On a three watch system you only work 8 hrs and you are allowed 12 hrs. So they will most likely be the officer of the watch for 8 hrs (navigational watch) and do his “overtime” as a winch operator for 4 hrs. This is common for like OSVs when they switch to “I” class for a big flotel. They still stand 12 hrs straight but you are the OICNW for 8 hrs and a lookout for four. As long as they log in and out properly in the ships log they will not violate any rules.