sailmaking

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301

Your point is that the curvature of the “missing material” between the seams might be significant, I think, and it is valid. And there is at least some validity to saying that the formers have to be beveled. It is interesting to me that formers with no thickness would not have to be beveled, because they would not force a zero curvature in the seams parallel to the luff (or leech - perpendicular to the curvature along the former, anyway). I infer from these two situations that if the formers are sanded on top so that they slope from foot to head as the intended sail shape does that one will arrive at a paneled sail of the intended shape - at least, close enough you can’t tell the difference. Polystyrene foam sands very easily, and I still think this approach would allow one to quickly and reliably put together a form for making a paneled sail shaped just as one wanted, very much as though assembling it on a full-scale “mold.” The only limitations on sail shape using a mold is in the flat pieces of cloth that make it up, and using a broad seaming block has exactly those same limitations, along with some difficulty in learning how to predict the resulting sail shape.

The extreme case of a hemispherical spinnaker is instructive, which is all I think you intended. I don’t believe anyone would expect to make such a sail using formers only at the seams. I also find it interesting to consider that one might use mid-formers between the seams, using a long enough sanding block to bevel the formers appropriately by spanning the gaps between them, so that one was using something very much like a broad seaming block. At that point, though, one is getting close to making the full-scale “mold.” Since polystyrene is so easy to work with, a full-scale mold isn’t especially difficult. The difficulty comes in making and storing molds for several different sails. Several sets of formers would probably fit in a shoe box.

Mike Biggs

302

Oh, I might have missed another item. I never suggested using one former at a time, and if you thought that was what I intended, then there really was some mis-communication. I suggested using the formers on a layout of the sail. Using something sticky enough to hold the panels temporarily in place on top of all the formers, such as masking tape glued on sticky-side up, the entire sail would be assembled before the panels are stuck together using sail tape, as usual.

Mike Biggs

303

Cougar

As we’ve suggested in this thread and elsewhere, we don’t think that we can achieve adequate accuracy when attempting to join seams to the low tolerances necessary on model sails by using patterns generated by software such as Sailcut 4 (or the new Sailcut CAD).

But let me tell about my own sailmaking over this past weekend.

I have been eager to give the Claudio Gadget a try, but have been unable to get comfort over the mathematical relationships between the degree of curve built into the Claudio Gadget, the influence of the outhaul setting, and the desired end result.

It occured to me that, while we don’t think we can use Sailcut 4 to cut and join sail panels accurately on sails of this scale, maybe we could use Sailcut 4 to create a template to “set” the Claudio Gadget curve, rather than the guesstimates suggested previously in this thread. M. Laine has arrived at his own solution, factoring in the relationship between outhaul tension and built-in-camber from foot to head - so why not try that?

So here’s what I did, for a set of Victoria sails I made over the weekend.

I designed my sails on Sailcut 4. I printed the patterns full size.

With Sailcut 4, the upper end of each panel contains the “curve” while the lower end of the adjoining panel is flat. I cut the paper pattern with scissors around the curve of the upper end of each panel. I used this curve as a template to “set” the shape of the Claudio Gadget, using small wedges at appropriate points until the Claudio Gadget matched the curve of the template as closely as I could tell to the eye. Obviously the Claudio Gadget is reset for each panel.

I otherwise made my sails as described elsewhere in this thread.

The result is promising.

For this exercise, I was just interested in investigating the practicality of the approach - the resulting sails have a bit of a rough finish. In particular, working alone, I rather messed up when fixing the luff-pocket to the mainsail (using self-adhesive sail reinforcing material ex GBMY), and have also over-reinforced the head (this is my first set of Victoria sails, and they are a little smaller than the sails I’m used to). The result of my mistakes will have damaged the mainsail shape - but I think the general idea of using Sailcut 4 to create curve templates for the Claudio Gadget might merit a second attempt.

By the way - I was working with cellophane plastic as the sail material. Although fragile and difficult to work with, it is so cheap that I can make “disposable” sails for the purposes of practice and experience.

Although the resulting prototypes aren’t pretty, I will take them sailing this week and if possible, take a few pictures.

One point - perhaps obvious and expected - the curve templates generated by Sailcut 4 for the jib had very little “shape” to them. I consider that the degree of luff sag built into the design of the jib is critical. I made my best guess, and the result, when the sail was hung on the rig, looks OK to the eye. The proof of the pudding will be in the eating. One beauty of making your own mainsail for a known mast, is that you can match the luff curve to your mast curve pretty well.

304

Mike,

I commented on a similar idea a little earlier in the thread. Here I think (about page 27).

http://www.rcsailing.net/forum1/showthread.php?p=23124#post23124

I think that the arrangement of the formers must describe an arc from head to foot if they are to work as a mold. Thus the mold (or the separate airfoil formers with space in between, will describe an arc in two dimensions - not only in the luff-to-leech direction, but also head-to-foot.

