As I mentioned in the last photo please use properly sized backing plates!
This is a prime example of DIY boat work gone bad. Ouch!! This stanchion base had NO sealant of any type installed. No polysulfide, no a polyurethane, no butyl and not even the dreaded silicone.
As a result of this unbelievably poor installation the core turned to mush. The thin fiberglass deck skins, combined with dinky little washers, could not withstand the forces applied on the 24" lever attached to the stanchion base, and ........ rip!