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Old 15-11-2013, 05:43   #271
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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This is a fantastic explanation including graphics of exactly what the "Lee Bow Effect" is and why it is non-existent
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I think this topic is going around in circles


"Lee Bow Effect"



1. Seaworthy and others have shown that velocity made good to wind ward is not affected by which side of the bow is presented to the current

it has also helped us see the effect of current on a windward heading





2.this link above proves the ''pinch" is not a viable strategy to gain to windward ,

although in very few cases can be an advantage if the cts has
been affected ( current or wind change) and a last minute tack would have a larger adverse affect, but this is called luffing a mark and is not the lee bow effect





Lee Bowing The Tide



Is a rule of thumb

Applied when making a ground fixed destination, to windward WITH THE TIDE ON YOUR BOW
where a plotted course to steer has not been worked
(you are sailing by the seat of your pants.)





The technique will help you to make judgements in strong variable tidal currents with a number of static visual fix to apply the best vectors to guess a favourable course to steer (heading induced wind, tidal/ current induced wind, leeway and true and ground referenced/true wind)





this is especially true when the stream of the tide is faster than your boat speed. ( this has yet to be fully discussed )




LEE BOWING THE TIDE 2



Is a loosely applied strategy for a starting tack



again it is used when the course will set the tacks with the wind on either BOW quarter.

eg: a plotted CTS on a passage such as the English channel where there is a known change in tideal current ( both time, direction and speed)


I see it as a strategy as we are racing against time to hit a tidal gate at our destination ( go do a passage plan, ... you will get my line of thought)


It states that the tack with the wind on the leeward bow should be your starting tack so that any veer or back in wind direction can be advantageous , by keeping you close to your ground line. when the tide changes the principle can be maintained by tacking at that point,

( it should be noted that this phrase came about before electronic navigation. whether it is as relevant today has not been discussed)
.................................................. ...................................
your comments please?
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Old 15-11-2013, 05:47   #272
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Angela, Unless we reference an object which is fixed to the sea bed, such as a racing mark, there is no favored tack or sailing angle in relation to current or wind.

Edit: and even then there is no benefit to be found unless there is a change in magnitude or direction over time or distance of one of these vectors.

If one is out of sight of land and sailing with another boat in a tidal current of x knots, the apparent wind shift affects both boats exactly the same tegardless of tack or sailing angle.

Both current and apparent wind are invisible to the boats. Only with the addition of an object which is fixed in space are we able to change our frame of reference to include the effects of current. The wind is still unasdressable and no benefit can be gained by sailing angle or tack.

In an environment where there is no change in current or wind over time or geography either in magnitude or direction there is NO favored tack.

Both tacks are affected by the current equally.

If the current is 5kts and 270degrees then regardless of what tou do and which tack you are on you will add 5 kts and 270degrees to your vectors.
The 'favourable tack' is by definition the tack which has you travelling closer to the CTS. It occurs when conditions are steady during a leg. It is not the advantageous tack (ie it would not get you to the mark any faster if you could predict the point to tack perfectly and if conditions remained constant). The general principle is that you take the favourable tack first.

This is what I posted a few posts back:

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Note:The key when tacking with steady wind and current (or with changes that you think will cancel each other out along the way) is to first be on the tack that is closest to the CTS (ie the favourable tack), not necessarily the one lifted by the current.
PS Or is the above definition of favourable tack incorrect? If so we are just talking at cross purposes LOL.
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Old 15-11-2013, 05:52   #273
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

This is the definition of favourable tack that I am using:

"When beating to windward often your desired destination although still in the no sail zone is not aligned directly upwind - to the eye of the wind. In this case one tack becomes more favorable than the other - it angles more closely in the direction you wish to travel than the other tack does. Then the best strategy is to stay on this favorable tack as much as possible, and shorten the time you need to sail on the unfavorable tack."

If conditions are steady and you could predict your tacks perfectly there is nothing advantageous about the favourable tack (you need to spend an equal amount of time on both tacks regardless of which one you take first).

This is how I have been using the term.
Do you consider this definition incorrect?
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Old 15-11-2013, 06:03   #274
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Favourable tack (a common term) is the tack that is closest to your CTS. In a perfect world where you could predict things perfectly and tack at exactly the perfect point for the final tack, then sailing the favourable tack first does not result in getting to the mark more quickly. Unless your true wind shifts, you need to sail both tacks. In practice that perfect point to tack is more difficult to judge the further away you are from the mark, so taking the favourable tack first is sensible.

The advantageous tack is what I would call the tack that there is a real advantage being on as it will shorten your time to reach the mark (possibly substantially.) This situation will only occur if the true wind is variable along that leg. It is in common practice to utilise this when the predicted change to come in true wind is due to variable ground wind. It also applies if there is variable current though. No one seems to mention this, but I am sure this is used by tacticians. There must be dozens of good books written about this.
FS, this is the definition I gave earlier.
Is this definition incorrect? It seems to be from what you are saying. I gather you use the terms favourable tack and advantageous tack to mean the same thing?

Is so, what do you call the tack that is closest to your CTS?
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Old 15-11-2013, 06:09   #275
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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
This is the definition of favourable tack that I am using:

"When beating to windward often your desired destination although still in the no sail zone is not aligned directly upwind - to the eye of the wind. In this case one tack becomes more favorable than the other - it angles more closely in the direction you wish to travel than the other tack does. Then the best strategy is to stay on this favorable tack as much as possible, and shorten the time you need to sail on the unfavorable tack."

