I have seen spin sheets that can be turned into a 2 to 1 system by having a block on the clew and enough sheet to pull the stopper knot to a cleat on the side stay...
is this what you mean by a doubler system?
PS my hands are still sore from a 30 minute spin run home on sunday where it was about 10knots.. pointing high... HATS OFF TO YOU WHO DID IT FOR 5DAYS!!!
It was 6 days and about 6 to 10 hours a day. no stop for potty, no stop for drinky, no stop for food. It was great!
