Recently, there are several problems in space, infra-structure, and facility in the contiguity of existing harbors due to the trend of enlarged container vessels. In this regard, the Mobile Harbor has been proposed conceptually as an effective solution for those problems. This concept is a kind of transfer loader of the containers from the large container ship to the harbor on land, which is a floating barge of a catamaran type. The catamaran-type vessel is well known for its advantage in maneuverability, resistance, and the effectiveness for working on board. For the safe and effective operation of the two floating bodies, a container ship and the mobile harbor in the near sea apart from the quay, robot arms, novel crane systems, and pneumatic fenders are specially devised with additional mooring facility or DP (dynamic positioning) system. The concept is to be verified through comparison and simulation studies under various environmental conditions. It is shown that the proposed concept is in general feasible but there are several areas for further investigation and improvement.