Down at the docks

Shopping trip down in Glasgow today to get the supplies in for our village hall chinese event on Friday. 
The last few times that I've driven past the Inchgreen dry docks in Port Glasgow, I've been fascinated by this structure which I assume is in getting repaired. I don't know what it is but assume it's something to position wind turbines. I've included an extra in case anyone else can shed any light on what it does.