Anyone know the thickness of the J/30 transom?

Am installing a fold-down swim ladder, am sizing the bolts that will attach. It's a four solid post folding ladder with a bottom hinge, built solidly and folding well into the water to accommodate my special needs fellow that can't work with a less rigid installation.

Bolts holding the ladder have to go through the skin, core, skin, backing plate, and have enough threads for a nut, but I'd rather not too much stick into the lazarette. I'm missing the thickness of the transom and not near the boat at the moment so I am hoping someone knows.

Also, am sharing my build plan in case there's any holes in said plan, things I should consider or do better. Please post concerns if you have any, I'm all ears.

Plan is to determine ladder's final location and clamp it to the outside of the transom. Some adjustment will be needed moving it around to make the location outboard enough to not interfere with the rudder going hard over, and miss everything that needs missed on the transom inside and out.

Then transfer drill one of the three holes in each post to locate everything precisely enough on the inside and provisionally attach it to the boat to be worked.

Going inside, I'll mix up some west system epoxy to a peanut butter, one by one attach the backing plates with (no holes yet) to the inside wall of the transom over the bolt pattern-to-be.

Then I'll transfer drill everything else out from the outside in, locating the holes. Removing everything for the moment, I'll remove just a little core from each hole and inject some more epoxy to seal those holes from the core.

Once the epoxy cures and I've redrilled those holes out, I'll bolt it up with 316 stainless hardware, making sure I isolate the aluminum backing plates.

It's a plan at the moment - any holes, better ways at this? Thanks to all.

Andy Radcliffe
Lady J #365