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Debunking Dodgy Sailing Theories

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Category: Dinghy classes
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Topic: Debunking Dodgy Sailing Theories
Posted By: Oatsandbeans
Subject: Debunking Dodgy Sailing Theories
Date Posted: 20 Oct 11 at 10:47am
Following the great success of the Lee Bow Effect thread ( we can all now see what utter cr*p that one was) I got to thinking about other unsound theories that get peddled around sometimes by those that should know better. 

Well I will start this one off, by a comment from a post that I saw yesterday saying that the benefit of having twist in sails is so that in instable wind conditions at least one section of the sail is set correctly.  Well it is surprising how many sailors hold this view. 

Well here goes- Rubbish- If you think a the sail as a number of horizontal strips, say 4, that due to the twist are at different angles of attack and only one section is set correctly. This means that 75% of the sail area is set incorrectly either not enough angle or too much angle of attack this is obviously very inefficient (and slow). 

The reason that twist works is because the sails have to operate in different conditions at different heights. The effects of wind speed variation, wind shear, and the large effect of the jib on the lower sections of the sail all mean that a sail with no twist will lead to a stalled head and or a undersheeted base. The optimum twist will depend on the boat, the conditions (wind and water) and what the helm is trying to do at the time ( foot, squeeze,or depower). A good indicator of  when the twist is right is streaming of the leach tell tales with the top one one the point of stalling (30%).

Hopefully this will bring some comments and maybe even some more unscientific sailing "theories".





Replies:
Posted By: G.R.F.
Date Posted: 20 Oct 11 at 10:48am
Never studied the action of power boat propellors then OaB?

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Posted By: Oatsandbeans
Date Posted: 20 Oct 11 at 11:27am
No I haven't - fill me in please!


Posted By: JimC
Date Posted: 20 Oct 11 at 11:47am
Originally posted by Oatsandbeans

that the benefit of having twist in sails is so that in instable wind conditions at least one section of the sail is set correctly.  Well it is surprising how many sailors hold this view. 

Well here goes- Rubbish-


Why do you think one precludes the other?

Twist can do a lot of things for you.

Yes, twist to deal with wind sheer is the most important thing most of the time, but that's not all...

An overtwisted rig is more tolerant in highly unstable winds when its impractical to have the sail sheeted correctly and correct twist set all the time.

Twist is also a tool in the armoury for depowering the rig, especially if you have a fully battened rig.

For example I sail on a raised reservoir, so the wind is very unstable on the final approach to the windward mark. I find it faster to release some kicker and overtwist the sail for the last few yards of the beat.


Posted By: 2547
Date Posted: 20 Oct 11 at 12:43pm
He's one ... the V Turd will be faster round the cans than a Laser Wacko


Posted By: RS400atC
Date Posted: 20 Oct 11 at 9:07pm
Originally posted by G.R.F.

Never studied the action of power boat propellors then OaB?


Power boat propellors have twist in the blades because for a constant pitch distance (the distance the prop would move forward with no slip in one turn) the pitch angle varies with the radius along the blade. The tip moves forward say 1ft in 1 metre of circumference, halfway alon the blae, it moves forward the same distance but runs through half the circumference, hence it must be at a steeper angle.
But it's made more complicated by other effects I'm sure.


Posted By: Menace
Date Posted: 20 Oct 11 at 9:09pm
Another load of crap, even pedalled by the RYA guys from time to time is that the jib causes a venturi effect accelerating flow through the slot gap. It's the other way round, creates an area of high pressure, hence the reason you get backwinding in the main when the slot is wrong and the wind is up. What effectively happens is the slot increases the stall angle of the main, allowing the main to operate at higher lift coefficient.


Posted By: Xpletive
Date Posted: 20 Oct 11 at 9:37pm
Originally posted by Menace

..... a venturi effect accelerating flow through the slot gap
 
Reminds me of a little known theory regarding the flight of birds actually being related to the discharge of wind from the anus. The wing flapping bit is to get as far away from it as possible.


Posted By: Peaky
Date Posted: 20 Oct 11 at 9:44pm
Aspect ratio, what it is and what effect it really has strikes me as generally poorly understood.

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Posted By: Xpletive
Date Posted: 20 Oct 11 at 9:50pm
Coincidentally, I am one of those who have an appalling understanding of what aspect ration is.... and, for that matter, what effect it really has.......I am humbly aware of how evident this may be in my posts.


Posted By: G.R.F.
Date Posted: 20 Oct 11 at 10:27pm
Originally posted by Oatsandbeans

No I haven't - fill me in please!

Well without getting over complicated both work in the same way, the flow over the surface needs to be exhausted, so it is the same as the propellor blade in water, the sail in air, both fluid flow over a foil generating a force propelling a boat forward.

Sails generally were slow acting foils, as speeds have increased, apparent wind increases, foils have twisted more and become higher in aspect ratio.

For a while windsurfing drove that increase in twist, but it has passed on to high aspect cat foils and even fixed wings have to have twist in order to function.

Old school dinghy sails had some twist but they were pin heads, so getting 'twist' used to be a complicated affair. With the advent of higher aspect (fatter headed) sails the twist is easier to dial in.

But twist is there for more than just the perceived variation of wind speed at different heights, that's another old wives tale. The primary reason is to increase the speed of the flow by exhausting without turbulence at the leech or tip vortices (like you try not to get with glider wings).


