reinforcing woodstrip canoe

charltons

Curious about Wooden Canoes
I have a 17' Redbird I built some years ago. It currently has a crack, mainly on the inside, where we got hung up on a sinker and a lot of weight was put on a small area. There was a little oilcanning, and then CRACK!

I don't really want to add too much more weight, and I don't really want to mess with fiberglass/resin for a while. I'm rebuilding a wood/ canvas, so it got me to thinking: what about a few ribs on the inside? It shouldn't take too many to reinforce it, white cedar wouldn't be that heavy, and it might look pretty cool. I could just epoxy them in and "clamp" them with weighted bags or something. Any thoughts?
 
Somewhere in the inside of your canoe, about where you were "hung up on a sinker," there's a crack in your 'glass work. All it needs is a patch.

Sand the area to give the next coat of resin some tooth, and put a patch of glass around it, about 2" on all sides of the crack. Epoxy it on, do a filler coat of epoxy or two, let it cure, sand it smooth... almost an invisible repair. Make sure the wood's dry before you patch it. It's much easier than glassing the entire boat, which you already did, when you built it... That's the short-term fix, to get the boat back on the water.

Longer term, you may want to put a larger "patch" of'glass in the "football" area inside the hull. This will help prevent further cracks from those rock-kissing events. Search the forum for cedar strip repairs; you'll find Todd Bradshaw's excellent description of how this all works.
 
Thanks for the reply. i've already patched an area on the inside from a similar incident. The problem is the relatively flat area between the bilge and keel line. It flexes, and when pressure is placed on a point it flexes and cracks. I'm just considering alternatives to having to glass the inside, and I'm not sure if even two layers will help the flexing much. But your suggestion is a definite possibility. Thanks again.
 
Just did a search on ribs for a composite-turns out it's a bad idea. I guess its a temp patch (procrastination will probably make it permanent) and then additional glass on the inside.
 
"procrastination will probably make it permanent"

But of course! After you fix it won't be broke, and if it ain't broke, why fix it? :)
 
What is the layup on the inside, because it obviously was not enough across the bottom of the boat? Unfortunately, strippers don't tolerate bottom bounce very well. You could try bending ribs into it, but the job would be a pain and you're also creating a potential maintenance problem and probably adding an awful lot of excess weight. A better, stronger, more durable and lighter bet for ribs would be glassed-over half ribs across the bottom, spaced every 12"-18" or so. These could have a cross section that is maybe 1" wide at the base, rounded on top and about 3/4" tall. You could use balsa (you can even buy pieces designed and pre-shaped for the leading edges of model airplane wings at hobby stores) but cedar would probably be better and isn't hard to shape. It's almost as light and does not soak up water like a sponge if any happens to get in. They could also be lower in profile, but wider if that suits you better. This is standard practice on a lot of fiberglass and Kevlar canoes. They will often have ribs a couple inches wide, 1/4"-1/2" thick, made from slabs of foam with the edges beveled and then the whole rib is glassed-over. The half-ribs should extend across the flat bottom and taper out where they meet the curve of the bilge. It would be very unusual to need them to also extend up the sides on a stripper, since the curves of the bilge add so much stiffness. You epoxy the wooden half-ribs on top of the bottom's glass. That forms the core. Then you lay at least two strips of fiberglass over the top of them, extending a couple of inches onto the flat bottom on each side. Fill, sand the edges of the glass to feather them out, or whatever you want to help blend them in with the cosmetics of the rest of the bottom.

These will stiffen the bottom substantially, but maintain at least some flexibility on impact. However, they do make stress risers (stiff spots in an otherwise more flexible area) which would be somewhat more prone to deep abrasion or damage from rock impacts. Compared to adding a uniform layer of glass over the bottom, they are probably similar in bottom stiffness, but not so much in overall durability. Their job is more to stiffen than strengthen, but removing bottom bounce from the equation will certainly help preserve the boat in the long run.

