VERTICAL RETRACTING THRUSTER

Abstract

A vertical retracting thruster for providing thrust to a vessel is disclosed, suitable for mounting within a hull of the vessel. The vertical retracting thruster comprises a fixed base and a movable base. A vertical height adjusting assembly is configured to move the movable base relative to the fixed base in a vertical direction. A thrust motor is mounted to the movable base. The vertical retracting thruster has a retracted configuration, in which the propeller is retracted into the hull, and a deployed configuration, in which the propeller projects from the hull. The vertical retracting thruster is operable to move between the retracted configuration and the deployed configuration.

Claims

1. A vertical retracting thruster for providing lateral thrust to a vessel, the vertical retracting thruster being suitable for mounting within a hull of the vessel, the vertical retracting thruster comprising: a fixed base separating a thrust motor side and a propeller side of the vertical retracting thruster; a movable base provided on the thrust motor side; a vertical height adjusting assembly configured to move the movable base relative to the fixed base in a vertical direction; a thrust motor mounted to the movable base; a propeller with an outer diameter in the range from 100 mm to 150 mm, the propeller being provided on the propeller side; a drive shaft linking the thrust motor to the propeller, the drive shaft extending in the vertical direction through the fixed base; a drive shaft casing provided around the drive shaft; and a seal disposed between an outer surface of the drive shaft casing and an internal surface of the fixed base, the seal providing water sealing between the thrust motor side and propeller side, wherein the vertical retracting thruster has a retracted configuration, in which the propeller is retracted into the hull, and a deployed configuration, in which the propeller projects from the hull, the vertical retracting thruster being operable to move between the retracted configuration and the deployed configuration, and wherein, when in the retracted configuration, the distance in the vertical direction between the movable base and the fixed base is less than 200 mm, and wherein the vertical height adjusting assembly comprises: a height adjustment motor; a gearbox with an output shaft, the output shaft being mechanically linked to the height adjustment motor; a bearing plate attached to the gearbox such that the output shaft of the gearbox is rotatable in the bearing plate; a height adjusting lead screw follower attached to the moveable base; and a height adjusting lead screw connected to and rotatable with the output shaft of the gearbox, the height adjusting lead screw extending in the vertical direction from the gearbox to the height adjusting lead screw follower, the height adjusting lead screw coupling with the height adjusting lead screw follower such that the height adjusting lead screw follower and movable base move in the vertical direction when the height adjusting lead screw is rotated via the height adjustment motor and gearbox, wherein the bearing plate and gearbox are attached to the fixed base with at least one fastener, said at least one fastener passing continuously through the bearing plate, the gearbox and the fixed base.

2. A vertical retracting thruster according to claim 1, wherein the drive shaft has a fixed length in the vertical direction.

3. A vertical retracting thruster according to any one of the preceding claims, wherein the total vertical height from the thruster motor to the propeller is less than 600 mm.

4. A vertical retracting thruster according to any one of the preceding claims, wherein the thrust motor is an electric motor.

5. A vertical retracting thruster for providing thrust to a vessel, the vertical retracting thruster being suitable for mounting within a hull of the vessel, the vertical retracting thruster comprising: a fixed base separating a thrust motor side and a propeller side of the vertical retracting thruster; a movable base provided on the thrust motor side; a vertical height adjusting assembly configured to move the movable base relative to the fixed base in a vertical direction; a thrust motor mounted to the movable base; a propeller with an outer diameter in the range from 100 mm to 150 mm, the propeller being provided on the propeller side; a drive shaft linking the thrust motor to the propeller, the drive shaft extending in the vertical direction through the fixed base; a drive shaft casing provided around the drive shaft; a seal disposed between an outer surface of the drive shaft casing and an internal surface of the fixed base, the seal providing water sealing between the thrust motor side and propeller side, wherein the vertical retracting thruster has a retracted configuration, in which the propeller is retracted into the hull, and a deployed configuration, in which the propeller projects from the hull, the vertical retracting thruster being operable to move between the retracted configuration and the deployed configuration, and wherein, when in the retracted configuration, the distance in the vertical direction between the movable base and the fixed base is less than 200 mm, and wherein the vertical retracting thruster further comprises a steering arrangement for control of the direction of an axis of rotation of the propeller and thereby the direction of thrust at least when the vertical retracting thruster is in the deployed configuration, the steering arrangement being configured to rotate the thrust motor, the drive shaft casing and the propeller with respect to the movable base and with respect to the fixed base.

6. A vertical retracting thruster according to claim 5 wherein the vertical height adjusting assembly comprises: a height adjustment motor; a gearbox with an output shaft, the output shaft being mechanically linked to the height adjustment motor; a bearing plate attached to the gearbox such that the output shaft of the gearbox is rotatable in the bearing plate; a height adjusting lead screw follower attached to the moveable base; and a height adjusting lead screw connected to and rotatable with the output shaft of the gearbox, the height adjusting lead screw extending in the vertical direction from the gearbox to the height adjusting lead screw follower, the height adjusting lead screw coupling with the height adjusting lead screw follower such that the height adjusting lead screw follower and movable base move in the vertical direction when the height adjusting lead screw is rotated via the height adjustment motor and gearbox.

7. A vertical retracting thruster according to claim 6 wherein the bearing plate and gearbox are attached to the fixed base with at least one fastener, said at least one fastener passing continuously through the bearing plate, the gearbox and the fixed base.

8. A vertical retracting thruster according to any one of claims 5 to 7 wherein the steering arrangement comprises a steering motor fixed with respect to the movable base, the steering motor configured to rotate the thrust motor, the drive shaft casing and the propeller with respect to the movable base and with respect to the fixed base.

9. A vertical retracting thruster according to any one of claims 5 to 8 wherein the steering arrangement comprises a slew ring bearing arranged to allow rotation between the drive shaft casing and the movable base and to retain the drive shaft casing in a vertical direction with respect to the movable base.

10. A vertical retracting thruster according to any one of claims 5 to 9, wherein the drive shaft has a fixed length in the vertical direction.

11. A vertical retracting thruster according to any one of claims 5 to 10, wherein the total vertical height from the thruster motor to the propeller is less than 600 mm.

12. A vertical retracting thruster according to any one of claims 5 to 11, wherein the thrust motor is an electric motor.

