Stuart,

I have been thinking along similar lines. It would be interesting to simply rip a panel from luff to leech mid between the battens and then insert a lens-shaped piece of cloth there. If you look up JRA Newsletter 30, you can see how I made a test panel before daring to cut a whole sail with cambered panels.

For the sake of science, I suggest someone make a similar, perfectly flat test panel with that lens added, preferably in a contrasting colour. If it turns out to work, it will be a quicker mod to make than the one you suggested, and a lot quicker and cheaper than making a new sail.

Even more; then there would be hundreds of flat HM-style sails out there waiting for that lens modification. However, one must remember to strengthen the modified sail with a boltrope around it, since the vertical loads have moved out to the luff and leech.

If the method does not turn out well, then there is the tuck (fold) method, shown in NL 26. This adds a bit camber, not so much, but better than a flat sail.

Arne

Sunday afternoon looking at pictures of junk sails on the web site and I was wondering if, assuming you had an old but serviceable flat junk sail it could be modified to a cambered sail using the 'shelf foot' method by cutting two segments either side of the battens of the existing sail and fitting a new flat section to the two edges of the segments, and adding new luff and leech tapes, thus saving making batten pockets etc.

Thinking about it if it was me I suspect that the most difficult part would be cutting into the perfectly good sail, but it would be a cheaper way of trying a cambered sail without all the work of making a completely new one, or if it turned out to be a disaster giving one experience for the making of a new one :)

Looking at pictures Arne's sails it is surprising how close their shape is to an elliptical planform.

 

Antoine Maartens wrote:

A sewing machine - my kingdom for a proper sewing machine!

Mine was an eBay purchase. I just searched for "sailmakers sewing machine" until a suitably sturdy and simple one came up (a couple of weeks). There were a few to choose from. It needed some minor repair. The machine was £70 and repairs £60 I think, at a local sewing shop.

You'd be welcome to borrow it. Just sail over!

Annie Hill wrote:

thousands of happy miles with sails sewn with straight stitching!  Zig zag is a luxury (that also disguises the wobbles in your sewing).

Ok, ok, Annie, you may be right, but I have a star argument for zig-zag machines:

If one gets a seam wrong, it is sooo much faster to rip  a zig-zag seam than a straight one...

Arne

Antoine Maartens wrote:

A sewing machine - my kingdom for a proper sewing machine!

You live on the European mainland, Antoine.

I bet there are thousands of good old sewing machines around, like my portable Pfaff 360 from the early sixties .These are seriously good. Model 260 is about the same, I think, but without the fancy pattern equipment. All you need is a stout machine that can produce zigzag seams.

Arne