AMPHIBIOUS CRAFT The present invention relates to amphibious craft and particularly to a boat adapted to be driven on land. Whilst amphibious vehicles are not new, most are in the form of amphibious motor cars (or armoured vehicles). One of the main problems with this configuration is that the volume of the car is small in relation to its weight, consequently when in water the vehicle will be deeply immersed. Haivng little freeboard the vehicle can easily be swamped in any knid of rough waer. There is also an insecurity for the occupants in being so low in the water. The design of a car is not approprate for water travel and therefore a speed only, in the region of 5 mph is possible in use. One example of such a vehicle is disclosed in U.K. Patent specification No 2134857B. In this vehicle both pairs of wheels are mounted on full width axles, the axles and wheels all being raised and lowered as a unit. The object of the present invention is to provide a boat that will perform well in water and will also perform well as a driven vehicle on land.

According to the present invention there is provided an amphibious craft having a hull and wheels for supporting the hull on land at least one pair of which is driveable by a motor on the craft, the craft comprising means for retracting the wheels into compartments in the hull, wherein the driven wheels are mounted on respective rotatable stub axles which stub axles are driven independently from one another via respective drive transmission mechanisms.

Advantageously the drive transmission mechanism for each wheel is housed in a respective rigid casing which casing also forms the main strut for the wheel when in use. The drive transmission mechanism may for example

include a chain and sprockets, or a system of bevel gears and shafts.

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

Figure 1 is a side view of an amphibious craft according to the invention.

Figure 2 is a schematic section view in plan of the craft of Figure 1 showing alternate engine positions, Figure 3 is a schematic view from inside the craft of a rear wheel retracted for water travel,

Figure 4 is a perspective view of the housing of Figure

3,

Figure 5 is a schematic view of the rear wheel of Figure 3 lowered for land use,

Figures 6a,6b, and 6d_,present an exploded view of the transmission arm of Figure 3,

Figure 6c_, is an alternative device for use instead of

6b, Figure 7 is a schematic front section showing one embodiment of the front wheel retraction mechanism and

Figures 8a_ _r 8b_- 8c_, and 8d _. , are schematic partial views of a second retraction mechanism for the front wheels.

The drawings illustrate an amphibious craft in the form of a boat converted so as to provide a means of driving the craft on land on wheels. The operation of the boat in water is substantially unimpaired other than due to the extra weight carried. The profile is unaltered and the drag is not substantially increased. The boat in water is driven either by an inboard motor normally in an aft position (such as shown at Y in Figure 2) or by an outboard motor (not shown). Where an inboard motor is used it could also power the wheels for use of the craft on land. If one or more outboard motors

is used on the boat, a secondary motor such as that shown at X would have to be provided to drive the wheels. In either case the boat wheels are driven in a manner similar to those on an automobile through a gear box G, a shaft S, a differential 14 and a shaft 15. Inboard brakes 10 would also be provided.

The wheels on the boat comprise a pair of steerable forward wheels designed to carry one third of the weight of the boat and set one either side of a keel 12 in the bow of the boat; and two drivable rear wheels 13 designed to carry two thirds of the weight of the boat. The rear wheels 13 are positioned on opposed sides of the boat inside the line of the hull. The use of a pair of forward wheels leaves the keel unimpaired in strength and so does not interfere with the strength of the boat structure.

In the present embodiment the differential 14 is situated between the rear wheels 13 and operates to transfer power from one of the motors X,Y, via respective shafts S1,S2 to drive shafts 15. The drive shafts 15 operate to drive the wheels indirectly via a respective drive transmission mechanism as will be described hereinafter with reference to Figure 6.

Each . rear wheel is housed in a respective box 16 providing a compartment attached to the inside of the . hull. The fitting of the box to the hull is entirely watertight so that water entering the compartment will not enter the boat. The compartment is closed by sliding doors (not shown) which need not be watertight. The top of the compartment is situated well above the water line and therefore any water seeping past the doors will remain in the compartment at a level equal to or below the water level outside the hull.

The box is strengthened by a metal frame reinforced where necessary. The frame inhcludes ribs formed by

metal bars and tubes including a T-bar 19 and an angle iron 21, both running longitudinally up the sloping top of the box 16. The angle iron 21 also includes a reinforcement flange 22. A bracket 30 is bolted to the reinforcement flange 22 for supporting the casing 27 described hereinafter. The flange 22 is apertured to allow access for the shaft 15 into the compartment.

When the wheels are lowered for land use the weight of the boat causes local stress on the points of contact between the wheel supports and the box 16. This stress is distributed throughout the width of the boat by the ribs 19,21 and by two fabricated cross-beams 24,25. The cross beams are held across the top of the box 16 by metal plates 26 fixed to the hull 18. The beams 24,25 are also fixed to fittings (not shown) at the bottom of the boat.

Power is transferred from the drive shaft 15 to a driven rear wheel stub axle (20) via a drive transmission mechanism housed in a rigid casing or transmission arm 27. The casing 27 also forms a pivot arm and main support for the wheel 13. The drive transmission mechanism can be of any appropriate type suitable to transfer rotation from the shaft 15 to drive the wheel stub axle. Two examples are shown. Figure 6b shows sprockets 28 which are fitted to the shaft 15 and sprockets 29 which are fitted to the wheel stub axle. The sprockets 29 are driven from the sprockets 28 by means of single or multiple chains 31. Figure 6c shows an alternative mechanism in the form of bevel gearing between the other end of the arm 33 and the wheel stub axle.

