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Old 16-11-2013, 16:17   #481
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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 View Post
No sorry , it has nothing to do with tacks at all ( or CTS) . The lee bow effect for example might be used where you are not quite able to lay a mark on a tack, upon realising the current in fine on the windward bow , you pinch up slightly to bring the current to the lee bow, Theres no tacking

Depending on the boat , the wind speed , the current strength , you then MAY get a net freeing of wind angle , allowing you to make the mark,

its got absolutely nothing to do with tacking

I race on a lake with currents, the effect on specific boats is there to see

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Sorry, Dave, that's a different Lee Bow Effect which has nothing whatsoever with the one we are talking about.

The one we are talking about deals only with tacking with a tide change to exploit the resulting change of true wind.

And speaking about that other Lee Bow Effect, there is no way that pinching will ever get you to any mark faster, lee bow, weather bow, current, no current, whatever, unless you have screwed up your CTS and ended up in the wrong place in the water relative to your mark. A pretty good proof was promulgated a couple of hundred () posts back.
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Old 16-11-2013, 16:21   #482
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Quote:
Originally Posted by goboatingnow View Post
Dave perry article is nonsense, pure nonsense, he mixes up his frames of reference, he was wrong for years , then he was fed further nonsense and the article is therefore nonsense. ( and it has been critiques several times) again he offers a textual description, where he uses this moving carpet analogy And he is right , in the open ocean it makes no difference to two boats. BUT is does make a difference to a racer attempting to lay a mark fixed to the ground. A point dave perry does not understand. dave
Challenging his position without demonstrating your own is pure nonsense.

Perhaps you missed the additional article I attached that made a very clear graphical proof of the fallacy of this effect, please illustrate your version that challenges this.
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Old 16-11-2013, 16:26   #483
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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 View Post
BUT is does make a difference to a racer attempting to lay a mark fixed to the ground. A point dave perry does not understand.

dave
To lay a windward mark across moving water, you've got to do two things:

1. You have to know what the correct line of advance across the water is -- that is, the shortest distance through the water. Because if you are advancing along a different line, you will end up uptide or downtide of your mark and will sail extra miles. This is your CTS calculation. It has nothing to do with sailing dynamics.

2. Then, you have to advance up that line as fast as you can. That's just ordinary sailing, like advancing towards the mark if the water were not moving. If you can't lay it in one tack, then you must sail at that angle to the wind which gives you the highest VMG to windward. That's such a simple concept that you could say that it's true "by definition" -- the velocity made good is highest. There is no way, ever, that pinching will ever get you there faster, unless you went the wrong way to begin with.

If you correctly separate these two things, your flavor of LBE disappears. It is pure snake oil, just a fudge for when you get your course wrong in the beginning.

Then there's 3:

3. If the current is changing, it is possible in some situations* to exploit the predictable wind shifts to get a lift from sailing closer to your CTS line (the line which would be your CTS if you could lay it) than you otherwise could, as per EuropaFlyer's drawing. Note Bene: The word "lee" didn't appear anywhere in this post. I say once again that I have no idea whatsoever how to define the set of conditions where the wind shift can be exploited in this manner.
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Old 16-11-2013, 16:31   #484
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

for an attempt at the debunk heres a typical example

Destination One Design - Preparation

Its misses several key issues

It just presents summaries and it talks about VMG. Lee bow is a wind angle effect, if you cannot exploit the wind angle , then it does nothing for you.

Secondly , current effects are ground referenced, hence the lee bow effect is only of use where you are trying to reach a ground referenced destination, it has no effect if there isn't one. thirdly due to the boat, the wind and the current the freeing of wind angle may not compensate for the loss of wind angle in the pinching process.Hence the boat may slow . At that point you have a tactical decision, is laying the mark ( i.e. exploiting the freer wind, make not compensate for the speed loss to transfer the current.

Thats doesnt mean there isn't a lee bow effect , merely that you cannot exploit it.

note that many pundits , try to explain that the lee bow effect cause the current to push you up to windward, thats nonsense, a current fine on the lee bow , has little or no effect , other then pushing you AWAY from the mark. The effect is wind angle nothing more.


futhermore , people talking about table mats or carpets, miss the point that racing marks are ground referenced destinations , not water referenced . for example that article and Dave perry , say that the current acts equally in all boats irrespective of heading. Yes in a water referenced system thats true, but if my racing mark is dead up current and my opponent is racing down dead down current to it , whose going to get there first. Sheesh….
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Old 16-11-2013, 16:43   #485
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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 View Post
futhermore , people talking about table mats or carpets, miss the point that racing marks are ground referenced destinations , not water referenced .
Absolutely not

Do you want to sail around in circles through the water until you reach your mark?

