Bert Qui wrote:

Slieve McGalliard wrote:

The last thing I want to do is to discourage anyone from experimenting, as who knows, they might just find the best answer or development stage to the next eureka moment. However – I believe you have to visualise the final 3 dimensional shape you are trying to achieve. I think you want the desired camber shape from luff to leech over as much of the whole height of the panel as you can get, and to bring the cambered shape in towards the stiff battens then you seem to need the surplus material close to the batten and not near the centreline of the panel.

Rather than just wonder about it, why not take a piece of paper and cut our the panel shapes and Sellotape them together and to a pair of broom handles or some other 'battens'. As David mentioned, I've tried this with the centre seam round just in case I'd missed something and wasn't surprised that I didn't like the panel shape at all.

Just try it and let us know how you get on.

Cheers, Slieve.

The truth about doing a cambered sail or follow the masters...

Slieve mentioned in the summer the odd sailshape of my main, when we had discussed the shape of the  jibs of Runa. I have had now time to relook over my sail and found that the toppanel should be improved. While I was thinking about how to do this and for the whole sail yet has been partly  spread out in the workspace I remembered the discussion about the main and made the decision to test the difference of the barrelcut and the middleseam method.

But first back to history:

In order to save cloth and time I decided to make the main panels out of big pieces of cloth (cloth width was 1,60 m). So I took the barrelshape approach, but instead of combining the panels along the batten I made a curved seam in the middle of the panel. So I had a straight line along the batten and no wrinkles I assumed. You can see here a schematic drawing: | = batten, )(= middleseam. So it looked like this |][|. All measurements for the barrelcut had been the same, so mathematically everything is wright, but geometrically there is a big difference, see the explanations of Slieve and the photos of the test in my album. Now, do I have to make the whole main panels new? No, I just have to shift the middleseam which is the combined and curved line of the panel to the battens and the upper half of the most upper toppanel will be sewn to the lowest part.

I have uploaded some photos which show the difference in a very drastic way.

http://www.junkrigassociation.org/Sys/PublicProfile/
37012360/PhotoAlbums/77689656

Bert

I quite agree with Arne that is is well worth making a large (half size?) test panel before committing to the full rig, but to me the advantage of paper test panels is that at a cost of some lengths of masking tape or sellotape, yesterdays news papers and less than 15 minutes of my time I can see how some wild idea would look in 3-D. In an hour you could test different 4 ideas, and trim and re-tape them to subtly change their parameters. If the panels are laid flat, gravity will help the paper fall into the camber shape. Even if the final cloth to be used has some stretch the paper will still give an indication of how it will look.

David T is right is say that most spinnakers are built with radial heads or as tri-radials these days, and there are good reason for this. David W's reasoning is good, but 'Cross Cut' spinnakers are not the simple sails that they appear to be. I have seen an amateur built cross cut spinnaker with parallel horizontal panels and the shape being made in the centre seam. It was awful, with a hump down the middle and would not set except on a dead run.

I have drawings and instructions on how to build a 'Horizontal Cut' spinnaker, and it is probably the most difficult 'chute to get right, hence the professionals moving to the easier radial cuts. Each and every horizontal panel is individually broadseamed at the top and bottom of each panel and at both the leech and the centre-line ends, and it is clear that if these are not right the sail will be a disaster. Getting the centre seam wrong can also ruin an otherwise good set of panels. I guess that to get one right there would be a lot of re-trying and re-building. No sailmaker has time for that.

Round and broadseam techniques are adequate for the mild cambers of Bermudan panels, but for the more pronounced (aggressive) cambers across the height of junk panels (perhaps about 25%) the broadseam has to be significant, or a better way found.

I'm happy with the round and broadseam main panels I've built, but am increasingly drawn to the angled 'shelf foot' method, as it effectively uses seams like the important tack seam in a Bermudan mainsail where major shaping can be done. The beauty of using the method with the junk panels is that the 'tack' seam runs up from the bottom luff corner and also down from the top luff corner, so the all important luff area can be well shaped. The problem with the method for a main panel is getting the panel length along the batten and length round the camber centre-line properly matched and is a calculation which cannot be ignored.

Cheers, Slieve.

I rather suggest that one makes a full size, or at least half size test panel, using some cheap tarpaulin or whatever (but not stiff sail cloth or paper). This lets one experiment with round, broadseams , shelf foot, or whatever method one has  in mind. By taking the panel outdoors, the wind will fill it and show its shape.

The photo below shows a test panel I made to learn more before constructing the blue, cambered sail for Malena (JRA NL 50, p.31). These days I would rather attach the test panel’s edges to the ‘battens’ in such a way that I could adjust tension easily and see what happens. On the shown test panel, I just tacked the panel to the frame. However, I at least got an answer on how much camber I could expect to get in the finished sail. I was aiming for 10% camber, but when the test panel only showed 8%, I decided that it was enough. I just built the sail with the same round of 20 cm, and could later measure the same camber in the sail, about 37cm, or 8%.

This full scale panel will also teach one a bit about the sewing process as well, which can be useful to a beginner.

Arne

Enlarge the photo to maximum to see more details...

The last thing I want to do is to discourage anyone from experimenting, as who knows, they might just find the best answer or development stage to the next eureka moment. However – I believe you have to visualise the final 3 dimensional shape you are trying to achieve. I think you want the desired camber shape from luff to leech over as much of the whole height of the panel as you can get, and to bring the cambered shape in towards the stiff battens then you seem to need the surplus material close to the batten and not near the centreline of the panel.

Rather than just wonder about it, why not take a piece of paper and cut our the panel shapes and Sellotape them together and to a pair of broom handles or some other 'battens'. As David mentioned, I've tried this with the centre seam round just in case I'd missed something and wasn't surprised that I didn't like the panel shape at all.

Just try it and let us know how you get on.

Cheers, Slieve.

David Webb wrote:

I have noticed that there have been numerous comments on darts and wrinkles having to be included/dealt with on cambered sails that are sewn with the cambered edge sewn to the batten pocket.

I wondered if anyone has considered/tried sewing the batten pocket into the middle of the cambered panel and then sew the cambered edges together midway between the battens?

Has anyone any thoughts on this suggestion??

Is this what you're thinking of? Seems to exactly describe your paragraph 2 above. I have not tryed the method.