Repair a pinned Raven

[jffdejongh]

I took the raven on the Allagash 2c weeks ago from churchill dam to allagash village.

About a mile into the trip in chase rapids I second guessed my line and went left too late. The stern stuck and I pinned on a big rock mid river.
We were able to get it off the rock, started to bail water when I lost my balance, stopped the upstream gunwale, re-filled the canoe with water and it smashedinto a downstream rock.

We got it to river left, whiteout the canoe and decided it was safe to paddle the 4 miles to bissonette bridge.

This the damage was most severe on the interior. One place where the 6 oz. E-glass split at the spot of biggest impact and several other places where the glass either broke or developed stress fractures along poor joints or weak wood grain.

My immediate thought is to repair with 4 oz. S- glass inside.

Thoughts?

 

[Cheeseandbeans]

Oof- sounds like it could have been much worse. I’m sure one of the strip building guys would know best. It will be good as new soon I’m sure.

Bob

 

[jffdejongh]

Oof- sounds like it could have been much worse. I’m sure one of the strip building guys would know best. It will be good as new soon I’m sure.

Bob

Yeah, after yard sale the pinned caused, lost paddle, sandal, sponge, hat... the point not left for me to pick up at bissonette was the hat (I didn't like it anyway).

 

[Glenn MacGrady]

Ouch, it hurts to wound a beautiful baby. But that doesn't look too bad, considering how much worse it could have been under the circumstances. The benefit of wood strip is that you should be able to make it look almost new again.

I'm not a builder, but I can research S glass vs. E glass:

"Compared to E-glass, S-fiberglass offers much higher tensile strength and elastic modulus as well as about 10% greater stiffness."

E-glass & S-Glass Fabrics | JPS Composite Materials

JPS Composite Materials is the largest weaver of glass fabrics, including E-Glass & S-Glass. This selection allows us to produce top ballistic material & more.

jpscm.com

 

[Skinny Moose]

That is unfortunate. Great to hear you are getting good use out of the Raven though!
I repaired a similar issue on my freighter canoe several years ago and it is holding up great and appears as strong as “new”. Lots of hours pounding through big waves with a 6 horse outboard and it’s been good. My crack appeared a bit more significant to the cedar core and less to the glass. Also not along seams but cracked diagonal to the strips.
I sanded through the glass and feathered it back (2 layers of 6 oz on bottom of this boat). Basically down to wood about 2-3” outside the crack and through one layer of the glass further out. Then I carefully cut out the offending section parallel to the crack and glued in replacement strips. I then did a 6 oz glass to cover the bare wood and another layer to overlay the single glass layer on the wood. That’s inside and out. Quick repair, mainly just time waiting for the epoxy to cure. In your case I would sand back the glass and try to flex the strips and force glue into the OG strip joints if that is possible. Then replace the glass as I did. I used 6 oz e-glass for the repair. Thinking you would have very little visible repair… although scars on a boat give it character!
Some photos of my damage and how I pulled it apart. I don’t have final photos post repair though.
I hope this helps and good luck.

 

[Jim Dodd]

If you build them ? You can Fix them !

I always double layer the outside football, to about the 3" waterline.

Looks like you have good control of the situation !

Jim

 

[Cruiser]

You should probably stick with e glass ... mixing materials of differing strengths can be counter productive in composites. If one material doesn't stretch/load like the other one, then all the load shifts to the other material and you have layers that don't work together well.

I would be tempted to see if you could lift the glass back from the cracks a bit (with heat) and cut a regular shape out, feather the glass edges, realign the cracked edges, add a new section of glass .... feather that and add a finish when cured.

And as your narrative and pics demonstrate quite nicely, if you take a hit on the outside of the hull, the inside will flex and create a stretching load on the interior fiberglass (hence the breakage), this is true in most situations where the hit is external. Fiberglass is strongest when in a stretching load and weakest in a compressive load. When you take that hit, the outside layer goes into compression and so most of the stress is passed on to the inside layer .... hence the inside rips.

If you add extra layers to the hull, you add them to the inside for strength and to the outside for abrasion resistance.


Brian

 

[jffdejongh]

You should probably stick with e glass ... mixing materials of differing strengths can be counter productive in composites. If one material doesn't stretch/load like the other one, then all the load shifts to the other material and you have layers that don't work together well.

I would be tempted to see if you could lift the glass back from the cracks a bit (with heat) and cut a regular shape out, feather the glass edges, realign the cracked edges, add a new section of glass .... feather that and add a finish when cured.

