Ah, I dug into this once for a reenactment/recreation build once!
What they do is loop the string around the front bow, and attach it to the rear bow. So instead of just pulling back, you pull both bows towards eachother, meaning you get (theoretically) double the power per centimeter of draw length. You can even do this with double “front” and “reverse” bows, looping multiple times, creating a long pull length with multiple short limbs.
Note that this DOES NOT work like this with the bowstring just wrapped around the wooden bow limbs as shown here. You absolutely need pulleys to make this work on anything you can use without a ratchet (or modern nylon low-friction bowstrings, and it’s still not great).
Ah, I dug into this once for a reenactment/recreation build once!
What they do is loop the string around the front bow, and attach it to the rear bow. So instead of just pulling back, you pull both bows towards eachother, meaning you get (theoretically) double the power per centimeter of draw length. You can even do this with double “front” and “reverse” bows, looping multiple times, creating a long pull length with multiple short limbs.
Note that this DOES NOT work like this with the bowstring just wrapped around the wooden bow limbs as shown here. You absolutely need pulleys to make this work on anything you can use without a ratchet (or modern nylon low-friction bowstrings, and it’s still not great).