Let's Get to the Bottom of the Lee-Bow Effect Once and For All

[Seaworthy Lass]

Originally Posted by europaflyer

Come on Seaworthy, let's stop quibbling over the name. You've made your point that it isn't true for all current angles on the lee side. Extending that to saying that a generally understood effect doesn't exist is a little silly.

The fact that it is not true for all currents on the lee side is not my point at all. My point is that is applies for the windward side as well. It just depends what the current direction is.

I think we all agree that current can alter true wind. Current can therefore, in some circumstances not necessarily involving the lee bow, create a favoured tack which swaps over when the current changes. We all agree that sailing on the favoured tack is good, therefore you need to tack when the current changes. Simple stuff, and a part I think of the RYA Yachtmaster syllabus. No myth, except to people who can't understand it.

All that has absolutely NOTHING to do with the current specifically being on the lee side. It does, however, have EVERYTHING to do with which tack places the current closer to being on the bow.

The classic case of the LBE where its effect is greatest requires keeping the current in the lee bow, as per my original diagram on post #159 which I copy below. You can't seriously deny that the effect here doesn't exist, and that the requirement in this case is to tack to keep the current on the lee bow. OK, there are cases where this doesn't hold but the effect won't be nearly as potent in these cases. The name does just describe the rule of thumb for this most important case.

You diagram is just specific for one current direction relative to the ground wind. For this current it happens that for the tack where the current is closest to being off the bow (the lifted tack) it just happens to be on the lee side. I repeat 'closer to the bow' is the key, 'lee' isn't.

This is the diagram you had attached (by the way, this diagram shows the lifted tack is the one with the current closer to being on the bow ).

[Seaworthy Lass]

Originally Posted by europaflyer

Challenge accepted!

I posted this one a while back and I forget if you ever responded. I've changed the wind names to what we agreed.

Current aft of the beam lifting the boat... or what?

Yes, no quarrel with that, but please show me the other tack. The current will be even further away from the bow . Simply illustrating my point .

My request was to show the two tacks so we can compare how close to the bow the current is on each.

Edited to add: Europaflyer, I will be so happy when the penny finally drops for you. You are a bright bloke, I know it will. It won't take you long to work around 360 degrees. There are no exceptions to what I am saying. As you work your way around the 360 degrees, you will see that that it works for the current falling on the windward side about half the time, so this too should convince you to ditch the term 'lee' and just stick to the term 'closer to the bow' for the lifted tack.

[Dockhead]

Originally Posted by europaflyer

I have provided diagrams. They did prove it in my mind, and I think to some others as well.

Like you, I mean this in the nicest possible way, but I have not heard a coherent argument against the effect as I have presented it, nor have I seen any diagrams which go against what I have posted. Rather, just a lot of confused thinking which I can often not begin to understand.

I post below my original diagram, this time with the terms changed to what we have agreed in this thread which I am happy with. It is the classic case of the so-called 'lee bow effect', and shows the boat with the current on the lee bow pointing far closer to the ground wind than the other boat. Without wanting to sound patronising, can you just state as clearly as possible what it is you dispute about this, because so far I really don't understand what people are disagreeing with me about.

Within some limits, which I don't yet comprehend, I actually think this is right.

It's the same as what I said back in Post #135:

http://www.cruisersforum.com/forums/...ml#post1388621

It could be that it is a very Channel-specific situation, and it could be that the range of circumstances in which it works is extremely limited.

I think we are again floundering in misunderstandings about what flavor of lee bowing we're talking about.

What this here is about, is the idea that if you tack with the change of tide, in the possibly very limited circumstances shown in these diagrams, your tacking angle around your CTS (or, if you like, What Would Be Your CTS If You Could Lay It), is reduced, meaning you sail fewer miles through the water and get there faster.

It is actually a simple concept; the problem is the limits.

[Hoofsmit]

Originally Posted by Dockhead

Within some limits, which I don't yet comprehend, I actually think this is right.

It's the same as what I said back in Post #135:

http://www.cruisersforum.com/forums/...ml#post1388621

It could be that it is a very Channel-specific situation, and it could be that the range of circumstances in which it works is extremely limited.

I think we are again floundering in misunderstandings about what flavor of lee bowing we're talking about.

What this here is about, is the idea that if you tack with the change of tide, in the possibly very limited circumstances shown in these diagrams, your tacking angle around your CTS (or, if you like, What Would Be Your CTS If You Could Lay It), is reduced, meaning you sail fewer miles through the water and get there faster.

It is actually a simple concept; the problem is the limits.

# 271........ 198 posts ago !

me to:

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?

[Seaworthy Lass]

Originally Posted by Dockhead

Within some limits, which I don't yet comprehend, I actually think this is right.