13. A vertical retracting thruster for providing thrust to a vessel, the vertical retracting thruster being suitable for mounting within a hull of the vessel, the vertical retracting thruster comprising: a fixed base for mounting with respect to the hull; a movable base; a vertical height adjusting assembly; a thrust motor; a propeller with an outer diameter in the range from 100 mm to 250 mm; wherein the vertical retracting thruster has a retracted configuration, in which the propeller is retracted into the hull, and a deployed configuration, in which the propeller projects from the hull, the vertical retracting thruster being operable to move between the retracted configuration and the deployed configuration, the vertical retracting thruster further comprising: a drive shaft linking the thrust motor to the propeller, the drive shaft extending in the vertical direction through the fixed base when the vertical retracting thruster is in the retracted configuration; a drive shaft casing provided around at least part of the drive shaft and extending from the movable base and through the fixed base; a seal disposed between an outer surface of the drive shaft casing and an internal surface of the fixed base, wherein the thrust motor is contained, at least in part, within the drive shaft casing, the vertical height adjusting assembly being configured to move the movable base, the drive shaft casing, the thrust motor and the drive shaft relative to the fixed base in a vertical direction.

14. A vertical retracting thruster according to claim 13 wherein the thrust motor is contained, in its entirety, within the drive shaft casing.

15. A vertical retracting thruster according to claim 13 or claim 14 further comprising a steering arrangement for control of the direction of an axis of rotation of the propeller and thereby the direction of thrust at least when the vertical retracting thruster is in the deployed configuration.

16. A vertical retracting thruster according to claim 15 wherein the steering arrangement is configured to rotate the thrust motor, the drive shaft casing and the propeller with respect to the movable base and with respect to the fixed base.

17. A vertical retracting thruster according to claim 15 or claim 16 wherein the steering arrangement comprises a steering motor fixed with respect to the movable base.

18. A vertical retracting thruster according to any one of claims 13 to 17 further comprising: a height adjustment motor; a gearbox with an output shaft, the output shaft being mechanically linked to the height adjustment motor; a bearing plate attached to the gearbox such that the output shaft of the gearbox is rotatable in the bearing plate; a height adjusting lead screw follower attached to the moveable base; and a height adjusting lead screw connected to and rotatable with the output shaft of the gearbox.

19. A vessel with a vertical retracting thruster according to any one of claims 1 to 18 installed inside a hull of the vessel.

20. A vessel according to claim 19, wherein the vessel is a pontoon style vessel.

21. A vessel according to claim 20, wherein the pontoon style vessel comprises three hulls.

22. A vessel according to claim 21, wherein the vertical retracting thruster is installed inside the central hull.

23. A vessel according to the any one of claims 19 to 22, wherein a vertical retracting thruster according to any one of claims 1 to 18 is installed inside a bow region of the hull and another vertical retracting thruster, of a same or different type, according to any one of claims 1 to 18 is installed inside a stern region of the hull.

Description

SUMMARY OF THE FIGURES

[0093] Embodiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0094] FIG. 1 shows a front perspective view of a vertical retracting thruster (VRTT) according to an embodiment of the invention, installed in a pontoon hull, with the thruster in a retracted configuration.

[0095] FIG. 2 shows a front perspective view of the VRTT of FIG. 1, with the VRTT in a deployed configuration.

[0096] FIG. 3a shows an enlarged front perspective view of the height adjusting assembly in FIG. 1.

[0097] FIG. 3b shows a further enlarged front perspective view of the bearing plate of the height adjusting assembly in FIG. 3a.

[0098] FIG. 4 shows a cross-sectional view of the height adjusting assembly in the Y-Z plane.

[0099] FIG. 5 shows a cross-sectional view of the drive shaft and the fixed base in the Y-Z plane.

[0100] FIG. 6 shows a side perspective view of a hull of a pontoon boat, with the VRTT of FIG. 1 installed within the hull at a bow region and another VRTT of FIG. 1 installed within the hull at a stern region.

[0101] FIG. 7 shows a perspective view of a vertical retracting thruster (VRTT) according to another embodiment of the invention, with the thruster in a retracted configuration.

[0102] FIG. 8 shows another view of the VRTT of FIG. 7, rotated about 60° around the axis of the drive shaft compared with the view of FIG. 7.

[0103] FIG. 9 shows the VRTT of FIG. 7 from a similar viewpoint but in partial cutaway view of the moveable base.

[0104] FIG. 10 shows an enlarged view of part of the VRTT shown in FIG. 9.

[0105] FIG. 11 shows a perspective view of a vertical retracting thruster (VRTT) according to a further embodiment of the invention, with the thruster in a retracted configuration. The view shows part of the hull of the vessel but omits the compartment to which the VRTT is attached.

[0106] FIG. 12 shows an enlarged view of the movable base of the VRTT of FIG. 11.

[0107] FIG. 13 shows a schematic perspective cross sectional view of the VRTT of FIG. 11.

[0108] FIG. 14 shows a cross sectional view of a modified version of the VRTT of FIG. 11, but omits the fixed plate from the view.

DETAILED DESCRIPTION OF THE INVENTION

[0109] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

[0110] Similar reference numbers are used throughout the drawings to identify similar features.

[0111] FIG. 1 shows a front perspective view of the vertical retracting thruster 100 (VRTT) in accordance with an embodiment of the present invention. The VRTT in FIG. 1 is in a retracted configuration.

[0112] The VRTT 100 is housed within a hull 102 of a vessel and is attached to a hull mount 104. The hull mount 104 may be integrated with the hull 102 or a separate piece that is fixed to the inner surface of the hull 102 through fasteners. The hull 102 has a tubular shape at the location of the VRTT 100, with the hull 102 extending along a longitudinal direction (i.e. in the x-direction). In this embodiments, the hull 102 has an inner diameter around 600 mm.

[0113] In general the VRTT 100 comprises a fixed base 106, a movable base 108, a vertical height adjusting assembly 110, a thrust motor 112, a propeller 114, a drive shaft 116 (not visible in FIG. 1 but shown in FIG. 5), a drive shaft casing 118 and a seal 120 (not visible in FIG. 1 but shown in FIG. 5).

[0114] The fixed base 106 is attached to the hull mount 104. The fixed base 106 comprises two parts that sandwich the hull mount 104, with fasteners passing through both the fixed base 106 and the hull mount 104 to achieve a secure connection.

[0115] The fixed base 106 separates a thrust motor side (in the upward z-direction relative to the fixed base 106) and a propeller side (in the downward z-direction relative to the fixed base 106). Unless stated otherwise, the z-direction corresponds to the ‘vertical’ direction.

