Not KM but 822m seems pretty close. I think you’re grossly overestimating the benefit from the kite. Seating’s current website says:
> A 1000m² sail surface to harness the power of the wind and tow ships. Based on modelling and preliminary land-based tests, Airseas estimates that the Seawing system can reduce fuel consumption and greenhouse gas emissions by an average of 20%.
I don’t think better routing will increase that to 80% even if you combine it with next gen tech that knows wave patterns and when a slot will be available to minimize speed and energy loss.
We need a path to remove fossil fuels from ships (& planes). There’s also industrial applications that need high heat that solar can’t really accomplish. Finally, solar & wind need insane battery capacity which when included pushes the economics strongly back in favor of fission and fusion.