Final answer:
When sighting a green can buoy on the starboard bow in dense fog, the best action is to 2. slow down and proceed with caution, maintaining your bearing and avoiding unnecessary course alterations or speed changes that could lead to peril.
Step-by-step explanation:
If your vessel is leaving New York harbor in dense fog and you sight a green can buoy on the starboard bow, the appropriate action would be to 2. slow down and proceed with caution.
Green can buoys are starboard hand markers which indicate the right side of the channel when returning from sea (the opposite direction in this case). You should not increase speed, alter course to port, nor stop and wait for the fog to clear as these could lead to dangerous situations or collisions.