When Google maps first went online, it showed a couple of large dunes at the tip of Crane Beach, one labelled “The Great Dune.” It was the tallest of the newer dunes, comparable in size to Wigwam Hill, which is an older well-established dune in the middle of Castle Neck. The Great Dune, alas, is no more. Using Google Earth, I was able to compare satellite images from 1995 and 2005 with the satellite view today. It is clear that the tip of Castle Neck, where the Great Dune once stood, is retreating, and the opening to Essex Bay between the tip of Castle Neck and the tip of Wingaersheek Beach has widened by perhaps a quarter-mile.
The newer dunes may have been a temporary phenomenon–they seem to have appeared after publication of the 1912 nautical map of Ipswich Bay, reaching prominence sometime in the middle of the 20th Century, then began their retreat. The crude map produced in 1786 and shown further down indicates that Castle Neck is, in fact, longer than it was 230 years ago.
The large new tree-less dunes at the tip of Castle Neck were short-lived. In the book, Sand Dunes and Salt Marshes, a study of the Ipswich dunes published by Charles Wendell Townsend in 1925, he includes the map below, drawn in 1786. In that map, Castle Neck is rounded at the end, and does not protrude so far into Essex Bay.