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Posted By: RS400atC
Date Posted: 21 Oct 11 at 8:19am
Originally posted by G.R.F.

[...
....
But twist is there for more than just the perceived variation of wind speed at different heights, that's another old wives tale. ....


Only in your world!
In the real world, we can measure the different windspeed (and direction) as a function of height. Its significance can vary, but sometimes you want a lot of twist for this reason.

Or were you taking the view that old wives sometimes knew a thing or two?


Posted By: 2547
Date Posted: 21 Oct 11 at 9:22am
Originally posted by G.R.F.

For a while windsurfing drove that increase in twist, but it has passed on to high aspect cat foils and even fixed wings have to have twist in order to function.


yeah ... after no doubt millions spend researching the matter look how heavily twisted they are running ...




Posted By: rogue
Date Posted: 21 Oct 11 at 9:47am
Seamonkey- it's a cat, it doesn't count, cats are not tactical, they are in GRF's words, "gehey"

of course, if you close the bow up and form the hull from one piece of plastic, then you get a tunnel-hulled scow... these of course are really cool.


Posted By: JohnW
Date Posted: 21 Oct 11 at 10:39am
Originally posted by seamonkey

Originally posted by G.R.F.

For a while windsurfing drove that increase in twist, but it has passed on to high aspect cat foils and even fixed wings have to have twist in order to function.


yeah ... after no doubt millions spend researching the matter look how heavily twisted they are running ...



I think if you do the vector maths, the twist required would be less when you have a large apparent wind component which is probably why cats such as the ACs dont appear to need much twist in their wings.

(EDIT: Im not a cat sailor, nor have I sailed with a wing sail - just considering the mathematical point of view which as we all know is often not as simple as we think).


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Posted By: fudheid
Date Posted: 21 Oct 11 at 10:41am
Originally posted by Menace

Another load of crap, even pedalled by the RYA guys from time to time is that the jib causes a venturi effect accelerating flow through the slot gap. It's the other way round, creates an area of high pressure, hence the reason you get backwinding in the main when the slot is wrong and the wind is up. What effectively happens is the slot increases the stall angle of the main, allowing the main to operate at higher lift coefficient.

this is an all time favourite of old dudes on 4ksbs


Posted By: JohnW
Date Posted: 21 Oct 11 at 10:51am
How about this old chestnut:

"the fastest way to round the leeward mark is 'wide in tight out' "




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Posted By: fudheid
Date Posted: 21 Oct 11 at 11:03am
Originally posted by JohnW

How about this old chestnut:

"the fastest way to round the leeward mark is 'wide in tight out' "


not the fastest but the best way, inside track upwind.....


Posted By: 2547
Date Posted: 21 Oct 11 at 11:08am
Originally posted by rogue

Seamonkey- it's a cat, it doesn't count, cats are not tactical, they are in GRF's words, "gehey"

of course, if you close the bow up and form the hull from one piece of plastic, then you get a tunnel-hulled scow... these of course are really cool.


Ah ... that would be a great idea ... then it would slap up & down on the chop to slow you down whilst the cats go creaming past ...


Posted By: I luv Wight
Date Posted: 21 Oct 11 at 11:23am
What is planing? and how do you define it?

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Posted By: JohnW
Date Posted: 21 Oct 11 at 11:32am
Originally posted by fudheid

Originally posted by JohnW

How about this old chestnut:

"the fastest way to round the leeward mark is 'wide in tight out' "


not the fastest but the best way, inside track upwind.....

No, not always the "best" way.

Agree wide in tight out has tactical advantages, but in the absence of other nearby boats an apex turn is faster by around a boat length (which in my book is generally better when racing). 

The myth is that being further "upwind" is better, in reality the apex turn puts you ahead of where you would have been if you had done the  "racing turn".  You may be slightly to leeward of the exit line from the mark, but because you sailed a shorter distance you are in fact ahead by about a boat length.




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Posted By: Isis
Date Posted: 21 Oct 11 at 11:36am
Originally posted by I luv Wight

What is planing? and how do you define it?


When a significant proportion of the displacement is supported by dynamic lift.

What qualifies as significant? thats the tricky bit.


Posted By: Beast of Bodmin
Date Posted: 21 Oct 11 at 11:38am
Was recently told that with only 5 knots at sea level you can regularly see 30 knots at mast tip ( 30ft for us ) .Came from a very reliable source but doesn't seem possible or apparent to me . What's your expereince ?


Posted By: rogue
Date Posted: 21 Oct 11 at 11:47am
Originally posted by I luv Wight

What is planing? and how do you define it?


it's the thing that means the same thing as planning on a sailing forum, however it is spelt correctly.


Posted By: RS400atC
Date Posted: 21 Oct 11 at 12:12pm
Originally posted by Beast of Bodmin

Was recently told that with only 5 knots at sea level you can regularly see 30 knots at mast tip ( 30ft for us ) .Came from a very reliable source but doesn't seem possible or apparent to me . What's your expereince ?


Depends what you mean by 'sea level'. 10cm? 1m?
If you measure at three metres and ten metres, there is usually a measurable difference, 20% is sometimes used as a rule of thumb, but it varies I believe.
The true wind direction also varies!
Air close to the ground spirals into the low pressure more steeply than faster moving air high up.

But in reality, these big picture simplifications are often obscured by local effects.


