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

[goboatingnow]

I've never understood LBE. how an a current on the nose , well just off the nose , lift you to weather.


I can see a current effect where you are sailing to a windward ground reference mark,( but not laying it ) and the current happens to be pushing you up , hence it looks like the boat is pointing higher then it is. , is that LBE.

dave

[Seaworthy Lass]

Originally Posted by europaflyer

Hi Seaworthy!
Hmm. As in my last post #249, I don't think the angle of the current relative to your boat is what matters, bur rather the angle of the current relative to apparent wind. Calling it 'lee bow effect' is more because people have applied this as a rule of thumb. The alternative names (apparent wind current angle favourable hemisphere effect?!) don't really bear thinking about. I'm happy with LBE in the same way that I'm happy calling a halliard a halliard even when it doesn't haul a yard.

I think I'm right in saying that your claim that 'there is no LBE' relates to the exact definition, rather than your thinking that the effect as I defined does not exist?:

Well the word 'Lee' is in the definition and I think it has absolutely nothing specifically to do with the lee side, and regardless, the lifted tack is not necessarily the favourable one, so there is not necessarily any significance to the lifting effect, so yes, I disagree with both the definition and the fact that it has any significance . The important thing with steady wind and current is to sail the favourable tack first. Nothing more complicated than that.

Keeping the current on the lee side for the channel crossing with the wind on the nose is just normal management of current in those particular circumstances (the current being roughly perpendicular and the wind direction roughly the CTS). You cannot look at very specific conditions and start calling it some 'effect'. Think about the channel crossing and what is advantageous - is it or is it not simply following the favourable tack and tacking when the current changes? Why start complicating it?

What you do with changing wind and current is just normal management of a change in the true wind (unexpected or predicted). If there is a predicted change to come, keep on the side of the CTS that will be knocked later. Nothing whatsoever to do with keeping the current on your lee side.

Originally Posted by europaflyer

Not sure I agree about the current on the bow thing. What do you think about my apparent wind angle theory?:

Hmmm. Do I know you well enough that I can say "nonsense" without you taking offence. . Look at my cone diagram to see why current on the bow is roughly where the lifting effect is maximum (I say roughly as it depends on the relative amounts of ground wind and current).

Originally Posted by europaflyer

It's great to have these discussions. I think we might actually be contributing something useful to sailing theory here! On the strength of that, I think I'll summon up the courage to read the 'course to steer' thread. Apparently you came up with an original method for calculating the CTS in that, and I look forward to finding out what it is. Tomorrow.

If you do that, it is this thread here that is the most important one:
http://www.cruisersforum.com/forums/...ame-94879.html
Start at roughly post # 180 (there was a lot of waffle before that LOL). That is an absolutely fascinating thread to see how lots of misconceptions were cleared up and how the new method for calculating the CTS evolved.

I am copying the most important 50 odd posts on why following a CTS is better than following the rhumb line, onto a new thread and will post that tomorrow.

There was more here following on regarding CTS:
http://www.cruisersforum.com/forums/...ine-97251.html

And the new CTS method was discussed here:
http://www.cruisersforum.com/forums/...hod-96579.html

I became very frustrated in this last thread (you will tell by the numerous items in bold and colour LOL), so please skim over that and just look at the substance, not the manner. I don't often lose my temper and i was getting close there for obvious reasons.

Have fun reading .
Gone 2:30 am here - it shows how keen I am on this LOL.
Night all.

[Seaworthy Lass]

Originally Posted by goboatingnow

I've never understood LBE. how an a current on the nose , well just off the nose , lift you to weather.

I can see a current effect where you are sailing to a windward ground reference mark,( but not laying it ) and the current happens to be pushing you up , hence it looks like the boat is pointing higher then it is. , is that LBE.

dave

No, that is not LBE. I will explain tomorrow (or I should say later today when I get up LOL), unless someone beats me to it.

[Hoofsmit]

Sorry got to butt in once more.......... It is a rule of thumb not an effect

The term in my opinion is a traditional one...... Used well before any cruiser or sailing work boat had wind instruments on board , nothing but experience and there senses to judge tide and wind affect on there head to wind course.

How many here have sailed up a estuary or tidal inlet on a ebb tide with no wind instruments and the feel of the boat and your senses ....... Have you ever stemmed a tide?

Try it you will have a very different approach to this topic

I need to go to Falmouth and talk to the guys on the Falmouth work boats who dredge the estuary ever day towing a scallop dredge behind them with no keel and portable ballast I'm sure I would learn something about the true meaning of lee bowing the tide might be.
I can guarantee not one gets out his pencil and works in tidal vectors

I have typed enough.... I need to learn more before I do

[Paul Elliott]

Originally Posted by europaflyer

[...]
As for the wind names debate, I don't really know about the names that modern instrument makers use. I think people are trying to make a distinction between the wind direction over the ground at slack water, and the minute change that friction between the air mass and a moving current will make.

The above (bolded) is absolutely NOT what any of us have been discussing. We have been trying to make the distinction between Ground-Referenced True Wind (as measured from the shore, or from an anchored buoy), Water-Referenced True Wind (as measured from a drifting platform), and Apparent Wind (as measured from a moving boat). This isn't the place to argue the names of these definitions, but it is critical that we agree on what we are talking about.

