WO2025034123A1

WO2025034123A1 - A retractable wheel assembly for an amphibious watercraft

Info

Publication number: WO2025034123A1
Application number: PCT/NZ2024/050086
Authority: WO
Inventors: James John MORTON
Original assignee: Tectrax Ltd
Current assignee: Tectrax Ltd
Priority date: 2023-08-10
Filing date: 2024-08-07
Publication date: 2025-02-13
Anticipated expiration: 2026-02-10

Abstract

A retractable wheel assembly comprises a base member for connection to a hull of a watercraft and an electric actuator assembly connected to the base member. The actuator assembly comprises an elongate threaded portion arranged substantially parallel to the base member and a motor to rotate the threaded portion. At least one support rail is connected to the base member substantially parallel to the base member and to the threaded portion. A nut block is slidably engaged with the at least one support rail and threadingly engaged with the threaded portion. A leg member is rotatably connected to the base member and has a wheel at a distal end. A connecting member is rotatably connected to the nut block at a first end and rotatably connected to the leg member at a second end, intermediate the connection of the leg member to the base member and the wheel.

Description

A RETRACTABLE WHEEL ASSEMBLY FOR AN AMPHIBIOUS WATERCRAFT

1. FIELD OF THE TECHNOLOGY

The present invention relates generally to the field of amphibious watercraft, in a particular, to a retractable wheel assembly for such watercraft, and to an amphibious watercraft comprising at least one such assembly.

2. BACKGROUND TO THE TECHNOLOGY

Amphibious vehicles can generally be divided into two categories: primarily road focussed vehicles which have limited capacity to operate in the water (e.g. amphibious vehicles), and primarily inwater focussed vehicles which have limited capacity to operate on land (e.g. amphibious watercraft). In many cases the on-land capability of an amphibious watercraft is limited to allowing the craft to drive out of the water onto a beach or loading ramp, thereby simplifying launching and landing. Such craft are typically not intended for extended on-land transportation.

One limiting factor for the popularity of amphibious watercraft is a need to customise the design of the hull of the watercraft to allow for provision of a plurality of wheel assemblies. Since amphibious watercraft are sold in lower volumes than their non-amphibious equivalents, the need to create a custom hull design means that it is difficult to achieve economies of scale in the production of the hulls, thereby driving up costs.

For efficient on-water performance, it is important that hydrodynamic drag is reduced. To this end, most amphibious watercraft comprise mechanisms to move the wheels of the craft at least partially above the waterline when the watercraft is in use on the water.

Many prior art amphibious watercraft designs use hydraulic actuators to extend and retract the wheel assemblies and to drive at least one of the wheels. This results in the need for a large hydraulic power pack and motor which can take up significant space within the hull. Hydraulic actuation also leads to a risk of spillage of hydraulic oil in the event of a failure, which can have adverse environmental consequences. In many cases, the hydraulic systems of the prior art amphibious watercraft is specified to be able to raise and lower the wheel assemblies while the vessel is in the water (e.g. while at least part of the weight of the vessel is supported by buoyancy forces) but are not sufficiently powerful to move the assemblies from a retracted or partially retracted configuration to a fully extended configuration while the vessel is on land.

3. OBJECT OF THE TECHNOLOGY

It is an object of the technology to provide a retractable wheel assembly for an amphibious watercraft which does not use hydraulics. Alternatively, it is an object of the technology to provide a retractable wheel assembly for an amphibious watercraft which is relatively compact. Alternatively, it is an object of the technology to provide a retractable wheel assembly for an amphibious watercraft which is easy to install on and/or retrofit to a hull of a watercraft.

Alternatively, it is an object of the technology to overcome or ameliorate at least one problem with the prior art and/or to at least provide the public with a useful choice.

4. SUMMARY OF THE TECHNOLOGY

According to one form of the technology there is provided a retractable wheel assembly for an amphibious watercraft comprising:

- a base member configured for connection to a hull of the watercraft,

- an electric actuator assembly connected to the base member, the actuator assembly comprising an elongate threaded portion arranged substantially parallel to the base member and a motor configured to rotate the threaded portion;

- at least one support rail connected to the base member and arranged substantially parallel to the base member and to the threaded portion,

- a nut block slidably engaged with the at least one support rail and threadingly engaged with the threaded portion,

- a leg member rotatably connected to the base member and including a wheel at a distal end to the connection, and - a connecting member rotatably connected to the nut block at a first end and rotatably connected to the leg member at a second end, wherein the connection between the connecting member and the leg member is intermediate the connection of the leg member to the base member and the wheel.

