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Old 13-11-2013, 10:13   #211
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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 Hoofsmit View Post
[...] i am sure the affect of the current angle to the keel and rudder have a influence why it works, but i will leave that to someone who knows more about hull and foil design than me
And this is what I don't understand. Your boat is floating in the current. The keel and rudder (foils) do not see the current. Now if your boat were riding on tracks bolted to the sea bed then we could talk about current against the foils. But it's not. All your boat sees is the water-referenced True Wind.

And yes, by definition the current will cause the True Wind to be different than the Ground Wind.

The current will affect the your course over ground, but not because of some special effect on your foils.
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Old 13-11-2013, 10:26   #212
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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 Hoofsmit View Post
English version

True
/tru/ Show Spelled [troo] Show IPA adjective, tru∑er, tru∑est, noun, adverb, verb, trued, tru∑ing or true∑ing.
adjective 1. being in accordance with the actual state or conditions; conforming to reality or fact; not false: a true story.


true wind = un affected by any other factors

Apparent applies to that which can readily be seen or perceived:

Apparent wind = what is perceived to be the wind direction at the helm position

angle and velocity influenced by induced heading wind , leeway, current/ tidal stream and any thing else that affects what you feel .... including bean induced
And so what is your term for the wind as measured by (say) a free-floating buoy, or a drifting sailboat? This is what most of us are calling True Wind, but if you want to call it something else that's fine with me. We can have the terminology argument in another thread.

Yes, to get Apparent Wind you take the vectors for Ground Wind, current, and boat speed-through-water/heading/leeway. Or, you use Ground Wind, SOG, and COG.

But in practice you start with measured Apparent Wind and calculate your way backwards to True (water) Wind using your water-speed, heading, and leeway. To go from measured Apparent Wind to calculated Ground Wind you use SOG/COG. Or you take calculated True (water) Wind, and if you know the current vector you can calculate Ground Wind.

I suppose my point is: This discussion is doomed unless we understand each others terminology.
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Old 13-11-2013, 12:17   #213
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

And so what is your term for the wind as measured by (say) a free-floating buoy, or a drifting sailboat?
tidal/current induced...... if there is enough flow velocity to even bother with it in any real situation, i have never sailed in a situation in 4 knots of tide to see it stop my sails from flapping !


We can have the terminology argument in another thread. maybe best
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Old 13-11-2013, 16:02   #214
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And this is what I don't understand. Your boat is floating in the current. The keel and rudder (foils) do not see the current. Now if your boat were riding on tracks bolted to the sea bed then we could talk about current against the foils. But it's not. All your boat sees is the water-referenced True Wind. And yes, by definition the current will cause the True Wind to be different than the Ground Wind. The current will affect the your course over ground, but not because of some special effect on your foils.
Lee bowing the tide means the foils route through the current is different than if the wind is on the windward bow . Now your going to be thinking windward or leeward current what's the difference..... This is where to me the definition of lee bowing comes into it, it is with in very fine vectors of wind current and heading...... I'm still trying to figure it out, my gut tells me it is right somewhere just can't explain it yet ... I know ..... Give me time and I might dig myself a hole.

Floating in the current ? Who said you can lee bow with no movement.....That's like saying a aeroplane wing can't provide lift when you only want to view it sat still on the airport Tarmac
I think laterial thinking outside of two dimensional vector drawings might get us to a different answer
My foils do not 'see the wind' they are in the water! But the angle they are presented to a current does affect what happens to my boats leeway..... But maybe that's another gut feeling.... Give me time..... But keep the questions coming . Digs or insults even.... It can only make me a better skipper
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Old 13-11-2013, 16:31   #215
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Lee bowing the tide means the foils route through the current is different than if the wind is on the windward bow . Now your going to be thinking windward or leeward current what's the difference..... This is where to me the definition of lee bowing comes into it, it is with in very fine vectors of wind current and heading...... I'm still trying to figure it out, my gut tells me it is right somewhere just can't explain it yet ... I know ..... Give me time and I might dig myself a hole.
I am looking forward to your explanation.

Quote:
Floating in the current ? Who said you can lee bow with no movement.....That's like saying a aeroplane wing can't provide lift when you only want to view it sat still on the airport Tarmac
I think laterial thinking outside of two dimensional vector drawings might get us to a different answer
By "floating in the current" I meant sailing through the water, while the current is causing the water to move. The earlier "tablecloth" analogy is a good one that illustrates this point. I'm not sure where we need more than a 2-dimensional vector analysis. We are ignoring wind shear, and assuming uniform current flow.

What greatly simplifies the analysis is to use the water (tablecloth) as our reference plane for everything else. This is why the True Wind (water-referenced) definition is important. Once we've done that, we can back up later and look at the land and COG. But first we need to understand the wind and the water.

Quote:
My foils do not 'see the wind' they are in the water! But the angle they are presented to a current does affect what happens to my boats leeway..... But maybe that's another gut feeling.... Give me time..... But keep the questions coming . Digs or insults even.... It can only make me a better skipper
Leeway is through the water, right? And that's a result of the AWA/AWS. Given the same AWA/AWS, and boat trim, the leeway on either tack should be identical. (We are ignoring waves against the hull.) With current your track over the ground will be different, but I don't think that's what is being discussed.

I hope nobody is seeing any of this as insulting! Even if it sounds like I think I know it all, I'm always eager to learn something new.
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Old 13-11-2013, 16:42   #216
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

ok.... here is another one to lend a shovel for my hole.
a planning dinghy is sailed flat in higher wind conditions to keep the hull planning there is a point when the wind is very light you add heel to get a better pointing angle to wind, this comes from my experience nothing more!
thinking about about it ( i never have done before) the planning side is hull dynamics but the heel works with displacement cruisers as well . why ?
and another ... Leeway we all know is affected by the angle at which we sail to the wind and its strength, but it must involve the resistance of the keel to sideways movement
If the whole lee bow affect is about current on the right side of our keel maybe wind induced infleuences is not where we should be looking

ok ok .... i'm digging !!!
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Old 13-11-2013, 16:56   #217
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

If the whole lee bow affect is about current on the right side of our keel maybe wind induced infleuences is not where we should be looking

sorry should have said

is about angle of current on the keel
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Old 13-11-2013, 17:11   #218
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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ok.... here is another one to lend a shovel for my hole.
a planning dinghy is sailed flat in higher wind conditions to keep the hull planning there is a point when the wind is very light you add heel to get a better pointing angle to wind, this comes from my experience nothing more!
thinking about about it ( i never have done before) the planning side is hull dynamics but the heel works with displacement cruisers as well . why ?
You sometimes heel a displacement boat to leeward in order to have gravity induce a little shape to your sails. Otherwise if there isn't enough wind to fill them, they just hang flat. You want some belly in them for so they provide lift. You might also heel a moderate-weight boat in order to roll-tack, which uses the hull shape to steer, giving less drag than the rudder would give. None of this really has anything to do with current though.
Quote:
and another ... Leeway we all know is affected by the angle at which we sail to the wind and its strength, but it must involve the resistance of the keel to sideways movement
If the whole lee bow affect is about angle of current on the keel [edited] maybe wind induced infleuences is not where we should be looking

ok ok .... i'm digging !!!
I still have a problem with "angle of current on the keel". Look at the tablecloth analogy again. We have wind, and we have water. This current doesn't flow through the water, it is the water! The water is the reference plane. I really don't understand the "current against the keel" concept.
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Old 13-11-2013, 17:50   #219
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You sometimes heel a displacement boat to leeward in order to have gravity induce a little shape to your sails. Otherwise if there isn't enough wind to fill them, they just hang flat. You want some belly in them for so they provide lift. You might also heel a moderate-weight boat in order to roll-tack, which uses the hull shape to steer, giving less drag than the rudder would give. None of this really has anything to do with current though. I still have a problem with "angle of current on the keel". Look at the tablecloth analogy again. We have wind, and we have water. This current doesn't flow through the water, it is the water! The water is the reference plane. I really don't understand the "current against the keel" concept.
Thanks for explanation of the heel totally understand . Interesting the hull shape needing less rudder is that it just provides more bouancy with the fuller beam or does it produce bow steer( something I know about from my 30years on fast cruisers in a big sea) ?

Understand the table cloth, what has been missed is that we are trying to get to the chair at end of the table not a point on the table cloth ...... Didn't get this spot in the water thing mentioned earlier .


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Probably completely wrong but hopefully explains my thinking
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Old 13-11-2013, 20:06   #220
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

ok ... i am now in my hole and about to bury myself without any help from anybody else.

After reading a fair bit on this subject i have come to the conclusion there is no magic element to the lee bow affect.

It is purely a common sense tactic to ensure you do not loose out to the tideal stream advantage on a windward leg or passage.

In the short explanation it is that after working out the cts on a changing current you start you course with the tide on your leeward bow


eg:The English channel with the wind forecast on your bow, you have done the classic of working out the tidal vectors leeway etc and plotted them on your chart at your starting point to give you a heading that will not head down the rumb line but to one side of it as the change of tide will never work out to be perfectly equal those that have done this will know what i mean!
Thus to head up wind you will be tacking at some point .

The lee bow rule just states that the advantage gained by having the tide on you lee bow means that if the wind veers you will be nearer your rhumb line as the tide has been to your advantage than if you started on a tack with the tide on your windward bow to start with. If you want to prove this - plot a tidal vector every hour along you ground /rhumb line

At the point the tide changes direction you should tack again to keep your lee bow to the tide thus again having an advantage over any wind veer or back .


Weirdly this was actzactly ( sorry ... bit of Cornish) what my dinghy racing tactics were in my youth where our top mark stuck right in the main tidal stream, which was to be rounded on one or the other sides by 180 degrees to go on the next leg on a run, the race committee knew that the small headland poking out from the shore created a veer 2 boat lengths before the mark along with a tidal current increase and direction change laying you off the mark and often they changed the marks position accordingly !
the lee bow always worked with the wind directly down the harbour safe guarding the veer if you dared to go on the other tack first you ended up doing a 720 degree penalty for being swept onto the mark or over shooting.


A few authors try to add a bit of meat by things like saying it will bring the wind aft thus giving a better heading to wind but

Every author agrees it is to advantage your heading nearer your rhumb line. After a cts for a passage has been calculated. not one states that workings should be included in the calculations as it is a rule of thumb tactic......... OBVIOUSLY unless a wind change is forecast ( but as a good navigator you would have worked this into you CTS !!!

the end
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Old 13-11-2013, 21:05   #221
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Aloha, Sailors.

Landlubbing Lurker of no and/or ill repute throwing my fish'n'chips ahoy in.

It seems to my tiny mind that were there marginal or no effect with friction and fraction, Anchors and Fenders would be optional as Reefing.

Ground could literally be brought into the equation, as with or without your friendly local Octopus providing extra grip and protest, a lesser Anchor or two positioned even oh, so carefully drags due to forces be they tidal, current and/or wind.

As such, there would be particularly *bad* angles of *defense* against nature when desire is to be at rest . . . which i turn could provide inspiration for *good* angles with nature when *offense* is needed for racing, or way back when, reaching distant shores in time of peace or war.

Then again, perhaps the origin of this whole static dynamic concept went something like . . .

- Dar go boat, Hairfire.

Grunt it, Bogdown. Wear Dinky?!

- Hmmmmm. *flint'n'stone sparks above head* You reeka!

No, you reeka, cuz Hairfire . . .

- Shup. Me think Leefect.

etc.
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Old 13-11-2013, 21:08   #222
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Thanks for explanation of the heel totally understand . Interesting the hull shape needing less rudder is that it just provides more bouancy with the fuller beam or does it produce bow steer( something I know about from my 30years on fast cruisers in a big sea) ?
I believe the roll-tack uses the hull shape and bow-steering to turn the boat. You can also just steer without turning the rudder by adjusting the heel, again using hull shape, and the fact that heeling the sails changes the center of effort, thus pivoting the boat around the center of resistance (keel / rudder / hull). This is also why you get weather helm when you heel too far. I'm no expert on this by any means.

Quote:
Understand the table cloth, what has been missed is that we are trying to get to the chair at end of the table not a point on the table cloth ...... Didn't get this spot in the water thing mentioned earlier .


Attachment 70348

Probably completely wrong but hopefully explains my thinking
I see that in your follow-on post you have re-thought the lee bow effect, but do look at your diagram of water flow over the keel. You are showing flow at an angle due to current. That doesn't happen (there is some angle due to leeway).

Redraw your picture assuming zero current. The water flow will be virtually from bow to stern, with whatever angle there is being due to leeway. You do need some leeway to generate lift from the keel, but on fast boats it's not much of an angle.

Now place your boat, sailing the same speed but in a current. Your entire boat will be swept by the current, but your movement through the water will be identical. The flow diagram will be the same. Your movement over the ground will be affected by the current, but not your movement through the water.

And yes, when trying to get to a mark, there may be a favored tack, and a strategy for minimizing the adverse effects of unanticipated wind shifts. The current can easily affect which tack is favored.
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Old 14-11-2013, 01:47   #223
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

Everyone, I am raising this again, as it has not been addressed:
There is nothing at all magical about having the current on the lee side of the boat.

The boat with the current closer in angle to being off the bow is lifted more (purely by virtue of you wanting to head into wind), simply because sailing into the current rather than away from the current is how you can take advantage of the shift in true wind direction that the current induces. It is actually just a 'Bow Effect' (you want the angle of the current to be close off the bow).

Sometimes the current will be on the lee side or the windward side on both tacks. The tack that is lifted more is the one where the current is closer to being off the bow. Sometimes you can get the current on opposite sides on the two tacks, but only one of those puts the current more on the bow. Because you are fighting to windward this just happens to be when the current is on the lee side of the boat.

Interestingly if you are going directly downwind and want to gybe to increase speed there is a 'Stern Effect' LOL, you want the current angle to be closer to being off the stern, something I have never heard racers fuss about, but it is also important also occurs.

Just look at the diagram below again to check all this out (draw the two boat headings going the other way if you want to check out the 'Stern Effect' when gybing).

Whether or not this lift from current also makes a tack favourable depends entirely on where the destination is. The destination is not going to always be directly to windward (and even if the rhumb line is to windward, your CTS is not if you have a constant amount of current and ground wind for a journey).

It is a 'BOW effect' that is the key, not whether or not you can get the current on the lee side of the boat AND it is only important if it shifts the angle of the tack enough to make it the favourable one (and this depends on your CTS, not your rhumb line).

But, so what? You are just following the principle of sailing the favourable leg. Your tacking angles relative to the CTS will give you this before the start. Those racing, other than following the general principle (that everyone on the windward leg will do with constant conditions ie sail the favourable leg first) how on earth do you use this mythical 'Lee Bow Effect' to your advantage? I think someone has just successfully managed to pull the wool over your eyes since they coined the term. By the way, who was it? They need to walk the plank LOL.

Note: The fact that it is just a 'Bow Effect' blows 'Pinching to Achieve the Lee Bow Effect' cleanly out of the water .

Written in bold and larger as I am trying to get your attention and I finally need to shout LOL. Apart from Paul, no one is responding to what I have found.

Next time it is going even bigger and in red until I get some response from you lot.

(PS That pretty cone arrangement off the circle of current directions will become taller or squatter depending on the amount of ground wind relative to current. Exactly the optimum angle of the current on the bow is very complex, as it depends on the relative amounts of ground wind and current. It is not actually right on the bow, although it may often approximate this.)
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Old 14-11-2013, 03:40   #224
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Aloha, Sailors.

Landlubbing Lurker of no and/or ill repute throwing my fish'n'chips ahoy in.

It seems to my tiny mind that were there marginal or no effect with friction and fraction, Anchors and Fenders would be optional as Reefing.

Ground could literally be brought into the equation, as with or without your friendly local Octopus providing extra grip and protest, a lesser Anchor or two positioned even oh, so carefully drags due to forces be they tidal, current and/or wind.

As such, there would be particularly *bad* angles of *defense* against nature when desire is to be at rest . . . which i turn could provide inspiration for *good* angles with nature when *offense* is needed for racing, or way back when, reaching distant shores in time of peace or war.

Then again, perhaps the origin of this whole static dynamic concept went something like . . .

- Dar go boat, Hairfire.

Grunt it, Bogdown. Wear Dinky?!

- Hmmmmm. *flint'n'stone sparks above head* You reeka!

No, you reeka, cuz Hairfire . . .

- Shup. Me think Leefect.

etc.
I like this ..... I might change my name to Flintstone
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Old 14-11-2013, 04:03   #225
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

pauls quote:
Now place your boat, sailing the same speed but in a current. Your entire boat will be swept by the current, but your movement through the water will be identical. The flow diagram will be the same. Your movement over the ground will be affected by the current, but not your movement through the water.
fine if you are going to a point on the table cloth not to the chair with the table cloth moving in a stable direct .
try putting your hand under a tap..... change the angle of you hand ... it creates side ways movement. if the tap moved but you kept you hand in the stream ... you would still have sideways movement ! ok maybe not the best explanation but if you stay still on the table cloth but the table cloth moves you are drifting, now... we are not in a bowl we are in a hull with dynamic design , other wise we would be sailing in tuperware bowls( no comments from the wooden boat gang lol )
do the same workings as a cts wind vector . wind on the sail has the same affect as current on the keel ... just I have to explain it

And yes, when trying to get to a mark, there may be a favored tack, and a strategy for minimizing the adverse effects of unanticipated wind shifts. The current can easily affect which tack is favored.
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