33 CFR § 117.641 - Pine River (Charlevoix).
(a) The draw of the U.S. 31 bridge, mile 0.3 at Charlevoix, shall be operated as follows:
(1) From April 1 through December 31, the draw shall open on signal; except from 6 a.m. to 10 p.m., April 1 to October 31, the draw need open only from three minutes before to three minutes after the hour and half-hour for recreational vessels. Public vessels of the United States, state or local vessels used for public safety, commercial vessels, vessels in distress, and vessels seeking shelter from severe weather shall be passed through the draw as soon as possible.
(2) From January 1, through March 31, the draw shall open on signal if at least 12 hours advance notice is provided prior to a vessel's intended time of passage.
(b) The owner of the bridge shall provide and keep in good legible condition two board gauges painted white with black figures not less than six inches high to indicate the vertical clearance under the closed draw at all water levels. The gages shall be placed on the bridge so that they are plainly visible to operators of vessels approaching the bridge either up or downstream.