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Kenny  Dumas

Leebow one last time?

Leebow one last time?  

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  1. 1. Leebow: Do you pinch upwind in opposing current on the favored tack?

    • No, It’s a moving carpet and the boat doesn’t care
      12
    • Yes, even in the middle of the ocean with no current relief in sight
      3
    • Yes, but only on rivers where I’ve seen it work
      6


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The classic old question. An old timer explained to me that the current pushes you to weather if you pinch. Dave Hubbard is quoted as saying it’s a moving carpet so just sail normally. For this question, assume there’s no current relief:  Constant opposing current with one tack favored, more into the current. 
 

Three little words may change your answer...

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7 minutes ago, Kenny Dumas said:

Lots of pretty interesting issues for aerodynamics in thin atmosphere and super light construction for our Mars chopper. Like 90 second flight time. 
Probably a significant basis for future sailing in alternate fluid environments. 

This is the first US Mars Rover I did not work on (I retired from JPL after Curiosity launched), so I don't have detailed knowledge of the Mars chopper. 

I am working on the octocopter (4 axis, counter rotating) for Saturn's moon Titan. Titan is great for helicopters because the atmosphere is very thick, and the gravity is much less, compared to Earth. We did the initial R&D using a more-or-less conventional drone we made. It uses counter rotating rotors because its more energy efficient, as the column of air going through the rotors does not waste energy by simply rotating. The entire vehicle, including mobility, sample handing, science instruments, communication, heating, etc., runs off batteries that are charged by a RTU, radioactive thermal energy conversion unit. The RTU only puts out about 100 watts of electricity, but also lots of "waste heat" we carefully use to keep from freezing. So we need to be extremely energy efficient. Otherwise, not all that unusual.

https://dragonfly.jhuapl.edu

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It's the moving carpet.  my Etchells skipper always talks about keeping the keel one side or other of the opposing current.  I disagree. It is a moving waterflow that we are all sailing through so that doesn't make sense.  But, you can't talk sense into the old timers, who are good, winning racers...

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Depends on what the wind and your competition are doing.

And if you're heading directly into the current and you can effectively tack the keel by pinching, it will lift  you to weather.

To a point. When it's light.

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It's called ferry gliding, we used to use it kayaking if you aim the bow slightly askew of the current it pushes you sideways.  I learned about in the. 60s from the. book Siddartha,  then she taught me tantric yoga which also involved sliding through a moving. energy field.

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If it sounds too good to be true...

Sail fast into a building breeze or into favorable current...take home trophies.

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16 minutes ago, guerdon said:

It's called ferry gliding, we used to use it kayaking if you aim the bow slightly askew of the current it pushes you sideways.  I learned about in the. 60s from the. book Siddartha,  then she taught me tantric yoga which also involved sliding through a moving. energy field.

I'm not sure we're talking about the same thing here:lol:

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Sailing on a river, 

With the tide (yes our river is tidal @ 19 miles inland by up to two mph incoming tide, 4 mph outgoing tide).

Pinch a lot in the middle as the tide pushes you up, spend as much time as possible in the middle, quick tacks off the bank  there's less tide there.

 Tacking against the tide, drop the nose a little, you want to cross the main tide in the middle fast, as you approach the bank, pull up, pinch and take a long slow tack, gaining windward distance. Tack, drop the nose, and get going fast again .... repeat...

Noting if you get it right, if there is a sold vertical quay heading you can balance the wash off your bow, against the backwash off  the quay, and hold it there longer..

 

Running  , of course, close to the bank down against the tide, only cross the river if you have to. With the tide, near the middle but furthest away from any air interference from trees and houses  on the bank.

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There is never a last time for any popular myth, and this one is no exception.

Personally I've always wondered how people can be so sure about the precise direction of local tidal flow that they can tell the difference between having the current one degree off the port bow and one degree off the starboard bow.

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Years ago when I was working as mate on a tug, the skipper used to insist that one of his old boats used to go faster against the tide than with it, not over the ground, through the water.
No matter how many times I tried to explain to him that the boat had no way of telling if it was going with the tide or against it,  he wouldn't have it.

