Dubai - Muscat, which polar
Post by iconPost by Ursus Maritimus | 2018-03-09 | 11:13:38

1. in the game interface with 5.6 kts wind and LG best vmg is at TWa 33

2. toxcct gives TWA 33

3. zezo routes with TWA 50

which one to believe?

commenticon 4 Comments
Post by iconPost by Ursus Maritimus | 2018-03-09 | 11:15:48
2. must be TWA 43 with toxcct
Post by iconPost by zezo | 2018-03-09 | 11:39:09
The peak is between 34 and 36, and it's a flat spot with the same wind speed, so you may get 34 if you count from one side and 36 if you count from the other.

In reality 37 or 38 may be 0.1% slower than the peak but lead you into wind that is 10% stronger and the overall speed is better.

BTW from my position the router actually goes at fixed heading until it reaches the maximum angle and then tacks.

Of course all of that does not mean that the predicted route will still be optimal in 3 hours with the new forecast, and there are cases when the router just misses the optimum VMG by few degrees (difference gets lost in the noise if small enough, so it may prefer 45 instead of 42 for a while)

Post by iconPost by zezo | 2018-03-09 | 11:31:40
The router does not have to sail the optimum angle. It's leading you in the direction where you will make best progress in the long run. That means:

1) Where there is more wind expected
2) Where there is favorable wind shift

In the current conditions the wind field rotates along the coast and sailing slightly lower may give you some advantage.
Post by iconPost by Ursus Maritimus | 2018-03-09 | 12:02:34
thank you Cvetan, quite clear to make my choices.

I didn't see anyone choose TWA below 40 so far
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