In order to investigate the influence of the clearance between sea bottom and suction mouth for lift of solid body, the room experiment was conducted by using model bed and circular suction mouth.
　The drag coefficient of the sphere initially increases due to the hasty increase of the velocity at the inlet of the mouth and gradually approachs the constant value. The similar flow around the suction mouth is given by adopting dimensionless paramenter.
　The numerical calculation utilised Finite Difference Method was carried out for potential flow in order to examine the similitude of the flow. As the result of this calculation the relation of the similitude is given approximately by the dimensionless parameter derived for the experimental data.