Judging true wind direction

[flaming]

OK, what I was trying to get at was something like a lift-keeler could tuck in to the shallows and avoid the the current where a deep fin keeler would be stuck out in the worst of it. You're right, I didn't word it well.

But that's a tidal stratergy, and regardless of which boat you were on, you'd be affected in the same way by the tide in the same place. (assuming you could float of course!)

I've always tried to keep an image of drift in my head when sailing. When planning I'd calculate drift and then just apply that to True Wind (as in against a fixed point on land) to get the apparent wind with no way on. Add in the estimated boat speed through the water and the heading and you get the estimated apparent wind. Done at the same time as planning the route. Mind you we didn't win many races...

Yes, that's what everyone has to do, as when you're doing your passage planning before departure, you are of course measuring the ground wind with your instruments, regardless of what mode you have them on!

Then if you're about to start a race and sailing around near the start line your true wind reading is now giving true wind (as distinct from ground wind). Assuming that your instruments don't have a ground wind setting (and that is a new thing) you are then looking at tide charts to try and predict if there will be a tidal effect on the breeze. And that's when you need to really understand what your instruments are telling you, and the distinction between true and ground winds.

And even cruising boats can find this sort of planning useful. Imagine a passage from the Solent, through the Alderny race to St Peter Port. If you've done your passage planning right, you will arrive at the Alderny race at the start of the west going tide. So it's quite possible that in the space of an hour or so you could have a tidal change of several knots. If the wind was a westerly, or a South Westerly, that will result in a correspondant increase in the true wind. Which is always nice to know is coming!