- Heat doesn't sound like a good idea, but I could get some freeze spray and see if that loosens them.
- Start with a screwdriver, and mangle the head. (A miracle could occur and it might just unscrew) Then when a screwdriver will no longer try to turn it, switch to vice-grips on the head. Prior experience hints that the vice-grips can generate enough torque to shear the head off, unless it comes out first.
- For ones with hex heads, the a wrench will probably provide enough torque to shear it off without the vicegrips
- I have a fairly powerful drill/driver, I could use it like an impact wrench, stepping up through the torque settings until the screw head is mangled or sheared off (or removed)
- Hammer on the long end on the bottom to try and break it loose or drive it out. I would probably put a nut back on it first so that I don't "peen" the small end over. I don't want to do this too hard, with a composite mast.
- After the head is sheared off, Grab it on the bottom with vice grips and try to twist it out. Some are already that way, and even bent too....a prior boat owner had the same problem, I guess.
- Give up entirely, cut them off, grind them flush, and drill them out if I need a hole in that place again. If all of the above fail, this is where I'll end up.
The paint is obviously in terrible condition, I roughly scraped the worst of it off. I expect to work re-painting this in with some epoxy and painting work on the mast itself.
Which ones on my list would you try?
On #1: You are right about heat. Freezing the aluminum will shrink it, and might free it up. I don't see any downside.
On #2: Since you are not going to reuse the screws, knock yourself out.
On #3: You are right, go ahead.
On #4: I don't hold much hope, but again, nothing to lose.
On #5: NO NO NO. You can fracture the carbon mast. You can't take back that last tap with the hammer.
On #6: As you note, probably a waste of time, but nothing to lose.
On #7: I would start here. If you need a hole in this location, get GOOD drill bits, the size of the hole, use a center punch backed up by an anvil or something equally as dense so that it doesn't transmit shock to the mast, and drill away. It will be the least like to do damage, both to the mast and to yourself.
HOWEVER, note that I am only looking at pictures, it's not my boat, and the guy on scene can get a better idea of how hard the bolts and screws are siezed in the holes. You don't seem to be cursed with impatience, and that's a good thing. Good luck.