If you’re heading to Maine or even thinking about cruising in Maine this summer, there’s still plenty of time to go all the way Down East to Somes Sound, the only fjord on the east coast of the United States and one of the prettiest cruising destinations around. The sound, about four miles long and often 150 feet deep, basically cuts Mount Desert Island in half and has the iconic boating communities of Southwest Harbor and Northeast Harbor at its lower end. And we’re approaching the best time of the year for cruising there, since that part of Maine generally…