Here are some fun things to do by boat leaving from The Harbor Marina in beautiful Three Mile Harbor:
You can dock in the historic whaling village of Sag Harbor, stroll the quaint streets, visit the whaling museum, buy some kites or toys at the Sag Harbor Kite Shop, get some ice cream at Buddhaberry or get lunch at The Dock House.
Carefully navigate to West Neck Harbor and visit the lovely SALT restaurant for lunch and cocktails (hire a captain for drinking outings, please!.)
Go swimming in Coecles Harbor, off pristine Mashomack Preserve in Shelter Island. Anchoring operations required!
Carefully navigate to find your own secret lee cove (Tobaccolot Bay is nice on a Southwest) and sunbathe.
Catch porgies, bluefish, sand sharks, sea robins, and striped bass (if you're lucky and know how to fish). Rental fishing gear available.
Run to Greenport, a 1600's era whaling village on the North Fork. Dock at Mitchell Park Marina (floating dock, side-to tie up). Perfect for kids - the carousel is an iconic attraction, and you can visit the Blacksmith shop. Shops, bars, restaurants. Try ST Prestons marine store.
Check out "The Ruins" off Bostwick Point - An old fort from the Spanish-American war, and a bomb-practice run. But don't go onshore.
Like to drive the boat? Try circumnavigating Shelter Island (2-4hrs depending on cruise speed), or circumnavigate Gardiners Island. YOU CANNOT LAND ON GARDINERS ISLAND (PRIVATE) OR CARTWRIGHT ISLANDS (PRIVATE AND BIRD SANCTUARY).
Go to Dering Harbor on the north side of Shelter Island - take photos of the fleet of Hereschoff 17' "Doughdish" sailboats on their moorings, stop at the town dock, visit Bliss Department Store for gelato and sandwiches, or hit the Dory Restaurant.
Go to Orient By The Sea restaurant - a pull-up and eat.