Repair of Carbon/Kevlar kayak hull

While carrying my kayak on top of my truck, I parked the truck on a village street while doing some shopping. When I got back to the truck, a tree limb had fallen and the lower hull was bent badly over the roof rack bar. When removed from the truck, I could see the outer gel-coat was cracked exposing the fibers that make up the hull. Looking inside the kayak, I could see inside where the cracks went out from the primary point of the pressure looking like a spiders legs. There doesn’t appear to be any through-the-hull points for water to enter, just fiber cracks. I want to have it repaired, a shop or myself. I live in central New York. Any suggestions as to where to be repaired or do it myself hints appreciated.

Post pictures it helps.

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Gel coat will often pretty effectively hide a lot of whatever is going on beneath it. I presume that the outer layers of the boat are carbon fiber cloth and the inner layers aramid (Kevlar). That is the more common and more logical arrangement.

Aramid fibers are very strong in tension and when the bottom of the hull got pushed in, fibers of the interior structural layers were subjected to tension. For aramid fibers the tensile strength of the fibers are usually stronger than the bond of those fibers to the resin matrix. Stressed fibers will often dissociate from the resin matrix creating a bunch of radiating white lines.

Carbon fiber behaves differently. Carbon fiber is very strong and quite stiff. So it does not have a lot of “give”. When subjected to stress above its limit it tends to fail catastrophically. Since carbon fiber is stiffer than virtually any polyester gel coat, it is possible that you have fractures in the carbon fiber hidden by the gel coat. You might be able to get an impression of this by pushing in on the damaged area of the hull and seeing if it feels soft.

If the area of damage inside the hull is accessible through the cockpit it would not be that difficult to apply a mulit-layer patch of aramid fabric over the damage extending at least 2 inches onto undamaged hull. If you suspect or see that the outer structural layers are damaged you are going to have to sand off the gel coat to determine the extent of damage.

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What tough luck. I would do what pblanc says, but used a mixed weave carbon. aramid fiber cloth. You can get it fairly cheap at RAKA.

Also buy a couple of Bondo squeegees.

Sand the area, put down a layer of epoxy, put down a layer of cloth and squeegee out the excess epoxy, to keep the cloth from floating.

Let it cure for a day and do it again. If you put down the second layer within 48 hours, you do not have to sand it, the epoxy will bond chemically.

Let the second layer cure and brush on a third coat of epoxy.

The mixed cloth will add back the rigidity from the cracked carbon fibers.

For what it is worth, Charlie Wilson advised on this message board (I think) against using mixed carbon fiber/aramid fiber fabrics.

The reason it the great difference in elastic modulus between carbon fiber and aramid fibers. Because carbon fiber has a much higher Young’s modulus (is much stiffer) when the fabric is stressed in tension the carbon takes up most of the stress and the aramid fibers relatively little. He also claimed, if I recall correctly, that the sharp edges of the carbon fibers tended to cut the softer aramid fibers.

I have not seen any evidence for this in my personal experience but I have never used that type of fabric, although I do have a boat that was repaired using it. If you do feel that the repair requires the greater stiffness of carbon fiber an option would be to apply a multi-layer internal patch using a layer of carbon followed by a layer of aramid.

