GB2088787A - Trimaran - Google Patents

Abstract

A multihulled craft (10) has a leading hull (12) and two parallel spaced trailing hulls (16) mounted on a frame (18). All three hulls are freely pivotably about horizontal axes to enable the hulls to follow wave motion and the leading hull is in addition steerable. <IMAGE>

Description

SPECIFICATION Trimaran The present invention relates to multihull sailing craft.

One of the problems associated with multihull sailing craft lies in the fact that the hulls or floats of the craft are rigidly secured to the body or framework of the craft. The float mountings and thus the craft framework are therefore subject to considerable stresses as the floats ride through the waves and the points through which buoyancy forces act change. Such craft also have a tendency to excessive pitching.

The present invention seeks to provide an improved form of multihulled sailing craft.

Accordingly, the present invention provides a multihull craft comprising body means having two substantially parallel spaced trailing hulls and a third, leading hull positioned between and ahead of the two spaced hulls, wherein at least one of said hulls is pivotable relative to said body means about a transverse substantially horizontal axis.

In a preferred embodiment of the invention either the two trailing hulls or the leading hull or all three are freely pivotably. Advantageously the leading hull is also steerable. The body means is preferably a tubular frame with a taut canvas deck.

The use of pivotable hulls reduces the stresses applied to the body structure, enabling lighter materials to be used to reduce weight, increase speed and facilitate dismantling and transport of small craft.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side elevation of a multihulled sailing craft according to the present invention; Figure 2 is a perspective view of the frame of the craft of Figure 1; Figure 3 is a perspective view of the mounting for a float which is both steerable and pivotable in a substantially vertical plane; and Figure 4 is a perspective view of a mounting for a pivotable float.

The drawings show a trimaran sailing craft 10 having three floats consisting of a leading float 12 and two trailing floats 1 6 mounted on a substantially triangular shaped frame 1 8. The three floats are secured to the frame 1 8 at their centres of buoyancy with the leading float 12 being secured adjacent the apex of the triangular frame and the two trailing floats at each of the trailing corners of the frames. All three floats are preferably secured to the frame so as to be pivotable about respective horizontal axes to allow the floats to change angle with the water surface.

An an alternative, either the leading float 12 or the two trailing floats 1 6 may be the only floats which are pivotably mounted. The leading float 12 is also preferably mounted as a steerable float.

The frame itself is conveniently constructed from tubing of, for example steel or alloy, with a mast stem tube 20 being welded to the frame at a convenient location to provide a mast for the craft.

The frame itself may be formed of a number of interconnectable tubular sections to enable dismantling of the frame for transportation purposes.

Referring particularly to Figure 3 which shows the pivotal mounting of the leading float 12 a horizontal pivot 22 is mounted adjacent the apex of the triangular frame, bridging the two side arms 24 with the ends of the pivot 22 rotatably supported, conveniently in depending flanges 26 secured to the side arms 24. The pivot 22 is constructed in the form of a T with the depending stem 28 engaging in a mounting 30 of the leading float 12. The mounting 30 is conveniently a substantially vertical tube 30 which is axially secured relative to the stem 28 but rotatable therewith. The mounting 30 is conveniently secured on the float vertically above the float centre of buoyancy but may be secured at any vertical position within the float if so desired.

A steering arm 32 is horizontally secured to the float 12, conveniently by way of the mounting 30, with a respective suitable steering cable or rod being secured to each end of the arm 32 to enable the float 12 to be pivoted about the vertical axis of the stem 28 by an operator to steer the craft.

Pivoting of the float 12 in a vertical plane relative to the plane of the frame is allowed, as will be appreciated, by the pivot arm 22. With regard to the engagement of the mounting 30 with the stem 28 suitable means may be provided for adjusting the relative vertical positions of these to vary the position of the float 12 below the frame 1 8.

Each rear float 14, 1 6 is pivotally mounted to the frame 18 at or adjacent its trailing end conveniently by way of a transverse support or strut 34. In its simplest form this is a tube telescopically engaged at each end with a respective horizontal portion of a support arm 36 secured to each trailing float. Each arm is secured to the float at some point which is vertically aligned with the centre of buoyancy of the float.

The manner in which the two trailing floats are pivoted on the frame 1 8 advantageously enables the overal! beam width of the craft to be varied simply by adjusting the degree of telescopic engagement of the strut 34 with the float arms 36. Suitable means may be provided axially to secure the strut and arms in any selected position while allowing pivoting of the floats about a horizontal axis coaxial with the strut 34.

The mounting of a trailing float is shown in detail in Figure 4 with the axial position of the arm 36 relative to the strut 34 secured by means of a bolt 38 or the like which engages through a selected one of a number of holes 40 in the strut into an arcuate slot 42 in the upper surface of the end portion of the arm 36. The slot 42 conveniently performs an additional function in setting the pivoting limits of the trailing float although any simple means for restricting pivoting can be employed. As will be appreciated, the angular length of the slot 42 may be made such that under normal circumstances pivoting of the trailing floats would not approach the limits set by the slot 42 and its cooperation with the bolt 38.

The mounting of the leading float may also be conveniently provided with suitable adjustable stops to limit the pivot angle of the float. One or more of the floats of the craft may also be locked at a preselected pivot angle, this conveniently being provided for with the trailing floats by suitable holes 44 in the end portion of the pivot arm 36, the bolt 38 engaging into a selected one of these holes.

