor and which extends through the transom of the watercraft, the propeller 12 being coupled to the propeller shaft 22. As such, the propeller shaft 22 drives and supports the propeller 12. With reference to Figure 4 of the drawings, the propulsion system 10 is shown mounted to the transom 27 of a monohull watercraft 30. Furthermore, with reference to Figure 5 of the drawings, a pair of propulsion systems 10 are mounted adjacent one another to the transom 27 of a monohull watercraft 30.1. The mounting arrangement 16 includes a propeller shaft bearing housing 23 which carries the propeller and the propeller shaft 22 and transmits forces developed by the propeller to the hull of the watercraft . The mounting arrangement 16 further includes a transom mounting plate 17 which can be attached to the transom of the watercraft and which supports the propeller shaft bearing housing 23.

The propeller 12 defines a central axis of rotation A and includes four propeller blades defining blade tips at their free ends.

The propulsion system includes a steering sub-system 22 which includes a pair of spaced opposed rudders 24.1 and 24.2 which are located at opposite sides of the propeller 12. The steering sub-system 22 includes a shroud 26 which is disposed above the propeller 12 and which extends between the rudders 24.1 and 24.2. More particularly, the shroud 26 is in the form of a flat convexly curved panel which extends over the propeller and which is connected at lower ends thereof to upper ends of the rudders 24.1 and 24.2.

The trim hydrofoil 18 is mounted between operative lower ends of the rudders 24.1 and 24.2. As such, the trim hydrofoil 18 is disposed a level operatively lower than the axis of rotation of the propeller 12 and more particularly, at a level operatively lower than the lowermost blade tips of the propeller blades as the propeller rotates, in use. The mounting arrangement 16 further includes a support plate 19 which extends outwardly from the moμnting plate 17 and to which the shroud 26 is pivotally mounted. The shroud 26 has a pivot pin fixedly connected to the apex thereof which is pivotally supported by the support plate 19 in arrangement wherein pivotal displacement of the shroud and the rudders from side to side is permitted.

The propulsion system 10 includes a steering and trim control sub-system designated generally by the reference numeral 28. The steering and trim control sub-system 28 includes a trim piston/cylinder mechanism 32 which can be actuated remotely from a control unit onboard the watercraft. With reference to Figure 6A of the drawings, the piston of the piston/cylinder mechanism 32 is operable to be displaced into an extended condition as indicated by arrow indicator O thereby tilting the steering sub-system about a fulcrum at the mounting point of the pivot pin to the support plate 19 causing the steering sub-system to be displaced forwardly thereby causing the trim hydrofoil 18 to be positioned directly below the propeller 12. In Figure 6B of the drawings, a neutral position is shown wherein the pivot pin is held in a substantially vertical position causing the trim hydrofoil 18 to be positioned slightly aft of the propeller. With reference to Figure 6C of the drawings, the piston of the piston/cylinder mechanism 32 is retracted in the direction indicated by indicator arrow P causing tilting of the steering sub-system 22 which in turn causes the trim hydrofoil 18 to be positioned relatively further aft of the propeller 12. In this manner the angle of attack the trim hydrofoil can be altered. The steering and trim control sub-system 28 further includes a steering piston/ cylinder mechanism 34 which is connected to a control arm 36 which is fixedly connected to the pivot pin thereby permitting pivotal displacement of the steering sub-system 22 to one side when the piston of the piston/cylinder mechanism 34 is extended and to the opposite side when the piston of the piston/cylinder mechanism 34 is retracted. With reference to Figures 3 A -C of the drawings, the steering sub-system 22 is shown in a neutral position (Figure 3A), pivoted towards starboard (Figure 3B) and pivoted towards port (Figure 3C), with the flow direction of water through the steering sub-system 22 being shown by arrows W in Figures 3 A - C.

The shroud 26 thus facilitates turning of the rudders to vary their steering angle and also tilting of the rudders to change the angle of attack of the hydrofoil 18. The rudders 24.1 and 24.2, in addition to facilitating steering of a watercraft to which the propulsion system 10 is mounted, also act as struts which carry the hydrofoil 18 and transmit the lift forces generated by the hydrofoil onto the propulsion system 10 and the watercraft. The shroud 26 is configured to control the flow of water into the propeller and to prevent the induction of air from a free surface about the propeller, when required. It is also configured and dimensioned to direct spray rearwardly of the propeller.

