Here are a number of documents that may help to clarify the role and responsibilities of a harbormaster:
Harbor Management -
The Right Tack: Charting Your Harbor's Future. A publication of the Maine Coastal Program and the Maine State Planning Office. (1995) PDF format.
Harbormaster Authority; A proposal by the Department of Conservation, Bureau of Public Lands (1986)
Maine Revised Statutes, Title 38, Chapter 1, Operation of Vessels, especially subchapter 1, has most of the State of Maine’s Laws pertaining to harbormasters