Although the new Humphreys-designed Aquatich 40 is likely to be the only new design racing the ORC Worlds in Trieste this month there will be plenty of super-optimised existing designs to measure her against; that said, the yacht went afloat late and good preparation is critical in the well-refined but predominantly cruiser-racer ORC fleet – more than half of which are entered in the professional division. The Aquatich’s modest draft with a large area fin and bulb puts her in between the short, squat fins popular in ORC and the deep fin/long bulbs of larger IRC racers
‘and for the IRC evaluation we ran two base trial ratings with gaps in parameters filled in using an “IRC calculator” that we have refined over the years from the many design trials our office has run. ‘The IRC calculator is pretty accurate and reliable, but we also validated the rating deltas against existing IRC trials we already hold for similar displacement increments for a 39ft IRC design that we worked on last year. So I can’t say I’m 100 per cent certain, but I’m confident they’d be within 1-2 points’ accuracy’ The big points to note from the graphs (overleaf) are that IRC and ORC ratings for moderate (and heavier) displacement designs appear to be quite similar, which is reflected in the similar rating and corrected time deltas. However, beyond the base displacement used in this study, going lighter is currently penalised more heavily under ORC than under IRC.
‘This exercise was based purely around a light to moderate displacement mid-tech racer-cruiser design of 40ft,’ Humphreys added. ‘TP52s have obviously been successful in ORC Class A for a number of seasons, so there is clearly a bit of a grey area in between, as is also the case under IRC currently. ‘We did also look at a lightweight IRC/HPR-style 40-footer based on hydro data we had from a previous project using the same CFD code. This also highlighted to us that at this smaller size, the lighter you go under ORC beyond a certain point the increasingly punitive the rating becomes compared to IRC.
‘However, this is a simplified comparison as once we start building reaching performance into the equation the lighter designs begin to show marked improvements in terms of performance against rating. This is true under both systems; however, under ORC, depend- ing a little on the scoring option used, the relative performance gains are not as significant as under IRC, with its single number scoring, as ORC obviously tries to account for the improved reaching performance due to a lighter displacement.’
Humphreys then frames the design trends in the context of the typical ORC racing format: ‘I suppose one contributing factor as to why ORC still seems to favour moderate to heavy designs in the smaller size range is that all major ORC championships are wind- ward/leeward inshore biased with only a small offshore component, whereas most IRC events typically comprise more varied courses with offshore races quite commonplace.’
Draft for the Aquatich is 2.55m. Humphreys says that, due to the moderate displacement, a longer fin with less bulb weight for the same righting moment was not necessary. The draft was ulti- mately driven to provide sufficient span and aspect ratio for efficient upwind performance but with an easy groove; a shallower draft was also studied but the loss in upwind performance was enough to result in a poorer corrected time over the course types considered. On sail areas Humphreys had these observations: ‘When isolating sail area we found that increasing upwind sail area appeared to be
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