I was going over the sails I got with my Pacific Cat this morning, finishing up my shopping list for when I hit town today. New headboard, check, new zipper for the jib, check.
That's when it hit me: There are NO telltales on any of the sails. None. Three sets of telltales, check!
But now for the fun question: I've got a couple of rough guides for setting up telltales on a cat. Phil Berman's book and Rick White's book have sections on this. But it's always fun to hear people's philosophies on where they like their telltales.
If you had a complete do-over on your telltales, how would you set them up?
This boat has one headsail, a genoa that looks like it has between a 5-10% overlap. It has two mains. The smaller of the two is a high aspect main that resembles a modern cat mainsail. The larger of the two is quite a bit larger, and is closer in aspect ratio to a monohull cruiser like a Catalina 22. Both are fully battened, as cat sails should be.
I'm trying not to wind up with a sail that looks like a shag carpet, but I ordered 42 telltales I can spread between the three sails. I hope to wind up with a couple of spares to stick in the ditty bag.
Tom
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Tom Benedict
Island of Hawaii
P-Cat 18 / Sail# 361 / HA 7633 H / "Smilodon"
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Telltales - Do-over!
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Posted: Mar 31, 2012 - 01:09 PM
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Posted: Mar 31, 2012 - 01:41 PM
i do 3 on the main...low, mid, and high...not on the far ends...8-9" from the mast. 2 on the jib not on the ends but kinda on the thirds 8-9" from the forestay. you get a decent picture of the wind for a small sail set. i don't sail without them! i use a bridal windvane because it's always in my siteline and you can make faster adjustments that way.
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bill harris
hattiesburg, mississippi
prindle 16- "BLUE RIBBON"
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Posted: Mar 31, 2012 - 04:51 PM
I use a bridle windvane also but totally independant of the tells - one for gross wind direction and one for trim
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North Carolina
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Posted: Mar 31, 2012 - 05:44 PM
I like a bunch about a foot back from the luff up and down the sail. I'm sure I'd benefit if I put any on the leach but I never look there, so why bother..
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Rob
OKC
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Posted: Apr 01, 2012 - 12:40 PM
Good food for thought. Thanks, guys. A lot of what you said jives with what I was thinking, just remembering how things were set up on my old Prindle, and from what Phil Berman and Rick White had in their books.
For now this is where I'm planning on putting telltales:
The ones on the foresail are pretty self-explanatory. The lower two near the mast are to check the slot. The upper two near the mast are to sample clear air above the slot.
I'd like to go ahead and stick some on the leach. Here's my reasoning: First, I've got two mains for this boat that are wildly different. So the twist is likely to be different depending on which sail I have up. Second, my traveler can be sheeted in past centerline, to windward. There's really no indicator on deck to let me know if I've done this, so chances are good I'm going to hook my leach a lot before I get a handle on this.
The upper telltales on the leach are to see how air is coming off a twisted sail. The lower ones are to see if I've sheeted the traveler in too far when I'm sailing close to the wind. I have no idea if this will prove to be useful, but it's a thought. In any case I have enough telltales coming to change my mind and lose or move a few after the fact.
I'll let you know how this works out on the water. Meanwhile, I need to go finish compounding my hulls before the sun gets too high.
Tom
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Tom Benedict
Island of Hawaii
P-Cat 18 / Sail# 361 / HA 7633 H / "Smilodon"
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Posted: Apr 01, 2012 - 12:47 PM
ARGH! Sorry, double-posting...
I had a bridle vane on my Prindle. It worked GREAT for just the reason you mentioned, coastrat: it was in my field of view all the time, and I could check the entrance angle to the jib against it as a sanity check.
The Pacific Cat 19 doesn't really have a front bridle. It's got a crossbeam with a pivot for a roller furling foresail. If I stick the vane under the crossbeam, it's below deck level. I can't really attach it to the forestay, either, since it's attached to a roller furler.
I'm thinking of making an arm out of 1/8" stainless that'll stick out in front of the roller furler at a 45 degree upward. This should get the vane clear ahead of the foresail, above the hulls, and just below the foot of the sail. At the forward end of the arm, I'll bend it up to vertical. A shaft collar just above the bend and a second one at the upper end of the arm should provide a good pivot for the vane. Not exactly jeweled bearings, but pretty simple.
