Any windage knocks upwind performance. I would have allowed for the beams. They are unfaired and the drag from round sections at low Re# is significant.
I did not include any contribution from planing because the drive is so high that the bows get depressed and then the planing surface will not lift. If it managed to hold planing at its top speed then it may have reached 30kts..
With crew as ballast there was potential to shift weight aft on the ww hull and that might get the bows up so planing might occur. I did not allow for moving CoG aft of the middle.
My VPP assumes calm surface. The pitching model is not included in the VPP. I consider pitching from the perspective of increased drag and potential to nose dive. The pitching analysis is also useful to assess the clearance required to prevent deck and beams from ploughing.
On 8 Jun 2018, at 11:33 pm, Björn bjornmail@gmail.com [harryproa] <harryproa@yahoogroups.com.au> wrote:Rick, It looks like I would've had very little chance of winning the competition for a sail on Bucketlist if your polar SW is accurate... =)Did you write it yourself?My guess was 18 knots boatspeed upwind (12 knots VMG), and 29 knots boatspeed on the best point of sail. I based it on a simple VPP in Excel, but it didn't take some factors into account, like pitching. It did take the aero drag of the hulls into account though, and had pretty good estimations of the hull resistance (from Michlet) and sail lift/drag (from XFLR5). I neglected the aero drag of the beams/tramp though, which might be the most significant aero drag on the boat.If Rob keeps the contest going for the new foiling version, I might have the best guesses though, because I think my guesses where the most optimistic of all submitted. =)
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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