I recently did repairs on my fiberglass tandem after it got run under a strainer by other paddlers and the deck crushed downward a couple inches. The damages sound similar - chunks of gelcoat broken off, cracks. I was lucky enough that with some pressure, it popped back up into its original shape. If you’re lucky enough to have this happen, it’s all just reinforcement and reapplying gelcoat.
My question regarding CraigF’s suggestion to let it cure for a day between adding layers of cloth. I used West Systems Epoxy 105/206 for resin on the layers of fiberglass I added on the inside. I added 3 layers of glass cloth, and the things that I read all pointed to applying all layers in one go - do not let it cure at all in between. So I sanded and cleaned, wetted the surface with resin, put the first layer, wetted it out, added the 2nd layer, wetted it out, added the third layer, wetted it out - all in one go. My research seemed fairly consistent that putting down all layers at once was the way to go - not to let it cure between layers. Are there reasons that one would want partial curing in between?
I cleared off all broken gelcoat from the outside of the kayak, and very carefully dremmeled a groove along the cracks without touching the fiberglass underneath. I then sanded the grooves, once again carefully avoiding ever hitting the composite material underneath. I then left the gelcoat piece until last, as the light coming through made it easy to see where the reinforcements were needed from the inside.
I didn’t add any resin or cloth to the outside of the kayak. I believe even the product itself said gelcoat doesn’t adhere to the cured epoxy resin well. My last step was adding gelcoat to the outside.
Anyway, I’m sure waiting for partial cure in between layers could “work just fine”. And applications where the weight of many fabric layers at verticle or upside-down angles could make the fabric sag might be reasons for partial cure in between. But other than that, it seemed everything suggested putting it all down at once to cure together would yield the best results. Are there other thoughts or facts on this that I missed?

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I have done quite a few multi-layer laminated patches using various fabrics and epoxy. My practice has always been to apply the layers one at a time but I only allow the epoxy of the previous layer to cure to a green state. Often it is still a little tacky when I put on the next layer of fabric.

In my hands this just seems to be neater. On the few times I have tried to apply a patch of multiple layers of fabric at the same time I just seem to get more fraying along the edges of the fabric.

In terms of achieving a “chemical bond” between the layers I don’t think this method is any better or worse than applying all the layers at once. I’m sure that if I repaired boats professionally I would adopt the “all at the same time” approach to save time.

One argument in favor of applying all the layers at ounce is if you use peel-ply. You would have to use a lot more peel-ply with the “one layer at a time” approach.

If you don’t want to take the DIY route you might give Dave Curtis a call at Hemlock Canoe in the Finger Lakes area. I don’t know if Dave’s shop does repairs but there’s a good chance that he would know if there’s someone local that can repair your boat for you.

The problem I have with the all at once method is the glass/aramid, carbon/mixed floating in the epoxy.

You want the repair actually adhered to the original surface. If there is too much epoxy the material will float and not actually form a bonded surface.

Westside became a big proponent of mixed aramid and carbon weave and I have not heard of any problems. I think that when the epoxy is dry it is a composite and not its various parts.

Thanks. I remember reading about the floating issue, whether a single layer or multiple layers. As more resin is added, and more uneven or steep surfaces exist, more of a possibility of pooling would exist, and the possibility of floating could arise. I was pretty careful with this, and there was no perceptible tendency as I worked through it. Nothing such as pressing with gloved fingertips and seeing the saturation increase, or the resin level rising higher compared with the fabric, or a spongy feeling. And it doesn’t have hours to slowly happen. The stuff kicks fairly quickly. The kayak itself has had a month of some good vibrations with trailer mileage, and been out 3 - 4 times a week getting ready for a longer trip. The deck feels solid, and a couple people checking out my repairs thought I only did gelcoat work, as they saw nothing noticeable from the inside on a quick once-over. That made me smile just a bit. Now the gelcoat work is another story. It was a half-hearted and failed attempt at matching the yellow, and just a single coat with no leveling or sanding, just to quickly get it back in the water for training. Structurally solid. Visibly something of a Frankenboat. Now the name “Strugglebus” seems quite appropriate. But I can always go back and sand down the gelcoat, and maybe even try to get the color to match. Then again, it’s a scar.
But so far so good. Based on this experience, I can see why putting all layers down at once is recommended. At least with the glass cloth I was using and the care I was taking with it, having worked with it. Do folks think fabric floating in this type of application would be more of an easily manageable concern, or a tendency?

I always do layers it quick succession. Letting each go till it’s still tacky. Wet the cloth and roll it good I never had pooling or floating problems. No problems if it’s upside down either.

Brit boats have use kevlar carbon weaves for years no?

Thank you. Trying to post pictures today.

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