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Old 12-11-2013, 02:58   #136
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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 Seaworthy Lass View Post
I would not call myself an exclusive "lee bower" LOL, although in a debate I know you need to pick sides .
Oooh, that's a low blow!

This is not a debate at all; more a colloquy. It's fun sometimes when people take sides in order to try to pick apart the problem from different points of view.

When I started the thread, I did not know either:

1. What the "lee bow effect" is, out of all the variants scattered around the Internet.

2. How it is supposed to work.

3. Or whether it is mythical or not, as many authors claim.

The reason for starting the thread was pure curiosity and desire to play, especially after we learned so enormously much from our CTS threads. This is very much a continuation of those discussions, building on them -- because it is another complex moving water problem.

I'm pleased with it so far -- have learned a lot. Still a long way to go, however.
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Old 12-11-2013, 03:12   #137
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OK, here's one possible formulation of the Lee Bow Effect idea. It's probably incomplete and oversimplified, but here goes. Whenever we are trying to lay a goal which is dead upwind, and assuming our boat as the same optimum VMG to windward angle on both tacks (and if not, you'd better find a rigger ), then both tacks will produce the same VMG to windward. If your tacking angle is 90 degrees including leeway (I wish!), then your VMG to windward is about 70.7% of boat speed, calculated geometrically. However, if the wind shifts so that your goal is no longer dead upwind, both tacks are not equal in terms of possible VMG to your goal. You'll have a higher VMG to your goal on that tack, the courseline of which is closer to the vector to your goal. You still have to make the "unfavored" tack, but the length of this one will be much less. For example, if you are sailing to a goal which bears 000, and the True Wind is blowing from 022, assuming the water is not moving, you can lay the goal in one long starboard tack on a heading (corrected for leeway) of 337, and one short tack on a heading of 067, or any combination of long and short tacks in the same aggregate proportion. Your average speed to your goal will not be equal to the VMG to your goal during your starboard tack, because you will knock down the average a bit during the unfavored tack, but your average speed will be higher than you could have achieved sailing to a goal dead upwind. This is pretty basic stuff, I guess, and real racers will probably be laughing at us cruisers trying to figure this stuff out. OK, so superficially, at least, it would seem that you ought to be able to harvest this effect in a changing current situation by sailing the favored tack on each tide. That would look something like this: In fact, if your lee bow is in the current, you are on the favored tack. Could that be all there is to it? This doesn't consider the fact that we are being swept back and forth by the tide, and that our mark is spot in the water since we're sailing a constant bearing according to our calculated CTS. On the other hand, the drawing is still valid, I think.
My take..... Apples to apples ..... Yours is an orange lol


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Old 12-11-2013, 03:16   #138
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The one on the right is what I call lee bowing, but I'm still learning

As my instructor said... When you think you know it all it's time to give up because you will be a danger to yourself and crew !
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Old 12-11-2013, 04:16   #139
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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The one on the right is what I call lee bowing, but I'm still learning
The yacht on the right has its windward, not lee bow in the current.

And you've got true and ground winds mixed up in that one.

What is it supposed to illustrate?
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Old 12-11-2013, 05:48   #140
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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OK, here's one possible formulation of the Lee Bow Effect idea. It's probably incomplete and oversimplified, but here goes.

Whenever we are trying to lay a goal which is dead upwind, and assuming our boat as the same optimum VMG to windward angle on both tacks (and if not, you'd better find a rigger ), then both tacks will produce the same VMG to windward. If your tacking angle is 90 degrees including leeway (I wish!), then your VMG to windward is about 70.7% of boat speed, calculated geometrically.

However, if the wind shifts so that your goal is no longer dead upwind, both tacks are not equal in terms of possible VMG to your goal. You'll have a higher VMG to your goal on that tack, the courseline of which is closer to the vector to your goal. You still have to make the "unfavored" tack, but the length of this one will be much less.

For example, if you are sailing to a goal which bears 000, and the True Wind is blowing from 022, assuming the water is not moving, you can lay the goal in one long starboard tack on a heading (corrected for leeway) of 337, and one short tack on a heading of 067, or any combination of long and short tacks in the same aggregate proportion. Your average speed to your goal will not be equal to the VMG to your goal during your starboard tack, because you will knock down the average a bit during the unfavored tack, but your average speed will be higher than you could have achieved sailing to a goal dead upwind.

This is pretty basic stuff, I guess, and real racers will probably be laughing at us cruisers trying to figure this stuff out.

OK, so superficially, at least, it would seem that you ought to be able to harvest this effect in a changing current situation by sailing the favored tack on each tide. That would look something like this:

Attachment 70224

In fact, if your lee bow is in the current, you are on the favored tack.

Could that be all there is to it?

This doesn't consider the fact that we are being swept back and forth by the tide, and that our mark is spot in the water since we're sailing a constant bearing according to our calculated CTS.

