Filling in a big hole

A thought -
Remove the existing plywood / veneer then epoxy 1/8-inch thick structural fiberglass sheet over the existing FRP and holes. No need to fill the holes.
Then apply the new wood over that.
The 1/8-inch structural fiberglass is super strong and will support anything you want to mount to it.
https://www.mcmaster.com/8537K52/

 

You say your moving things around. So your going to need that thickness if where you move things to and find your partially over one of the old cutouts. Myself, I would only fill in where I need to. Make it easier on yourself when patching in the panel backing.

When I had to put in a patch panel or fill in a hole like this, I would mix up resin with milled fiber and get the mix as thick as I could. Then use cab-o-sil or micro balloons to get it to the thickness I needed. Then use mat or cloth with the mixed putty to back it. Then fill in the space around the edges with the putty using a wide tounge depresser or my modified 1.5" metal putty knife, making sure I got the putty in and the air out. I have used peel ply on the back to make sure everything stays and reduce any runs. I would wipe the front down with acetone to get it as clean as I could and if leaving for a customer, tape in some cellophane sheeting to make the front side nice and smooth. But this was in a composites shop and I mostly worked on kitplane parts, race car bodies and maxum boats. Did a lot of Van's RV parts and repairs to RV-10 cabins and all cowlings. We also got in on some new space helmet clear visors and bubble canopies like on P-51c models.

If you have a fiberglass shop around, they might let you scrounge around in their cut offs and screw ups for pieces big enough for the repairs.

 

Have someone like https://www.tecnografic.com/ make you a complete new panel. I would bet they deal with this all the time.

 

What TT said will work just fine - as long as that extra 1/8" on the front doesn't cause any fitment issues by the front side now protruding that 1/8" further. Probably won't be an issue - but I'm not sure how tight the tolerance is between the wood panel and how the tan-colored "surround" attaches.

Another method - similar to your idea, but a little easier - would be to epoxy the 1/8" panel on the backside of the existing glass. You'd only need this 1/8" piece to be about an inch or two bigger than the hole... and really, you could just epoxy strips around the backside of the hole instead. The strips wouldn't even have to be perfectly cut to size. You're just creating a "ledge" for your 3/8" filler piece to sit onto.

Use a minimal amount of thickened epoxy to attach the filler piece to your "ledge" so the 3/8" filler doesn't sit proud of the rest of the fiberglass. It would be REALLY good if you could avoid sanding! This filler piece doesn't have to be cut exact, either - and there's no need to fill in the remaining gap around the perimeter of the filler piece. Do a test fit and drill some holes to use thru-bolts to tighten the filler piece to the backer/ledge - this is again to get that filler piece flush with the existing glass. If you coat the bolts in wax they should come back out very easily. Better yet, though, get some nylon bolts/nuts. Still coat in wax - but if for some reason they are stuck, they're easy to cut off.

 

Brad, I am with Tom on the FRP panel. I have used this before and they are very strong and no need to fill in the back unless the surrounding structure needs the reinforcement. But if a good epoxy is used to a fix it then that should resolve any stability issues. If space is the issue then Al's method is would fit the bill. But as mentioned try not to sand. I am still getting FG dust out on my wiring from when doing this myself this spring. Good luck, I am sure it will come out great.

 

Adding the "thickness" concern... if the hood is held on by screws, moving the hood an 1/8" could be a bit problematic since you'd be making new screw holes only an 1/8" away... essentially making each hole bigger. However, maybe there's some wiggle room where the screw can still be put into the original hole but a slight angle? Or use a fender washer to cover an enlarged hole in the "base structure" where the screw first goes through.

Or... I'm guessing completely wrong with how it's attached!

Either way, you've got a couple good options and once you look at things closer you'll pick the one that works best for your setup.

 

The panel with the Raymarine MFD was completely redone using a powder coated aluminum replacement panel. It has a silk screened boarder to match the factory original panel with the gauges immediately above it. The replacement panel is mounted Over the the old helm which is gel coated fiberglass on top of the 3/4” plywood Tiara used to built the helm station. There are various holes under the new aluminum panel but it looks as if the factory did the installation.