Can you ever have too much draft?

Stu Jackson · Jun 2, 2015

Daveinet said:
While I did try different positions on the traveler, I did not move it all the way to windward. Maybe I should have?

Moving the traveler has more to do with BOOM position than TRAVELER position. The trick is to USE the traveler to get the boom to almost amidships position. How far the traveler has to go to do that has lots to do with how tight the mainsheet is, too, since the mainsheet is an important element of twist.

RichH · Jun 2, 2015

Daveinet said:
So while we are on the subject, I do have lower telltails on the jib. There is only one set on the luff in the lower third. Often I find the lower windward tell tail flying nearly straight up. (this is without any significant heal) Not sure what that means other than I have wind shooting up the sail instead of flowing aft.

With the sail attached onto a furling foil, the foil having thickness and apparent 'roundness', the tell tale very close to the leading edge of the sail, what you are probably seeing is the action of the foil disturbing the flow of air and creating a small wind turbulance 'rotor' directly downstream (normal air flow) of the foil ... plus a slight heel to the boat which tends to distort the normal air flow to go 'up' along the sail as well as aft.

The normal aerodynamic 'circulation flow' around a sail also contributes to this leading edge turbulence effect - especially seen just behind 'thick furler foils' and sails that are partly rolled up on the foil .... and sails that have a 'roundness' to their luff shape.
With a hanked on sail or a sail held in a well aerodynamically shaped foil (tuff luff, etc.) and with a racing cut (non-rounded luff shape) this anomaly will be greatly lessened. In your case, the round or thick foil itself is probably acting as a totally independent lifting surface.

Rx: move your tell tales slightly back and away from leading edge by several inches.

For a more 'precise' way to set up tell tales, especially look at where tales 9, 11, 13 are set-up (on the mainsail, and in proximity to the leech of the jib !!!) ... and approximately how far the tales are from the leading edge of the jib

;-)

RichH · Jun 2, 2015

Jackdaw said:
OK now not quite clear. In your first post you said mostly light. Now you say mostly overpowered?

Anyway, assuming you were overpowered.

Many sailors (in particular on fractional boats) think it is enough to flatten the sailplan when the breeze comes on. This is NOT THE CASE.

To do this, many will flatten the main (tension everything, lots of sheet etc) and then lower the traveler when a puff hits. The whole sail just luffs and shakes in the breeze generating no lift but tons of drag.

The KEY is to ADD TWIST. Bring your traveler way up. You want the boom and the bottom 1/3 of the mainsail on the centerline or slightly above. And now then ease the sheet. Vang loose. The top 1/3 of the sail will just weathervane into the stronger breeze aloft, buts that OK. You'll sail the bottom 2/3s. The boat will flatten out and speed way up. The goal is keel the boat flat. Speed will take care of itself.

Remember that when it is breezy, sailing effectively is all about dealing with excess pressure.

Good post!!!!
Until you overcome small trepidations about letting a boat heel over in a breeze, the natural tendency will be to overreact, over-flatten, over-twist, over-trim, etc.
Once you arrive at a comfort level of 'pushing' a boat hard in a breeze and letting it heel, all this initial 'over-conservatism and caution' (causing mal-trim, etc.) will disappear.
Such a learning curve can be steep, .... some never allow it to happen.

RichH · Jun 2, 2015

Daveinet said:
Just a clarification, Saturday had some wind that died to nearly nothing. Monday was 20+.

As far as twist, ...................... While I did try different positions on the traveler, I did not move it all the way to windward. Maybe I should have?

windward????????
The only time you should be pulling the traveller to windward of the centerline is in 'super light' wind conditions and where the mass/weight of the boom is causing the sail have nearly ZERO so-called twist.
The only other time I can think of pulling the traveller to windward and above the centerline is when you need to panic stop the boat in an emergency by radically backwinding the mainsail.

Jackdaw · Jun 2, 2015

RichH said:
windward????????
The only time you should be pulling the traveller to windward of the centerline is in 'super light' wind conditions and where the mass/weight of the boom is causing the sail have nearly ZERO so-called twist.
The only other time I can think of pulling the traveller to windward and above the centerline is when you need to panic stop the boat in an emergency by radically backwinding the mainsail.

Rich, maybe we're miscommunicating but in a solid breeze, pulling the traveler car to windward while easing the sheet is a time-tested technique to get proper shape in the lower 2/3 of the sail while the top 1/3 is allowed to twist off in the higher breeze.

If you do that with the boom below the centerline the whole sail just luffs.

To the OP: the trick is BALANCE. You want the boom close to the centerline or maybe just windward. Easing the sheet to add twist will let to move leeward so it might have to come up more. Balance.

RichH · Jun 2, 2015

OK your talkin' 'survival conditions', I was thinking of sailing under a full aerodynamic shape ..... and following the topic thread of amount of draft and its control.

But again Im not one who would twist off nor advocate to twist off to depower, etc. .... as one who would prefer to 'blade-out' a sail to depower which lessens surprise 'power-ups' in especially unstable wind conditions.
FWIW - In planing/sport boats, we call those who over-twist - potential submarines and 'surprised swimmers'. ;-)

I'll have to watch the thread drift more carefully.

