Pioneering integrated performance development

by Tracey Johnstone on 16 Feb 2008 Going into the 18-foot skiff World Championship, the JJ Giltinan Shield, on Sydney Harbour this weekend three of the competing skiffs carry pioneering integrated sail and spar technology developed by the North Sails group.

The further development of North’s 3DL sail production technology and a relatively new partnership with spar-maker Southern Spars gives these skiffs a significant advantage over their fleet rivals.

Two years ago North Sails Australia, led by managing director and ex-18-foot skiff sailor Michael Coxon, saw the opportunity of applying 3Dr sails and North’s Flow and MemBrain computer program to the next phase of 18-foot skiff development.

The technology is not new. It has been well-tested on a range of large yachts by some of the best sail-designer minds. The difference for Coxon and his team is the application of that technology on significantly smaller, but still high-performance boat.

Where did it all start ?

The modern America’s Cup rule has always encouraged big roach mainsails and as materials and technology have advanced in both spars and sails, North Sails has lead the development of big-top sails. The lessons learnt from successive America’s Cup were then applied to maxi yachts such as Alfa Romeo and Wild Oats XI, as well as Volvo Race boats.

The North sail-designers found big-top mainsails on ridged masts had a nice twist profile, automatically controlling power as they go up and down the wind range, rather than as traditionally found on a skiff with a relatively soft mast where the mainsail relies on the mast to do the work and the sail to follow behind.

The designers also found on these yachts that the stiffer the mast, the more control they had over the sail and the more the sail worked for them. This concept was then taken into the maxi yachts. Again, they found the stiffer they made the masts in the maxi yachts, the more successful the big-roach mainsail was, as they searched for stability in the sail and in the mast. Achieving stability meant the large roach mainsail could do its work.
Another interesting lesson from the big boat programs was that the bigger roach sails reduced rudder angles for weather helm on the yachts.

'Basically, by putting more area up high, most people would think that was aft of the centre of effort of the rig and you would end up increasing weather helm. But, because of the trip profile working automatically, it actually decreases helm. We found with the pin-head mainsail the rudder angles are up around the five to six degrees. When we put the big-roach mainsail on, we reduced down to about three degrees.

'Less rudder angle means less drag so you get better performance,' Coxon explained.

This was another factor that Coxon considered a potential positive for the 18s.

Pioneering 18 footer development

With these lessons under their belt and a long-held passion for 18-foot skiff sailing, Coxon embarked in 2006 on a development program with two boats – Fiat (Michael Coxon, the nephew of North’s Michael Coxon) and Gotta Love it 7 (Seve Jarvin).

The development program started with the crews making changes to their carbon 18 footer rigs to make them stiffer. Previously the 18s raced with aluminium rigs with a luff curve of about 550 to 600mm. Changing to carbon rigs, five years ago, reduced the luff curve down to about 480mm but did not really change the characteristics of the boat and how it was sailed.

The rig changes during the 2006/07 season were achieved through changing from an aluminium track to a carbon track right the way through the rig. The new carbon track increased the stiffness of the rig by around 12 to 13 per cent. They also cut off parts of the tapered section of the rig leaving a fatter section. Both of these innovations gave them a rig about 20 per cent stiffer than the boats had previously.

It was the first major step in improving the performance of the boats.

The North Sails team then introduced the two skippers to 3Dr sails. 'Their boats require very durable sails that hold their shape for a long period of time because the club owns all the boats and all the sails. So, what they don’t want to be doing is replacing sails every year. The 3Dr product is ideal as it has very, very good longevity both in strength and in holding its design shape where panel sails tend to lose their design shape fairly quickly,' Coxon said.

As you could imagine, skiff sailors are tough on sails which includes high impact during swims. With 3Dr now in its second season on 18ft skiffs, North Sails have not had a sail failure.

'The sails are so much lighter than any panel equivalent. Which is a big saving to the boats and the crews, as we know, dead weight slows you up.'

3Dr has been in the development phase for the last ten years. It is a derivative of the 3DL North Sails technology that took the sailing world by storm 15 years ago.

The 3Dr sails are moulded on a rotating drum. The sail is formed over the drum as it moulds into the sails shape, as it goes over the drum, it is moulded and cured instantly. This method of production allows for more than one sail of a similar denier, or yarn weight, to be moulded at one time. North’s can now produce a larger number of thermo-moulded sails quickly and cost-effectively.

'Whenever you look at a moulded 3Dr sail, the leech twist is just beautiful. It is really, really fair. Getting the fair leech twist is one of the key parts to getting the boats performing on the water,' Coxon said.

Both Fiat and Gotta Love it 7 carried these new sails in the 2006/07 season. As a result of the two-boat development program they dominated the results during that season, and finished first and second, respectively, in the 2007 World Championships. 'The two boats were considered to be quite a step above everything else,' Coxon said.

Coxon at this point was simply not willing to let the development program come to an end without utilising North’s then newly-available Flow and MemBrain program. With the support of Fiat sponsor Neville Crichton and Gotta Love it 7 sponsorship manager Iain Murray, Coxon put the boats back on the water for a winter of intensive development and testing work under the guidance of 7’s coach Andrew Palfrey and Coxon.

'Over the winter months between April through to June last year (2007) we decided to leave 7 as standard, which had the first step towards a stiffer rig, but make modifications to Fiat on their number one rig. We then took the 06/07 Fiat mast, which was identical to 7’s 06/07 rig, and started to wrap carbon around it.

'We thought it looked good, but could go some more. We ended up stiffening it quite a bit to reduce mast bend significantly again,' Coxon said.

They re-cut the Fiat mainsail putting a new luff curve onto it and increased the roach. 'We knew we could push the roach larger as we got stiffer, so we went out over winter and did extensive testing of this. The feeling was we were going in the right direction.

'We would go off Sydney heads and Palm Beach for hours where in winter you can get nice flat seas and constant winds. Our conclusion at the end of this testing period; the rig was not only competitive going to windward, it also was faster downwind.'

These testing outcomes led the development team to sign off on the sails, but then pursue further development of the rigs.

Southern Spars, a member of the North Marine Group, was asked to look at the 18 footer project. Their one-design expert John Clinton sat down with North’s sail designer, Keith Lorenz. A set of parameters were established and the team of Clinton and Lorenz went to work on designing a new rig.

This approach to sail and rig design is an innovation of the North Sails group utilising a very powerful computer program which gives the sail designer the power to analyse the rig and the sail tog