This through hull replacement project has turned into another case of discovering things done wrong. When you have a composite cored hull, it is important to keep water from being able to get to the core. When water penetrates, it can cause the core material to separate from the fiberglass skins, and that significantly weakens the structure. As I previously mentioned, some people with Leopards have reported that they have found through hulls where the core was not properly sealed. So, needless to say, I was a bit worried about this project, despite the pre-purchase survey finding no indications of moisture around the fittings.
Well, the good news is that all the factory through hulls are in solid fiberglass, no core material visible. Unfortunately, it appears that a couple of my through hulls were not done at the factory. The two through hulls that feed raw water to cool the air conditioners were not installed properly. The holes were drilled through the cored hull, and no measures were taken, other than the bedding sealant used, to seal off the core. In addition, they didn't even bother to remove the bottom paint from the area before the through hulls were installed. It was a ticking time bomb.
Fortunately, we seem to have caught it in time. The sealant that managed to stick to the through hulls and the small amounts of exposed gel coat that weren't covered in bottom paint had just started to fail, and there was only a very small amount of moisture in the cores right at the holes.
The proper way to put a hole through a cored hull is to drill a hole larger than the one you need, fill it with epoxy fiberglass, and then drill the smaller size hole you need in the new fiberglass. This results in a solid fiberglass sleeve that not only seals the core material from any potential water leaks, but also provides a surface with higher compression resistance for the clamping of the through hull. Since I already have a hole and drilling a larger hole isn't really an option at this point, the repair technique I will be using consists of digging out some of the core material around the hole (this will also get rid of any wet core material) and then filling the created gap with a thickened epoxy to create the solid sleeve and seal off the remaining core.
|Cleaned up holes packed with silica gel.|
Most of yesterday was spent cleaning off the old bottom paint that was found underneath the through hull (how does pressure washing take this stuff off and yet a scraper and sandpaper have such a tough time with it) and digging out the old core material to about the diameter of the through hull head (3/4" deep or more). It took quite a while to chip out the balsa with a Dremel tool, screwdriver, and hex wrench (think bent piece of wire).
Once I had the groove cut out and could see good balsa all the way around the holes, I decided I really wanted to make sure that all the moisture was gone. I started with a heat gun, but wasn't making any real progress...and I didn't want to sit there for a day or more waving the heat gun back and forth across the holes. Then I remembered I had a bunch of extra silica gel from making those desiccant packs for my tool storage containers. We took some tape and sealed over the bottom of the holes, then filled the holes up with silica gel, working it into the areas where I removed the core and taped off the top to prevent atmospheric moisture from interfering with the gel. Hopefully, leaving this stuff in there until we are ready to fill it with epoxy will extract any latent moisture.
We were lucky. The poor practices of the original installer were caught before any significant damage was done. If it weren't for the need to replace a couple through hulls and the decision to replace them all, we might not have found this issue until much more extensive and costly delamination repairs would be required. And getting things done right is how we ended up in a boatyard doing work ourselves in the first place...well that and the cost of getting things done by "professionals". Now is my chance to do it over and do it right.