Ed. - 'twist' is adjusted by vang tension. So if one eases out the mainsheet to increase 'twist' then either the boat doesnt have a vang, its not employed or its simply too weak to handle 'twist' control because the vang control lines are stretching unduly. ;-)

Jackdaw · Jun 2, 2015

RichH said:
OK your talkin' 'survival conditions', I was thinking of sailing under a full aerodynamic shape ..... and following the topic thread of amount of draft and its control.

But again Im not one who would twist off nor advocate to twist off to depower, etc. .... as one who would prefer to 'blade-out' a sail to depower which lessens surprise 'power-ups' in especially unstable wind conditions.
FWIW - In planing/sport boats, we call those who over-twist - potential submarines and 'surprised swimmers'. ;-)

I'll have to watch the thread drift more carefully.

No I'm not talking about survival conditions. I'm talking about going upwind in 18 knots of TWS on a modern race boat.

On both our First 260 and First 36.7 'blading out' simply makes the entire mainsail luff and shake. It certainly depowers it as flow detaches down the entire length. Reefing of course is an option, but now you have NO way to deal with the lulls.

So traveler up, and adjust the sheet until the boat flattens and stays on its VMG speed and heel. No need to watch the tell tails. Its all about boat speed and heel angle now. And we TORCH anyone around us not doing the same.

Jackdaw · Jun 2, 2015

Daveinet said:
BTW: Jackdaw, I was just up in Bayfield last Thursday. Took a slight detour on my way from Ironwood to St Paul. Any town that can turn old broken down fishing boats into yard art in a park is my kind of town. Kind of has the feel of Grand River, OH near where I grew up. When I was much younger, there were always old boats laying around in various states of disrepair. There were a couple of boat manufacturers there including Ray Mcleod and Sandy Douglass building Thistles. My dad actually sailed with Ray's son a couple of times as a kid. C&C/Tarten is still there. So I have fond memories of an old marine town. Bayfield brought some of that back.

How cool! We just missed you; we made it up Friday at noon as we had a race at WYC thursday night. Yes Bayfield is a funky old town. Maybe you saw it; there is actually a park with dilapidated fishing boats on display. But still a very active fishing fleet, and sailboats outnumber residents 4:1. Locals are cool. The local bars are cooler.

RichH · Jun 2, 2015

Jackdaw said:
No I'm not talking about survival conditions. I'm talking about going upwind in 18 knots of TWS on a modern race boat.

On both our First 260 and First 36.7 'blading out' simply makes the entire mainsail luff and shake. It certainly depowers it as flow detaches down the entire length. Reefing of course is an option, but now you have NO way to deal with the lulls.

So traveler up, and adjust the sheet until the boat flattens and stays on its VMG speed and heel. No need to watch the tell tails. Its all about boat speed and heel angle now. And we TORCH anyone around us not doing the same.

Twist is usually controlled on most boat by a simple vang. If the boom is lifting in high-moderate conditions, then clearly the vang is too weak and its control lines are stretching ... or the boat doesnt have a vang.

Second, in most climatic conditions increasing wind without radical changes in humidity will decrease the amount of wind 'gradient' close to the water; thus, reducing the need for 'twist' - exception is when a boat is down very deep into a trough or bottom of a swell.

Third, if you dont want to reef, then flatten or drop the traveller and blade-out. Most will go 'up' in the slows and 'down' in the blows (for best VMG) - while 'playing' the traveller to keep the boat on its feet and 'driving'. Over-twisting the main leaves one very vulnerable for a 'dunkin' especially in unstable winds as then unstable wind gusts 'may' hit directly to that lower section of the sail which now possibly may be well over-trimmed and as it hits the backside of the flogging upper part of the sail. Blading out is far better than trying to guess which part of the twisted up sail is going to fully attach - faster, more easily controlled, less guessing as the angle of attack remains constant - top to bottom. With a well twisted off sail the angle of attack is always 'different' from top to bottom - vulnerable to unexpected power-ups and luffing.

VANG !!!!! ... one that is strong enough!

Jackdaw · Jun 2, 2015

RichH said:
Twist is usually controlled on most boat by a simple vang. If the boom is lifting in high-moderate conditions, then clearly the vang is too weak and its control lines are stretching ... or the boat doesnt have a vang.

Second, in most climatic conditions increasing wind without radical changes in humidity will decrease the amount of wind 'gradient' close to the water; thus, reducing the need for 'twist' - exception is when a boat is down very deep into a trough or bottom of a swell.

Third, if you dont want to reef, then flatten or drop the traveller and blade-out. Most will go 'up' in the slows and 'down' in the blows (for best VMG) - while 'playing' the traveller to keep the boat on its feet and 'driving'. Over-twisting the main leaves one very vulnerable for a 'dunkin' especially in unstable winds as then unstable wind gusts 'may' hit directly to that lower section of the sail which now possibly may be well over-trimmed and as it hits the backside of the flogging upper part of the sail. Blading out is far better than trying to guess which part of the twisted up sail is going to fully attach - faster, more easily controlled, less guessing as the angle of attack remains constant - top to bottom. With a well twisted off sail the angle of attack is always 'different' from top to bottom - vulnerable to unexpected power-ups and luffing.