This is not, in my mind, a distinction important to sailing. I see only two wind names relevant here - the true wind which is what is blowing over the ground or seabed, and the apparent wind which is the true wind with the vectors added to it of the wind created by the boats motion ('headwind'?) and the motion of the current ('current induced wind' in my diagram - a more elegant name might be 'tide wind'?). [...]

Again, there are different definitions for True Wind. Let's at least describe which ones we are using. If you are interested, another thread has been started to work on the definitions: http://www.cruisersforum.com/forums/...ur-115308.html

[Seaworthy Lass]

Originally Posted by goboatingnow

I've never understood LBE. how an a current on the nose , well just off the nose , lift you to weather.

I can see a current effect where you are sailing to a windward ground reference mark,( but not laying it ) and the current happens to be pushing you up , hence it looks like the boat is pointing higher then it is. , is that LBE.

dave

Hi Dave
Here is an explanation of the 'Bow Effect' (my new name as there is no such thing as a 'Lee Bow Effect').

I would call the 'Bow Effect' this:
The tack with current closer to being on the bow is the tack that is lifted by the current.

There is no great significance to this, as it does not necessarily make this tack the favourable one (it depends where the mark is relative to the CTS, the mark need not be exactly upwind).

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. In tack as soon as the other tack is closer to the CTS.

This is how the Bow Effect works: In the example I have shown the current is actually on the windward bow (it can be either bow, so it is utterly stupid calling it the Lee Bow Effect).

The current is closer to the bow on one tack rather than the other. The wind induced by the current adds to the ground wind to shift the wind more favourably on this tack and you can point higher. In this case, note that even after the lift the current is still on the windward side of the bow.

I think I have very successfully shown with my elegant cone diagram that there is no such thing as a 'Lee Bow Effect' as half the time it is a 'Windward Bow Effect' LOL. As the cone diagram shows, the effect of different current directions is centred on the ground wind. Nothing to do with the lee or windward side of the boat.

Since it is just a 'Bow Effect' it makes it particularly ludicrous that pinching to put the current on your lee bow gives you some magical advantage. All hot air and voodoo LOL. If it works in real life it just means the fleet hasn't judged conditions on the course too well and have misjudged when to tack .

PS Europaflyer, I hope this explains why the effect is not centred on the apparent wind as you suggested. By the way, the optimum is not exactly into current. It has nothing to do with the boat, it is just that the angle between tacks puts it roughly there. It is actually very complicated as it depends on the amount of ground wind compared to current wind, but 'on the bow' is a close enough approximation.

[Dockhead]

Originally Posted by europaflyer

That's not the LBE as I have ever understood it, read it or been taught about it. That's more a sort of funny ferry-gliding pinching effect, made by someone who does not understand that the motion of the current is not what affects boat performance, but rather the movement of the boat relative to the current.

I think much of the disagreement about the LBE comes from people who understand it to relate to something other than what I am talking about.

exactly.

There are several quite different things which get called "Lee Bow Effect". That one has not been discussed much, because it is generally agreed that that one is nonsense and a myth, resulting from exactly the misunderstanding Europaflyer mentions here.

As to the other "Lee Bow Effect", the one we have discussed in some depth here, I think Seaworthy is sowing a little confusion by repeating "there is no Lee Bow Effect", right after proving that the effect we have been referring to as Lee Bow Effect is actually no myth. She's saying it for effect, I think, since she appears to have shown that the effect does not necessarily require the current on the lee bow, despite it's name, and she's justifiably proud of this discovery

[Dockhead]

Originally Posted by goboatingnow

I've never understood LBE. how an a current on the nose , well just off the nose , lift you to weather.

I can see a current effect where you are sailing to a windward ground reference mark,( but not laying it ) and the current happens to be pushing you up , hence it looks like the boat is pointing higher then it is. , is that LBE.

dave

Read the thread from the beginning Dave! It's a bit of a tortured journey, but believe me, it is worth it!!

[Seaworthy Lass]

Originally Posted by Dockhead

As to the other "Lee Bow Effect", the one we have discussed in some depth here, I think Seaworthy is sowing a little confusion by repeating "there is no Lee Bow Effect", right after proving that the effect we have been referring to as Lee Bow Effect is actually no myth. She's saying it for effect, I think, since she appears to have shown that the effect does not necessarily require the current on the lee bow, despite it's name, and she's justifiably proud of this discovery

Not sowing any confusion LOL. The word 'Lee' should not be mentioned and the effect should not be granted any great significance. The tack with current closer to being on the bow is simply the tack that is lifted by the current. The favourable tack may or may not be the one the lift from current is occurring on. It depends where the mark is. There is no big deal about this effect. And it does not necessarily tell you anything at all about the tack to be on .

[Dockhead]

Originally Posted by Seaworthy Lass

Not sowing any confusion LOL. The word 'Lee' should not be mentioned and the effect should not be granted any great significance. The tack with current closer to being on the bow is simply the tack that is lifted by the current. The favourable tack may or may not be the one the lift from current is occurring on. It depends where the mark is. There is no big deal about this effect. And it does not necessarily tell you anything at all about the tack to be on .

