[usrusr]

Platforms are does-not-scale hard though: they require mooring and every bit of ocean floor is different. Drilling platforms come in multiple "species", as different as spiders, fish and birds. Roaming hydrolysers on the other hand would be one design fits any ocean. You'd want to build lots of them, more Model T than Death Star. And where a stationary platform would have to be able to brace a hurricane, the roaming unit would just go to a neighboring sea with a friendlier forecast. Or ride along on the edge, if power throughput has enough headroom.