Too heavy . Diesel/turbine electric used only if the power is small, or if the weight is not an issue.Thanks for the explanation. Why not a full diesel electric power system where propeller is only powered by electric motors? This would eliminate need for gear boxes used by the gas turbine. You can put the generators in the center of the ship, and route power to the motors near the propellers. No need for long shaft, which increases both space efficiency and power efficiency.