Multi-link suspension for multi-hulled vessels

Abstract

A suspension system for a water craft, the water craft including a chassis which is at least partially suspended above or relative to at least a first hull and a second hull. The suspension system includes a first hull locating arrangement for at least partially constraining the first hull in a lateral, a yaw, a roll and a longitudinal direction relative to the chassis, the first hull locating arrangement comprising a first, a second, a third and a fourth link arranged to directly or indirectly connect between the hull and the chassis. The first, second and third links each extend in at least a lateral direction relative to the chassis and contribute to a lateral constraint on the first hull relative to the chassis. The second link is longitudinally spaced from the first link relative to the chassis to contribute to a hull yaw constraint on the first hull relative to the chassis. The third link is vertically spaced from the first and/or second link to contribute to a hull roll constraint on the first hull relative to the chassis. The fourth link extends in at least a longitudinal direction relative to the chassis to at least contribute to a longitudinal constraint on the first hull relative to the chassis and may be adjustable in length to vary the lateral spacing between the first and second hulls and thereby vary the overall width of the vessel.

Claims

1. A suspension system for a water craft, the water craft including a chassis and at least a first hull and a second hull, the suspension system including a first hull locating arrangement for at least partially constraining the first hull in a lateral, a yaw, a roll and a longitudinal direction relative to the chassis, the first hull locating arrangement comprising a first, a second, a third and a fourth link arranged to directly or indirectly connect between the hull and the chassis, the first, second and third links each extending in at least a lateral direction relative to the chassis and contributing to a lateral constraint on the first hull relative to the chassis, the second link being longitudinally spaced from the first link relative to the chassis to contribute to a hull yaw constraint on the first hull relative to the chassis, the third link being vertically spaced from the first and/or second link to contribute to a hull roll constraint on the first hull relative to the chassis, the fourth link extending in at least a longitudinal direction relative to the chassis to contribute to a longitudinal constraint on the first hull relative to the chassis.

2. A suspension system as claimed in claim 1 further including variable length supports between the chassis and the at least two hulls for providing at least partial support of the chassis relative to the at least two hulls.

3. A suspension system as claimed in claim 2 wherein at least one of said variable length supports includes a support cylinder for providing support and damping forces.

4. A suspension system as claimed in claim 2 wherein at least one of said variable length supports includes an electromagnetic actuator, an air spring or a mechanical spring.

5. A suspension system as claimed in claim 2 wherein at least one of said variable length supports is connected between the chassis and the first hull.

6. A suspension system as claimed in claim 2 wherein at least one of said variable length supports is connected between the chassis and one of the first, second, third or fourth links.

7. A suspension system as claimed in claim 2 wherein at least one of said variable length supports is connected between the first hull and one of the first, second, third or fourth links.

8. A suspension system as claimed in claim 1 wherein each of said respective first, second, third and fourth links is connected to the chassis by a respective first, second, third and fourth chassis joint and is connected to the hull by a respective first, second, third and fourth hull joint.

9. A suspension system as claimed in claim 8 wherein at least one of said chassis or hull joints provides substantially linear motion constraints and permits at least limited rotational motion.

10. A suspension system as claimed in claim 8 wherein each of said four links includes a chassis joint and a hull joint.

11. A suspension system as claimed in claim 8 wherein two chassis joints of the first, second, third or fourth chassis joints are combined or wherein the fourth hull joint and one of the first, second or third hull joints are combined.

12. A suspension system as claimed in claim 8 wherein the hull joint of the fourth link is fixed to one of the first, second or third links or wherein the chassis joint of one of the first, second or third links is fixed to the fourth link.

13. A suspension system as claimed in claim 8 wherein at least one of the first, second and third hull joints connect the respective link to an up-stand projecting above the first hull.

14. A suspension system as claimed in claim 8 wherein the third link is longitudinally spaced between the first and second links.

15. A suspension system as claimed in claim 8 wherein the fourth link is positioned nearer to the bow of the first hull than the stern of the first hull, the fourth hull joint of the fourth link being forward of the fourth chassis joint of the fourth link.

