Sail Shape---a question for the true sailors....

[Scott MacCready]

I'm always looking to get the most from my sails and am looking for advice from those more knowledgeable. I received this picture of my boat taken during the trip over to Ocracoke this past week. As can be seen, I was on a broad reach. Can any of you suggest how I could trim for better shape? It seems if I got those creases out, it would be more efficient.
[img]http://www.geocities.com/travel-rn/3Feathers.jpg[/img]

[Dave H]

Hi Scott, How old is your main? Your wrinkle from clew toward head looks like the wrinkle i had in my old main. Dave Hedlund

[rtbates]

That's my first thought on the wrinkles from clew to mast wrinkles.

[tartansailor]

Way too much twist in your headsail. You are spilling alot of power. Bring your clew block slightly forward and tighten the sheet more.

Get a copy of "Sail Power" by Wally Ross, Alfred Knopf, 1977.

Dick

[Carl Thunberg]

Scott,

I have to admit you have guts opening yourself up for people to critique your sail trim. But since you asked for it, folds that radiate from the end of the boom to the luff usually mean too much backstay tension, which in effect shortens the leech. I don't think it's the outhaul tension. If the outhaul was too tight you'd start to see folds parallel to the boom, which I don't see. Ease off on the backstay and see what happens to that wrinkle. That being said, the length of your bow wake shows you're pretty close to hull speed, so you're doing something right.

Carl

[tartansailor]

Hello folks,
As Carl said, Scott is looking for constructive criticism, and to my way of thinking it is a gift to be treasured, because there is too much of the other kind in this world.
Now,
Look at the foot of the head sail. How can it be accelerating the flow over the lower portion of the main if it is not in line with the lower portion of the main?

The foot of both sails should be parallel to the deck.
So both sails are not pulling as they certainly could. Bring the clew block forward and tighten the sheet big time.
Dick

[Scott MacCready]

Hi All,
I appreciate all the comments; I'm not so vain to let them offend me. That's why I posted the question. We have a great resource here with this board. I admit I'd rather hear, "Wow! I wish mine looked like that!" , but that really wouldn't help me tweak out those extra tenths of a knot.
As far as the age of the sails, I can't say with 100% certainty, but the previous owner claimed they were all only 2 years old. Their overall condition lends me to believe that to be true, certainly less than 5 years old. The boat had another complete set that were somewhat older that now are being used on other board members' ketches.
I will try moving the genoa sheet blocks forward more. I recently added telltails to the main,jib and mizzen, but ran out before I got to the genoa. I've found they help me somewhat but adjusting the twist of both the headsails and the main eludes me yet. With the main, I adjusted the boom in several various positions using the traveler and a boom vang but could never get it just perfect though as Carl pointed out, I was at or close to hull speed. Of course, with enough wind I can't take the credit. I'm trying to improve my light wind sailing ability.
As far as the foot of the genoa Dick, I'll have to examine it more closely. When I first looked at the picture, I just assumed the clew was cut high to avoid the stantions and other things on the deck.
And as far as the backstay Carl, I don't have an adjustable one, In fact I don't have one but two. My backstay splits to avoid the mizzen mast. Are you suggesting I make a permenant anjustment (reverse rake)?
Finally having someone take a picture of my boat while sailing is a great tool as is this board. I'm not afraid to try new things and enjoy learning. I single hand exclusively but still manage to use my full arsenal of sails. Thanks, Scott

[Carl Thunberg]

Too bad on the backstay. I have an adjustable backstay (wheel type) and love it. This wrinkle in your main isn't severe and I certainly wouldn't make a permanent change that would result in reverse rake. Maybe a professional rigger would recommend it for other reasons. It's really a great opportunity to get photos from a distance. Things that look really obvious from afar (genoa twist), may not be so obvious up close. It really helps to get that "outside" perspective. This has been a great discussion. Thanks for posting it.

