AU8100787A

AU8100787A - Sail

Info

Publication number: AU8100787A
Application number: AU81007/87A
Authority: AU
Inventors: James Frederick Byam Shaw
Original assignee: SHAW J F BYAM
Current assignee: SHAW J F BYAM
Priority date: 1986-10-29
Filing date: 1987-10-26
Publication date: 1988-05-25
Also published as: EP0337992A1; GB2196595B; GB2196595A; GB8625840D0; WO1988003111A1

Description

SAIL

This invention relates to sailing vessels-

Most sailing boats are rigged with a Bermudan rig consisting of a jib and a mainsail. A Bermudan rig has triangular-shaped sails and is simple to construct. However, a Bermudan rig suffers from certain disadvantages.

For example, drag which is produced by turbulence may be reduced, for all planforms of sail, by increasing the aspect ratio (defined as the square of the height of the sail divided by the area of the sail) of the sail. This means that a Bermudan rig requires a tall mast which raises the geometric centre of the sail and also increases the rigging drag. An increase in mast to sail interference also occurs.

Another disadvantage of a triangular-shaped sail is its tendency to cause a significant amount of turbulence at its apex and hence drag, compared to other planforms, for a given aspect ratio.

Previous attempts have been made to reduce the drag by changing the planforms of the mainsails. Horizontal gaffs, curved gaffs, curved yards, sprits and full length battens have been used at some extra expense and complexity. These are seldom popular with cruising men and also rating rules tend to legislate against them.

According to the present invention there is provided a jib for a Bermudan jig having a generally trapezium planform arranged to be rigged with its top edge generally horizontal.

The planform may appear as a conventional jib with its apex removed and preferably produces a jib with a chord tip to chord root ratio in the range from 0.10 to 0.40. Preferably a head stick between the two top corners is used to fix the camber of the top of the jib.

Preferably eyelets are provided at each corner at the top of the jib. A bridle made from any suitable low stretch material, for example wire or Kevlar (trade mark), may be used to replace the original lines of luff and leech.

Preferred embodiments of the jib of the present invention will now be described, by way of example, with reference to the accompanying schematic drawings in which:

Figure 1 shows a Bermudan rig with a conventional jib.

Figure 2 shows a Bermudan rig with an embodiment of a jib of the present invention.

Figure 3 shows an embodiment of a jib for use in normal weather conditions.

Figure 4 shows an embodiment of a jib for use in heavy weather conditions.

Referring to Figure 1,_ here is illustrated therein turbulence 1 at the apex of both a mainsail 2 and a jib 3. I have found that the turbulance formed at the apex of the jib 3 tends to reduce the efficiency of the main sail 2. I believe this is due to the turbulence interfering with air flow across the rear surface of the mainsail 2.

Referring to Figure 2,_ there is il ustrated therein a reduction in the effect of turbulence 4 at the apex of the jib 3,_ due to a modification in the planform of the jib 3 in accordance with the present invention. This leads to a significant practical improvement in the efficiency of the sailing rig. Referring to Figure 3,_ there is shown therein an otherwise conventionally shaped jib 3,_ having an aspect ratio of about 3,_ in which the apex has been removed as shown. The jib 3 is shaped so that the chord tip 5 to chord root 6 ratio is 0.1. According to basic aerodynamics theory a reduction in drag per unit area of about 0.876 should be acquired, compared to that obtained using a conventional triangular-shaped jib. The loss in area is 1% and the loss in aspect ratio is 18%, however, the loss in aspect ratio has a negligable affect compared to the net gain of thrust, which is approximately 11%.

The top of the jib 3 is horizontal, having a head stick 7 attached at each corner 8. An eyelet 9 is provided in each corner 8,_ and the head cloth 10 is reinforced. A bridle 11 is used to follow the original lines of luff and leech to the projected apex of the jib 3. The original running rigging 12 is used.

In a vessel using the described jib 3 the geometric centre of effort is lowered. The aerodynamic centre of effort is also lowered in relation to the geometric centre of effort. The thrust should be increased beyond the theoretical 11% that is expected by calculation, due to the reduction in air disturbance caused by turbulance across the main sail. The heeling moment of the vessel also tends to be reduced.

The benefits described may be exploited in a further embodiment of jib 3 shown in Figure 4,_ for use as a storm sail. The chord tip 5 to chord root 6 ratio is 0.32,_ taken as the optimum aerodynamic value from a well known aerodynamics theoretical graph, for a trapezium shape. Because of the area required in heavy weather there is little reduction in aspect ratio. The storm jib is approximately 80% the height of an otherwise conventional jib.

By means of embodiments of the present invention the performance of sailing vessels can be significantly improved. This is achieved in effect by modifying the shape of the jib as described to reduce turbulence. In addition, this in turn improves the thrust from the main sail.

The described jibs may be used on all types of sailing vessels.

It will be seen in Figures 2 to 4 that the jibs of the present invention have generally trapezium planforms. The top edge is always horizontal or nearly horizontal in use and the lower edge is parallel or nearly parallel to the top edge. According to the definition of a trapezium, it is a shape having four sides of which two sides are parallel. The trapezium referred to herein has its parallel sides (which may not be exactly parallel) arranged horizontally in use. Naturally the phrase "trapezium planform" is intended to include a planform with rounded corners.

Claims

CLAIMS:

1. A jib for a Bermudan rig having a generally trapezium planform arranged to be rigged with its top edge generally horizontal .

2. A jib according to claim l,_in which the planform appears as a conventional jib with its apex removed.

3. A jib according to claims 1, in which the jib has a chord tip to chord root ratio in the range from 0.10 to 0.40.

4. A jib according to claim 1,_ comprising a head stick between the two top corners to fix the camber of the top of the jib.

5. A jib according to claim 1,_ in which an eyelet is provided at each corner at the top of the jib.

6 A jib to claim l,_in which a bridle replaces the conventional lines of luff and leach.

7. A jib according to claim 6,_in which the bridle is made from Kevlar.

8. A jib substantially as hereinbefore described with reference to any one or more of Figures 2 to 4 of the accompanying drawings.

9. A Bermudan rig including a jib having a generally trapezium platform arranged to be rigged with its top edge generally horizontal .

10. A rig according to claim 9 including a head stick for the jib between the two top corners thereof to fix the camber of the top of the jib.