A system and method for heating a hot cargo on a watergoing vessel using a heat source on another watergoing vessel. The heat may be transferred to the hot cargo via heat umbilicals configured to carry heat in a heat transfer fluid. The heat transfer fluid may be circulated in a hot cargo heat exchanger configured to move heat into the hot cargo. The heat source on the another watergoing vessel may be a propulsion motor, exhaust heat, or non-propulsion heat source. The method may include heating the hot cargo. The method may also include switching between heat sources when both vessels are configured to heat the hot cargo.