LEE BOW EFFECT

I think the best way to have this debate is to drop the term "lee bow effect" all together. As concluded earlier different people are using it to mean different things, so we are arguing at crossed purposes. The question I think we debating is can the tide have an effect on your apparent wind?

I'm of the camp definitely yes. Simple geometry can demonstrate it by saying: if you have East going tide of 5 knots with a westerly wind of 10 knots (so both in the same direction) and you are floating (pointing north for arguments sake) and stationary in the water, how much wind do you feel? Answer should be 5 knots. If the tide turns and you have a 5 knot west going tide against the wind you will feel 15 knots of wind.

As you are not moving through the water do you call this apparent wind? Doesn't matter really, because in the same situation with a moving boat the tide is making a difference for the same reason as above. The difference will be less because of apparent wind due to boat speed. Now you can take this further by saying as long as their is a component of tide against the wind and it is pushing from the leeward side of the boat you will get some lift towards the wind.

Can we agree on that?

Originally posted by G.R.F. Originally posted by sargesail No it doesn't!  The apparent wind is a combination of a moving volume of air (True or Ground wind) and a moving carpet (OK volume but in practice it's 2D) of tide (the tidal wind), and your boat speed and your angle to the wind (I'll call it induced wind).   Pinching or footing changes the induced wind but it can not change the tidal wind. dude.. sailing 101. True wind generates movement. Movement generates "created wind" opposite to movement direction Both True and Created combined = Apparent wind. So Favorable tide on lee bow increases apparent wind by increased vector pressure on true wind Tide on weather bow decreases apparent wind inversely. Edited for accuracy..

Originally posted by JimC .... Same term, different meanings... it sounds as if you've never come across the traditional lee bow fallacy. That says that if the tide is more or less bang on the nose you should pinch up so that the tide is fractionally on the lee bow because even though you'll go more slowly the tide will push you up to windward. Its nothing to do with the choice of which tack is favoured and thus which you should be on, which is what I believe you are talking about.

Quite succinctly put, Jim.


One element that messes with your head is the fact that because the boat is slow relative to the ground, the apparent wind does not move forward as you expect it to, therefore you seem to be able to pinch without slowing the boat.
This feels like a strange effect, which some people seem to roll into 'the lee bow magick'
We tend to think in the 'land and marks' frame of reference, whereas the boat is operating in the water frame.

But we need someone clever to do some vectors!

No it doesn't!  The apparent wind is a combination of a moving volume of air (True or Ground wind) and a moving carpet (OK volume but in practice it's 2D) of tide (the tidal wind), and your boat speed and your angle to the wind (I'll call it induced wind).   Pinching or footing changes the induced wind but it can not change the tidal wind.