Kevlar

[Muskrat]

Yes, the coremat soaks up resin. It is polyester mat with microspheres imbedded in it. That is another reason I will use the thinner mat next time, so it doesn't soak up as much resin. I do like that is soaks up some resin though as it seems to make a more solid or bonded laminate. Coremat comes in rectangular sheets, 39" by 36" if I remember correctly, and I cut it with a razor blade and straight edge. Next time I will try to cut it at 45 degree angle so the edge is less sharp. If you know any artists they use a special tool for cutting mat board that should work perfect. Looks like this...

http://www.amazon.com/Logan-Graphic...d=1427291637&sr=8-7&keywords=mat+board+cutter

Personally I feel that the pink foam is too thick for ribs. Watching my canoe flex from the stern seat and watching the ribs flex too, I would be nervous with that thick of a rib. I think it was brought up on myccr a long time ago by Charlie or Ezwater, but they talk about stress risers, basically edges that focus stress at the transition of a thin composite to a thick foam cored rib. Two layers of Kevlar tape over the coremat has worked well for me. It is stiff enough and allows a lot of movement still. My canoe grounds out a lot in the shallow sandy rivers I paddle.

Resin, I wish you hadn't got me started on that. The first canoe I was working on is up in the rafters of my dad's barn. I used pro build from Northwest canoe. I like the resin, but the pump for the resin wasn't metering correctly and then it failed all together. I measured the rest as best I could under the circumstances. That shell never set up right. A costly mistake. For the next canoe that I completed and most of the guideboat I used MVS epoxy. I will never use their product again! As I was laminating the canoe I ran out of hardener well before resin, and I was panicking thinking I mixed wrong. Not the case, I took the cans to my lab the next day and weighed them. MVS had shorted me on the hardener, and they had shorted the entire lot. They sent me some more hardener, but only the exact amount they decided I was missing. Nothing extra, no thanks for doing their QC job for them. So, on to the next boat build, I have leftover MVS and order another gallon just to make sure I have enough. The lamination is going fine until I get to that new batch. I mix it up and it is BRIGHT RED. One cup went on to finish what I was working on, and I then switched back to Pro Build for the final fill coat. I contacted MVS and they didn't believe me, saying nothing is wrong, until their sales rep who lives close to me sees it and confirms what I was saying. It turns out they sent me a batch that was something like five years old. That is my rant. Be warned.

As far as wetting out the Kevlar, it helps a lot to roll a coat out on the mold and then lay the Kevlar down on that. Then proceed like normal and add more to the top. It takes some time to wet out so just be patient and use slow set epoxy. I like to roll some epoxy on and move to another spot. Come back to the first spot after a few minutes at work it again. It will seem like you are putting down a lot of resin for that first layer, but when you put your glass on over it takes hardly any to wet it out because the glass will soak up the extra resin floating around the Kevlar.

 

[Alan Gage]

Having never worked with Kevlar how do you tell it's fully wetted out?

Alan

 

[Muskrat]

It changes color. It's hard to describe exactly, but you know when it's wet. It gets darker when it's wet like a shirt or any other fabric. It just takes time for it to soak in.

https://www.redrockstore.com/canoes/wenonahrepair/damagewenonah/repairprocess/applypatchoutside.jpg

You can see in the picture along the edges where it isn't wet.

 

[Jim Dodd]

Having never worked with Kevlar how do you tell it's fully wetted out?

Alan

I've been PLAYING with the new Kevlar from Noah, 8.9 oz, and the RAKA, 9 oz.
Muskrat is right. It doesn't change color radically like E-glass. It gets darker and shiny. I also agree it would be great to wet the surface below the Kevlar first. That might be easier said than done.
With my samples, I simply laid them on a plastic jug, and wet them out with a small brush. There were voids beneath the cloth, and the plastic on both. Not big voids, but small voids, that followed the weave.

I'm thinking I need a laminating roller.

Muskrat. I feel your the pain with the different epoxies ! These type forums helped me make the right choices with epoxy !

I've also been testing the new UV inhibited epoxy from RAKA.
That I'll start a new thread with.

