Thank you, Ken. I was going to say something about Randy Smyth (and Rick White, too) not believing in leech telltales having any value.

But I will leave it to Rick to explain his (and Randy's) position about this. It might be a few days, because Rick is PRO for the Shark Nationals here at Put-in-Bay right now.

Mary,

looking forward to hear what Rick has to say on the subject. Tried searching for any references to what Randy might have said, but did not find anything.

Timbo, I remember Bethwaite writing about peppering his sails with telltales in "High performance sailing", but dont remember exactly the context or results.
I agree with your aircraft wing analogy. A fuller main and a bit more mast rotation gives more power and drag, but gets you up on one hull earlier. But as we dont have a manual to sailshape, you need to know by feel and rough eyesight/experience where the limits are. I have read a lot of sailing and sailmaking books, and they all stop quite fast when they get into just what shapes are fast under which conditions. Bethwaite and Tom Whiddens book are the best I have found on the subject, but they are far from exhaustive (I guess you would need to write a book for every class of boat if it was to be meaningful).
I have found some advice I got from an old Tornado class olympian to be very good, and fast: "Put on more downhaul and mainsheet than you think you need, get your head out of the boat and go".

I was there when Randy said that and I didn't put leech tales on a main for years later because of that. It's hard to argue with expertise like Smyth and White. However, I did put them on at the mid-point last year because of some European comments I heard and I've found them to be very useful. I have people that comment on copying my downwind trim in light air because we're pretty quick downhill. In my opinion, the right amount of traveler and twist is pretty hard to get correct without more information than just the regular tales can provide. They also provide a reference to how much to sheet in upwind too. It's not that I try to get them to stream straight back all the time, but you want them to stream back about 75% of the time to indicate good flow.

Yes Rolf, Bethwaite's book is excellent, and he is (or was) also a competition glider pilot, he mentions that there are very many similarites between wings and sails. I'm still trying to figure out how to build a "soft" (collapsable) hard wing type sail. Maybe with inflateable battens or something? Like the C class cats but with kevlar and mylar instead of a hard wing.

Timbo, the windsurfers have experimented with this for years. There was something called camber inducers for a while, battens that split at the mast with a double layer of cloth there. When tacking/jibing, the battens popped over by themself. I think the same was tried on some older C-class sails, but I think the technology is pretty much dead now as it is not as efficient as a wingmast+soft sail combo or rigid wing.
For fun, why not try a 50%wingmast with a soft sail as flap <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" /> Would be fun to sail, probably, but a beast on the beach.

Maybe we should be looking at the Kite boarders--their newest kites have inflatable ribs/battens.

I don't think Darren Bundock or Glenn Ashby uses any tell tales in their sails and they are world champions. So maybe we need to tell Randy to get rid of his tell tales near the mast as well ?

Personally I think there are some sailors in this world who are so talented that they can sail any boat fast just by feel. This does not mean that lesser talented sailors like myself will do better by removing any aids we have and trying to imitate what these talented sailors can.

I'm personally very much helped by the leech tell tales. Like this I'm personally faster while I would be slower if I did it the Smyth/Bundock or Ashby way. So going the Smyth/Bundock and Ashby way would be downright foolish for me.

Wouter

Camber inducers fail to live up to expectations because they are in the separation bubble behind the round mast. Minimizing turbulance in this region requires changes to the leading edge of the mast, not the trailing edge, according to Bethwaite.

--Glenn

Optimal = "just popping in and out" according to Bethwaite, but he assumes the reader knows what this means. I think he means supercritical: streaming aft, but with the sail trimmed in just enough that they occasionally pop behind the sail... much like Smyth's supercritical luff telltales.

Having just finished reading Bethwaite's book, I'm convinced I want to add two or three "leech ribbons" as the aussies call them. He points out that leach ribbons are a useful backup for when the luff telltales are not backlighted and cannot be seen. He does not advocate using them exclusively.

Bethwaite does have a diagram of a sail covered with telltales, but that's just to demonstrate which ones really matter: only the luff telltales.

He also mentions the fact that a properly trimmed sail will have a little turbulance due to air leakage around the leach. This is why they should be acting up a little when the sail is properly trimmed.

Bethwaite seems to advocate telltales or leech ribbons at different times, depending on the point of sail and sea state and wind strength. I'm going to have to reread to figure out when and why. However, using the two in combination seems like a great idea in most conditions because the luff telltales tell you about the size of the separation bubble (front-edge supercriticality) and the leech ribbons tell you about rear edge separation, and you want to be on the edge of both types of separation for maximum power, which requires getting the right camber (outhaul+downhaul+prebend) and the right angle of attack (sheet and traveller + helm). So, the leech ribbons do give some useful additional information not provided by luff telltales.

Also note that a small amount trailing edge separation is normal, but oversheeting increases the size of this separation, increasing drag and reducing power. The leech telltales indicate when this is happening, and large separation should always be avoided (except in light air for the bottom 2/3 of the sail...). In a breeze, you always want the leech ribbons streaming or "just popping in or out".

