This paper reports the result of vertical shock forces on a spud of working craft for sand, gravel, concrete and granite, and also reports the calculation method of actual shock forces of the KUROSHIO in rolling and heaving under the wave heights, 1.0, 2.0 and 3.0m.
　From the result of our test, the ratio of max. shock force to spud's static weight, differnt in dropping speed of spud, is between 1.0～2.0 for 1.0m/s dropping speed of spud.
　The value is also differnt in soils. The ratio of max. Shock force to spud's static weight is near to 1.0, for sand and gravel, and 2.0 for granite.
　We propose that the max. Shock force which occurs between spud and hard rocks should be taken the twice of spud's static weight 'included added mass).