The sailcloth manufacturing business - past, present and future

Adam Rice

Sailcloth has come a long way since flax canvas, and some of to- day‘s synthetic fibres are eminently suitable for the purpose. In this article, Adam Rice looks at the history of sailcloth manufac- ture, and some of the more recent developments in the area.

Until steam technology in shipping bccanie widespread in the early part of the 20th century, the sailcloth industry was of key importance to any country with significant maritime interests, whether military or economic, and it is only during this century that the sailcloth industry has changed from one of strategic importance to one of support to the leisure marine business.

sailcloth manufacture in Britain is in the diaries of Samuel Pepys in an entry of 12 December 1664, in which it describes the news that Louis XIV of France had placed an embargo on the export of canvas to Britain, presumably in an attempt to cripple the Royal Navy and merchant fleet. I t is shortly after this that significant wcaving of flax canvas for sails began in Britain. The industry was centred on Somerset for two reasons. Firstly, the climate and soil were suitable for the growing of flax, and secondly the persecution of the French Huguenots from tht, time of Elizabeth I right up to thc Edict of Nantes of 1685, which excluded Huguenots from professions and most trades, had given rise to a substantial immigration to Britain of these highly skilled weavers. They had settled mainly in Somerset, and were idcdly placed to take up the demand for a local source of sail canvas.

The industry up to about 1800 was principally cottage based, with each farmer having a hand loom at home, and carrying ou t the whole process from sowing the flax to providing the sailcloth merchants with woven canvas. The merchants of the time were businessmen who ordered and purchased cloth from the farmer/manufacturer and then sold it on Lo the Navy, sailmakers or ship owners. To a large extent, the sailcloth merchants’ position in the industry has remained intact right up to the present day.

One of the earliest references to

The sailcloth industry was relatively slow to mechanise in the last century. In Dundee, hand-spun flax was quoted in the market until 1822 and Haywards, a Somerset manufacturer based in Crewkerne, has its earliest records of mill spinning in 1823.

Fibres Flax was for many years the preferred fibre for sail canvas and was largely unrivalled until around 1850, when Egyptian and American cotton began to be used; the Americans began to use cotton canvas ahead of Britain and Europe. The advantages of flax are that it has a very high strength for a natural fibre and it remains essentially unchanged when wet, which means that the sails stay flexible and pliable in wet and/or cold weather. The disadvantages are that the fibre is self-abrasive, and with use the sails become thinner and weaker until the canvas fails.

Further, and most importantly, the dimensional stability of flax canvas is poor and technology changes from ships with predominantly loose-footed square sails to gaff type fore and aft sails has

1 .

Square rigged sailing ship; cloth stretch in these sails is not critical

A gaff rigged vessel; this rig design requires cloth with controlled stretch for efficient operation

demanded higher resistance to stretch than flax canvas could readily deliver.

The advantages of cotton are that, because of the rough nature of the fibre surface, the spun yarns have much improved resistance to stretch undrr Itt,xi and, once woven, the bias stretch of the fabric was much lower than that of flax. The cloth also lasts longer than flax canvas. The disadvantage is that cotton swells with moisture, and this makes sails hard and stiff when wet, a serious problem for hand furling sails onto yards in bad weather.

As sail canvas moved out of the commercial and military areas and became concentrated on yachts for racing and pleasure, cotton took over as the fibrr of choice, and this remained the case rip to the 1950s when filament polyester c u d nylon became readily availdbk.

These fibres offer massive advantagtbs over cotton not only because of their resistance to stretch and wear as well as much higher strength to weight ratio, b u ~ also in terms of reduced maintenance. Modern sails can readily be packed whilst wet and left in damp salty conditions f o r

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long periods without serious consequences. This sort of treatment would have produced catastrophic results on a cotton sail.

The search for sail materials that will give even lower stretch and greater strength to weight ratio sails goes on. In the last 20 years the sailmaking industry has been quick to utilise modern technoloby for sailcloths, and the modem range of 'exotic' fibres such as aramids, gel-spun high-density polyethylenes, and even carbon fibres are all now readily available, offering lower stretch and lighter weight than ever before. The advances in adhesive technology and extruded polyester films have given rise to composite fabrics of woven and film layers which resolve a fundamental problem with woven structures in sailcloth, that o f lower resistance to stretch in the bias direction, compared to the warp and weft directions. With computer plotting technology, sails are now being manufactured by laying straight yarns onto polyester films in the predicted stress pattern for a particular sail and then laminating the layers into a sandwich construction. This concentrates the strength of the sail only in the predicted high stress areas, as well as resolving the other fundamental problem of woven structures in sailcloth, that of yarn crimp which is a major contributor to stretch.