This may be what you are envisaging anyway, and perhaps I am just not picking up on it. I think it is perfectly viable. Such a mold will incorporate the bevel effect - so necessary to avoid flat panels joined with a shape in only one dimension from producing a flat result. Any former above of below a given former, will have the adjoining side level with the adjacent former. Thus if there were four panels in a sail, and thus three formers between head and foot, there would be three distinct “kinks” in the arrangement of the formers from head to foot. I probably need to draw a picture to describe what I mean.

By way of observation - the key difference between this approach and that taken by North Sails’ 3DL technology, is that in the latter, the sail material itself is manufactured in it’s final form over the mold, and not applied as flat panel sheets.

305

Hi Murray

Nice approach! I’d be very interested in knowing if the result, as seen in a sail photo (hopefully with the sail hung in a reproducible position in a Claudio-type jig) and as measured by Accumeasure, more or less reproduced the template curve.

I consider that the degree of luff sag built into the design of the jib is critical

Absolutely! Sail photos of the jib with some variations in jibstay tension would show the effect of luff sag on the resulting shape…

306

Ah ha! I knew you would ask for that Lester.

It may have to wait a while. I will need to build the jig in order to hang the sails and take some photos suitable for Accumeasure. I’ve hung the sails on the rig and am keen to get the boat onto the water. As I said - I rather botched up the mainsail in that I managed to crease the luff when applying tape to create a luff pocket through which my luffline runs. This was entirely the fault of my fat fingers and trying to work without help.

I suspect I will be building a second mainsail very soon, and will take the time to build a jig for analytical purposes.

307

I was never all that worried about achieving sails that would not lie flat, if the sails were capable of assuming the shape I wanted via the “mold” I was using. But it is correct that if there is curvature in two perpendicular directions of the filled sail that the sail will not lie flat (neglecting any stretching of the material). I think it is not generally necessary to have intermediate formers, but if one does, the result could be very much like a broad seaming block with a bevel. I think it is sufficient to just have different cambers in the seam formers.

To that end, this morning I made a main for the US One Meter I’m building. So far I have no mast, and have only the basic hull, right off the mold (described in a post to an old thread, German rubber method). All I can do at this point to show that the sail will not lie flat, that it therefore has additional curvature, is to show a picture of the sail not lying flat on a table. I also took a couple of shots of the construction process.

Step 1 shows the formers glued to the sail layout, with masking tape glued to the tops of the formers, both using spray-on adhesive. The polystyrene insulation was not as easy to work with as I remembered, but it does work. Balsa would be easier to work with, I think. The polystyrene sands, but there is also a tendency for the individual spherical “beads” to rip out of the matrix. Further, the resulting formers are flexible enough to distort sideways when the sail material is gently pulled tight. Otherwise, the technique generally worked well, with the masking tape allowing the panels to be positioned and repositioned before beginning to apply the tape to lock the panels together.

Step 2 shows the result after taping the panels together. I think the slight sags apparent on the photo are generally due to the tendency of the formers to flex sideways, such that when I worked from the head to the foot, panels I had completed sagged a little when I moved to the next seam.

And Step 3 shows the sail not lying flat on a table, indicating that the sail is not part of a simple cylinder, but in fact has curvature in two perpendicular directions.

Those with sharp eyes might note that the former at the foot is flatter than at the first seam. I did this to force additional material into the sail at the first seam. I first intended to flatten the sail as I worked toward the head, but then decided I’d increase the curvature at the top, where mast bend would tend to flatten the sail anyway. So the top former has more camber than the next seam down, and probably has the most camber of all the formers.

Needless to say, this discussion I’m providing proves I did not carefully calculate much of anything, so maybe I’m optimistic in expecting the sail to work decently. But I also have little time and effort invested, and I start out knowing that the sail is at least capable of returning to the shape it had on the construction table. Nearly all the curvature in our loose-footed sails comes from the outhaul position, and the cut of the luff versus the bending of the mast can account for much of the variation in curvature from head to foot. I’m more worried about having a baggy main than I am about having one without enough curvature, because even a single panel main can be tuned to work reasonably well.

Mike Biggs

308

A picture is worth 1,000 words!

Thanks Mike.

309

Hi Mike

I was reaching for Accumeasure when I realised that the photo was of your sail draped over the formers and that it didn’t actually have sail stripes to measure against (smile). Would you be able to put stripes on each seam, peg it out (with appropriate outhaul setting), and take another photo or two? It would be very interesting to see how its suspended (ie ‘flying in light airs’) shape relates to the shape of the formers.

310

Hi Murray

Sure, a jig is necessary to get serious about the science, but if you have the enthusiasm, a photo of it roughly pegged out would do nicely to keep us going… (smile)

311

Don’t quite follow what you are asking for when you say “peg it out.” Are you talking about supporting it along the luff and at the clew, with gravity alone to fill out the sail? I’m not sure the Tri-spi 25 I used will drape all that smoothly, and don’t know that I can locate a working portable fan in our home these days.

I plan to put draft stripes on the sail eventually, along with everything else it needs: jackline attachment fittings; head, tack, and clew reinforcements and grommets; and sail numbers. I hadn’t planned to do that anytime soon, but maybe I can speed things up a bit.

