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How fast?


Azzurra and Robertissima navigator Bruno Zirilli talks raceboat performance with Rob Weiland, focusing on the relative pace of today’s pinnacle two grand prix classes – the Maxi72 and the TP52


40 SEAHORSE


Maxi 72 versus TP52 Rob Weiland: You are a world champion in both these two classes so how do you see the comparison in terms of both competitiveness under IRC and outright performance? Bruno Zirilli: Before we make a direct comparison between the TP52 and the Maxi72 under IRC it is good to see how they behave on the water against their VPPs. The TP52 VPP I have used is not the most recent one, to get a fuller picture I have used a TP52 in 2015 configuration for which we have a full year’s data. We could do the same for a Maxi72 of course but that would take another page or six… The graphs in Figure 1/2 display a large amount of information which it is worth investigating further. The most interesting difference is between the real data VMG and the VPP predictions. The best way to understand this difference is to study the graph on the right-hand side of Figure 1/2. These numbers are expressed in percentage terms to allow a better feeling rather than a bare comparison of the pure VMG in


knots. Figure 3 translates the differential for the TP52 to seconds/mile which is even more demonstrable than percentage VMG. The left-hand graph in Figure 3 shows upwind data, with the light wind range of 6-8kt being where the recorded data and VPP differ the most. At 6kt TWS upwind our model TP52 is slower and lower in angle than predicted by 50 sec/mile. At 8kt TWS upwind the boat becomes faster than the VPP by 25 sec/mile due to good speed combined with a higher sailing angle. Then as the wind increases the differences get smaller and oscillate around zero until we reach the top of the measured range at 22kt TWS.


It appears that in light wind conditions performances are much more difficult to predict. Moreover, in the small TWS step going from 6 to 8kt, the VPP error goes from over-estimation to under-estimation of VMG. Above 10kt TWS the situation is much better and the VPP is very accurate, being bang on the numbers in the 14-20kt TWS range.


With respect to speed alone (ie not


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