The modern American super carriers are big ships. They are 1,100 feet long and 250 feet high. When the giant ships dock in San Francisco Bay they have to go under the Golden Gate Bridge and sometimes the Bay Bridge. Clearance on both bridges at high tide is 220 feet. To clear the bridges the ships have to wait for extreme low tide. This allows just enough room for the mega ships to pass under. But just enough room, the top of the radar mast usually has 18 inches of clearance from the bottom of the bridges.
Passing under the Bay Bridge