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Old 29-11-2013, 12:58   #751
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It is certainly provable. But calculating individual special cases cannot ever prove your claim (that the effect never exists), unless you can also prove that those special cases represent all possible "optima" for the reverse claim. As you say, it's a vector calculation where an optimum is to be found. I suspect it would be easier to prove the general case as a simple algebraic (eg using variables rather than specific values) calculus problem. I think the only assumption we would have to make to do that is that the polar curve in the relevant upwind range is some sort of smooth 2nd order curve and does not have any funny kinks. I could do this, but am not going to bother, because I think the steady state case is useless and we all agree on the changing state case. As you point out, one individual case would/could prove the reverse claim (that it does exist at least in some situations). Today, to look for that, a mathematician might simply program a computer to throw random numbers into a vector calculation, and let it run for an hour, and see if it finds such a case. That is not "rigorous", and not a proof of your claim if it failed, but would probably find a counter case if one existed. There is certainly a more elegant way to look for an example, but brute force has mostly replaced elegance since I left school.
Totally agree , the variables is why the term is used.

You will never come to a creditable conclusion because those variables are what happens in the real world of sailing in tidal areas. Go round Portland bill on a calm day then come back and see if you can disprove the term.

Cross the English Channel and see if the wind is dead on 15 knots and from 98 degrees through your passage, ?

A question for Dockhead

Does the wind come round with the tide on a steady arc with the tidal stream when you sail the channel

This is written nicely.... I'm just trying to state my opinion ,I'm not waving a finger just don't see how the discussion fits .. I am open to correction.... It is the only way to learn and this thread has definitely taught me a lot
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Old 29-11-2013, 13:56   #752
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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A question for Dockhead

Does the wind come round with the tide on a steady arc with the tidal stream when you sail the channel

This is written nicely.... I'm just trying to state my opinion ,I'm not waving a finger just don't see how the discussion fits .. I am open to correction.... It is the only way to learn and this thread has definitely taught me a lot
Dockhead does not seem to be around at the moment, but may I comment on this? (I will anyway LOL)

Yes, of course a variable tide with a steady ground wind will shift the true wind (the true wind is just the sum of ground wind and wind induced by current). This leads to the adage of "lee bowing the tide" ie making use of the lifted tack as appropriate.

It has absolutely nothing to do with the erroneous "lee bow effect" where pinching to get the current on the lee side of the bow is supposed to create some extra lift.
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Old 29-11-2013, 14:10   #753
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

I am truly dumbfounded by the proposition that since the real world is full of variables then we should not attempt a "first principles" analysis. That's how we begin to understand what is going on. Then, if the wind shifts, or the current changes, we can reapply our understanding to the new conditions. If the variables become so complicated that we can't reasonably arrive at a mathematically correct answer (within reasonable limits) then we make reasonable approximations, or just wing it and get close enough.

If we are indeed debating the Seaworthy Lass definition of LBE, would someone please explain how it is supposed to work? Or at least provide an example that we can analyze?
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Old 29-11-2013, 14:24   #754
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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sailing in a current on the bow , in effect causes a wind that produces an increases in apparent wind angle over a situation where there is no current. The net effect of that is it allows a helm to head up slightly over the situation where there is no current on the bow.
Dave, I believe we all agree with you on this.
Sorry, we do not all agree. I don't.

Sailing with current on the bow does NOT "cause a wind that produces an increase in apparent wind angle".

This thinking is partly (mostly?) where the problem stems. The shift in the true wind does not depend on where the boat is pointing. In fact it does not depend on the boat at all. You could be sitting drifting on a raft and you would feel this change in true wind.

Altering where the bow is pointing does not alter the true wind. Your apparent wind is of course altered as you change heading, but only in exactly the same way as it is when you change heading with no current.

