This is just hypothetical, not yet another change, but it’s always puzzled me as to why they’d run it:
This sailplan appears to militate against all we know or try to do, i.e. we like to keep max area low, taper it towards the top, even with quad rigs like the lug. This one though seems to defy science.
For example, a major drawback has always been reefability or the ability to quickly shorten sail, not easy with these – they use a system of brails to kill flow but that seems tricky to me if you have more than one sail – unless you have a large crew, which I do not.
1. It’s quite obvious that it gets the sails out of the way aloft – more people room below. However, anything aloft must be held down by lines, ropes or sheets and looking closely at such craft, there are lines all over the place.
Getting the yards up high also allows for high ‘fences’ around the ‘peopled’ area of the deck, which seems quite a safe and sound idea for crew protection.
2. Seems to me we need to look at the proa crab claw for the answer – this from one of the foil designers of the 80s/90s:
I think the advantage of the crab claw sail is related to where it originated. That is for sailing in the Pacific ocean swells. The large sail area up high is still able to grab a bit of wind when the hull is in a trough between wave crests. It also means that the CE is up high and heeling moment is high, calling for a high stability hull system.
3. Yes, that last bit is the issue, although I did see some Polynesian working boats and they were able to do something quite interesting – they could angle the sail lower or higher by lowering the supporting yard/mast. The aft sail was low, giving horizontal drive, the for’ard was angled up, giving lift.
4. Simplicity of the sail [replacement difficulty] is also a major plus.
5. One advantage I see is that the vortex effect of the crab claw, which appears to fly in the face of airflow theory, allows for smaller sail area overall – a good thing within an available space.
6. Looking at that aft or lower yard, running multiple point blocks up and down the yard, angled either side, spreads the load, reducing stress, a good thing.
7. Coming back to brails, one thing those using the rig have pointed out is that keeping the two yards [on any one sail] apart and flattening the sail is what gets the vortex working. Release the sheet, the sail bellies and instantly loses drive.
From my point of view, that’s not a drawback, it’s a boon – sail only sets with effort, left to its own devices, it loses shape and drive.
Interesting rig. Certainly looks nice.