[0116] The lateral thrust produced by the VRTT 100 is derived from the propeller 114. The propeller 114 has a diameter in the range of 100 mm to 150 mm. It has been found that, in combination with a suitable electric motor, this provides adequate lateral thrust for typical pontoon boats. The propeller 114 is provided on the propeller side of the fixed base 106 and is oriented transverse to the vertical direction and the longitudinal direction, i.e. in the y-direction.

[0117] A thrust motor 112 is provided to power the propeller 114. It is envisaged that the thrust motor 112 is an electric motor. Electric motors are available of suitable power but also of a suitably small size. The thrust motor 112 is mounted and attached to a movable base 108 through fasteners. The thrust motor 112 and movable base 108 are located on the thrust motor side of the fixed base 106.

[0118] A drive shaft 116 mechanically links the thrust motor 112 with the propeller 114. The drive shaft 116 extends between the thrust motor 112 and to the propeller 114 in the vertical direction.

[0119] Surrounding the drive shaft 116 is a drive shaft casing 118. For clarity, FIG. 5 shows a cross-sectional view of the drive shaft 116 in the drive shaft casing 118. The drive shaft casing 118 protects the drive shaft 116 from impacts and water damage during operation. Both the drive shaft 116 and the drive shaft casing 118 extend entirely through the movable base 108 and the fixed base 106.

[0120] As the propeller 114 is aligned perpendicular with respect to the drive shaft 116, the drive shaft 116 is connected to the propeller 114 through a right angle propeller gearbox 122. This right angle propeller gearbox 122 may be a 1:1, step-up or step-down gearbox.

[0121] FIG. 2 shows a front perspective view of the VRTT 100 in a deployed configuration. When in the deployed configuration, the propeller 114 projects out from the hull 102. Furthermore, in the deployed configuration, rotation of the propeller 114 generates lateral thrust to the hull 102. In order for the VRTT 100 to transition from the retracted configuration to the deployed configuration, the thrust motor 112, movable base 108, drive shaft 116 and drive shaft casing 118 all move downward in the vertical direction.

[0122] The vertical height adjusting assembly 110 is configured to move the movable base 108 relative to the fixed base 106 in a vertical direction. Accordingly, because the propeller 114 is linked to the movable base 108 via the thrust motor 112 and drive shaft 116, moving the movable base 108 also moves the propeller 114 relative to the fixed base 106.

[0123] FIG. 3a shows an enlarged view of the vertical height adjusting assembly 110, when the VRTT 100 is in the retracted configuration. The vertical height adjusting assembly 110 comprises a height adjustment motor 302, a gearbox 304, a bearing plate 306, a height adjusting lead screw 308 and a height adjusting lead screw follower 310.

[0124] To move the movable base 108 relative to the fixed base 106 in the vertical direction, the height adjustment motor 302 rotates the height adjusting lead screw 308, which in turn couples with the height adjusting lead screw follower 310.

[0125] The height adjusting lead screw follower 310 is fixed in position with respect to the movable base 108. The height adjusting lead screw follower 310 has a hole 312, with a threaded inner wall. The height adjusting lead screw follower 310 extends vertically and continuously through the movable base 108.

[0126] The height adjusting lead screw 308 consists of a threaded shaft that extends in the vertical direction. The height adjusting lead screw 308 is configured to couple with the threaded inner wall at the hole 312 of the height adjusting lead screw follower 310, such that the height adjusting lead screw 308 is rotatable within the height adjusting lead screw follower 310. The height adjusting lead screw follower 310 and movable base 108 move in the vertical direction relative to the height adjusting lead screw 308, when the height adjusting lead screw 308 rotates.

[0127] The vertical height adjusting assembly 110 has a height adjustment motor 302 to rotate the height adjusting lead screw 308. The height adjustment motor 302 is an electric motor, which has its principal axis (corresponding to the axis of rotation of the rotor within the motor) oriented transverse to the vertical direction. In the exemplary embodiment, the height adjustment motor 302 is oriented in the longitudinal direction of the hull 102 (in the x-direction). This orientation reduces the vertical height taken up by the height adjustment motor 302 and uses instead the relatively plentiful longitudinal space available in the hull.

[0128] The height adjustment motor 302 is connected to a gearbox 304. The gearbox 304 is a right angle gearbox and may be a 1:1, step-up or step-down gearbox. Preferably the gearbox is a step down gear box and may for example utilise a worm and worm wheel arrangement. The gearbox 304 includes an input shaft connected to the height adjustment motor 302 and an output shaft 314 connected to the height adjusting lead screw 308. The input shaft and the output shaft 314 are arranged to be orthogonal to each other. The gearbox 304 has a gearbox casing 315, which partially houses the inner shaft and the output shaft 314. The gearbox 304 is attached to the fixed base 106, with the bottom of the gearbox casing 315 abutting the top of the fixed base 106.

[0129] Attached to the top of the gearbox 304 is a bearing plate 306. The bearing plate may also provide the upper part of the gearbox casing. As shown in FIG. 3b, the bearing plate 306 has an annular portion 316 with protrusions 318 extending radially from the outer circumference of the annular portion 316. In the exemplary embodiment, the bearing plate 306 has three protrusions 318, however more or fewer protrusions 318 may be provided. The protrusions 318 each surround a respective screw hole for fastening the bearing plate 306 to the gearbox 304 and to the fixed base 106.

[0130] FIG. 4 shows a cross-sectional view of the gearbox 304, the bearing plate 306 and the height adjusting lead screw 308. Inside the gearbox 304, the output shaft 314 rotates about a rotational axis, the rotational axis being in the vertical direction. When rotating, the output shaft 314 is supported by a pin 402 and the bearing plate 306. The output shaft 314 extends through the centre of the annular region of the bearing plate 306 and is rotatable in the bearing plate 306.

[0131] The gearbox 304 and bearing plate 306 are attached to the fixed base 106 by fasteners 404. In FIG. 4, fastener 404 extends in the vertical direction and passes continuously through the screw hole surrounded by protrusion 318 of the bearing plate 306, the gearbox 304 and the fixed base 106. The advantage associated with this fastening arrangement is that the vertical height taken up by the gearbox 304 and bearing plate 306 is relatively small. For instance, because the bottom of the gearbox 304 abuts the fixed base 106, and the bearing plate 306 provides the top of the gearbox 304, the only excess vertical height from attaching the gearbox 304 and bearing plate 306 to the fixed base 106 is from the head of the fastener 404, which is relatively insignificant. Therefore, the movable base 108 is able to get very close to the fixed base 106 when the VRTT 100 is in the deployed configuration, because it is not inhibited by the height of the gearbox 304 and bearing plate 306.

