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LEE BOW EFFECT

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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: 11 Oct 11 at 4:45pm
One of the main sources of confusion in this topic is that not everyone's talking about the same thing...
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rb_stretch View Drop Down
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Post Options Post Options   Quote rb_stretch Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 4:46pm
Just to add to others, it's definitely very real. I've mostly thought about it in keel boats. As anyway knows tide rarely goes in a straight line for any distance near shores. The navigator will often be thinking about the course that maximises any lee bow effect and minimises the opposite. Of course you are still having to balance that against tidal strength, eddies, gates etc for overall maximum gain, but it is one of the factors.


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tgruitt View Drop Down
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Post Options Post Options   Quote tgruitt Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 4:59pm
Originally posted by JimC

One of the main sources of confusion in this topic is that not everyone's talking about the same thing...


I always thought a lee bow was tacking under someone and being sucked up to windward a bit by the air rushing between the close proximity of the rigs?
Needs to sail more...
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Post Options Post Options   Quote rb_stretch Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 5:08pm
I don't type fast enough and just seen the other answers. I think there is probably is confusion about the definition. I think the point about just pointing a little higher making a difference is probably the myth part as I kind of recycled it as I heard it.

For me the bit I experience as real is the difference between a tide coming in on the lee bow versus the windward bow. That's why you try on be on the tack with lee bow rather than the opposite.




Edited by rb_stretch - 11 Oct 11 at 5:39pm
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Post Options Post Options   Quote rb_stretch Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 5:12pm
Originally posted by tgruitt

Originally posted by JimC

One of the main sources of confusion in this topic is that not everyone's talking about the same thing...


I always thought a lee bow was tacking under someone and being sucked up to windward a bit by the air rushing between the close proximity of the rigs?


Have to say I've only heard lee bow in reference to tide. I believe the air ahead of a boat is only affected for a very short distance so you would have to be incredibly close, like the distance between main and jib.

Having someone just under your lee bow I always assumed to be the start of when you are getting dirty air...


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G.R.F. View Drop Down
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Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 5:17pm
Perry, that's the chap, be cool to race against him in some tidal venues..

One point he makes is true, pinching rarely helps, not even to just get the tide on the knock because it doesn't help what you're looking for. Which is an increased power supply by combining the true wind with the created tidal wind thus increasing the apparent wind on one tack. The water may well be moving over the bottom and away from the mark, but one of the boats on it will be moving faster over that water than the other simply down to the increase in wind - sure they'll have to tack, but where and when, becomes important. (the tide might be faster offshore than inshore, the wind might be less inshore than out to sea, the current very rarely is acting constantly over the entire course (you tell this by looking at the water).

Trust me, he's wrong.

We once sailed an entire windless race without pumping, up the Thames, entirely on the wind created by the currents movement against still air - that's the effect you're looking for, created tidal wind to combine with the true wind, think of it that way.. In that instance it was a favourable lee bow tide on both tacks, the guys that did better were those that spotted where the current was fastest (on the inside of the bends).

Many a day back home in a drifter, we sail home choosing the tack that puts the tide on the lee bow, those that don't just drift downtide. (You can't tell some folk)


Edited by G.R.F. - 11 Oct 11 at 5:19pm
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rb_stretch View Drop Down
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Post Options Post Options   Quote rb_stretch Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 5:38pm
Glad it isn't just me who has experienced this as real!


Edited by rb_stretch - 11 Oct 11 at 5:38pm
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Post Options Post Options   Quote r2d2 Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 5:41pm
Originally posted by rb_stretch

Originally posted by tgruitt

Originally posted by JimC

One of the main sources of confusion in this topic is that not everyone's talking about the same thing...


I always thought a lee bow was tacking under someone and being sucked up to windward a bit by the air rushing between the close proximity of the rigs?


Have to say I've only heard lee bow in reference to tide. I believe the air ahead of a boat is only affected for a very short distance so you would have to be incredibly close, like the distance between main and jib.

Having someone just under your lee bow I always assumed to be the start of when you are getting dirty air...


I have heard both the tide thing and the issue of tacking just under another boats lee bow. 
 
I understood that the idea of tacking just under another boats lee bow was that it slowed them down enough either to make them tack off or enough so that after a short while you can then tack across them
 
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Rupert View Drop Down
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Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 5:45pm
You are talking about 2 totally different things, Jim and GRF. Of course where you are in the tide has a massive effect, but the very specific effect of the tide pushing just on the lee side of your bow having a magic effect compared to it coming straight on is what the lee bow effect is, so making pointing very slightly higher worthwhile.
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Post Options Post Options   Quote Presuming Ed Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 5:45pm
Originally posted by rb_stretch

Just to add to others, it's definitely very real. I've mostly thought about it in keel boats. As anyway knows tide rarely goes in a straight line for any distance near shores. The navigator will often be thinking about the course that maximises any lee bow effect and minimises the opposite. Of course you are still having to balance that against tidal strength, eddies, gates etc for overall maximum gain, but it is one of the factors.

That's different. If the tidal flow varies across the course, then obviously the wind shifts resulting from the tide will vary across the course, and a good (or even semi competent) navigator should take advantage of that - looking for the maximal tidal lifts, and minimising the knocks. 

If, however, the tide is even across the area of the course, then the lift you get on one tack (relative to the ground wind) will be offset by the knock you get on the other tack (again, relative to ground wind). What you gain on the swings, you lose on the roundabouts. 
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