A tabular iceberg is used as an energy source for a propulsion system which propels the iceberg across vast distances of the ocean with minimal fuel consumption. The iceberg thus becomes, in effect, a self-propelled vessel in which potential energy associated with the iceberg is converted to kinetic energy to power the propulsion system. Two propulsion mechanisms can be used, preferably in conjunction. The first mechanism uses the gravity flow of melting ice to provide propulsive thrust, while the second mechanism utilizes the temperature differential between the iceberg and the surrounding water to power a heat cycle engine, which, in turn, drives a generator to provide electricity which runs propeller drive motors.