Sail patch sizes and sailing with telltales

Hi MIK,

I have the floor of our living room covered up with all the parts for a new sail for my narrow Quick Canoe. It is almost twice the size of the previous sail, from your Drop-in Sailing Rig. When I made the 21 sq ft sail I consulted with you to get the rounding right but I forgot to scale the patches... I just used the same size patches called for in the 89 sq ft PDR lugsail plans. That coupled with a splice of material, lots of fiberglass carpet tape and its small size caused that sail to have an extremely stiff luff. This time I am using guidelines form Sailmakers Apprentice and trying to get the reinforcement patches scaled better and the reef nettles elevated properly.

I noticed that Andy Linn used patch sizes directly from your 89 for his
76. That worked out fine for him since it was only a 15% variance.
My 21 (with the overly stiff luff) was a 76% reduction from the 89, and this new one (at 41 sq ft) is about half way between, so I am trying to scale everything including the flex in the yard and boom.

Sailmaker's Apprentice recommends that the largest corner patch should have an inch of edge for each foot of material along that edge and that each patch should terminate at least an inch from any other patch. I wonder if 10% might be close enough and work more handily with metric measurements.

Andy brought up that Sailmaker's Apprentice does not deal with polytarp which set me to wondering if these rules of thumb apply and if so, what about the different weights of polytarp?

I know that's a lot of questions for one post...but it's a rainy day! :)

Paul

--
Mount Storm!
Mount Storm Windmill Joust

Fifty-eight pieces to sew up into a sail.

http://farm5.static.flickr.com/4141/...5ebf7075f8.jpg

Lots of pieces for the new sail. on Flickr - Photo Sharing!

Hi Paul,

With our sails we started from our experience with dacron sails, built the PDR sails out of the cheap polytarp and saw how they held up then modified the construction again to cover the weak points.

If i had some regular sailcloth floating around when building a polytarp sail i would be very tempted to include it in one layer of the corner patches. Polytarp alone really does rely on lots of layers to reduce the distortion at the corner eyes.

As far as patch sizes ... I have seen so many different variations that I doubt that 10% makes any difference whatsoever.

A large factor in the stiffness of Andy's sail may have been using the glassfibre tape as a reinforcement. If the sail is properly sewn then there is no need. The 89 made as per the instructions is not particularly stiff if made out of a 3oz polytarp, which is about double the weight of the super cheap blue polytarp you buy at a big box store. If he sewed it and added the glass fibre tape, the stiffness was added at that point.

You have to consider the purpose of the book too. It is to give a guideline that will do in most cases - so will be on the conservative side if it is well researched.

I am not sure ... but if it is the book that talks about roping around the whole outside perimeter of the sail then it is somewhat anachronistic. But should be OK for corner patch calculation - but for the polytarp I would expect you would need 2 or three layers of corner patching. the main thing is that the first patch is not too small.

Then the bigger ones will be an OK size. I think the minimum 1" step between patch sizes sounds too small and will result in the largest patch being too small unless the first one is quite large.

Reef eyelets in the body of the sail have really changed function compared to the era of the Rigger's apprentice, except maybe for ocean going cruisers. They are really just a method for bundling up the excess sail area so it doesn't get in your way and often shockcord (bungee) is used for the reefing lacing.

That way if one of your main reef lines break the reef points won't rip the guts out of the sail as they have been tied off with a shock cord wrapped spirally around the boom.

I would guess the riggers apprentice says that there has to be many more reef lacing eyelets than really needed. Probably two is enough if you use the bungee method.

Best wishes
MIK

I added a few photos of the new sail and measurements of the bend in boom and yard: Flickr: helbert.paul's Photostream

The smaller old sail never did luff because it was so stiff from all that fiberglass tape. This sail has very little of that. One strip along the edge of the luff and one around the perimeter and a few spots to hold for sewing. Tomorrow's forecast for my nearest lake is F2 winds. This sail is twice as big so four times the force.

