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Old 29-11-2013, 15:51   #766
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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 estarzinger View Post
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).
We are not discussing variable current at all as far as I am aware. We are discussing constant current and if there is any benefit to altering your heading when close hauled to achieve a lift of some sort.

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Originally Posted by estarzinger View Post
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.
Evans, I think no one including Dave is arguing that cross current alters tacking angles, lifting one tack and knocking the other relative to the absence of current. This is indisputable, as true wind is just the sum of ground wind and wind induce by current.

What we are discussing arguing over is whether there is any benefit in CONSTANT current altering your heading when you are close hauled (and the current is close to being directly on your bow) to shift the current from your windward bow to your lee bow.

Dave is arguing that there is because he thinks current on the the lee bow is the reason a lift is occurring on a tack in conditions of constant current. Your comments are purely clouding the issue.
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Old 29-11-2013, 15:59   #767
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

SL,

You are simply not reading Dave's posts correctly.

He is very explicitly talking about a case with (constant) current vs a case without current.

The starboard tack scenario I described just above is simply and exactly what he is saying.

He has said above that I understand his point exactly.

It is a very simple point. It is really not debatable.

It is not the point you want to talk about.
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Old 29-11-2013, 16:06   #768
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

Well, I'm glad we agree on something as fundamental as that.
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Originally Posted by estarzinger View Post
[...]It's of little value to continue the arm waving.. . . Anyway I am done, unless someone's wants help with a real proof.
Yes, but a proof of WHAT?

Dockhead originally posed the question. Seaworthy Lass recently suggested a definition of Lee Bow Effect and says that it's fundamentally flawed (I agree with her).

Others have claimed that she's wrong, and then they proceed to defend their claim with diagrams and statements that are either proving something completely different, or merely restating general principals. I believe that they do not understand the problem as it has been framed.

This is merely an intellectual exercise for me. I'm not likely to try to use the Lee Bow Effect. In simple situations I will perhaps do some simple calculations. In more chaotic or complicated situations I will probably use one of the Monte Carlo style routing programs, as well as a big grain of salt.

I'm taking a break from this now.
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Old 29-11-2013, 16:13   #769
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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 estarzinger View Post
SL,

You are simply not reading Dave's posts correctly.

He is very explicitly talking about a case with (constant) current vs a case without current.

He has said above that I understand his point exactly.

It is a very simple point. It is really not debatable.

It is not the point you want to talk about.
If I misunderstood what Dave was saying in this regard, then I apologise. I do not think anyone here is arguing that a cross current will not produce a lift on one tack and a knock on the other relative to no current.

It is just that the current does not have to be on the lee bow to do so. Dave has repeatedly stated it does and that was part of that paragraph I initially disagreed with.
He has just repeated this by stating:
"A boat close hauled with a current behind it will always result in a decrease in apparent wind angle. Simple logic shows it so."
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Old 29-11-2013, 16:15   #770
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Yes, but a proof of WHAT?
.
The proofs I suggested above would answer SL case as a special case of the more general question "does current ever change the optimal water referenced sailing angle".
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Old 29-11-2013, 16:23   #771
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Quote:
Originally Posted by Seaworthy Lass View Post

If I misunderstood what Dave was saying in this regard, then I apologise. I do not think anyone here is arguing that a cross current will not produce a lift on one tack and a knock on the other relative to no current.

It is just that the current does not have to be on the lee bow to do so. Dave has repeatedly stated it does and that was part of that paragraph I initially disagreed with.
He has just repeated this by stating:
"A boat close hauled with a current behind it will always result in a decrease in apparent wind angle. Simple logic shows it so."
Again you seek to obfuscate. I merely drew attention to that case , it is not relevant to the bow current case I mentioned. We can debate this new one if you like , nor have I mentioned that the current " has to be " on the lee bow. I merely illustrated the effect by having the current dead on the bow and heading up , resulting in the current ending up on the lee now. In other posts I have said the effect occurs elsewhere too.

Please note my case has nothing to do with tacking , please , You need to get that out of your head.

Evans has put my point simply and clearly and as far as I'm concerned no one is disagreeing with me.

There is a danger of this becoming shrill
Dave .
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Old 29-11-2013, 16:26   #772
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Old 02-12-2013, 10:47   #773
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

Hi,
it is of course a technique that works, if you do it with the right timing:
You sail from A to B with wind from ahead.

On the first tack you have the tide running from left to right.
In the middle of your way you have slack water. Then you tack.
On the second half of your way the tide runs from right to left.

Take a pencil and draw it. Tide on lee bow is shorter.

Klaus
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Old 02-12-2013, 10:51   #774
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Originally Posted by Klaus_S View Post
Hi,
it is of course a technique that works, if you do it with the right timing:
You sail from A to B with wind from ahead.

On the first tack you have the tide running from left to right.
In the middle of your way you have slack water. Then you tack.
On the second half of your way the tide runs from right to left.

Take a pencil and draw it. Tide on lee bow is shorter.

Klaus
Lee bow , means a current fine on the bow. Much a beam current AFAIK

Dave
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Old 02-12-2013, 12:40   #775
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

Quote:
Originally Posted by Klaus_S View Post
Hi,
it is of course a technique that works, if you do it with the right timing:
You sail from A to B with wind from ahead.

On the first tack you have the tide running from left to right.
In the middle of your way you have slack water. Then you tack.
On the second half of your way the tide runs from right to left.

Take a pencil and draw it. Tide on lee bow is shorter.

Klaus
Klaus, this is what I think the old timers meant when they used the term "lee bowing the tide". For the adage "keep the current close your lee bow" to work when tacking to reach a destination (ie to give the shortest time taken), I see that very limited criteria need to apply:

- The destination must be directly into the ground wind (equal time needs to be spent on both tacks)
- The current must exactly cancel out for the journey
- The cross current is not roughly between the ground wind and your heading close hauled (then you keep the current on the windward bow).

Otherwise, the rule of "keep the current on the lee bow" may work in some portions of a journey when tacking to a destination with a variable cross current, but it is not something that can be blindly followed.

I think the correct strategy when tacking to a destination with a cross current is to use your CTS as your basis and be on port tack as much as needed when the current is between 0 and 180 from the ground wind (use the greatest amount of current if not all of it is needed) and on starboard tack when it is 180 to 360 (again choose the greatest amount if not all the time is needed on this tack). You will see your scenario fits into this.

Removing the terms "lee" and "bow" completely eliminates the confusion surrounding why this strategy works and it fits when current comes from absolutely any direction relative to the ground wind.

(PS: As far as I can gather this is probably why the myth of the "lee bow effect arose" where it is claimed that pinching to put the current on your lee bow is beneficial)
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