The author presents here in this report on some experiments upon the impact stress caused on the each materials composing grab-bucket and the special character of grabing of it at the touch of earth dropping through water.
　These experiments are necessary for the drawing of design and plan standard of grab-bucket for dredging. Here in this first report, we present on the fundamental research and some preliminary experimental results on the drawing of the standard.
　Through tne preliminary experimental results carried out lately, some fundamental date upon the method of full-scale experiments which we are going to do here after were gained.