Ken is correct, the autopilot should not be effected if operating in NAV mode as long as the GPS has a clear view of the sky. However, if in COMPASS mode bridges will definitely effect the compass autopilot. A few years ago I was helping a friend deliver his Whaleback from Annapolis to Solomons. As we passed beneath a bridge on the Severn River the compass swung a full 30*. Personally, I wouldn't rely on the autopilot in that situation. Hand steer...it's fun! Regards, Randy Pickelmann Morning Star lying Calvert Marina, Solomons, MD Sent from my iPad