Optimum geometrical decision-making method for ship collision avoidance

When two vessels meeting so close to result in risk of collision,what kind of action should be taken by one of the vessels to avoid collision can be got by plotting geometrically on the paper. But with plotting method only safety is considered, no attention is paid to the economy. How to combine geometrical plotting with optimum method to get optimum action that is safe and economy is not solved. Author tries to solve the problem in this paper and puts forward an optimum geometrical method for collision avoidance.