It would probably remain DC all the way to the shore, then conversion from DC to AC is done with an inverter. While they're not as big as what they would use, you can buy DC-AC converters at any electronics shop, or at Wal-Mart where it plugs into your cigarette lighter.
--thanks--I go all the way back to Ward-Leonard systems on AC-DC--have been around a few windmill setups from the highway--was curious about the big outfits with three hundred foot blades and the high-voltage three-phase conversion---