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15 minutes ago, MiddayGun said:

Years ago when I was working as mate on a tug, the skipper used to insist that one of his old boats used to go faster against the tide than with it, not over the ground, through the water.
No matter how many times I tried to explain to him that the boat had no way of telling if it was going with the tide or against it,  he wouldn't have it.

Probably equating more bow wave and wake with higher speed.. while actually going slower..

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look, this my final word on the subject;

Well, Prince, so Genoa and Lucca are now just family estates of the Buonapartes. But I warn you, if you don’t tell me that this means war, if you still try to defend the infamies and horrors perpetrated by that Antichrist—I really believe he is Antichrist—I will have nothing more to do with you and you are no longer my friend, no longer my ‘faithful slave,’ as you call yourself! But how do you do? I see I have frightened you—sit down and tell me all the news.”

It was in July, 1805, and the speaker was the well-known Anna Pávlovna Schérer, maid of honor and favorite of the Empress Márya Fëdorovna. With these words she greeted Prince Vasíli Kurágin, a man of high rank and importance, who was the first to arrive at her reception. Anna Pávlovna had had a cough for some days. She was, as she said, suffering from la grippe; grippe being then a new word in St. Petersburg, used only by the elite.

All her invitations without exception, written in French, and delivered by a scarlet-liveried footman that morning, ran as follows:

“If you have nothing better to do, Count (or Prince), and if the prospect of spending an evening with a poor invalid is not too terrible, I shall be very charmed to see you tonight between 7 and 10—Annette Schérer.”

“Heavens! what a virulent attack!” replied the prince, not in the least disconcerted by this reception. He had just entered, wearing an embroidered court uniform, knee breeches, and shoes, and had stars on his breast and a serene expression on his flat face. He spoke in that refined French in which our grandfathers not only spoke but thought, and with the gentle, patronizing intonation natural to a man of importance who had grown old in society and at court. He went up to Anna Pávlovna, kissed her hand, presenting to her his bald, scented, and shining head, and complacently seated himself on the sofa.

“First of all, dear friend, tell me how you are. Set your friend’s mind at rest,” said he without altering his tone, beneath the politeness and affected sympathy of which indifference and even irony could be discerned.

“Can one be well while suffering morally? Can one be calm in times like these if one has any feeling?” said Anna Pávlovna. “You are staying the whole evening, I hope?”

“And the fete at the English ambassador’s? Today is Wednesday. I must put in an appearance there,” said the prince. “My daughter is coming for me to take me there.”

“I thought today’s fete had been canceled. I confess all these festivities and fireworks are becoming wearisome.”

“If they had known that you wished it, the entertainment would have been put off,” said the prince, who, like a wound-up clock, by force of habit said things he did not even wish to be believed.

“Don’t tease! Well, and what has been decided about Novosíltsev’s dispatch? You know everything.”

“What can one say about it?” replied the prince in a cold, listless tone. “What has been decided? They have decided that Buonaparte has burnt his boats, and I believe that we are ready to burn ours.”

Prince Vasíli always spoke languidly, like an actor repeating a stale part. Anna Pávlovna Schérer on the contrary, despite her forty years, overflowed with animation and impulsiveness. To be an enthusiast had become her social vocation and, sometimes even when she did not feel like it, she became enthusiastic in order not to disappoint the expectations of those who knew her. The subdued smile which, though it did not suit her faded features, always played round her lips expressed, as in a spoiled child, a continual consciousness of her charming defect, which she neither wished, nor could, nor considered it necessary, to correct.

