medieval engineering - cranes

[Wynnara]

Does anyone have any good medieval engineering resources? I have something in my head in terms of an action sequence, but I'm not entirely sure it would work with technology.

The sequence revolves around a harbour crane designed to lift cargo from fishing craft below to the top of the cliff where the villagers live. I've been doing some research on both a winch-style windlass and treadwheel-style windlass, but I'm having trouble digging up what kind of mechanism would've prevented gravity from simply dropping the weight back down again? Was it possible to release something and send the crane's cargo into free fall?

 

[CupofJoe]

The Romans had worked out a ratchet/brake to stop just that happening with their cranes so I would imagine that more advanced structure would have had something like that too.
Mind you accidents did and do happen and you could imagine that a well aimed blow would make the ratchet skip or fail...
And I think I remember seeing a winch for a Portcullis that had a similar "quick release" mechanism [a defender could hit the "other" end of the ratchet to make it lift and let the gate to fall...] while in Normandy a few years ago.

 

[Butterfly]

Leonardo Da Vinci - one source to look at. He had a crane. Rotatable crane » The Models » Leonardo da Vinci Saw it in some film once.