The pursuit of economy has resulted in the large tankers so-called VLCC or ULCC. Deeper draught is, of course, advantageous for the purpose of increasing the tanker size, but naturally it is not unlimited. In this paper, authors tried to survey through the simulation technique for the optimal dimensions of ULCC with respect to building cost under restricted draught which can stand against the conventional tankers free from draught restriction. Consequently, it was found that lower L / B makes building cost cheaper and that severer draught restriction makes this tendency notable. Reflecting the study, authors have developed the new design of 400, 000 dwt ULCC with L / B as low as 5 and with restricted draught of 22.15 meters. And to materialize the design, authors have made extensive feasibility study regarding controllability, propulsion and structure for hull using many sizes of models including large model of 30 meters length. As a result, authors have convinced themselves that the large wide beam tankers of which L / B is as low as 5 can be realized.