(a) When two power-driven vessels are meeting
on reciprocal or nearly reciprocal courses so as to involve risk of
collision each shall alter her course to starboard so that each shall
pass on the port side of the other.
(b) Such a situation shall be deemed to exist
when a vessel sees the other ahead or nearly ahead and by night she
could see the masthead lights of the other in a line or nearly in
a line and/or both sidelights and by day she observes the corresponding
aspect of the other vessel.
(c) When a vessel is in any doubt as to whether
such a situation exists she shall assume that it does exist and act
accordingly.