Hmmm I don't know if that is true but if it is then get some loosenall type of bolt unfreezing liquid raise up the hull so the fluid will seep in around the bolt and try to turn it. Problem is how to turn it.

Ther only way I can think would be to use screw extractors but they work the wrong direction, so you would drill a hole and put a small screw driver that is larger than the hole and bang it in with the hammer and try it.

Just be careful you don't ruin everything in the process.

It looks like cmerrill is right but proceed carefully whatever you do.