In the midst of a conversation on political matters Anna Pávlovna burst out:

“Oh, don’t speak to me of Austria. Perhaps I don’t understand things, but Austria never has wished, and does not wish, for war. She is betraying us! Russia alone must save Europe. Our gracious sovereign recognizes his high vocation and will be true to it. That is the one thing I have faith in! Our good and wonderful sovereign has to perform the noblest role on earth, and he is so virtuous and noble that God will not forsake him. He will fulfill his vocation and crush the hydra of revolution, which has become more terrible than ever in the person of this murderer and villain! We alone must avenge the blood of the just one.... Whom, I ask you, can we rely on?... England with her commercial spirit will not and cannot understand the Emperor Alexander’s loftiness of soul. She has refused to evacuate Malta. She wanted to find, and still seeks, some secret motive in our actions. What answer did Novosíltsev get? None. The English have not understood and cannot understand the self-abnegation of our Emperor who wants nothing for himself, but only desires the good of mankind. And what have they promised? Nothing! And what little they have promised they will not perform! Prussia has always declared that Buonaparte is invincible, and that all Europe is powerless before him.... And I don’t believe a word that Hardenburg says, or Haugwitz either. This famous Prussian neutrality is just a trap. I have faith only in God and the lofty destiny of our adored monarch. He will save Europe!”

She suddenly paused, smiling at her own impetuosity.

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Well, "lee-bowing the current" is kind of an awkward phrase to describe a fairly simple geometry problem. And it leads to at least one erroneous conclusion.

The boat sails thru the water. It has no idea which direction the body of water is moving, if there is current. The boat only moves thru the water, and it moves thru the water in the same way, relative to the wind, that it does whether the water is moving or not.

Relative to the ground, the boat does a bunch of different things. Obviously when there is current, the motion of the water carries the boat with it, and this is easily solved with vectors, or and it can be solved with great precision (if you know the angles and speeds) with trigonometry. But we don't need to get that complicated, we only need a clear picture.

laylines-current_01dsk.gif.915b1f0307a02d5e8a00edab81852ae8.gif

 

A current from left to right will carry the boats along with it, moving to the right as they progress normally relative to the wind.

It will shift the laylines of a fixed mark, but it won't change whether one boat will clear another on starboard etc etc. The boat n starboard would not be on the layline, in the absence of current, but will now fetch it. Opposite for the other boat, she looks to be fetching easily and may be planning a move to duck and then tack for the mark and force the other boat behind her in the rounding... too clever, as they will meet further out on the layline and possibly outside the zone.

Now, let's take a look at what happens when the boats sail differently relative to the wind. If the Stb pinches, she moves more slowly thru the water and thus current has more time to affect her motion. Her track will be even more skewed, and I think this what the old-timers mean with their 'lee-bow the tide' talk. But the boat will be going slower, and her progress directly to windward will most likely be slower (it's possible that her VMG may be greater but this is case where the angles and speeds being measured precisely must come into play).

Last, this makes clear that the motion of the current relative to the boat is not what makes the difference. It's the angle of motion of current to the wind. ANY current with a compnent to the right, will have the same effect. A current could be sweeping upward at 45deg, left to right, in other words directly astern of the Port boat, or downwards (directly abeam of Port, on the nose of Stb), and it would have the same basic effect.

FB- Doug

 

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4 hours ago, toad said:

look, this my final word on the subject;

Well, Prince, so Genoa and Lucca are now just family estates of the Buonapartes. But I warn you, if you don’t tell me that this means war, if you still try to defend the infamies and horrors perpetrated by that Antichrist—I really believe he is Antichrist—I will have nothing more to do with you and you are no longer my friend, no longer my ‘faithful slave,’ as you call yourself! But how do you do? I see I have frightened you—sit down and tell me all the news.”

It was in July, 1805, and the speaker was the well-known Anna Pávlovna Schérer, maid of honor and favorite of the Empress Márya Fëdorovna. With these words she greeted Prince Vasíli Kurágin, a man of high rank and importance, who was the first to arrive at her reception. Anna Pávlovna had had a cough for some days. She was, as she said, suffering from la grippe; grippe being then a new word in St. Petersburg, used only by the elite.

All her invitations without exception, written in French, and delivered by a scarlet-liveried footman that morning, ran as follows:

“If you have nothing better to do, Count (or Prince), and if the prospect of spending an evening with a poor invalid is not too terrible, I shall be very charmed to see you tonight between 7 and 10—Annette Schérer.”

