It Worked.

You know, sometimes I even surprise myself.  This through hull replacement turned fix the cored hull seems to have turned out as good as I could have hoped.  In my last post I talked about how two through hulls were not put in properly on the boat and the negligence could have allowed water to soak into the core and cause delamination (a very serious structural problem on cored composite boats). As it turned out, there were actually three through-hulls that were apparently installed by the same people, but in one of the cases they got lucky and didn't drill through cored fiberglass.  The only evidence all three were done by the same folks were they were all related to the AC system (or generator to power them) and that they failed to remove the old bottom paint before installing any of the three the through hulls.  Ablative bottom paint isn't the best surface to try and create a seal against..since it ablates after all.

To fix the prior installation issues, I spent a lot of time with a small screwdriver, a Dremel tool, and even a hex wrench to remove any wet core material I found and create a void between the fiberglass skin layers. I could then fill the void with epoxy to seal the remaining core and create a better mounting surface for the through hull. Before adding the epoxy my wife and I, for good measure, packed the holes with silica gel (a desiccant) to pull out any possible residual moisture in the core.
We let that sit for a day or two as we worked on cleaning up the other through hull holes and located parts for another unexpected project.

Yesterday we continued work on these two through hull holes. We started by removing the tape and silica gel we had packed into the holes.  Did I mention that the location of these two through hulls is in one of the least accessible parts of the boat, directly underneath the stairs that lead from the salon to the starboard hull.  The only access is via a cabinet door under the desk and that door leads to a chase that runs aft under the stairs.  And these holes are located just about a full arms length from that cabinet door.  Add in the air conditioner lines, raw water pumps, and other hoses and wires that are run through this space, and working in it can be...well...a challenge.

View from the access location.
The short black posts are the wrapped PVC pipe
in the holes in the hull.

Using my Dremel tool, I drilled several holes through the inner skin of the hull and into the area where I had removed the balsa core material so I could inject epoxy into the voids.  I then took some plastic (trash bag actually) and wrapped two small pieces of PVC and inserted them into the the two holes.  These would create a mold for the hole I want to remain and allow me to inject epoxy into the voids without it all spilling through the holes and ending up on the ground.

I mixed up some West System G-flex thickened epoxy, placed it in a syringe, and began injecting the stuff into the holes.  I started at the bottom injection hole and would squirt epoxy in until I saw it come out the next two holes above it.  I then took some cellophane tape and covered over the lower hole and started injecting from the next holes up in order to try and prevent any air from being trapped inside the repair. Oh, and to see the holes, I needed to use an inspection mirror attached to a flexible shaft that I could wrap around whatever was convenient or have my wife hold and position to get a look at my work. It took about two full West System epoxy syringes worth of epoxy, and I have no idea how many colorful metaphors, to fill the area around each hole.

The holes sealed and ready for replacement through hulls.

The epoxy takes between 7 and 10 hours to cure, so I couldn't see the results of all the work until this morning.  When I got up this morning, I was a little concerned how easy it would be to remove the PVC "molds".  Luckily, they slid right out and exposed a very nice cylindrical hole lined with epoxy. The results look very nice and I'm sure this will keep the core sealed and provide a good structure for re-mounting the through hull. Hopefully we can get some of those re-installed tomorrow.