Reduce speed, stop engines, navigate with caution. There can be little doubt that there will be very few legal obligations that are so consistently ignored as Rule 16 of the Collision Regulations at Sea. Yet the circumstance to which Rule 16 applies, reduced visibility, is only one of the causes for reducing speed and the factors involved in the decision to accept delay may prove interesting and revealing. It is the purpose of this paper to stimulate further investigation into the subject, an investigation that will certainly require the cooperation of ship owners associations and master mariner organizations and which could well be carried out by the Marine Science Departments of such advanced educational institutions as for example University of Wales Institute of Science and Technology in Cardiff.