Saw a ship at night off our stern quarter 17 miles off. Looked through binoculars to check her lights and see which way she was heading; one white light means a boat is less than 50 metres long, two white masthead lights more than 50m the lower one is at the bow. Red light shows portside, green starboard so you can work out if it is coming towards or going away. This was a ship bigger than 50m. Looking on AIS (collision avoidance system) which gives details, she was heading for Bruges. Saw a second boat briefly touching the arc of our horizon. Ditto a plane. Then nothing. Our own little world back to us again.