‘String’ sail politics

Further to his article on the world’s biggest sail loft in YM’s July issue, Nigel Calder explains the political dimension to cutting-edge sail technology…

The original patents for ‘string’ sails were taken out by Peter Conrad, the owner of Sobstad sails. The patents included two core concepts. One, known as ‘Airframe 639’, described the use of fibres laid out according to the load path on a sail, with the fibres continuous from sail corner to sail corner; the other, known as ‘Genesis’, described the use of discontinuous fibres laid out according to the load path, and matched from panel to panel.

Tom Whidden, Peter Conrad’s partner, took the Airframe 639 concept to North Sails, where it has been implemented as ‘North 3DL’. Membrane panels are draped over a ‘mould’ that contains hundreds of hydraulic jacks, which are adjusted to create the desired sail draft. An operator is suspended above the mold in a rig that allows continuous fibres to be laid down from one corner of the sail to the other, curved according to the load path. A second set of membrane panels is then applied and the entire sail is bonded into a single panel.

Years of patent infringement litigation between Peter Conrad and North ended in a settlement in 2002. In the meantime, the original ‘Airframe 639’ patent has expired, but North has a patent on its ‘mould’, although there are those in the industry who dispute its validity.

In the meantime, UK Sails developed a technique for applying continuous fibres after a sail is made, as opposed to during construction. This was trademarked as a ‘Tape Drive’ sail under a license from Sobstad (the ‘Airframe 639’ patent). In essence, it involves bonding the reinforcing (load path) fibres onto a finished sail. The patent for this process expired in 2004. CSF has been making this type of sail under the name of ‘Structural Tape Sails’.

Just as with ‘Airframe 639’ and ‘Tape Drive’ sails, the ‘Genesis’ concept starts with a sail design that positions reinforcing fibres according to the load paths. The software then divides the sail into panels whose width is determined by the lamination method (narrow panel material is laminated by passing it through rollers on a machine, while wide panel material is laminated using a steamroller type of laminator that is rolled up and down the material on the sail loft floor).

A computerised string machine lays in the fibres for the individual sail panels on a sheet of membrane such that when the panels are cut out and assembled, the same load paths are recreated as with a continuous fibre sail.

The disadvantage is the necessary discontinuity and seaming of the fibres. The advantage is an easier manufacturing process. Additionally, with the narrow panel material the top membrane layer is applied to the lower one after the fibres have been laid down, but before the individual panels have been cut out, which enables the laminate to be run through heated rollers under high pressure, creating a better laminate bond than with an ‘Airframe 639’ sail (the ‘Airframe 639’ sail is vacuum-bagged for bonding, which limits the bonding pressure to one atmosphere – i.e. 14 psi).

Peter Conrad sold the ‘Genesis’ patent rights to ‘Genesis International’ – which was owned by rival sailmaker Elvstrom – and merged Sobstad into Elvstrom. The patent did not apply in Australia, where Bob Fraser developed a similar process and sold cloth to sailmakers outside of Australia.

The Doyle group of sailmakers marketed this as ‘D4’. Elvstrom-Sobstad then gave sailcloth manufacturer Dimension Polyant a license to make the ‘Genesis’ material. Dimension Polyant bought Bob Fraser. Doyle now buys D4 material from Dimension Polyant, and Elvstrom-Sobstad is getting its royalties, so everyone is happy!

The ‘Genesis’ patent expired in the USA in 2006 and will expire in Europe in 2007.
CSF has been manufacturing a narrow-panel version of ‘Genesis’ sailcloth under license from Elvstrom/Sobstad. It is currently setting up to manufacture full-width panels in 2008.