16. A suspension system as claimed in claim 8 wherein the fourth link is positioned nearer to the stern of the first hull than the bow of the first hull, the fourth hull joint of the fourth link being rearward of the fourth chassis joint of the fourth link.

17. A suspension system as claimed in claim 1 wherein a length of the third link is different from a length of the first and/or second link to adjust the roll attitude of the hull relative to the chassis as the hull is displaced vertically relative to the chassis.

18. A suspension system as claimed in claim 1 wherein the fourth link is connected directly or indirectly to the chassis by a fourth chassis joint and is connected directly or indirectly to the hull by a fourth hull joint, the fourth chassis joint being above the fourth hull joint at a ride height.

19. A suspension system as claimed in claim 1 wherein the fourth link includes a length adjustment device for adjusting the length of the fourth link between a fourth chassis joint and a fourth hull joint, or wherein the fourth link is length adjustable by a length adjustment device such that a straight line distance between the fourth chassis joint and the fourth hull joint may be adjusted.

20. A suspension system as claimed in claim 19 wherein the length adjustment device is adjustable between a wide hull spacing position and a narrow hull spacing position where in the wide hull spacing position the first hull is spaced further away from a centre-line of the chassis than in the narrow hull spacing position.

21. A suspension system as claimed in claim 20 wherein in the wide hull spacing position at least one of the first, second or third links also extend in a longitudinal direction relative to the chassis.

22. A suspension system as claimed in claim 20 wherein in the narrow hull spacing position at least one of the first, second or third links also extend in a longitudinal direction relative to the chassis.

23. A suspension system as claimed in claim 20 wherein first supports are arranged between the chassis and the first hull or any of the first, second, third or fourth links, each support being effectively connected to the chassis by a chassis mounting point and effectively connected to the hull by a hull mounting point on the first hull or on any of the first, second third or fourth links, the chassis and hull mounting points being arranged such that when adjusting the length adjustment device of the fourth link from the wide hull spacing position to the narrow hull spacing position, an inclination of each support is increased, reducing a vertical support force relative to the chassis so that a height of the chassis relative to the hulls is reduced.

24. A suspension system as claimed in claim 19 wherein the fourth link also extends in a lateral direction relative to the chassis.

25. A suspension system as claimed in claim 1 wherein the fourth link of the first hull locating arrangement is length adjustable and wherein adjusting a length of the fourth link displaces the first hull laterally and longitudinally relative to the chassis.

26. A water craft including the suspension system of claim 1.

27. A multi-hulled vessel or water craft including a chassis, two moveable hulls and a suspension system, the suspension system including a respective hull locating arrangement for each respective moveable hull to provide linear and rotational constraints on motion of the hull relative to the chassis, wherein one or each of the respective hull locating arrangements comprises four links, each link being connected directly or indirectly between the respective hull and the chassis, the four links consisting of a first, second, third and fourth link, each link having a chassis joint between the link and the chassis and a hull joint between the link and the hull or one of the other of the four links, the first and second links each extending in at least a lateral direction relative to the chassis, the second link being longitudinally spaced from the first link relative to the chassis, at least the fourth link extending in at least a longitudinal direction, the fourth link providing a longitudinal constraint on motion of the respective hull relative to the chassis, the first second and third links adding a lateral, a yaw and a roll constraint on motion of the respective hull relative to the chassis, such that pitch and heave motions of the respective hull relative to the chassis are not constrained.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) In the drawings:

(2) FIG. 1 is a perspective view of water craft including a suspension system according to the present invention.

(3) FIG. 2 is a perspective view of the hulls and suspension system of the water craft of FIG. 1.

(4) FIG. 3 is a plan view of the water craft of FIG. 1.

(5) FIG. 4 is a side view of the water craft of FIG. 1.

(6) FIG. 5 is a perspective view of the water craft of FIG. 1 with the hulls articulated in the warp mode.

(7) FIG. 6 is a side view of the water craft of FIG. 1 with the hulls articulated in the roll mode.

(8) FIG. 7 is a plan view of the water craft of FIG. 1 in a narrow track configuration.

(9) FIG. 8 is a side view of the water craft of FIG. 7.

