After you have determined that the spider cracking is not a result of structural issue, then decide on your tolerance level for perfect, less than perfect or the dreaded good enough finish.
Some one else will come along soon with a close to perfect solution but if you just want to go sailing and are willing to accept good enough...
Clean the spider crack area, widen and clean out the cracks with an awl or sharpened screwdriver, clean again with a solvent. Butter the cracks with a filler epoxy compound, sand and prep for painting with a one or two part top side paint.
Not perfect but will look OK from across the fairway.
1970 Havsfidra 20 by Fisksatra
On the Delaware River at Fox Grove Marina Essington PA