transom ladder installation
You need a backing plate; and (as Paulk says) Aluminum would be better than sealed wood backer.
Donít forget to seal the transom mounting hole edges (epoxy), then bed the bolts & ladder mounting plate.
Drill the bolt-holes perpendicular to the mounting surface.
If your transom is cored, you should back-cut & remove the coring and in-fill with thickened epoxy (for crush-resistance, etc).