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:confused I could use a little feedback from builders. I am in the process of sanding the hull of my 15' Ranger/Prspector and trying to make up my mind what weight fiberglass
cloth to use.
I was looking at using 5 oz RAKA inside and outside. Now, I am told that RAKA no longer
has 5 oz. So my question is; Is 4 oz outside w/ an extra layer on the bottom and one layer of 5 oz on the inside enough for lake (stillwater) use ??? .
I sure would like to hear from folks that may have used the same or similar material.
PS; I am going for a light canoe fisherguytoo@volcano.net
I use 6oz outside and 4oz inside, on my past two boats.
I'm planning on using 4 oz inside & out on my next solo canoe.
I will be doing a double 4oz layer on the (very, high use)outside, bottom.
I will be doing the similar on the inside, with a (2-3") overlap.
Doug
"Some people hear the song in the quiet mist of a cold morning..... But for other people the song is loudest in the evening when they are sitting in front of a tent, basking in the camp fire's warmth. This is when I hear it loudest ...." BM
I am going to use lighter glass cloth such as 4 oz. If you lap it by 4 - 6 inches down the center line and you will still have plenty of strength in the high abrasion area.
Also I am going to use 4 oz inside but instead of using one piece from front to back use 38" cloth across the boat. Lap each section by 4". This creates a kind of "frame" stiffener.
All will be in order to lighten up the (Osprey) canoe.
Doug
"Some people hear the song in the quiet mist of a cold morning..... But for other people the song is loudest in the evening when they are sitting in front of a tent, basking in the camp fire's warmth. This is when I hear it loudest ...." BM
A lot depends on the bottom of your canoe. If it is really flat bottomed, I doubt if one 4oz layer in and out will be enough to prevent oil-canning of the bottom. The bottom of my 38SPL solo canoe is really curved all the length, and 4oz would be enough for that. For a larger 2 seater canoe with a flat bottom however, I would lay an extra 4oz cloth layer in and out.
Always try to maintain the same thickness in and out, the sandwich construction is ideal that way. If you prefer to add an extra layer to one sie only, the inside is more likely 'cause it takes all the stress when hitting things.
In a thread a few months back "Hellp! - split along a join", the discussion eventually turned toward fiberglass and hull strength. I pulled this response from a "Guest" to add to this discussion but you might want to search from that thread and read more.
Stripper construction is somewhat like making a "I-beam". You have two load-bearing skins (the glass - similar to the top and bottom of the beam) seperated by a non-compressable core (the wood, which performs the function of the I-beam's web keeping them apart). When flexed, the thicker the coring between the skins, the more differently the skins will be stressed. If you layup four layers of six ounce cloth, stacked on a sheet of waxed paper and let it cure, you'll find that you can bend the finished piece a long way before it fractures. The layers on the inside of the bend will primarily be in compression and those near the outside primarily in tension, but since the piece is quite thin, all the layers are "moving" a fairly similar amount. If you lay up another sample, this time with a 1/4" wood core between each pair of glass layers the I-beam effect will yield a much stiffer panel. Test bending will show that it won't bend nearly as far or as easily as the non-cored panel without fracturing (or sometimes delaminating) and it's always going to fracture worse on the outside (the tension side) of the bend. This is because the fiberglass on the outside of the bend has to move and/or stretch much farther than that on the inside of the bend.
A stiff hull is very good at moving efficiently through the water, but if that stiffness is gained by making a thicker I-beam (as it is with a stripper) it comes with the limitation that it won't flex very far without over-stressing the fiberglass on the tension side of the layup. When you paddle over a rock, or if you build a hull which exhibits a lot of "bottom bounce" in flat water, it's always going to bounce or flex primarily inward. This puts the tension on the inside layers of fiberglass. The inside of the hull becomes the more vulnerable "outside" of the bend.
I cringe every time I read a post on a stripper board where someone states that they doubled the six ounce glass on the outside for durability, but then used a single layer of four ounce cloth inside to save weight. They've essentially built an I beam where the top plate is only one third as strong as the bottom plate and they are now going to flex it from below, putting the majority of the destructive force on the top plate. All too often, their next post is something like "I took my boat out for only the second time and the fiberglass split on the inside. In addition, every time you flex a piece of fiberglass (or wood, for that matter) you break some fibers. You may not see them, but they're there. Unfortunately, they don't grow back. Your I-beam gets slightly weaker and loses a tiny bit of it's original stiffness every time your hull flexes. The ski industry is well aware of this and it's a major reason that laminated, cored fiberglass skis lose their camber over time.
New builders don't seem to have a problem understanding that a tough outside will protect their stripper, but the often don't seem to grasp the fact that without an equally strong inside, you won't have a strong I-beam or a strong boat. In fact, if the inside isn't up to the task, the outside will probably never get stressed enough to need the extra reinforcement because by the time it comes into play, the inside has already broken. Consequently, a stripper's outside skin has a fairly easy job - resist rocks. On the other hand, the inside skin has a much tougher job - keep the boat in one piece - and do it while surviving more stress. I suspect that the "ideal" stripper layup would have more glass inside, but don't know if anybody has done real tests and figured out the best equation. I've always had good luck using balanced construction with equal amounts inside and out (not counting bow and stern, lower stem reinforcements for abrasion).