Here's a pic of the foam I used.

That's a 1/4" bolt for comparison.

Jim

 

[Muskrat]

That foam looks pretty good. Most other homemade kevlar canoe builders have used the half inch or thicker pink foam. They have had problems with the ribs popping out especially when only using one layer of glass over the top. The stuff you have should work pretty good. Just make sure to put two layers of Kevlar over the top and have a generous amount of Kevlar overhang so there is a good kevlar to kevlar bond since the foam is basically just a spacer adding no strength on it's own. If you are using the 8.9 oz you probably only need one layer. Two for 5.5 oz

 

[Jim Dodd]

I spent a couple hours in my first Kevlar, this afternoon, and may again tomorrow.
I like it, and the bottom seemed fine. I may try some sand bags in it. The sides have a little flex,

I'm definitely going to build another, off a different hull this Summer !

Gotta love a 35# hull, over a 50# ! Can you tell I'm getting older ?

 

[charlie wilson]

Structural foam for bottoms is normally <1cm thick, remembering that the strength of the core increases with the square of the thickness. Cores need their sides beveled to allow fabric to cover smoothly without voids, and rib tops need similar treatment. Looking back, WeNoNah stopped using ribs almost two decades ago. They probably had a reason for that sea change. Iy seems Souris River's rib usage is a manufacturing decision rather than an engineering choice.

Noah offers Corecell, Express Composites Airex, so structural foam is available to the home builder who, I think, should use pre-scored material to eliminate the need to oven shape the core. That said, I don't think home builders should use foam cores. Wet bagging a core into a putty is problematic, and vacuum pump, perforated ply, breather layer, nylon bag, sticky tape and all the spiral cut and non tubing and fitting add lots of expensive new things to the shop with multiple opportunities for serious problems. Infusion beds the core better, but requires all of the above plus a different release film, core perforations of exact size and placement in the core layer, and a larger vacuum pump, actually two because if one fails a second pump needs be at hand to preclude a rather expensive disastrous failure to infuse. Infusion also requires the ability to adjust very precise resin chemistry.

Coremat was the key bottom stiffener for Bell's White Gold laminate, a price pointed lamination. It stiffens the bottom wonderfully, eliminates the void issues under improperly installed foam cores but increases hull weight and is somewhat brittle. It is easier to add fabric partials, shaped pieces of fabric layered in progressively to reinforce bottom, sidewalls and stems. The result is almost as light as coring the hull and the hull stronger but more flexible than many foam cored units with minimal opportunity to generate weakening voids. Additional advantages are one less material in the shop and the option to insert fabric partials on bias to strengthen the laminate.

We want the shaped bottom partial set and ribs to be innies, irregularities inside the finished hull rather than irregularities on the outer surface. Colden, Hemlock and Placid all use solid cores built up of multiple overlapping partials, but they use female molds, so build up their partial sets between full blanket layers to minimize voids around the edges.

Using a male mold, we'd need to progressively lay 2-3 layers down, maybe sneaking in one partial set, then pull the hull and add the remainder of the partials on the inside before capping with a final full blanket. Ribs can be built up as needed, but a four layer hull like Souris uses shouldn't need more in the sidewalls except at seat placements.

 

[Muskrat]

Charlie, what would you recommend for us home builders without female molds and vacuum bags? Ribs or full bottom cores with ribs up the sidewall? What material? I'm assuming Wenonah being race minded lost the ribs to have a very stiff bottom the whole length. Considering they still use Kevlar outers I doubt durability was their intention, but I'm no expert. Thanks for taking the time on the forums. I think you're the only industry insider we have.

 

[pblanc]

I have been following this thread with some interest and did not want to hijack it but I have some questions pertaining to Coremat that I would like to throw out and welcome any thoughts that anyone might have. I am attempting to repair an Esquif Mistral tandem canoe constructed from their Twintex material. This was an early Mistral that Esquif had chosen to put a balsa core hull bottom in (why???). The original balsa core was 5mm thick, sandwiched between and inner and outer layer of Twintex. Twintex consists of fiberglass fabric imbedded in some sort of polypropylene matrix. The material was a commercial flop because it proved completely impractical to repair.

