Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 160, § 121

Every such drawbridge shall be kept closed at all times, except while open for the actual passage of vessels. The draw tender shall at all hours of the day and night be ready to open the draw; shall decide, having regard to the convenient and secure passage of engines and trains and the state of the tide, when and in what order vessels may pass, allowing no unnecessary detention; and shall give all the necessary advice and furnish proper facilities for such passing.