Woodstrip VS. Canonball

[Mihun09]

We need to get Christine's stripper into the shop and repair the puncture from a couple years ago. Sharp pointy rock with a heavy load pushing down on it, split the glass inside and broke the strips. I will be putting a second layer on the football at that point.

 

[Alan Gage]

I have had two failures, both caused by sharp impact with a lot of weight overtop. In both cases, the exterior glass held, the interior glass split. It would seem to be that a sensible builder looking for enhanced strength would double layer the interior. However, I can't bring myself to do this, and still double layer the exterior.

That's what I did on the tandem I just finished and I'll be doing it on the solo I'm working on as well. The current solo will be getting 6 oz. S-glass, rather than E-glass, on the outside football for better abrasion resistance. Kevlar on the inside football would be ideal and is very tempting but vacuum bagging would be necessary and I don't know if I could get a good seal between the bag and the wood hull. The fast solo I built early this winter got a single layer outside and a small double layer on the inside (center 7'). On my future builds that I don't expect to see much abuse as far as abrasion goes I'll be doubling the inside only if I feel I need more strength.

As to if it will actually a make a difference in real life only time will tell.

Alan

 

[Alan Gage]

I have had two failures, both caused by sharp impact with a lot of weight overtop. In both cases, the exterior glass held, the interior glass split. It would seem to be that a sensible builder looking for enhanced strength would double layer the interior. However, I can't bring myself to do this, and still double layer the exterior.

If it's because of weight, and we all know what a gram weenie you are, you could think about doing a full layer of 4 oz inside and out and then a layer of 6oz, inside and out, below the water line. That would keep weight down and give you the most strength and abrasion resistance where you really need it.

Alan

 

[memaquay]

I thought about doing that for this build, but where would the justice be in trying to lighten things up? I gotta save those sub 40 pounders for when I really need them, if I start using them now, I'll want sub 30's in another 10 years.

 

[Jim Dodd]

Planning on ordering epoxy from RAKA Monday. I'll quiz them on adding the xylene.

It sounds like Dennis gives credit to applying cloth to wet penetrating epoxy, to improve durablity
.
I guess I'm a little fearful of handling the cloth when the hull is wet. Worried about distorting the weave.

Guess I need to set up a smaller test. Or maybe Alan will try it ?

Thanks again for the info Alan ! The stripping world is experiencing some new changes ! I like the evolution !


Jim

 

[Iskweo]

We need to get Christine's stripper into the shop and repair the puncture from a couple years ago. Sharp pointy rock with a heavy load pushing down on it, split the glass inside and broke the strips. I will be putting a second layer on the football at that point.

If any one has a boat that they need tested then I am available as a product tester. Simply ship me your latest creation with three blank cheques to cover my tripping expenses and I will gladly put it through my own special brand of torture. Pictures and handwritten report are available at a small extra cost.

Christy

 

[Alan Gage]

Planning on ordering epoxy from RAKA Monday. I'll quiz them on adding the xylene.

It sounds like Dennis gives credit to applying cloth to wet penetrating epoxy, to improve durablity
.
I guess I'm a little fearful of handling the cloth when the hull is wet. Worried about distorting the weave.

Jim

From the little research I did most manufacturers recommend against adding thinners like Xylene and some have their own thinners which sound like a mix of mainly xylene and alcohol with some other goodies mixed in that presumably make it play well with the resin. That being said it also sounds like thinning with xylene is pretty common practice and I didn't see anyone reporting poor results. But if it actually affects the strength or bond I really don't know and I didn't see any testing either way.

I took it that Dennis was applying the fiberglass to green epoxy, not wet. In other words he was letting it setup so that it was just a little tacky to create a chemical bond and to eliminate the need to sand. I figure if it feels dry to a light touch but has a slight tack when you press hard with a finger or a finger nail still dents it easily that would be the time to apply the fiberglass as the epoxy isn't cured yet but is set up enough that the dry fiberglass should still slide for positioning. Hopefully I'll let you know tomorrow how that works out....

Alan

 

[memaquay]

Epoxy has different "green" times. System three says chemical bonding is still good for up to 72 hours. If anyone here hasn't used system three clearcoat for initial coating and wetout, I would encourage you to give it a try. Thinnest epoxy I have used, very good penetrating qualities.

 

[wysedav]

I don't think I've ever seen a epoxy failure between coats not sure you need a chemical bond. I thought the reason to limit time between coats is because of amine blush. I use blush free version of epoxy and don't do any prep between coats and haven't had any issues. To mee the most surprising part of the test was the benefit of the pin roller. I don't think I'm going to do that though benefit or not.

 

[wysedav]

Oh I just read last night that adding 5% solvent significantly reduces the strength of the epoxy. I'll look for it again.

 

[Jim Dodd]

I've been spending a lot of time watching Dennis's Shop videos on youtube, TOO much time !. They are upwards of 5 hours long. I fast forward to get to the"GOOD STUFF"

In one of the videos, Dennis is glassing a tandem, that he had built. It sure looked to me like he rolled on a seal coat, and then laid the cloth out on it. With gloves he proceded to position the cloth. You could tell the seal coat was wetting the cloth.

I've never done that, just to scared I guess ! Dennis didn't seem hurried at all.
These videos wheren't of the best clarity, and no sound.
I think I picked up a few tricks !

