Nowadays, construction and planning of marinas, which moor pleasure boats, are promoted. Most facilities are used to construct calm area sheltered well by bay or penisla, but recently some of them are planned at the area where ocean wave easily enters. Thus, in the design of floating piers in a marina, it is important to consider not only motions of both floating piers and pleasure boats but also bending moments and shear forces of floating piers.
　At first, motions of pleasure boats and floating piers and strain of floating piers are measured by hydraulic model tests scaled 1/20. Models of floating piers are both single rectangular one and comb-shaped one. The effect on the motion both of floating piers and pleasure boats and strains acting on floating piers due to the diferfrence of the rigidity of floating piers, the mooring conditionsof floating pier and the presence of pleasure boats at a pier are discussed.
　Secondly, the motions and forces of floating piers and pleasure boats are analyzed by use of three dimensional source technique taking into account the interaction such as the effect on hydro-dynamic interaction between floating bodies and mooring forces acting on mooring components connecting floating bodies.