If conditions are steady and you could predict your tacks perfectly there is nothing advantageous about the favourable tack (you need to spend an equal amount of time on both tacks regardless of which one you take first).

This is how I have been using the term.
Do you consider this definition incorrect?
Nope.

Now that I see both the first paragraph together with the second I understand where you are coming from, its perfect.

Thanks.

I thought you were referring to a favored tack that actually created a real benefit in terms of changing the distance or time sailed to a fixed point in our little mathematically perfect imaginary scenarios where nothing changes over time or space.

But now it is clear that the term "favourable tack" you are talking about a benefit that is created by minimizing the real world errors associated with navigating - which is an important concept and effective technique to create benefit in the changing real world.

But it still isnt an "effect" of any sort - it is a risk and error minimization strategy designed to offset the natural errors inherent in the fleshy part of a navigation system.

edit: Which is what you have already said a couple of posts ago...
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Old 15-11-2013, 06:10   #276
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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
This is the definition of favourable tack that I am using:

"When beating to windward often your desired destination although still in the no sail zone is not aligned directly upwind - to the eye of the wind. In this case one tack becomes more favorable than the other - it angles more closely in the direction you wish to travel than the other tack does. Then the best strategy is to stay on this favorable tack as much as possible, and shorten the time you need to sail on the unfavorable tack."

If conditions are steady and you could predict your tacks perfectly there is nothing advantageous about the favourable tack (you need to spend an equal amount of time on both tacks regardless of which one you take first).



This is how I have been using the term.
Do you consider this definition incorrect?

it is the definition as I have used it above
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Old 15-11-2013, 06:13   #277
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Nope.

Now that I see both the first paragraph together with the second I understand where you are coming from, its perfect.

Thanks.

I thought you were referring to a favored tack that actually created a real benefit in terms of changing the distance or time sailed to a fixed point in our little mathematically perfect imaginary scenarios where nothing changes over time or space.

But now it is clear that the term "favourable tack" you are talking about a benefit that is created by minimizing the real world errors associated with navigating - which is an important concept and effective technique to create benefit in the changing real world.

But it still isnt an "effect" of any sort - it is a risk and error minimization strategy designed to offset the natural errors inherent in the fleshy part of a navigation system.
Agree 100%. I was not under the impression that sailing the 'favourable' tack was any quicker, it is just hedging your bets and making the final tack easier to judge.

I had always considered the favourable tack the one closest to your rhumb line though, before I learned all about CTS .
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Old 15-11-2013, 06:16   #278
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

hmmm,

that said - there is no CTS when going upwind. There is only VMG to a fixed reference point.

Wouldnt CTS really only applies to a destination that can be made without tacking?

edit: assuming a constant environment again...
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Old 15-11-2013, 06:20   #279
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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hmmm,

that said - there is no CTS when going upwind. There is only VMG to a fixed reference point.

Wouldnt CTS really only applies to a destination that can be made without tacking?
Nope. You still have a CTS, you just can't lay it. All your references are to this CTS initially. The sides of the course are on either side of the CTS, not on either side of the rhumb line (at least as far as I can see, why do you think otherwise?).
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Old 15-11-2013, 06:21   #280
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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hmmm,

that said - there is no CTS when going upwind. There is only VMG to a fixed reference point.

Wouldnt CTS really only applies to a destination that can be made without tacking?

edit: assuming a constant environment again...
Oh dear ... we are back to termenology..... go for it seaworthy
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Old 15-11-2013, 06:25   #281
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

FS, think of your tablecloth. The shortest distance to travel is a straight line between A and B on the tablecloth (ie constant heading), regardless of how the table cloth is moving. The sides of the course are either side of that line, not either side of the rhumb line.
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Old 15-11-2013, 06:27   #282
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Oh dear ... we are back to termenology..... go for it seaworthy
Not terminology. If an object is upwind you are sailing as close to the wind as your VMG allows and VMG will also tell you when to tack. VMG is not a course it is a velocity calculation that tells you if your course is optimal to a fixed point.

CTS is completely different - it is a calculated course based on current and expected vectors of force (wind and current) that when folowed guanantees the optimal velocity to a point.

They are the opposite sides of the same equation and used for different purposes.
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Old 15-11-2013, 06:29   #283
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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FS, think of your tablecloth. The shortest distance to travel is a straight line between A and B on the tablecloth (ie constant heading), regardless of how the table cloth is moving. The sides of the course are either side of that line, not either side of the rhumb line.
Im comfortable with the CTS discussion from the other thread. But sailing upwind in steady current to a fixed point is not the same as sailing a single tack in the same current and calculating a CTS.

edit: Even if the current is a real world example like sailing across the Solent with a variable over time and distance current to a point dead upwind. You will not be calculating a CTS you will instead estimate the correct times to tack based on your estimates of magnitude and direction of current since sailing up wind requres the boat to be hard on the wind the whole time.
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Old 15-11-2013, 06:34   #284
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Im comfortable with the CTS discussion from the other thread. But sailing upwind in steady current to a fixed point is not the same as sailing a single tack in the same current and calculating a CTS.
Why not? If you had some miraculous boat and could sail into wind, that is the heading you would choose. It is a straight line through the water between A and B. The "course" is your course through water, not relative to the ground. With no current it is the same as the course relative to land.

It just happens that when B is into wind you can't lay it. I don't think it alters that you have two sides to the "course" relative to your CTS. Why would it?
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Old 15-11-2013, 06:39   #285
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

ok..... I see it as a course to steer....you are just doing another one when your vectors change.
but my opinion seems unworthy of comment to most
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