Posted By: fudheid
Date Posted: 21 Oct 11 at 1:50pm
Originally posted by JohnW

Originally posted by fudheid

Originally posted by JohnW

How about this old chestnut:

"the fastest way to round the leeward mark is 'wide in tight out' "


not the fastest but the best way, inside track upwind.....

No, not always the "best" way.

Agree wide in tight out has tactical advantages, but in the absence of other nearby boats an apex turn is faster by around a boat length (which in my book is generally better when racing). 

The myth is that being further "upwind" is better, in reality the apex turn puts you ahead of where you would have been if you had done the  "racing turn".  You may be slightly to leeward of the exit line from the mark, but because you sailed a shorter distance you are in fact ahead by about a boat length.



Don't you just do the apex turn so you come out next to the mark??


Posted By: JohnW
Date Posted: 21 Oct 11 at 2:31pm
Originally posted by fudheid

Don't you just do the apex turn so you come out next to the mark??

If you come out next to the mark it is not an Apex turn.  I was going to draw a diagram, but this article explains it better than I could:

http://www.sailingworld.com/experts/a-better-way-to-round-the-leeward-mark - http://www.sailingworld.com/experts/a-better-way-to-round-the-leeward-mark  




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Posted By: I luv Wight
Date Posted: 21 Oct 11 at 10:29pm
Originally posted by I luv Wight

What is planing? 

This is definitely planing, ( ie exceeding the hull speed of a foot = 1.43 knots according to some theories)
http://youtu.be/IlruXNU9i6k - http://youtu.be/IlruXNU9i6k


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Posted By: Peaky
Date Posted: 21 Oct 11 at 10:48pm
No no no no no. Planing has nothing to do with exceeding a particular speed.
I can't see the video at the moment, hope it's a good one!

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Posted By: I luv Wight
Date Posted: 21 Oct 11 at 11:04pm
Originally posted by Peaky

No no no no no. Planing has nothing to do with exceeding a particular speed.
I can't see the video at the moment, hope it's a good one!



Err... see the title of the thread!




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Posted By: SoggyBadger
Date Posted: 22 Oct 11 at 8:31am
Originally posted by I luv Wight

Originally posted by I luv Wight

What is planing? 

This is definitely planing, ( ie exceeding the hull speed of a foot = 1.43 knots according to some theories)
http://youtu.be/IlruXNU9i6k - http://youtu.be/IlruXNU9i6k


There has to be a more dignified way to have colonic irrigation than that.


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SB



Posted By: fudheid
Date Posted: 22 Oct 11 at 1:44pm
Originally posted by JohnW

Originally posted by fudheid

Don't you just do the apex turn so you come out next to the mark??

If you come out next to the mark it is not an Apex turn.  I was going to draw a diagram, but this article explains it better than I could:

http://www.sailingworld.com/experts/a-better-way-to-round-the-leeward-mark - http://www.sailingworld.com/experts/a-better-way-to-round-the-leeward-mark  



The article goes on to state that it is when you are tacking after the mark because you keep more speed through the tack putting you ahead and the other yacht on your windward hip. if the two boats round doing an 'apex turn' surely the one who is closest or 'tightest' to the mark has the advantage?


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Posted By: Peaky
Date Posted: 22 Oct 11 at 4:02pm
Originally posted by I luv Wight


Originally posted by Peaky

No no no no no. Planing has nothing to do with exceeding a particular speed.
I can't see the video at the moment, hope it's a good one!
Err... see the title of the thread!

doh! Fair enough...

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Posted By: G.R.F.
Date Posted: 22 Oct 11 at 5:28pm
Planing? Isn't that when you overtake your own bow wave and surf down the front?

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Posted By: gbrspratt
Date Posted: 23 Oct 11 at 9:49am
Originally posted by fudheid


Originally posted by JohnW


Originally posted by fudheid

Don't you just do the apex turn so you come out next to the mark??

If you come out next to the mark it is not an Apex turn.  I was going to draw a diagram, but this article explains it better than I could:
http://www.sailingworld.com/experts/a-better-way-to-round-the-leeward-mark - http://www.sailingworld.com/experts/a-better-way-to-round-the-leeward-mark  
The article goes on to state that it is when you are tacking after the mark because you keep more speed through the tack putting you ahead and the other yacht on your windward hip. if the two boats round doing an 'apex turn' surely the one who is closest or 'tightest' to the mark has the advantage?



Totally agree!


Posted By: JohnW
Date Posted: 23 Oct 11 at 8:24pm
Originally posted by gbrspratt

Originally posted by fudheid


Originally posted by JohnW


Originally posted by fudheid

Don't you just do the apex turn so you come out next to the mark??

If you come out next to the mark it is not an Apex turn.  I was going to draw a diagram, but this article explains it better than I could:
http://www.sailingworld.com/experts/a-better-way-to-round-the-leeward-mark - http://www.sailingworld.com/experts/a-better-way-to-round-the-leeward-mark  
The article goes on to state that it is when you are tacking after the mark because you keep more speed through the tack putting you ahead and the other yacht on your windward hip. if the two boats round doing an 'apex turn' surely the one who is closest or 'tightest' to the mark has the advantage?



Totally agree!

I think you you are both missing the point I am making.

I agree with you that "wide in tight out"  has tactical advantages when other boats are about, however in the absence of nearby boats the fastest way round the course is doing apex turns.  So if you are in a handicap race and rounding the mark away from other boats,  apex turns will get you a better elapsed time.

