I'm surprised no-one has chimed in on this one - perhaps they're celebrating or commiserating...

I'n no expert, but I try to keep the main trimmed downwind. John Pearce put it best for me: "the sails don't know they're going downwind" - so trim them! Having said that, the spinni is the main engine, but the mainsail makes a difference too, especially if you're trying to lift the hull.

Yes, the main is acting as a backstay - but it doesn't have to be tight like the shouds - just don't let it go. And if you do, grab it quick!