[0132] According to the embodiment, when the VRTT 100 is in the retracted configuration, the distance in the vertical direction between the movable base 108 and the fixed base 106 is less than 200 mm. This distance determines the maximum available vertical stroke of the VRTT 100. As will be understood, such a vertical stroke can be ensured to be sufficient to allow full retraction and full deployment of the propeller previously described.

[0133] Another advantage associated with this fastening arrangement is that the bearing plate 306 does not have to be integrated within the gearbox 304, which makes the vertical height adjusting assembly 110 less expensive, and easier to assemble and maintain.

[0134] To further reduce the vertical height taken by the gearbox 304, the upper surface of the fixed base 106 includes a recess 406. This recess 406 provides space for motor gearbox registry and clearance for shaft retaining screw 402. Screw 406, and washer 403 above it, retain the shaft 314 inside the gearbox. This stops the shaft 314 and leadscrew 308 assembly from being pulled upwards, instead of the movable base being pulled down. Shaft retaining screw 402 and washer 403 rotate with the shaft.

[0135] The output shaft 314 extends out of the bearing plate 306, where it forms a tubular portion 408. This tubular portion 408 is configured to cooperate with an end of height adjusting lead screw 308. To connect the tubular portion 408 to the height adjusting lead screw 308, the end of the height adjusting lead screw 308 is inserted into the tubular portion 408 of the output shaft 314 and a bolt 410 is passed through both pieces. Resultantly, the height adjusting lead screw 308 rotates with the output shaft 314.

[0136] Referring back to FIG. 3a, the vertical height adjusting assembly 110 has a height adjusting limiter 320. The height adjusting limiter 320 comprises an elongate rod 322 and stoppers 324. The elongate rod 322 is fixed to the fixed base 106. The elongate rod 322 extends in the vertical direction through and past the movable base 108. Positioned along the length of elongate rod 322 are stoppers 324, with one stopper 324 being on either side of the movable base 108. Each stopper 324 is configured to activate a respective switch 323a, 323b, to deactivate the height adjustment motor 304 when the respective switch contacts the relevant stopper 324. This limits the range of movement of the movable base 108. The vertical positions of the stoppers 324 are adjustable, as shown in the drawings.

[0137] FIG. 3a shows that the drive shaft casing 118 has a failsafe retainer screw 351 extending through the drive shaft casing 118, located just below the movable base 108. A corresponding failsafe retainer screw (not shown) is disposed on the opposing side of the drive shaft casing. The head of the failsafe retainer screw acts as a lug that would prevent the drive shaft casing from passing completely through the collar 502. This therefore prevents loss of the drive shaft and propeller, in the event of mechanical failure or breakage of the thruster.

[0138] Referring to FIG. 1, the VRTT 100 has a vertical guide support 124. The vertical guide support 124 is an elongate pole attached to the fixed base 106 and extending in the vertical direction through and past the movable base 108. The vertical guide support 124 stabilises the movable base 108 when the vertical position of the movable base 108 is being adjusted. This ensures the movable base 108 remains aligned with the fixed base 106 during operation, which protects the vertical height adjusting assembly 110.

[0139] FIG. 5 shows a partial cross-sectional view of the fixed base 106, drive shaft 116 and drive shaft casing 118. In the embodiment, the fixed base 106 has a collar portion 502. The collar portion 502 may be an integrated part of the fixed base 106 or may be a separate part, which is attached through fasteners. The collar portion 502 resists lateral loads that act on the drive shaft 116 when the propeller 114 is deployed.

[0140] The VRTT 100 further comprises various seals. For example seal 120 is identified in FIG. 5. The seal 120 is disposed between an outer surface of the drive shaft casing 118 and an internal surface of bearing piece 503 that is attached to the fixed base 106, in this case within the collar portion 502. The seal 120 provides water sealing between the thrust motor side and the propeller side. This water sealing will be understood as not only being important for protecting the VRTT but also for maintaining the water-tight integrity of the hull. Bearing piece 503 provides a reservoir of grease. This acts as ingress protection, in addition to lubricating the shaft and seals. As can be seen in FIG. 5, bearing piece 503 is provided with screw holes at its upper face and bearing piece 503 is fixed to the collar part 502 via corresponding screws. A lip seal is also provided at the base of collar portion 502 as the primary seal for ingress protection.

[0141] Circumferentially surrounding the propeller 114 and the propeller gearbox 122 is a propeller tunnel 506. In the drawings, this is shown in partial cutaway view. The propeller tunnel 506 has a flared tubular shape that extends in a direction parallel to the rotational axis of the propeller 114 (i.e. extending in the y-direction) and has a slightly larger inner diameter than to the propeller 114. The propeller tunnel 506 protects the propeller 114 from making contact with the seabed.

[0142] Connected to the bottom of the propeller tunnel is a hull plug 508. The hull plug 508 has the same curvature as the hull 102, such that when the VRTT 100 is in the retracted configuration, the hull plug 508 fills the gap in the hull through which the VRTT protrudes when the VRTT is in the deployed configuration (as seen in FIG. 1). The hull plug 508 may have seals (not shown) around the outer edges to create a water sealing with the hull 102, when the VRTT 100 is in the retracted configuration.

[0143] In order to be installed within the hull 102, the total vertical height of the VRTT 100, from the thruster motor to the base of the propeller tunnel 506 is less than 600 mm.

[0144] The VRTT 100 may be installed in the hull 102 of a pontoon boat. FIG. 6 shows a central pontoon hull 600 of a pontoon boat (the pontoon boat in this example would have three pontoons). Within the central pontoon is a windlass 602, a pressurised fore compartment 604, brackets 606 for attachment to a pontoon deck, a first VRTT 100x and a second VRTT 100y. The first VRTT 100x and second VRTT 100y each correspond to the VRTT 100 described above. The first VRTT 100x is installed within the bow region of the hull and the second VRTT 100y being installed toward the stern region of the hull. The first VRTT 100x is installed between the windlass 602 and the pressurised tank 604. The pressurised tank 604 is provided to withstand water impacts at the front of the pontoon hull 102.

