Making the junk sail – part 2 – camber choice

I selected the following figures for camber and jiblet angle of incidence. These are based on looking at the graphs of the shapes, gut feel and hope.

The Owl sail has reducing camber as the panels go up the mast. I didn’t do this on this sail on the parallel batten panels due to lack of time – it is probably a good idea and I might regret it later. Or maybe not – we’ll see. The main focus is getting this sail finished on time!

Jiblets panels all have 16º angle of incidence. The camber is as follows from the bottom upwards:

  • 10%
  • 10%
  • 10%
  • 10%
  • 8%
  • 4%

The main panels have similar camber figures. Of course they have 0º angle of incidence. The difference is that I remembered something from the Owl sail: when the camber changes the top of one panel is no longer the same length as the bottom of the panel above it. Thus it is better to keep the same camber curve along a batten both for the panel above and below the batten. I did have to do some fudging of the jiblets to correct for this, but it was more important with the greater length of the mainlets.

Thus:

  • The parallel sided panels are all 10% camber top and bottom;
  • The very top panel is 4% camber top and bottom;
  • The second panel down (the yellow one) has 4% camber at the top and 10% camber at its bottom edge. We’ll see if this is visible when the sail is up – I can’t see why it would matter.

Even using the same curve there will be a bit of difference due to inaccuracies when sewing along the panel edges, but this can be taken up in the hem allowance at the trailing edge.

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