Polar table speed or Sailing data correlation
Post by iconPost by alexpanzeri | 2020-11-09 | 20:11:43

Good Evening Team,

one of our lady member of the Team has notice a strange value of the polar on IMOCA60 (both foiling and not):
- from 12 to 13[kts] of Wind speed and upwind, the boast speed decreases, while VMG increase, and after passed the range the boat speed is back to rise proportionally with wind. is it a glitch ? a table mistake? an aerodynamic effect of the IMOCA?

- checking this, I noticed also that the Jib is never selected in any range if full pack is on, even at Wv=15[kts] angle around 40-50° it remain in the LJ light Jib, is it a UI problem? IMOCA feature?

May these two affect the calculation?

Thank a lot again,
Alex p.

commenticon 4 Comments
Post by iconPost by zezo | 2020-11-09 | 20:32:20
Interesting observation.

That could be based on reality. If using the same sail (Genoa/Jib, whatever) there comes a point where the drag overcomes lift, heel angle gets worse and performance drops. Then you reef your main and change headsails.

Something similar happens above 30 knots. In the real world boat performance suffers because it's not only the wind. The wind generates waves. The risk of breaking something becomes higher. You have to wind down a bit.
Post by iconPost by alexpanzeri | 2020-11-10 | 09:12:46
Thanks a lot,
so it's just weird fluid/aerodynamic reality that I have learned at university :-)))

Post by iconPost by BooBill | 2020-11-09 | 22:05:01
It's actually from 12knts to 13.8knts. Both speed and VMG decrease, while wind speed increases. Above, I thought the observation was that VMG increased, while boat speed decreased. At constant TWA, that would defy Euclidian geometry.

I like Cvetan's explanation. Induced drag.
Post by iconPost by toxcct | 2020-11-10 | 00:19:28
Ah ah, I got a direct email about that exact observation.
Glad you guys come with the same kind of replies after all :)

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