Graph 1
Graph 2
In developing the Aquatich the Humphreys office ran an unusually specific dual-system analysis of relative and rated performance, varying design parameters and then scoring their candidate designs under both IRC and ORC. The results (above) are interesting and bear out what is seen on the water: IRC (red line) does not particularly like small, light boats but ORC (blue line) evidently likes them a whole lot less. Once DSPL increases above the base boat (above) the treatment by both systems does even up though IRC is always kinder to the lighter design. And then there’s the other big effect of boat size… for smaller IRC designs the French school led the way with conservative fin keels, as seen here (top left) on the hugely successful JPK 10.80. Go up in size and this IRC-based Fast40+ (left) from Shaun Carkeek is all deep fin and slender bulb. But 40-foot is still a grey area in IRC… however, by TP52 size the full-on racer is away over the horizon. It is often a similar story in ORC where TP52s have proved equally successful when well sailed
costlier under ORC than IRC. We did have two IRC trials to confirm this and the rating delta for an increase in upwind sail area through a taller, higher aspect ratio rig was distinctly more under ORC compared to IRC. The work we did, in terms of performance against rating, seemed to encourage a lower aspect ratio rig in ORC with longer J and E than the relatively high aspect ratio rigs with tall P and short E which have become typical under IRC. Consequently we ended up pushing the girths to increase area, with what is a relatively large headboard for a fixed backstay arrangement.’ However, the study Humphreys did on downwind sail area did
challenge a common assumption that ORC penalises large spin- nakers more severely than IRC. This may have become apparent at the last meeting of ORC’s International Technical Committee in Southampton in March, where Humphreys and other observers attended to exchange ideas. ‘Based on what I’d noticed over the years in ORC, I was expecting
large spinnaker areas to be heavily penalised. However, this didn’t appear to be the case, and the penalty in spinnaker area, at the sizes we looked at, was less under ORC than under IRC. I think this is partly because of a shape function introduced by the ITC a few years ago to encourage larger spinnakers – with the ORC VPP now trying to account for a loss of efficiency for a big spinnaker below 12kt TWS.’ The Aquatich will have a carbon rig from Pauger, and bucking the ORC norm will fly spinnakers from a fixed bowsprit. In summary, Humphreys said, ‘We started this process assuming
we would have a narrow, heavy, boxy design with a small rig so it has been a pleasure to see we ended with a nice, well-rounded design.’ Besides the Aquatich, there is one other ‘new’ ORC design that
was supposed to debut in Trieste but builder delays mean that it will now first race at the ORC Europeans in Gdansk. In fact, the successful 2015 Maurizio Cossutti design Katariina has been in Estonia having a new hull fitted under the existing deck. Cossutti promises this boat will be ‘rather different’ in hull shape from the old design when it does reappear.
28 SEAHORSE An experienced master at ORC design optimisation, Cossutti
has numerous clients competing at Trieste, particularly in the small- boat Class C where a great deal of work has been done on optimising designs to hit the top of the class limit. Among the Cossutti designs in Trieste are a racier version of the
production Salona 380, built lighter and with a deeper keel, an older Vrolijk 37 now armed with a dramatic appendage update and, perhaps most interesting, the heavily reworked Melges 32 Airis: here a shorter steel keel blade has replaced the original carbon foil, plus a still undecided array of out-of-class sailplan options that are being considered to boost light-air performance. And if the wind does pipe up watch out for the Cossutti-optimised
First 40.7 Mareus: this big boat is hundreds of kilos lighter than any other 40.7 yet with less draft rates just under the Class C limit... Finally, in Class C Cossutti also has his repeatedly modified Next
37 design Mercedes AMG, revised yet again this time with a long bowsprit and large masthead gennakers. Cossutti’s former protégé Matteo Polli has also been active,
working on many of his pretty Italia 9.98 designs, of which there are no fewer than five in the Trieste fleet including the 2015 Class C champion Low Noise II. Polli says that he has advocated increasing horsepower on all his designs to be competitive in the light air and, like Humphreys, he reckons there are no rating disadvantages in reverting to big masthead symmetric spinnakers hung on long conventional poles to maximise VMG in crowded tactical situations. Old school. Another trend Polli is chasing is in designing keels that are even
lower aspect in shape with shallower draft. He believes that these can be more efficient because ‘they have more effective draft presented to the fluid flow, and allow for less constraint in support structures’ than typical high-aspect keels. Short-span ‘squat’ keels have been a feature of optimised ORC
designs for several years so it is interesting that Polli now considers the approach can be pushed even further. Bilge keels, anyone? Dobbs Davis
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