I have a childhood buddy that works for the boat basin, and over the years they've made us feel like family. As I'm sure you appreciate Nantucket harbor can be pretty rolly with anything but the usual wind, but I miss swimming when we're tied up somewhere.That's one of my favorite anchorages down that way. We've spent many nights just out of the lower edge of the frame.
Last time we were there they gave us a book called "Sailing Around Nantucket" by Alfie Sanford. Fun read with a lot of science on how the sand moves around in areas like that.