In some isolated islands far from the Japanese main island, port facilities like a quay, sea wall and breskwater have not been completed. Mooring buoys are often employed to moor vessels at the quay walls exposed to the open sea. Joints of the buoy-mooring chain prove to break when large impulsive tensions occur during rough seas.
　Several countermeasures against the impulsive mooring tension are proposed and tested experimentally in this study. The following concepts for the countermeasures are examined and evaluated, 1)to improve the shape of buoy-body, 2)to employ the elastic mooringline and 3)to develope the elastic anchoring. The elastic mooring line was proved to be most advantageous to avoid the impulsive tension.
　Chain coated with rubber (rubber chain) is applicable as an elastic mooring line for buoys. In the later part of the paper, the magnitude of impulsive tension in the rubber chain is also examined in a large-scale model test. A numerical model has been developed to estimate the mooring tensions in the rubber chain. The experimental and numerical results demonstrate that the even partial substitution of the mooring chain by rubber chain is fairly effective to reduce the impulsive tension.