More brainstorming here:

1) Use a drilling rig that is used to drill a well.


2) I'm thinking of a sewer drain razor cleaner. I believe that there are some that are spring loaded and compliant to conform to the size of the drain pipe.

I wonder if turned slowly enough if it could conform to the varying diameter of an oval mast. I also wonder if the rivets will allow the tool to pass.

If this method was used, I would go very slowly while trying not to get snagged on rivets.

3) Apply a hot iron to a sample of the foam to see if it looses it's adhesion and shrinks. If so, perhaps an electric charge could be used at each end of the mast to send a current from one end to the other to heat the entire mast evenly.

A variable voltage generator as used by home made hot wire foam cutters would probably work well.

Then perhaps you could press the entire core out from the top to the bottom, while it is hot and in a state of surface melt.

I'm curious if you have an estimate of how much all that foam weighs.

GARY