Huge earthquakes have occurred continuously for at least 1000 years along the Nankai Trough, which is located in the Pacific Ocean off Shikoku Island, Japan. There is great concern over the possible occurrence of huge earthquakes, named Toukai, Tonankai, and Nankai earthquakes, along this trough. A tsunami generated by an earthquake in a coastal area not only raises the sea level, but also creates strong horizontal flows in bays. Any ships in the area are subject to these strong lateral flows. Since these phenomena can make a ship's movement uncontrollable, subject piers to tremendous forces, slam ships into breakwaters, and set vessels adrift and ground them, it is very important to understand them and the resulting movement of a ship, and to consider possible countermeasures. It is particularly urgent to evaluate the effects of a tsunami on ships carrying hazardous materials, such as VLCCs (Very Large Crude Carriers), sailing near the coast or moored to a jetty, and to consider and evaluate ways of countering these effects. From this viewpoint, basic analyses of a VLCC's movement resulting from a tsunami are carried out, and then countermeasures for avoiding this motion are investigated. First, this paper describes mathematical models of a tsunami flow and the maneuvers of sailing and moored ships. Next, computer simulations of the evacuation maneuvers of a ship at berth to avoid the effects of a tsunami are discussed. Finally, the paper reports additional simulations of the lateral motion of a ship moored at anchor when a tsunami hits.