With many thanks to the South Street Seaport Museum! Visit them at http://southstreetseaportmuseum.org/ or at Pier 16 in New York. These days, if you have dangerous, underwater shoals and you need a lighthouse, you build a big tower and anchor it to the seabed. But a hundred years ago, that technology wasn't there: and so you'd build a lightvessel: a floating lighthouse with a crew of twelve, who's stay out in the dangerous channel in all weathers. At the South Street Seaport Museum, Mike Weiss, the waterfront foreman, gave me a tour around the Lightship Ambrose. (Apologies for the audio on this one: I was shooting quickly, and it turns out it's windy on the East River in New York!)