Captain P. A. Thompson's paper, Revised Rules for Preventing Collisions at Sea, in the January issue of the Journal should be discussed. I agree with him that ‘rules (the ones which are mainly based on the operational aspect of the collision problem, i.e. manœuvring rules) to cover every conceivable circumstance would be of such length as to be impracticable.’ However, in my opinion, rules based on the principles—the organic aspects—can cope practically because then the object of the rules is to define the collision problem and its solution so that use of the rules can be immediate, easy and effective. For example, by establishing a safety distance the passing operation would have to be carried out such that the miss distance would always be greater than the safety distance. Furthermore, by keeping the ship's range above the safety distance, one ensures that the entire operation is correctly carried out.