EP0353901B1

EP0353901B1 - Improvements relating to sailing catamarans

Info

Publication number: EP0353901B1
Application number: EP19890307251
Authority: EP
Inventors: Anthony Richard Wood Rogers
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-07-19
Filing date: 1989-07-18
Publication date: 1993-10-20
Anticipated expiration: 2009-07-18
Also published as: GB8817184D0; EP0353901A1; DE68910039D1

Description

It is an objective of this invention to provide a sailing catamaran which is relatively small and lightweight in construction and therefore easily transportable as well as having good speed and manoeuvrability characteristics.
Standard catamaran designs provided with planing hulls are known, for example, from the Patent Specifications of U.S. Patent No. 2712293 and French Patent No. 2588216. In order to generate some side force such catamaran designs incorporate either a central keel member or possibly individual keel members under each of the hulls.
In accordance with the present invention there is provided a sailing catamaran comprising a support frame having forward and rearward ends and two sides, a pair of planing hulls formed with substantially vertical side faces along at least part of their length interconnected by the support frame along the two sides of the support frame, the catamaran having a centre-line equidistant between the two hulls, a mast with a sail, a mast base mounting positioned on said centreline towards the forward end of the support frame and forming part of the support frame, characterised in that a rudder and a keel member linked together to form a skeg-rudder is mounted towards the rearward end of the support frame and positioned along the centreline.
With such a design the necessary side force is generated, partly by the vertical side faces of the planing hulls, but more importantly by the deeply immersed skeg-rudder positioned centrally and at the rear of the catamaran structure. The provision of the keel at the rear of the craft as part of the skeg-rudder creates significant handling advantages and capabilities as compared with a design where a keel member is provided separately at the centre of a catamaran structure.
The overall combination of the invention provides excellent speed characteristics and also enables the mast to be set well back from the forward end of the catamaran so that it is less liable to tip over in a forward direction during sailing.
Speed is achieved by utilising planing hulls which do not themselves incorporate any form of standard keel or dagger plate. It may be preferred that only the rear portions of the planing hulls should be formed with substantially vertical side faces which will provide significant resistance to sideways thrusts whilst the catamaran is being sailed. This assists in the control of the direction of the catamaran during sailing, in combination with the skeg-rudder.
It is preferred that the skeg-rudder should be pivotally mounted on the support frame so that it can be pivoted into a condition wherein parts thereof do not project below the plane occupied by the bases of the two hulls. This allows the catamaran to be sailed to shore through shallow waters.
If the sail is connected to the mast by a wishbone rig, then conventional mast stays can be eliminated and also the sail can rotate through 360° for safety and simplicity.
The support frame is ideally constructed as an assembly which can be disconnected from the hulls and broken down into individual parts. This enables the catamaran to be transported easily, for example on a car roof rack.
The invention may be performed in various ways and a preferred embodiment thereof will now be described with reference to the accompanying drawings, in which:-

Figure 1 is a side view of a sailing catamaran of this invention;
Figures 2 and 3 are plan and front view of the main parts of the catamaran shown in Figure 1;
Figure 4 shows sections through a planing hull of the catamaran;
Figure 5 shows details of a support frame of the catamaran; and
Figures 6 and 7 are a side view and a horizontal section respectively of the skeg rudder used on the catamaran.

The sailing catamaran shown in the drawings comprises a pair of planing hulls 1 held together by a support frame 2 which incorporates a mounting 3 for a mast 4 carrying a sail 5 and a wishbone boom 6. Centrally of the rear strut of the frame 2 there is mounted a skeg rudder 7. As shown in Figure 6 in particular, this skeg rudder comprises a skeg 8, at the rear end of which is pivotally mounted on rudder 9. A support member 10 attached to the skeg 8 is mounted in a bracket 11 by means of a pivot pin 12. A locking pin 13 restrains the skeg rudder against pivoting during normal sailing use but with the locking pin 13 removed, the skeg rudder can tilt backwards so that the normal forward edge 20 will be generally parallel with the plane of the bases of the two hulls 1.
Each planing hull has a generally flat lower surface and Figure 4 illustrates the change in section along the length of the planing hull (from front to rear) at the points marked 1 to 7. As can be seen, the rear portion of each planing hull has substantially vertical side faces which therefore provide resistance to sideways motion (in combination with that provided by the skeg rudder 7) towards the rear only of the catamaran.
The support frame 2 is constructed from a number of struts 14 interconnected by socket joints 15. Legs 16 terminate in tubular feet 17 which are vertically disposed and will be mounted within sockets 18 in the planing hulls 2. A trampoline 19 is supported by the struts 14. This support frame can readily be dismantled for storage purposes.
Although a wishbone rig is preferred, the frame is equally suitable for rigging with a conventional mast and stays.
The use of planing hulls allows a short catamaran to exceed the established performance/length criteria which limit conventional displacement catamarans. Planing hulls have inherently less lateral force generation capability than displacement forms. This fact is used to advantage by concentrating the keel force at the rear of the craft. This rearward keel force allows a more rearward mast position and rearward raking of the mast. Both of these reduce the diagonally forward roll-over moment which limits the performance of conventional catamarans; indeed the mast rake also provides a lift element which enhances planing performance. Keels are more efficient at generating side force than hulls.
The novel frame design allows a single centrally mounted keel in the form of a skeg rudder. Since this is designed to be a unit functioning in the same way as a flapped aerofoil, very high lift (keel force) forces can be generated at excellent efficiencies. The design of the skeg rudder is important and in general is most efficient when the chord (width) of the skeg is less than 25% of the chord of the rudder. The shallow draft of the planing hulls combined with the pivoting of the skeg rudder allows the craft to be sailed in very shallow water (less than 1 ft. deep).
The use of an unstayed mast with a wishbone style sail support has two advantages. Firstly, compression loads on the frame and mast are avoided, allowing a light construction. Also, full 360° sail rotation is possible thus providing great simplicity and safety, especially for beginners.
The hulls are most efficient if the sidewalls are vertical throughout and this feature can be utilised provided it is combined with suitable plan and profile shapes, hull characteristics can be achieved whereby a limited amount of sidethrust (keel effect) is provided by the hulls which aids stability at speed and in particular provides a force which tends to turn the craft into the wind if excessive angles of 'heel' are reached. This limited sidethrust is much less than that provided by conventional deep 'V' catamaran hulls and always works in conjunction with the skeg-rudder.

Claims

A sailing catamaran comprising a support frame (2) having forward and rearward ends and two sides, a pair of planing hulls (1) formed with substantially vertical side faces along at least part of their length interconnected by the support frame along the two sides of the support frame, the catamaran having a centreline equidistant between the two hulls, a mast (4) with a sail (5), a mast base mounting (3) positioned on said centreline towards the forward end of the support frame (2) and forming part of the support frame, characterised in that a rudder (9) and a keel member (8) linked together to form a skeg-rudder (7) is mounted towards the rearward end of the support frame and positioned along the centreline.
A catamaran according to Claim 1, further characterised in that only the rearward portions of the hulls (1) are formed with substantially vertical side faces.
A catamaran according to Claim 1 or Claim 2, further characterised in that the skeg-rudder (7) is pivotally mounted on the support frame (2) for pivoting into a condition wherein parts thereof do not project below the plane occupied by the bases of the two hulls (1).
A catamaran according to any one of Claims 1 to 3, further characterised in that the mast (4) is unstayed and a wishbone boom (6) is mounted on the mast and to the sail (5).
A catamaran according to any one of Claims 1 to 4, further characterised in that the support frame (2) is formed as an assembly which can be disconnected into a compact state.