Not sure I see any advantage other than the crew can pull from the midboom. From what I can tell from your description, purchase from the two triples plus single on the becket is 7:1 and the two tails do not add more.
Also, doesn't pulling a line from the midboom cause the boom to move towards you against the sail force, making you pulls less effective? I get this sometimes from the main traveller if it's out a bit (reaching in heavy air) and needing to sheet in the mainsheet after a gust...traveller comes up until near center before main sheet comes in.
Why not just stay with the helm handing mainsheet off to the crew for extra grunt?
I've got a picture of Hunt and Kris sailing upwind, but it a professionally done pic, so I'm not sure I can post it. Plus it doesnt really show the midboom sheeting very well.
The interesting thing he did was figure out how much he needed to play upwind and put a big stopper ball just past that point. So he could drop it and play the spin downwind.
Looking at the picture, they used a triple block on the boom, a triple with a becket and a cam cleat on the travelor, with a single on the becket and then a single block on the boom in front of the triple and a rachetmatic midboom with a big stopper ball 2 feet past the mid boom block and then enough tail to allow trimming from the trap.
Most cats have the triple and triple with a becket/cam. It pretty easy to add the two singles and the rachematic.
Hope that helps.
Bill
