Stitch and Glue Repair Manual: chine patching
Stitch and glue construction has many advantages. It's lighter and stronger at the same time. That's a hard combination to beat. Still not convinced? Let's throw in more durable. Another way of saying that is "less maintenance." Now you're talking. But that isn't to say there aren't drawbacks too.
Stitch and glue construction is more expensive, for both labor and materials. In addition to expense, you do have to worry about moisture penetration. Stitch and glue boats constist of plywood covered with fiberglass. If that fiberglass skin gets punctured (usually at the chine) then moisture can and will penetrate into the plywood, if the punctured fiberglass skin is left unpatched for too long. If you build your own boat, occcasional chine patching is no big deal. But chine patching does make a plywood bottom (skinned with epoxy fiberglass) unsuitable as a consumer product. Most boat owners who want to buy a finished boat don't know how to patch a dinged chine, and they wouldn't do it even if they knew how.
Jason Cajune (http:/montanaboatbuilders.com) has solved that problem by building stitch and glue wood/fiberglass boats that don't have a wood/fiberglass bottom. Jason is a smart guy. I don't know the details of Jason's layup, and I wouldn't say exactly what it is even if I did know. But I do know Jason builds his boat bottoms with polyethelene honeycomb core skinned with glass fabric and kevlar, with Line-x polyurthane truck bed liner applied (by the Line-x dealer) on the outside bottom. That's a pretty bullet proof bottom.
If you do build with a plywood/fiberglass bottom (know matter who you get the plans or kit from) you should consider paying your local Line-x dealer to skin the outside bottom with truck bed liner. If you do that, you've still got a bullet proof, maintenance free bottom.
I've never done it. It's hard to teach an old dog new tricks. And Line-x does add some considerable weight. I like the lightest possible boat. And I know how to patch a chine. I've been building wood fiberglass stitch and sew boats since 1981. I do a few hours of chine patching every fall. And I've got two boats in my driveway right now that are both over 20 years old, that look great. I'm happy to keep on patching. If I do get a bad ding, halfway through the season, I make a temporary patch and then redo it the right way during the winter. Gives me something to do besides fly tying and computer programming during winter. Here's how I do it:
1) temporary patches. If I badly ding a chine during the season (which I seldom do anymore, now that I don't guide all summer anymore) I take a day off from floating. I cut the edges of the split fiberglass with a sheetrock knife, if needed, to expose at least an 1/8" slit in the glass, instead of a hairline fracture. If it's a really bad ding, I grind it out a little. Then I dry the spot out with a heat gun (a hair dryer or a bathroom heater works fine too). I do that in the morning, wait 'till evening and patch it up in the evening. I'm ready to go again the next morning. To make the patch I soak the slit glass with warm epoxy resin. Then I trowel in some resin thickened with microballoons (refer to the MRB online boat building instructions if you need more detail than that), and then I put a small patch of glass fabric over the slit, wet the fabric and then cover the patch with a small (maybe 3" x 3") patch of heavy visqueen. Then I use duct tape to secure one edge of the visqueen to the side of the boat. Then I pull the visqueen tight and duct tape the other edge. That's a final patch for minor dings. The visqueen keeps the resin from dripping out before it hardens, and it makes an automatically smooth finish surface. All you have to do is pull the visqueen the following morning and go fishing.
Later that fall, if the patch doesn't look right, you can grind that spot out a little wider, and do the same thing all over again, this time going a little slower and working a little more carefully.
For major dings, the process is still the same. You just might have to use more visqueen. There is an irrigation diversion on the lower Big Hole, below the the right channel at Pennington Bridge, that has about a 3' vertical drop in the late season, when the water is low. I've rowed right over top of that damn dam many times. But I missed it once, and fell 3' straight down onto a water melon sized boulder. I hit so hard I broke the rower's seat and tweaked my back. The chine had a soft spot about 3" in diameter. I made a temporary patch, like that, a few days later. Worked just fine.
The only time you have to do more work than that is when you get lazy and don't make the patch right away. If you let the ding go unpatched all season long, moisture will migrate into the plywood, and then you might end up grinding out 12" or more of the chine. That's a real pain in the rear end. But it still isn't all that bad, when you get right down to it. If the plywood is soaking wet, and turning black, you have to grind off the glass and wait until it's dry. That might take a week, if you've really been lazy. Once it's dry, soak the plywood with unthickened resin (assume the boat is upside down). Trowel on some resin thickened with microballoons. Patch with one layer of 3" fiberglass tape, and another layer with 6" tape. Now cut some rectangles of visqueen about 6" x 6". Foreach rectangle, fasten one edge securely to the boat with duct tape. Stretch the visqeen tight and tape off the other edge. Now lay on another square of visqueen, so it overlaps the last one by 3" or so, as if you were applying ridge shingles to the top of a roof. Continue left to right (or visa versa) until you've covered the patch. Now you're done. That's how I do chine patching. If you do it right away (within a day or two of the ding) you seldom (if ever) need more than than 2 or 3" patch. If you get lazy and let the water soak in, you might have to patch a foot or two. That's why wood/fiberglass bottoms don't work for people who buy boats. If you're a boat builder however, it isn't a big deal.
If you don't want to do chine patching, then cover your boat bottom with Line-x or Rhino truck bed liner. Line-x does seem to be the better choice, by the way. But that's hearsay. I've never actually used it.