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

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Originally posted by mozzy If you can't explain its relevance than yes, we are.

Originally posted by iGRF Both fluids contain energy to be harnessed, sorry it's a fact and don't ask me to draw you a vectorgram whatever..

Ah, well now we have to be very careful, because there are considerable traps for the unwary here.
The energy to *sail* comes from the difference in velocity between air and water, and that energy is the same whether there's 5 knots of tide and no wind, or 5 knots of wind and no tide. And as we should all know, if there's 5 knots of wind and 5 knots of tide in the same direction, we feel no wind on the boat and can't sail. After the boat has passed both wind and water are moving at a lower *relative* velocity, be it all in eddies and things.

However the current is also moving the boat (or not) in a separate energy mechanism where the boat just drifts, the moving carpet if you like, and that moving carpet is providing energy from a different mechanism. And that adds or subtracts from the wind/water relative motion energy.

Edited by JimC - 26 Sep 19 at 7:07pm

Let me add -apart from any affect that the movement of the water has on the apparent wind on the sails (the vector sum of the true wind and the tide induced wind)

I read recently that my schoolboy knowledge of lifting sections (Bernoulli principle) is a myth and lift is simply down to angle of attack.