RadVlad

Hello I have been playing AOS for a few months now and have a question regarding shooting. The scenario is that I have just fired three wounding shots at a screaming skull catapult. Now who is it hitting? The crew or the catapult? It seems incredibly easy to quickly kill the crew if they all hit them with their saving throw of 6+ ,and why would the catapult have 5 wounds and a 4+ saving throw if you can just can kill the crew so quickly? Surely the wounds would be split between the catapult and the crew? The rules don't seem clear to me so any help would be appreciated!