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

[Dockhead]

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

There are a few different things which are called "Lee bow effect." We have not much discussed Perry's flavor because we all agreed early on that it is nonsense.

But Channel sailors, at least, are referring to something different with the term - the real lift you get if you can sail two or more favored tacks Ian changing current, which gives you a predictable, exploitable wind shift.

Europaflyer explains it well above. I'm in planes and haven't studied SWLs materials to the end, but I'm pretty sure she has expanded the same concept.

Your racers brain will be extremely valuable in this discussion - read the whole thread from the beginning and you'll see exactly what we were talking about.

[Dockhead]

Originally Posted by Seaworthy Lass

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?).

Exactly And this is extraordinarily important, essential.

[Dockhead]

Originally Posted by foolishsailor

Because a CTS is a Course to Steer - and you are not steering that course if it falls within your tacking angle and therefore it provides no benefit.

I can see how you could use the CTS as a center point if you wished to short tack up the CTS or almost like a CTE to let you know how far off you are when tacking...

...however it yields no benefit and can be very misleading, especially as on your last tack to lay your destination you will be nowhere near your CTS and if you are going dead upwind and have a tacking angle of 100°, depending on the magnitude of and direction of current you could be over 50° off your CTS.

I can CTS being used as an element in upwind strategy with current but not the same way it is used with a single tack course to lay a mark like discussed in the other thread..

For example see the drawing I just made,it is a real world example of a winning strategy that happened in Cowes Week this year in the quarter tonner class. An example of immense forethought and risk that in retrospect we all thought to ourselves - why didnt we do that? The currents are approximate but very close to the day based on my Winning Tides tidal planner for the Solent.

CTS played a role in two places - The winning boat choosing its CTS to cross sailing the least time and distance and the final Sailing angle to lay the mark the remaionder of the fleet choose - but more importantly would be calculating current relief and assist and where a change in tack will optimize this.

You tack around it, striving for average heading equal to CTS. You can't do this problem without it.

[Hoofsmit]

Originally Posted by Dockhead

There are a few different things which are called "Lee bow effect." We have not much discussed Perry's flavor because we all agreed early on that it is nonsense.

But Channel sailors, at least, are referring to something different with the term - the real lift you get if you can sail two or more favored tacks Ian changing current, which gives you a predictable, exploitable wind shift.

Europaflyer explains it well above. I'm in planes and haven't studied SWLs materials to the end, but I'm pretty sure she has expanded the same concept.

Your racers brain will be extremely valuable in this discussion - read the whole thread from the beginning and you'll see exactly what we were talking about.

Nice to have you back

As OP can you read # 271 and pick one please?

[Seaworthy Lass]

Originally Posted by Dockhead

There are a few different things which are called "Lee bow effect." We have not much discussed Perry's flavor because we all agreed early on that it is nonsense.

But Channel sailors, at least, are referring to something different with the term - the real lift you get if you can sail two or more favored tacks Ian changing current, which gives you a predictable, exploitable wind shift.

Europaflyer explains it well above. I'm in planes and haven't studied SWLs materials to the end, but I'm pretty sure she has expanded the same concept.

Your racers brain will be extremely valuable in this discussion - read the whole thread from the beginning and you'll see exactly what we were talking about.

Hi Dockhead
So nice to see you back. You need to catch up with the threads first . There is no lee bow effect. Only one thing actually refers to this and that is the theory that pinching to achieve it helps and we have discounted this.

I made this comment earlier:
"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."

Crossing the channel into wind is just a special set of circumstances. It just happens with these conditions that the tack closest to the CTS (or FS is arguing that it is the rhumb line) is the one when the current is on your lee bow.

It is completely wrong to talk about this as some kind of effect, as if there is something special about the current being on the lee bow. There isn't. In other circumstances it may be on your windward bow .

[Paul Elliott]

Foolishsailor, the term CTS that Seaworthy is using does *not* necessarily mean that you will be pointing your bow at that heading. "CTS" is a term that we have been using to describe the straight-line path we would sail through the water to get us to the mark if we weren't tacking, weren't trying to maintain optimum VMG, and weren't considering current eddies or countercurrents. "CTS" was a method developed here in the analysis of sailing through uniform current fields (the current is equal at all points), where this uniform current changes over time.

Add the need to tack upwind, then you will sail your best VMG tacks, with your goal being to sail the average course given by the CTS method.

Add in nonuniform currents, such as the current-relief along shore that you have diagrammed, then the CTS method (and the previous flawed piloting methods that CTS was developed to replace) must be tossed out the window.

So, unless we are all trying to solve the same problem, we are never going to agree on the solution.

Yes, you might think that the term "CTS" implies that we actually steer the boat to this course. This is confusing and unfortunate. CTS is the course we would steer if we didn't have to tack for best VMG.

[Paul Elliott]

I suppose I am inclined to say "The lee-bow effect is bunk!" and leave it at that. The lee-bow effect definition that I am familiar with is the "pinching" one, and it is obviously false.

These other methods for optimizing our course should be called something else, since in my opinion the term "lee-bow effect" is already taken. I suggest we not even use "bow effect", since my first impression is that this is just an abbreviation for LBE.