[0145] FIG. 7 shows a perspective view of a vertical retracting thruster (VRTT) according to another embodiment of the invention, with the thruster in a retracted configuration. FIG. 8 shows another view of the VRTT of FIG. 7, rotated about 60° around the axis of the drive shaft compared with the view of FIG. 7. FIG. 9 shows the VRTT of FIG. 7 from a similar viewpoint but in partial cutaway view of the moveable base. FIG. 10 shows an enlarged view of part of the VRTT shown in FIG. 9.

[0146] This embodiment shares many features in common with the embodiment described with respect to FIGS. 1 to 6. Where appropriate, similar reference numbers are used to describe similar features between the two embodiments, but with the embodiment of FIGS. 7-10 having reference numbers with the suffix “a”.

[0147] FIG. 7 shows a front perspective view of the vertical retracting thruster 100a (VRTT) in accordance with a further embodiment of the present invention, which is a modification of the embodiment of FIGS. 1-6. The VRTT in FIG. 7 is in a retracted configuration. The VRTT of FIG. 7 is intended to be housed within a hull of a vessel and to be attached to a hull mount in a similar manner to the VRTT of FIG. 1.

[0148] In general the VRTT 100a comprises a fixed base 106a, a movable base 108a, a vertical height adjusting assembly 110a, a thrust motor 112a, a propeller 114a, a drive shaft (not visible in FIG. 7), a drive shaft casing 118a and a seal (not visible in FIG. 7).

[0149] The fixed base 106a is attachable to the hull mount. The fixed base 106a comprises two parts that sandwich the hull mount, with fasteners passing through both the fixed base 106a and the hull mount to achieve a secure connection.

[0150] The fixed base 106a separates a thrust motor side (in the upward direction relative to the fixed base 106a) and a propeller side (in the downward direction relative to the fixed base 106a).

[0151] The thrust produced by the VRTT 100a is derived from the propeller 114a. The propeller 114a has a diameter in the range of 100 mm to 150 mm. It has been found that, in combination with a suitable electric motor, this provides adequate lateral thrust (and other low speed manoeuvring thrust) for typical pontoon boats. The propeller 114a is provided on the propeller side of the fixed base 106a and is oriented so that its axis of rotation lies in a plane perpendicular to the vertical direction and, as explained below, this axis of rotation can be varied within this plane in order to vary the direction of thrust. In the embodiment shown, the storage configuration may have the axis of rotation of the propeller perpendicular to the longitudinal direction of the hull (in a similar orientation to the first embodiment). However, in other embodiments the axis or rotation of the propeller in the storage configuration may be aligned with the longitudinal direction of the hull, or may be in another direction.

[0152] A thrust motor 112a is provided to power the propeller 114a. It is envisaged that the thrust motor 112a is an electric motor. Electric motors are available of suitable power but also of a suitably small size. The thrust motor 112a is mounted and attached to the movable base 108a as described in more detail below. The thrust motor 112a and movable base 108a are located on the thrust motor side of the fixed base 106a. Note that the thrust motor 112a of this embodiment has a slightly different appearance to the thrust motor 112 shown in FIG. 1. The thrust motor of FIG. 1 may be a series wound field DC motor, for example. The thrust motor of FIG. 7 may be a brushless DC motor, for example. The brushless DC motor may constitute a more efficient motor in a smaller overall format. However, in principle the motors may be used interchangeably.

[0153] A drive shaft (not shown) mechanically links the thrust motor 112a with the propeller 114a. The drive shaft extends between the thrust motor 112a and the propeller 114a in the vertical direction.

[0154] Surrounding the drive shaft is a drive shaft casing 118a. FIGS. 9 and 10 show the drive shaft casing 118a in partial cross-sectional view. The drive shaft casing 118a protects the drive shaft from impacts and water damage during operation. Both the drive shaft and the drive shaft casing 118a extend entirely through the movable base 108a and the fixed base 106a.

[0155] As the propeller 114a is aligned perpendicular with respect to the drive shaft 116a, the drive shaft 116a is connected to the propeller 114a through a right angle propeller gearbox (not shown), similar to that indicated in FIGS. 1-6. This right angle propeller gearbox may be a 1:1, step-up or step-down gearbox.

[0156] Although not shown in FIGS. 7-10, the VRTT 100a can move from the retracted configuration to the deployed configuration. When in the deployed configuration, the propeller 114a projects out from the hull. Furthermore, in the deployed configuration, rotation of the propeller 114a generates thrust to the hull. In order for the VRTT 100a to transition from the retracted configuration to the deployed configuration, the thrust motor 112a, movable base 108a, drive shaft and drive shaft casing 118a all move downward in the vertical direction.

[0157] The vertical height adjusting assembly 110a is configured to move the movable base 108a relative to the fixed base 106a in a vertical direction. Accordingly, because the propeller 114a is linked to the movable base 108a via the thrust motor 112a and drive shaft, moving the movable base 108a also moves the propeller 114a relative to the fixed base 106a.

[0158] The vertical height adjusting assembly 110a has a similar construction and operation to that described with respect to FIGS. 1-6. The vertical height adjusting assembly 110 comprises a height adjustment motor 302a, a gearbox 304a, a bearing plate 306a, a height adjusting lead screw 308a and a height adjusting lead screw follower (not shown).

[0159] To move the movable base 108a relative to the fixed base 106a in the vertical direction, the height adjustment motor 302a rotates the height adjusting lead screw 308a, which in turn couples with the height adjusting lead screw follower.

[0160] The height adjusting lead screw follower is fixed in position with respect to the movable base 108a. The height adjusting lead screw follower has a hole with a threaded inner wall. The height adjusting lead screw follower extends vertically and continuously through the movable base 108a.

[0161] The height adjusting lead screw 308a consists of a threaded shaft that extends in the vertical direction. The height adjusting lead screw 308a is configured to couple with the threaded inner wall at the hole of the height adjusting lead screw follower, such that the height adjusting lead screw 308a is rotatable within the height adjusting lead screw follower 310a. The height adjusting lead screw follower and movable base 108a move in the vertical direction relative to the height adjusting lead screw 308a, when the height adjusting lead screw 308a rotates.

