The double purchase was installed in 1990 
The original fly was standard old hemp and sand bag! 
Double purchase actually kind of sucks,. but it helps when space is limited... a single purchase fly is much easier to operate.. less friction fighting you.
They went double in this case as there was no room on the deck to spare.. with double the travel distance is half on the weight side what it is on stage,. (but you have to double the amount of counterweight
) this is so the lock rail can be up off the stage floor.