It the two boats you mention are both doing an apex turn (optimal rate of turn for the boat, with the mark at the apex) then the will both exit the same distance from the mark.

You cant do a real apex turn and come out tight to the mark - if you are tight to the mark on exit your apex was downwind of the mark so you sailed further. Despite what you have been told, you will be behind where you would have been if you were not so close to the mark on exit.






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Posted By: Dougal
Date Posted: 24 Oct 11 at 11:18am
Originally posted by G.R.F.

Planing? Isn't that when you overtake your own bow wave and surf down the front?
 
 
Or to put it more simply....
 
http://www.bluejacketboats.com/planing_boat_theory.htm - http://www.bluejacketboats.com/planing_boat_theory.htm
 
 


Posted By: JimC
Date Posted: 24 Oct 11 at 11:51am
Interesting piece that one. Good find. There's a lot of mileage in considering what motorboat designers have to offer in that particular design area: its something they have to think about a lot with other design factors being simpler. .I like the point about speed and wake size: its so obvious you need to include the time factor and yet it hadn't occurred to me...


Posted By: Menace
Date Posted: 24 Oct 11 at 7:36pm
Originally posted by I luv Wight

What is planing? and how do you define it?
 
It's a woodwork techniquie where strips of wood are effectively shaved off by a plane. Next question please.


Posted By: themeaningoflife
Date Posted: 24 Oct 11 at 8:35pm
Originally posted by JohnW


I think you you are both missing the point I am making.

I agree with you that "wide in tight out"  has tactical advantages when other boats are about, however in the absence of nearby boats the fastest way round the course is doing apex turns.  So if you are in a handicap race and rounding the mark away from other boats,  apex turns will get you a better elapsed time.

It the two boats you mention are both doing an apex turn (optimal rate of turn for the boat, with the mark at the apex) then the will both exit the same distance from the mark.

You cant do a real apex turn and come out tight to the mark - if you are tight to the mark on exit your apex was downwind of the mark so you sailed further. Despite what you have been told, you will be behind where you would have been if you were not so close to the mark on exit.



This is true for a car and most other racing forms, but with sailing, because there is such a large disparity in speed between upwind and downwind, the quickest way around the course is to spend as little time as possible going upwind, thus tight in, wide out at a windward mark and wide in, tight out at a leeward mark.
What is true however is that at a gybe mark or similar, where there is little speed change, the quickest route is and apex turn. Smile


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Posted By: JohnW
Date Posted: 24 Oct 11 at 8:53pm
Originally posted by themeaningoflife

 
This is true for a car and most other racing forms, but with sailing, because there is such a large disparity in speed between upwind and downwind, the quickest way around the course is to spend as little time as possible going upwind, thus tight in, wide out at a windward mark and wide in, tight out at a leeward mark.
What is true however is that at a gybe mark or similar, where there is little speed change, the quickest route is and apex turn. Smile

NO!  

Look at the title of the thread.
  
You have fallen into the trap in thinking that if you come out tight you sail less distance upwind.  
True you sail less distance from the leeward mark to the windward mark but you are forgetting that you have already sailed an extra boat length or more below the leeward mark because the apex of your turn has to be below the the mark in order to come out tight.




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Posted By: gbrspratt
Date Posted: 25 Oct 11 at 10:52am
Why are you presuming that to go in wide and out tight people dont actually go around the mark? When going in wide surely you just make a shallower  turn (keeping your speed on), come in close to go around the mark and then come out tight? 


Posted By: rogue
Date Posted: 25 Oct 11 at 11:28am
I think the quickest way around the mark is in an RS class event. Sail over it.


Posted By: JohnW
Date Posted: 25 Oct 11 at 2:06pm
Originally posted by gbrspratt

Why are you presuming that to go in wide and out tight people dont actually go around the mark? When going in wide surely you just make a shallower  turn (keeping your speed on), come in close to go around the mark and then come out tight? 

I'm not presuming anything.  If you exit close to the mark, then the mark cant be at the apex of the turn.

I said earlier that for a given optimum rate of turn, the Apex turn is faster. If you have a boat that has a tight optimum rate of turn then yes, you can come out tighter but you will still gain (albeit less) if the mark is at the apex of your turn.

In the following the black path is an Apex turn around red, the blue path is a "racing" turn around red.  The blue path is effectively doing an apex turn around an imaginary mark (blue).  
If the red and blue marks were a leeward gate which one would you choose to round?



Edit: forgot to say, wind blowing down the page.


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Posted By: RS400atC
Date Posted: 25 Oct 11 at 8:19pm
I wonder if the 'in wide out tight' mantra makes more sense when you are rounding from a dead run?
There is also the 'soft science' factor, it's not the line people actually take you have to convince them about, it's the line they think they are taking. By attempting to come out tight to the mark, do people actually get closer to a true apex turn?


Posted By: JimC
Date Posted: 25 Oct 11 at 10:28pm
I suspect a lot depends on how you are actually approaching the mark... If you are coming in hot with plenty of speed then the best choice might well be different to the choice if you ended up high of the mark and are losing speed as you try and soak down to it...


