best method for removing concrete ballast

Several good ideas already, especially Hoytedow's dry ice.
I would drill the holes he suggests, but pour hydrochloric acid in them and keep adding more when the foaming subsides. The acid breaks the cement matrix so you can spoon out the aggregate.

This is a time consuming project, but it does work! I know a few guys who silently made a tunnel in rock that way.

 

I got to ask, if its in the keel and probably the shape of an Ice lolley mold could you not attach a lifting eye and haul it out in one go.

I guess you wont be replacing it!!!

I heard that you can now get spent Uranium that has timed out and is safe. I heard it is extremely heavy, maybe I dreamed it.

 

Couple of GRP boats i worked on had concrete ballast. Wasnt too bad to get out, drilled lines of holes & employed lump hammer & cold chisel. Both boats had bad osmosis issues under the concrete. Just to cheer you up!

 

Little dynamites, huh? Well why the h-e-double hockey sticks not?

Just drill the holes smaller to be a better fit for the sticks!

 

There's a fine line between genius and insanity. I have erased this line.
Oscar Levant
(1906 - 1972)