In examples: the base member comprises a flat plate; the base member comprises a mounting face, wherein the elongate threaded portion is provided on the opposite side of the base member to the mounting face; the assembly comprises a first support rail on a first side of the elongate threaded portion, and a second support rail provided on a second side of the elongate threaded portion, opposite the first side; the electric actuator comprises an actuator motor provided on the same side of the base member as the mounting face; a gearbox is provided between the actuator motor and the elongate threaded portion; the gearbox is provided adjacent one end of the base member; the gearbox may extend through the base member; the leg member comprises a first leg portion comprising a steering actuator, and a second leg portion mounted to the steering actuator so as to be rotatable relative to the first leg portion about a steering axis, the second leg portion comprising the at least one wheel; the leg member is bifurcated to define a first forked portion and a second forked portion spaced apart from the first forked portion, and the connecting member extends between the first and second forked portions; the assembly comprises a waterproof housing over the elongate threaded portion; the assembly comprises a flexible waterproof cover member connected to the waterproof housing, where the waterproof cover member extends over at least a portion of the connecting member; and/or the flexible waterproof cover member is provided with a concertina formation to increase its flexibility and its ability to extend and contract;

According to another form of the technology there is provided an amphibious watercraft comprising at least one retractable wheel assembly of the first form of the technology.

In examples; the watercraft comprises a single retractable wheel assembly at the bow of the watercraft and a pair of retractable wheel assemblies at the stern of the watercraft; the wheel assemblies are configured such that the wheels of each assembly are substantially above a waterline of the watercraft when the wheel assemblies are in a retracted configuration; the watercraft does not include any hydraulically actuated wheel assembly components; and/or the watercraft comprises a battery and a control box within the hull.

Further aspects of the technology, which should be considered in all its novel aspects, will become apparent to those skilled in the art upon reading of the following description which provides at least one example of a practical application of the technology.

5. BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the technology will be described below by way of example only, and without intending to be limiting, with reference to the following drawings, in which:

Figure 1 is a side view of an amphibious watercraft comprising bow and stern retractable wheel assemblies according to one example of the invention.

Figure 2 is an isometric view of the bow wheel assembly of the watercraft of Figure 1 in a fully extended configuration.

Figure 3 is a view from the starboard side of the bow wheel assembly of Figure 2, in the extended configuration. Figure 4 is a view from the port side of the bow wheel assembly of Figure 2, with the watertight housing and flexible cover removed.

Figure 5 is a view from the starboard side of the bow wheel assembly of Figure 2, with the watertight housing and flexible cover removed.

Figure 6 is a front view of the bow wheel assembly shown in Figure 2, with the watertight housing and flexible cover member removed.

Figure 7 is a rear view of the bow wheel assembly shown in Figure 2, with the clamping member removed.

Figure 8 is an exploded view of the watertight housing and flexible cover member of the bow wheel assembly shown in Figure 2.

Figure 9 is an enlarged view of the first end of the base member of the bow wheel assembly, with the watertight housing and clamping member removed.

Figure 10 is a view from the port side of the bow wheel assembly shown in Figure 2 in the fully retracted position.

Figure 11 is an isometric view of the bow wheel assembly shown in Figure 2, in a fully retracted configuration.

Figure 12 is a view from the port side of the stern wheel assembly of the watercraft shown in Figure 1 , in a fully extended configuration.

Figure 13 is a front view of the stem wheel assembly of Figure 12.

Figure 14 is a rear view of the stern wheel assembly of Figure 12, with the watertight housing and flexible cover member removed.

Figure 15 is an isometric view of the stern wheel assembly of Figure 12, with the watertight housing and flexible cover member removed.

Figure 16 is a view from the starboard side of the stern wheel assembly of Figure 12.

Figure 17 is a view from the port side of the stern wheel assembly shown in Figure 12, in a fully retracted configuration.

Figure 18 is a view from the port side of the stern wheel assembly shown in Figure 12, in a fully retracted configuration, with the watertight housing and flexible cover member removed.

Figure 19 is an isometric view of the stern wheel assembly shown in Figure 12, in a fully retracted configuration, with the watertight housing and flexible cover member removed. Figure 20 is a cross-section side view of a base member and actuator of a stern wheel assembly according to another form of the technology, with the housing removed for clarity.

Figure 21 is a side view of a bow wheel assembly in an extended configuration according to another form of the technology.

Figure 22 is an isometric view of the bow wheel assembly of Figure 21, with a gearbox cover portion removed.