(10) FIG. 9 is a schematic view of a variation to the hull and associated suspension system of FIGS. 1-4.

(11) FIG. 10 is a schematic view of a variation to a hull and associated suspension system.

(12) FIG. 11 is a schematic view of a further variation to a hull and associated suspension system.

(13) FIG. 12 is a side view of a water craft including a suspension system according to the present invention.

(14) FIG. 13 is a plan view of the water craft of FIG. 12.

(15) FIG. 14 is an end view of the front suspension of the water craft of FIG. 12 at full extension.

(16) FIG. 15 is an end view of the front suspension of the water craft of FIG. 12 at a ride height.

(17) FIG. 16 is an end view of the front suspension of the water craft of FIG. 12 at full compression.

(18) FIG. 17 is an end view of the rear suspension of the water craft of FIG. 12 at full extension.

(19) FIG. 18 is an end view of the rear suspension of the water craft of FIG. 12 at a ride height.

(20) FIG. 19 is an end view of the rear suspension of the water craft of FIG. 12 at full compression.

(21) FIG. 20 is a side view of the water craft of FIG. 12 at full extension.

(22) FIG. 21 is a side view of the water craft of FIG. 12 at full compression.

DESCRIPTION OF PREFERRED EMBODIMENT

(23) Referring initially to FIG. 1, there is shown a water craft 1 having a body portion or chassis 2 shown in dashed lines and transparency to enable the left and right hulls 3 and 4 and the suspension system 5 to be more revealed.

(24) Throughout the specification where the term chassis is used it is referring to the structure to which the hulls are located by the suspension system and can be interchangeable with the term body portion. The chassis can be a simple platform or include gunwales, a passenger cabin, cargo area. For example, as in automotive use, the chassis can be a ladder frame, or it can combine a ladder frame with a fixed cabin where the suspension loads are primarily input into the ladder frame, or it can be a monocoque where the suspension loads are input into a shell structure including the cabin. The water craft is shown at ride height, i.e. somewhere between the maximum and minimum height of the chassis above the hulls, typically between 30 and 70% of that total travel between maximum and minimum height. FIG. 2 shows the same view with the body portion or chassis 2 hidden from view entirely to improve the visibility of the components of the suspension system 5. Like components or features are assigned like reference numerals throughout the drawings.

(25) Each hull 3 or 4 is connected to the chassis 2 by a locating arrangement comprising four links 10, 11, 12 and 13 or 20, 21, 22 and 23. The first link, which in this example is the front link 10 is connected to the hull at joint 10a and to the chassis at joint 10b. Throughout this specification, where the term joint is used it may be referring to a ball joint or other spherical joint, a resilient bushing or any other form of joint that permits at least limited rotation about at least one, two or all three mutually perpendicular axes and provides a constraint on linear motion in at least two or all three mutually perpendicular directions.

(26) The second link, which in this example is the back link 11 is connected to the hull (in this example, via an up-stand 14 which is rigidly connected to the hull) at joint 11a and to the chassis at joint 11b. The longitudinal spacing of the front and back links 10 and 11 provides some yaw location of the hull relative to the chassis. For example, when the other links are providing stability through other constraints such as roll and longitudinal constraints on motion of the hull relative to the chassis, then the front and back links are able to provide at least some of the forces required to react yaw and lateral motions of the hull relative to the chassis. So the first and second links (the front and back links 10 and 11 in this example) at least assist in providing a yaw constraint on the hull relative to the chassis.

(27) The third link, which in this example is the upper link 12 is connected to the hull at joint 12a (in this example on the same up-stand 14 as the back link 11) and to the chassis at joint 12b. The vertical spacing of the upper link from one or both of the front and back links provides some roll location of the hull 3 (substantially about a longitudinal or roll axis of the hull). For example, when the other links are providing stability through other constraints such as yaw, longitudinal and some lateral constraints on motion of the hull relative to the chassis, then the third link together with at least one of the front and back links are able to provide at least some of the forces required to react roll and lateral motions of the hull relative to the chassis. So the third link (the upper link 12 in this example) assists in providing a roll constraint on the hull relative to the chassis.

