Hi Geids.
I'm reassured that you calculated and think well your project, I've seen a couple of "silly projects" one with a Mighty Servant III which is just an insult to Archimedes ... The other one is a semi-sub oil rig with same kind of unprepared work. A lot of will power and drem : let's go with wood, tools, pictures of the real one ... and a result out of Archimedes laws again !
What is the size of your dock and what weight for the lifted ship on it ?
Please post pics, I really like this kind of challenge, I used to have a student work on floating dock stability and it's a nice souvenir, don't forget to lift and sink it not horizontally to avoid lost of stability in one time.
Xtian