We've already got this problem with "True Wind" -- let's not add to the confusion!

[Hoofsmit]

Originally Posted by Seaworthy Lass

Hi Dockhead
So nice to see you back. You need to catch up with the threads first . There is no lee bow effect. Only one thing actually refers to this and that is the theory that pinching to achieve it helps and we have discounted this.

I made this comment earlier:
"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."

Crossing the channel into wind is just a special set of circumstances. It just happens with these conditions that the tack closest to the CTS (or FS is arguing that it is the rhumb line) is the one when the current is on your lee bow.

It is completely wrong to talk about this as some kind of effect, as if there is something special about the current being on the lee bow. There isn't. In other circumstances it may be on your windward bow .

sw... dame......... did we?

approach it from FS picture in the solent

there are definitely times when it is more advantageous in very heavy tidal streams with low wind , mainly when the on the port hand side route, look at the current change , I would be pinching on ever port take .... as a rule of thumb

I think this was my statement very early on !

[Hoofsmit]

Originally Posted by Paul Elliott

I suppose I am inclined to say "The lee-bow effect is bunk!" and leave it at that. The lee-bow effect definition that I am familiar with is the "pinching" one, and it is obviously false.

These other methods for optimizing our course should be called something else, since in my opinion the term "lee-bow effect" is already taken. I suggest we not even use "bow effect", since my first impression is that this is just an abbreviation for LBE.

We've already got this problem with "True Wind" -- let's not add to the confusion!

Paul have you read # 271 yet?

Europaflyer explains it well above. I'm in planes and haven't studied SWLs materials to the end, but I'm pretty sure she has expanded the same concept.

I tried with the affect of foils to current but was promptly put in my place..... the vectors of flow were never applied which I am looking into

[europaflyer]

Originally Posted by Seaworthy Lass

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).

As your post #223 shows, there is either a lifting or knocking effect for any direction of tide. I think we agree on this point.

I am saying that the points when the tide direction changes from producing a beneficial effect on one tack to beneficial on the other are at 360 and 180 degrees tidal stream relative to apparent wind, as shown on your diagram. These are the points when there is no effect of tide on apparent wind direction.

You are saying that current lifts when forward of the beam ('bow effect') and knocks when aft. I dispute this, and here is a diagram to show a scanario where a tide aft of the beam is shifting the apparent wind aft (ie. favouring the boat). Although the creation of a favoured tack does not in this case follow your 'bow theory', it does follow my 'apparent wind current angle theory' - the current is between 360 and 180 apparent, and so creates a favourable port tack.

I don't see how the angle of the current relative to the boat is relevant to the creation of a shift in apparent wind. This will be felt regardless of where the boat is pointing. Imagine if the boat is stationary in the water - where the bow and stern are doesn't matter a bit, but the apparent wind will still be shifted by the current. If the destination is exactly in the eye of the true (ground) wind, then the apparent wind now creates a favoured tack - because of the effect of current. When the current changes direction, the favoured tack will also change.

We are in total agreement that calling the effect the 'lee bow effect' is misleading. However, you are still following that mentality by trying to explain the effect as you see it by talking about the angle of the tide relative to the boat. As the effect relates to the effect of tide on wind direction, what matters here is the angle of the tide relative to the wind.

By my continuing to use the term 'lee bow effect' I am not trying to say that what matters is that the current is on the leeward side, or on the bow. I am just using the generally accepted term for what is a generally accepted effect that any good book on sailing theory will discuss. It happens that the effect is strongest (ie. biggest shift in apparent wind) when the current is at 90 or 270 degrees to the apparent wind. The effect is only relevant tactically when closehauled, which for this most important case of the effect would place the current on the lee bow. I have no complaint with this nomenclature, even though it my create the misleading impression that the CAUSE of the effect relates to the angle of the current relative to the boat rather than to the wind. The name is just due to the most common rule of thumb for the use of the effect.

[europaflyer]

Oh and by the way Seaworthy, your definition of 'favourable tack' is the same as how I understand it. IE, one tack allows you to make ground towards the destination more quickly, and although in theory it takes the same time for a boat to start out on favourable as unfavourable, in reality the possibility of a wind shift suddenly swapping the favour of the tacks round makes it sensible to first sail the one which gives you the most ground towards the destination.

[europaflyer]

Originally Posted by Seaworthy Lass

It is completely wrong to talk about this as some kind of effect, as if there is something special about the current being on the lee bow. There isn't. In other circumstances it may be on your windward bow .

Although in theory we can prove that a tide on the windward bow will produce a helpful wind shift in some cases (although, incidentally, only my apparent wind tide angle theory tells you when it will help, whereas your bow theory doesn't), in reality we know that the effect of a tide on the bow will always be bad for ground made good to destination, regardless of the fact that the boat may be pointing a bit closer to the true wind. In the REAL WORLD, the most potent, classic case of the effect is when the tide is on the lee bow, hence the name. The name chosen is just a rule of thumb, so people who can't understand all the theory we discuss know when and how to exploit this very real, very powerful effect.