“Heavens! what a virulent attack!” replied the prince, not in the least disconcerted by this reception. He had just entered, wearing an embroidered court uniform, knee breeches, and shoes, and had stars on his breast and a serene expression on his flat face. He spoke in that refined French in which our grandfathers not only spoke but thought, and with the gentle, patronizing intonation natural to a man of importance who had grown old in society and at court. He went up to Anna Pávlovna, kissed her hand, presenting to her his bald, scented, and shining head, and complacently seated himself on the sofa.

“First of all, dear friend, tell me how you are. Set your friend’s mind at rest,” said he without altering his tone, beneath the politeness and affected sympathy of which indifference and even irony could be discerned.

“Can one be well while suffering morally? Can one be calm in times like these if one has any feeling?” said Anna Pávlovna. “You are staying the whole evening, I hope?”

“And the fete at the English ambassador’s? Today is Wednesday. I must put in an appearance there,” said the prince. “My daughter is coming for me to take me there.”

“I thought today’s fete had been canceled. I confess all these festivities and fireworks are becoming wearisome.”

“If they had known that you wished it, the entertainment would have been put off,” said the prince, who, like a wound-up clock, by force of habit said things he did not even wish to be believed.

“Don’t tease! Well, and what has been decided about Novosíltsev’s dispatch? You know everything.”

“What can one say about it?” replied the prince in a cold, listless tone. “What has been decided? They have decided that Buonaparte has burnt his boats, and I believe that we are ready to burn ours.”

Prince Vasíli always spoke languidly, like an actor repeating a stale part. Anna Pávlovna Schérer on the contrary, despite her forty years, overflowed with animation and impulsiveness. To be an enthusiast had become her social vocation and, sometimes even when she did not feel like it, she became enthusiastic in order not to disappoint the expectations of those who knew her. The subdued smile which, though it did not suit her faded features, always played round her lips expressed, as in a spoiled child, a continual consciousness of her charming defect, which she neither wished, nor could, nor considered it necessary, to correct.

In the midst of a conversation on political matters Anna Pávlovna burst out:

“Oh, don’t speak to me of Austria. Perhaps I don’t understand things, but Austria never has wished, and does not wish, for war. She is betraying us! Russia alone must save Europe. Our gracious sovereign recognizes his high vocation and will be true to it. That is the one thing I have faith in! Our good and wonderful sovereign has to perform the noblest role on earth, and he is so virtuous and noble that God will not forsake him. He will fulfill his vocation and crush the hydra of revolution, which has become more terrible than ever in the person of this murderer and villain! We alone must avenge the blood of the just one.... Whom, I ask you, can we rely on?... England with her commercial spirit will not and cannot understand the Emperor Alexander’s loftiness of soul. She has refused to evacuate Malta. She wanted to find, and still seeks, some secret motive in our actions. What answer did Novosíltsev get? None. The English have not understood and cannot understand the self-abnegation of our Emperor who wants nothing for himself, but only desires the good of mankind. And what have they promised? Nothing! And what little they have promised they will not perform! Prussia has always declared that Buonaparte is invincible, and that all Europe is powerless before him.... And I don’t believe a word that Hardenburg says, or Haugwitz either. This famous Prussian neutrality is just a trap. I have faith only in God and the lofty destiny of our adored monarch. He will save Europe!”

She suddenly paused, smiling at her own impetuosity.

Wow, this is the most literary thread drift I've seen in a while. Well done sir!

FB- Doug

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I confess to having sailed to weather for decades in opposing current on the Columbia and Oregon Offshore before figuring this out. It’s a wonderful puzzle that certainly requires an understanding of vectors and apparent wind. The answer is 2 of course. I really think one of you guys will figure this out so I won’t spoil it for a few days. 


And thanks for the thread drift!

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current only changes your awa since the surface is moving so the story is BS. (it's not your boat being moved by the current but the surface your boat foats on....)

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On 7/30/2020 at 8:27 PM, billy backstay said:

It's the moving carpet.  my Etchells skipper always talks about keeping the keel one side or other of the opposing current.  I disagree. It is a moving waterflow that we are all sailing through so that doesn't make sense.  But, you can't talk sense into the old timers, who are good, winning racers...

but you have to keep the keel in alignment with the rudder or you end up with 20* weather helm...   unless it's tuesday.