However, all of these new materials have so far been limited in their share of the sailcloth market for reasons of price, which is high relative to woven sailcloth, and also longevity. The 'exotic' fabrics have relatively poor flex and abrasion

Modern racing yacht; highly complex computer aided design and construction using aramid/polyester film composite cloth for max strength to weight ratio and minimum stretch

Spinnaker; showing two attachment points on mast and spinnaker pole and complex curved shape

resistance and short working lives, limiting them mainly to top level competitive racing applications.

Cloth for spinnakers has a somewhat different set of requirements, and this has meant a rather different approach compared to cloth for fore and aft sails,

The weight of a spinnaker cloth is of prime importance because, as well as the problem of having weight far above the centre of gravity of the boat, this sail relies on the wind keeping it full for its shape, being fixed to the boat at only two points, the masthead and the tack, or end of the spinnaker pole. The lighter the sail the less wind is required to fill it to its designed shape and the more efficient the sail will be. Because its dimensions are not fixed by a mast and boom cloth stretch needs to be controlled and engineered to the sail, rather than eliminated as in the case of fore and aft sails. As the sail frequently collapses and fills suddenly, the ability to absorb energy is a vital property.

Because of the above requirements, nylon 6.6 has become the fibre of choice for this application. Although the Young's modulus of nylon is not as high as that of polyester, its lower density (1.14 compared to 1.38), better strength to weight ratio, and substantially higher energy of rupture than polyester, weigh strongly in its favour for spinnakers.

techniques have had little impact on spinnaker cloths. Cloth weights including coating as low as around 30 g/m2, and seldom higher than 80 g/m2, and the demand for energy absorption and tear resistance coming before low stretch, has tended to make these types of cloths less suitable for the properties offered by

Exotic fibres and production

exotic fibres. Development of this area has been more concentrated on coating technology, sail design and construction, rather than cloth technology.

Woven polyester sailcloth processing The design and processing of sailcloth for fore and aft sails is centred on achieving certain quite specific properties, which can be summarised as follows: 1. Specific stretch and recovery

properties in the warp, weft and bias directions

2. Specific cloth stiffness imparted by resin application

3. Specific stretch retention after flexing and bending to break down the resin finish

4. Cloth of maximum flatness with no curve along the length, and heat sealed parallel edges.

Cloths are typically designed as plain weave, very high-density constructions using high-shrinkage, high-tenacity yarns. The high weave density imparts inherent bias stability to the fabric, and the cloth is allowed to achieve its maximum shrinkage in finishing to further stabilise the structure. The yarn decitexes are chosen to give the required cloth weights (typically from 150 g/m2 up to 650 g/m2) and to influence the balance of stretch properties. For maximum bias stability, warp and weft yarns of approximately equal linear density are used; however, if a relatively heavy weft is used then minimum weft stretch will be emphasised because of the transfer of the woven crimp from weft to warp as well as the increased weft proportions. If a relatively heavy warp is used, the converse largely applies.

All the wet processing and subsequent heat setting is done opcn width to allow for shrinkage and avoid creasing and cloth distortion. Dyeing, where this is a requirement, is commonly done on pressure jigs or pad-Thermos01 ranges after scouring and drying, whilst heat setting and resinating is done on continuous open-width ranges. Resination is usually via a pad mangle system, and typical resin systems are often combinations of melamine formaldehyde and acrylic binders with other additional components. The resin serves primarily to further reduce the bias stretch and stiffen the cloth so as to facilitate the subsequent high-precision cutting and sewing operations involved in sail manufacture. Heat setting is done at temperatures ranging up to 210"c, often in two or even three stages. Control of cloth tension and temperature in these stages is vital to assure cloth flatness and avoid curvature.

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Ihdly, the cloth is calendered to glaze the surface and then the selvedges precision trimmed and heat sealed.

Woven nylon for spinnakers The requirements for spinnaker cloth can be summarised as follows: 1. Minimum weight consistent with

2. High tear strength 3. Specific low-stretch properties, but not

rcquired strength properties

necessanly minimum stretch.

