It is confirmed that a wave pattern and a wave making resistance at large Reynold's number are determined by the potential component of the flow field, and that the effect of the rotational component is negligible, by means of a linearized theory for ship waves in a viscous fluid under assumptions of Oseen's equation and equivalent laminar wake. In order to know a modified potential flow, boundary layer and viscous wake, as well as wave pattern, are measured. It is discovered that turbulence occurs beside and behind a ship near the free surface, and that it originates another sort of viscous wake. Making use of measured displacement thickness, the wave pattern and the wave making resistance are calculated and compared with measured values. A qualitative but plausible agreement is obtained.