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I've won more races on rivers and lakes than I have in the sea. Current or no current, you sail the conditions as fast and efficiently as you can. It's just a geometry problem as Steam says. That being said, if you don't have an intricate knowledge of the current on the river, you are at a significant disadvantage.

I learned some good tricks in the current on the Delaware from Ted Hunn. Boy was he good at that!

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8 hours ago, Kenny Dumas said:

Hint:  What happens in a lull on each tack?  (with true wind direction constant)

What kind of boat am I sailing?

FB- Doug

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So let's pose this dead horse of a question another way:  If you think it is advantageous to pinch when the current is coming from your lee bow, is it also advantageous to foot when the current is coming from your weather bow?  

Assuming, that there is not some wonderful current relief right up along the shore.  

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Standard 4KSB, easiest to visualize in light air barely making way upstream on favored tack. Steady state. Decrease wind speed. What happens?
Then try it on the bad tack. 

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8 hours ago, Kenny Dumas said:

Standard 4KSB, easiest to visualize in light air barely making way upstream on favored tack. Steady state. Decrease wind speed. What happens?
Then try it on the bad tack. 

It's possible for conditions to exist where a boat sailing on one tack will make way over ground straight upwind, while the boat on the other tack makes no progress upwind.

But the current doesn't change the basics of VMG. If you would gain VMG by pinching, then you would do so in current.

When a lull comes along, there's a range of things you can do. If you're in a heavy boat, with good momentum, you can luff (or drop) the jib and turn straight for the finish and coast acorss the line. I've done this in Ensigns and gone from 4th to first that way.

FB- Doug

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14 hours ago, Left Shift said:

So let's pose this dead horse of a question another way:  If you think it is advantageous to pinch when the current is coming from your lee bow, is it also advantageous to foot when the current is coming from your weather bow?  

Assuming, that there is not some wonderful current relief right up along the shore.  

Great question because it shows why this is so important. The generalized form will influence your decisions in almost every race:

”If tacks are assymetric, prolong the favored tack by pinching”

That probably means you foot the bad tack but I’m not sure. But I do know that on the bad tack “lulls are amplified headers”. Do the vectors and be amazed. 

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Start with a boat pinching 5 degrees so that it is making way directly upstream. It feels like magic because the “lulls are lifts”. You go slower with less pressure but can stop pinching while still sailing directly upstream. 
The bad tack is hell

 

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3 hours ago, Kenny Dumas said:

The generalized form will influence your decisions in almost every race:

”If tacks are assymetric, prolong the favored tack by pinching”

That probably means you foot the bad tack but I’m not sure. But I do know that on the bad tack “lulls are amplified headers”. Do the vectors and be amazed. 

So sailing below target speed on a long, asymmetrical port tack is the way to go? 

Take that vector analysis to the logical extreme of prolonging the favored tack to zero.  So is there a performance curve for going slightly slower than target at slightly higher into the favorable current published anywhere?  Because the reductio ad absurdum is indeed absurd.

Now in zero wind, with 3 knots of current from abeam, yeah, you will get a current-created wind.  We all have sailed in those conditions more than we want to.  But when the average current is just off to the lee side of the bow on an upwind course, it is far better to use the wind efficiently than to being downspeed trying to use -within a few degrees- the current which is, by its nature wobbly in direction and velocity.  

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Thanks for playing guys. I’m pretty sure about this so please baseline your position with the following questions:

Do assymetric conditions exist?  (Most obvious case is waves coming from one side)

Are there conditions where you win by sailing above your polars to minimize the pain on the bad tack?

Does a change in wind speed shift the “sailing wind” ?

Does the sailing wind shift more on the bad tack?

 

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here's the polar for this .... or not

9 Best maps charts and diagrams (useful, useless and sometimes elucidating)  images | Funny charts, Geek humor, Emerson quotes

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and the argument against ... Venn diagram | Venn diagram, Steve miller band, Funniest hilarious memes

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Sailboats fly thru two bodies of different fluids at the same time. One wing in water the other in air. 
 