Spinnakers typically use high-tenacity nylon 6.6 yarns in both warp and weft in a ripstop d e s i p which improves the tear strength. Because of the limitation on how fine filament yarns can be made, maximum density constructions are not usually possible, and the cloth is woven to give the required strength properties at the permissible cloth weight. The cloth is typically atmospheric jig-dyed and stenter set to a fixed width.

The cloth is then coated using spread coating techniques, although in some cases impregnation is still favoured. The coating which is applied provides a much larger proportion of the stretch stability in spinnaker than in polyester sailcloth, and therefore the coating formulation and application are very important to the success of the cloth. In coating, both surfaces are normally coated with mean coating thickness for each surface as low as 5 to 6 pm. A key feature in coating is that in general terms tear strength is approximately inversely proportional to stability and coating technology is centred around increasing stability without loss of tear strength or stretch recovery, and balancing stretch and tear values to give a consistent useful mix of properties in the finished cloth. Many polymers are used in coating, including polyurethanes, epoxies and silicones, each providing slightly difftwnt attributes to the cloth.

Coloration The original tan colour of sails owed more to the requirement of cloth protection than aesthetics, and the colour was as a result of the use of various ochres in the applied mixes which imparted certain desirable characteristics to the preparation. The coating was primarily to minimise rot and also to protect the cloth and seams from abrasion against the vessels’ running and standing rigging. I t also served to make the canvas impermeable to air, thus improving the sail’s performance. A recipe used on the sails of Thames barges well into this

Electron micrograph of silicone-coated spinnaker nylon before stretch treatment

Same cloth as above showing permanent coating damage after excessive stretch

century, used equal proportions by weight of cod liver oil, water and a mixture of red and yellow ochre. This was well mixed and spread onto the sails on a flat floor. Both sides were treated, and once dry the sails were ready for use. This treatment would be repeated many times during the sail’s life.

Modern dyeing of sailcloth is principally for aesthetic reasons, more often than not to reproduce the traditional colours of treated tan sails or Egyptian cotton, although other colours have also become common.

Before dyeing, polyester sailcloth has to be scoured for the removal of size, usually polyester based, as the dyestuff has a greater affinity for the size than the fibre. The cloth is then dyed and set.

pressure jigs using pre-selected disperse dyes. All components of a dye combination must exhaust synchronously to help promote level dyeing. Dyestuffs used must also have high fastness to wet processing, light, seawater, rub fastness and wash fastness - it is not uncommon to see a crew member scrubbing sails with a yard brush and a bucket of hot soapy water.

Another important factor to take into consideration is the amount of colour change that takes place during polymerisation of the resin applied after

Dyeing is typically carried out on

dyeing. The colour change with incompatible dyestuffs and resin can bt, quite dramatic - light blue changing to khaki, or bright red to port wine. This, ot course, is minimised by careful dyestuff selection and recipes that compensate f o r colour changes.

The dye performance criteria on spinnaker nylon are similar to that of polyester; however, atmospheric jigs are typically used and the dye chemistry used is appropriate for nylon 6.6 dyeing.

Conclusion The sailcloth industry has evolved in this century form one of strategic necessity to catering principally for a luxury leisure market. The focus of the business is now as a relatively small niche area of the technical fabrics industry, and because d the demands of top level competition such as the Americas Cup and the Whitbread Round the World race the technical requirements throughout the industry have become of paramount importance. The industry has drawn on technical innovations made for many other highly demanding technical fabric applications, and incorporated them into sailcloths with continually upgraded technical and performance specifications. Sails are still the only practical form of propulsion using readily available non- polluting natural energy sources, and the efficiency of the use of this power will continue to improve with time. It is entirely possible that in the distant future, sails will once again provide the maritime power of nations.

Acknowledgements Roy Mumford of Merlin Dyers and Finishing for his technical input on the coloration of polyester sailcloth.

James Lawrence of James Lawrence Sailmakers for the treatment of Thames barge sails.

Bibliography Association of British Sailmakers Journal ‘The Mainsheet’, April 1992 and May 1993.

Adam Rice is marketing manager of Richard Hayward Sailcloth, division of John Heathcoat and Co. Ltd, Tiverton, Devon.

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