WO2011121266A1

WO2011121266A1 - Aero luff spar

Info

Publication number: WO2011121266A1
Application number: PCT/GB2011/000019
Authority: WO
Inventors: Ralph Maurice Roberts
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-03-29
Filing date: 2011-01-10
Publication date: 2011-10-06
Anticipated expiration: 2012-09-29

Abstract

A small diameter luff spar (6) having a high strength to weight ratio, comprising of a luff wire (5) encapsulated within a fibre based material tube (1). Metal end sleeves (2) fastened onto the tube, engage thimbles (4), formed at each end of the luff wire (5) in receiving slots, and fastened to resist any operational longitudinal forces, as well as transmit any rotational movement along the length of the luff spar (6). A foresail having an extended luff sleeve (8) through which the luff spar is passed, with no cringles (reinforced holes) at the tack (9) or peak (10), and reduced stiffening and sail reinforcement at the tack (9) and peak (10) of the sail, is also disclosed.

Description

AERO LUFF SPAR

DESCRIPTION

(i) TECHNICAL FIELD:

The Aero LufF Spar concerns the improvement in the performance of a foresail, particularly relating to the smaller, dinghy type sailing craft. All foresails are supported at the leading edge, or luff of the sail, by means of a wire, rope, or spar. The foresail luff is tensioned between the bow of the boat and a point on the mast by the use of a foresail halyard. Replacing the luff wire, rope (or, with reference to points (a) and (b), the current reefing spars available) with an Aero Luff Spar, improves the performance of a foresail in the following 3 areas:

(a) Create an improved aerodynamic entry shape to the luff of a foresail.

The luff wire, usually only 3mm dia. for a small sailing craft, enclosed within the luff sleeve of a foresail, provides no effective aerofoil shape to the leading edge of the sail (Fig 6). A luff rope, though of a larger diameter, with the potential to improve the aerodynamic entry shape of the luff of the foresail, is an inefficient means of supporting the foresail luff because of its tendency to stretch under tension. The current luff spars available are of too large a diameter to create an ideal aerofoil entry shape to the luff of a foresail.

(b) Prevent the luff wire or rope from stretching under load with any increase in wind pressure.

The efficiency of a foresail is compromised by even a small amount of stretch in the luff wire or rope induced by a stronger breeze or gust of wind, as it causes the luff of the foresail to 'sag' slightly out of shape. This increases the entry curve of the luff of the sail (Fig. 7), which reduces the efficiency of the sail, as well as the boat's ability to point as high as possible towards the wind.

(c) Reef the foresail to reduce its size to suit stronger wind conditions.

A luff wire on its own has only limited torsional rigidity. The use of a furling drum at the bow of the boat and a top swivel at the peak of the sail will allow the foresail to be furled (wrapped) around the luff wire, but it is not possible to use this system to reef the sail to a smaller size, since the top of the foresail will start to unfurl whenever tension is put on the clew (bottom free corner) of the foresail by the foresail sheet (rope). A luff rope has no torsional rigidity, and is unable to support even the furling of a foresail. (ii) BACKGROUND ART: Current foresail systems.

With reference to: (a) Improving the aerodynamic entry shape of the luff of a foresail.

The luff spar systems presently available to increase the aerodynamic efficiency of a foresail relate to larger yachts rather than the smaller, dinghy type sailing craft, and all consist of an aluminium spar with a provision for the foresail luff to be fed into some sort of groove or slot within the spar, rather than the spar being encapsulated within the luff sleeve of the sail, as with the Aero Luff Spar.

With reference to: (b) Preventing the luff wire from stretching under load due to an increase in wind pressure.

No system or product is currently known to be available to prevent this occurrence in a luff wire (or luff rope). The current reefing spars available for a smaller, dinghy type sailing vessel are all supported by a rigging or luff wire through the centre of the spar, which bears the same liability to stretch.

With reference to: (c) Reefing the foresail to reduce its size to suit stronger wind conditions.

There are four known (European) systems currently available for smaller sailing craft, which enable the foresail to be reefed.