I generally have used regular 6 oz. fabric because it's cheap, available without a hunt and hasn't failed me yet. Some of my oversized boats (fur trade canoe, drift boat, etc.) had cloth up to 10 oz. and strips up to 3/8" thick, but six ounce seems to give me as much durability as I need without having to baby the boat too much. I've also installed glassed-over, cedar or balsa "half-ribs" (half-round, 3/4"-1" wide with tapered-out ends) across a couple of wider-than-normal bottoms to prevent bounce. They worked fine, but tend to concentrate hull damage if you run over rocks as they make stiff spots in the hull. I may play with some more exotic, lighter cloth on future tripping boats, because I'm not getting any younger and portages aren't getting any shorter, but the layup, inside and out, will certainly be balanced.
That was me. I don't know what I screwed-up that day, but it logged me on as "Guest". Rebuttals can be aimed in my direction.... The 22' long boat you see on the left is built that way with 10 oz. cloth and hollow fiberglass half-ribs in the bottom. It's almost 30 years old and currently sitting in the back yard under a tarp and doing fine.
I've used Raka's 5 oz, 6oz, and 3.2 oz tight weave on boats that I've built. It's too bad that the 5 oz is gone, because it seemed to make a very light boat, although it was a pain in the butt to wet out and it would occasionally have weird visible lines running through it. When I used 3.2oz tight weave, I used it in three layers, and although I don't know how the final weight would compare to the same boat built with 6 oz glass, I expect that the three layers of 3.2oz would be lighter than one layer of 6oz, and probably stronger. Someone else will have to speak to the engineering involved with multiple vs. single layers of glass, because I just read an arguement somewhere and bought into it. The 3.2 used very little epoxy compared to 6 oz, and it was easy to work with.
My Freedom has two layers of 6 oz on the bottom and although Todd's description makes a lot of sense to me, the bottom of my canoe gets beat up on shallow slow rocky rivers, so I'm concerned more about cuts, abrasions, and gouges over hard impacts, and thus the extra sacrificially layer.
For hand layup, like we do on strippers, multiple layers of 3.2 oz. cloth make it possible to get a higher glassfiber-to-resin ratio, which translates almost directly to higher impact strength and more of it for a given laminate weight. Along with this, it's can also produce more trapped bubbles between the layers, less clarity, etc. though it's certainly possible to do a great job that looks outstanding if you're careful. The weight factor is tied as much to the number of filler coats needed as it is to anything else and finer, tighter cloth takes less resin to fill than normal cloth.
This can be a double-edged sword though, in terms of abrasion. Unless cleanly and evenly abraded (as with sandpaper) glass fibers tend to fracture somewhat. Running over rocks hard enough to scratch down into the cloth will usually leave a mark that's nearly impossible to repair to the point of not showing. The plain resin built up on the surface in the form of filler coats is pretty hard and can, to a certain extent, help keep the scratch from going all the way down, deeply into the cloth where it starts fracturing fibers. The typical 6 oz. cloth has much higher "hills and valleys" in it's weave than the smoother 3oz. & 4 oz. varieties. These higher peaks need more filler coats (yielding more weight added) but I suspect you could probably scratch the finished canoe twice as deeply without getting down into the main part of the weave and approaching the point of cosmetic non-repairability. You might clip off some peaks, but the foothills and valleys of the cloth weave will likely be OK.
If you use a stripper long enough, you're bound to hit some stuff. Every year or two, when you refurbish the bottom - maybe filling a few dings, sanding a bit and revarnishing, you'll find that a certain percentage of the repaired trouble spots were deep enough to leave a permanent mark. The others disappear with the fresh coat of varnish. I haven't seen or done any kind of studies of the issue, but I suspect that the thicker fill needed on six ounce cloth may yield fewer of these permanent, non-repairable marks than the thin fills used on tighter, flatter, lighter weights of fabric.
I just ordered 12 yards of Raka 6 oz cloth to use on our Redbird (next weekend!) :praying Any advice specific to this cloth (we're using West System 105/207 epoxy)?
My Freedom has two layers of 6 oz on the bottom and although Todd's description makes a lot of sense to me, the bottom of my canoe gets beat up on shallow slow rocky rivers, so I'm concerned more about cuts, abrasions, and gouges over hard impacts...
I also applied a double layer of 6 oz on the underside of my Huron, although if I had read Todd's post back then, I probably would gave added another layer on the inside as well.
I agree that it's abrasion that eventually destroys canoes, and the obvious material to reduce this is Kevlar - it has about 10-12 times the shear strength of fiberglass and is very resistant to tearing. Problems are in the color (the ouside will need to be painted which still might not look bad), difficulty in sanding smooth, fuzzing up with time, and no easy way of knowing how much epoxy to wet out with (since it isn't transparent). Maybe someone here has tried it with strippers, but applying extra layers of fiberglass might be the easier thing to do, maintenance-wise.
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