It's the same as what I said back in Post #135:

http://www.cruisersforum.com/forums/...ml#post1388621

It could be that it is a very Channel-specific situation, and it could be that the range of circumstances in which it works is extremely limited.

I think we are again floundering in misunderstandings about what flavor of lee bowing we're talking about.

What this here is about, is the idea that if you tack with the change of tide, in the possibly very limited circumstances shown in these diagrams, your tacking angle around your CTS (or, if you like, What Would Be Your CTS If You Could Lay It), is reduced, meaning you sail fewer miles through the water and get there faster.

It is actually a simple concept; the problem is the limits.

This is the beginning and end of the post you attached a link to:

Originally Posted by Dockhead

OK, here's one possible formulation of the Lee Bow Effect idea. It's probably incomplete and oversimplified, but here goes.
..........
In fact, if your lee bow is in the current, you are on the favored tack.

Could that be all there is to it?

Dockhead, it is not like you to make such sweeping generalisations.

From your example all you can say is that "if the current is perpendicular to the ground wind and your lee bow is in the current, you are on the lifted tack."

The current can come from any direction relative to the ground wind. Almost half the time the lifted tack is the one where the current is on the windward side. The side of the boat is irrelevant. It is the fact that it is closer to the bow that is the key and this is very simply because you are trying to point your bow into wind.

If you are heading downwind and want to gybe, the better gybe is the one where the current is closer to your stern, simply because you are trying to head downwind.

You are still fixated on the word 'lee', maybe because this is what applies to the channel crossing you are so familiar with. It has nothing specifically to do with 'lee'. It has everything to do with 'closer to the bow' instead. The term 'lee is not a problem at the limits, it is a problem roughly half the time.

Europaflyer is hopefully searching for an example to contradict what I am saying. He will not succeed and i hope realisation dawns for him.
Maybe try doing the exercise I set for him? ie work around 360 degrees for the current angle relative to the wind. I think it will be a very useful exercise.

x

[foolishsailor]

Agreed Angela. Europaflyer - things arent serious - I just want to make sure my directness in my posts is not misperceived as me being a dick

I appreciate the diagrams you have drawn but they still dont show multiple tacks and more importantly they dont show the results of your theory over a serious of tacks.

The only way you can prove your position and prove Angela and myself wrong is to illustrate from origin to destination over as little as two tacks how your theory benefits against a boat that doesnt use it to get to a destination.

If you dont feel like the work - give me all your parameters and I will draw it and submit it for discussion.

Mind you I am at a fund raiser for one of my midgets school tomorrow so will only be irritating everyone by smart phone until later...

[goboatingnow]

i attach a drawing , to illustrate how I see the lee bow effect

this example converts everything into ground referenced wind, because lee bow effect is about wind angle and only wind angle.

you can see that by switching the current from the windward bow to the leeward bow the apparent wind angle increases.

In real life you have a trade off between pinching ( i.e. i.e. less wind angle in order to get the lee bow effect ) and the freeing effect of the lee bow. In many cases especially with poor pointing boats, the effect is negative, because the current effect is usually small in comparison with the ground wind and the boat speed.

note I have specifically ignored the effect of moving the boats orientation in relation to the original ground wind. the change in that angle could be large or small in relation to the subsequent change in apparent wind due to the lee bow effect. its really taken up in the "pinching" trade off. in racing we are often talking about 2 -5 degrees of orientation change

note that the lee bow effect is only for situations where the current is almost on the nose , not elsewhere ( this has been covered by SL)

Sorry just noticed a label error . the current wind win word bow, should be labelled apparent wind windward bow , I've now fixed that

I stand by, in my lambs costume!

dave

[europaflyer]

Originally Posted by Seaworthy Lass

Yes, no quarrel with that, but please show me the other tack. The current will be even further away from the bow . Simply illustrating my point .

My request was to show the two tacks so we can compare how close to the bow the current is on each.

Edited to add: Europaflyer, I will be so happy when the penny finally drops for you. You are a bright bloke, I know it will. It won't take you long to work around 360 degrees. There are no exceptions to what I am saying. As you work your way around the 360 degrees, you will see that that it works for the current falling on the windward side about half the time, so this too should convince you to ditch the term 'lee' and just stick to the term 'closer to the bow' for the lifted tack.

Aaaaaaah. I think I get you. I had been thinking before that before you meant 'on the bow' (ie. forward of the beams) rather than 'closest to the bow'.

I think we might just both be right. Your idea that the boat with the current closest to the bow (which I think I may have heard stated by you a little differently before ) I now realise is a good one.