Three of these systems - Bartel (DE), Holman (GB), and Plastimo (FR) - all use a luff spar of extruded aluminium section, with a furling drum and top swivel incorporated into the system. These systems, whilst being perfectly adequate for the purpose of reefing a foresail, reduce the efficiency of a normal (unreefed) foresail in the following ways:

1. The size and design of the reefing spar makes the entry shape of the leading edge less efficient than a foresail with only a luff wire.

2. The furling drum of the reefing system raises the height of the foot of the foresail, causing the sail to work less efficiently.

3. The additional weight of the above reefing systems at the bow of the boat reduces any small sailing boat's sailing efficiency.

The fourth known foresail reefing system is the Helyer (GB) system. This uses a flexible polypropylene type material as the reefing spar, with the spar being directly attached to a (separate) furling drum and top swivel. This system, also perfectly adequate for the purpose of reefing a foresail, reduces the efficiency of a normal (unreefed) foresail for the following reasons:

1. The spar, being flexible, doesn't prevent the luff of the foresail from stretching, and 'sagging' out of shape.

2. The method of attachment of the foresail to the spar is such that it raises the height of the foot of the sail, causing the foresail to work less efficiently.

3. The increased weight of the spar compared to that of a foresail with only a luff wire is a disadvantage to a small sailing boat's sailing efficiency. (iii) DISCLOSURE OF INVENTION:

(a) Unique and/or key features.

The Aero luff spar being made from a fibre based material having a high strength to weight ratio, encapsulates the luff wire and is securely fastened to the ends of the luff wire by means of metal end sleeves. The completed assembly converts a foresail luff wire into an integrated, longitudinal and torsionally rigid, foresail luff spar unit.

The Aero luff spar being fitted through the luff sleeve of a foresail in the same manner as a luff wire or rope is fitted through the luff sleeve of a foresail.

The Aero luff spar assembly being fixed to the attachment points for a foresail on a sailing craft in an identical manner to that of a foresail with only a luff wire or rope.

The Aero luff spar being of a diameter of 8mm, rather than the 3mm of the luff wire, and creating an improved aerofoil entry shape to that of a foresail having only a luff wire.

The Aero luff spar, being longitudinally rigid and securely fixed to the thimbles of the luff wire, which does not stretch under additional loads caused by stronger wind conditions.

The Aero luff spar, being torsionally rigid and securely fixed to the thimbles of the luff wire, which directly transmits any rotational force at one end of the luff spar to the other end of the spar.

The Aero luff spar having an overall weight of less than 0.5 Kg, which constitutes a neglible weight disadvantage with regard to the performance of a small sailing craft.

(b) Description of Aero luff spar with reference to drawings

A fibre based spar (Fig 1) being made to the length required for the luff sleeve of the foresail (8) to which it is being fitted (Fig 5).

Two metal tubes (2), of varying lengths, being placed over the fibre tube (1) such that the cut-out slots on one end of both metal tubes (2) face the open ends of fibre tube (1).

A luff wire (5) being inserted through the centre of the fibre tube (1), with thimbles (4) swaged onto either end to make it an identical length to the luff wire of the foresail for the type of boat for which the luff spar is to be fitted. The luff wire (5) being permanently retained within the fibre tube (1) after assembly (Fig 3).

The metal tubes (2), being engaged over the swaged ferrules (3) of the thimbles (4) at each end, such that the metal tubes (2) are locked onto the ferrule (3) by means of the cut-out slot engaging over the thimble (4) at the ends of the luff wire (5). The longer of the two metal tubes (2) being positioned at the top (peak) end of the fibre tube (1) to take up any slack in the luffwire (5) (Fig 4). The metal tubes (2) being locked onto the fibre tube (1) and swaged ferrules (3), and secured such that the completed assembly becomes the fixed, integrated unit of the Aero luff spar (Fig 4, & (6) in Fig 5).

The luff spar (6) being inserted into the luff sleeve (8) of a foresail with the following features: an extended luff sleeve (8); no cringles (reinforced holes) at the tack (9) or peak (10); and reduced stiffening and sail reinforcement at the tack (9) and peak (10) of the sail.

The foresail being secured to the 'Aero' luff spar (6) by means of two double- sided clamps (7). The luff tension along the length of the foresail luff (8) being adjusted by positioning the clamps (7) as required (Fig 5).