Posted By: ham4sand
Date Posted: 25 Oct 11 at 10:38pm
and if you want the highest lane when going back upwind, that makes a difference to your tactics

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Posted By: rogue
Date Posted: 25 Oct 11 at 11:10pm
Originally posted by JimC

I suspect a lot depends on how you are actually approaching the mark... If you are coming in hot with plenty of speed then the best choice might well be different to the choice if you ended up high of the mark and are losing speed as you try and soak down to it...


agreed- especially if that soak is all part of the plan to give you time to get the flappy thing down at the front.


Posted By: Rupert
Date Posted: 08 Nov 11 at 4:41pm
Just found this thread...
 
How is that drawing anything like a mark rounding? If I'm rounding in wide out tight, my curve still wouldn't take me below the mark - in fact, I'm not sure it would be a smooth curve at all, especially if there was a gybe involved. Also, racing is about clear wind. If I go round the mark with the apex thing you are talking about, and supposedly gain a boat length, if that puts me in another boat's dirty wind, I'll loose far more up the next beat. If I get inside the boat I was following, I have the tactical upper hand.
 
Another myth - the outhaul should be pulled tight in light winds upwind.


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Firefly 2324, Lightning 130, Puffin 229, Minisail 3446


Posted By: JohnW
Date Posted: 08 Nov 11 at 5:37pm
Originally posted by Rupert

Just found this thread...

How is that drawing anything like a mark rounding? If I'm rounding in wide out tight, my curve still wouldn't take me below the mark - in fact, I'm not sure it would be a smooth curve at all, especially if there was a gybe involved. Also, racing is about clear wind. If I go round the mark with the apex thing you are talking about, and supposedly gain a boat length, if that puts me in another boat's dirty wind, I'll loose far more up the next beat. If I get inside the boat I was following, I have the tactical upper hand.

If you come out tight then you cant be doing an apex turn (unless the mark has the same radius as your turn) and therefore by definition you are rounding below the mark.  

My post says that the apex turn is the fastest, not always the best tactically. But when there are no other boats about it is faster.

 
Originally posted by Rupert

Another myth - the outhaul should be pulled tight in light winds upwind.

OK, I'l bite.  

Surely that depends on the boat and the cut of the sail.



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Posted By: Menace
Date Posted: 08 Nov 11 at 6:06pm
Originally posted by JohnW

Originally posted by Rupert

Just found this thread...

How is that drawing anything like a mark rounding? If I'm rounding in wide out tight, my curve still wouldn't take me below the mark - in fact, I'm not sure it would be a smooth curve at all, especially if there was a gybe involved. Also, racing is about clear wind. If I go round the mark with the apex thing you are talking about, and supposedly gain a boat length, if that puts me in another boat's dirty wind, I'll loose far more up the next beat. If I get inside the boat I was following, I have the tactical upper hand.

If you come out tight then you cant be doing an apex turn (unless the mark has the same radius as your turn) and therefore by definition you are rounding below the mark.  

My post says that the apex turn is the fastest, not always the best tactically. But when there are no other boats about it is faster.

 
Originally posted by Rupert

Another myth - the outhaul should be pulled tight in light winds upwind.

OK, I'l bite.  

Surely that depends on the boat and the cut of the sail.

 
On the sail thing, slightly more shape provides higher lift, doesn't really matter the boat or cut of sail. Light winds, from an aero point, looking for max lift, flattening sails reduces drag but your lift falls off significantly too. Have a little giggle when I see some of the skiff guys, with one default outhall setting, tight or tight...


Posted By: craiggo
Date Posted: 08 Nov 11 at 8:27pm
Depending on sail cut, the outhaul has differing effects. On most sails it can only be used to control the draught of the lower 1/3 of the sail. The amount of travel needed on a skiff outhaul is small as generally the rig is pretty powerful and controlling the top and middle sections with cunningham and kicker is more critical.
In general though for light wind sailing it is essential to keep the flow attached to the sail, and too much draught can lead to the flow running out of energy leading to seperation. A tight outhaul while sailing a little free-er will ensure minimum drag but max forward drive.


Posted By: Oatsandbeans
Date Posted: 08 Nov 11 at 9:47pm
I agree that lots of sailors bang the outhaul on tight in most conditions ( and really tight when its windy), and its not fast. Obviously in a drifter you can have it out tight, but as soon as there is a bit of "weight" in the wind and all the tell tales are flowing, you can afford to put some depth in the base of the main. As long as you don't overdo this and make it too deep ( very slow!) it will give you a really good profile to the lower leach of the main ( return at the bottom batten) which can be used to give you great pointing ability. This will work up to max power conditions when you will then have to flatten things off again.






Posted By: Rupert
Date Posted: 08 Nov 11 at 11:19pm
Why have it out tight in a drifter? I've been winning in no wind for as long as I can remember (wish I could do so in breeze) with a fairly full sail. All very well having attached flow, but with no drive and a board flat sail that is impossible to read the windshifts with, you'll be going in the wrong direction, slowly. Let the sail breathe. I'm always amazed at seeing creases in the foot of a sail in those conditions.

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Firefly 2324, Lightning 130, Puffin 229, Minisail 3446


Posted By: JohnW
Date Posted: 08 Nov 11 at 11:40pm
Originally posted by Rupert

Why have it out tight in a drifter? I've been winning in no wind for as long as I can remember (wish I could do so in breeze) with a fairly full sail. All very well having attached flow, but with no drive and a board flat sail that is impossible to read the windshifts with, you'll be going in the wrong direction, slowly. Let the sail breathe. I'm always amazed at seeing creases in the foot of a sail in those conditions.

