If this is an attached fin keel then I would be more concerned with the long
term effect of the compression load where the keel is attached..

Say the ballast only accounts for 4 to 6 tons, the remainder of the 10 ton
will be concentrated on the faying surface between the keel and the hull..
This could ultimately cause damage to the internal keels support
structures..

I recommend you consult the boat designer or builder or a competent naval
architect..

Again, I find not fault in holding the boat upright with the mast but this
provides not under hull support.


--
My opinion and experience. FWIW

Steve
s/v Good Intentions