Best TWA to windward
Post by iconPost by Frankfurt | 2010-03-10 | 23:00:21

Hi Cvetan,

quite often your tool suggests 40° TWA to windward, while VRTouToulz and PacoTool suggest 36° (for many wind speeds currently in Clipper / pro sails).

Where does the difference come from? I am quite sure that it is not a question of trajectory. Is it due to the limited angle resolution the tool is using?

Thanks for clarifying.

commenticon 7 Comments
Post by iconPost by zezo | 2010-03-10 | 23:29:31
36° gives the best VMG above 14 kt wind spped, but 40° is very close, so if you are not going directly upwind (VMC != VMG) the optimizer may see 36 better on port tack and 40 better on starboard (or vice versa)
Post by iconPost by Frankfurt | 2010-03-10 | 23:43:06
O.k. Let's consider wind coming from 0° and the desired course is 10°.

Your optimizer might than suggest 42° on starbord tack and -28° on port tack, if I understood you correctly.

PacoTool would probably suggest 60% (or the like) of the time with +36° and 40% with -36°. And that is what my own calculations suggest.

I agree that it is all very close, but as we all know, to win the game you need to be 1 mile better after 5000 miles. So details count.

And for the other folks: I donated again.
Post by iconPost by Frankfurt | 2010-03-14 | 13:34:35
I made the calculation complete new again, independent of the first calculation - and of course of Paco's calculation. It again supports Paco's recommendation.

I can give details or send the excel file with the calculation.
Post by iconPost by zezo | 2010-03-14 | 18:21:21
You have a point. I'll take a closer look tomorrow. There may be off by one error if it does this every time (but I'm not sure it does)
Post by iconPost by Frankfurt | 2010-05-02 | 18:15:51
O.k. Cvetan,

haven't seen you around the Forum for quite a while. I hope, you are doing well.

Here comes the ultimate answer: Paco is right.

The reason can be understood quite simply: If we are looking for the best course to +10°, we need optimum speed to north, 0°, and a certain amount of way to east. When beating, as we all agree, the way to east is easily achieved. The optimum way to north can be taken from the polars and is - in the example above - +/-36°.

Therefore, the quickest way to +10° is beating with + and -36°, the two alternatives in a suitable ratio to end up at +10°, i.e. a little more often +36° than -36°.

Every other tacking angle will be slower to north, and hence slower to +10°.
Post by iconPost by jaruska | 2010-03-21 | 17:32:01
Je serais très intéressé de recevoir ce fichier excel, travaillant sur un programme de routage moi aussi
jaruska.
Post by iconPost by pcayrol | 2010-05-04 | 09:00:55
I spend a long time on this issue... I'm happy that someone agree with me... ;-) It's just a question of geometry ! ;-)
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