floating out precast elements and assemble them to giant structures has a long history one of the better known examples is the floating harbor for the D-day invasion that was shipped from england to france with the troops.
Mulberry harbour a giant floating cube element serving as breakwater.
Newer examples: boxes floated out for costal wave defense and creation of artificial harbors.
Suggested floating port in U shape
Stadion seastead – just a big plate the size of a football stadion (stadium) – has been built and floated out already – just for use as a storage tank – not a seastead.
Palm Jebel Ali
Ecofisk tank ring breakwater floating out into the north sea in segments to be assembled on site.
Waterworld film set – built in 6 segments – assembled in the high seas of hawaii, film made in the open water weather exposed relaying on the protection of the lagoon – later disassembled into 6 segments and towed over the pacific to San Diego.
So most of the tasks for assembling a floating island of any size from precast elements is proven and tested engineering – it has just (not yet) been applied to seasteading