In terms of a typical force vector diagram the keel/board proves enough lift to counteract the leeward sucking direction of sail lift. It is designed in size to balance the sail plane so the boat goes in a straight direction upwind. 
 

This is obvious in a dinghy. Pull up the board and you side slip. Use a jibing centerboard and you can point higher. Oversize the daggerboard like a Laser and you can out point most other dinghies by approximately 5 degrees. 
 

The 4th dimension is current. Unless you have sailed in an area with decent current  2-3kts it’s hard to contemplate how important it is when racing. 

I grew up in Fisher’s Island Sound. 0-3kts current 4 times a day. I’ve seen plenty of current. That area is also renowned for it’s dying southwesterly. There are completely becalmed days. Zero measurable wind with 3 knots current.  
 

We would follow the current around the sound doing the bump and run on beaches, hide behind the islands all those things that put you in front. 

The Important thing with the current is It’s angle to the boats direction. The board/keel doesn’t care if it’s getting dragged thru non moving water by the sail plan or there is a river of current flowing past it. It just needs flow so it creates lift. Give it the correct direction of low and it generates lift. Wrong angle and it generates drag. 
 

Drop the wind completely and add current. Steer the boat very carefully until the correct angle of attack and you get lift. It’s the opposite to sailing in flat water. 

I crewed for one of those old guys who won shite loads of races. He’s also an engineer, so he knows the vectors. He had this beautiful custom Chance 32. He liked to go upwind(figures that’s where you win the race). The obviously larger than most keels generated enough lift to sail 5 degrees higher than a J30 or J35 at the same hull speed. We smoked the other boats upwind. 
 

On a becalmed day we put 8hrs into the Fall Offsoundings fleet by lee bowing the current and sailing on her racing anchor. The 3kt current was on the nose at the Mark. We tickled her around race rock and away we went to Greenport. The other boats had to wait for the tide to switch. Good sailors and a thick keel let’s you sail on the current. 

The original question requires knowledge of wind speed and current speed. We steer and adjust the sails to match the wind. The result is the board is pushed by the current. Generating no extra lift. If the wind is light and you steer the boat in regards to the keel it may provide more lift than the sail offers in drive. Very light winds. Otherwise the current is pushing you sideways.


 

 

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1 hour ago, CaptainAhab said:

Sailboats fly thru two bodies of different fluids at the same time. One wing in water the other in air. 
 

In terms of a typical force vector diagram the keel/board proves enough lift to counteract the leeward sucking direction of sail lift. It is designed in size to balance the sail plane so the boat goes in a straight direction upwind. 
 

This is obvious in a dinghy. Pull up the board and you side slip. Use a jibing centerboard and you can point higher. Oversize the daggerboard like a Laser and you can out point most other dinghies by approximately 5 degrees. 
 

The 4th dimension is current. Unless you have sailed in an area with decent current  2-3kts it’s hard to contemplate how important it is when racing. 

I grew up in Fisher’s Island Sound. 0-3kts current 4 times a day. I’ve seen plenty of current. That area is also renowned for it’s dying southwesterly. There are completely becalmed days. Zero measurable wind with 3 knots current.  
 

We would follow the current around the sound doing the bump and run on beaches, hide behind the islands all those things that put you in front. 

The Important thing with the current is It’s angle to the boats direction. The board/keel doesn’t care if it’s getting dragged thru non moving water by the sail plan or there is a river of current flowing past it. It just needs flow so it creates lift. Give it the correct direction of low and it generates lift. Wrong angle and it generates drag. 
 

Drop the wind completely and add current. Steer the boat very carefully until the correct angle of attack and you get lift. It’s the opposite to sailing in flat water. 

I crewed for one of those old guys who won shite loads of races. He’s also an engineer, so he knows the vectors. He had this beautiful custom Chance 32. He liked to go upwind(figures that’s where you win the race). The obviously larger than most keels generated enough lift to sail 5 degrees higher than a J30 or J35 at the same hull speed. We smoked the other boats upwind. 
 

On a becalmed day we put 8hrs into the Fall Offsoundings fleet by lee bowing the current and sailing on her racing anchor. The 3kt current was on the nose at the Mark. We tickled her around race rock and away we went to Greenport. The other boats had to wait for the tide to switch. Good sailors and a thick keel let’s you sail on the current. 