When I built my big canoe I added half a dozen half-ribs, just to help stiffen the flat bottom. In this case, I followed a tip I read somewhere and used flexible plastic tubing for the cores. It was tacked to the bottom with a hot glue gun and then glassed-over. It worked, but it was hard to get the tubing to lie straight and neatly. In the long run, simple wooden cores or foam cores would have produced nicer looking ribs.
 

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"A better, stronger, more durable and lighter bet for ribs would be glassed-over half ribs across the bottom, spaced every 12"-18" or so. "
I typed ribs, but I was thinking half- ribs. I used 4oz to try and save weight ( the first version was very heavy) but it seems too delicate. It's totally sheathed in glass, but the problem comes when something like a branch or sinker causes the hull bottom to flex. The inside glass breaks more than the outside.
Half ribs are a nice solution, and gives it a more traditional look. I didn't think about glassing over them. Thanks.
 
The little cedar half-ribs have fairly minimal strength and stiffness by themselves. It is the curved layers of fiberglass on top of them that are doing most of the actual stiffening and what strength increase the system is providing.

You might want to read the last couple of paragraphs of a post I made yesterday on Tex's Old Town Trapper thread (page six, post #51) because unfortunately, your boat is a perfect example of what I was talking about there.
http://forums.wcha.org/showthread.php?3081-Fiberglass-Structural-Strength-Old-Town-Trapper/page6

I was a sculpture major in college and worked mostly with polyester resin, epoxy resin and fiberglass. I had three professors that I worked under or for who were all pioneers in different types of composite sculpture technology, so I had to learn that stuff. At the time, fiberglass canoe technology was still pretty much heavy, flimsy, chopper gun constructions with wood or aluminum ribs buried inside to try to hold the bottom shape. These days, the composite canoe and resin technology has advanced drastically and with all the manuals and books available (and about half of the information on the internet - the other half is BS) I am amazed at how little the average boat builder bothers to learn about the subject before they start slathering resin and/or telling others how to do it. Epoxy and fiberglass can do some pretty neat things, but only if the builder knows what to do with it and the basics of how it works or doesn't work. It is not an instant way to make the boat stronger or strong enough, and in some cases, it may not add any strength at all. With the price of materials these days, most of us can't afford to throw away a couple boats before we finally decide to actually study what the materials can do and how to get the most out of them. Maybe it's a generational thing and the current generation is only interested in instant results, but as far as I can tell, nobody is born a great fiberglasser and it's either going to require some study work or trial and error with a bunch of failed or poorly constructed boats in order to become one. Rant over.
 
"but as far as I can tell, nobody is born a great fiberglasser and it's either going to require some study work or trial and error with a bunch of failed or poorly constructed boats in order to become one. "

That's the truth. I actually went through three tries on my woodstrip before I was happy with it. The first one turned milky white. rebuilding a wood canvas has been a real eye opener as to the different construction methods. I definitely appreciate the older ways more. For sure I've found out that fiberglass and epoxy doesn't = indestructible. The reason I am looking into half ribs is I remember you stating somewhere that two layers of fiberglass is about as thick as a milk jug. That puts it into perspective.
 
That was something that I was never really aware of and hadn't thought about until I saw it with my own eyes. I was building a set of really fancy Kevlar sails for my mini 12 Metre sailboat and needed four fiberglass leech battens about 12" long, tapered in thickness toward their inner ends to flex easily and built up to be pretty stiff at their aft ends. I had some leftover six-ounce cloth and plenty of epoxy, so rather than just buying battens, I figured I'd make my own. I sarted laying up graduated layers of cloth on a sheet of plastic and simply couldn't believe how many layers it took to finally arrive at a thickness that had some body to it and wasn't limp as a noodle. As I remember, I ended up using six to seven layers just to get the forward "soft" end substantial enough to work and a whole bunch more for the stiffer aft end. When they make battens in a factory, they only use lengthwise directional strands and a lot of them, then they saturate it with resin and put it in a heated press under a lot of pressure to get a very high glass-to-resin ratio. Mine eventually worked OK, but making them was a lot more work that I had thought it would be.
 
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