Sunday, October 27, 2013

Water In The Bulkhead, Part 2

After a lot of online research and some phone calls, we've decided to continue with the epoxy and microballoons approach. Here's the reasoning behind our choice, not in any particular order.

1. Microballoons are relatively easy to replace, so if a different repair is required, it isn't too difficult to attack the filler with a grinder to remove them. Yes, it is messy. However, it is a doable job.

2. I talked with the Gougeon tech support staff about our proposed approach and they didn't see any problem with it. That's not to say that they are the definitive source of good advice. I was particularly interested in any studies and testing that they may have done regarding the strength of panels in which the balsa core was replaced with epoxy/microballoons. The person I talked with wasn't aware of any specific tests. So while this isn't really a reason to use epoxy/microballoons; it is more like disclosure of what we found in our research.

3. If the repair were made with anything but more balsa, it would result in butt splices at the edges. I don't think that it is possible to do a good scarf joint to the exiting balsa core as the repair approaches the center vertical support beam without affecting the integrity of the structural connection of the bulkhead to the main the support beam. I'm an electrical engineer, not a structural engineer, so this is my impression based on my past experience and is not based on specific technical knowledge of the materials and structure.

4. There was some discussion about the use of  different core materials that have different tensile, sheer, and compression characteristics than that of balsa. CoreCell foam could be used (5lb/cu-ft density) as the core, but would have butt-joint problems as well as getting it to adhere to the existing panels. The existing fiberglass panel on the locker side of the bulkhead could be cut out and re-used by a tapered fiberglass joint around the edge. Or the panel could be cut out and replaced with new layup of fiberglass and unidirectional glass. I can't comment on which might be better.

5. We were told that polyester won't adhere well to epoxy, suggesting that gelcoat (a polyester) won't adhere to epoxy. Gougeon has done some testing that indicates that gelcoat adheres well to epoxy when compared with gelcoat adhesion to polyester fiberglass panels.
The contrary argument appears here:
For our purposes, in the forward locker, we can do the necessary preparation to assure a good bond. It doesn't have to be the same kind of finish as if the repair would be on the exterior.

6. Epoxy has great adhesive properties, about 10x that of polyester resin, according to the WEST epoxy site. Now I can't find the reference I read. I'll edit this if I find it.

7. Epoxy will elongate up to 4% (polyester is about 1%), allowing the core material to flex somewhat in use without collapsing.

Finally, LUX is about to start the winter charter season and we need to do something now. Since we can change it in the future (see #1), it makes sense to use epoxy and microballoons while we collect more information.

A useful reference is Fiberglass Boat Repair and Maintenance:

I find their testing reports more useful though, because they tend to have more pure test results.

The repair went well, taking all afternoon. We mixed about 6 oz of epoxy at a time and applied it with a caulk gun and an empty caulk tube. We cut the caulk tube down to just hold 6 oz, making it easier (less distance) to force the plunger back out of the tube. The small amount also reduced the exothermic reaction, preventing overheating. We waited 20 minutes between applications to allow the heat to dissipate. One of our portable fans (see Ceiling Fans!) was used to blow air onto the panel, which helped remove the heat. It was a messy job, but we eventually finished it just after dinner. We were able to drill the holes for the fresh water feed-through fitting and get water running again before retiring for the night. Gee and Peggy did a great job of fixing and cleaning up dinner with water from several pitchers. 


1 comment:

Terry said...

See prior post on this topic: