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Old 16-11-2013, 06:44   #391
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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TALKING ABOUT VARIABLES :
when do we start bringing this lot in ?

1.2.2 Acting forcesThe forces acting on a yacht can be divided in six groups:
  1. gravity force
  2. hydrostatic force of buoyancy on the hull
  3. aerodynamic forces on any emerged item, mostly on the sails
  4. hydrodynamic forces on any submerged item, specially made up by side forces on the keel and the rudder
  5. wave drag on the hull, due to the presence of the free surface of separation between air and water
  6. inertial forces.
It must be said here that for side force we intend generally the component of the fluid-dynamic force perpendicular to the far field flow direction and to the vertical axis of the boat. For the similarity of the phenomena involved it is often called lift even if, unlike on aircraft, it is not needed to balance the gravity but other forces.
Those are already all added in - the boats COG and SOG are already a summation of all those vectors of force.
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Old 16-11-2013, 06:48   #392
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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You're a moderator, can't you just delete it? Or is that considered an abuse of power? If you'd like I could go back and report it as offensive, then you'd be justified
ROFL, yes it would be a terrible abuse of power, so I can't just delete it .

Your idea of reporting it certainly has merit though. The post does clearly have the potential to corrupt the minds of members and this is a family forum .
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Old 16-11-2013, 06:54   #393
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No, I thought this thread was trying to evaluate and understand important concepts that can play a huge role in passage times. By removing certain variables it is easier to determine the validity of the ones that remain.
Then why introduce a shoreline? We were in open water before.... I was merely commenting on the variables you introduced. So you are saying that only the variables you want to introduce are valid?
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Old 16-11-2013, 06:58   #394
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Europaflyer,

Would these conditions work for you to demonstrate the course you would take to illustrate your ideas? If not let me know what set of conditions would work and I will draw them up so we can work it out on a grid.
A complicated situation. Just sail the favoured tack at all times, whether that favoured tack is created by the lee bow effect, by wind shifts, by somebody's tablecloth or by space aliens. That is all the skipper needs to worry about. We have HUGELY overcomplicated what is really a very simple problem.

When people say 'lee bow effect' all they mean is that sitting in an alternating current can create alternating favoured tacks, which you need to tack to exploit. This is all it is. Phew!
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Old 16-11-2013, 07:00   #395
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Then why introduce a shoreline? We were in open water before.... I was merely commenting on the variables you introduced. So you are saying that only the variables you want to introduce are valid?
Remove the shoreline then, it is irrelevant to the point. Just make it two fixed gps coordinates for origin and destination.

The point of the exercise was to demonstrate in a simple exercise that CTS is irrelevant in upwind and upcurent situations, it wasnt to introduce a million other related real world variables.

You can introduce whatever variables you like and we can discuss them. It doesnt change the point, just makes it harder to explain.
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Old 16-11-2013, 07:02   #396
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Originally Posted by foolishsailor View Post

Exactly!

This is one of the reasons I say CTS has no value in upwind upcurrent situations.

You sail to your telltales - course is irrelelvant.


Umm, the theory is no less valid as a theory, just because it's hard to implement when sailing around the cans.

But sailing around the cans, neither will you encounter changing tide.

Try crossing the Channel, without a Course to Steer (or Desired Course to Steer, if you like), just sailing to your telltale. You're as likely to end up in Weymouth or Easthampton as Needles, or clawing like hell uptide at the end, if you don't work that out. Just because you're tacking, doesn't mean there's not a course across the water you REALLY need to be advancing along, if you don't want to end up downtide of your destination, making you miss cocktail hour altogether on the other side

I'm presently under sail and single handed in the Solent, en route to Yarmouth, so off line for a while. The docking will be - shall we say - interesting.
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Old 16-11-2013, 07:03   #397
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Fair enough. I withdraw my protest.
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Old 16-11-2013, 07:12   #398
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Umm, the theory is no less valid as a theory, just because it's hard to implement when sailing around the cans.

But sailing around the cans, neither will you encounter changing tide.

Try crossing the Channel, without a Course to Steer (or Desired Course to Steer, if you like), just sailing to your telltale. You're as likely to end up in Weymouth or Easthampton as Needles, or clawing like hell uptide at the end, if you don't work that out. Just because you're tacking, doesn't mean there's not a course across the water you REALLY need to be advancing along, if you don't want to end up downtide of your destination, making you miss cocktail hour altogether on the other side

I'm presently under sail and single handed in the Solent, en route to Yarmouth, so off line for a while. The docking will be - shall we say - interesting.
Yes, I agree completely. If you have variable current over time I am sure the CTS is what you need to be tacking around, staying on the tack closest to you CTS and tacking when this flips to the other tack (until the end, you still need to judge that final tack). I plan to work up an example.

Good luck with your docking!
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Old 16-11-2013, 07:14   #399
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Umm, the theory is no less valid as a theory, just because it's hard to implement when sailing around the cans. But sailing around the cans, neither will you encounter changing tide. Try crossing the Channel, without a Course to Steer (or Desired Course to Steer, if you like), just sailing to your telltale. You're as likely to end up in Weymouth or Easthampton as Needles, or clawing like hell uptide at the end, if you don't work that out. Just because you're tacking, doesn't mean there's not a course across the water you REALLY need to be advancing along, if you don't want to end up downtide of your destination, making you miss cocktail hour altogether on the other side

So can we all agree it is advantageous to start out heading into the current to avoid getting swept later except when we know that the current will reverse before we reach our destination?

I'm presently under sail and single handed in the Solent, en route to Yarmouth, so off line for a while. The docking will be - shall we say - interesting.
Yikes! Good luck, hope you are able to enjoy that.
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Old 16-11-2013, 07:26   #400
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Originally Posted by Seaworthy Lass View Post
Yes, I agree completely. If you have variable current over time I am sure the CTS is what you need to be tacking around, staying on the tack closest to you CTS and tacking when this flips to the other tack (until the end, you still need to judge that final tack). I plan to work up an example.

Good luck with your docking!
Really ? why

it is common sense to anybody who has done a tidal CTS

ooPS wrong course to steer terminology

could you take this all back to CTS threads as it has been slogged to death in this one?

I think there are factors of hull lift I need to put forward to the Lee Bow effect that may prove there is more to it than an the correct tack ?
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Old 16-11-2013, 07:27   #401
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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 Dockhead View Post
Umm, the theory is no less valid as a theory, just because it's hard to implement when sailing around the cans.

But sailing around the cans, neither will you encounter changing tide.

Try crossing the Channel, without a Course to Steer (or Desired Course to Steer, if you like), just sailing to your telltale. You're as likely to end up in Weymouth or Easthampton as Needles, or clawing like hell uptide at the end, if you don't work that out. Just because you're tacking, doesn't mean there's not a course across the water you REALLY need to be advancing along, if you don't want to end up downtide of your destination, making you miss cocktail hour altogether on the other side

I'm presently under sail and single handed in the Solent, en route to Yarmouth, so off line for a while. The docking will be - shall we say - interesting.
I think we need to clarify the vast differences in what "sailing round the cans" means.

Sailing round the cans can mean very short windward and leeward courses that are completed in an hour - it can also mean, as it does when you participate in Cowes Week races, that a single course on a given day will be between 15 and 25NM long and will purposely cross tidal streams multiple times. For example when the Race committe is feeling particularly sadistic and the weather conditions are right they will send us from the Royal Squadron start line up towards the Needles and make us repeatedly cross from shore to shore on the way up, and back.

We experience both varying currents across geography and the changing tide that changes the location, direction and magnitude of the various tidal streams.

You do not need the CTS to tell you how you are progressing, as it actually doesnt when you are tacking up wind. What tells you you are progressing to your goal upwind is your VMG.

If when going upwind to a target and you cant get there when sailing to your telltales that can only mean the current is moving faster than your boats current speed - thats it.

You can't end up downtide of your goal if you are using your VMG. Remember we are talking about upwind and upcurrent situations here - even though this would also work the other way.

What we arent talking about is single tack situations where you can lay your course to your destination without tacking or gybing - which is where CTS comes into play.

This doesnt just apply to racers and it doesnt just apply to confined areas like the Solent.

Think "Gulf Stream"

If you are outside the gulfstream and tacking upwind to a destination on the other side of the Gulf Stream - then you are in the exact same situation that I outlined in the image a few posts back - and you cant determine the optimal course when there are variable currents speed and direction over space by using a CTS calculation in the same way you can when dealing with variable currents speed and direction over time.
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Old 16-11-2013, 07:29   #402
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

Good luck with the docking Camaron - that is a big boat to drive in yourself.
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Old 16-11-2013, 07:42   #403
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Good luck with the docking Camaron - that is a big boat to drive in yourself.
Agreed , never knew he was a east coast sailor, he ought to have Seaworthy as navigator , that would be interesting

I did Grimsby to Dover in August, great nav exercise , especially hitting the 'gats'
on the Thames approachs and tidal streams on the Wash
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Old 16-11-2013, 07:43   #404
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

If anyone still believes the rhumb line is the best course to follow with variable current (over time) ie following a straight line from A to B on the chartplotter, you need to be coverted .

A thread discussed this earlier this year, but all the relevant posts were deeply buried. I have pulled them out and formed a "diluted" thread with 50 of the most relevant posts. The way the persuasive arguments unfolded and how the reality dawned on the disbelievers makes interesting reading:

CTS vs Following Rhumb Line - DILUTED THREAD
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Old 16-11-2013, 07:50   #405
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A really great thread. Capt Force's incredibly graceful and hilarious capitulation is one of the best posts of all time on this forum.

I love the last sentenance.

Im going to go back and reread the distilled version.

Thanks Angela for taking the time to do that.
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