In shipyards facing toward narrow river or sea, drag weights are used to stop a launched ship. Recently, newly built ships have greater dimensions, which circumstance requires heavier drag weights and obliges to estimate frictional coefficient more precisely. We re-measured frictional coefficient of concrete blocks and chains used in our shipyard at present. Moreover, experiments were made on concrete blocks placed on wooden sleigh, concrete blocks painted with Semtex, concrete blocks on building way covered with river sand, etc. We found that frictional coefficient of concrete blocks on building way covered with river sand is approximately 0.48 and is twice as high as without sand. This results has been applied to launchings of newly built ships and weight of drags could be decreased to about 63%.
