Their is a trick you can do, to get a fifty foot mast under a 45 foot bridge, i saw this done a couple of times, but never tried it myself. (never needed to) you unhook the main, and jib halyards, tie a couple of fifty gallon water drums full of water to them, (more water drums if you need it) you set the water drums at a calculated hight from the eater, you tie the water drums together, and fill them with water, you set them on the deck, so they can clear the rails and everything else, then you turn the boat, either hard to port, or hard to starboard, the drums swing out the opposite direction, and pull the boat over, and will only stop pulling the boat over, when they hit the water, (if you have done it all correctly that is) then you can steer any direction you want, with the boat listed over to scary angles, wich allows you to pass under a bridge you dont have the clearance for. when you want the boat back up, you just slack away the halyards, very carefully, due to the weight that is on them. You can see someone do just that, on utube, here is the link
http://www.youtube.com/watch?v=WGAzt-8minI