[0162] The vertical height adjusting assembly 110a has a height adjustment motor 302a to rotate the height adjusting lead screw 308a. The height adjustment motor 302a is an electric motor, which has its principal axis (corresponding to the axis of rotation of the rotor within the motor) oriented transverse to the vertical direction. In this embodiment, the height adjustment motor 302a may be oriented in the longitudinal direction of the hull. This orientation reduces the vertical height taken up by the height adjustment motor 302a and uses instead the relatively plentiful longitudinal space available in the hull.

[0163] The height adjustment motor 302a is connected to a gearbox 304a. The gearbox 304a is a right angle gearbox and may be a 1:1, step-up or step-down gearbox. Preferably the gearbox is a step down gear box and may for example utilise a worm and worm wheel arrangement. The gearbox 304a includes an input shaft connected to the height adjustment motor 302a and an output shaft 314a connected to the height adjusting lead screw 308. The input shaft and the output shaft 314 are arranged to be orthogonal to each other. The gearbox 304a has a gearbox casing, which partially houses the inner shaft and the output shaft 314a. The gearbox 304a is attached to the fixed base 106a, with the bottom of the gearbox casing abutting the top of the fixed base 106a.

[0164] Attached to the top of the gearbox 304a is a bearing plate 306a. The bearing plate may also provide the upper part of the gearbox casing. As shown with respect to FIGS. 1-6, the bearing plate 306a has an annular portion with three protrusions extending radially from the outer circumference of the annular portion, permitting fastening of the bearing plate and gearbox to the fixed base 106a.

[0165] According to this embodiment, as for the previous embodiment, when the VRTT 100a is in the retracted configuration, the distance in the vertical direction between the movable base 108a and the fixed base 106a is less than 200 mm. This distance determines the maximum available vertical stroke of the VRTT 100a. As will be understood, such a vertical stroke can be ensured to be sufficient to allow full retraction and full deployment of the propeller previously described.

[0166] Referring to FIG. 8, the vertical height adjusting assembly 110a has a height adjusting limiter 320a. The height adjusting limiter 320a comprises an elongate rod 322a and stoppers 324a. The elongate rod 322a is fixed to the fixed base 106a. The elongate rod 322a extends in the vertical direction through and past the movable base 108a. Positioned along the length of elongate rod 322a are stoppers 324a, with one stopper 324a being on either side of the movable base 108a. Each stopper 324a is configured to activate a respective switch 323aa, 323ba, to deactivate the height adjustment motor 304a when the respective switch contacts the relevant stopper 324a. This limits the range of movement of the movable base 108a. The vertical positions of the stoppers 324a are adjustable, as shown in the drawings.

[0167] The VRTT 100a has vertical guide supports 124a, 125a. The vertical guide supports 124a, 125a are elongate poles attached to the fixed base 106a and extending in the vertical direction through and past the movable base 108a. The vertical guide supports 124a, 125a stabilise the movable base 108a when the vertical position of the movable base 108a is being adjusted. This ensures the movable base 108a remains aligned with the fixed base 106a during operation, which protects the vertical height adjusting assembly 110a.

[0168] In the embodiment of FIGS. 7-10, the construction and operation of the fixed base 106a, collar portion 502a and the various seals are similar to the explanations already provided with respect to FIG. 5.

[0169] Circumferentially surrounding the propeller 114a and the propeller gearbox is a propeller tunnel 506a. The propeller tunnel 506a has a flared tubular shape that extends in a direction parallel to the rotational axis of the propeller 114a and has a slightly larger inner diameter than the propeller 114a. The propeller tunnel 506a protects the propeller 114a from making contact with the seabed.

[0170] Connected to the bottom of the propeller tunnel is a hull plug 508a. The hull plug 508a has the same curvature as the hull, such that when the VRTT 100a is in the retracted configuration, the hull plug 508a fills the gap in the hull through which the VRTT protrudes when the VRTT is in the deployed configuration (as seen in the embodiment of FIG. 1). The hull plug 508a may have seals (not shown) around the outer edges to create a water sealing with the hull, when the VRTT 100a is in the retracted configuration.

[0171] In order to be installed within the hull, the total vertical height of the VRTT 100a, from the thruster motor to the base of the propeller tunnel 506a is less than 600 mm, in a similar manner to the embodiment of FIGS. 1-6.

[0172] A significant difference between the embodiment of FIGS. 1-6 and the embodiment of FIGS. 7-10 is that the embodiment of FIGS. 1-6 is intended to the used purely as a lateral thruster. Once fitted to the hull, the rotational axis of the propeller is disposed to be horizontal and perpendicular to the longitudinal direction of the hull. Thus when deployed, the thruster is available to provide lateral thrust to the hull. Other than deployment and retraction in the vertical direction, the rotational axis of the propeller is intended to be fixed with respect to the longitudinal direction of the hull. In contrast, in the embodiment of FIGS. 7-10, the rotational axis of the propeller with respect to the longitudinal direction of the hull can be varied, at least when the thruster is in the deployed configuration. This is achievable due to a steering arrangement 200a that will now be described in more detail. The effect of this construction is that the thruster can be used not only to provide lateral thrust but thrust in any direction in the horizontal plane. This allows the thruster to provide useful steering control of the boat in low speed manoeuvring, for example during mooring procedures.

[0173] Steering arrangement 200a provides the effect of rotating the thrust motor 112a, the drive shaft casing 118a, the propeller 114a and the tunnel 506a and hull plug 508a with respect to the moveable base 108a and the fixed base 106a. This rotation is around the axis of rotation A of the drive shaft, which in use is intended to be oriented in the vertical direction. Given that the fixed base 106a is for attachment with respect to the hull, the steering arrangement permits orientation of the thrust direction provided by the propeller in any direction within a plane perpendicular to axis A.

[0174] Thrust motor 112a is attached to motor mount ring 210a with the drive shaft 212a of the motor 112a extending through a central aperture 214a of motor mount ring 210a. Gear ring 218a is sandwiched between the motor mount ring 210a and a main leg fixing piece 216a and the motor mount ring 210a, gear ring 218a and main leg fixing piece 216a are fixed together via screws 220a. The drive shaft casing 118a is attached to the main leg fixing piece 216a and is rotatable with the main leg fixing piece 216a within aperture 109a formed through the movable base 108a.

[0175] Slew ring bearing 224a comprises an inner ring 226a fixed to the movable base 108a and an outer ring 228a which is rotatable with respect to the inner ring 226a via bearings (not shown) which permit said rotation but which prevent relative axial translational movement between the inner ring and outer ring. The annularly outer part of the main leg fixing piece 216a is attached to the outer ring 228a. By this arrangement, the thrust motor 112a, motor mount ring, gear ring 218a, main leg fixing piece 216a, drive shaft casing 118a and outer ring 228a of the slew ring bearing 224a are rotatable together about axis A relative to the movable base 108a and inner ring 226a of the slew ring bearing 224a.

