Lee-Bow..... Windsurfers...etc (Dons tin hat)

That’s because in the no tide case the green boat is sailing at 45d to the true wind (inertial frame, ie land observer) and at 28d to the apparent wind. In other words best VMG is when sailing at 28d to the AW.

In the tidal case, the boat is going nowhere (relative to the land), so the apparent wind is the same as the true wind ie it sails at 28d to the true wind. Therefore all the vectors are rotated 17d and the red boat gets ahead.

Because it is wrong. If the vmg is the same at all angles then it’s the same in tide unless you work in the mythical LBE. 

Edited by L123456 - 30 Sep 19 at 7:42pm

Originally posted by Peaky ...tacit agreement that true wind is wind over land.

The trouble with tacit agreements is that no-one has agreed to them. Banal, but nevertheless true. And that's why the subject gets so very complicated. Everyone uses the same words in subtly different ways, and its a very human thing to assume that everyone else is using the words with exactly the same shades of meaning you are.

So the result is that people argue past each other because they are using the same words, but with subtly different meanings. Its reasonable, with the current UK dinghy sailor's vocabulary, to use 'true wind' for both the wind direction over the water and the wind over the land, because for different applications both are useful, but it would be a lot easier if different terms were used. I was going to suggest tidal wind and land wind, but land wind sounds like land breeze which is something else entirely...

I now see why a certain kind of academic likes to invent brand new words with nothing of the portmanteau about them: it may make their work completely incomprehensible to the casual reader, but if you can penetrate the gobbledegook its at least clear.

Edited by JimC - 01 Oct 19 at 7:58am

was that a first sign of some moderation in these threads... or was that post by GRF a figment of my imagination brought on by PTS?

Edited by mozzy - 01 Oct 19 at 12:34pm

All instruments whether hand held or part of a nav set up measure apparent wind. 

Edited by mozzy - 01 Oct 19 at 12:32pm