I have very full fat sails, and find that the leech is hooked without any out-haul on in the lighter stuff. Pulling the out-haul on opens up the leech and my sails work better for me.  

Mike McNamara (who I believe knows a thing or two about sails and certainly way more than me) is an advocate of this. His tuning guides suggest outhaul fully on in all wind conditions up wind, only let it off on the reaches.




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Posted By: Menace
Date Posted: 09 Nov 11 at 8:27pm
Originally posted by Rupert

Why have it out tight in a drifter? I've been winning in no wind for as long as I can remember (wish I could do so in breeze) with a fairly full sail. All very well having attached flow, but with no drive and a board flat sail that is impossible to read the windshifts with, you'll be going in the wrong direction, slowly. Let the sail breathe. I'm always amazed at seeing creases in the foot of a sail in those conditions.
 
I am 100 percent with you on this one Rupert! A lot of research work NACA have done on foils sort of supports that, foils with a little bit more chamber operate better at lower flow speeds and provide maximum lift, doesn't really matter if you're on a 49er or a firefly, the basic principals apply.
 
Not going to bang on about it, as I'm not that fussed about giving away what can make me sail faster. I'd prefer the people I race against to gaze at a gybing board, or a specifc fancy boat polish and think that's quick over a fundamental thing like getting sail dynamics or quick gybes right if they want.


Posted By: craiggo
Date Posted: 09 Nov 11 at 8:44pm
Menace,
You aren't wrong regarding the NACA studies, but remember NACA studies were performed in wind tunnels with solid wooden models, not soft sails. On a solid aerofoil the boundary layer flow may seperate but will ultimately continue flowing around the section enabling re-attachment. Outside of the boundary layer the flow may stay laminar and perform reasonably well. With a soft sail seperation leads also to loss of shape, which in turn makes re-attachment difficult. A tight foot will minimise the likelyhood of seperations but will limit the ultimate rig forces. Sailing free-er gets you back some of the lost drive.

As you alude to, if you can keep flow attached over a deep section then it will be quicker, but in zephyr conditions this takes very careful and sensitive trimming and most people won't be able to keep it going. If you can then well done.


Posted By: fudheid
Date Posted: 10 Nov 11 at 10:48am
Originally posted by craiggo

Menace,
You aren't wrong regarding the NACA studies, but remember NACA studies were performed in wind tunnels with solid wooden models, not soft sails. On a solid aerofoil the boundary layer flow may seperate but will ultimately continue flowing around the section enabling re-attachment. Outside of the boundary layer the flow may stay laminar and perform reasonably well. With a soft sail seperation leads also to loss of shape, which in turn makes re-attachment difficult. A tight foot will minimise the likelyhood of seperations but will limit the ultimate rig forces. Sailing free-er gets you back some of the lost drive.

As you alude to, if you can keep flow attached over a deep section then it will be quicker, but in zephyr conditions this takes very careful and sensitive trimming and most people won't be able to keep it going. If you can then well done.
Clap
 
I think the critical thing here is 'tight' i don't think the suggestion is to have the outhaul bar tight like you would to flatten the sail in high/strong winds. But to flatten the camber slightly so flow stays attached, if your maximum camber is when you are fully powered up on a laser this used to be measured off the mid boom point say 6" (15cm) as you get to drifting conditions this comes tighter say around 2-3"(5-7.5cm). So the point is not to wind it on like a gorilla but to tune your sail to keep flow attached.


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Cheers you

only me from over the sea......


Posted By: RS400atC
Date Posted: 10 Nov 11 at 7:04pm
In a light wind which is not steady, the apparent wind can be a long way forwards in the lulls. A fairly flat main helps avoid or limit backwinding when this happens.

Sails and rigs vary. If you are sailing a boat where you ease the sheet a lot in light stuff to get more twist, the main can get very full on some boats unless the outhaul is pulled on reasonably, because the lack of mast bend will make the sail fuller than on a beat in F3.
It may help to try to talk about % camber rather than how far the clew is pulled out.

A two-boat drag race helps work out what works in a particular boat.

Also, what some people call 'light' others are thinking, 'let's postpone until the wind arrives'. I'm thinking about those days when we struggle to make progress at all against the tide.


Posted By: Menace
Date Posted: 10 Nov 11 at 7:42pm
Originally posted by RS400atC

In a light wind which is not steady, the apparent wind can be a long way forwards in the lulls. A fairly flat main helps avoid or limit backwinding when this happens.

Sails and rigs vary. If you are sailing a boat where you ease the sheet a lot in light stuff to get more twist, the main can get very full on some boats unless the outhaul is pulled on reasonably, because the lack of mast bend will make the sail fuller than on a beat in F3.
It may help to try to talk about % camber rather than how far the clew is pulled out.

A two-boat drag race helps work out what works in a particular boat.

Also, what some people call 'light' others are thinking, 'let's postpone until the wind arrives'. I'm thinking about those days when we struggle to make progress at all against the tide.
 
You've just opened another massive can of worms there - light winds unsteady? Do you mean wind strength, direction, heated air, cooled air, on the sea, on a lake, etc. Sorry if I'm being a bit facetious, but there is a lot more to it in my opinion than simply saying flat sails are fast in light winds due to them being unsteady. There is good argument for if you can't adjust quick enough, it's more of a penalty to adjust wrongly in unsteady winds. One of the major plus points of automatic rigs in my opinion. 
 