The inner layer of Twintex was extensively delaminating up off of the balsa core of this boat. My hope was that I could remove the inner layer of Twintex off the core, repair the core as necessary, then cover the core with several layers of fiberglass cloth. After exposing the core I was dismayed, but not surprised, to find it extensively rotted and beyond repair. I had no recourse but to remove the rotted out wood core.

I was left with a canoe, the center bottom of which consists of one layer of floppy Twintex material. I don't know what thickness this corresponds to relative to fabrics but my guess would be it is roughly equivalent to 2 layers of 6 oz 'glass in thickness and stiffness. This layer is pretty much intact, except for the pinholes that let the water in that rotted the core out. The core occupied the shape of a truncated diamond, measuring 36 inches amidships and around 16 inches in width at each end. It did not extend all the way out to the sharply concave stems so the surface it occupied is relatively gently curved.

My ability to repair this beast will hinge on whether I can get a successful bond between the Twintex and my first fabric layer. To test this, I have bonded about 9 test strips of 8 ounce/sq. yd. fiberglass tape transversely across the hull bottom denuded of balsa core, using G Flex epoxy after careful sanding, washing, and flame oxidation. I did this last fall and have been flexing the hull bottom and watching for any signs of delamination. Thus far, the bond seems to be good.

Assuming I can cover this entire area previously covered by the core with a layer of fabric and get a good bond, I will need to rebuild the canoe bottom with something that will provide reasonable stiffness. I intend to use E 'glass as the first layer, since it takes up epoxy very well and is cheap so that I won't be out much if the bond proves to be a failure. I have some 5.8 oz/sq. yd. 2x2 twill weave carbon fiber fabric that I was intending to use as the final (inner) layer. I realize that carbon is probably best used as an external layer, but that is not practical here, and the carbon will more or less match the appearance of the Twintex hull interior. I am hoping the carbon will add some much-needed stiffness to the hull bottom.

In between the first 'glass layer and the carbon I was thinking about just laying in layers of 'glass until the stiffness seemed close to what I wanted but I am concerned that the weight would be excessive. It sounds as if Coremat could be layed in using just hand lamination, since I don't have facilities for vacuum bagging. For those who have used Coremat, have you found it necessary to weight the surface to achieve a good bond inside a female mold? Also, I am assuming that after taking up as much epoxy resin as it wants to, Coremat has a specific gravity greater than 1, unlike some foams, not so? If I try Coremat does anyone have a suggestion for either 2 or 4mm thickness? The Coremat would be sandwiched between at least one layer of 6 oz 'glass with an outer layer of Twintex and an inner layer of carbon fiber.

 

[Jim Dodd]

Thanks Charlie !
Just what I needed !

Jim

 

[Alan Gage]

Thank you for that, Charlie. Very interesting little read.

That sounds like quite a project you've got yourself there, Pblanc. I wish I could tell you something that would help but "better you than me" probably doesn't qualify.

I've got an old Wabash Valley X-cell C1 from the 80's that has a partially rotted out core as well. It sees very little usage so I haven't bothered doing anything with it.

Alan

 

[charlie wilson]

Alright, a new posting for Pete and something I forgot to mention for everyone else.

I do not know a thing about TwinTex but do know that every balsa core I have ever seen was rotten to the core / in the core. I suppose if I had to try to fix a TT hull I'd rough sand the TT, clean with acetone let it flash off and try epoxy. Might as well use CoreMat because the likelihood of success, low, doesn't justify the expense of carbon which would be stiffer. If I was in a production shop I'd use carbon scrap or kevlar scrap or glass scrap.

For wetting out, the group should be introduced to paint rollers, special rollers available from Express Composites, Noah boatbuilders and Sweet Composites and the bubble buster, also available from the same three. Layup goes lots faster and with less frustration.

bon chance! CEW

 

[pblanc]

Thanks Charlie. I realize that this project probably makes less sense than just standing on the riverbank and tossing $20 bills into the current, but I think I am going to give it a go. In the words of one of my former partners, "I've come so far not even common sense can make me turn back now."