Gel-Coat Cracks in oc1 canoes
What to do and what not to do when repairing your outrigger canoe.
In the last article I talked about the construction of the canoes, the materials used, epoxy, carbon fiber, core-mat (a foam core), and gel-coat. The gel-coat is the color, and being a polyester resin product, is brittle. As I said last time, if there is any flexing of the canoe, the epoxy, carbon fiber laminate can handle it, but the gel-coat might crack, especially if it is thick like most of the older boats are. Some manufacturers have gotten wise to this and are applying their gel-coat as thin as possible and still make an even color. Although this makes repairs a little more difficult, it is much better and eliminates most gel-coat cracking.
The bonding of the epoxy laminate to the gel-coat is another critical thing. Manufacturers have learned and improved on this process, and for the most part the bonding is excellent on the newer boats. I have seen many older boats, however, where, once there is a gel-coat crack, you can literally chip off the gel-coat with your fingernail. The learning curve of the manufacturers has all but eliminated this problem, and if you have a new boat that does this, something is wrong.
An interesting and important fact about the relationship of epoxies and polyester resins is that epoxy will adhere to cured polyester, but polyester will NOT bond to epoxy. Because of this repairs should not be made with polyester resin. I have repaired many of these "polyester repairs", and although it may seem to work, in the long run if there is any stress to the area, the bond will let go, causing further problems. Make sure whoever repairs your epoxy canoes, uses epoxy. Now, you can understand the repair dilemmaï¿½ I never use gel-coat, a polyester resin, for repairs. Instead, after making the structural repair, and fairing it, I spray with and an epoxy primer, and then spray a quality linear polyurethane paint. The color is matched with computer color matching. If it is gel-coat crack only (common in older boats with thick gel-coat), I sand the crack out, making sure the surrounding gel-coat has a good bond, fill with thickened epoxy, fair, prime and paint. That being said, for the home repair job of a gel-coat only crack, using the stock color gel-coat would be easier, filling the sanded out area. The gel-coat can then be sanded smooth, finer and finer (to 1500 grit) and then polished out. I really don't recommend this except the smallest of hairline cracks on the older, thick gel-coat boats. In larger cracks the bonding problem of gel-coat to cured epoxy becomes an issue.
If the area around a crack is soft, or after you gently sand the gel-coat off, you can see a stress line in the carbon fiber, then some reinforcement repairs are needed. One other note while we are on the subject. The Hurricane, a very popular canoe by Maui Fiberglass, does not use gel-coat. Hurricanes are painted with a linear polyurethane paint, which I think is an excellent idea, but from a manufacturer's viewpoint, adds many new production problems, including cost and time.
In the next article, I would like to address the steering systems on OC1s, and especially from the safety standpoint, checking your cables. Aloha for now.
Posted by SteveGates on Sat, 12/14/2002 - 6:22pm