That's just a fairing compound, the cracks are because fairing compound really has no strength.
Un Tension the standing rigging
, if the mast is stepped, and place a 4x4, a 3/4" piece of plywood
on the floor and under the bottle jack, be sure to find a spot on the floor that can be supported by dispersing the load with the plywood
piece and supported under the floor to something solid, not a flimsy area.
Support the 4x4 with some framing to hold it upright and inline with the place you will jack on as near the compression post centered under the mast base as close to the compression post base as you can. Remove the mast step bolts on he outside deck going thru the step plate and cabin
As you have un tensioned the rigging, the mast will not be loaded by the rigging, just under weight of the mast.
You can use the bottle jack to take the load off of the compression post and remove it.
Then your free to grind that area out under the mast and build up with epoxy
and 6oz mat glass, the final layer of glass should be roving weave, if you laminate all the layers together you'll build it stronger and save yourself grinding to add layers of glass.
After its hardened, re drill your holes for the mast step, you can also add a plate of metal to the built up area, for the post to sit on, if you do, use 3/8 to 1/2" aluminum
plate or stainless, aluminum
is easier to drill, drill the step holes carefully and replace with new bolts.
The total build up will be about 3/4" to 1".
The post may need to be shortened to fit in here now, a simple measure and cut a section out an reweld.
It's a bit of a pain, I did it last winter to my step and never took the mast down, and it now is as solid as can be.
Sent from SV Cloud Duster