I'm going to stay firmly in Rupert's camp on this one. I don't think either of us are on about having bellowing sails, just a little bit more shape. I find it quicker on my boat, may be the way I sail though.
 
For what it's worth, Bethwaite supports flatter sails are fast in light winds, but sort of aludes to the fuller sail theory, don't think he notices he does it though. I'd have the same argument with him. The tell for me was when a good friend of mine asked me how I sailed in light winds. Think he was looking for a bite as he teaches sail dynamics and I walked straight into it. I argued the point about flat sails being fast on skiffs due to reduced drag and then he came back at me with all the NACA stuff and foil theory. I begrudgingly tried it in a drifter and it worked.


Posted By: RS400atC
Date Posted: 10 Nov 11 at 8:54pm
We're avoiding the issue of saying how flat we mean by flat.
I haven't measured it, but I would guess I'm talking about 8% depth being about what seems to work, looking at the lowest batten on a 400 main. That's for a beat when not only is the crew sat to leeward, but the helm is sat forward and as leeward as possible.

Sometimes of course, you can avoid beating because light winds will 'always' shift, and it's better to be moving than pointing......


Posted By: Chris 249
Date Posted: 14 Nov 11 at 10:33am
"I begrudginly tried in in a drifter and it worked"

Ummm, a lot of people in some classes have tried the tight outhaul in drifters and found that it worked for them, too. And they are certainly not all skiffies; even in 1989 IOR 50s some America's Cup winners had the outhaul tight all the time.

Certainly it doesn't work in all craft and no one who has read the stuff I write would pretend that I feel that skiffs are any better than any other boat, but have you any evidence (ie skiff worlds victories as well as the 505 ones I presume you have) that you are right and they are wrong?

For what it's worth, I was surprised when I saw the tight-outhaul theory in action too, but the information I got was that generating more power from increasing camber in the lower part of the mainsail was not as effective as losing efficiency in that area in exchange for being able to sheet more tightly. Trying to sheet tightly with a deep mainsail foot just lead to a stalled slot (to use that term loosely).

Of course easing the outhaul works in most boats, but surely there is one hell of a jump from you finding that it didn't work in your boat, to saying that everyone who uses a tight outhaul in any class is getting it wrong? I know in one class I sail, the fast high-wind settings for camber in the top 1/3 of the sail is (at a guess) about 6%, in another it may be 5%, whereas in another class it's negative camber, with the top battens inverting.  

If upper camber can vary so much in a breeze depending on class, why not lower camber?


Posted By: JimC
Date Posted: 14 Nov 11 at 10:47am
The trouble is because sails vary so much in design and shape, and because one thing affects another its difficult to be too dogmatic... You may find setting one aspect of the shape right according to theory sets another aspect comprehensively wrong and its just a question of seeking the best compromise.


Posted By: furtive
Date Posted: 14 Nov 11 at 11:08am

And all this assumes that what works for one sailor/team will work for another. Just because one setting/sail shape/mode of sailing/etc. is (supposedly) theoretically faster, and indeed faster for a particular sailor, it doesn't necessarily mean that all the other sailors in that fleet, with their enormous ranges of skill, experience, technique, fitness, strength, weight, tactical awareness, etc, etc, will automatically go faster by aiming for (and quite possibly not achieving) the same set up. Or indeed that a completely different set up can be argued as being theoretically (and actually) faster.

Isn't that one of the sport's most attractive features? There are many many ways to skin the many cats involved.


Posted By: Rupert
Date Posted: 14 Nov 11 at 11:16am
Who'd have thought one throwaway line would cause such upset...
 
I'm sure it works for many cuts of sail, but I've seen many boats going nowhere at all with outhaul bar tight having read in a book that it needs to be tight in a drifter. People actually need to question ALL the statements made in books and articles about what makes a boat go fast, and use them as a starting point. Sadly, many take what is written as gospel and follow it blindly.


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Firefly 2324, Lightning 130, Puffin 229, Minisail 3446


Posted By: dics
Date Posted: 14 Nov 11 at 1:27pm

Windward heel. How does it is work? Or is it a myth?



Posted By: Contender443
Date Posted: 14 Nov 11 at 2:04pm
Originally posted by dics

Windward heel. How does it is work? Or is it a myth?

It works! Anyone who sails without a rudder knows how it works.
 
Next time you are out don't hike too hard and heel the boat to leeward and the boat will turn into the wind. Now ease the sheet and have some windward heel and the boat will now bear away.
 
So this is not a theory it is a fact.


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Bonnie Lass Contender 1764


Posted By: Rupert
Date Posted: 14 Nov 11 at 3:07pm
Originally posted by dics

Windward heel. How does it is work? Or is it a myth?

Do you mean sailing in straight lines heeled to windward, like Steve Cockeril advocates? Seems to work for him, but I think it takes a lot of practice to get right. Must experiment this winter, while there are fewer leaves on the tres rond the lake, so the winds are steadier.

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Firefly 2324, Lightning 130, Puffin 229, Minisail 3446


Posted By: dics
Date Posted: 14 Nov 11 at 3:47pm
Yep.
 Windward heel sailing upwind to the windward mark. I do it and I get get lifted up nicely. No-one else seems to do it at the club. Whenever I have been out with the Tasers they have shunned the idea prefering to keep the boat "flat" (in taser terms means 30 degrees to leeward it seems!!). So I thought why does it work? How do the foils give you the lift? How does the hull shape affect it? Also it seems half the people I talk to say it works and others say it does not (but they seem to be the people who can not do it).


