Left: the mighty fast TP52 looks pretty humble when directly compared to its big sister. While the Maxi72 struggles to get going in light air, compared to the nimble 52, from 9kt TWS up it is always relatively faster upwind. But the downwind gains by the smaller boat outweigh the upwind losses as soon as it is blowing harder. Of note is that IRC gets the faster offwind boat back into the frame in a breeze while under ORCi the heavier design’s upwind speed will leave it largely unassailable
calculate how much this all means in terms of the elapsed time margin necessary for the larger boat to keep the lead. For example, at 11kt TWS the Maxi72 wins the race by 190 seconds on corrected time, leaving the TP behind by 11 minutes 21 seconds on the water (however, what we usually want to know is how much margin must the Maxi72 have on the water to win on corrected time.) RW: So what am I really looking at here? Are the Maxi72s for some reason highly
optimised for 9-14kt of breeze or is there an imbalance or distortion in the TP52 optimisation driven by the class box rule, or a difference in how IRC appreciates the two boats – or a combination of all of the above? BZ: I believe that in the lower range the Maxi72 is relatively too heavy and, despite their optimisation towards lighter dis- placement, the larger boat simply struggles to build speed, especially downwind. In the mid to upper wind range, the fast
upwind VMG of the Maxi72 gives it a boost and if you take just the upwind part of the race it is unbeatable on corrected time. TP52s, on the other hand, have all their advantage downwind, due to their favourable weight/sail area ratio – that looks to be encouraged by IRC. I don’t think there is an imbalance in the optimisation created by the TP52 box rule but probably the TP could be better if it were IRC-optimised for upwind sailing? Looking at how IRC appreciates differ- ent boats, assuming that both classes represent the current state of the art in IRC optimisation, you could feel that IRC gives a bit too much advantage to the bigger boat upwind while leaving the downwind part of the race favouring the smaller and relatively lighter hulls.
Since the IRC maths remains secret and we can only see the overall result it is difficult for me to draw strong conclu- sions… but this is certainly what we generally see on the IRC racecourse across the various different sizes of boat.
q
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