This report deals with a feasibility study of a wide-beam tanker (L/B=5) with respect to ship-controllability. The report consists of the following three parts ; 1) To estimate the indices of manoeuvring characteristics of the ship by the method of series tests using similar models which are 4 m, 10 m and 30 m in length. 2) To check whether or no the ship is unstable in course keeping mainly owing to so-called unusual phenomena. 3) To check the feeling of control of the ship which has the manoeuvring characteristics estimated by item 1), by the method of simulation apparatus of ship manoeuvre. The results hereby obtained show that if a big large wide-beam tanker has an enough large rudder area ratio, the ship is feasible in the viewpoint of ship-controllability.