Furthermore, the current does not have to be on the bow at all when you are on the tack lifted by the current. It could easily be coming more from the rear when you are close hauled.
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Old 29-11-2013, 14:38   #755
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Originally Posted by Seaworthy Lass View Post

Dockhead does not seem to be around at the moment, but may I comment on this? (I will anyway LOL)

Yes, of course a variable tide with a steady ground wind will shift the true wind (the true wind is just the sum of ground wind and wind induced by current). This leads to the adage of "lee bowing the tide" ie making use of the lifted tack as appropriate.

It has absolutely nothing to do with the erroneous "lee bow effect" where pinching to get the current on the lee side of the bow is supposed to create some extra lift.
Your mixing up things. If a constant tide on the bow and a constant wind then the next affect is to generate a small increase in wind angle over the situation where the tide is not present. Because of that the boat can in theory cone slightly higher then without the current. If you do that with the current on the bow , the current ends up on the lee bow.

The effect is seen elsewhere on the compass but that's not the issue.

Le Bowing the tide is a different issue and that's about beneficial tacks etc

The pinching issue is a red herring by the way

Dave
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Old 29-11-2013, 14:40   #756
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Sorry, we do not all agree. I don't.

Sailing with current on the bow does NOT "cause a wind that produces an increase in apparent wind angle".

This thinking is partly (mostly?) where the problem stems. The shift in the true wind does not depend on where the boat is pointing. In fact it does not depend on the boat at all. You could be sitting drifting on a raft and you would feel this change in true wind.

.
SL,

I believe you are talking true (water referenced) wind direction (eg a compass direction) and Dave is talking wind angle with respect to the boat (eg an angle from the bow).

Just consider zero ground wind and 10 kts of current. To your point, the true (water referenced) wind will be 10 kts in the direction opposite to the current flow. This is true no matter the orientation of the boat.

But, to Dave's point it is also completely obvious that the wind angle (with respect to the boat - eg as measured as an angle from the bow, as most wind instrument systems do) will be determined by the orientation of the boat with respect to the current. If the bow is directly into the current you will have a 10kt wind over the stern (180 degrees on the wind instruments) while if the stern is pointed at the current you will have a 10 kt wind over the bow (0 degrees on the wind instruments).

We do in fact all agree with this, even you, you just don't realize it is what Dave is saying.
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Old 29-11-2013, 14:47   #757
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Originally Posted by Seaworthy Lass View Post

Sorry, we do not all agree. I don't.

Sailing with current on the bow does NOT "cause a wind that produces an increase in apparent wind angle".

This thinking is partly (mostly?) where the problem stems. The shift in the true wind does not depend on where the boat is pointing. In fact it does not depend on the boat at all. You could be sitting drifting on a raft and you would feel this change in true wind.

Altering where the bow is pointing does not alter the true wind. Your apparent wind is of course altered as you change heading, but only in exactly the same way as it is when you change heading with no current.

Furthermore, the current does not have to be on the bow at all when you are on the tack lifted by the current. It could easily be coming more from the rear when you are close hauled.
Seaworthy , you are mixing up winds. A boat sails in the apparent wind. It does not sail in the true wind.

Hence you must look at the effect of apparent wind angle.

What I have said is there is an effect of increase in wind angle , that's apparent wind angle , when the current is in the bow which allows an apparent improvement in wind angle over the situation where the current is not there.

PS. A boat close hauled with a current behind it will always result in a decrease in apparent wind angle. Simple logic shows it so. On other compass points it varies.

Whether that's a lee bow effect I'm describing I'm open to debate.

Dave
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Old 29-11-2013, 14:47   #758
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SL,

I believe you are talking true (water referenced) wind and Dave is talking apparent wind angle.

The position of the bow does in fact affect how the wind shifts with respect to the boat. (eg apparent wind angle).

If the bow is pointed toward the current then the current will cause the apparent wind to shift aft (eg Dave's increase in apparent wind angle) vs a no current situation.