MIK, last year at Allatoona, you went around and affixed witnesses (strips of polytarp sail material with double stick tape) to the leech of sails. How high up the leech (as percentage) were you placing them? What is the way to use them effectively? If it wraps around, I need to let out the sheet until it flies out behind the sail? Is that right?

Thanks,

Paul

They ended up being too stiff paul.

Replaced with something lighter it works really well.

Basically if you pull the sail on too tight the ribbon will stop flying and disappear around the back of the sail.

The optimum is usually to have it flicking around the back about 5% of the time but mostly flowing nicely ... just an occasional flick out of sight.

This is only true when you have the airflow split down both sides of the sail - so upwind and reaching.

When the leach ribbon wont' fly and the boom is already out at 80 or 90 degrees then the airflow is stalled, so the ribbon won't fly whatever you do.

MIK

I found a couple of articles which others might want to study:

Telltails and Sail Trimming
On the Wire - Feature

Thanks!

Howdy Paul,

Sailing with telltales is really useful for learning about how the sail works.

In the past people only were able to see if the sail was luffing or not. Then telltales in the body of the sail started to appear.

Finally the leach ribbons appeared.

I think after some time of sailing with telltales in the body of the sail plus a leach ribbon or two that for a cruising/racing attitude you can get away with just looking at the luffing and use a couple of leach ribbons as well.

That would be my minimal setup. The second article above mentions the leach ribbons but only in conjunction with twist.

That is true, but also they are the only guide for how "powered up" the sail is. The normal way to get the sail fully powered up is not to have the leach ribbons flying all the time perfectly, but to tighten the sail a fraction more so the "flick" to the back of the sail about 5% of the time. If it is more than this the sail has stalled or is too close. But if they just flick back behind it means that there is a little eddy at the back edge of the sail but the air is still flowing smoothly over the body of it. The little eddy forms just before the sail stalls out completely ... when maximum power is developed.

If the flicking behind starts to get up to 10% of the time you need to ease the sail or point higher.

With very high pointing and fast boats you might not want it flicking around the back at all, but for most of my designs you do.

When you want to start getting rid of power you ease the sail a bit and the flicking stops, reducing power but not increasing drag, then ease more and the sail starts luffing which reduces power and starts creating some drag.

Best wishes
Michael

I read that using thin wool yarn is the way to go. Now I am wondering if "wool" means wool or are they using the term generically. Would synthetic "wools" be better or worse than real wool for telltales? One of my daughters is an expert knitter and could bring me a bit of whatever I want when she comes to the Mount Storm Messabout in two weeks.

Anybody want to share experience making telltales?

Tnx,

Paul

Mount Storm! Mo Wetta - Mo Betta!
Mount Storm Windmill Joust
Larger sails, smaller boats!

Paul, synthetic yarns will dry faster, which is a good thing. Any yarn can temporarily get snagged on nearby stitching, so it's wise to keep them away from seams as much as possible.

Some people use narrow strips of colored nylon sailcloth -- or even old magnetic recording tape. CD's and DVD's don't seem to work as well, for some reason ... ;-)

Grant

Quote:

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Is it a British article? The Commonwealth word for "yarn" is "wool." I'll bring a variety (to the Mount Storm Messabout) and we can do some testing!

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--Edith, my knitting daughter.

So, what do British, and their Commonwealth descendants call the wool shorn from sheep?

I second the tape suggestion from Old Yeller - I find tape from old music cassettes works really well. Stays dry, does not stick to the sail & is light enough to fly in a very light breeze. A 90 minute tape will last you for years.

Also I tie some tape to the shrouds for apparrent wind indication.

Perfect from Old Yeller. Thanks Grant

I do use spinnaker cloth for leach ribbons as I find the cassette tape a bit hard to spot as a leach ribbon and it can stick to the sail for a long period if it gets wet, whereas a sythetic wool will dry out sooner or later.

MIK

Hi Everyone,

It seems to me that recycling the tape from old VHS or even Beta video cassettes ( if you can still find any ) would at least be more visible as telltales, as they are about 4 times the width of audio cassette tape. :2tsup: