X1 - Venture - Argo Test Sails

No idea really - I've never given it much thought, except to appreciate that it ain't easy to find a set up that doesn't gouge your head and is operable throughout the range of the boom's swing, where the angle of sheet to boom changes significantly.

You might find this thread interesting - similar probs to yours:

But we're now way off-topic.

Obviously, a decent ratchet block on the boom is crucial to all this - perhaps why off-the boom didn't take off in the 60's.  Snipes used potentially head-gouging Holt jammers up on the boom, but they do have very high booms.

Messrs Hollands and Thompson  (D&D to you)  of your very own club seem to be world experts in this field. You need to talk to them

It's the little finger that wears on my gloves, so yes, little finger closest to the boom.

On Minisails - or indeed any other singlehander with a traveller wherein the lower mainsheet block(s) float from side to side, you can of course have the problem that when you try to pull yourself into the boat in a lull, all that happens is the boom comes towards you! No such problem with a lower block(s) fixed on the centreline on a bridle.

Off-the-boom sheet loads are lower because the final fall pulls usefully sideways rather than down - you don't waste so much effort doing what the kicker should be doing. But as to why square top (and indeed other large roach mainsails) are easier to sheet compared to triangular sails of the same area, I think may be because the chord  (width) if the sail is generally shorter, putting the centre of pressure closer to the mast.  When switching from Laser 2 to L3k, I noticed that gybing was easier for what I presume is the same reason - the centre of pressure isn't moving so far (plus - so far a gybing benefits are concerned, the boom is correspondingly shorter).

That said, I'm not entirely convinced that square or large roach mains really do give do more thrust for your heeling moment as current fashion dictates. More thrust in upriver conditions, sure, where all the breeze is aloft, but you pay a heeling moment penalty in open waters.  A better lift/drag ratio, maybe - this is where everyone gets off on the aircraft theory - but not necessarily lift/heeling moment.  Aircraft are much less worried about the moment generated by the load - heeling moment so crucial to us, is merely bending moment at the wing root to them, and is balanced by the other wing!

The really crucial thing for wing efficiency, aspect ratio aside, is the profile.  Planform (e.g. square top or triangular for us) is very much secondary, and it seems to me that it is much easier to cut a well-shaped sail profile on a triangular rig; with all those battens supporting the big high roach, it is hard to reliably build in a good shape over the full range of conditions.  Look how quick 505's and Fireballs are to windward, despite having far less righting moment than current skiffs (my Fireball used to regularly beat the local 800's to the windward mark in a F.5). Must be down to rig efficiency - sheer power it ain't.