6. BRIEF DESCRIPTION OF EXEMPLARY FORMS OF THE TECHNOLOGY

Referring first to Figure 1, an amphibious watercraft 100 is shown having a hull 1 and a least one retractable wheel assembly 200. In the example shown the watercraft 100 has at least one first or bow retractable wheel assembly 201 connected to the hull 1 at the bow 2, and a plurality of second or stern retractable wheel assemblies 202 (only one of which is visible in Figure 1) connected to the hull 1 at the stern 3 of the watercraft. Typically, such a watercraft 100 may have a single bow wheel assembly 201 and a pair of stern wheel assemblies 202, although other configurations are possible, for example a pair of bow wheel assemblies 201 and a pair of stern wheel assemblies 202.

Referring next to Figures 2-11, an exemplary retractable wheel assembly 200 configured as a bow wheel assembly 201, is shown.

The bow wheel assembly 201 comprises a base member 4 which comprises a substantially planar mounting face 5, best seen in Figures 7 and 9. The base member 4 is configured for connection to a hull 1 of the watercraft 100. In the example shown, the base member 4 is a substantially rectangular member, e.g. an aluminium plate. In use, the base member 4 is mounted to a suitable portion of the hull 1. In one example, a clamping member 6 is engaged with the base member 4 (e.g. by suitable fasteners 7 such as studs and nuts), to clamp the base member 4 to a suitable portion of the hull 1.

An electric actuator 300 is connected to the base member 4. In one example the actuator 300 comprises an electric motor 10, a gearbox 12, and an elongate threaded portion 14 (e.g. a lead screw). The gearbox 12 may be provided at a first end 8 of the base member 4. The elongate threaded portion 14 extends substantially parallel to the base member 4, e.g., parallel to the plane of the base member 4, and substantially parallel to a central axis A of the base member 4 (see Fig. 6). The threaded portion 14 may be supported by a bearing block 16 provided at the distal end of the threaded portion 14 to the gearbox 12. In examples, a second bearing block 18 is also provided adjacent the actuator motor 10 and gearbox 12, whereby the threaded portion 14 extends through the second bearing block 18.

As best seen in Figure 9, in one example the electric motor 10 is connected to the mounting face 5 of the base member 4 (or at least to the same side of the base member 4 as the mounting face 5) and the gearbox 12 extends through the base member 4. This configuration may assist in keeping the actuator 300 compact.

In examples, at least one support rail 20 (preferably a pair of support rails 20) is provided substantially parallel to the threaded portion 14. The, or each, support rail 20 may extend between the bearing blocks 16, 18. In examples, the support rails 20 have a substantially uniform cross-section, for example a circular cross-section.

A nut block 22 is threadingly engaged with the elongate threaded portion 14 of the actuator, and slidably engaged with the or each support rail 20, such that rotation of the elongate threaded portion 14 causes movement of the nut block 22 along the elongate threaded portion 14, either toward or away from the first end 8 of the base member 4.

A leg member 24 is rotatably connected to the base member 4 at a second end 26 of the base member 4, opposite the first end 8, for example by a hinge connection 27. At least one wheel 28 is provided at the distal end 30 of the leg member 24 to the connection 27 with the base member 4. In many examples, the leg member 24 comprises a first portion 32 and a second portion 34, wherein the second portion 34 is rotatable relative to the first portion 32 about as steering axis S (see Fig. 6) which is substantially parallel to the central axis A of the first portion 32, to thereby allow the wheel 28 to be steered. In examples, the first portion 32 comprises a steering actuator 36, e.g. a rotary actuator, more preferably an electric rotary actuator (see Fig. 11) and the second portion 34 is connected to the steering actuator 36. In examples the second portion 34 is substantially “L” shaped, such that the steering axis S passes through a centre of the wheel 28 (see Figure 6). In the example shown, the assembly 201 is configured such that the leg member 24 is substantially vertical when fully extended.

In examples, the wheel 28 is connected to a motor 38 (preferably an electric motor) which is configured to drive the wheel 28 when required. In some examples (not shown), each leg member 24 may be provided with a pair of wheels 28.

