COLREG 9

Vessel B is stand-on (SO) vessel.
Rule 18. Responsibilities between vessels
Except where Rules 9, 10 and 13 otherwise require:
(a) A power-driven vessel underway shall keep out of
the way of:
(i) a vessel not under command;

[xLrz.._]

Vessel B, cause it's not under command and therefore unable to keep out of the way and cannot abide by the rules