We addressed the same problem last year.
Initially we used an old pruning saw blade inserted in the gap between the cb and trunk to see if a shell or barnacle were fouling - be careful to loosen the pennant ony slightly as the cb is solid iron and weighs maybe 75 lbs; so you don't want it crashing down if it lets loose. We also tried to loop a line over the back end of the cb and lever it down.
We were unsuccessful at freeing it in the water and ended up hauling the boat
and put on high stands with double blocking of the keel fore and aft of the c/b to allow for a reciprocating saw to be used - again, be careful. We also removed the pin and finally freed it.
We removed the scale with a cold chisel on an air hammer, wire wheel
and nitric acid and then put 5 coats of epoxy
primer, faired with epoxy
and then painted with bottom paint
. We used circles of melamine centered on the pin to act as a washer between the cb and trunk walls - to inhibit growth and scale and decrease friction. It needed a new bushing to securely hold the pin through the board and we replaced the pennant at the same time.
We tried to clean up the trunk and coat it as well though this was to access.
It has worked well for 1 1/2 seasons so far... (touch wood).