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

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

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)

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

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

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