Sounds good, but hardly new technology.
Hitler used the Fischer Tropsch process to make coal into petrol and diesel. South africa still does that using gas from Mozambique.
There would be too little CO2 dissolved in the sea water to provide the necessary carbon, by a long way.
So the shortfall would be carbon. The ships could carry coal, and convert it as they go-
http://www.sasol.com/innovation/gas-liquids/technology
