  This paper presents a novel method to quantify seafarers' good seamanship
during navigation scenarios with multi-vessel encounters -- in open and
confined waters --, and to compute COLREG's-compliant trajectories for avoiding
collision and grounding. The quantification of good seamanship requires
knowledge about the state of the vessels (position, heading, and speed) and the
surrounding sailing environment. Such information is accessible through the AIS
system and the electronic nautical chart. The proposed method evaluates mutual
collision risk by examining domain violations of each vessel, and comparing
them to the seaman's actions. This results in a comprehensive metric of good
seamanship. As risk free actions are not always possible in the resolution of a
potential collision and grounding, the method adopts a branch-and-bound scheme
to identify achievable maneuvers that minimize the risk. Further, the dynamic
nature of vessel speed in congested scenarios is considered, recognizing
potential changes in both own and target vessels' forward speeds. The proposed
method is experimentally evaluated using historical AIS data and sea charts of
Danish waters. This research contributes to the field by providing a more
realistic perspective on seamanship in complex maritime environments.