And as your narrative and pics demonstrate quite nicely, if you take a hit on the outside of the hull, the inside will flex and create a stretching load on the interior fiberglass (hence the breakage), this is true in most situations where the hit is external. Fiberglass is strongest when in a stretching load and weakest in a compressive load. When you take that hit, the outside layer goes into compression and so most of the stress is passed on to the inside layer .... hence the inside rips.

If you add extra layers to the hull, you add them to the inside for strength and to the outside for abrasion resistance.


Brian

Thanks Brian that makes sense. I'm going to start the repair in a couple of days and will post progress. Sticking with e glass will be cheaper. I believe I'm going to fix the cracks as you and skinny moose described. I have done that on another canoe with a desalination. I think adding another layer of e-glass inside will also be helpful.

 

[Glenn MacGrady]

You should probably stick with e glass ... mixing materials of differing strengths can be counter productive in composites. If one material doesn't stretch/load like the other one, then all the load shifts to the other material and you have layers that don't work together well.

I hesitate to respond to this since I don't build or repair composite canoes.

However, I own and know for a fact that it has been common for at least 50 years to mix layers of different laminate materials in canoes and kayaks. In fact, it's much harder today to find a one-fabric canoe than a multi-fabric canoe. Mixing layers of fiberglass/Kevlar, glass/polyester, carbon/Kevlar, glass/Kevlar/polyester, glass/Kevlar/carbon, Innegra/carbon, glass/wood, glass/foam/Kevlar, and other laminate combinations are ubiquitous. There are also fabric bi-weaves of carbon and Kevlar and other bi-weaves. The different tensile strengths, compressive strengths and abrasion resistances of the different fabric combinations are seen to be an advantage not a disadvantage.

I suspect the difference between the properties of E-glass and S-glass is less than that of these other composite fabric combinations. Maybe the decision should just be made on the basis of cost, ease of application, and maybe added weight. (That is, maybe 4 oz. S-glass would be as effective as 6 oz. E-glass).

 

[Cruiser]

However, I own and know for a fact that it has been common for at least 50 years to mix layers of different laminate materials in canoes and kayaks. In fact, it's much harder today to find a one-fabric canoe than a multi-fabric canoe. Mixing layers of fiberglass/Kevlar, glass/polyester, carbon/Kevlar, glass/Kevlar/polyester, glass/Kevlar/carbon, Innegra/carbon, glass/wood, glass/foam/Kevlar, and other laminate combinations are ubiquitous. There are also fabric bi-weaves of carbon and Kevlar and other bi-weaves. The different tensile strengths, compressive strengths and abrasion resistances of the different fabric combinations are seen to be an advantage not a disadvantage

There really is no disagreement here, in my view a modern strip (FG/wood/FG) canoe is a composite build, as well as the various modern layups that are used by canoe manufacturers. The multilayer/multimaterial/multistrandorientation composites used by the professional manufacturers are not arrived at by accident, they design the layups to work together to achieve the characteristics of the various hulls. These layups are the end result of some pretty smart material engineers .... going way beyond what is used in a simple strip build. I interpreted the question of using a lighter S glass, as a suggestion that it may make a superior repair and that triggers all the questions on strength, compatibility of layers, cost, availability etc and there just didn't seem to be any good reason to wander from the current material layup.

I guess what I am suggesting is that if you are asking the question, it may be prudent to jut stick with what you know and have used, because it takes some knowledge/skilset to start successfully altering or creating new composite layups. I agree that , in this case it is likely a small difference in performance .... but the 4 oz will cost more and not likely result in any performance advantages and is 25-30% thinner meaning it will require a little more fiddling to make it disappear. Hence the suggestion of not mixing and matching ... same answer with similar explanations IMO.

 

[Glenn MacGrady]

There really is no disagreement here

Maybe, but I'm not sure. I will continue this discussion not because I want to debate, but simply because I think it is a simple and likely recurrent canoe repair question as to whether it is "counter productive" to repair E-glass with S-glass. I state the issue that way because I was responding to this assertion:

You should probably stick with e glass ... mixing materials of differing strengths can be counter productive in composites.

Given all the other lamination materials that are commonly combined to make a composite hull, I simply don't know what the evidence is that S-glass over E-glass will cause problems. Maybe there is evidence but I'm just not aware of it.

It makes sense to me to repair cracked 6 oz. E-glass, and a possibly weakened wood substructure, with 6 oz. S-glass because, according the the world's largest manufacturer, S-glass "offers much higher tensile strength and elastic modulus as well as about 10% greater stiffness." That all seems pro-productive to me, not counter-productive, for repair to a damaged area.

