The draw of the S165 bridge, mile 20.2 at Chesapeake, shall open on signal; except that, from 6 a.m. to 7 p.m., the draw need be opened only on the hour and half hour for the passage of pleasure craft. Public vessels of the United States, commercial vessels, and vessels in an emergency endangering life or property shall be passed at any time.
33 C.F.R. §117.1021