(28) If the first, second and third links (in this example, the front link 10, back link 11 and upper link 12) are all of equal length, are all oriented laterally in plan view (i.e. when viewed from above) and are all oriented parallel to each other in end view (such as front view) then the hull will not roll about its primary (longitudinal) axis nor yaw relative to the chassis if the hull moves in heave mode only. Through the heave stroke of the hull there will be some lateral motion of the hull relative to the chassis, but that can be minimised by the use of long links (i.e. maximising the distance between the hull and chassis joints of each link) and/or having the links oriented horizontally at a preferred ride height or at mid stroke.

(29) The fourth link 13 is a leading arm in this example, connected to the hull 3 at joint 13a and to the chassis at joint 13b and runs in an at least partially longitudinal direction relative to the chassis. The fourth link helps to define the longitudinal position of the hull relative to the chassis. For example, when the other links are providing stability through other constraints such as yaw, roll and lateral constraints on motion of the hull relative to the chassis, then the fourth link is able to provide at least some of the forces required to react longitudinal motions of the hull relative to the chassis. So the fourth link at least assists in providing a longitudinal constraint on the hull relative to the chassis. In this example, the fourth link 14 provides a substantially longitudinal constraint between the hull and the chassis. The use of such a forward positioned leading arm can be beneficial as it can be angled upwards as it runs backwards, i.e. the chassis joint 13b can be higher than the hull joint 13a at ride height, to assist in control of the pitch attitude of the chassis as the water craft slows or accelerates in a fore-aft direction. The four links 10, 11, 12 and 13 of the left hull locating arrangement together provide lateral, yaw, roll and longitudinal constraints on the motion of the left hull 3 relative to the chassis 2, permitting heave and pitch motions of the hull relative to the chassis. The front link 20, back link 21, upper link 22 and fourth link 23 between the right hull 4 and the body or chassis 2 similarly form a right hull locating arrangement constraining lateral, yaw roll and longitudinal motions of the hull 4 relative to the chassis 2, while permitting heave and pitch motions of the hull relative to the chassis. The back links 21 and 22 are connected to an up-stand 24 that is rigidly connected to the hull. This helps provide a vertical spacing between the upper and lower back links 21 and 22 with roll torques on the hull being reacted by compressive and tensile forces in the upper and lower links and the vertical spacing between said links.

(30) The left leading arm 13 and the right leading arm 23 can be rigid links. Alternatively, as shown in the FIGS. 1 to 8 each fourth link 13 or 23 can be adjustable in length, for example to provide a rigid link of two different lengths such as an operating length and a storage length. Although the fourth links could be continuously adjustable, or be controlled to include three or more preset lengths, it is preferred that the fourth links are only adjusted to two lengths such as a maximum and a minimum length, which can correspond to the operating length and the storage length. As a further alternative, each link 13 or 23 can provide a limited amount of resilient length change to reduce the peak magnitude of impacts transmitted from the hull to the chassis. The links shown in FIGS. 1 to 8 are telescopically adjustable in length, having two portions, which if they are hydraulically adjustable for example, can be a bore or cylinder portion 15 or 25 and a rod portion 16 or 26.

(31) The body or chassis 2 is supported above each of the left and right hulls 3 and 4 by longitudinally spaced supports such as the front left support or ram 17, back left support or ram 18, front right support or ram 27 and back right support or ram 28. The supports 17, 18, 27, and 28 are shown as rams and can be or include any known resilient or controllable support such as hydraulic rams, electromagnetic actuators, air springs or mechanical springs such as coil springs. Although the supports 17, 18, 27 and 28 are shown acting directly onto the hulls 3 or 4, they can be positioned between the body or chassis 2 and any of the four links or indeed additional links arranged to provide transmission of support forces ideally without providing additional locational constraints.

(32) The water craft 1 is shown in plan view in FIG. 3 with the outline of the body portion or chassis 2 shown in dashed lines. In the example shown, the front, back and upper links 10, 11, 12 or 20, 21, 22 are all similar in length and oriented substantially laterally. Although this is not necessary, it does prevent changes in the yaw and roll of the individually hulls 3 or 4 relative to the body or chassis 2. The fourth links 13 and 23 are oriented longitudinally although again this is not necessary. FIG. 4 shows a side view of the same water craft at ride height as FIGS. 1-3 and with the outline of the upper and lower portions of the chassis 2 shown in dashed lines.

