Also this would especially be thanks to all which could now be delivered up by geostationary cable lift systems at low cost, often using surface Solar light and wind turbines generated electricity till well above all clouds or dust, then simply more Solar generated electricity ever higher up.
To form a cylinder sea, robotic construction devices saved from earlier work could be exploited. And by now there were several helpfully available useful source asteroids orbiting closer than Jupiter, good for robotically forming and sending all which would be required over years to first form a huge containing cylinder, plus foundations for its islands, maybe all to become of big radius 25km and length 100km, good for many islands and much good sea surface area.
A big cylinder for an artificial sea was robotically formed using very many loads of robotically prepared parts formed and sent from source asteroids. This was named Cyl Sea. It was attached to the new bigger cylinder settlement at one pole end. Settlers could in the future easily enjoy future visits into there, after taking a lift down inside, suspended from the axis to reach any island.
The attachment was an air lock allowing Cyl Sea to slip turning differently relative to the cylinder settlement, since they had much different radii and turning speeds, while Cyl Sea 25km radius meant that to have 1Atm centrifugal force air pressure down at sea level, air pressure up by the axis had to be kept lower.
Cyl sea rotation was only what was needed for half Earth weight at sea level, to keep Cyl Sea easier to have well supported. Sea life shouldn't care much since they floated effectively nearly weightless. Birds and island life could love how easy it was here to fly, jump, etc. And most of those visiting islands would prefer having at most half Earth weight. (Half weight conveniently made it easier to cable support everything, and to hold outside the extra thick insulating and protective layer.)
Cyl Sea's surface at 24km radius meant that for 1/2 Earth sea level weights, it should be spun at 343 m/s, turning once in 440s=7.33min.
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