This paper deals with an analysis of collision avoidance manoeuvring, excluding control of the propeller, but taking the of steering gear, speed so defined here, into account. The rudder has a great effect turning delay time, and consequence, the collision avoiding performance of small ships, whose response is not much slower than the motion of steering gears. In this paper, a ship is represented with an oval-shape whose length is L and breadth B, where L denotes ship length and B breadth. When two oval shapes contact with each other, we regard it as collision. From the statistical analysis of actual collision cases and also seamen's practice, we set up at first a model situation which two ships are on position and catch sight of each other at a distance of the threefold length of the ship. Under these assumptions we define the the permissible maximum turning delay time to avoid collision. The turning delay is composed of two parts, one the delay of ship motion and the other the delay of steering gear. Then we can estimate the least necessary rudder conjunction with ship's response time. Next step is to find the least necessary distance between two ships to avoid collision case of nearly end on and crossing, when both ships are equipped to have the least necessary rudder thus defined. Analyses nearly end on and crossing conditions are performed for the following two cases: (1) the privileged (standing on) vessel continues in extremis, tht is, the time a risk of collision situation when any action taken by the burdened vessel alone cannot prevent collision: both ships take the action this case.