Drag suction dredgers are actively used at various places tody, especially for the dredging in the route where marine traffics are frequent or in the narrow water ways.
　The problem on the operation of these drag suction dredgers is that numerical values for the loading efficiency of soil into hopper are not known yet.
　So the designers and operaters of drag suction dredger have often been troubled and tool pains over this problem. In order to solve this problem, we experimented by using model hoppers, the same type of which are contained in the drag suction dredger Kaiho-maru and Kairin-maru, and formularized the loading effeiciency of soil into hopper as follow;
　η=1-e(-α(VS/UH))
　Where Vs settling velocity of particles, UH is the average horizontal velocity in hopper, α is a constant, that is α≒2.5, and was determined from the experimental results using model hoppers and from those of performance tests of drag suction dredgers.
　But this equation can be used only for loading sands, and it must be corrected when it is applied to mud.
　Moreover, the average loading efficiency and loading time in hopper were formulized theoretically.
　We don't show here in this report the research how to determine the capacity of dredging pump. Considering only through the relation of volume of the hopper and other important factors, the capacity of dredging pump was determined from the average loading efficiency and minimum loading time, and found to be proportioned according to the settling velocity of particles.