RedactedNarrative: Vessel operator stated he was returning to his homeport with 4 persons on board. in low visibility / darkness and believed he struck a buoy and did not recall seeing a green light prior to impact. Operator further stated he was taking on water quickly, attempted a VHF 16 mayday call, had all passengers don PFDs and the vessel went down quickly. He further stated a nearby civilian boat pulled the 4 occupants from the water shortly before the arrival of the Bay Constables. All occupants denied injury to the undersigned.