As Captain Dave notes below, it’s a very good idea to call the bridge tender prior to your arrival at her/his span, to check on the latest vertical clearance stats.

Subject: Bridge clearances
Cruising News: The Socastee and Wrightsville Bridges both have 20 foot clearances listed. When we passed Socastee they had 22 feet which allowed us to pass without an opening – and Wrightsville Bridge a short time later had 17 feet which did require an opening as we need 20\’. We learned that a call ahead to ask what the real clearance is proved useful.
Dave
on GB 46 At Last