In order to provide a preselected amount of resistance to pivoting of the trailing floats respective sleeves 46 of a relatively high friction material such as rubber may be provided on the end of the strut 34 and on the end portion of the arm 36 such that when the strut and arm are telescopically engaged the adjacent edges of the two sleeves 46 abut one another. Suitable means for adjusting the axial pressure of each sleeve on the other may be provided, for example in the form of two outer sleeves which are screw-threadedly engaged and bear against the free ends of-the sleeves 46 to draw the two sleeves together as the outer screw-threaded sleeves are screwed together. Alternatively, a strip of relatively high friction material having a width equal to that of the two sleeves 46 may be bound tightly about the two sleeves, the material conveniently being rubber.

The particular mounting of the two trailing floats allows the overall beam width of the craft to be adjusted quickly to take account of, for example, weather conditions and the number of crew.

As is best seen in Figure 2 the strut 34 also pivotally mounts a tiller 48 substantially at its midpoint, the tiller including a substantially vertical rod 50 which is rotatably mounted to the strut 34 and carries at or adjacent its lower end a substantially horizontal steering plate 52 similar to the steering plate 32, the two being interconnected by suitable steering cables or rods.

Although the above-described craft is primarily intended as a trimaran sailing craft the floats can easily and quickly be replaced by, for example wheels, skates or skis, to convert the craft into a sand or snow yacht or the like and the term "hull" used herein should be construed accordingly in broad manner.

The above-described and illustrated sailing craft exhibits an improved resistance to heeling and a reduction in pitching and is therefore a more efficient sailing craft. Mounting the three floats independently on respective pivots at the respective centres of buoyancy reduces wave stresses on the structure and allows the floats to change angle to plane up rapidly as the craft speed increases, so reducing the "wet" area of each float.

The low pitched angle of the craft through the waves allows a more constant air flow past the sail to improve sail efficiency.

The provision of a leading float which is steerable is a more efficient method of steering than a stern rudder, providing a quick and accurate steering response. Providing the leading float with one or more fixed leeway plates assists steering with the plates required to be only half their normal depth. The pivoting of the leading float also provides a greater steering efficiency owing to the float being able to follow the changing angle of the water surface.

As is mentioned previously each float is preferably pivoted along a horizontal axis which is vertically aligned with the centre of buoyancy of the float. However, the pivot axis may be positioned slightly to the rear of the centre of buoyancy. This ensures that the float sits on the water horizontally, or nearly so, when the craft is stationary on still water. If the pivot axis needs to be positioned at some distance behind or ahead of the centre of buoyancy then it will be necessary to provide the float with a counterweight to ensure that the float sits on the water correctly.

As is mentioned above the pivoting of the floats reduces the wave stresses on the structure, the pivoting allowing the floats to change angle with the angle of the water surface and also to ride over waves and not through them at the float takes the line of least resistance, this also being conducive to low water drag. In addition, a tendency for the craft to crash dive is greatly reduced, especially whan the craft is running before the wind, this arising as a result of the lifting planing action at speed of the leading float.

The deck of the craft is conveniently in trampoline form, for example being provided by a canvas or the like which is secured taut by ropes or shock cord or the like to the frame 18. The tension in the canvas and cord also serves the purpose of retaining the interlocked frame tubing sections together, thus avoiding the need for bolts or other form of locking mechanisms.

With reference to the pivotability of the leading float this has an additional advantage when the leading float is also steered in that structural damage can result in the steering mechanism and lee boards if the float comes out of and down a wave at a horizontal attitude when the craft is turning.

Finally, the manner of construction of the craft allows easily assembly and disassembly to facilitate transportation. Where larger craft are concerned the spacing of the trailing floats can be adjusted by means of a rack and worm gear for example for convenience of negotiating narrow passages and the like. The float pivot may also underhang the float, the latter being pivoted for example by way of its leeway plate.

Although the invention has been described with reference to a trimaran it will be appreciated by those skilled in the art that the same principles also apply to other types of multihulled craft such as catamarans or craft having four or more floats or hulls.

Claims (12)

1. A multihull craft comprising body means having two substantially parallel spaced trailing hulls and a third, leading hull positioned between and ahead of the two spaced hulls, wherein at least one of said hulls is pivotable relative to said body means above a transverse substantially horizontal axis.

2. A craft as claimed in claim 1 wherein both said trailing hulls are pivotable about respective transverse horizontal axes.

3. A craft as claimed in claim 1 or 2 wherein said leading hull is pivotable about a transverse horizontal axis.

4. A craft as claimed in any of claims 1 to 3 wherein the heading of said leading hull is alterable relative to that of the trailing hulls for enabling steering of the craft.

5. A craft as claimed in any of claims 1 to 4 wherein the or at least one of the pivotable hulls is pivotable between preselectable extreme limits.

6. A craft as claimed in any of claims 1 to 4 wherein the or at least one of the pivotable hulls is freely pivotable.

7. A craft as claimed in any of claims 1 to 6 wherein said body means comprises a frame interconnecting said hulls.

8. A craft as claimed in claim 7 wherein said body means includes a deck supported by said frame.

9. A craft as claimed in claim 8 wherein said deck comprises a flexible sheet secured in a tensioned manner to said frame.

10. A craft as claimed in claim 7, 8 or 9 wherein said frame is made of detachably interconnected tubular members.

11. A craft as claimed in any of claims 1 to 10 wherein the spacing between said trailing hulls is adjustable.

12. A multihulled craft substantially as hereinbefore described with reference to the accompanying drawings.