With reference to Figure 2 of the drawings, the propulsion system 10 includes a cover 35 which substantially covers the steering and trim control sub-system 28. The propulsion system 10 provides for integrated propulsion, steering and trim control. The propulsion system 10 can be utilised with all forms of conventional monohull and catamaran watercraft. Motion control systems including hydrofoils, trim tabs and other devices known as interceptors which are attached to the hull of a watercraft so as to achieve motion control, are well known. Such motion control devices are used to counteract heaving, pitching and rolling caused by variations in the surface of the water caused by wave, swell, chop and wakes, etc. which are undesirable and result in discomfort, fatigue and sea-sickness in crew and passengers. These motions are also undesirable for cargo, payload and systems that are sometimes required to operate on such boats. As such, conventional motion control systems which are attached to the hull of the vessel are utilised to act on the hull of the vessel to reduce the magnitude of the heaving, pitching and rolling motion experienced by the watercraft. In contrast to existing conventional motion control systems which are attached to the hull of a watercraft, the trim hydrofoil 18 forms part of the propulsion system for a watercraft. The trim hydrofoil is thus automatically installed when the propulsion system is fitted to the hull of a watercraft. This obviates the need to install a hydrofoil separately to the hull of the watercraft.

The functional integration of the trim hydrofoil with the steering system and the drive 14 of the propulsion system, achieves a degree of trim control, steering control and speed control that cannot be achieved by watercraft having propulsion systems that are not integrated as described hereinabove. By utilising a trim hydrofoil which operates below the operating waterline at all times, the propulsion system 10 is able to generate hydrodynamic lift and carry a portion of the weight of the boat at the stern, more effectively and efficiently than the hull itself. The integrated propulsion system 10 thus ensures that a watercraft to which it is fitted, operates at the optimal trim angle throughout the speed range without the compromise of tilting the propeller away from its optimal thrust direction. This ensures that a watercraft to which the propulsion system 10 is fitted always achieves minimum drag and thereby facilitates reduced fuel consumption.

The trim hydrofoil 18 is disposed at a level below the axis of rotation of the surface piercing propeller 12 to ensure that the hydrofoil operates below the water surface so as to provide adequate hydrodynamic lift at both sub-planing and planing speeds. In a single propulsion system installation as illustrated in Figure 4 of the drawings, the trim hydrofoil 18 provides dynamic pitch control as well as ensuring that the watercraft operates at an optimal trim angle at all speeds. This is achieved by tilting the steering sub-system 22 as is explained hereinabove. When increased lift is required at the stern of the watercraft, e.g. when the watercraft is travelling at low speed such as sub-planing speed, the steering sub-system 22 is tilted as shown in Figure 6A, causing the angle of attack of the trim hydrofoil 18 to be increased, thus causing water to be deflected downwardly along flow path W. In this position of the steering subsystem 22, the trim hydrofoil is operated at a high angle of attack. If the amount of lift at the stern of the watercraft needs to be reduced, the steering sub-system is tilted out towards the position shown in Figure 6B of the drawings wherein the trim hydrofoil 18 is operated at a reduced angle of attack, with water flow over the trim hydrofoil being deflected relatively less than is the case with the position of the steering sub-system 22 shown in Figure 6A. With reference to Figure 6C of the drawings, the angle of attack of the trim hydrofoil 18 can be reduced further still by tilting the steering subsystem 22 further thereby causing the trim hydrofoil 18 to be orientated at a neutral or even a negative angle of attack so as to generate little or even negative lift.

It will be appreciated that in twin engine installations such as that shown in Figure 5 of the drawings, the propulsion system 10 can facilitate roll control in addition to pitch control by tilting the steering sub-systems 22 independently of one another.