(33) A chassis supported above four variable length supports can have four modes of motion: roll, pitch, heave and warp. As mentioned above, the four links locating each hull permit heave (vertical) and pitch motions of each hull relative to the chassis. Pitch motions of the left and right hulls 3 and 4 in opposite directions as shown in FIG. 5 are known as warp mode motions so the suspension system of the water craft can accommodate the warp mode. In FIG. 5 the left hull 3 is pitch nose up and the right hull 4 is pitched nose down. As with the previous Figures the mounting structures for the tops of the supports 17, 18, 27, 28 on the chassis have been omitted for clarity.

(34) Conversely, heave motions of the left and right hulls 3 and 4 in opposite directions provides roll of the body or chassis 2 relative the hulls 3 and 4 (which is different from a roll motion of an individual hull relative to the chassis, i.e. a hull rotating about a longitudinal axis while the remainder of the water craft is fixed for example). In FIG. 6 the left hull 3 is in a fully down or extended position with the associated supports (not visible) fully extended and the right hull is in a fully up or compressed position. As the fourth link or leading arm providing longitudinal location is substantially horizontal at ride height in this example (as shown in FIG. 4) and the vertical displacement from ride height is equal and opposite from left to right for a pure roll motion, the left hull moves back slightly as the left leading arm rotates downwards and the right hull moves back a similar amount as the right leading arm 23 rotates upwards.

(35) In all of the drawings so far (i.e. FIGS. 1 to 6) the fourth link has been a leading arm of unchanging length, for example a fixed length arm or an adjustable arm at an operating length, i.e. in an operational or wide track position. However, as each fourth link can optionally be adjustable in length, changing the position of the respective hull 3 or 4 relative to the chassis 2 in at least one of the suspension constraint directions is possible by adjusting the length of the fourth link. As shown in FIG. 7, when the fourth links 13 and 23 of the vessel in FIGS. 1 to 6 are adjusted to a storage length, i.e. in this example fully retracted, the hulls 3 and 4 are moved longitudinally (rearwards) relative to the chassis 2 and inwards relative to the chassis and each other. This adjustment can be done by a manually or preferably automatically controlled length adjustment device such as for example a linear actuator, or hydraulic cylinder and reduces the width of the water engaging footprint of the vessel, i.e. it reduces the track of the hulls of the water craft, reducing the lateral spacing between the hulls. Being able to adjust the track of the hulls of the water craft between a narrow width and a wide width can be useful for a number of reasons. For example, being able to adjust the track of the vessel hulls to a narrow width that ensures that the outer edges of the hulls are the same or slightly less widely spaced than the width of the chassis or body portion can be beneficial in accessing and negotiating around confined areas such as ports and marinas, to berth the vessel or to transport the vessel overland by road on a trailer. However in such a narrow width track configuration, if vessel height is maintained or even increased at sea to allow larger waves to pass under the chassis or body portion, the stability of the vessel would be reduced when compared to the same vessel with the hulls more widely spaced. Therefore, the lateral position of the hulls and the length of the adjustable length fourth links 13 and 23 in FIGS. 1 to 6 are all shown at the operating position i.e. the wide width track configuration for operating at sea. Although the operating length of the adjustable length fourth links is the fully extended length, if different joint locations are chosen, it is possible that the operating length at which the hulls are in the wide track configuration could be the fully retracted length, i.e. the storage length of the adjustable fourth links may be longer than the operating length, while the spacing between the hulls at the operating length is still greater than at the storage length. Changing between the two positions, i.e. adjusting the length of the adjustable length fourth links between the storage and operating lengths, can be controlled manually, i.e. with an operational/storage selection button, or automatically, or a combination of the two such as an operator controlled switch to indicate intention and a safety override that prevents adoption of the storage position at speed or in large sea states for example.

