i am searching for an application which can design and simulate mechanical pieces on water. Is this software what i am searching for?
You can certainly use BRL-CAD to design mechanical pieces, but it's not going to directly simulate fluid interactions. You'd have to write that analysis portion or use another piece of fluid dynamics software to do that part.
I came across this post; perhaps you've read it already:
Though I understand this project is still a work in progress, I think you're looking for something like this for your purposes.
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