In the decision of a collision avoidance action for navigators and intelligent ships, it is necessary to evaluate the degree of surrounding risks and to control them effectively. In this paper, we propose the new methodology for navigational risk evaluation and control at sea. In the methodology, navigation risk is evaluated in two dimensions using Even Risk Contour on the basis of the concept of contour line. In addition, the movement information of dangerous targets is assessed continuously and precisely with wide band data. The presented technique is useful for the safety navigation at the heavy traffic sea and will be applied for the ultra automatic ship.