(36) Rather than change between two positions, it is possible alternatively to adjust the track of the hulls in proportion to the ride height of the vessel. Many variations are possible such as adjusting the track of the hulls in proportion to a sensed height of a body portion or chassis centre of mass for example. Or the sea state may be used to determine the track, although it is more usual to use sea state to determine ride height and then in turn the ride height can optionally be used to determine the track.

(37) In the example geometry shown in FIGS. 1 to 8, the supports are substantially vertically oriented rams in the wide track position of FIGS. 1 to 4 and when the fourth links 13 and 23 are then retracted to narrow the track as in FIGS. 7 and 8, the supports 17, 18, 27 and 28 become inclined due to the lateral and longitudinal displacements of the hull joints 17a, 18a, 27a and 28a relative to the chassis joints 17b, 18b, 27b and 28b. In order to maintain a constant ride height, i.e. the height of the body portion or chassis 2 above the hulls 3 and 4, then the lengths of the supports must be adjusted (increased in this case, to maintain a similar vertical distance between the hull and chassis mounts at the ends of each support) as the track of the hulls is reduced. However if the length of each support is not adjusted, or if the length of each support is maintained constant as the track is reduced, then the body portion or chassis will be lowered at least a little relative to the hulls. Similarly if the supports are the hydraulic rams of a hydraulic or hydro-pneumatic support arrangement and if no fluid is added to or removed from the support arrangement as the track is reduced, then the ride height will also be reduced. If such supports are resilient hydro-pneumatic supports, then as they are further inclined away from vertical, their lines of action also incline further away from vertical, so the linear force in the hydro-pneumatic support that is required to support the vessel is increased. Then if no fluid is added the supports will contract further lowering the body portion or chassis of the vessel. So through careful choice of geometry parameters (the coordinates of the various link and support joints to the chassis and the hulls) it is possible to ensure that the ride height increases as the track is increased and conversely that the ride height reduces as the track is reduced without having to make adjustments to the supports.

(38) FIG. 9 shows a simplified diagram of a single hull, in this case a left hull 3 with the related suspension system 5 components. The arrangement is very similar to that in FIGS. 1 to 4, the main differences being that the hull joints are at the edge of the hull rather than towards the centre in plan view and that the leading arm or fourth link 13 is positioned further backwards, spaced from the front link 10 and inclined upwards. The fourth link is also rigid rather than adjustable in length.

(39) FIG. 10 is a modification to the arrangement of FIG. 9, the front link 10 still being horizontal and oriented laterally, but the hull joint 10a is inboard on the hull and the hull joint 13a for the adjustable fourth link 13 is fixed to the front link 10 rather than directly to the hull. In all of the preceding Figures, the upper link 12 has been the same length as and parallel to the back link 11. However, changing the length of the link (i.e. 12) that is vertically separated from the other lateral location providing links (such as 10 and 11) allows the roll attitude of the hull to be adjusted relative to the chassis as the hull is displaced vertically relative to the chassis, to provide control of camber and roll centres, as is well known in double-wishbone type automotive suspension geometries, for example.

(40) In FIG. 11, the front link 10 is now angled and not oriented laterally, while the back link 11 still is oriented laterally. The fourth link 13 is still able to work with the front link 10 to provide longitudinal location of the hull 3 relative to the chassis, but if the length of the fourth link were adjusted, the hull would yaw in addition to moving laterally unless the back link 11 is similarly oriented to the front link 10 in plan view. So as in this example the fourth link is not shown as an adjustable length link, the front link 10 and the fourth link 13 are combined into a rigid A-frame or wishbone 30, both for strength and to enable the hull joints of the front and fourth links to be combined into a single hull joint 30a. Also in FIG. 11 the upper link is spaced longitudinally from the front and back links 10 and 11 as its longitudinal position is not critical, although affecting torsional loadings in the hull 3 and also some roll of the hull 3 can be induced through the combination of pitch and heave motions of the hull 3 relative to the chassis.