Each casing forms a watertight housing for the chosen drive transmission and comprises an elongate box 27a with cylindrical ends, having a lid 27b which is removably fitted with bolts via holes 35. The box 27a. is

apertured at 36 for the shaft 15 and at 37 for the wheels stub axle. The lid 27b has a single aperture 38 opposite the aperture 36 to receive the shaft 15. The casing 27 is sealed watertight and incorporates a quantity of lubricating oil which also acts to protect the drive transmission from corrosion.

The casing, which acts as a strut and pivot arm for the wheel 13, is pivotally mounted at each end respectively to the box 16 and the wheel 13. The mounting to the box includes a bracket .30 firmly fixed to the underside of the box and bolted to the T-bar and the bracket (not shown) bolted to the angle iron 22. The pivotal movement is controlled by a hydraulic ram 39,which can be remotely actuated, and is connected between a pivotal mounting 40 bolted to the T-bar 19 and a suitable pivotal mounting on the casing 27. Extension of the ram lowers the wheel 13, the weight of the boat being supported by the ram and the casing 27. Retraction of the ram 39 raises the wheel 13 into the compartment 16 until the casing is substantially horizontal. The casing is sealed for normal use but can be opened for repair and maintenance.

The front wheels 11 are supported on stub axles (41a) mounted on a forked wheel support or "forks" 41, the upper end of which is in the form of a square- sectioned collar 42. The collar 42 is slidably mounted on a square-sectioned central pillar 43, the upper and lower ends of which pillar are pivotally mounted to the boat structure at 44 and 45. The pillar 43 is pivoted to steer the craft on land by movement of a steering arm 46 which action turns the collar 42 to turn the wheels 11. When the wheels are in the lowered position they can be held in position by security locks. The wheels are raised and lowered by a hydraulic ram (not shown) which operates between respective brackets on the pillar and

collar. The pillar, the collar and the ram form elements of a retraction mechanism for the wheels.In the raised position the wheels are stowed in a watertight compartment in the bow of the boat. As with the rear wheels the fitting of the doors need not be watertight. hen the compartment is closed the profile of the boat is maintained^by two doors 47 hinged at 48 which are closed against the bottom 49 of the boat. The actual portion of the bottom of the boat that is cut away to form the doors 47 is important as sufficient room must be left for the wheel "forks" 41 to turn the wheels in the lowered position without collision or interference with or from the boat structure.

The arrangement of the steering arm above the water line of the boat makes for a simpler mechanism. Moreover with this sliding collar arrangement the wheels can be steered successfully in any position of the collar on the pillar.

In some boats there may not be sufficient room for a large front wheel compartment with the wheel "forks" 41 stored substantially vertically. Figure 8 shows an alternative arrangement to cater for storage in a smaller deck to keel depth. Each drawing shows only part of the arrangement and it may be necessary to refer to Figure 7 to understand the whole.

Figure 8a is a front view of the lower part of the mechanism showing the wheel forks 41 and one wheel 11. The wheel "forks" 41 are pivotally mounted at 51 to the collar 42 and are connected together by a bar 52. Respective bars 53 are pivotally mounted to opposed sides of the bar 52 at one end and at the other end 50 are pivotally mounted to opposed sides of the central pillar 43. A shoulder 54 on the collar 42 provides a lower mounting point for the ram now shown at 55 and the pivotal mounting of the central pillar 43 to the keel 12

is also shown. Figure 8b is a side view of Figure 8a showing the central area of the mechanism with the wheels in the lowered position. It will be noted that as the ram 55 draws the collar 42 up until it abuts the pivotal mounting 50 the pivoted bars operate as a lever mechanism to lift the wheels until the "forks" 41 lie along the line of the boat substantially horizontally.

Figure 8c illustrates the connection of the central pillar 43 at the upper end of the pillar. The same pivotal connection and height adjustment pieces and fillers may be used at the lower pivotal mounting 45. The connection comprises a sub-assembly of a mounting block 56, a thrust bearing 57 and a nut 61. The upper race of the thrust bearing 57 has a pivot mounting 58 for attachment to the deck. The lower race of the bearing 57 is located by a threaded bolt portion 59. The bolt 59 is threaded through the centre of the mounting block 56 and is screw threaded into the nut 61. This sub-assembly is then fitted into the top end of the pillar 43 to which it is bolted via holes 63 in the block and 64 in the pillar. The length of the pillar 43 is selected in accordance with the distance between the deck (or strong mounting) and the keel on any particular boat and any fine adjustment to the fitting is achieved using shims (not shown).

In each case the hydraulic ram is connected to a hydraulic pump powered by the motor X or Y or alternatively driven by an electric motor on the craft. It is envisaged that the craft will not be expected to travel more than 25 miles per hour on land. In this case floatation tyres can be used absolving the need for suspension. If a greater land speed is required then higher pressure road tyres will be needed and probably

some springing or other suspension. The gearing in the chain casing 27 and the gear box G can be of any desired ratio.