The experimental results on dredging capacities of model grab buckets (dredging volume if about 50 litters) for sand and gravel are discussed with an analysis of the dredging capacity. For the clam shell type grab. the following expression for the weight of grabed soil Ws has bee established:
　Ws/Wg=(KL√(B/2Wg))-C
　where Wg, L, and B are the weight, open length, and width of grad buckt, respectively. K is a factor representing the effects of the nature of soil and type of bucket, and C is a constant. Design diagrams of Ws/Wg versus L√B/2Wg based on this equatipn will be very useful for the design of the most effective grab bucket for the given quality of soil.