[Paul Elliott]

Originally Posted by europaflyer

As your post #249 shows, there is either a lifting or knocking effect for any direction of tide. I think we agree on this point.

I am saying that the points when the tide direction changes from producing a beneficial effect on one tack to beneficial on the other are at 360 and 180 degrees tidal stream relative to apparent wind, as shown on your diagram. These are the points when there is no effect of tide on apparent wind direction.

You are saying that current lifts when forward of the beam ('bow effect') and knocks when aft. I dispute this, and here is a diagram to show a scanario where a tide aft of the beam is shifting the apparent wind aft (ie. favouring the boat). Although the creation of a favoured tack does not in this case follow your 'bow theory', it does follow my 'apparent wind current angle theory' - the current is between 360 and 180 apparent, and so creates a favourable port tack.

I don't see how the angle of the current relative to the boat is relevant to the creation of a shift in apparent wind. This will be felt regardless of where the boat is pointing. Imagine if the boat is stationary in the water - where the bow and stern are doesn't matter a bit, but the apparent wind will still be shifted by the current. If the destination is exactly in the eye of the true (ground) wind, then the apparent wind now creates a favoured tack - because of the effect of current. When the current changes direction, the favoured tack will also change.

We are in total agreement that calling the effect the 'lee bow effect' is misleading. However, you are still following that mentality by trying to explain the effect as you see it by talking about the angle of the tide relative to the boat. As the effect relates to the effect of tide on wind direction, what matters here is the angle of the tide relative to the wind.

By my continuing to use the term 'lee bow effect' I am not trying to say that what matters is that the current is on the leeward side, or on the bow. I am just using the generally accepted term for what is a generally accepted effect that any good book on sailing theory will discuss. It happens that the effect is strongest (ie. biggest shift in apparent wind) when the current is at 90 or 270 degrees to the apparent wind. The effect is only relevant tactically when closehauled, which for this most important case of the effect would place the current on the lee bow. I have no complaint with this nomenclature, even though it my create the misleading impression that the CAUSE of the effect relates to the angle of the current relative to the boat rather than to the wind. The name is just due to the most common rule of thumb for the use of the effect.

Just to be clear, your diagram is using ground-referenced True Wind. Obviously if we use water-referenced True Wind then there is no shift in Apparent Wind due to current, as the current effects are already factored into the water-referenced True Wind. I'm still trying to figure out how your "Headwind" is derived [edit: Oh, it is the headwind caused by the boat's motion].

But yes, using ground-referenced True Wind, your diagram correctly shows the effects of current and boat motion on Apparent Wind.

Since our ultimate goal is to reach a mark on shore, and current is certainly ground-referenced, I suppose I can live with using ground-referenced wind in the analysis.

Hoofsmit, yes I did read post #271. If there are accepted valid definitions of "Lee Bow" effects other than the bogus "pinching" definition, I can live with that as well. I had only been familiar with the bogus one.

[europaflyer]

Originally Posted by Paul Elliott

Just to be clear, your diagram is using ground-referenced True Wind. Obviously if we use water-referenced True Wind then there is no shift in Apparent Wind due to current, as the current effects are already factored into the water-referenced True Wind (which is your "Headwind" in the diagram).

But yes, using ground-referenced True Wind, your diagram correctly shows the effects of current and boat motion on Apparent Wind.

Since our ultimate goal is to reach a mark on shore, and current is certainly ground-referenced, I suppose I can live with using ground-referenced wind in the analysis.

Ah. I think I start to see where some of the disagreement comes from. If your definition of 'true wind' takes in to account the effect of current on the wind (which is what this effect is all about) then I can see how my posts might confuse people. Just to check that I understand your definitions,

Ground wind (or the more ugly 'ground referenced true wind') - wind over the ground, or seabed.

True wind (water referenced) - wind on a free floating object (ie. accounting for current wind effects)

Apparent wind - wind on the boat, ie. true wind accounting for boat speed as well.

If this is the case, then for 'true wind' in my posts, read 'ground wind'. Otherwise, I stand by the points I have made.

Oh, and the current wind in my diagram is NOT your water referenced true wind. It is just the wind due to current, with no ground wind at all. My true wind plus current wind is your 'water referenced true wind'. All very confusing.

[Hoofsmit]

Originally Posted by europaflyer

Ah. I think I start to see where some of the disagreement comes from. If your definition of 'true wind' takes in to account the effect of current on the wind (which is what this effect is all about) then I can see how my posts might confuse people. Just to check that I understand your definitions,

Ground wind (or the more ugly 'ground referenced true wind') - wind over the ground, or seabed.

True wind (water referenced) - wind on a free floating object (ie. accounting for current wind effects)

Apparent wind - wind on the boat, ie. true wind accounting for boat speed as well.

If this is the case, then for 'true wind' in my posts, read 'ground wind'. Otherwise, I stand by the points I have made.

Oh, and the current wind in my diagram is NOT your water referenced true wind. It is just the wind due to current, with no ground wind at all. My true wind plus current wind is your 'water referenced true wind'. All very confusing.

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