If you think you will get there faster by sailing a straight line through the water -- something which was robustly proven in our CTS thread -- you have to translate to water-reference.

If someone is downtide from the mark, that is not the result of sailing dynamics. That is the result of their having failed to calculate along what line through the water they need to be sailing in order to reach the mark most directly. It's purely a failure of navigation.

If you get navigation mixed up with sailing dynamics, you are in a total morass, requiring, I guess, some kind of voodoo such as this brand of LBE to reduce the effect of the screwup. You cannot have sailing dynamics in relation to a ground-referenced mark, when the water is moving.
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Old 16-11-2013, 17:03   #486
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Absolutely not

Do you want to sail around in circles through the water until you reach your mark?

If you think you will get there faster by sailing a straight line through the water -- something which was robustly proven in our CTS thread -- you have to translate to water-reference.

If someone is downtide from the mark, that is not the result of sailing dynamics. That is the result of their having failed to calculate along what line through the water they need to be sailing in order to reach the mark most directly. It's purely a failure of navigation.

If you get navigation mixed up with sailing dynamics, you are in a total morass, requiring, I guess, some kind of voodoo such as this brand of LBE to reduce the effect of the screwup. You cannot have sailing dynamics in relation to a ground-referenced mark, when the water is moving.
jeepers talk about taking me out of context.

What I was illustrating is that racing uses ground referenced marks, hence currents do not have an equal effect on boats irrespective of heading, a claim made by dave perry et all and the lee bow myth busters.

we have CTS calculations precisely because the destination is ATTACHED to the ground. If you merely wanted to sale 140 miles on a course of 100 degrees , you have no need of CTS or currents or anything ground referenced,

Jeepers.
Dave
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Old 16-11-2013, 17:10   #487
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

Dave have you read the post I have attached below and thought carefully about it?

If you agree with the five points it logically follows that there is no benefit to pinching to get the current on your lee bow.

If you don't agree with any of the five points, which ones are they?

I will look at all the recent posts in the morning - it has gone 2 am here and I am falling asleep .

Thanks everyone for the interesting discussion.
'Night.
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Quote:
Originally Posted by Seaworthy Lass View Post
Dave, I have just thought of another way of looking at it.
Consider these 5 points carefully and tell me which if any you disagree with:

1. The ground wind does not depend on what angle your boat is pointing or in fact whether or not there is a boat LOL does it?

2. The wind induced by current does not depend on which way your boat is pointing either (or again it would be the same if there was no boat at all).

3. The true wind is just the addition of the ground wind and wind induced by current. It is totally independent of the boat or where it is pointing.

4. You sail to the true wind not to the direction of the ground wind or current.

5. If you try and pinch when you are close hauled, it will slow you down. If not you were not close hauled to start with. Pinching will never get you to the mark more quickly.

These five sentences added together are really powerful, far more so than any diagram. Really read them and ponder on this. The 'Lee Bow Effect' is absolutely a myth. It is in fact laughable .
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Old 16-11-2013, 17:11   #488
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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If someone is downtide from the mark, that is not the result of sailing dynamics. That is the result of their having failed to calculate along what line through the water they need to be sailing in order to reach the mark most directly. It's purely a failure of navigation.

If you get navigation mixed up with sailing dynamics, you are in a total morass, requiring, I guess, some kind of voodoo such as this brand of LBE to reduce the effect of the screwup. You cannot have sailing dynamics in relation to a ground-referenced mark, when the water is moving.
Again you are taking my discussion about round the cans racing and applying it to your experience of cruising, In racing depending on the specific tatics, if may be that you arrive uptide ( or current) or downside ( or current ) , its is not a failure of navigation, to do so , its is a failure of attics, if your racing buddy beats you to the mark , irrespective of whether you're up or down tide!

LBE is just that an "effect" its not called the LB advantage , or the LB sure fire method . Its merely an effect , I am not defending the point that it may be useful or not useful to you , merely that as an effect it exists, it may never be an advantage

The effect is that there is a freeing of wind on transferring to a lee bow current, there is no guarantee there is a NET freeing of wind, or that your VMG holds up etc. way different subject,

How the hell CTS it mixed up with LBE is beyond me

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Old 16-11-2013, 17:23   #489
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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
Dave, I have just thought of another way of looking at it.
Consider these 5 points carefully and tell me which if any you disagree with:

1. The ground wind does not depend on what angle your boat is pointing or in fact whether or not there is a boat LOL does it?

2. The wind induced by current does not depend on which way your boat is pointing either (or again it would be the same if there was no boat at all).

3. The true wind is just the addition of the ground wind and wind induced by current. It is totally independent of the boat or where it is pointing.