A connecting member 40 is rotatably connected to the nut block 22 at a first end of the connecting member, e.g. by a hinge joint 42, and to the leg member 24 at a second end of the connecting member 40, e.g. by a further hinge joint 44. The connecting member 40 is connected to the leg member 24 intermediate the rotatable connection 27 to the base member 4 and the wheel 28. In one example, the distance between the connection 27 of the leg member 24 to the base member 4 and the connection 44 between the connecting member 40 and the leg member 24 is approximately * of the distance from the connection 27 between the leg member 24 to the base member 4 and the connection of the leg member 24 to the wheel 28. In one example the leg member 24 is bifurcated so as to define spaced apart first and second forked portions 24a, 24b (see Fig. 6), and the connecting member 40 extends between the first and second portions forked 24a, 24b.

As shown in Figures 3 and 8, in examples a substantially watertight housing 50 is provided over the electric actuator 300. A suitable seal 52, e.g. a gasket (best seen in Fig. 6), may be provided between the watertight housing 50 and the base member 4, in order to prevent water ingress.

Referring next to Figure 8 in particular, the watertight housing 50 may be provided with an aperture 54 shaped to allow the connecting member 40 to extend through the housing 50 and to move over its entire range. The housing 50 may be made from a suitably rigid material such as a plastic.

A flexible cover member 56 (e.g. a “gaiter” or “boot”) may extend over at least a portion of (and preferably substantially the entirety of) the connecting member 40. Alternatively, the flexible cover may extend over the threaded potion 14 or a combination of the threaded portion 14 and one or more support rails 20. The flexible cover member may be made from a suitably flexible and/or stretchable material such as a rubber. The cover member 56 may be connected (e.g. in a substantially watertight manner) to the housing 50 at a first end, around the aperture 54, and may engage the connecting member 40 in a substantially sealing manner at the second end. The cover member 56 may be substantially watertight. In examples the cover member 56 may have a “concertina” configuration to increase its flexibility and its ability to extend and contract.

Referring next to Figures 10 and 11 in particular, in order to retract the wheel assembly 201 from the extended position shown in Figures 2-7 to the retracted position shown in Figures 10 and 11, the elongate threaded portion 14 is rotated by the electric actuator motor 10 in a direction which causes the nut block 22 to move away from the rotatable connection 27 between the base member 4 and the leg member 24 (e.g. toward the first end 8 of the base member 4). Since the leg member 24 is connected to the nut block 22 via the connecting member 40, the leg member 24 rotates around the rotatable connection 27 such that the wheel 28 moves towards the base member 4 to the retracted position. In one example, the leg member 24 rotates through substantially 100 degrees between the fully extended and fully retracted positions. An advantage of the actuator 300 described is that the nut block 22 (and hence the entire leg assembly 201) is effectively locked in position when the elongate threaded portion 14 is stationary. A further advantage is that the total length of the actuator 300, when the wheel assembly 201 is fully extended, is only slightly larger than the maximum distance of travel of the nut block 22 (conceptually equivalent to the “stroke” of a hydraulic linear actuator), meaning that the actuator 300 is compact. By contrast, the total length of a hydraulic linear actuator at full extension would necessarily be at least twice the length of the stroke of the actuator.

In one example of the invention, a bearing plate 58 (best seen in Figure 11) is connected to the base member 4 near the second end. The bearing plate 58 is configured to abut a surface of the nut block 22, opposite the connection of the nut block 22 to the connecting member 40, when the wheel assembly is in the fully extended position (see Figure 2). In this way the bearing plate 58 assists in transmitting forces from the connecting member 40 into the base member 4.

In examples, the wheel assembly 201 is configured such that the connecting member 40 is approximately perpendicular to the leg member 24 when the lowest part of the wheel 28 extends below the lowermost point of the hull 1 (e.g. during movement of the assembly 201 from the retracted to the extended configurations). This ensures that the actuator 300 has substantially optimal mechanical advantage when lifting the watercraft 100 on land. Those skilled in the art will appreciate that it is less important for the connecting member 40 to be perpendicular to the leg member 24 when the leg is nearly fully extended, since at this point the angle of the leg is close to vertical, and the tangential force necessary to continue the movement of the leg member 24 towards the fully extended (e.g. vertical) position is reduced.

Referring next to Figures 12-19, in another example a second or stern wheel assembly 202 may comprise substantially the same components as the first or bow wheel assembly 201. The second or stern wheel assembly 202 may differ from the first or bow wheel assembly 201 in the dimensions of the components, and the lack of provision for steering the wheel 28, meaning that the leg member 24 may be one piece, rather than an assembly of first and second portions 32, 34 (although in some examples the stern wheels may be steered using a similar mechanism to that described above in relation to the bow wheels). Furthermore, as shown in Figures 12-19, in examples of the second or stern wheel assembly 202 the actuator motor 10 may be provided on the same side of the base member 4 as the elongate threaded portion 14, rather than on the same side as the mounting face 5.