Thanks Dennis !


Jim

 

[Jim Dodd]

Epoxy has different "green" times. System three says chemical bonding is still good for up to 72 hours. If anyone here hasn't used system three clearcoat for initial coating and wetout, I would encourage you to give it a try. Thinnest epoxy I have used, very good penetrating qualities.

I used System Three's Clear Coat, until it got real expensive. On two different occasions, we ordered 15gal kits.
It did wet out good, but required about two extra coats to fill the weave.

 

[memaquay]

Yes, well the way I have used clear coat is only for wet out, and fill with a thicker epoxy such as general purpose, or west or silver tip. I can imagine it would be a tough one to use for fills.

 

[sailsman63]

Yes, well the way I have used clear coat is only for wet out, and fill with a thicker epoxy such as general purpose, or west or silver tip.

How well did this technique work for you? I'm currently contemplating my third strip build, and I'm still not entirely satisfied with the epoxy jobs on the last two. On the first, I've used West System + 207, which wet out well, but I didn't like some of the other handleing, including the funky mix ratio.
On the second, I used System Three Silvertip. Loved a lot of things about it, but didn't seem to like to saturate the glass and work into the strips quite as well as I had hoped.

 

[memaquay]

I think the perfect mix would be Clear Coat for wet out and Silvertip for fill. That would be a very clear and tough finish. The general purpose is good for fill coats too, but it has a decidely yellowish tinge, unlike the silvertip.

 

[wgiles]

There are a few thoughts that come to my mind after watching these tests.

The cannon ball test may be a bit extreme, but it does provide a reasonable approximation of impact damage.

The failure is on the bottom side of the test panel, which is the tension side. The outer surface of the canoe, which is the side that is impacted, is in compression while the inner side is in tension.

For the most part, the wood makes very little difference in the results. The bond between the wood and the cover material may matter, but the penetrating epoxies and the porcupine roller seem to increase the strength of the outer fibers of the wood strips. That the porcupine roller would make a significant difference is interesting, since the wood is porous to begin with.

Since the failure appears to be mainly in the tension side, additional reinforcement on the inside may be more effective than reinforcement on both sides and should definitely be more effective than additional reinforcement on the outside.

Curvature does add strength, but is only significant if the impact is at a point where there is significant curvature. If you hit a rock with the bow of the canoe, there is considerable stiffness provided by the curvature. If you hit a rock amidships, on the side or bottom, curvature is not as much a factor.

The tests were conducted with the sample panel restrained on both edges. A canoe is restrained only by the water pressure on each side and the mass contained in the canoe. If the test panels had been supported by foam on each edge, it might be more representative of real world canoeing. A canoe can bounce off a rock. The fact that the cannon ball bounced several times on one of the test panels indicated that that panel was very rigid. Drop a cannon ball on to a piece of foam and see how many times the cannon ball bounces. The foam won't be damaged because it absorbs the energy of the impact. This may explain why the Royalex sample appeared to perform well. The skin is resilient and the foam core allows considerable deflection. Fiberglass epoxy systems are fairly rigid and won't allow for much deflection before failure. Kevlar should handle much more deflection before failure and should make a significant difference when used on the inside, the tension side. The epoxy is the binder, while the fabric provides the strength. I think that Kevlar should have much higher tensile strength than fiberglass. I'd like to see an impact test of a panel with fiberglass on the top and Kevlar on the bottom. Then again, I could be wrong.

 

[stripperguy]

Mr giles,

Do you have any experience modeling these composite structures?
Or how about a modulus number for some of the common layups like glass/cedar/glass?
I find it very difficult to predict the stresses and deflections for the composite hulls, the geometries are easy enough (with modern FEA) but what values to assign!??

 

[wgiles]

Mr giles,

Do you have any experience modeling these composite structures?
Or how about a modulus number for some of the common layups like glass/cedar/glass?
I find it very difficult to predict the stresses and deflections for the composite hulls, the geometries are easy enough (with modern FEA) but what values to assign!??

I wish that I did have experience with these composites, but I don't. Most of my experience has been with more mundane composites, like reinforced concrete. None the less, the principles are the same. I wonder how useful analysis of these composites would be since there appears to be a lot of variability in otherwise similar systems.

 

[stripperguy]

I wonder how useful analysis of these composites would be since there appears to be a lot of variability in otherwise similar systems.

Any analysis is just a prediction, but it would be nice to get close the first time around, no?
From what I have seen in the commercial hulls, and talking with industry insiders, they sound like AF or ARMY researchers...strictly build and bust.
I'm surprised at the designs of the production boats, I suppose monetary constraints overpower all else.
There seems to be much room for improvement.
Even with our strip builds, the integration of high strength synthetics can be optimized, with a little forethought and application of engineering principles.
To that end, we strip builders have been virtually collaborating here...many thanks to Alan, mihun, JimD, memaquay, et al for pooling our knowledge.

 

[sailsman63]

The general purpose is good for fill coats too, but it has a decidely yellowish tinge, unlike the silvertip.

Another reason I went away from the West system.

Now, possibly way OT, and if this belongs in another thread, I'd be glad to start one, has anyone tried SystemThree's WR-LPU? Seems expensive, but the claims are impressive...