The original question requires knowledge of wind speed and current speed. We steer and adjust the sails to match the wind. The result is the board is pushed by the current. Generating no extra lift. If the wind is light and you steer the boat in regards to the keel it may provide more lift than the sail offers in drive. Very light winds. Otherwise the current is pushing you sideways.


 

 

I designed my  small Mini keel boat with a fairly large keel for that reason. Many of our local designs  have a surprisingly large keel, when you consider how much tacking we do. The worst I've done was a tack every minute or so for 5 hours going up river mostly with the tide... 

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1 hour ago, CaptainAhab said:

Sailboats fly thru two bodies of different fluids at the same time. One wing in water the other in air. 
 

In terms of a typical force vector diagram the keel/board proves enough lift to counteract the leeward sucking direction of sail lift. It is designed in size to balance the sail plane so the boat goes in a straight direction upwind. 
 

This is obvious in a dinghy. Pull up the board and you side slip. Use a jibing centerboard and you can point higher. Oversize the daggerboard like a Laser and you can out point most other dinghies by approximately 5 degrees. 
 

The 4th dimension is current. Unless you have sailed in an area with decent current  2-3kts it’s hard to contemplate how important it is when racing. 

I grew up in Fisher’s Island Sound. 0-3kts current 4 times a day. I’ve seen plenty of current. That area is also renowned for it’s dying southwesterly. There are completely becalmed days. Zero measurable wind with 3 knots current.  
 

We would follow the current around the sound doing the bump and run on beaches, hide behind the islands all those things that put you in front. 

The Important thing with the current is It’s angle to the boats direction. The board/keel doesn’t care if it’s getting dragged thru non moving water by the sail plan or there is a river of current flowing past it. It just needs flow so it creates lift. Give it the correct direction of low and it generates lift. Wrong angle and it generates drag. 
 

Drop the wind completely and add current. Steer the boat very carefully until the correct angle of attack and you get lift. It’s the opposite to sailing in flat water. 

I crewed for one of those old guys who won shite loads of races. He’s also an engineer, so he knows the vectors. He had this beautiful custom Chance 32. He liked to go upwind(figures that’s where you win the race). The obviously larger than most keels generated enough lift to sail 5 degrees higher than a J30 or J35 at the same hull speed. We smoked the other boats upwind. 
 

On a becalmed day we put 8hrs into the Fall Offsoundings fleet by lee bowing the current and sailing on her racing anchor. The 3kt current was on the nose at the Mark. We tickled her around race rock and away we went to Greenport. The other boats had to wait for the tide to switch. Good sailors and a thick keel let’s you sail on the current. 

The original question requires knowledge of wind speed and current speed. We steer and adjust the sails to match the wind. The result is the board is pushed by the current. Generating no extra lift. If the wind is light and you steer the boat in regards to the keel it may provide more lift than the sail offers in drive. Very light winds. Otherwise the current is pushing you sideways.


 

 

Yeah nah.. if you are in a body of moving water of say 3kts in a vacuum then all you will do is move with the current as there is no flow over the board whatsoever. Remove the vacuum and still have zero breeze your 3kt current is now generating tide wind so you will have an apparent breeze of 3kts to sail with. Any breeze from any angle on the tide is vectors and simple math. Fat keel, skinny keel  no difference as far as current is concerned but you also have to be aware that boat speed plays a massive part in this leebow illusion.

Example if you are in a 10kt current and you boat does 10 kts directly into it the you are standing still over the ground, if you boat does 12kts then you are smoking all the 10kt boats. Fast boats slay the opposition in tide for that reason alone.

 

 

 

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Certainly in the ocean, the "lee bow" phenomena does not exist.  Either you are in favourable current or you're not.

But maybe in a river, or some other shallow body of water there will be a velocity gradient so the bottom of the keel could encounter an apparent current angle different from that at the bow - maybe.  Just spit ballin' here because I sail in the ocean and what happens in a river is of little or no concern to me. 

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