With reference to Figure 8 of the drawings, another embodiment of a propulsion system in accordance with the invention, is designated generally by the reference numeral 100. Those features of the propulsion system 100 which are the same as or similar to those of the propulsion system 10 are designated in Figure 8 of the drawings by the same and/or similar reference numerals. The propulsion system 100 is identical to the propulsion system 10, with the only difference being that the propulsion system 100 includes a steering sub-system 122 which includes an auxiliary trim hydrofoil 50 and two additional auxiliary trim hydrofoils 52.1 and 52.2. The hydrofoil 50 extends between the rudders 24.1 and 24.2 and is disposed operatively aft of the propeller 12 above the axis of rotation A of the propeller. The trim hydrofoils 52.1 and 52.2 extend laterally outwardly from each of the rudders 24.1 and 24.2, respectively, at a level which is slightly lower than that of the hydrofoil 50 and which is below the level of the axis of rotation A of the propeller 12. The hydrofoil 50 is designed to operate in the wake of the propeller and thus generate lift even when the boat has little or no forward speed by deflecting water accelerated by the propeller. As the trim hydrofoil 50 is disposed above the axis of rotation A of the propeller, it will be effective at low speeds when the propeller is fully submerged in the water, but will become ineffective at higher speeds when the water level aft of the propeller drops to a level below the axis of rotation of the propeller. The benefit of the trim hydrofoil 50 is that it provides for motion control at relatively low speed when the trim hydrofoil 18 may not experience adequate water velocity to affect sufficient control. The result is that at low speeds, the trim hydrofoils 50 and 52.1 and 52.2 are all active and work together with the trim hydrofoil 18 in order to generate adequate lift while at high speeds the hydrofoil 50 is disposed above the water surface and thus become deactivated. At higher speeds the trim hydrofoils 18 and 52.1 and 52.2 are able to generate adequate lift to facilitate motion control. The Applicant envisages that for certain applications, the hydrofoil 18 may be able to generate adequate lift at high speeds to facilitate motion control, in which case the trim hydrofoils 52.1 and 52.2 can be located at a level above the axis of rotation of the propeller 12 thereby to generate additional lift at low speeds only. It will be appreciated that the trim hydrofoils 52.1 and 52.2 may extend outwardly from the rudders 24.1 and 24.2 at different angles to produce a different motion control effect. With reference to Figure 9 of the drawings, yet another embodiment of a propulsion system in accordance with the invention, is designated generally by the reference numeral 200. Those features of the propulsion system 200 which are the same as or similar to those of the propulsion system 10 are designated in Figure 9 by the same and/or similar reference numerals. The propulsion system 200 comprises, broadly, jet propulsion means in the form of a nozzle 212, drive means in the form of a jet drive comprising an engine 204 and a water pump 206, propulsion mounting means in the form of a mounting arrangement in the form of a housing 216 for mounting the nozzle 212 to the transom 17 of a watercraft 250 and a trim hydrofoil 218. The water pump 206 has a water intake 272 in the base of the hull of the watercraft and is coupled to the engine 204 via a drive shaft 274. The waterflow direction through the water pump and the nozzle 212 and over the trim hydrofoil 218 is illustrated by the direction indicator arrows W.

The nozzle 212 has an upper end 276. The propulsion system 200 includes a trim control sub-system designated generally by the reference numeral 228 which includes a trim piston/cylinder mechanism 232 which can be actuated remotely from a control unit onboard the watercraft 250. The propulsion system 200 further includes a hydrofoil mounting assembly 278 which is pivotally mounted to the nozzle 212 via pivot pins 282.1 and 282.2 and which is pivotally displaced by the piston/cylinder mechanism 232. The trim hydrofoil is supported by two spaced opposed support members 284.1 and 284.2 forming part of the mounting assembly 278, at a level below that of the nozzle 212. The mounting assembly 278 includes a shroud 226 which extends above the nozzle 212 between the members 284.1 and 284.2.

With reference to Figures 10 A - 10 C of the drawings, the angle of attack of the trim hydrofoil 218 can be altered by pivotal displacement of the hydrofoil mounting assembly 278. With reference to Figure 10A of the drawings, the piston of the piston/cylinder mechanism 232 is displaced into an extended condition as indicated by arrow indicator O, thereby tilting the hydrofoil 218 mounting assembly 278 causing the angle of attack of the trim hydrofoil to be increased to provide greater lift L, thus causing water to be deflected downwardly along flow path W. The direction of the lift forces generated by the hydrofoil 218, is designated by the arrows L in Figures 10 A - C.

