Hi Jamie
How much camber is too much for the jiblets and/or what is the supposedly suitable range?
You will see from Slieve’s notes that the camber for Poppy’s jibs was 7% and the sheeting angle was 8 degrees. Subsequent development has seen these number increased.
Slieve reported that he was pleased with the way Poppy sailed, so I suppose we can say that 7% camber and 8 degrees sheeting angle is at the lower end of what is “supposedly suitable.”
I think on the first sail for Amiina these numbers were increased. By the second iteration of Amiina’s sail, the camber of the jibs had been increased again, to 10% camber and sheeting angle 12 degrees.
Here is what Slieve wrote to me: “Yes, the latest thinking is 12° sheeting angle and 10% camber for the jibs, and 7% camber for the mains. As to whether it is better than the earlier figures we cannot be sure, but in theory it should be better and there are no stalling problems. Even with the 'blunter' entry the boat still points well so there must be more 'upwash' which is desirable, and there seems to be more drive into a seaway. If building another rig for myself I would certainly be looking at even increasing these numbers, but for the moment these numbers are known to work well.”
I used 12 degrees and 10% camber, and 8% camber for the mains, and its fine, but sometimes in light wind the jibs don’t inflate as nicely, but Amiina's look good in the photographs, so maybe that might be my poor sail-making. Unlike a conventional jib, there is no sheeting tension and the little panel just has to inflate and find its own shape. I notice from photographs of Amiina that they are using little leech battens and support strings so I wonder if it is near the limit of what is practical.
Should the sheeting angle and camber make the leech of the jiblets fly so far from the battens that the luff goes past the mast even when it's on the lee side (to make sure the air flows freely from the slot to the lee side of the main) - or not? I am sorry, I don’t understand the question. I have not paid any attention to the so-called “slot effect” and I am not sure if it even applies to SJR. As I understand it, it is desirable to allow the air to flow freely from the slot to the lee side of the mains, but you don't have the luxury (or the burden) of adjusting the sheeting angle while sailing, so the slot width is a compromise and I am not sure if it is all that critical. Maybe other things are more important to worry about. It works, anyway. I think these questions are all open to further research.
Good luck with your project.