Tom
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Tom Benedict
Island of Hawaii
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Posted: Apr 02, 2012 - 08:54 AM
leach tails rock! I look at them often. -
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Posted: Apr 02, 2012 - 09:10 AM
how does one tune with leach tails? Never had them. -
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Posted: Apr 02, 2012 - 11:04 AM
I had never had leach tells because the standard Hobie mains don't come with them. So when I upgraded to a Pentex Square-head main I only put the "black beauty" tells along the luff like the Dacron Hobie sails.
This turned out to be a big mistake. I didn't realize how much different the sheeting/traveling would be with the new sail and I was cranking hard on the mainsheet just like I did on the Dacron. That resulted in stalling the main and that is the reason for using leach tell-tales. By making sure that the leach tells are streaming you know that there is attached airflow over the main, which means you are sailing the sails as they were designed and getting full power.
I actually hardly worry about the main luff tell-tails because they are harder to see (have to looks straight up) and aren't exposed to as much apparent wind as the luff.
You'll drive yourself crazy trying to get all the tells streaming at once, but here is a tip I got that I can pass on.
On a day with steady wind, sail close-hauled and use a GPS to monitor your speed. Vary your course up and down wind by a few degrees watching the tell-tails and having the crew read out your speed. You may find that the ideal course for "velocity made good" upwind has some combination of inside and outside tells streaming. Do the same thing sailing downwind at 90 degrees apparent to figure out your tells and traveler settings.
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Damon Linkous
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Posted: Apr 02, 2012 - 11:30 AM
Thanks for the insight Damon, I'll give it a shot. -
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Posted: Apr 02, 2012 - 11:52 AM
a friend of mine used to fly a flag behind his main.
He said he never realized how bad he was trimming till he looked up and the flag was flying towards the mast... not behind the boat...
Edited by MN3 on Apr 02, 2012 - 11:52 AM. -
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Posted: Apr 02, 2012 - 02:14 PM
Damon do you have source for Black Beauties. I have found that they can be very difficult to come by? I really don't like the Red/green ones that much
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Dustin Finlinson • Magna, UT
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Posted: Apr 02, 2012 - 06:12 PM
i do the ole sheet in til they are all flowing back except the top inside one which is flipping up for the main. then sheet in the jib, on my p16, jib setting has the most to do with boat speed-slight adjustments will greatly affect the boat speed. then i use the rudders/windvane to sail the wind and keep teltales flying right unless i'm cruizing then i don't care i just drink beer!
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bill harris
hattiesburg, mississippi
prindle 16- "BLUE RIBBON"
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Posted: Apr 03, 2012 - 01:22 PM
I'm pretty sure there were times on my old P16 when I felt like I was flying, but was likely standing still because of how I had the slot set. This is probably old hat, but I found something neat the other day. There are a whole slew of speedometer apps for smart phones that will give your speed in kph, mph, and knots. I downloaded one and tried it yesterday. I was driving and my son was reading out the speed in knots. A little laggy, but certainly good enough to be useful in tuning a boat and tuning a skipper's eye for telltales.
I'm about two weeks from getting my boat out on the water. Can't wait to give this a try.
Tom
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Tom Benedict
Island of Hawaii
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Posted: Apr 03, 2012 - 04:59 PM
Hi Tom,
The truth about telltales can be found here:
http://www.arvelgentry.com/tuft.htm
but it's a lot of work and frustrating if you thought you knew the truth before.
The app I use on my phone is MotionX-GPS. It was only a couple of bucks, but has a lot of functionality. It will work in walking, driving or sailing modes, and has free access to NOAA marine maping data.
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Posted: Apr 03, 2012 - 05:15 PM
looking at your drawing
you might want your 4 mainsail luff telltales at least 2 foot, 60cm back from the mast
as otherwise they will be badly affected by the eddies off the thick mast -
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Posted: Apr 03, 2012 - 05:51 PM
Bob, that was very VERY interesting. Thanks for posting that.
Last year some of my co-workers and I spent some time using the water tunnel at the University of Washington doing airflow analysis on a scale model of our building. We couldn't get anywhere near the Reynolds number we needed in the water tunnel (though it proved to be the tool of choice for flow visualization). So one afternoon we took our model and stuck it in the University's smaller wind tunnel (not the Kirsten Wind Tunnel, which is their main one.) Prepping for that afternoon involved (you guessed it) taping gobs of little telltales all over the model.
When I clicked on the link you posted, I thought, "Hey, that looks like our model!" Nope. It's a sectional view of a sail. But the tufts sure looked like the ones from our model!
