Darren
I think we are talking a bit past each other.

As I see it, the telltales at the leech are only there to prevent one from stalling the sail, as when over-sheeting it (too high angle of incidence). When in the groove, they should fly aft, nicely (unless the 15° hinge provokes separation), and only fall behind the sail when it is over-sheeted.

When pinching the boat closer and closer into the wind, the angle of incidence (i.e. the wind’s attack angle) of the sail will be reduced until the luff start to flutter, as you describe. At this point the sail is luffing, not stalling. I would expect the leech talltales to fly nicely even if the sail is luffed.

Have I misunderstood something?

Arne

Telltales help one to stay in the groove

This sounds good.

BTW, I keep repeating that all junk sails (all sails, indeed) would benefit from using telltales, at the leech, at least. These will warn against a beginning stall (separation starts at the leech with rising angle of incidence).

When going from a wing sail, with its forgiving leading edge, to a junk sail, it is easier to oversheet it and lose power. See Broremann's telltales here (click to enlarge).

The use of telltales at the leech is also useful in getting the twist right  -  all the telltales should collapse simultaneously when falling off without easing the sheet.

Arne

PS: Weather or not ordinary Bermuda style telltales at the luff work, I am not sure. The sails I have used have not been so translucent, so windows would have been needed to make full use of them. Have anyone tested them on junk sails?

I went sailing with Darren Bos yesterday, and cast him off in the dinghy to take some sailing photos .

The windward performance is quite OK. In flat water and about 12knots of wind, we were making 5 knots and tacking through 100 degrees. That's as good as I need. The wingsail might have been a shade better, but not much.

David Tyler wrote:

I suspect that your tube-in-tube hinges would have given you somewhat less camber than 8.5%.

Yes, my first (and only) set of hinged battens had 4 'knuckles', each bending 8 degrees. This gave about 10% camber and was mighty powerful. With a symmetric airfoil, the CP moved aft , compared to the flat sail, so the weather helm increased a bit. I soon reduced the play in the aft hinges of the 2 upper, horizontal battenss  to reduce the forces a bit (the top batten had no hinges).

Still the lower battens bent 8 x 4 =32 degrees, so no wonder that sail was powerful.

Arne

David,

I can imagine that this setup will work well. I generally have found that higher AR sails (Broremann, AR=2.15) need less help from control lines to set well than those of low AR (Johanna, AR=1.87).  Those who report about problems with their hi-AR sails, all seem to have schooner rigs with very steep sheeting angles. On Tystie (as on Broremann) this is no problem.

Actually, when fitting hinges to my first sail on Malena, I soon added a throat hauling parrel to hold the top aft. This let me disconnect the standard PJR luff hauling parrel, further down. The LHP had hindered the hinges from working in light winds. Your single hinge on each batten sits further aft of the mast, so should never flip the wrong way, anyway.

The single hinge setup may produce a quite moderate camber, but I am pretty sure even this is a lot more powerful than a flat sail. Any camber is better than no camber.

In short, this sail shows simple, efficient elegance  -  that’s what I call an improvement!

Cheers, Arne