33 CFR § 117.1089 - Manitowoc River.
(1) From April 1 through October 31, Monday through Friday, the bridges need not open from 6:50 a.m. to 7 a.m., 7:50 a.m. to 8 a.m., 11:55 a.m. to 12:10 p.m., and 12:45 p.m. to 1 p.m., except federal holidays. From 10:30 p.m. to 4:30 a.m. the draws shall open on signal if at least a 6 hour advance notice is given.
(2) From November 1 through March 31 the draws shall open on signal if at least a 12 hour advance notice is given.
(3) The opening signals for these bridges are:
(i) Eighth Street - one prolonged blast followed by one short blast.
(ii) Tenth Street - two short blasts followed by one prolonged blast.