A foresail with the Aero luff spar being fitted to the bow fitting(s) and foresail halyard of a sailing vessel, in an identical way to that of a foresail with only the normal luff wire or rope. (Figs 9, 10, 11, and 12) (iv) DESCRIPTION OF DRAWINGS g 1. Illustrates a length of fibre based tube (1), being the main component of the Aero Luff Spar (Fig 4). g 2. Illustrates the metal tubes (2), with a slot cut into one end of each tube. g 3. Illustrates the luff wire (5) inserted through the centre of the fibre tube (1), with thimbles (4) swaged onto either end. g 4. Illustrates the metal tubes (2) fitted over the ends of the fibre tube (1) and swaged ferrules (3), and locked into position over the thimbles (4) of the luff wire (5), making up the fixed, integrated unit of the Aero Luff Spar (6). g 5. Illustrates the Aero Luff Spar (6), inserted through the luff sleeve of a foresail (8) and secured into position by double sided clamps (7). g 6. Illustrates a cross section of a luff wire (5) inserted through the luff sleeve (8) of a foresail and tensioned to give the desired luff entry shape. g 7. Illustrates a cross section of the shape of the luff of a foresail (11) after the luff wire (5) within the luff sleeve (8), has stretched under load and compromised the shape of the foresail's luff. g 8. Illustrates a cross section of an Aero Luff Spar (6) inserted through the luff sleeve (8) of a foresail, demonstrating its aerofoil entry shape and the manner in which it maintains the shape of the foresail luff under load. g 9. Illustrates a foresail with only a luff wire, attached to the bow of a small sailing craft. g 10. Illustrates a foresail with an Aero Luff Spar, attached to the bow of a small sailing craft. g 11. Illustrates a foresail with only a luff wire attached to the furling drum of a small sailing craft, which allows the foresail to be furled. g 12. Illustrates a foresail with an Aero Luff Spar attached to the furling drum of a small sailing craft, which allows the foresail to be reefed.

Claims

1. A luff spar adapted to encapsulate the luff wire of a foresail, such that the swaged loops (thimbles) at each end are secured to the luff spar by means of metal sleeves to form a fixed, integrated unit.

2. A luff spar as claimed in Claim 1, in which the inner diameter of the metal end sleeves is closely matched to the outer diameter of the luff spar and outer diameter of the ferrule of the luff wire thimble, and securely fixed to both such that the assembled spar is able to withstand all longitudinal and rotational forces, under normal operating conditions.

3. A luff spar as claimed in the preceding claims, which being constrained within the luff sleeve of a foresail, provides a consistent aerodynamic profile along the length of the luff and of optimal diameter such that it reduces air turbulence at the luff, thereby increasing aerodynamic efficiency in operational use.

4. A luff spar as claimed in Claim 3, in which the spar supports the luff of the sail so as to provide an aerodynamic profile at the leading edge of the foresail and substantially eliminate the possibility of the leading edge of the foresail sagging, which occurs when a luff wire, rope, or other rigging device within the luff sleeve, stretches under load.

5. A luff spar as claimed in any one of the preceding claims, in which the material of the cylindrical tube is selected from carbon fibre, glass fibre and similar fibre based materials having high strength to weight ratios capable of withstanding all longitudinal and rotational forces under all normal operating conditions.

6. A foresail having a luff sleeve with extended luff sleeve ends, adapted to accommodate a luff spar and receive collars or clamps to tension and secure the extended luff sleeve ends of the foresail to the metal end sleeves of the luff spar, comprising a luff wire located within a fibre based material cylindrical tube having thimbles at each end, as claimed in the preceding claims.

7. A foresail in which there are no clew or peak cringles, being the conventional method of attaching the foresail to the thimbles of the luff wire, and reduced sail reinforcement in these areas, which are necessarily added to a sail to support sail cringles.

8. A foresail in which tension in the luff of the sail is set by securing the top collar or clamp, and subsequently positioning and securing the second clamp or collar to achieve the required tension along the luff sleeve.

9. A foresail which may be removed from the luff spar by means of unfastening the bolts on the collars or clamps securing the foresail to the spar.