Some examples of a stern wheel assembly 202 may be made in a mirror image of that shown in Figures 12-19, e.g. such that for watercraft having two stem wheel assemblies 202, the wheel 28 of each assembly is on the outer side of the leg member 24 of the respective assembly.

The second wheel assembly 202 may be configured such that the base member 4 can be mounted in a more nearly vertical orientation than the base member 4 of the first wheel assembly. For example, the first wheel assembly may be configured such that the mounting face 5 is mounted to a surface which is between 10 and 25 degrees to the vertical, preferably around 20 degrees. The second wheel assembly be configured such that the mounting face 5 is mounted to a surface which is between 0 and 10 degrees to the vertical, preferably around 0 degrees (e.g. preferably substantially vertical).

In examples, the leg member 24 of the second wheel assembly may move through an angle of approximately 100 degrees between the fully extend configuration and the fully retracted configuration. In the example shown, the stern wheel assembly is configured such that the leg member 24 is at an angle of approximately 20 degrees to the vertical when fully extended. To illustrate how compact examples of the present invention may be, reference is made next to Figure 18. In one example a wheel assembly 202, when in a fully retracted configuration, may have an overall length L (when viewed parallel to the axis of rotation of the leg member 24) which is no more than 20% greater than the diameter D of the wheel 28. When fully retracted, the assembly 202 may have an overall height H (when viewed parallel to the axis of rotation of the leg member) which is no more than 20% greater than the diameter D of the wheel. In other examples, e.g. as shown in Figures 1-11, the overall length L of the fully retracted assembly may be no more than 100% greater than the overall length L, and the height H may be no more than 30% greater than the diameter D.

Referring next to Figure 20, a modified example of a retractable wheel assembly 200, shown as a second or stern wheel assembly 202 is shown. In this example a pair of compressible sleeves 62 may be provided over the elongate threaded portion 14, one on each side of the nut block 22. In one example the sleeves 62 have a concertina configuration to allow them to be compressed and expanded. The sleeves 62 may be made from a suitably flexible material such as a rubber.

The sleeves 62 may substantially prevent contaminants from impinging between the nut block 22 and the elongate threaded portion 14. In some examples, the sleeves 62 may be sealed at their upper and lower ends to prevent water ingress, but in other examples the sleeves are not sealed. The sleeves 62 may be used in combination with the housing 50 and/or cover member 56 described above, but this is not essential. In some examples where the sleeves 62 are used, the housing 60 and cover member 56 may also be used, but the cover member 56 may not be sealed to the connecting member 40. In some examples (not shown) similar pairs of sleeves 62 may be provided to each support rail 20.

Referring next to Figures 21 and 22, an alternative example of a first or bow wheel assembly 201 is shown. In this example a steering gearbox 64, for example a cycloidal gearbox, may be provided between the steering actuator 36 and the second leg portion 34. This may allow greater control of the steering when using an electric steering actuator.

Referring back to Figure 1, in examples only minor modifications to the hull 1 of a watercraft 100 may be required to allow for mounting of the first and second retractable wheel assemblies 201, 202. In the example shown, an aperture 60 is provided at the bow 2 of the hull 1, above the waterline, to allow the first end 8 of the base member 4 of the first or bow wheel assembly 201 to extend inside the hull 1. However, in other examples (e.g. those with a more steeply raked prow) it may not be necessary to modify the hull 1 in this way.

As can also be seen in Figure 1, in examples, it may not be necessary to penetrate the stern of the vessel (other than as required for the fasteners) in order to mount the second or stern wheel assemblies 202. Because of the relatively minor modifications necessary to mount the wheel assemblies 201, 202 of the present invention to the hull 1, substantially the same basic hull construction may be used for both amphibious and non-amphibious examples. Furthermore, leg assemblies 200 of the present invention may be particularly suitable for retrofitting to existing watercraft. In examples, the legs and actuators are connected to the hull exclusively through the base member 4, that is, it is not necessary to provide other mounts for actuators or leg components to the hull 1.

In one non-limiting example, an amphibious watercraft 100 of the present invention as shown in Figure 1 may have a displacement of approximately 2000kg. The watercraft 100 may be provided with a single bow wheel assembly 201 of the present invention and a pair of stern wheel assemblies 202 of the present invention. The electric motor 10 of each wheel assembly 201, 202 may be configured to generate a maximum torque of 3Nm, and may generate a maximum torque of 150Nm at the lead screw. In such an example, the wheel assemblies 201, 202 may be configured such that they are able to move from a partially retracted configuration (whereby the hull 1 of the watercraft 100 is almost resting on the ground) to a fully extended configuration when the watercraft 100 is entirely out of the water (e.g. is not supported by the water). This may assist in allowing users to embark and disembark when the watercraft 100 is on land, and load the boat onto a flat trailer on land for transport.