[0176] Steering motor 230a has a horizontal rotational output at a steering motor output shaft (not shown) which drive gearbox 232a which rotates steering gear wheel 234a which is mounted behind protective cover 236a. Toothed belt 238a wraps around steering gear wheel 234a and around ring gear 218a. Accordingly, operation of steering motor 230a rotates steering gear wheel 234a to rotate ring gear 218a via toothed belt, which therefore causes rotation of the thrust motor 112a, motor mount ring, gear ring 218a, main leg fixing piece 216a, drive shaft casing 118a and outer ring 228a of the slew ring bearing 224a together about axis A relative to the movable base 108a and inner ring 226a of the slew ring bearing 224a. Rotation of the drive shaft casing 118a through the fixed base 106a causes rotation of the propeller 114a and the tunnel 506a, allowing control of the direction of thrust from the propeller in the horizontal plane.

[0177] As will be understood, the present embodiment is illustrated as providing a reduction in gearing between the steering motor 230a and the drive shaft casing 118a. However, various different implementations of control of the rotational position of the drive shaft casing 118a and ultimately of the propeller 114a in the horizontal plane will be apparent on the basis of the present disclosure. An exemplary further embodiment is set out below. FIG. 11 shows a perspective view of a vertical retracting thruster (VRTT) according to a further embodiment of the invention, with the thruster in a retracted configuration. The view shows part of the hull of the vessel but omits the compartment to which the VRTT is attached. FIG. 12 shows an enlarged view of the movable base of the VRTT of FIG. 11. FIG. 13 shows a schematic perspective cross sectional view of the VRTT of FIG. 11. FIG. 14 shows a cross sectional view of a modified version of the VRTT of FIG. 11.

[0178] This embodiment shares many features in common with the embodiments described with respect to FIGS. 7-10 and FIGS. 1-6. Where appropriate, similar reference numbers are used to describe similar features between the two embodiments, but with the embodiment of FIGS. 11-14 having reference numbers with the suffix “b”.

[0179] FIG. 11 shows a front perspective view of the vertical retracting thruster 100b (VRTT) in accordance with a further embodiment of the present invention, which is a modification of the embodiment of FIGS. 7-10. The VRTT in FIG. 11 is in a retracted configuration. The VRTT of FIG. 11 is intended to be housed within a hull 102b of a vessel and to be attached to a hull mount in a similar manner to the VRTT of FIG. 1. Note that in FIG. 11 only part of the hull 102b is shown, in order for the VRTT to be visible more easily.

[0180] In general the VRTT 100b comprises a fixed base 106b, a movable base 108b, a vertical height adjusting assembly 110b, a thrust motor (not visible in FIG. 11), a propeller 114b, a drive shaft (not visible in FIG. 11), a drive shaft casing 118b and a seal (not visible in FIG. 11).

[0181] The fixed base 106b is attachable to a hull mount (not shown in FIG. 11). The fixed base 106b comprises two parts that sandwich the hull mount, with fasteners passing through both the fixed base 106b and the hull mount to achieve a secure connection.

[0182] The fixed base 106b separates a thrust motor side (in the upward direction relative to the fixed base 106b) and a propeller side (in the downward direction relative to the fixed base 106b). However, note that in view of the location of the motor, described below, it is possible that in the deployed configuration at least part of the motor may project through the fixed base.

[0183] The thrust produced by the VRTT 100b is derived from the propeller 114b. The propeller 114b has a diameter in the range of 100 mm to 250 mm. The upper limit of the propeller diameter is larger than for the previous embodiments, even when the VRTT is installed in a hull identical that that described with respect to the previous embodiments. This is described in more detail below. A larger propeller diameter, in combination with a suitable electric motor, provides increased lateral thrust (and other low speed manoeuvring thrust) for typical pontoon boats.

[0184] The propeller 114b is provided on the propeller side of the fixed base 106b and is oriented so that its axis of rotation lies in a plane perpendicular to the vertical direction and, as explained below, this axis of rotation can be varied within this plane in order to vary the direction of thrust. In the embodiment shown, the storage configuration may have the axis of rotation of the propeller parallel to the longitudinal direction of the hull. Based on geometric considerations in particular for pontoon boats with substantially cylindrical hulls, it is possible to fit a slightly larger propeller tunnel in the hull in the storage configuration when the propeller and tunnel is oriented in this manner. However, in other embodiments the axis of rotation of the propeller in the storage configuration may be aligned perpendicular with the longitudinal direction of the hull, or may be in another direction.

[0185] A thrust motor 112b (see FIGS. 13 and 14) is provided to power the propeller 114b. It is envisaged that the thrust motor 112b is an electric motor. Electric motors are available of suitable power but also of a suitably small size. The thrust motor 112b inside the drive shaft casing 118b as described in more detail below. The thrust motor of the present embodiment may be a brushless DC motor, for example. The brushless DC motor may constitute a more efficient motor in a smaller overall format. However, in principle the motors may be used interchangeably. Motor power and control leads 113b are provided for the motor 112b.

[0186] A drive shaft 115b (see FIG. 13) mechanically links the thrust motor 112b with the propeller 114b. The drive shaft extends between the thrust motor 112b and the propeller 114b in the vertical direction.

[0187] Surrounding the drive shaft is a drive shaft casing 118b. FIG. 13 shows the drive shaft casing 118b in partial cross-sectional view. The drive shaft casing 118b protects the drive shaft from impacts and water damage during operation. The drive shaft casing 118b extends entirely through the movable base 108b and the fixed base 106b.

[0188] As the propeller 114b is aligned perpendicular with respect to the drive shaft 116a, the drive shaft 116b is connected to the propeller 114b through a right angle propeller gearbox 122b, similar to that indicated in FIGS. 1-6. This right angle propeller gearbox may be a 1:1, step-up or step-down gearbox.

[0189] Although not shown in FIGS. 11-14, the VRTT 100b can move from the retracted configuration to the deployed configuration. When in the deployed configuration, the propeller 114b projects out from the hull. Furthermore, in the deployed configuration, rotation of the propeller 114b generates thrust to the hull. In order for the VRTT 100b to transition from the retracted configuration to the deployed configuration, the thrust motor 112b, movable base 108b, drive shaft 115b and drive shaft casing 118b all move downward in the vertical direction.