On the other hand, the drawing is still valid, I think.
Having current on the lee bow certainly makes it the favoured tack as you get a lift from the wind induced by current (a condition present in constant current) which means it is taking you closer to the CTS. If you can judge it perfectly there is no advantage to being on this tack though as you still have to tack the other way at some point to get to B. You will not get to B any faster taking the favoured tack first if you can judge it perfectly. Starting off on the other tack makes the decision of when to tack precisely to get you to B difficult, so unless there is a good reason, you aways take the favoured tack first (ask any racer ).

The scenario I am looking at though, is which side the current has to be on to gain an advantage when the current will vary (ie the tack that will get you to B faster). I do not think that it is necessarily on the lee bow then, although there are some situations when it is.

What we really want is a definition of 'the lee bow effect'. Are people just discussing the favourable tack, not the advantageous tack?

Those racers reading this thread, what do you understand to be the 'lee bow effect'? Are you just talking about a favoured tack, or an advantageous tack?
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Old 12-11-2013, 06:02   #141
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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 Seaworthy Lass View Post
Having current on the lee bow certainly makes it the favoured tack as you get a lift from the wind induced by current (a condition present in constant current) which means it is taking you closer to the CTS. If you can judge it perfectly there is no advantage to being on this tack though as you still have to tack the other way at some point to get to B. You will not get to B any faster taking the favoured tack first if you can judge it perfectly. Starting off on the other tack makes the decision of when to tack precisely to get you to B difficult, so unless there is a good reason, you aways take the favoured tack first (ask any racer ).

The scenario I am looking at though, is which side the current has to be on to gain an advantage when the current will vary (ie the tack that will get you to B faster). I do not think that it is necessarily on the lee bow then, although there are some situations when it is.

What we really want is a definition of 'the lee bow effect'. Are people just discussing the favourable tack, not the advantageous tack?

Those racers reading this thread, what do you understand to be the 'lee bow effect'? Are you just talking about a favoured tack, or an advantageous tack?
Looks like we're swapping sides! This is fun!

I'm just laughing, because what you are saying is exactly the way it looked to me at first.

But now after clearing away the CTS visualization issues, I think I maybe can see at least one version of a lee bow effect which actually works.

If I'm understanding it right, you can cheat the average wind direction by using the favored tack on each tide.

Let's stretch the scenario a little -- imagine, if you will, that the current is so strong that it shifts the wind over 45 degrees so that you can actually sail your CTS without tacking. OK, then the current drops off, changes direction, and you just go with it, following the wind direction at your optimum angle, then tacking, the following it around and finally you're again sailing on the CTS. If all this is symmetrical and you lay the mark without further tacking.

Cool, huh? You've just sailed much faster, obviously, then you would have had the wind been on the nose the whole time and you have been doing symmetrical 45 degree tacks. You've sailed much faster because you were even sailing right on your CTS at times, and at no point was your course more than 45 degrees from your CTS. Remember, sailing 22 degrees is already giving you 90-odd percent of boat speed as VMG in your desired direction.

So if it clearly works in a symmetrical, exaggerated scenario, can it work in assymetrical, normal scenarios?

I already don't see why not, because there is no "conservation of tacking angles" going on. You're concretely making more miles made good, when you're sailing closer to your CTS than 45 degrees. You do need another tack, as you point out, but it's a little one, littler and littler, the closer you are sailing to your CTS. You do not have to make a symmetrical opposite tack, for miles sailed closer to your CTS than 45 degrees, which you were able to sail closer because of the wind shift.
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Old 12-11-2013, 06:03   #142
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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 lass:
Thanks for your explanation , I think the RYA book of navigation obviously uses different terminology to this thread, I'm still getting my head round it!
What terminology does the RYA use?

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What I still don't get this we still have not definitely confirmed what everybody thinks lee bowing is.
As I understand it (and I am only guessing), the mysterious lee bow effect is that the advantageous tack (not just favoured tack, ie one closest to the Course To Steer) is when the current is on your lee bow.
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Old 12-11-2013, 06:15   #143
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Looks like we're swapping sides! This is fun!
I am not swapping sides, the favoured tack will not get you there quicker when you have constant current if you judge when to tack perfectly on both tacks (sorry, I put it in brackets, but did not explain that is what I was commenting on).

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I'm just laughing, because what you are saying is exactly the way it looked to me at first.

But now after clearing away the CTS visualization issues, I think I maybe can see at least one version of a lee bow effect which actually works.

If I'm understanding it right, you can cheat the average wind direction by using the favored tack on each tide.
Yes, yes yes, cheering here LOL. So pleased.
There are advantageous tacks to be on that will get you to B faster when the current is varying. This is what I am on about.

In lots of situations, having the current on your less side is advantageous, BUT not all situations.

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Let's stretch the scenario a little -- imagine, if you will, that the current is so strong that it shifts the wind over 45 degrees so that you can actually sail your CTS without tacking. OK, then the current drops off, changes direction, and you just go with it, following the wind direction at your optimum angle, then tacking, the following it around and finally you're again sailing on the CTS. If all this is symmetrical and you lay the mark without further tacking.
Cool, huh?
Yep, it is cool .