I've got enough telltales coming to give Gentry's system a try. Have you tried it on your boat? I'm curious how effective you find it.
And erice, thanks for pointing that out. Yeah, I probably do want to move those back.
Tom
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Tom Benedict
Island of Hawaii
P-Cat 18 / Sail# 361 / HA 7633 H / "Smilodon"
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Posted: Apr 05, 2012 - 06:08 PM
This conversation could get real thick real quick, so I'll speak in generalities here in the forum. Arvel Gentry was the first person to use known physics and engineering to explain how sails (like wings) work. In the following thirty years only Olympic and world class sailors (read America's Cup) have really caught on to his gift to sailing.
The Gentry Tuft system uses short telltales (tufts) that start right next to the luff tape on the jib, and has three or four 3" tufts in a row, end to end trailing back. He does this to identify excatly where in the stalling/luffing predicament your head sail is upwind.
The eddies erice is trying to aviod is exactly what Arvel Gentry wants to look at so he can keep the main sail as powered up as possible, though he does use longer telltales set back a bit further from the luff compared to the jib. We have to keep the mast at it's proper rotation on a given point of sail to ensure that the mast is working with the sail and not just in the way. Accurate mast rotation is hard to set well on most of our (old) beach cats, so we are in the position that erice describes- having to look at telltales further back.
I am currently doing the research I needed to place tufts on my sails for the most benefit. I can post progress here in the forum. It involoves measuring how much list I have with one hull just kissing the water upwind while sailing double trapped, and then projectoing the resulting 3D flow of air on the sails with a laser level to map the true airflow- placing the tufts and telltales on this line.
By coincidence, Arvel Gentry was an engineer for Boeing in Washington while doing his wind tunnel research.
Sheet In!
Bob
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Posted: Apr 05, 2012 - 07:29 PM
You're right, it could get pretty thick pretty fast. But that's actually why I started this thread before sticking telltales on my sails. I wanted to get input.
It's funny seeing how each skipper looks for different things in their telltales. I just finished re-reading Rick White's "Catamaran Racing" book. If I remember right, Rick White only ever really talks about telltales on the jib. Some of the other authors mention mainsail telltales, some even mention leach telltales on the main, but some of those don't mention telltales on the jib. Piecing together a good comprehensive plan for telltales is a little like trying to reverse-engineer the jib sheeting system on the P-Cat.
So no, I appreciate your posting about Arvel Gentry's system. And I look forward to reading about your experiments.
Your second to last paragraph says something that caught my eye: So your plan is to measure the angle of your boat off of vertical while at the best attitude of sail (windward hull just kissing the water, I'm guessing transoms just coming out of the water), and use a laser level to indicate a level-with-the-water line across your sails (jib and main, both?). This line across your sails would be the line along which you'd want the 3" end-to-end Gentry telltales to be placed. Is that right?
Please do let me know how this turns out. This is really intriguing.
Tom
P.S. Wait a sec... Arvel Gentry was with Boeing in Washington? Cripes, he may have used the same wind tunnel I did. THAT'S COOL!
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Tom Benedict
Island of Hawaii
P-Cat 18 / Sail# 361 / HA 7633 H / "Smilodon"
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Posted: Apr 06, 2012 - 01:30 AM
Tom,
You are reading White's yellow paperback, not the blue (older) hardback version? I only ask because someone first gave me the blue one and I threw it out after the first few chapters. The yellow one is still good information, decades later.
Arvel's style is to put telltales in certain places on both sails, sail upwind and trim the jib lead blocks first to get it to luff top and bottom simultaneously, then do the same thing for the main, shaping it with the downhaul, outhaul and sheet. All this is done while maintaining that perfect angle to the wind of just beginning to stall the first tuft.. He also pays strict attention to the slot.
It is complex to visualize while reading, but in practice it comes together surprisingly fast. He has a series of four articles he published in a magazine that I can send you in a pdf format if you like. Just send me a private message with a regular email address for you.
As for the laser-level thing, you are right on the nose. Strong work on your part, deciphering my ramblings.
I had the same thought when I read about your work with the wind tunnel. The Boeing shop is just north of Seattle, and I'm betting yours was down the road a bit south of Seattle. Considering the availability of wind facilities when he was doing his research, you and he may have stood in the same place. Small world.
I am pa'u hana, my friend!
Bob
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