I agree a 9m turntable would take some time to make. But once made you could crank these vessels out very fast. 4mm skin sounds OK and I am sure there are some

I agree a 9m turntable would take some time to make. But once made you could crank these vessels out very fast. 4mm skin sounds OK and I am sure there are some structural supports inside to keep it from collapsing. I am not a weld engineer so I cannot say if Sub-Arc would be the best technique. I know that ships skins are being built with it.