I have spent more than a few anxious moments wondering if the mast would clear the bridge. It's more like terror when it's a power line. Obviously if it's on the chart and it's normal water level there isn't much to worry about. But I've done a lot of sailing on TVA lakes. I even talked to some guys who were trapped in a cove when they dropped the lake during the night. They were in a fishing boat and dug a short channel to deeper water. I've thought about trigonometry but for that you'd need an accurate rangefinder. I've never hit the mast on a bridge but have came close. I even thought of a laser pointer on the mast top that you could see with binnocculars but that seemed too much. Some bridges are easy in that they paint numbers on the bridge showing the clearance. This has been an issue in that in the fall when they drop the lakes it opens up a lot of new water to explore. Any clever solutions???