In Figure 1OB of the drawings, a neutral position is shown wherein the angle of attack of the trim hydrofoil 218 is slightly reduced with waterflow over the trim hydrofoil being deflected relatively less than is the case with the position of the hydrofoil mounting assembly 278 shown in Figure 10A. With reference to Figure 10C of the drawings, the angle of attack of the trim hydrofoil 218 is reduced further still by actuating the piston/cylinder mechanism 232 to retract the piston in direction P and tilt the hydrofoil mounting assembly 278 further thereby to provide a neutral or even negative angle of attack of the trim hydrofoil 218 to produce little or negative lift L. It will be appreciated that the exact configuration of the propulsion system in accordance with the invention may vary greatly while still incorporating the essential features of the invention as described and defined hereinabove.

Claims

1. A propulsion system for a watercraft, including:

drive means for driving the propulsion means;

propulsion mounting means for mounting the propulsion means at the stern of the watercraft; and

a trim hydrofoil which is disposed at a level operatively lower than the upper side of the propulsion means.

2. The propulsion systems as claimed in claim 1 , wherein the trim hydrofoil is disposed of aft of the propulsion means.

3. The propulsion system as claimed in claim 1 , wherein the trim hydrofoil is disposed fore of the propulsion means.

4. The propulsion system as claimed in claim 1, wherein the trim hydrofoil is disposed below the propulsion means.

5. The propulsion system as claimed in any one of claims 1 to 4, wherein the propulsion means is in the form of a jet nozzle having an upper side and a lower side and the drive means is in the form of a jet drive, the trim hydrofoil being disposed at a level operatively lower than the upper side of the nozzle.

6. The propulsion system as claimed in any one of claims 1 to 4, wherein the propulsion means is in the form of a propeller defining an axis of rotation, the trim hydrofoil being disposed at a level operatively lower than the tips of the propeller blades of the propeller, at their highest point of travel.

7. The propulsion system as claimed in claim 6, wherein the trim hydrofoil is disposed below the axis of rotation of the propeller.

8. The propulsion system as claimed in claim 6 or claim 7, wherein the propeller is in the form of a surface-piercing propeller.

9. The propulsion system as claimed in claim 8, which includes at least one auxiliary trim hydrofoil which is disposed aft of the propeller operatively above the axis of rotation of the propeller.

10. The propulsion system as claimed in claim 9, wherein the auxiliary trim hydrofoil is disposed at a height between the axis of rotation of the propeller and an upper tip of the propeller.

11. The propulsion system as claimed in any one of claims 1 to 10, which includes a steering sub-system including steering means which is mountable to the propulsion mounting means and which is operable to interfere with water moving relative to the watercraft, in use, thereby to alter the direction of travel of the watercraft.

12. The propulsion system as claimed in any claim 11 , wherein the steering means includes at least one rudder and steering mounting means for mounting the rudder to the propulsion mounting means, and rudder control means for controlling the movement of the rudder.

13. The propulsion system as claimed in claim 12, wherein the steering means includes a pair of spaced, opposed rudders which are each located at a different one of the opposite sides of the propeller.

14. The propulsion system as claimed in claim 13, wherein the trim hydrofoil is mounted to and extends between the rudders.

15. The propulsion system as claimed in claim 14, wherein the auxiliary trim hydrofoil is mounted to and extends between the rudders.

16. The propulsion system as claimed in any one of claims 13 to 15, which includes at least one additional auxiliary trim hydrofoil which is mounted to and extends laterally outwardly from one of the rudders.

17. The propulsion system as claimed in claim 16, which includes two additional auxiliary trim hydrofoils wherein each additional auxiliary trim hydrofoil extends laterally outwardly from a different one of the rudders.

18. The propulsion system as claimed in any one of claims 13 to 17, wherein the steering sub-system includes a shroud which is disposed above the propeller and which extends between the rudders.

19. The propulsion system as claimed in claim 18, wherein the shroud is in the form of a convexly curved panel.

20. The propulsion system as claimed in claim 19, wherein the steering mounting means is hingedly mounted to the shroud, thereby permitting hinged displacement of the shroud and thereby the rudders relative to the watercraft.

21. The propulsion system as claimed in claim 20, wherein the steering mounting means is pivotally connected to the shroud in an arrangement permitting pivotal displacement of the shroud about a pivot axis, the control means being operable to control pivotal displacement of the shroud and thereby the rudders, in use

22. A watercraft having the propulsion system as claimed in any one of claims 1 to 21 , mounted to the stern thereof.

23. A watercraft having a pair of the propulsion systems as claimed in any one of claims 1 to 21 , mounted to the stern thereof.