Since the speed and other quantities of ship dynamics are closely related to the ship length, L_<pp>, these quantities and the traffic capacity are sought as linear functions of λ(=LogL_<pp>). Starting from a linear representation of λ for the dimension of the effective area of ships, the maximum density of ship group, ρ_<max> is also obtained as a linear function of λ by assuming "solid sphere" potential. The traffic capacity is equal to the product of the maximum density and the speed, and hence, the basic traffic capacity, C^<co>_<basic>, corresponding to the probable values of the speed, V^<co>, is given as a linear function of λ. A small deviation of the speed from the probable value, V-V^<co>, requires a small correction to the function.