We got all that, but the effect is in fact what has been called for decades Lee Bow Effect. Maybe the precisioned and expanded theory should be renamed in your honor, the Seaworthy Lass Effect. But it is fundamentally Lee Bow Effect, better understood

[foolishsailor]

Originally Posted by Dockhead

We got all that, but the effect is in fact what has been called for decades Lee Bow Effect. Maybe the precisioned and expanded theory should be renamed in your honor, the Seaworthy Lass Effect. But it is fundamentally Lee Bow Effect, better understood

No, it isnt. What we are talking about now is just Sailing Strategy and Vector Optimization - which is why what we are talking about works - becuase it is real.

Lets clarify what "Lee Bow Effect" is so we can understand why it is controversial and why it doesn't exist.

From Dave Perry

THERE IS NO LEE-BOW EFFECT - Dave Perry

One of the most fascinating and timeless controversies in our sport is over what effect current has on
how we sail and race our boats. Beginning in early 1979, Peter Isler and I filled hours of time debating
the effects of current, and it wasn't until mid-1980 that he finally parted my clouds and shook me loose
from years of misconceptions and incorrect assumptions. Here then is my understanding of the effects
of current, substantiated by several of my more mathematically-clever friends.

Assuming that we're sailing in constant current direction and strength, No! As we've determined, the
direction and strength of the current created wind is the same no matter at what angle the boat is aiming
or at what speed it is moving. The presumption of the lee-bow effect is that if you are sailing directly into
the current you can pinch slightly, putting the current on your leeward bow, and the current will push you
up to weather. This is obviously false because the only direction the current can move you is in the
direction it is going (the stick on the river).

The presumption of those who believe that in current a boat will have a different apparent wind direction
and strength on opposite tacks, is that on one tack the boat will be slowed more by the current than on
the other. The extreme example is when port tack takes you right into the current, and starboard tack
takes you across it. The illusion is that on port tack it would seem that the boat is still going forward
toward the wind, but that on starboard the boat is being swept away from the wind by the current.
Therefore, the apparent winds must be different on the two tacks.

The fallacy here, though, is that the judgment of going toward the wind and being swept away are made
in reference to fixed objects such as the mark, an anchored boat, or land. In reality, both boats are being
affected equally by the current and the wind "sees" both boats in the same way. In other words, if you
were following the race in a motorboat and were in the ocean where you couldn't see any land for
reference, the boats would look identical on either tack, and in fact you would have no clue that there
even was current unless you knew from charts or perhaps from the surface condition of the water. Put
another way, if you're sailing on a boat with apparent wind strength and direction instruments, they'll
read the same on both tacks because the boat is affected in the same way by the current on either tacks
(the stick in the river again).

-- Excerpt from Winning in One-Designs by Dave Perry,
http://www.ussailing.org/member/library/wiodcurrent.htm

[foolishsailor]

This is a fantastic explanation including graphics of exactly what the "Lee Bow Effect" is and why it is non-existent

Destination One Design - Preparation

[Seaworthy Lass]

Originally Posted by Dockhead

We got all that, but the effect is in fact what has been called for decades Lee Bow Effect. Maybe the precisioned and expanded theory should be renamed in your honor, the Seaworthy Lass Effect. But it is fundamentally Lee Bow Effect, better understood

Originally Posted by foolishsailor

No, it isnt. What we are talking about now is just Sailing Strategy and Vector Optimization - which is why what we are talking about works - becuase it is real.

Lets clarify what "Lee Bow Effect" is so we can understand why it is controversial and why it doesn't exist.

From Dave Perry....

I agree with FS, there is no 'special' effect, and it definitely should not have the word 'lee' in it. What I am describing is just which tack is lifted with current (the one with the current on the bow more). It does not tell you which tack to be on. It does not tell you when to tack. If you had to call it anything you would call it the 'bow effect', but it is not really worthy of any name.

The term 'Lee Bow Effect' was obviously coined to describe a possible lift if you can pinch to get the current from your windward bow to your lee one. We have definitely concluded that is rubbish. There is nothing more to the famed affect.

What has occurred is that lots of sailors (including knowledgable ones like Europaflyer) have somehow extended this to say there is something favourable or advantageous to the current being on the lee side at other times. There is none, at least no more than it is favourable or advantageous to having the current on the windward side at times.

Even I got caught up with all the diagrams showing that it is the tack with the current on the lee bow that is lifted. The diagrams are terribly misleading as they only look at the current being roughly perpendicular to the ground wind. Examine the current all the way around the compass and suddenly it is apparent there is has absolutely nothing to do with the lee or starboard sides (can be either).

[foolishsailor]

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.

[foolishsailor]

This applies even to the CTS as well.

If you only need one tack to arrive at a destination then there is no favored tack as only one tack will take you to your target. Such as a reach across a current to a destination in the Solent.

This discussion is only relevent to events where one is sailing to a point upwind and likely beating or sailing to a target downwind and can choose gybing angles.