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

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JimC View Drop Down
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 1:15pm
There's a lot of confused thinking about this topic, and more than one definition of lee bow effect. As stated, GRFs definition of lee bow effect is different to the definition that was found in some old books and was complete nonsense.

In practice it makes very little difference whether the tide is half a degree one side or the other of the direction the boat is pointing, and personally I have my doubts that many people can really be sure to that degree of precision where the tide is anyway, especially as it will vary anyway. But one thing's for sure, if you can manage to point five degrees higher than everyone else without losing speed then no tide explanation is needed as to why you left the rest behind!

Edited by JimC - 16 Sep 19 at 1:16pm
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iGRF View Drop Down
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 2:24pm
It happened co incidently this very weekend almost the entire fleet took an early tack which in the face of it was the right thing to do, but the tide actually curves across the course, so as they initialy set off they have the tide on the lee bow, then as they continue up the beat they can try the bit where we all agree pinching to keep it there doesn't work until they pass the point where it is no longer on the leebow, whereas a short tack further out to ensure a better angle keeps a stronger lee bow force in place the entire beat even though we are all essentially on the same tack.

I can see I'll have to come up with another term for it, fluid vector confluence, or something similarly confusing maybe then it'll stick.

It is true that the words 'lee bow effect' are confusing especially as they describe the effect of the boat beneath you off the start line, which is why I used the tidal prefix.

Tide may well be like a conveyor belt in some places, but it ain't where I sail, nor is it in the multiple places I have sailed this past forty years from Whitely to Pevensey Bay, Hartlepool to Hayling, Felixtowe to Falmouth, Plymouth to Portland and without it sailing would be a much duller activity.

Tide for us coastal sailors makes up for not having the shifts inland sailors enjoy in my view and many a time it's provided, just like last sunday, a get out of jail free card.
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JimC View Drop Down
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 2:33pm
Tide's always like a conveyor belt in its effect on the individual boat, but its a wobbly and bendy conveyor belt that changes speed all the time...

I do recall racing one time at a reservoir where they were pumping in so much water that there was a current radiating out from the inlet. That was very odd!
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 4:36pm
I think it requires a different mindset, you have to think of yourself as existing between two moving fluids and work out the best way to have the sum of their joint forces working for you.
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 4:57pm
Originally posted by iGRF

...you have to think of yourself as existing between two moving fluids...

Which is exactly what is happening anyway.
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 5:47pm
Originally posted by JimC

Originally posted by iGRF

...you have to think of yourself as existing between two moving fluids...

Which is exactly what is happening anyway.


Obviously, but lots of folk don't think like that, they focus on the wind and other boats, when the real focus should be the next mark and the fastest approach you can make to it.
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Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 5:52pm
This is interesting. At one end we have the die hard “lee bow” fraternity that from their “gut feeling “ and experience says that this is real, and the other camp that have worked out the vectors and other such maths and conclude that it all is b***ocks.
What if they are both right (sort of!)
I admit I am in the latter group, but I ask why do the other lot swear that it is real?
So maybe they are seeing something a putting it down to the LBE.
So 2 boats are beating into a strong tide on the same tack.
It will take a long time as they are hardly making any ground. If one is able to outpoint the other it will appear to make a lot of ground to windward as the leg is so slow. Think of it magnifying the effects of the small differences in height (pointing)that the two boats have. So by the end of the leg the boat that has pointed higher will have a good advantage over the other boat and he could easily put that down to the old LBE, and his ability to squeeze that last 5deg to lee how the tide.

What do you think?
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Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 6:07pm
Another thought - if you were on the beach watching this going on all you would see would be the small movement forward of the two boats and the significant move sideways from the boat that was pointing higher-I think that even I would be converted seeing that!
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Post Options Post Options   Quote GarethT Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 6:15pm
Yup. Watching from behind. He started behind and to leeward (in fouler tide), and ended up ahead and to windward. It was very obvious watching that something was going on. Even my non sailing wife noticed!
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By The Lee View Drop Down
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Post Options Post Options   Quote By The Lee Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 6:18pm
Does the tide push on your lee bow? NO as others have said consider it as a conveyor belt. Can the tide change your apparent wind which would change how high you point? YES
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