This paper follows the preceding paper of the authors in 1956. Now it may be concluded that ; (1) Steering quality of a ship may be described by a transfer function of the form K (1+ T₃p ) / (1+ T₁p ) (1+ T₂p ) or a set of the steering quality indices K, T₁, T₂ and T₃. These indices are functions of hull form, rudder size and other particulars of a ship. Analytically, they are composed of coefficients of governing equations of motion. (2) In a more practical sense, steering motions of ships are described substantially by a first-order equation of motion T d θ/ dt +θ= K δ. Accordingly steering quality may be described in brief by two fundamental indices K and T. (3) Use of the transient response test and frequency response test of a free self-propelled model is an effective means of providing a full description of steering quality in terms of K, T₁, T₂ and T₃, through a procedure not so lengthy as the usual approach of resistance derivatives. (4) Kempf's zig-zag test followed by an analysis employing the first-order equation of motion provides a figure of merit for steering qualities of actual ships in terms of K and T. The zig-zag test would bring out many things about steering quality if it were carried out for many ships. (5) Refering the values of K and T for a number of actual ships, it may be said that (a) improvement of turning ability (increase of K) brings necessarily some reduction of quick-responsibility and stability in steering (increase of T), if the relative rudder size remains constant, (b) rudder size, cut-up of dead-wood and other similar arrangement have fair effects for steering quality, while main hull form has much smaller effects for it. (6) It may be expected that the present expression of steering quality would provide a reasonable basis for design work relating to steering and turning. In this connection, consideration of a feed-back system composed of a ship, a steering gear and a helmsman or anautopilot may be an important aid.