4. You sail to the true wind not to the direction of the ground wind or current.

5. If you try and pinch when you are close hauled, it will slow you down. If not you were not close hauled to start with. Pinching will never get you to the mark more quickly.

These five sentences added together are really powerful, far more so than any diagram. Really read them and ponder on this. The 'Lee Bow Effect' is absolutely a myth. It is in fact laughable .
1. The boats ability to sail to a ground referenced mark ( i.e. racing) depends completely on its aspect to ground wind. but its controlled by the apparent wind of course. i.e. the apparent wind has in in a component of ground wind ( both direction and speed).

2. the wind induced by current has an effect on your apparent wind , hence if can determine your heading ( over the ground) ( like when close hauled) over the ground is important , thats where the marks and destinations are attached to.

3.The TRUE wind, that abomination constructed by sailing instrument makers and the producers of boat polars is irrelevant , you never experience that so called true wind, you only experience apparent wind, thats all that exists,

4. You sail to the apparent wind , NOTHING else, its the only real wind your boat does not sail to the TRUE or ground or any other wind, just apparent wind , thats what you trim your sails to . Thats what determines where you can sail to.

5. Pinching slows you down, how much it slows you down is very much a function of a large number variables. You've obviously never seen pinching up to round marks, gain short term advantage in a race etc, in some cases depending on the layout of a race course the local winds, eddies, current effects bad wind from other racers, it may be better to pinch and lay a mark , bear away and run fast, and tack and return, Ive seen all them used on race courses by skilled races. Race courses have a multitude of reasons as to what speed, and direction is best to round a mark before your enemy.

Lee bowing is not a myth , but its rarely practical , an advantage , or usable , but thats not to say its not an "effect" ( or an instantaneous effect as some poster called it). Some people are confused by tacking , CTS arguments etc, racers do not symmetrically tack to a windward mark for example



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Old 16-11-2013, 17:35   #490
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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 View Post
jeepers talk about taking me out of context.

What I was illustrating is that racing uses ground referenced marks, hence currents do not have an equal effect on boats irrespective of heading, a claim made by dave perry et all and the lee bow myth busters.

we have CTS calculations precisely because the destination is ATTACHED to the ground. If you merely wanted to sale 140 miles on a course of 100 degrees , you have no need of CTS or currents or anything ground referenced,

Jeepers.
Dave

My friend ...... you will convince them not as they are contrived to there egos of a cts calculation that they consider superior to all others which as it happens is water referenced...... they have not other way of supporting there finding


I have spent 4 hours scanning the web to prove that hull and keel dynamics have a part to play in this, all but these members consider looking at this effect reference to a static/ ground point of reference to heading to calculate the resistence from the water of the design of there hull and foil shapes they use this to determine the productivity of lift to windward ,interestingly there calculus look at resistance to leeway, this shows you can not take tidal wind affect as the rate of current as it is reduced by the design of the hull and foil , just one design varied from between 4 to 6 degrees when heading to windward dependant on angle of current to foil, this was calculated a the same velocity . the varients are incomprehensible with hull shapes and keel and rudder designs of all the craft that sail.... although hydrofoils cut it down a bit

you did start to convince seaworthy when looking at racing strategies when you suggest to tack across a strong current, unfortunately she went straight by to her theory of cts and lost applicable points of reference, no consideration was given to wetted area , it is common sense that a folk boat would not use this strategy but a planning hulled racer might if there is enough wind

There tunnelled vision will not even allow them to consider current has an affect on the angle and velocity that the hull moves through the water.

until some one like you can convince them to look out side of there box we will never get near convincing away from there theories
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Old 16-11-2013, 19:26   #491
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

Just found this thread. The idea makes sense to me just as the aeroplane wing lift works with the lump on the top.(Lee bow being the top side)
Maybe water goes above super-critical and lowers the bow wave on that lee side while the water remains sub-critical on the windward side.
I imagine it would work best at certain speeds and bow shapes.
Probably not very significant for yachts.
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Old 16-11-2013, 19:36   #492
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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 sliding table cloth doesnt work as well as an analogy when at a given point in time there are different speeds of current in a body of water. It only works effectively when the whole body of water is moving at same speed or at varying speeds as a whole.