[Matt Cawthorne]

Scott,
I have learned to plaster my sail with telltales. The main has a set at the leech, but also a set about 2 feet back from the mast, a set half way to the leech and a set 3/4 of the way. You can learn a great deal about sailing on a beam or close reach or close hauled that way. Off the wind you don't get much info. Next time my Yankee is off I will do the same.

Matt

[Stan W.]

Look at the foot of the head sail. How can it be accelerating the flow over the lower portion of the main if it is not in line with the lower portion of the main?

I used to think this too but windtunnel testing has shown that this is not how the genoa and main interact.

In fact, it is more a case of the main benefiting the genny than the genny benefiting the main. In very simple terms, there is a circular flow of air around both sails a small distance from their surface--counterclockwise on starboard tack and clockwise on port tack. The interaction of the two circulations forces additional air to leeward of the genoa making that sail more effective.

Google the name "Arvel Gentry" for much more on this.

[tartansailor]

Stan, You are entitled to your opinion - which I respect - but I learned mine from professional skippers who win races, from Olympic gold medal winners who give seminars, and from sail makers with CAD who design around the slot effect.
Another words Stan, the real world.

A wind tunnel is one thing, strain gages on the sheets and stays shows whats really happening, and that is the basis for substantiating the slot effect.

Matt Cawthorne hit the nail on the head with telltales. Look at the main telltales, both windward and leeward, with and without a head sail and see the difference.

Respectfully,

Dick

[Harold H]

That's sure a pretty boat.

Did you have full hoist on your main halyard?

It looks like the main might be overtrimmed for a broad reach. And from the look of the boom it looks like your boom vang might need to be eased off just a bit.

I agree with the other posters about the headsail sheet lead position.

[Al Levesque]

I agree with Carl that hull speed means you are doing very well. I would add the observation that the angle of heel and the set of the sails mean that wind strength doesn't get the credit.

The wrinkle from clew toward head usually means, as Harold suggested, that the sail is not pulled up as high as it should go, or there is too much sail for the space along the mast. I think I may also detect slight wrinkling near the lower slugs. The luff seems not to be stretched enough. A cunningham would verify that or a line to the first reef cringle might also.

In any case, that big dip in the wave amidships is about as good as it gets. We will practice to get that good.

[Stan W.]

Stan, You are entitled to your opinion - which I respect - but I learned mine from professional skippers who win races, from Olympic gold medal winners who give seminars, and from sail makers with CAD who design around the slot effect.
Another words Stan, the real world.

A wind tunnel is one thing, strain gages on the sheets and stays shows whats really happening, and that is the basis for substantiating the slot effect.

Matt Cawthorne hit the nail on the head with telltales. Look at the main telltales, both windward and leeward, with and without a head sail and see the difference.

Respectfully,

Dick

For some reason I find this subject fascinating and I am very interested in hearing all sides so I hope you don't mind if I pursue it a little further.

What exactly are the strain gauges and telltales showing that validates the venturi model or refutes the circulation model? In particular, telltales show whether the surface flow is attached but they don't tell you whether anything is accelerating and the circular flow Gentry is talking about occurrs away from the surface. Also note that Gentry does not say that there is no "slot effect" in the broad sense of a beneficial interaction between the sails. He just says there is no venturi effect, i.e. no acceleration of airflow through the slot.

It appears to me that many sailmakers actually do accept the circulation model over the venturi model. Do you know of anything written in the past 25 years that scientifically disputes Gentry's conclusions?

Not trying to pick a fight, just trying to learn.

[Carl Thunberg]

Well, I just finished reading enough of the information about Arvel Gentry's research to intrigue me, even if I don't fully understand it. Stan, thanks for putting it out there. I will be reading more on this subject. I'm left wondering if this changes how us mere mortals (i.e. cruisers), who never have any ambitions of an America's Cup, Volvo Open Ocean Race, or Sydney Hobart race victory will actually trim our sails. All I know is, if I trim my sails ASSUMING the venturi slot effect is correct, my boat goes faster. If I do anything different, I slow down. So, Dick's sail trimming advice would appear to still be correct, even if the established venturi theory of the slot effect isn't exactly how the main and genny interact. Is this a fair summary?