I have watched most of Karl’s video.
I don’t think that his findings from his little wind-tunnel test of small scale models is enough to draw any conclusion:
- · When sailing a real boat fully close-hauled, say at 30-35° from the apparent wind, the main contributor to heeling the boat is actually the sail’s lift. The drag of the sail mainly slows the boat down. When heading closer and closer to the wind, the driving component of the lift rapidly shrinks until the boat stops.
- · Karl mentions that the slotted sail will have twice as long leading edge. Sorry, that doesn’t help. What matters is how much the total sail deflects the incoming wind. Big deflection angle gives much lift at the cost of relatively more drag. Little deflection (less camber or angle of attack) gives less lift and even less drag. The result is better lift/drag, which is useful for upwind work.
- · Size and aspect ratio matter. The total planform of any sail (and wing) has a big influence of the L/D ratio. Taller sail, higher L/D.
A few days ago, Karl sent me the shown JR sailplan and wanted me to have a look. It appears to be based on a Johanna 70 master sail with AR=2.10. This sail shows how much area and luff length this sailplan can produce for a given mast length. I am biased, of course, but I think that looks good.
However, Karl has already fitted a Ljungström rig, which is almost ready for test-sailing. I suggest he does some test-sailing with this rig first, and uses its performance as a reference if he later tries a JR. My hunch is that the Lj-rig is second to none for upwind work.
Arne
(Full size diagram at Arne's sketches, section 9-17...)