In examples, the actuators/motors for the wheel assemblies, including the steering actuator and the drive actuators, may all be electric. A battery and a control unit (not shown) for the wheel assemblies may be provided within the hull. This may simplify the process of fitting the actuators to the hull 1 in comparison to examples in which one or more of the actuators are hydraulic, and may also eliminate the possibility of hydraulic oil spillage. 6.1. Other Remarks

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to”.

The entire disclosures of all applications, patents and publications cited above and below, if any, are herein incorporated by reference.

Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavour in any country in the world.

The technology may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features.

Where in the foregoing description reference has been made to integers or components having known equivalents thereof, those integers are herein incorporated as if individually set forth.

It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the technology and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be included within the present technology.

Claims

7. CLAIMS

1. A retractable wheel assembly for an amphibious watercraft comprising: a base member configured for connection to a hull of the watercraft; an electric actuator assembly connected to the base member, the actuator assembly comprising an elongate threaded portion arranged substantially parallel to the base member and a motor configured to rotate the threaded portion; at least one support rail connected to the base member and arranged substantially parallel to the base member and to the threaded portion; a nut block slidably engaged with the at least one support rail and threadingly engaged with the threaded portion; a leg member rotatably connected to the base member and including a wheel at a distal end to the connection; and a connecting member rotatably connected to the nut block at a first end and rotatably connected to the leg member at a second end, wherein the connection between the connecting member and the leg member is intermediate the connection of the leg member to the base member and the wheel.

2. The retractable wheel assembly of claim 1 , wherein the base member comprises a flat plate.

3. The retractable wheel assembly of claim 1 or 2, wherein the base member comprises a mounting face, wherein the elongate threaded portion is provided on the opposite side of the base member to the mounting face.

4. The retractable wheel assembly of claim 3, wherein the electric actuator comprises an actuator motor provided on the same side of the base member as the mounting face.

5. The retractable wheel assembly of any one of claims 1 to 4, wherein the assembly comprises a first support rail on a first side of the elongate threaded portion, and a second support rail provided on a second side of the elongate threaded portion, opposite the first side.

6. The retractable wheel assembly of any one of claims 1 to 5, wherein a gearbox is provided between the actuator motor and the elongate threaded portion.

7. The retractable wheel assembly of claim 6, wherein the gearbox is provided adjacent one end of the base member.

8. The retractable wheel assembly of claim 6 or 7, wherein the gearbox extends through the base member.

9. The retractable wheel assembly of any one of claims 1 to 8, wherein the leg member comprises a first leg portion comprising a steering actuator, and a second leg portion mounted to the steering actuator so as to be rotatable relative to the first leg portion about a steering axis, the second leg portion comprising the at least one wheel.

10. The retractable wheel assembly of any one of claims 1 to 9, wherein the leg member is bifurcated to define a first forked portion and a second forked portion spaced apart from the first forked portion, and the connecting member extends between the first and second forked portions.

11. The retractable wheel assembly of any one of the preceding claims, wherein the assembly comprises a waterproof housing over the elongate threaded portion.

12. The retractable wheel assembly of claim 11, wherein the assembly comprises a flexible waterproof cover member connected to the waterproof housing, where the waterproof cover member extends over at least a portion of the connecting member.

13. The retractable wheel assembly of claim 11, wherein the flexible waterproof cover member is provided with a concertina formation to increase its flexibility and its ability to extend and contract.

14. An amphibious watercraft comprising at least one retractable wheel assembly according to any one of claims 1 to 13.

15. The amphibious watercraft of claim 14, comprising a single retractable wheel assembly at the bow of the watercraft and a pair of retractable wheel assemblies at the stern of the watercraft.

16. The amphibious watercraft of claim 15, wherein the wheel assemblies are configured such that the wheels of each assembly are substantially above a waterline of the watercraft when the wheel assemblies are in a retracted configuration.

17. The amphibious watercraft of claim 14, 15 or 16, wherein the watercraft does not include any hydraulically actuated wheel assembly components.

18. The amphibious watercraft of any one of claims 14 to 17, wherein the watercraft comprises a battery and a control box within the hull.