If a boat is sailing upwind on a bearing of 200 @ 6kts STW straight against a current of 3 knots and a boat perpinduclar to that boat 500 yards away is also sailing upwind on a bearing of 200 @ 6kts STW against a current of 1.5kts

Who will reach their destination more quickly? Obviously the boat in lesser current. The table cloth does not move all boats equally - it moves the boats the speed of the current they are in.
seaworthy: did you get this?

my comment of cutting the tablecloth in to 50 non parallel strips then moving them at different velocities is one I stand by, it cannot be used in your cts to steer unless you draw a new vector for each strip and then understand your hull also alters the leeway to each vector, can you understand where we are coming from?

please don't ignore this
or at least prove us wrong on each strip, I can not understand your reference to water moving at one velocity and one direction as your main reference in this senario
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Old 16-11-2013, 19:45   #493
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Just found this thread. The idea makes sense to me just as the aeroplane wing lift works with the lump on the top.(Lee bow being the top side)
Maybe water goes above super-critical and lowers the bow wave on that lee side while the water remains sub-critical on the windward side.
I imagine it would work best at certain speeds and bow shapes.
Probably not very significant for yachts.
Thanks for at least looking at the consept, your perception is correct, think of the shape of the hull on a heeled boat, the arc of the hull in the water rotating around the keel is a big factor to pointing up.

this is why as a dinghy racer we induced heel and so called pinched the last 2 boat lengths to lay a mark to windward it was even more efficient when you had current on the lee bow as that gave you excelliration , why, I cannot explain yet but It was a tactic well used by the fleet
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Old 16-11-2013, 19:53   #494
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

although I have not experienced it in a yacht, if it was sailing on its optimal polar and then tightened to windward ( sails and helm) it would have an effect for a limited period before its way was reduced
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Old 17-11-2013, 01:05   #495
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

'Morning all!

Gorgeous morning here, but guests are due on board in a few hours, so if they are to eat anything other than crackers, I need to put on my chef's hat. Sorry if I can't address everyone's comments until much later.

Before we go any further, I would like to make clear what we are discussing in this thread. Could everyone contributing to this thread please read this so that we are not all talking at cross purposes:

FACTS:
1. If we are tacking with any amount of cross current relative to ground wind then one tack is lifted and one is knocked (simply because the wind induced by current vector alters the direction if the true wind and the tacking angles swing around).
Although this may not lift the tack enough to more closely lay the mark, in many cases it will.
This can be used to great advantage if the current is reversing over a leg of a journey (eg the Channel crossing).
No one is disputing this (I hope LOL).

2. In general when racing (with or without current) pinching may be beneficial if you are very close to the mark and you have misjudged your previous tack, and it also may be beneficial tactically when another boat is very close anywhere along the windward leg.
I don't think one single person is disputing this either.

3. "Your boat sails in the interface between water and air. Your boat has no idea what the seabed below it is doing. It feels the seabed no more than it feels the earth rotating on its axis, or rotating around the sun."
Dockhead wrote this and Foolish Sailor almost developed a 'man crush' on him hearing it worded so well (no comments about my reaction LOL ).
Unfortunately some people (eg Hoofsmit) still don't understand this and think that the current is somehow acting differently on the two side of the hull creating some kind of lift when the current is on the lee side of the boat. It does NOT.


MYTH:
There is some magical property ascribed to the current being on the lee side of the boat.

This myth leads to two things:
1. Fact number one above is called the LBE (Lee Bow Effect)
2. When the current is almost on the bow (but a little on the windward side) then pinching to put the current on the lee side is advantageous (nothing to do with pinching for reasons above).

I think everyone responding recently on this thread (apart from Hoofsmit and GoboatingNow) agree that pinching to achieve the current on the lee bow is detrimental.

I am presenting over and over and over and over (someone likened it to the patience of Job LOL) that the lift in the true wind achieved by cross current has nothing specifically to do with what side of the boat the current is falling.

It should not be called the "Lee Bow Effect", the term "Bow Effect" is more appropriate (the effect of cross current lifting one tack simply occurs for the tack where the current is closest to being off the bow when comparing the two tacks). This also reinforces that pinching to move the current from one side of the bow to the other is a ludicrous concept.


UNPROVEN:
When tacking with cross current (steady or variable with time over the leg, as opposed to variable current in different areas of the course at any one time) the CST is still relevant.
I think it is (so does Dockhead I think, FoolishSailor strongly disagees).

-------------------

I have successfully debunked the myths I think. Europaflyer has finally seen the light that there is no special significance to the lee side, Dockhead is very close to it. FoolishSailor is the only one who understood right from the beginning that the myths are just myths.

I keep thinking we can move on to the "unproven", but unfortunately some people are still trying to argue erroneously that the myths are correct.

I will drop it after today. For me, this will mean it is the end of the "Lee Bow" discussion. It is a waste of time continually repeating myself just to try and convince people the term is meaningless. Even Job had his limits. Because I have dropped it it does NOT mean I have gone over to the dark side LOL.

Tomorrow I am turning to the issue of CTS relevance when tacking with a cross current (variable or otherwise) . Shall we start a new thread on that?
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