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

Originally posted by sargesail Originally posted by iGRF As to those who would decry the 'Ferry Gliding' example simply because it doesn't correspond with their lee bow debunkingposition. I would suggest the following. If you have say a 4knot current one way with your craft headed the other directly into the flow balanced exactly by a four knot wind on a dead run. Brought effectively to a standstill over the ground. What would happen if the plate gybed to the left (or right) even just one degree (rudder still centred)? If the others are to be believed nothing would happen. But the fact is the craft would shift right or left even though the water it is sailing in doesn't 'know' anything has happened. Sorry whatever they're reading it's been misleading them. Ok which of these 2? It may not be relevant but I’d like to know what assumption we are making about impossible performance envelopes!

Both boats would have the sensation of normal movement as generated by the wind on the given craft lets assume they're super efficent and as it down wind they acheive the actual wind speed over the water.

So the boat on the left would appear to be travelling at 4 knots over the water and the boat on the right would be tavelling at 8knots.

But if we introduce a land based destination, the boat on the left aint going anywhere but the boat on the right would be making 4 knots progress..

I would assume we'd all agreed on this?

Originally posted by Oatsandbeans This is my last effort to explain this as simply as possible ( no mention of vectors I promise). Here is a simple analogy to consider. We take 10 young laser sailors that have never sailed on the sea and take them to the coast. We take them off shore where they cannot see the shoreline. We tell them that they have to race around some buoys as normal, but the buoys and start line will be moving. They think this is weird but they soon get the hang of it and they learn hat the moving buoys affect the lay lines and it is easy to over stand the marks if they haven't taken into account the speed and direction of the buoys. The smart ones also notice that the wind shifts when the buoys change direction. At the end of the week they all agree that this is just like sailing their lasers inland as long as you keep an eye on what those pesky buoys are up to! Think about it!

Hmmm. Let’s extend it a little. Not only can they not see the shore but there is also layer cloud everywhere and it is hard to see where the sun is.

I contend that they would in fact not make the observations you suggest. The most aware might note that the course appeared to get a little longer or shorter or right or left skewed as the tide turned. They would also note increases or decreases in wind strength as tides changed. That would also affect the height of the waves.

They would observe that untethered marks drift at different rates in different wind strengths and that bigger waves on the sea mean the rate of drift is faster.

Moving lay lines would only relate to this rate of drift.

I like it. 

IGrf - what happens next? I’ve gybed the board for you. Specifically which way does the boat move? What happens to the sail?

Edited by sargesail - 03 Oct 19 at 10:26pm

[QUOTE=JimC] There are at least 3 "Lee bow effects".Two of them are real, and one is a myth.

The first (true) is nothing to do with tide, and is to do with the wind bend that heads a boat which has another boat close on its lee bow.

The second (true) is the general principle that tide on the lee side tends to be more favourable than tide on the windward side, and so its good to bear that in mind, especially if the tide varies across the course or will change during the leg.

The third, the myth, seems to have been propagated in a book by one of the Melges family in the US. Its not in any book I have. Ironically I cannot find a good copy of this to quote it exactly, all I can find is text where people are debunking it. It goes something like this. If you are sailing nearly directly into the tide, with the tide say 1 degree off the windward bow, the tide will be pushing you steadily to leeward. If you pinch up, so the tide is say 1 degree on the leeward bow, then the tide will be pushing you steadily to windward. Superficially this sounds very convincing but actually in both cases the tide is pushing you in the same direction by the same amount. And if the tide is almost exactly on the bow, the actual amount of lateral component from the current is nearly nothing anyway.

[/QUOTE

I’m pretty sure that the myth can be found in one of the early great (other than LBE!) works on dinghy tactics. Until I’m not going to say who or which until I get home and can check - cos I don’t want to wrongly slander one of the greats.