1. Your head. As I learned on my solo crossing of the Atlantic.
2. Other boats. Sound carries over the water much better than on land. People sitting on a boat quite a distance away can be heard clearly.
3. The radios. Most of us leave our radios on all the time as a safety measure. "Hey it looks like you're dragging anchor!" During the day there is a lot of traffic as the radio also is the telephone and the text messaging service. At night they are very quiet. When you are asleep and hear talking your (my) tired brain does not put together it is the radio. I think someone is on the boat. Funny.
Fair winds and following seas :)
Debut, Indonesia 24 July 2017