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Old 18-11-2013, 01:53   #601
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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 s/v Moondancer View Post
So after 581 posts you finally worked out that you put the tide on the bow that allows you stay closest to the rhumb line and closes the tacking angle...great work!

Now Seaworthy Lass can continue with her massive thread proving that she knows more about crossing the Channel than the RYA.

Moderators, like children, should be seen and not heard!
She does, and she clearly proved it.

For those that understood her method it is clear that it was both easier and more precise than the RYA method

No reason to be irritated that you dont understand something, perhaps you would benefit from re-reading that thread and if not we both would benefit if you used the ignore button.
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Old 18-11-2013, 02:09   #602
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Interesting question --

Some Channel sailors believe that the LBE works because it shortens your distance sailed over ground. This is obvious nonsense, and it threw me off -- that's why when we started this thread, my hunch was that there is no such thing.

Now we know that there definitely is such a thing, and lee bowing, at least in the standard Channel situation does keep you closer to the rhumb line.

Interesting coincidence.
I think I can envisage lots of situations where this formula for tacking will simply not work ie keeping the current in the lee bow. That works ideally where the CTS is directly upwind. What about more oblique angles of wind where you are getting closer to laying the mark on one tack. I don't see how it works then. I will try and give an example later, just heading ashore now.

Do you see what I am getting at, or is this just another one of my whacky ideas LOL? The extreme case of this is actually laying the CTS on one of the tacks. No use tacking with the current then. Without a CTS you would not know this.
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Old 18-11-2013, 02:49   #603
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Look, think about it like this:

No current, zero boat speed -- zero forces.

10 knots of current, zero boat speed -- zero forces - identical.

No current, 6 knots of boat speed -- certain forces.

10 knots of current, 6 knots of boat speed -- those exact same forces.


All the forces come from the relative motion between boat and water. I brought up the boat dead in the water only because it would be most obvious in that case.

ha ha ........ 10 + 6 = 16 into the tablecloth

10 - 6 = 4

I will be back
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Old 18-11-2013, 02:52   #604
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

do not forget you are moving to a ground based chair at the end of the table
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Old 18-11-2013, 02:57   #605
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

if you where heading to the fork at the place setting on your port side
I agree
lift by the way, is not the correct term when used to correcting your course to steer by the variance of a wind affect
lift is what is provided by the dynamics of your hull and it angle to the water
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Old 18-11-2013, 06:05   #606
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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I think I can envisage lots of situations where this formula for tacking will simply not work ie keeping the current in the lee bow. That works ideally where the CTS is directly upwind. What about more oblique angles of wind where you are getting closer to laying the mark on one tack. I don't see how it works then. I will try and give an example later, just heading ashore now.

Do you see what I am getting at, or is this just another one of my whacky ideas LOL? The extreme case of this is actually laying the CTS on one of the tacks. No use tacking with the current then. Without a CTS you would not know this.
are you thinking about playing around with leeway?
If you are, which I hope you are , start to think what affects leeway and why
If you are applying it as a uniform vector then your findings, how every hard you work will be disproved, I really hope they are not, as the effort you have put in is valid in cts, but it would never show any relevance to lee bow effect and to a lesser degree , lee bowing the tide
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Old 18-11-2013, 06:23   #607
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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are you thinking about playing around with leeway?
If you are, which I hope you, start to think what affects leeway and why
If you are applying it as a uniform vector then your findings, how every hard you work will be disproved, I really hope they are not, as the effort you have put in is valid in cts, but it would never show any relevance to lee bow effect and to a lesser degree , lee bowing the tide
This subject is unbelievably complex
We have yet to look at wind reduced to water movement, ie: its stronger at the top of your mast than at base as any harbour sailer will tell you and no that is not geographical influence ,(but that does have a bearing on tactics and strategy) ---- it is resistance
Waves are created by this resistance , the effect on the hull to waves , the effect that the vector of wind to current must have an effect on the waves approach to the hull, no wonder some of the experience tidal sailers come up with " I will ignore this cts stuff and poo poo it, but it does not mean we cannot learn from it
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Old 18-11-2013, 08:15   #608
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

[QUOTE=Paul Elliott;1393566]If that's your point then I don't think anybody here would disagree.

When there is a current our optimum course can be different from the no-current course. Current and Ground Wind affect the True Wind (water-ref), and (as if I need to say it) they also affect the Apparent Wind as seen on the deck of the boat. Course changes also affect the Apparent Wind. Any change in Apparent Wind will change the angle of attack (or leeway) of the foils, and change the shape of the immersed hull, thus affecting the hydrodynamics.

Can you show me where anybody has claimed otherwise?[/QUOTE

yep...... me , but I am not going to copy and past anymore ! and I was wrong but.....

Dockhead said.....]Leeway is included in the tacking angle. Boat tacks through 90 degrees over ground, for example - includes apparent to true and leeway.

we have found the fatal vector ....... leeway is not uniform but is being applied uniformally to these equations
Leeway as any sailor knows has variable from wind which is being accounted for, but the apparent vector of water resistance and lift is not

I have the proof of keel lift varience per design ( on a fairly standard keel design.... not got to Hydrofoils yet) but not the the vectors of approach as these need to be worked on an equation relative to cts that has been used so far ,I am still working on these to ensure there relivence or else this will be dismissed without question

there is an old saying " if you cant beat them -- join them " at least in their basis of reference but it is a lot easier to turn it upside down and look at it with the water approach to keel and hull, dame and rudder ,... more resistance ! No not drag as well
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Old 18-11-2013, 08:41   #609
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Quote:
Originally Posted by Seaworthy Lass View Post

I think I can envisage lots of situations where this formula for tacking will simply not work ie keeping the current in the lee bow. That works ideally where the CTS is directly upwind. What about more oblique angles of wind where you are getting closer to laying the mark on one tack. I don't see how it works then. I will try and give an example later, just heading ashore now.

