rules heavily penalise adjustable forestay tension. In that case, you can just vary tack tension to change the ratio.’
implication is that forestay sizes can be dramatically reduced. ‘On a superyacht, you could potentially reduce forestay diameter by as much as 75 per cent,’ Sanderson says. The benefits quickly cascade to other areas. In percentage terms, the mast does not receive the full benefit of the forestay load reduction, but Sanderson argues that even a 20 per cent reduction in mast compression creates a virtuous cycle which would produce a quite different boat.
‘It means the rig can be lighter, which means the keel can be lighter, which means the chainplates and structure can be lighter, all of which means the boat would require a smaller engine. The really exciting thing is that this could be the first real development that could bring down the cost of a superyacht.’ In racing applications, Sanderson envisages trimmers learning new skills as they play with the ratios between forestay and tack tensions to adjust sail depths. ‘It is almost a little bit backwards,’ he says. ‘If you want the sail fuller, then you have the forestay tighter relative to the jib luff and vice versa. ‘Some classes specify a fixed forestay tension and some rating
Top: the supermaxi Comanche fully powered up flying a cable-less J-0 and storm jib staysail from Doyle. The initial performance gains for superyachts are especially huge as luff sag becomes such a major issue on the much larger yachts. Above:
it works on smaller boats, too. This latest brand new suit of see-through Doyle sails on the MC38 Lazy Dog is the state of the art in Structured Luff sail technology
Structured Luff development for mainsails is still in its early stages. While the gains from a rig standpoint might not be quite the same as with jibs, there is distinct promise. Taking a square top mainsail on a Maxi 72 as an example, if you add a lens with a specific fibre layout along the luff loadline, you can redistribute the loads. When sailing upwind, by adding compression on the luff, the clew and therefore the mainsheet load would drastically reduce while still achieving the same degree of mid-leech twist. ‘A ram at the mast capable of adding more cunningham tension may not cost much extra weight in the middle of the boat, while a different mainsail structure that allows you to significantly reduce the mainsheet load means you can cut back on the size of travellers, cars and winches in a more weight-critical area of the boat.’
Sanderson concedes that by making the sails carry so much more of the load themselves, their weight does increase. ‘But the weight gain is totally disproportionate to the advantage gain,’ he says. ‘We are talking about a 30 per cent reduction in compression loads on the rig, with the massive trickle-down effect that has on the rest of the boat, and we are only talking about an increase in sail weight of a few kilograms. ‘Effectively, we are talking about tons gained in exchange for kilograms spent. If you add just two to three kilos of fibre into a Maxi 72 sail, it represents a huge increase in dpi. The reality is that the weight increase is quite insignificant compared with the load reduction. Sanderson says the Structured Luff technology evolved directly from investigating how to make Doyle’s cable-less sails work in a wider application. ‘It is a little bit
embarrassing,’ he admits, ‘because we really just stumbled upon the cable-less idea.’
This came from IRC code zeros Doyle Sails built several years ago, where they dispensed with a luff cable and introduced the lens concept, enabling them to achieve the required 75 per cent mid-girth measurement by adding area to the leading edge of the sail. As the apparent wind came forward, the leading edge folded back on the leeward side, effectively reducing the mid-girth measurement to about 62 per cent without breaking the rule. ‘We were blown away by how the luff stayed on the centreline,’ Sanderson recalls. ‘When we took bow-on
photographs, the sail was standing upright. It was a bit of a head- scratcher. The concept of the luff folding certainly upset some people at the time.’ Sanderson shrugs. ‘It is our job to come up with ways to win regattas within the rules.’ Sanderson says the market reaction was interesting. Rival lofts started out by dismissing the concept, but many have since attempted to imitate it. ‘It has been a fantastic opportunity for us. Boats where we never had a look-in before came to buy our code zeros. Then, when they found they enjoyed dealing with us, we got an opportunity to talk about the rest of their sails.
‘At the Maxi Worlds this year, the first three 72s were using full cable- less code zeros and genoa staysails. Bella Mente was using a spinnaker staysail as well. It has certainly been a big deal for us as a brand, but we have to keep leading the charge as much as possible.
‘While others are playing catch-up in code zero world, we are moving on, which is where all this Structured Luff innovation has come from. There is still a long way to go with it.’
www.doylesails.com
q SEAHORSE 75
KYLE LANGFORD
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