I don't talk much about my work, but we had a boat with a 65' mast, circumstances forced us to take it uop the intracoastal between Beaufort NC and Norfolk VA, thereby missing Cape Hatteras.
The bridges are supposed to be 65' high, there is one that is (reliably informed by forumite HR) 64'
The authorities give you a nice gauge.
We hung fuel cans and water cans and the liferaft on the end of the boom and guyed it out (we'd already done the trigonometry (SOCAHTOA) and worked out the angle needed
This picture shows the angle nicely
We backed slowly under the bridge, many Aussies will recognise
Captain Murray Jacob