I think you mean you have sheared a bolt for your beam, which beam front or rear? There are a few threads on this forum covering this but I can't find them. First step is to spray some CRC, Inox or similar around the sheared bolt now so it can try to soak down the thread, then get a very sharp punch and tap a centering hole in the exact middle of the bolt, then use a very small drill bit to drill a hole in the exact middle of the bolt, then use a drill bit big enough to get an easy out in. An easy out is square in shape and you tap it into the hole then turn the bolt. Once your easy out is in try to turn it the wrong way first then the right way with small movements. If the problem is with the bit of the bolt exposed inside the hull having build up on it you may be able to keep winding it down until it drops inside the boat. If the easy out doesn't work you can keep drilling your hole bigger then rethread it for your bolt. The success of that depends on your first punch mark and drill hole. Good luck