Thankfully for my ego, it is not incompatible with my idea about the 'wind current angle theory'. The point where the current switches from being closest to the bow of one boat to being closest to the bow of the other is at 180 degrees current relative to true wind. This is also the point where the favour switches from one boat to the other. My points earlier about it being relative to apparent wind were when I was looking at each tack in isolation. The point when a current switches from lifting to knocking a boat on a given tack compared to the no-current condition is at 180 degrees relative to apparent wind. I got that bit right. I reproduce my diagram proving this below. I didn't think that, for any boatspeed greater than zero, at the point where the current is around 180 degrees to true wind there is a zone where BOTH boats are being lifted relative to no-current condition! Similarly, when the current is coming from very near to the true wind, there is a zone where both boats are being knocked (a product of headwind, these zones disappear when boatspeed is zero). This is where my 'apparent wind angle theory' falls down as a way of predicting which is the favoured tack, to be replaced with 'true wind angle theory'. Happily, it works out exactly the same as your 'bow effect' theory, it's just expressed differently.

ie...

For current between 0 and 180 degrees relative to true wind, port tack will be favoured. In these conditions, the port tack boat will also always have the current closer to the bow than the other boat. For 180 to 360, the starboard tack is favoured, and that boat will also have the current closer to the bow.

Using either theory in the real world in situations when the difference is slight would require a bit of thinking, but it can be done. Maybe we can discuss the real-world application of this a bit more now I think we are in agreement.

I don't deny that there are situations where a lifting current can come from the windward side. (I'm pretty sure I never have done ). These situations are when the direction of the current is close to the direction of the ground wind. What I thought you were trying to deny previously is that the effect, whatever we call it, exists. It does exist, it's just that 'lee bow effect' is a misleading name for it.

Now that the penny has dropped for me for your 'bow effect' theory, it would cheer me up if you agreed that this is the same thing as my 'true wind current angle' theory...

Originally Posted by Dockhead

It is actually a simple concept; the problem is the limits.

With you on that one!

[Dockhead]

Originally Posted by Seaworthy Lass

This is the beginning and end of the post you attached a link to:



Dockhead, it is not like you to make such sweeping generalisations.

From your example all you can say is that "if the current is perpendicular to the ground wind and your lee bow is in the current, you are on the lifted tack."

The current can come from any direction relative to the ground wind. Almost half the time the lifted tack is the one where the current is on the windward side. The side of the boat is irrelevant. It is the fact that it is closer to the bow that is the key and this is very simply because you are trying to point your bow into wind.

If you are heading downwind and want to gybe, the better gybe is the one where the current is closer to your stern, simply because you are trying to head downwind.

You are still fixated on the word 'lee', maybe because this is what applies to the channel crossing you are so familiar with. It has nothing specifically to do with 'lee'. It has everything to do with 'closer to the bow' instead. The term 'lee is not a problem at the limits, it is a problem roughly half the time.

Europaflyer is hopefully searching for an example to contradict what I am saying. He will not succeed and i hope realisation dawns for him.
Maybe try doing the exercise I set for him? ie work around 360 degrees for the current angle relative to the wind. I think it will be a very useful exercise.

x

I very carefully avoided making any sweeping generalization. I very carefully stipulated that I have only one idealized example and no general rule or principle.

[foolishsailor]

Dave that is a brilliant diagram, especially because it is referenced to a graph - but it is not fundamentally different to what has been posted previously by posters such as Europaflyer and it has the same flaw...

...it is still only an instantaneous benefit.

To prove this effect works you need to show the cumulative effect over tacks, even just two as well as how this effect benefits against a boat in the same conditions that doesnt use it.

I knok this is a pain and takes work.

To prove this requires the following, and I will gladly take part.

1. Create specific conditons that include: origin, destination, wind direction and velocity, current direction and velocity, boat tacking angles and boat speed when on polar for beating

2. Additionally if there are any variations in current over space they must be described or illustrated - and for this execise the current speed changes should be discrete, like my previous attached image, so that we can avoid any attempts to use diff calculus as a solution

3. Avoid any change of current over time as it complicates the solution without adding benefit

This is all a pain to do, but is less time than discussing for 20 pages and whne drawn out makes clear everyones position.

Most importantly once you have drawn your own theory out it allows you to look at it as well.

[goboatingnow]

Originally Posted by foolishsailor

Dave that is a brilliant diagram, especially because it is referenced to a graph - but it is not fundamentally different to what has been posted previously by posters such as Europaflyer and it has the same flaw...

...it is still only an instantaneous benefit.

To prove this effect works you need to show the cumulative effect over tacks, even just two as well as how this effect benefits against a boat in the same conditions that doesnt use it.

I knok this is a pain and takes work.

