Here is video I just completed on how I have gone about dealing with wet balsa. I'm just about finished with drying 85% of the hull below the waterline. The other 15% is the 12" just below the waterline that was adequately dry when I started. Having done this much work I did sort out a couple of techniques to make this tolerable work. This video is about getting to dry balsa/new core. I will do another on the filling and glassing, but that is well covered in many places elsewhere on the web.
I apologize in advance for the video and editing work, but I think it is important for owners of these boats to know they can be repaired and restored.
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Dave, thanks for posting this, it is extremely helpful and timely for me. These are some of the things I am wondering as I watch it:
Is it worth it, or even possible, to fix more than a 2 sq foot space at a time? Could it cause structural issues if you go bigger?
You mentioned that if some of the surrounding areas to the patch are wet, then they will seep into the patched area soon enough, and that this is where the closed cell foam comes into play instead of using balsa. But then you probably have to scarf the connection between the surrounding wet balsa and new foam. Does the scarf hold up if the balsa is not fully dry?
What thickness of divinycell have you been using on the sides just above/below the waterline? Is it 3/4"? Any particular product number you've found to be the best: H45, H80, etc.?
When I started I was concerned about the amount of area open or exposed at any given time. But then I got over it. I think if the boat is reasonably well supported you can open areas larger than 2' x 2' and for sure I have. I didn't open everything up all at once, but did have two or three open areas around the bottom of hull. It kind of becomes a progression and each area is getting a different kind of attention. The big concern I had was that when I had exposed bare balsa I for sure had to be confident that it wouldn't rain until I got the balsa fully dried and covered with the epoxy fairing filler. The filler provided plenty of protection against the rain until I was ready to glass the section back in.
I used the Divincyl because I had it and it does solve the moisture moving around problem. But you can use balsa too, but you have epoxy coat the balsa next to the area you are working to stop moisture migration. All of the core you will be dealing with below the waterline will be 3/4". At the junction of new and old work and any gaps and there were several I simply filled them with West 407 low density fairing filler. If you have the time and inclination to cut core to shape have at it. I just figured I could fill gaps faster than cut core to shape. Epoxy filler is much more expensive than core, but it quickly solves the boundary issues between old and new work. It is also going to be slightly heavier than core, but..............oh well.
Low density foam core is adequate for this work. Remember that you don't have to replace it all, just the bits that get damaged removing skin, or is so punky after drying as to be useless, or the stuff that refuses to dry out. On my boat where I have gone after everything below the waterline that was wet I think I may have replaced about 10% of the balsa core. The rest dried out and stiffened up and as far as I am concerned is good to go.
My boat now has multiple new layers of glass on it. It is entirely possible that with all of the work that has been done that this hull is slightly different shape than it was when it was new. Again, oh well. I suspect that it is going to also be stiffer than the original hull was because the epoxy resin is stronger and the biaxial, triaxial and cloth is stronger than the woven roving and all of the chop strand material that was used to build the boat. You do have to pay attention to section thickness wherever you are working. On my boat down by the keel and out 18" the thickness is 1/4" and above that it is less than 1/8" of actual glass. The resin is often thicker, but that is a function of how they were bonding core to the glass.
It has been a busy couple of days here in my boatyard. I have been getting lots of fiberglass on the hull and am starting to think through how to get some of the coming steps done. But I wanted to get another video together to show how I have gone about this part of the process. No doubt there are lots of ways to do this kind of crazy work, but I haven't seen anyone else actually doing an entire hull. You can find lots of information about doing core work on decks and there have been many J30 guys that have done area repairs, but I don't think I have seen anyone that has actually gone after the entire wet area of the hull below the waterline.
I really think of this boat the same way guys that restore old cars would look at their project. A little intimidating at times, overwhelming sometimes and then sometimes the whole thing reminds me of making sausage. A little ugly, but the end result should be worth the effort.
To that end the video I shot for this segment shows what might look like some ugly glass work. But that is in part the result of doing this work overhead and it shows the glass before it got sanded out, so don't get too excited yet. Also, there are many light spots you see that you might think are bubbles or poor bonding. In fact it is the result of using some Interlux Watertite Epoxy Filler that is light blue color. While most of the filling I have done is with West products I wanted to use something that was more like Bondo in the way it applied and was mixed. This filler is nice because it is stable as soon as it is mixed and it cures fairly quickly, but is easily worked.
So go get a beer or something much stiffer and you can see how I have been doing this work.
I will add some new images of the pretty work from today as soon as my computer gets rebooted.
Also I apologize for the low audio level at the tail end of this, I found out after the fact that it was the computer mic and not the stand mic that actually got used for the voice over section. Maybe someday I will figure this stuff out, or not.