May have to spend today helping the wife replant the yard we lost. We finally received the sand fill and grass plugs, and it’s only been eight months since Katrina. Not that we exactly ordered all that stuff the day after the storm passed through…

If it helps, as I taped each seam the two panels involved conformed well to the three formers involved. Because of the lateral flexibility of the formers, panels not involved in the seam tended to sag a little, as did the completed sail when I was no longer applying any tension.

Mike Biggs

312

Hi Mike

Almost. Just supporting it at three points (head, tack, clew) in a roughly horizontal plane, and letting gravity do its work. Pretty much like the Claudio jig, but without the, ah, jig…

313

It’s a no-go, I’m afraid. Adding the draft stripes was easy, with my trusty Sharpie. And the battens I forgot to mention when I wrote about all that still needed to be done before it’s a finished sail weren’t much more difficult. They were especially necessary because the sail material still wants to curl up in the roll it was shipped to me in.

But masking tape, clamps, and odds and ends of lumber did not allow the sail to take up anything like a natural shape. The sail does not yet have reinforcing patches at the head, tack, and clew, nor grommets. My attempts to clamp the corners to the edges of triangular blocks almost worked, but not quite, and clamping them to flat blocks definitely distorted the shape.

I’m not familiar with the Claudio jig that I’ve seen mentions several times, so I’ll have to take your word for no support along the luff. In my attempts to clamp the sail at the corners I pulled a hard line from head to clew before I lifted the middle of the sail off the board. Maybe when I get the reinforcements and grommets installed, I can try again.

I’ve tried to be careful when I describe this technique I put forth not to claim that the sail will take up the shape it had on the forms, only that it is capable of taking up that shape. I don’t see that this is a particular drawback to the technique as it appears to me to be universal. The actual shape taken up by any sail will always be strongly conditional upon all the usual factors: luff tension, vang adjustment, outhaul position, mast curvature, and the like.

Mike Biggs

314

Hi Mike

It is illustrated in an earlier page in this thread.

315

I wish that were true. I looked once and there was a link to a page where he was describing it on a bulletin board in a foreign language (french I believe) but it was all removed. And it made reference to it was moved to a book. I think it is cool that he got a book out of it, but I don’t believe it is out there anymore. If I am wrong, please point me it to it.
Bob

316

Within this thread, go to post # 213. It has the photo of the jig.

And look at posting #280 - which shows the jig with a sail hung on it.

C’est marveilleux!

317

Hi Murray

Thanks for finding 'em! I also have a photo of the SAILSetc jig on my Web site, in case that helps anyone: http://www.onemetre.net/Race/Outhaul/Outhaul.htm

318

I uploaded a second reply with the pictures, but alas, either I hit the wrong button or it got lost in the forum move. So here’s Attempt Two.

I had some difficulty getting a good placement for the tie points. This was about the best I was able to do. I tried to get the camera in the same relative position as when I took the pictures on the formers, but no guarantees.

Since I took the picture of the US One Meter sail, I also made a new main for my Marblehead using the same technique. As for the One Meter sail, I put more curvature near the head, figuring that it needed more because it derives less benefit from the curvature induced by the clew location, and because additional mast flex would tend to flatten the sail more. Unfortunately the new Marblehead main retained way too much of the curvature in the upper third of the sail, so I’ve since pulled the seams apart and adjusted them. I haven’t had a chance yet to see how the sail works after the readjustment. The technique of building the sail on formers laid on top of the sail plan seems capable of building in considerable curvature - although it is always possible it’s more due to a poor taping job on my part.

That said, I’m thinking about making myself a broad-seaming block. I think the advantage of building on formers on the sail plan is that you may come closer to seeing what you’ll get beforehand. The broad-seaming block is probably a little faster to use, since individual formers for the seams take a little time to make, even when using foam insulation.

I’ve included a picture of my unlimited class R/C boat. Okay, okay, it actually is not an R/C boat, but an almost-bluewater cruiser. Katrina unloaded about a 100 yards of marsh grass in the bayou between me and Lake Pontchartrain, so this boat isn’t going anywhere anytime soon. For anyone interested in seeing before and after pictures of our home and boat, they’re on my website: http://webpages.charter.net/mikebiggs/. Another website has write-ups from some sailboat cruises, and the like:
http://home.earthlink.net/~mikebiggs02/.

Ok, this time maybe I got the pictures in!

Mike Biggs

319

But the pictures failed to upload, and I didn’t notice the failure. Still can’t get pictures to upload. I’ll try to send the pictures along later. Sorry.

Mike

320

Test - using imageshack. http://imageshack.us/

Mike - you might want to try this. The image is hosted by Imageshack (free) and you just post the link provided into the message.

By the way - the photo below is of the sails I made last week using the “Claudio Gadget” as explained in the earlier post. The jib came out pretty well. the main has some issues - accentuated by the inadequate boom vang tension in the photo below (too much twist).