Post by
zezo | 2014-01-31 | 17:53:06
It's a long story ;-)
First, there may be +/- 1 difference between the router and the game because of rounding errors. Sometimes there is 1 degree difference even in the game itself - when sailing at fixed TWA you are presented with false TWA value. If you set it at 140 the game will sail at 140 but show you values up to 141 which can be confusing. And at some points of the polars that one degree matters.
About the router, you will notice that wind direction, heading and TWA don't usually sum up to 0/360. That's because the "heading" is is direction to a point a bit down the route, and if the route is curved the directions don't match.
Also, small changes in direction/TWA (below 5 degrees) are not indicated by black dots, otherwise there would be infinite number of dots with interpolated winds, so the general direction of the track may diverge from the indicated heading without notice.
Personally, I use the track tool to find the best approximation, fixed heading or fixed TWA (red/green lines) that will get me the same result as the router (circles lying on the isochrones)
If you go by the numbers it would be better to use TWA if sailing at fixed TWA and possibly the heading, in relatively straight segments.
This one should go to the FAQ, but I was waiting for someone to ask first ;-)
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