(41) FIGS. 12 and 13 show a water craft at a ride height, in side and plan view respectively. FIG. 15 shows the front suspension at the same ride height and FIG. 18 shows the rear suspension at the same ride height. There can be many selectable or auto-selected ride heights depending on the conditions and other operating parameters. The same vessel is shown with the suspension at full extension in FIGS. 14, 17 and 20 and with the suspension at full compression in FIGS. 16, 19 and 21. The arrangement of upper and rear lower links 12, 22 and 11, 21, with each upper link connected to an up-stand 14, 24 is similar to that shown for the left hull in FIGS. 9 and 10 with links 11 and 12 and the up-stand 14.

(42) As can be best seen in FIGS. 17 to 19, the chassis 2 of the vessel includes a structure or framework 31 to provide secure location of the upper link chassis joints 12b and 22b. The upper and rear lower link on each side, i.e. 12 and 11 on the left and 22 and 21 on the right, are parallel and of equal length, to maintain the roll attitude of the respective hull constant relative to the chassis. The length and angle of the support 18, comprising two rams 18 and 18, or support 28 comprising rams 28 and 28, defines both the motion ratio and any non-linearity of the motion ratio. That is to say, for any given pair of parallel lateral links, the relative distance between the hull and chassis joints at the ends of each support can be chosen to provide for example a motion ratio of two times from the ram to the hull, which doubles the force in the ram compared to a support that is vertical relative to the chassis. The motion ratio can vary through the travel of the suspension as the hull moves up and down relative to the chassis and the support rams contract and extend and the length and angle of each support can be chosen to provide a desirable non-linear motion ratio, for example to provide some compensation for changes in track and/or non-linear spring rates. However, the actual position of each support is not critical, so once the required length and angle is known, the support rams can be positioned by moving them vertically or laterally, without changing longitudinal position, nor length and angle, so the best packaging and/or structural arrangement can be found. For a constant roll attitude hull geometry, such as that shown at the rear, and with a front lateral link of similar length in end view, the front rams have a similar property and their position can be moved (without changing length or angle) to suit packaging requirements for example, or to align with structural members of the hulls and/or chassis to ensure an efficient design.

(43) FIGS. 14 to 16 and FIG. 20 best show the front up-stand 19 or 29 provided to raise the hull joints of the suspension above the hull at that longitudinal position. As can be seen in FIG. 13, the geometry is a further variation on the front and fourth links 10 and 13 in FIG. 10. In FIG. 13 each front link 10, 20 is oriented substantially laterally relative to the chassis 2 of the vessel and each fourth link 13, 23 is angled so that it extends in combination of longitudinal and lateral directions. The chassis joint 13b, 23b of the fourth links are each at a similar distance from the centreline 33 of the vessel to the chassis joints 10b, 20b of the front links. However the hull joints 10a, 20a of the fourth links are on the hulls and separate to the lateral links 10, 20. The fourth links are of substantially fixed length in this example where the front portion of each hull rises significantly and would interfere with the body portion or chassis 2 or require larger allowance for motion and therefore less deck space if the fourth links had a variable length causing lateral and longitudinal motion of each hull relative to the chassis. The geometry formed by the four links constraining each hull laterally, longitudinally and in yaw and roll relative to the chassis is still suitable for use with variable length fourth links, albeit with alterations required to the shapes of the hulls and/or chassis.

(44) In all of the disclosed geometry arrangements of four links herein, each hull is able to heave and pitch relative to the chassis, providing the left and right hulls of a catamaran incorporating such a suspension system with the ability to together move relative to the chassis in the modes of pitch, heave and warp, with the chassis being able to roll relative to the average vertical position of the left and right hulls. The waterline 34 is indicated in FIG. 12 and FIGS. 14 to 21.

(45) The supports (such as for example 17, 18, 27, 28 in FIG. 1) can be or include, as noted previously, any known resilient or controllable support such as hydraulic rams, electromagnetic actuators, air springs or mechanical springs such as coil springs. The supports can be independent or interconnected as disclosed for example in the Applicant's international patent application publication numbers WO2011/143692 and WO2011/143694, details of which are incorporated herein by reference. For example, each of these supports can include multiple elements, such as the twin hydraulic rams 17 and 17, 18 and 18, 27 and 27, 28 and 28, in FIG. 13. Those rams can then interconnected to provide modal functionality such as a passively or inherently different stiffness in at least two suspension modes from roll, warp, pitch and heave.

(46) Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.