Posted By: Contender443
Date Posted: 14 Nov 11 at 4:48pm
I think we are talking more about balance here. What you think of as flat is usually a slight heel to leeward and windward heel to you is probably flat.
 
If your rudder is set up properly then a flat boat will give neutral helm and therefore no drag.


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Bonnie Lass Contender 1764


Posted By: Roger
Date Posted: 14 Nov 11 at 5:21pm
Originally posted by Contender443

I think we are talking more about balance here. What you think of as flat is usually a slight heel to leeward and windward heel to you is probably flat.
 
If your rudder is set up properly then a flat boat will give neutral helm and therefore no drag.
 
I thought the question was with regards to the theory that heeling a boat to windward on the beat would make it point higher! at least for the same speed anyway.
 
I seem to recall some thinking the hull shape in the water made a difference when heeled to windward, and others believed the rig performed better when heeled to windward, hence canting rigs to windward in Melins (recently) and Flying Dutchman (many years ago)
 
There is of course always the theory that what you think is flat isnt, and you should always feel that the rig is pointing to windward, but thats different.
 
 
 
 


Posted By: Rupert
Date Posted: 14 Nov 11 at 5:38pm
One of the Rooster vids goes into it in some detail. Easier to see it happening than to explain, at least for me...

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Firefly 2324, Lightning 130, Puffin 229, Minisail 3446


Posted By: themeaningoflife
Date Posted: 14 Nov 11 at 6:30pm
Plus if a gust hits when the boat is heeled to windward, as it comes flat it is in the best position to accelerate from and thus more speed and height!

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Cambridge University Lightweight Rowing Club
RS800 1128

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Posted By: SoggyBadger
Date Posted: 14 Nov 11 at 7:08pm
Originally posted by Roger

hence canting rigs to windward in Melins (recently)


Kevin Haynes was doing that in the 70s, which is recent on a geological scale of course Wink


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Best wishes from deep in the woods

SB



Posted By: zippyRN
Date Posted: 22 Dec 11 at 11:44pm
Originally posted by craiggo

Depending on sail cut, the outhaul has differing effects. On most sails it can only be used to control the draught of the lower 1/3 of the sail. The amount of travel needed on a skiff outhaul is small as generally the rig is pretty powerful and controlling the top and middle sections with cunningham and kicker is more critical.
In general though for light wind sailing it is essential to keep the flow attached to the sail, and too much draught can lead to the flow running out of energy leading to seperation. A tight outhaul while sailing a little free-er will ensure minimum drag but max forward drive.

exactly keeping flow attached , it also depends, as you say on the rig  - with the extremes of the laser / topper style shroudless una rig  at one end  and the all singing all dancing 27 pieces of string  of a merlin or somesuch at the other  as to what influence the outhaul and  the cunningham has - basically by what opposes it's actions 


Posted By: zippyRN
Date Posted: 22 Dec 11 at 11:46pm
Originally posted by RS400atC

<snip>
Also, what some people call 'light' others are thinking, 'let's postpone until the wind arrives'. I'm thinking about those days when we struggle to make progress at all against the tide.


(some) pond sailors will sail if there's one wind ripple per square metre of water's surface or less, where in tidal waters you 'd just be being pushed around by the tide 


Posted By: zippyRN
Date Posted: 22 Dec 11 at 11:48pm
Originally posted by Contender443

I think we are talking more about balance here. What you think of as flat is usually a slight heel to leeward and windward heel to you is probably flat.
 
If your rudder is set up properly then a flat boat will give neutral helm and therefore no drag.

 exactly ...


Posted By: JohnW
Date Posted: 23 Dec 11 at 11:01am
Originally posted by zippyRN

 

(some) pond sailors will sail if there's one wind ripple per square metre of water's surface 

That's blowing a hoolie on our lake! 

The other week the race was run (by popular request) when the only ripples were caused by fish jumping and ducks swimming!  (and it was foggy).

I was glad I was on race duty that day.

I dont recall how many boats had their clew outhaul on hard though.



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Posted By: Peaky
Date Posted: 28 Dec 11 at 10:51pm
Originally posted by zippyRN


Originally posted by Contender443

I think we are talking more about balance here. What you think of as flat is usually a slight heel to leeward and windward heel to you is probably flat.
 

If your rudder is set up properly then a flat boat will give neutral helm and therefore no drag.

 exactly ...

The rudder will always have drag, just like the centreboard. A light helm does not mean no drag, it just means it is better balanced.

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Posted By: RS400atC
Date Posted: 29 Dec 11 at 7:16pm
Originally posted by Peaky


The rudder will always have drag, just like the centreboard. A light helm does not mean no drag, it just means it is better balanced.


A rudder that is continuously providing lift to counteract weather helm will create more drag than one which is not.


Posted By: I luv Wight
Date Posted: 29 Dec 11 at 10:35pm
Originally posted by RS400atC

Originally posted by Peaky


The rudder will always have drag, just like the centreboard. A light helm does not mean no drag, it just means it is better balanced.


A rudder that is continuously providing lift to counteract weather helm will create more drag than one which is not.


A rudder that is continuously providing lift to counteract weather helm will create more drag than one which is not, BUT it will reduce the lift and drag from the centreboard.



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