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Old 07-11-2017, 05:04 PM   #1
Gbuck

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Default Novice Seeking Repair Advice for Fancy Prepreg Kayak

Hello,

I'm a composites novice. About every 5 years I build something like a sailing dingy that calls for fiberglass and epoxy. It turns out okay. That said, I'm pretty handy. Jack of all trades.

I gave my high end ultra light weight carbon kayak (actually an outrigger canoe) an unwanted nose job. It's constructed of prepreg carbon and cured in an autoclave. According to the advertisement it's "high temp cured 4x modulus monocoque construction cured under high heat and pressure and covered in epoxy polyurethane marine paint." Pretty fancy.

Long story short, the bow fell off my car and scrapped down the road, while the stern stayed attached to the car. I was pretty lucky. The only real damage that I can see is that the topside of the bow as ground off. I carry the boat upside down. No damage below the waterline.

I did some online research and thought I had a plan, which was to create a patch made out of multiple pieces of fiberglass cloth (not sure what weight) that were wetted to each other with the epoxy/hardener (West system 105 & 205), wet the inner surface of the kayak and then slide the patch which was laying over my finger like a wet napkin into the bow of the canoe so that there was about an inch and a half of overlap between the kayak and the wet cloth. Then I was going to use my finger or a paint brush handle to press the cloth to the kayak. When the patch cured, I was going to add more layers of cloth to the patch until I had something that matched the boats contours, then cover the patch with epoxy mixed with fairing compound yadda yadda.

Pictures attached.

Then it all went sideways. I did the prep, created a cardboard mock up of the patch. Cut about 5 pieces of thin cloth that I had lying around to laminate for the patch, wetted the inside of the kayak where the patch was going to be applied, laminated the cloth, waited until the patch was slightly tacky and tried to slide the sticky patch of unruly layers into that thin hole. The patch went into that hole like a cat goes into a bag. It was a mess. The patch ended up more like a wadded up piece of wet toilet paper. I pulled it out and walked away to lick my wounds.

My daydream was that the patch would harden enough, but not too much so that I could slide it in the hole without too much trouble. That said, I'm not sure if that was realistic or not. Also, during the process, I started getting nervous that if I waited too long the patch would suddenly harden and I'd be screwed.

Back to the drawing boards. Any and all advice is welcome.

Do I stick with a similar version of the plan?
-For example do one layer of the patch at a time?
-Try a single layer of heavier cloth?
-Try less epoxy on the patch?
-Let the patch harden more before sliding in the thin hole?
-Or is there some entirely different approach that's reasonable?

While I don't want to add a bunch of weight, I'm not trying to mimic the ultra light and stiff construction of the kayak. I simply want a sound patch.

Thanks in advance.
Attached Images
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File Type: jpg IMG_20170709_164457.jpg (2.50 MB, 23 views)
File Type: jpg IMG_20170711_163614.jpg (2.74 MB, 25 views)
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Old 07-11-2017, 07:43 PM   #2
martinb73

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Carve out a piece of foam in place, shape and fair to the match the missing shape of the boat, cover with glass/epoxy.
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Gbuck (07-12-2017)
Old 07-11-2017, 08:50 PM   #3
Timbuck

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KISS method

I'm with Martin. Just shape up a piece of foam or use some expanding PU foam then shape it and a few layers of carbon and it will be fine.

I would use PU foam. As you could make up a cardboard base that you could stick down inside the hole and tape it into place , this would allow the PU to expand up and out of the hole and then you could shape it perfectly and then do your carbon laminate over it.
The key here is , this allows you to use a small amount of "high dencity PU" that would give you a very light and very very strong end result.
Something in the 50 to 90kg/m3 range would be bullet proof.

I've done repaires like this many times , they are easy and very effective. After expantion I find using a serrated knife to carve the shape and then Finnish perfect with 120 grit then do you lay up.

Cheers

Tim
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Old 07-12-2017, 12:26 AM   #4
Hanaldo

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Concur.

2 part PU foam for sure. You could fill that hole with just 20-30 grams of foam, and then as Tim said a couple layers of carbon would be all it needs, so it is by far both the easiest and lightest repair method.
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Old 07-12-2017, 07:22 AM   #5
Gbuck

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Default PU foam it is.

Thanks for the help.

Cheers!

Gabe
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