Re: BOLT head in the Bilge...
one other way of getting a bolt out is to freeze it, coke also eats rust, a butane torch really doesn't get it that hot. it may be a stud and once you remove the bracket you might have enough to grip it. you can drill out a hole in the center and use a screw extractor set.
one trick is try to tighten the bolt then spray wd40 on it then try to loosen it.