VANG !!!!! ... one that is strong enough!

Vang controls twings only if you don't want your mainstreet to. Upwind in these conditions we ease the vang so easing the sheet adds twist to the sail, and NOT just bladed it off. The TRICK is to have the majority of the sail at the right AOA and generating lift. The rest of it? Who cares? We've got to much power anyway. The goal is to manage it.

Climate? What does Climate theory have to do with this? I'm talking about real conditions that affect boat speed in an observable, repeatable way. We set the twist to optimise speed. Its that simple. We deal with gradient of all levels, as well as shear caused by very cold water. We have telltails all over our boat, pretty much every 10 feet on the stays.

Reefing sets your max sailplan (and power) at a point often below what will be needed on the course over the life of the race. If you are OK with being underpowered for a percentage of the time, fine. Reef. Lose.

If you are not, then do what I do. I'm not making this stuff up. This is SOP on modern race boats everywhere. Any boat that just blades in the puffs will either be overpowered and over healed, or luffing and slow. Either way they get crushed.

RichH · Jun 3, 2015

Your original statement omitted releasing/easing of the vang. BIG difference!

FWIW - humidity % and temperature affects air density hence air viscosity. Viscosity of the air is the SINGULAR most important reason that the air transfers energy to the sails/boat. Thats 'real world'.

Sail shape distortion such as twist reduces upwash hence efficiency loss and partial loss of the all important 'kutta condition' at the leeches. In rising air velocity partly blading-out allows a higher VMG, uniform upwash, more consistently controlled AOA, and less loss of 'upwash' .... 'kutta' remains constant albeit reduced.

Joe · Jun 3, 2015

Daveinet said:
And back to the thread. My boat doesn't really need a vang, the weight of the boom seems to over power any adjustment in the main sheet/traveler. Possibly when running down wind, but so far, I've not seen my boom ever lift. The attachment point is well aft of the clew, so there is an excessive amount of leverage pulling the boom down.

So even on the 20+ kt day you recently experienced, the boom was still weighting down the sail? Sorry... just not getting your point then... if you have sail trim questions it means there's something you don't understand... so you shouldn't counter perfectly good advice with platitudes that you don't really need a vang because the boom's too heavy. Then you said you used a bungy to allow the boom to react to puffs. What's the deal?

When I sailed last year, in moderate conditions, I would hook a bunji cord on the traveler, so as the sail became over powered, it would spill the air automatically

Davidasailor26 · Jun 3, 2015

Daveinet said:
As I think more about it, I did loose power out of the main, because the boat often needed to be held from turning downwind. I've never had this problem before, I actually missed a tack once, which has not ever happened in the past.

Something's not right if you have to hold the boat from turning downwind, especially in heavier wind. The boat should want to turn up slightly if properly balanced. Turning down (Lee helm) leads to increased leeway and suggests that the center of effort is way too far forward. I wonder if whatever's causing that imbalance is related to your other issues.

Scott T-Bird · Jun 3, 2015

Absolutely ...

Davidasailor26 said:
Something's not right if you have to hold the boat from turning downwind, especially in heavier wind. The boat should want to turn up slightly if properly balanced. Turning down (Lee helm) leads to increased leeway and suggests that the center of effort is way too far forward. I wonder if whatever's causing that imbalance is related to your other issues.

Lee helm to that extreme is unusual, and it led me to wondering if rake was altered significantly with the adjustments for mast bend.

In any case, based on last year's discussion, it seems that sail shape issues are still a mystery. Without making adjustments in real-time, and being able to observe real shape, opposed to photographs that can't show the entire picture, corrective advise on a forum for your particular problems is largely in the dark (particularly when you are dismissive). However, the advise you get in general from this forum is right on target with respect to sail trim issues.

With all due respect, I agree with Joe ... some of your comments are a little off the wall with respect to not needing a vang because the boom is too heavy or using a bungy for traveler control. I also wondered what you meant by the "attachment point" being aft of the clew and the leverage issue. Do you mean that the main sheet is end-boom sheeting? Yes, that does increase leverage, but it has nothing to do with vang control or preventing the boom from lifting. The boom lifts and swings out as a function of how much the mainsheet (and the vang) is let out. The more the sheet is eased, the potential for twist is increased to the extent that the vang is eased as well. But you seem to be telling us that you haven't been able to ease the leech without increasing bend significantly, which now seems to be negatively impacting performance.

In answer to your original question in this thread ... yes, TOO MUCH draft is a performance killer in all conditions. Too much draft, in the wrong places, is generally speaking, a sign of a blown-out sail.

If the mystery continues, find a good sailmaker for advise. You may REALLY need a new sail (how are we to know??). The photographs and descriptions from the post last Fall seem to indicate (to me anyway) that the sail is either mismatched for the boat, in need of re-shaping, or beyond help. North Sails have reps who really know this stuff, and they are more than willing to take a look at your sail ON YOUR BOAT when there is even just the potential for a sale. They won't lie to you. You'll get the straight information and then you can decide.