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ISo if it clearly works in a symmetrical, exaggerated scenario, can it work in assymetrical, normal scenarios?
That is the burning question!
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Old 12-11-2013, 06:45   #144
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The yacht on the right has its windward, not lee bow in the current. And you've got true and ground winds mixed up in that one. What is it supposed to illustrate?
Sorry ment the left diagram

I was trying to show that a lee bow tack has the advantage of the current.
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Old 12-11-2013, 06:53   #145
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Having current on the lee bow certainly makes it the favoured tack as you get a lift from the wind induced by current (a condition present in constant current) which means it is taking you closer to the CTS. If you can judge it perfectly there is no advantage to being on this tack though as you still have to tack the other way at some point to get to B. You will not get to B any faster taking the favoured tack first if you can judge it perfectly. Starting off on the other tack makes the decision of when to tack precisely to get you to B difficult, so unless there is a good reason, you aways take the favoured tack first (ask any racer ). The scenario I am looking at though, is which side the current has to be on to gain an advantage when the current will vary (ie the tack that will get you to B faster). I do not think that it is necessarily on the lee bow then, although there are some situations when it is. What we really want is a definition of 'the lee bow effect'. Are people just discussing the favourable tack, not the advantageous tack? Those racers reading this thread, what do you understand to be the 'lee bow effect'? Are you just talking about a favoured tack, or an advantageous tack?
My point entirely
(,I'm not a racer now!)
But I did not do very well getting my point across

Lee bow to me means having a favoured tack dew to the affects of the current, it will be also the advantageous tack as if you spend longer on the other tack you are headed off from you goal ,point B
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Old 12-11-2013, 07:01   #146
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When sailing upwind lee bow to the current, the current will sweep you towards the mark increasing your VMG. While theoretically the apparent wind will indeed shift aft, giving a lift, in my experience the effect is not nearly as noticeable as that of being swept by the current towards the mark.

The only example I can conceive of where pinching would be beneficial, would be if one were not quite fetching the windward mark by a very small margin in light air and strong current. By pinching forward momentum would be decreased allowing the current to sweep the boat past the mark whereupon falling off would allow for a rounding. This only applies when wind and current are such that if the boat were tacked the lost ground could not be regained.

As for the current changing, yes the favored tack changes with the tidal flow.

I race in San Francisco Bay where knowing, and planning for the current, are regularly part of the strategy.
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Old 12-11-2013, 07:02   #147
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Lee bow to me means having a favoured tack dew to the affects of the current, it will be also the advantageous tack as if you spend longer on the other tack you are headed off from you goal ,point B
Really? Is that all it means? But there is no mystery to that. That is no fun LOL.

So the only thing that people are questioning is whether or not pinching to get the bow on the lee side will work?
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Old 12-11-2013, 07:08   #148
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I am not swapping sides, the favoured tack will not get you there quicker when you have constant current if you judge when to tack perfectly on both tacks (sorry, I put it in brackets, but did not explain that is what I was commenting on). Yes, yes yes, cheering here LOL. So pleased. There are advantageous tacks to be on that will get you to B faster when the current is varying. This is what I am on about. In lots of situations, having the current on your less side is advantageous, BUT not all situations. Yep, it is cool . That is the burning question!
The picture ( the induced wind ) I posted are from a ' the RYA book of navigation ' by Tim Bartlett
If the current does not give you lift on the lee bow it's not lee bowing ....... Simplies
Lee bowing to me means it is CTS using the current to your advantage , not shore the current wind makes enough difference to wind in your sails to have a noticeable affect but pretty shore as I posted above, the affect on the foils and wave affect does...... But at the moment we are still getting a starting point that we can agree what is ment by the term
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Old 12-11-2013, 07:11   #149
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When sailing upwind lee bow to the current, the current will sweep you towards the mark increasing your VMG. While theoretically the apparent wind will indeed shift aft, giving a lift, in my experience the effect is not nearly as noticeable as that of being swept by the current towards the mark. The only example I can conceive of where pinching would be beneficial, would be if one were not quite fetching the windward mark by a very small margin in light air and strong current. By pinching forward momentum would be decreased allowing the current to sweep the boat past the mark whereupon falling off would allow for a rounding. This only applies when wind and current are such that if the boat were tacked the lost ground could not be regained. As for the current changing, yes the favored tack changes with the tidal flow. I race in San Francisco Bay where knowing, and planning for the current, are regularly part of the strategy.

What I said ....... But better written
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Old 12-11-2013, 07:15   #150
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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The picture ( the induced wind ) I posted are from a ' the RYA book of navigation ' by Tim Bartlett
Explains a lot LOL

(Sorry, GBN, I am no angel. I have been so good lately, but I just couldn't resist that )
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