Last Wednesday in the process of moving my boat to its summer port: I had been motoring in dense fog for a couple of hours. Then I heard a ship's fog horn close behind me. (I don't have radar.) Got on the radio and made contact. Was told they had me on radar and were following about a half-mile behind. After another half-hour the ship called to tell me it would be cutting in front of me to head into Stoneport. Didn't see it until it was about 100 yards away.