The basis for this apparent catch 22 is that the Rules cannot possibly cover every conceivable situation of vessel encounter. The Rules are written for usual or likely situations; atypical situations are termed "special circumstances." A complete list of special circumstances is, of course, impossible to provide. A number of examples should give some idea of the term's meaning.
During routine operations, almost all vessels engage in maneuvers that are not covered by the Rules. These maneuvers, which normally take a very short time, may occur near other vessels. Vessels entering or leaving a slip, for instance, do not follow the steady course needed for Rule applications. Likewise, vessels proceeding stern-first are considered to be in special circumstances.