To rig two double blocks correctly the blocks should be a 90 degrees of each. Lifting a load the way he rigs them the lower block will twist. Just consult any good rigging manual.
its a double tackle and would recommend at least 240 foot of rope as shown it attaches to one, then it goes through first pulley for two lengths, then the tackle first pulley for three lengths, simply put its 5 lengths, the extra in this case is so you will need it for a starting length to pull on and be left short on rope and gives a 4 to 1 mechanical advantage