Just consider zero ground wind and 10 kts of current. It is completely obvious that the apparent wind angle will be determined by the orientation of the boat with respect to the current. If the bow is directly into the current you will have a 10kt wind over the stern (180 degrees apparent) while if the stern is pointed at the current you will have a 10 kt wind over the bow.

We do in fact all agree with this, even you, you just don't realize it is what Dave is saying.
Tks Evans , you understand perfectly

Dave
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Old 29-11-2013, 14:49   #759
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Your mixing up things. If a constant tide on the bow and a constant wind then the next affect is to generate a small increase in wind angle over the situation where the tide is not present. Because of that the boat can in theory cone slightly higher then without the current. If you do that with the current on the bow , the current ends up on the lee bow.
Nope, sorry, if "you do that with current on the bow", the current could easily be on the windward bow on the lifted tack. This adds even more weight to the premise that shifting the current from the windward bow to the lee bow does nothing whatsoever to increase the lift.

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Le Bowing the tide is a different issue and that's about beneficial tacks etc
Great we see eye to eye on something

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The pinching issue is a red herring by the way
Are you now saying that pinching to get the current on the lee bow has no effect other than that produced by pinching without current? Have you finally converted your thinking and seen the light as I did LOL?
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Old 29-11-2013, 15:10   #760
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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SL,

I believe you are talking true (water referenced) wind and Dave is talking apparent wind angle.

Just consider zero ground wind and 10 kts of current. To your point, the true (water referenced) wind will be 10 kts in the direction opposite to the current flow. This is true no matter the orientation of the boat.

But, to Dave's point it is also completely obvious that the apparent wind angle will be determined by the orientation of the boat with respect to the current. If the bow is directly into the current you will have a 10kt wind over the stern (180 degrees apparent) while if the stern is pointed at the current you will have a 10 kt wind over the bow.

We do in fact all agree with this, even you, you just don't realize it is what Dave is saying.
We are discussing only one situation here - close hauled.

And of course if you have any boat speed through water, as you alter heading your apparent wind will alter . If you have no boat speed then the true wind equals the apparent wind.

And Dave was in fact discussing both true and apparent wind when he incorrectly stated:
"sailing in a current on the bow , in effect causes a wind that produces an increases in apparent wind angle over a situation where there is no current."
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Old 29-11-2013, 15:17   #761
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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SL,

I believe you are talking true (water referenced) wind direction (eg a compass direction) and Dave is talking wind angle with respect to the boat (eg an angle from the bow).

Just consider zero ground wind and 10 kts of current. To your point, the true (water referenced) wind will be 10 kts in the direction opposite to the current flow. This is true no matter the orientation of the boat.

But, to Dave's point it is also completely obvious that the wind angle (with respect to the boat - eg as measured as an angle from the bow, as most wind instrument systems do) will be determined by the orientation of the boat with respect to the current. If the bow is directly into the current you will have a 10kt wind over the stern (180 degrees on the wind instruments) while if the stern is pointed at the current you will have a 10 kt wind over the bow (0 degrees on the wind instruments).

We do in fact all agree with this, even you, you just don't realize it is what Dave is saying.
And so why is this even an issue? What exactly are we arguing about? OF COURSE the apparent wind changes when the boat changes orientation (assuming non-zero wind). And the True (water-referenced) Wind is affected by the current. As Seaworthy and I have said several times, that is the definition we are using for True Wind: the combination of the Ground Wind and Current vectors.

It's damn hard to have a productive debate when nobody agrees on what issues are being debated.

Dave, and Evans, for what it's worth I completely agree that the Apparent Wind changes with boat orientation. Now what?
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Old 29-11-2013, 15:19   #762
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Seaworthy , you are mixing up winds. A boat sails in the apparent wind. It does not sail in the true wind.

Hence you must look at the effect of apparent wind angle.
I am not mixing up wind LOL. Yes, of course the boat sails to apparent wind, but apparent wind is just the sum of true wind and wind induced by boat speed and leeway.