Do you see what I am getting at, or is this just another one of my whacky ideas LOL? The extreme case of this is actually laying the CTS on one of the tacks. No use tacking with the current then. Without a CTS you would not know this.
Yes, now understanding it much more deeply, thanks to this thread and everyone who contributed, I would not just keep the current on the lee bow. I would work up the problem, starting with CTS calculation, then figure out best tacking strategy concretely.

Oblique currents and goal not dead upwind might put the current on the other side in a marginal case. More often in a boat with a wide tacking angle. Probably pretty rarely, since the more oblique the current, the less dead upwind the goal, the less there is any Effect.

I can't say enough, however, how valuable it is to have been freed from the idea that the Effect is CAUSED by current on the lee bow. I'm afraid without Seaeorty's work, we would not have figured that out.

For me, this has been a great lesson in tacking strategy. I just didn't know a lot of stuff which is elementary to hard core racers like Foolish Sailor. The principles are broader and more widely applicable than the narrow case of Lee Bow Effect.
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Old 18-11-2013, 09:32   #610
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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, now understanding it much more deeply, thanks to this thread and everyone who contributed, I would not just keep the current on the lee bow. I would work up the problem, starting with CTS calculation, then figure out best tacking strategy concretely.

Oblique currents and goal not dead upwind might put the current on the other side in a marginal case. More often in a boat with a wide tacking angle. Probably pretty rarely, since the more oblique the current, the less dead upwind the goal, the less there is any Effect.

I can't say enough, however, how valuable it is to have been freed from the idea that the Effect is CAUSED by current on the lee bow. I'm afraid without Seaeorty's work, we would not have figured that out.

For me, this has been a great lesson in tacking strategy. I just didn't know a lot of stuff which is elementary to hard core racers like Foolish Sailor. The principles are broader and more widely applicable than the narrow case of Lee Bow Effect.
Dockhead, the speed will vary over each portion of the leg as the amount of true wind varies with the current. I had not thought of this earlier in the year, but it does complicate things and should be factored in.

I have learned a tremendous amount on this thread too. It has been very enjoyable and eyeopening.
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Old 18-11-2013, 09:51   #611
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Dockhead, the speed will vary over each portion of the leg as the amount of true wind varies with the current. I had not thought of this earlier in the year, but it does complicate things and should be factored in.

I have learned a tremendous amount on this thread too. It has been very enjoyable and eyeopening.
me to
nice to see that you stay open minded enough to look at your theory and find fault

is there any point me posting my findings, it comes in to affect in tight tidal gradients, but its a dame of a job because the varients are so high that in one design leeway alters from between 4 to 6 degrees on one apparent wind angle and the true wind angle differs from one tack to another
read this


Unfortunately this wind direction change directly affects our true wind angle. The result you experience is that your true wind angle you afford to sail with is not the one displayed from the sensor, mounted on the mast head and corrected to the 10m level.
In other words, you can’t achieve your usual true wind angle on one tack, while you have incredibly low true wind angles on the other tack. This is because your sails "see" the result of the wind flowing across the complete sail. And since the wind direction is different aloft and on deck, there will be an "average" wind direction your sails experience.
this wind angle not speed thats where I have stopped
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Old 18-11-2013, 09:58   #612
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

I think I am done

I can/t prove it im to thick

I think I will perceive these effects and sail to them ( I know when it works ! my butt tells me

I enjoy seat of the pants sailing
off to figure out your cts for my passage plan
more learning
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Old 18-11-2013, 10:26   #613
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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me to
nice to see that you stay open minded enough to look at your theory and find fault
Hi Hoof
The wonderful thing with discussions such as this is that ideas and "theories" are tossed about and flaws detected. Much less is gained if anyone starts off with a closed mind .

I find in forming a theory and then trying to defend it (even if it is the wrong theory), a huge amount can be gained if I am prepared to present "proof", rather then just voicing an unsubstantiated opinion. It makes me understand a hell of a lot more about a topic. This thread has been invaluable in this way.

If anyone else has followed the arguments closely, I think they too will have gained a huge amount .

Even all your scepticism has been useful as clear explanations have been presented by several members in several different ways about the effect of current on the underwater profile. This has hopefully cleared things up for lots of other people reading this thread, even if they have not contributed to the discussion.
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Old 18-11-2013, 10:33   #614
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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[...] lift by the way, is not the correct term when used to correcting your course to steer by the variance of a wind affect
lift is what is provided by the dynamics of your hull and it angle to the water
Lift is exactly the right term to use when the wind shifts away from your bow, allowing you to sail closer to your mark. When used in this context it has nothing to do with hydrodynamics, aerodynamics, or foils.

This is the language of sailing. When the wind shifts towards your bow that's called a "header" (or apparently "being knocked".) When the wind shifts away from your bow that's called a "lift".

You know, the same way the rope attached to the clew of a sail is called a "sheet", where most non-sailors use that term for certain pieces of fabric that are put on the bed.
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Old 18-11-2013, 11:28   #615
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Lift is exactly the right term to use when the wind shifts away from your bow, allowing you to sail closer to your mark. When used in this context it has nothing to do with hydrodynamics, aerodynamics, or foils.

This is the language of sailing. When the wind shifts towards your bow that's called a "header" (or apparently "being knocked".) When the wind shifts away from your bow that's called a "lift".

You know, the same way the rope attached to the clew of a sail is called a "sheet", where most non-sailors use that term for certain pieces of fabric that are put on the bed.
I agree and stand with head bowed( no pun intended) I did a post on this in thus started the terminology thread
but I should have said the coefficient of hydrodynamic lift
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