David Tyler wrote:
The sheet, being steeply angled at the top of the leech, will not be very effective at controlling twist. With the yard at a shallow angle and suspended at its mid point, the greater amount of balance will offset this.
Also on the sailplan on page 24 (pdf), note that there is a throat hauling parrel to peak up the yard. And the boom doesn't appear to be sheeted, which is strange.
David
Good point. To follow on, when running off the wind, presumably more balance would be introduced lower down the sail. However, the distribution of the fixed parrels doesn't appear to allow this - instead, the top of the sail appears to be the bit that is moved fore and aft - though this would require reefing from the bottom first, or the 'clew' drops into the boat.
Alternatively, if the rake of the mast is variable, as it seems it might be from the simple sketch, perhaps the parrel distribution is explained, allowing the same set of the sail for varying mast rake.