Quote:
Originally Posted by goboatingnow View Post
What I have said is there is an effect of increase in wind angle , that's apparent wind angle , when the current is in the bow which allows an apparent improvement in wind angle over the situation where the current is not there.

PS. A boat close hauled with a current behind it will always result in a decrease in apparent wind angle. Simple logic shows it so. On other compass points it varies.

Whether that's a lee bow effect I'm describing I'm open to debate.

Dave
Dave this is completely wrong. A boat close hauled with current behind it (abaft the beam) can of course result in an increase in the apparent wind angle. Why on earth wouldn't it? The lift has nothing to do with where the current is hitting the boat. It is to do with what tack you are on.
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Old 29-11-2013, 15:28   #763
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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>>Originally Posted by goboatingnow
>>If a constant tide on the bow and a constant wind then
>>the next affect is to generate a small increase in wind angle over the situation >>where the tide is not present. Because of that the boat can in theory cone >>slightly higher then without the current. If you do that with the current on the >>bow , the current ends up on the lee bow.

Nope, sorry, if "you do that with current on the bow", the current could easily be on the windward bow on the lifted tack. This adds even more weight to the premise that shifting the current from the windward bow to the lee bow does nothing whatsoever to increase the lift.
No, again you must be misunderstanding what Dave is saying.

Let's say you are sailing closed hauled in no current, with the apparent wind 30 degrees on starboard (let's say that is the water referenced optimal angle)

Then a current directly on the bow suddenly happens.

The apparent wind will shift aft on starboard, and you can now turn a little to starboard (eg "up" ) to bring the angle back to 30 degrees.

The current will now be a little on your port (eg lee) bow.

There is no way the current ends up on your windward bow in this situation.

This is all Dave is saying. It is simple, obvious and not debatable (except perhaps on the internet).

Quote:
Originally Posted by Seaworthy Lass View Post

And Dave was in fact discussing both true and apparent wind when he incorrectly stated:

"sailing in a current on the bow , in effect causes a wind that produces an increases in apparent wind angle over a situation where there is no current."
Perhaps you should take a break. In the sentence you have quoted Dave says explicitly he is talking about apparent wind angle. . . . Why would you try to claim he was talking about true?

As I showed in the post above both his and your points are correct and both completely consistent. We DO in fact all agree (on Dave's point) . . . For some reason you just don't want to see it. . . . . You really might consider talking a little time away from this.
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Old 29-11-2013, 15:39   #764
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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And Dave was in fact discussing both true and apparent wind when he incorrectly stated:
"sailing in a current on the bow , in effect causes a wind that produces an increases in apparent wind angle over a situation where there is no current."
If you have the current on your bow, you are being pushed backwards, slowing your forward progress over the ground. The True(*) and Apparent Wind Directions will shift aft ("in increase in the apparent wind angle") when compared to the same ground wind and zero current. So I guess that's correct. Of course the True Wind Speed will also be affected by the current.

But this is merely restating the True Wind equation that we've already agreed on. Once we have Ground Wind and Current, we have True Wind. As has been pointed out, we sail in the interface between True Wind and Water.

Somebody please remind me what exactly we are arguing about?

(*) Water-referenced
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Old 29-11-2013, 15:42   #765
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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And so why is this even an issue? ....

Dave, and Evans, for what it's worth I completely agree that the Apparent Wind changes with boat orientation. Now what?
Paul,

yes, Dave' point is that simple and we do all agree with it.

It is only being debated because SL is for some reason (almost willfully) misunderstanding what he is saying.

As to what's next . . . Either someone actually pursue one of the proof methods I suggested (or any other rigorous proof) . . Or hang up the thread.

I suggest the later because the constant current assumption is so unrealistic it's of little use to us as sailors, and we all agree on the variable current opportunity.

It's of little value to continue the arm waving.. . . Anyway I am done, unless someone's wants help with a real proof.
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