At least, that's my understanding after reading the book.

Thank you Glenn, a very good and clear write-up.


With rotating wingmasts, I think the windward separation bubble is quite small, unless you are beating with a very deep main.

I believe that telltales are only necessary until you know your sail and settings and thereafter are un-necessary and even possibly a distraction.
Guys like Asby have so many hours on the water, they know what works and what doesn't and they simply trim by experience and feel.

For us duffers, until we reach that level of excellence, I'm afraid we are stuck with streamers <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" />

I once had the pleasure of haveing a National Champion crew for me. He spent very little time looking at my sails, which were older than most of the others out there. He almost NEVER took his eyes off the water and wind ahead of us and had me tacking about twice as much as I normally would on a lake in shifty wind. Thanks to me, we got 3 bad starts but he turned that into 3 first place finishes, all because he was wathcing the wind, called the shifts correctly and worried very little about sail trim. THAT is why those guys don't use telltales. If you never look at them anyway, why put all that drag on your sail? (Me? I need them!)

I am in the same school as Randy -- leech telltales are pretty useless unless you are a monoslug sailor.
As in airplane wings the stall on a sail comes from the back edge and goes forward. The lift is in the highest camber of the wing.
At the lift area the aft telltales should be flowing. The leech telltales should always be stalling (that is where the stall begins)
If your leech telltales flow, that means "you are loosing gobs of power," as a quote from Randy Smyth himself.
Randy and I have always concurred that you need your telltales at the high lift area of the sail. On most sails that is about 9 inches aft of the luff, assuming you are using a rotating mast. That usually puts the telltales right around the highest point of the lift of the sail.

Some folks put another set about 9 more inches back and keep them between a stall and flowing and this seems very fast. These are just to let you know where the stall coming from the leech is located and how far forward it has come.

On airplanes you have the same situation -- the back part of the wing is providing no lift, just the area where the highest curve is located.

Think about it. Why do you suppose modern sails have gone from low apect ration to tall, skinny, high-aspect ratio sails? Because the leech of the sail is not nearly as productive as the area that creates the lift. Jet wings are much more high-aspect say than a DC 3.

Some food for thought. Thanks for listening.
Rick

Just to clarify: Rick is only talking about upwind sailing.

Rick, thank you for explaining what you and Randy use and how you think about it (and thank you to Mary for bringing the topic to your attention).

I am having trouble with this line of reasoning. A stall, the premature separation of flow, creates lots of drag. This drag is lost power generated in the high-lift section of the sail when you look at the sum of forces.
When we stall our mainsail due to oversheeting, we can feel the boat wanting to heel over (due to the extra sideways force created by separation), but it dont want to go forward very fast. Sailing with the mainsail on the brink of stalling on the other hand, is fast in my experience. This is the trim we are looking for and are achieving when the leech telltales flick forward now and then (sail is then having early separation in the leech area some of the time, but reestablish quickly). This is especially so sub-trapeze conditions, in more wind we find it hard to oversheet the main as the wind has enough energy to follow the surface almost no matter what we do.
Who is up for some two-boat testing <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Ashby had lots of telltales and leech ribbons when he won the A-cat nationals, according to the press photos on his web site.



Note that he makes his own sails, so he doesn't necessarily use all of them for sail trim during racing. Some might be there to evaluate the performance of the properly trimmed sail, for modifications to future designs.

Or he use them for downwind trim..

My 1970's era Tornado pintop had rows of telltales, so it has been tried. ;-)

However, it is now generally agreed that they are not useful because they will pretty much all stall with the leading telltalle, with the exception of leech ribbons, which behave differently.

See Frank Bethwaite's "High Performance Sailing", or wait for Randy to publish his perspective. ;-)

P.S.: Has anybody read Whidden's book as a tie-breaker?

I assume you mean upwind, since you hooked the sail:

Sorry to keep beating the Bethwaite drum here in the land of Smyth and White, especially since he's a Skiff (not Cat) sailor, but his flat water light air advice for Cats is to forget about the bottom 2/3 of the sail, as the only significant wind is aloft <5kts. Use a mast head balanced feather (or mast head streamer) to reveal the apparent wind aloft, maintain the upper sail 20 degrees to this apparent wind at all times, even if the skipper has to hand-hold the boom instead of using the sheet. Foot off to get some "reasonable" speed, and then head up as high as you can maintain this speed, footing immediately at any sign of lost power, and continually maintaining upper sail trim. Keep powered and keep moving, because if you stall the top of the sail it will take a long time at these wind speeds to recover (long enough for wind to pass 6 times across the sail front-to-pack). He says the boats that keep moving always win, even if much of that movement is cross wind.

Do you mean Tom Whiddens "Art and science of sailmaking"? Yes, I have read that one as well. Much good information in there, even if it is geared toward monos.

The 6cycles wait is probably to start circulation again. Dont remember if Bethwaite had discovered circulation when he wrote his book.