Editor's Note: This is an excerpt from WBUR's Saturday morning newsletter, The Weekender. If you like what you read and want it in your inbox, sign up here. The water surrounding Boston is dotted with sailboats year-round, and now that summer’s nearly begun, you’re sure to see plenty of them cruising through the Charles River and Boston Harbor on pleasant, breezy days. The question is: How can you get on one?