I belong to the Hempstead Harbour Club that was mentioned earlier. PM me if you'd like some info.
Coming from the city, I wouldn't consider going farther out than Northport. Manhasset Bay, Sea Cliff/Glen Cove, Oyster Bay, Huntington, and Northport all have LIRR train service. Station in Oyster Bay is closest to the waterfront. Others would require a cab. All have a mix of marinas with slips, commercial moorings and yacht clubs. And while the wind is not as reliable in the summer as the south shore, it's not as bad as you are lead to believe. And the deep water and endless cruising options make up for the lighter summer winds.