[0190] The vertical height adjusting assembly 110b is configured to move the movable base 108b relative to the fixed base 106b in a vertical direction as described with respect to the preceding embodiments.

[0191] According to this embodiment, when the VRTT 100b is in the retracted configuration, the distance in the vertical direction between the movable base 108b and the fixed base 106b may be more than 200 mm. For example this distance may be 250 mm or less, or even up to 300 mm or less. This distance determines the maximum available vertical stroke of the VRTT 100b. As will be understood, such a vertical stroke can be ensured to be sufficient to allow full retraction and full deployment of the propeller previously described.

[0192] A significant difference between the present embodiments and the embodiments described above is the location of thrust motor 112b. In FIGS. 7 and 8, the thrust motor cannot be seen because it is located within the drive shaft casing 118b. This provides the significant advantage that the thrust motor in this embodiment does not stand proud (or does not stand significantly proud) from the movable base 108b. In turn, this reduces the profile of the VRTT and means that the headroom required for retraction of the VRTT is smaller and therefore that a larger diameter propeller can be used.

[0193] In the embodiment shown in FIG. 13, the motor 112b (shown schematically) has an external diameter substantially corresponding to the internal diameter of the drive shaft casing 118b. The output shaft 130b of the motor attaches to a proximal end of the drive shaft 115b via shear pins 132b. The distal end of the drive shaft 115b attaches to an input shaft 134b of the gearbox 112b to allow driving of the propeller 114b.

[0194] FIG. 14 shows a slightly modified embodiment in which the location of the motor is similar to FIG. 13 but the output shaft 130c of the motor 112c is connected to a planetary gearbox 140c which in tuns connects to the drive shaft 115c which connects to an input shaft 134c to the gearbox 112. As can be seen in FIG. 14, gearbox 122b uses a bevel gear arrangement. It is intended that a similar construction gearbox can also be used in the other embodiments.

[0195] In the embodiments of FIGS. 11-14, the construction and operation of the fixed base 106b, collar portion 502b and the various seals are similar to the explanations already provided with respect to FIG. 5.

[0196] Circumferentially surrounding the propeller 114b and the propeller gearbox is a propeller tunnel 506b. The propeller tunnel 506b has a flared tubular shape that extends in a direction parallel to the rotational axis of the propeller 114b and has a slightly larger inner diameter than the propeller 114b. The propeller tunnel 506b protects the propeller 114b from making contact with the seabed.

[0197] Connected to the bottom of the propeller tunnel is a hull plug 508b. The hull plug 508b has the same curvature as the hull, such that when the VRTT 100b is in the retracted configuration, the hull plug 508b fills the gap in the hull through which the VRTT protrudes when the VRTT is in the deployed configuration (as seen in the embodiment of FIG. 1). The hull plug 508b may have seals (not shown) around the outer edges to create a water sealing with the hull, when the VRTT 100b is in the retracted configuration.

[0198] In order to be installed within the hull (assuming that the inner diameter of the hull is 600 mm), the total vertical height of the VRTT 100b, from the top of the VRTT to the base of the propeller tunnel 506b is less than 600 mm, in a similar manner to the embodiments of FIGS. 1-6 and FIGS. 7-10.

[0199] As for the embodiment of FIGS. 7-10, the embodiments of FIGS. 11-14 allow the rotational axis of the propeller with respect to the longitudinal direction of the hull to be varied, at least when the thruster is in the deployed configuration. This is achievable due to a steering arrangement 200b that will now be described in more detail and has a modified construction compared with FIGS. 7-10. The effect of the steering arrangement is that the thruster can be used not only to provide lateral thrust but thrust in any direction in the horizontal plane. This allows the thruster to provide useful steering control of the boat in low speed manoeuvring, for example during mooring procedures.

[0200] Steering arrangement 200b provides the effect of rotating the thrust motor 112b, the drive shaft casing 118b, the propeller 114b and the tunnel 506b and hull plug 508b with respect to the moveable base 108b and the fixed base 106b. This rotation is around the axis of rotation A of the drive shaft, which in use is intended to be oriented in the vertical direction. Given that the fixed base 106b is for attachment with respect to the hull, the steering arrangement permits orientation of the thrust direction provided by the propeller in any direction within a plane perpendicular to axis A.

[0201] Thrust motor 112b is attached to motor mount plate 210b with the motor extending below the motor mount plate 210b within the drive shaft casing 118b as already described. Worm ring 218b is attached to the motor mount plate and ultimately to the drive shaft casing 118b via suitable screws. The drive shaft casing 118b is rotatable within aperture 109b formed through the movable base 108b.

[0202] Slew ring bearing 224b comprises an inner ring 226b and an outer ring 228b. Outer ring 228b is fixed with respect to the movable base 108b and the inner ring 226b is rotatable with respect to the outer ring 228b via bearings (not shown) which permit said rotation but which prevent relative axial translational movement between the inner ring and outer ring.

[0203] The drive shaft casing 118b is attached to the inner ring 226b. By this arrangement, the thrust motor 112b, motor mount plate 210b, worm ring 218b, drive shaft casing 118b and inner ring 226b of the slew ring bearing 224b are rotatable together about axis A relative to the movable base 108b and outer ring 228b of the slew ring bearing 224b.

[0204] Steering motor 230b has a horizontal rotational output at a steering motor output shaft (not shown) which drive worm gear 233b which meshes with worm ring 218b. Accordingly, operation of steering motor 230b rotates worm ring 218b via the worm gear 233b, which therefore causes rotation of the thrust motor 112b, motor mount plate 210b, drive shaft casing 118a and inner ring 226b of the slew ring bearing 224b together about axis A relative to the movable base 108b and outer ring 226b of the slew ring bearing 224b. Rotation of the drive shaft casing 118b through the fixed base 106b causes rotation of the propeller 114b and the tunnel 506b, allowing control of the direction of thrust from the propeller in the horizontal plane.

[0205] In other embodiments, it is possible for the VRTT not to include a steering arrangement but to use the thrust motor configuration shown in FIGS. 11-14. Accordingly, the embodiment of FIGS. 1-6 can be modified to use the thrust motor configuration shown in FIGS. 11-14.

[0206] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0207] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0208] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0209] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0210] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0211] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example +/−10%.