The classification of electric ship

Electric boats propulsion, there are two main categorises: dc propulsion and communication.
Dc propulsion
Is to use dc motor, dc motor speed adjusting range is broad and smooth, overloading starting and braking torque, reversal good running characteristics.
Ac propulsion
Is to use ac motor, ac motor although has big output power, high limit speed, simple structure, low cost, small volume, reliable operation, etc, but limited to the technical limitations, difficulties of speed regulation, and the application is less.
Some small surface ships or underwater vessels, the use of diesel engine, or steam turbines generator power generation, propulsion ship propulsion motor rotation