Slieve McGalliard wrote: David also wrote – ‘However, I remember seeing a patent application for a stepped leech, so that in effect, there were a multiple of top edges, each generating a tip vortex of its own. It was claimed that the sum of the drag from all these vortices was less than the drag from a single tip vortex.’

Ian Hanny (years ago I flew as his co-pilot) wrote a paper on this for AYRS many years ago. It made very convincing reading. Add in the current interest on humped leading edge whale fins, and the use of humped or saw-tooth leading edges on wind generators and even racing propellers on model aeroplanes and it seems there is gain to be made in chopping a wing or sail into span wise sections. I wonder if cambered panels with stiff battens has this sort of effect?

There is still a lot to learn. One thing for sure, vortex drag and tip losses are a killer to performance. Huge sums are being spent on tip design.
Cheers, Slieve.

Daniel Collins wrote:

Kurt Jon UlmerThe top triangle alone is a usable crab-claw sort of sail, which can be set up to be taut or wind-spilling. 

Ok, see I did kind of like that about the sails - it's sort of like what Dave Z. is doing on the Triloboat rig... just without quite the loss of area in the severely hollowed leech.

• One CC theory (Marchaz?) has it that the apex is a turbulent vortex generator. Turbulent whorls of 'hard air' (high pressure) roll along the limbs, generating lift. The cloth in between, in this theory, doesn't contribute much, though conic shape generate airfoil sections very naturally.
  
  
• Some traditional CCs have extreme hollow... theory (getting speculative) goes that, in lighter winds, the whorls stick to the limbs, producing lift along light, flexible limbs. In higher winds, the whorls blow away from the limbs as sail cloth area reduces, leaving the remaining cloth acting as per normal. In very heavy winds, pressure draws the limbs together, spoiling the the shape of the remaining cloth. In all three cases, reefing is near automatic (some rigs sport a control line to draw the limbs together).
  
  Caveat is that most of the extreme hollows are found on tradewind craft... there's little data (reported or extant?) about how such rigs work on the wind.
  
  
• On LUNA, with a two panel upper triangle, Hassler/McCleod standard, we found when deep-reefed that the CE of the upper panel(s) was high enough to round us up in heavy gusts.
  
  The deep hollowed leach on SLACKTIDE (successfully) brings that CE forward/inboard, and we haven't since had the round-up problem.
  
  It may be, however, that LUNA's ultra-shoal draft, full-length rocker and high-aspect off-centerboards (which make her an extremely nimble sailor) are merely a combination that make her particularly vulnerable to round-up.
  
  SLACKTIDE is similar, but with a long, full-depth mid-body; she is less nimble but tracks exceptionally well, and therefore may be less prone to round-up, anyway.

One of these days, I would love to try a JR/CC sail that is a fanned stack of flexi-limbed CCs... each 'batten' would be two light limbs, joined forward and separating aft as canted Ys. Extreme hollowed panels separate and laced in place. Double sheeted. Doodles work out... maybe on a PDR?

Totally impractical as a cruising rig, but it would be a wild treat for connoisseurs of the odd! For a small boat, it might even work out, though the reefed bundle would be a mess.  8)