For anyone who hasn’t seen the word before the ocean gyres are the spots in the “middle” of a circle of ocean currents. There are six (seven really but Antarctica is in the middle of one) .
What is important about them is that everything floating on the seas that does not get washed ashore or sink eventually finds it way to the middle of a gyre. For this reason all the plastic and other floaty crap seven billion humans throw in the rivers and seas collects there. It upsets environmentalists a lot.
Most of us have probably considered the South Atlantic gyre, the one between S. America and Africa, as the best place for a seastead. In addition to current powered position control it has the calmest weather available on Earth.
So here is the simple plan:
install a plastic recycling facility on a barge, paddle out to the gyre, start scooping plastic out of the water and building modular seastead units.
Power would still be an issue, it will take energy to process the plastic but less than a typical plastic recycling plant because the first step is grinding the plastic into very small pieces and for most of the plastic at the gyre the sea has already done that. It would also be a good place to employ solar power.Using a solar furnace design you could work cheap during daylight. Even the little toy pictured below will melt metal.
Trying to capture wind would push you out of position of course.
So, after you have made a half acre of seastead you can move onto it and no longer need the barge.
By typical seastead standards this is a very inexpensive plan: old barge with fuel, small recycling plant, semi-skilled 3rd world labor. Provisions and emergency rescue. That’s the whole shopping list.
I would do the math myself if I was familiar with the industry but I would not be shocked if by selling plastic products this thing could actually make money.