To prove this requires the following, and I will gladly take part.

1. Create specific conditons that include: origin, destination, wind direction and velocity, current direction and velocity, boat tacking angles and boat speed when on polar for beating

2. Additionally if there are any variations in current over space they must be described or illustrated - and for this execise the current speed changes should be discrete, like my previous attached image, so that we can avoid any attempts to use diff calculus as a solution

3. Avoid any change of current over time as it complicates the solution without adding benefit

This is all a pain to do, but is less time than discussing for 20 pages and whne drawn out makes clear everyones position.

Most importantly once you have drawn your own theory out it allows you to look at it as well.

your are describing something completely different, what you describe is not the lee bow effect.

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, ( because nothing is that simple)

its got absolutely nothing to do with tacking, in racing the object is to make the windward mark with preferably no tacks, or perhaps only a short tack at the end etc. racers do not symmetrically tack to the mark.

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

the lee bow effect is in effect a benefit on a single tack to a mark, its not about an analysis of symmetrical tacking. in symmetrical tacking the effect is cancelled out . But thats irrelevant

dave

[foolishsailor]

Originally Posted by europaflyer

Aaaaaaah. I think I get you. I had been thinking before that before you meant 'on the bow' (ie. forward of the beams) rather than 'closest to the bow'. I think we might just both be right. Your idea that the boat with the current closest to the bow (which I think I may have heard stated by you a little differently before ) I now realise is a good one. Thankfully for my ego, it is not incompatible with my idea about the 'wind current angle theory'. The point where the current switches from being closest to the bow of one boat to being closest to the bow of the other is at 180 degrees relative to true wind. This is also the point where the favour switches from one boat to the other. My points earlier about it being relative to apparent wind were when I was looking at each tack in isolation. The point when a current switches from lifting to knocking a boat on a given tack compared to the no-current condition is at 180 degrees relative to apparent wind. I got that bit right. I reproduce my diagram proving this below. I didn't think that, for any boatspeed greater than zero, at the point where the current is around 180 degrees to true wind there is a zone where BOTH boats are being lifted relative to no-current condition! Similarly, when the current is coming from very near to the true wind, there is a zone where both boats are being knocked (a product of headwind, these zones disappear when boatspeed is zero). This is where my 'apparent wind angle theory' falls down as a way of predicting which is the favoured tack, to be replaced with 'true wind angle theory'. Happily, it works out exactly the same as your 'bow effect' theory, it's just expressed differently. ie... For current between 0 and 180 degrees relative to true wind, port tack will be favoured. In these conditions, the port tack boat will also always have the current closer to the bow than the other boat. For 180 to 360, the starboard tack is favoured, and that boat will also have the current closer to the bow. Using either theory in the real world in situations when the difference is slight would require a bit of thinking, but it can be done. Maybe we can discuss the real-world application of this a bit more now I think we are in agreement. I don't deny that there are situations where a lifting current can come from the windward side. (I'm pretty sure I never have done ). These situations are when the direction of the current is close to the direction of the ground wind. What I thought you were trying to deny previously is that the effect, whatever we call it, exists. It does exist, it's just that 'lee bow effect' is a misleading name for it. Now that the penny has dropped for me for your 'bow effect' theory, it would cheer me up if you agreed that this is the same thing as my 'true wind current angle' theory... With you on that one!

I still wish you would take this image, apply it to a real world solution - one kf your choosing with yourt parameters - from origin to destination on a graphed solution.

I am sure you would find the benefit was non-existent. And if you didnt and were able to prove something - I would be delighted as I would haveearned something new and would add it to my book of tricks.

Until then an image of a static moment proves nothing

Work with me - give me your parameters and I will draw up a solution and we can back and forth until you are happy with the full input of those participating in this thread.

[foolishsailor]

Originally Posted by goboatingnow

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,

Dave,

This has been proven to be categorically false. Please see the links and attachments I made several pages ago.

The articles include authors such as Dave Perry. Google him and the effect you are discussing.

It is irrefutably nonexistent and an old myth.

Edit: and you are right, we arent discussing the LBE as we have moved past it as we all agree that the LBE as it is traditionally defined and as you have defined it here, does not exist. If you go back some pages and read and you will see this discussio

[goboatingnow]

fundamentally what some are arguing here is not about lee bow effects . you are arguing about a system ecosystems of factors , including whether any given boat can exploit a theoretical lee bow effect. thats great , but its not the point

[goboatingnow]

Originally Posted by foolishsailor

Dave,

This has been proven to be categorically false. Please see the links and attachments I made several pages ago.

The articles include authors such as Dave Perry.

Google him and the effect you are discussing. It is irrefutably nonexistent and an old myth.

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