I was probably unclear when I mentioned 4 oz. S-glass. I brought that possibility up only in the context of a way to reduce the weight of the repair, which may not be a consideration for Jeff at all. Personally, I'd stick with 6 oz glass.

There perhaps is no disagreement that the prime decision factors should be cost and ease of repair. If what one has on hand is E-glass, or if one doesn't want to spend money on S-glass, then it probably makes sense just to use the E-glass. But I'm not convinced by any of the discussion so far that using S-glass would produce some sort of counter-productive tensile or compression strength incompatibility.

 

[Woodpuppy]

I wonder if the significant thing is that we’re talking about a patch of a material of some relevant (or not) differing behavior under temperature, compression, tension, and/or torsion. The blended composites have their differing strands at some regular interval, dispersed evenly through the fabric. Patch adhesion can be an issue for sure, perhaps more significant than differing material properties.

 

[Glenn MacGrady]

I wonder if the significant thing is that we’re talking about a patch of a material of some relevant (or not) differing behavior under temperature, compression, tension, and/or torsion. The blended composites have their differing strands at some regular interval, dispersed evenly through the fabric. Patch adhesion can be an issue for sure, perhaps more significant than differing material properties.

An interesting speculation. However, multi-fabric hulls are not built with just equal full sheets of the differing materials. A composite canoe lamination schedule can contain more than 40 pieces of different-sized, different materials placed in different places to reinforce or strengthen those different places. These are all like "patches" in a sense. So are the foam footballs and ribs that are commonly sandwiched between layers of fabric.

A Kevlar, S-glass or Dynel skid plate on an E-glass, Kevlar, carbon, or Royalex canoe could be considered a "patch".

I honestly don't recall anyone worrying about the differing tensile strengths or elastic moduli of these various patches—other than very general abrasion/compression considerations such as putting the sheets of S-glass on the outside of the hull and the Kevlar on the inside.

But I could be wrong on some micro-technical level.

However, on a canoe I personally am not usually interested in micro-incompatibilities. Rather, I'm interested in the hull having the macro characteristics of maximum puncture, fracture and abrasion strength for the given (light) weight that I want. For my many whitewater and flat water canoes and kayaks that contain some fiberglass, I have always chosen higher cost S-glass over lower performing E-glass, and I believe that has been the better price/performance decision over the now 40+ year long run.

 

[Cruiser]

Just to back this discussion up a bit and make sure we are on the same page ... the original post was to repair a 6 oz e glass composite hull, using a 4 oz s glass patch.
The response was that rather than mix materials, stick with the 6 oz e glass for the repair ... I stand by that, if for no other reason that 4 oz s glass would be a close second in performance to the 6 oz e glass .... regardless of cost or thickness issues.

As far as the discussion goes I am not trying to say you don't/can't/shouldn't mix materials, i am saying there are non optimum ways of doing it.
The standard 6 oz e glass on wood hull is likely the most used combination IMO mainly because it allows the wood to show and it is the most cost effective solution, not necessarily an optimum strength solution (granted strong enough for purpose). If you consider an external impact (as above), the exterior FG has very little compressive strength, so it simply compresses and passes the load to the internal layer which goes into stretch and bears the entire load. If you wanted to strengthen that composite, you could instead use carbon fiber on the exterior, which has much better compressive strength ... under impact, both the external and internal layer are working together, contributing strength to resist the impact. If you reverse that composite and put the carbon on the inside .... well it is compromised, the glass will lend no strength and the carbon is left to bear the brunt of the impact. Using the same materials in a different order will definitely produce different results.

The caution was to point out that you need to make sure you have considered the relative characteristics of those materials you intend to put together for a particular application. In this case,I have to concur that mixing s and e glass for a patch likely doesn't matter in any significant way.

 

[Glenn MacGrady]

Just to back this discussion up a bit and make sure we are on the same page ... the original post was to repair a 6 oz e glass composite hull, using a 4 oz s glass patch.

You're absolutely right. I try to be careful with quotes and apologize for misremembering the OP. I was proceeding on the erroneous assumption that Jeff was trying to decide between 6 oz. S-glass and 6 oz. E-glass. So, this discussion at least had the benefit of clearing up my own confusion.

I agree that if 6 oz. glass is cracked on both the inside and outside of the wood, it should be replaced with 6 oz. patches. However, unless cost or convenience is more important, I would still be inclined to use S rather than E because S is superior in both tensile and compression strength, which would better protect the potentially weakened wood core.

The standard 6 oz e glass on wood hull is likely the most used combination IMO mainly because it allows the wood to show and it is the most cost effective solution, not necessarily an optimum strength solution (granted strong enough for purpose).

