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

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CT249 View Drop Down
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    Posted: 18 Sep 19 at 10:14pm
Yes, 432, but that's not the mythical "lee bow effect". The tide does affect apparent wind and no one denies that. 

The mythical "lee bow effect" is that the tide (not the apparent wind, but the tide itself) will affect two adjacent boats differently, which is like saying that two parcels sitting next to each other on a conveyor belt will move differently depending on which way they are pointing.
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 19 at 10:51pm
Well I hate to add further complications, but now we've established that we work between two fluids, I should also point out that the second fluid is very much like the first and has similar vagueries, 'shifts' 'bends' 'gusts'( variety of flow and thus energy rate) just as the geography of the land effects the wind, so the geography of the sea or river bed affects the strength and variety of the flow rate and energy available. So just as one helm might pick up a lift from the wind missed by another helm to his lee, then so it is with the angulation to the shifts in direction of tidal current and like it or not some helms are better at it than others, so one helm may very well move differently to the other 'parcel' on the conveyor belt, after all conveyor belts are not fluid.

Now I would be the first to accept any variation is felt more easily on a sailboard than in a dinghy, indeed it's been my experience in some areas, Portishead springs to mind where that flow can make the difference between planing and not. The Columbia River Gorge has areas with both positive and negative current within a few hundred yards of each other, back eddys and the like. Any river sailor will tell you of the search for such things whilst racing.

So, I'm surprised by assertions earlier in this thread that no reference to such things is present in the myriad sailing books and articles in self help guides or have they all been 'debunked' by the infernal Perry?


Edited by iGRF - 18 Sep 19 at 10:52pm
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Post Options Post Options   Quote CT249 Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep 19 at 12:36am
Of course the tactics related to the variation in tides from place to place, even very close together, is known. If it's not written about much it's probably because it's so obvious. The variation in tidal effect caused by shallows etc was much debated as early as the 1850s in discussions about centreboards, for example.

To say it again, Perry is talking about something completely different. He is not talking about the effect of tides on vessels in different locations where each is experiencing different currents. He is talking about the effect (or actually the lack of effect) of tides on vessels in the same location where they experience the same current. 




Edited by CT249 - 19 Sep 19 at 1:34am
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Post Options Post Options   Quote CT249 Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep 19 at 1:33am
Originally posted by Sam.Spoons

I think the 'ferry glide' analogy is the best explanation, it seems to explain the 'being pushed to windward' bit very neatly.

My yachts used to be moored on a fast flowing river, where we used the ferry glide lots when mooring. But it's very different to the lee bow effect, because the ferry glide is essentially about two moving objects (a boat and the current) and one stationary object (the shore or a mooring).

In contrast the mythical "lee bow effect" is about three or more moving objects; all of the boats and the current. That makes it very different.
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Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep 19 at 5:15am
Page 8 and we get to the realisation that GRF has never seen a book with decent tidal tactics in it. Mine are woeful, though I honed my river current tactics right through childhood, so those are good, but I'm pretty sure I've read excellent recent stuff as well as Start to Win.

But maybe many are woeful. In a level 1 sailing course, the very basics should be part of the 5 essentials. Cheating the tide isn't just a racing thing.
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Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep 19 at 6:07am
Ok, so the mythical bit is middle boat in a pack all beating on port, suddenly heads straight for the Mark, punching the air and shouting 'Lee bow' ?
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Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep 19 at 6:41am
I have now come to the conclusion that all this bother on the LBE is due to two completetly different ways of mental processing. Science based and arty baed ( non rational- gut feeling).
I am a scientist and I live in a house of arty females ( wife and daughters) and I see on a daily basis that our minds work completely differntly. When I get a problem I work out the basic rules that are underly the issue and then try to sort out the problem. Arty types do it differently they use their experience and come to a decison based on gut feeling. Their approach is usually quicker than the science based one and often they are right.
This type of problem is not dissimilar to what I do 9 to 5 at work and whilst not bragging it is what I enjoy and I am now quite good at, however even at work some of my colleagues can perplex me with arty thinking leading to dumb decisions.

So, in reflection we will never square this. The guys that use their gut feeling will never think like the science based guys and it is best not to get worked up about it.
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep 19 at 7:02am
Originally posted by Oatsandbeans

...our minds work completely differntly. When I get a problem I work out the basic rules that are underly the issue and then try to sort out the problem. Arty types do it differently they use their experience and come to a decison based on gut feeling. Their approach is usually quicker than the science based one and often they are right.

I recommend Thinking Fast and Slow, by Daniel Kahneman. Doesn’t cover tidal tactics but still a superb book.
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Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep 19 at 7:29am
Peaky- thanks I will check it out
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep 19 at 9:02am
Originally posted by CT249

Originally posted by Sam.Spoons

I think the 'ferry glide' analogy is the best explanation, it seems to explain the 'being pushed to windward' bit very neatly.

My yachts used to be moored on a fast flowing river, where we used the ferry glide lots when mooring. But it's very different to the lee bow effect, because the ferry glide is essentially about two moving objects (a boat and the current) and one stationary object (the shore or a mooring).

In contrast the mythical "lee bow effect" is about three or more moving objects; all of the boats and the current. That makes it very different.

Yup, I'm not saying the LBE is real but that the Ferry Glide Effect might explain what is going on when somebody claims to have experienced the LBE.

In the OP's example with the tide passing through the harbour entrance a board getting the bow pointing slightly to windward of the tidal flow would FG to windward, one sailing free with the tide on the windward bow would FG to leeward. The effect of the former would increase the apparent wind and the latter decrease it?

Just trying to find a sensible explanation for the observed phenomenon.



Edited by Sam.Spoons - 19 Sep 19 at 9:03am
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