I'll take your word for what is the most cost effective and common glass to use for strippers. But because the Raven hull was specifically designed to be a whitewater tripping canoe, and Jeff obviously uses his in rocky rapids, I'd have made that particular kind of stipper with the stronger S-glass, unless cost prohibited it. And if that Raven is likely to be used in future rapids or rocky rivers, that would be another reason I'd patch it with the stronger glass. The Allagash pins prove that the E-glass was not strong enough to prevent pin ruptures. Future pins and rock bounces are likely to happen in the same places on the hull. JMO.

If you reverse that composite and put the carbon on the inside

This relates to the interesting issue of which material to put on the inside and outside of a composite hull. Since it's really a tangent to the Raven repair, I'll just refer interested readers to THIS POST where I discussed the issue in some detail (I think correctly).

 

[memaquay]

I split the inside glass of a big 18 footer way back on the Steel river. The split was almost two feet long. The outside glass held for the rest of the trip, but we exited as soon as we could, as the inside hull oilcanned along the split like a hungry alligator. When I got it home, I sanded off the ragged glass, then squeegied in some thickened epoxy to makes a level surface when I applied the new glass. This was a quick and dirty fix, I put a couple of layers of six ounce e cloth over the epoxy filled split, and never had a problem after that.

 

[Cruiser]

You're absolutely right. I try to be careful with quotes and apologize for misremembering the OP. I was proceeding on the erroneous assumption that Jeff was trying to decide between 6 oz. S-glass and 6 oz. E-glass. So, this discussion at least had the benefit of clearing up my own confusion.

I agree that if 6 oz. glass is cracked on both the inside and outside of the wood, it should be replaced with 6 oz. patches. However, unless cost or convenience is more important, I would still be inclined to use S rather than E because S is superior in both tensile and compression strength, which would better protect the potentially weakened wood core.


I'll take your word for what is the most cost effective and common glass to use for strippers. But because the Raven hull was specifically designed to be a whitewater tripping canoe, and Jeff obviously uses his in rocky rapids, I'd have made that particular kind of stipper with the stronger S-glass, unless cost prohibited it. And if that Raven is likely to be used in future rapids or rocky rivers, that would be another reason I'd patch it with the stronger glass. The Allagash pins prove that the E-glass was not strong enough to prevent pin ruptures. Future pins and rock bounces are likely to happen in the same places on the hull. JMO.



This relates to the interesting issue of which material to put on the inside and outside of a composite hull. Since it's really a tangent to the Raven repair, I'll just refer interested readers to THIS POST where I discussed the issue in some detail (I think correctly).

Fun fact, that was where I learned the importance of how to layer the composites, but couldn't find it again, so thank you, lol

 

[Woodpuppy]

Seems to me that if glass is weak in the inside of the canoe that another material might be better. I get that cedar strip boats are beautiful; but would Kevlar be a better performing interior layer?

 

[Cruiser]

Seems to me that if glass is weak in the inside of the canoe that another material might be better. I get that cedar strip boats are beautiful; but would Kevlar be a better performing interior layer?

Actually, glass is quite good on the inside .... as I understand the mechanics of it, glass isn't as good on the outside. When you take an impact on the outside, the exterior layer goes into compression and the interior layer goes into tension. Glass isn't so good in compression and the outside layer doesn't really add much strength to resist the impact and allows the impact load to pass mostly to the inside layer, which is in tension and able to resist, so when the impact load exceeds the inside layer strength, you see the damage on the inside glass.

The more you discus composite structures/layers the more apparent it is that you really need to define what it is you want the final product to do. In this case, I made the assumption that breakage on the inside is a bad thing ..... if the composite design was deliberate, that the exterior layer was designed to allow a lot of flex, just to handle this scenario ... the inside absorbs the impact and if necessary breaks, while the exterior skin remains intact, keeping the hull water tight integrity at the cost of some structural strength ... that may not be a bad trade off.

So to your query with kevlar ... depends what you are looking for, it's harder to handle, more expensive, has a visual issue with wood and will offer better (but not substantially better) performance.

This is a useful discussion for me, as I have just finished figuring the layup for my next boat and the more you think on things the fuller your understanding becomes, and while this can be a pretty complicated subject, it all seems to come back to the idea of "Good Enough".
Backing away from the abyss of the "what ifs" and staying in the main lane of your requirements, the typical 6 oz layup is strong enough to do the routine job of rivers/streams/lakes easily. However as Glen pointed out (and I missed) this is more of a white water situation, which takes it into another realm of requirements, and that is another lane.

 

[Woodpuppy]

Well then my reading comprehension is bass ackwards.