Kevlar

[Jim Dodd]

OK seems a few people have been into various tests. And It's about time I come up with one.

This Summer, if all goes well, I'm going to attempt my second Kevlar canoe.

I will be using the stripper, that I'm building now as the male mold.

Years ago I purchased 9oz Stitched Kevlar from RAKA.It must have been designed for bullet proof vests, as I had a MOST difficult time cutting this Kevlar. It was also quite difficult to wet out. At that time I was using System Three's Clear Coat, which normally wets out E-glass quite easily.

As RAKA didn't have this in stock, lately. I ordered 8.9oz 2x2Kevlar twill from Noah. I cut a small piece to see how it compared to the RAKA 9oz stitched.
Noahs 8.9oz cut much easier, and wet out much easier.

Tomorrow I'll check on the pieces that I wet out, as far as stiffness, and cut ability.

As of right now, I'm really liking the Noah's 8.9 Kevlar.

If anyone has some Kevlar experience to share, Please post !!!!

RAKA 9oz Stitched on the left, Noah's 8.9oz 2x2 Kevlar Twill, on the right.

Jim

 

[Alan Gage]

I'll be interested to see your results and even more interested to see one of your homebuilt kevlar canoes. That stitched stuff on the left looks like a nightmare from looking at the picture.

Alan

 

[Jim Dodd]

I'll get my first Kevlar out today for a pic.
Here is what I have from last Summer. I didn't use the cedar for the bottom, instead opted for pink foam.

 

[Alan Gage]

Very interesting. I was thinking it was too bad you couldn't build a tumblehomed hull using your method but there you are with a tumblehomed hull from a male mold! I assume not doing the stems allowed enough flex in the hull for removal? Were the stems molded separate and then attached to the hull after it came off the mold? Was it difficult to remove from the mold?

Looks like a fun project. What will you do different for the next one?

Alan

 

[Jim Dodd]

I've got a handle on the tumblehome thing. I think !

I'll use double sided tape to hold the release film against the hull. It should remedy that

I had no trouble getting the Kevlar off the plug.

As for the ends, I had to use a small Angle grinder to trim. I spring clamped them together and epoxied. Then covered with Kevlar felt, inside, and out.

Have to say it's kinda ugly, but it floats.

Jim

 

[Jim Dodd]

No Laughing ! Ha ! Here is a pic of last Winters Baptizing of the Kevlar.

 

[Alan Gage]

Looks good from here. What was the finished weight?

Alan

 

[Jim Dodd]

I knew you would ask. I didn't weigh it, but I will later. I have some fresh cut Ash planks to stack for drying after dinner.
It's quite a bit lighter than my strippers, that's for sure !

Another pic I took today.

You can see Owens -Cornings, Pink Panther from the bottom side !

That's a Bell replacement seat, that I picked up on clearance.

Jim

 

[Jim Dodd]

Just weighed the Kevlar, 36-37# by an old spring scale.

Also checked on test pieces.

Even though the Old RAKA 9oz stitched was hard to cut, and wet out, it out performs Noahs 8.9 Kevlar 2x2 twill.

If people have the idea that Kevlar, is tough, It's not ! Noahs was easily but with scissors, both dry, and coated with epoxy.

I'll probably have to add an extra layer of cloth, besides laminating foam and a layer glass.

Jim

 

[charlie wilson]

There are four kinds of Kevlar, 49 and 149, 29 and 129. The Kevlar used in bulletproof vests and fireproof clothing, 29 and 129, can be colored but do not laminate well and should not be used in composites. Maximum recommended composite K29 content is 25%, which describes Bell's, Northstar's and Souris River's "tweed" fabric.

Kevlar 49 does not laminate terribly well either and is hydrophyllic, which should be an issue in a hull laminated on a male mold. [The standard female molded products have the advantage of a gel or skin coat to protect the Kevlar from cuts and water penetration.]

It usually takes a minimum of two layers of material to yield a waterproof composite, so two layers of 5 oz Kevlar will be preferable to one layer of 9oz.

After a nice, thirty year, run as a top composite material, Kevlar may be on the cusp of replacement by Innegra in combination with basalt or carbon.

We'll know by fall 2015.

 

[Jim Dodd]

Thanks Charlie !

I plan on the 8.9Kevlar as the first layer on the mold, followed by 6 oz of E-glass, and then a a layer of 6 oz S-glass as much as a 40" width will cover.

Once cured, and pulled off the mold.
I'll put 1/4" foam(Pink) then a layer of either S-glass, or E-glass on top of that, and up to the seat area, for more reinforcement..

I'd love to get your thoughts !!

Jim

 

[Alan Gage]

From the little I understand about composites and how they work together/against each other I believe kevlar is at its best in tension, which would be the inside of the hull. So perhaps the strongest layup would be fiberglass on the outside and kevlar on the inside? Maybe a light layer of fiberglass over the kevlar on the inside to make sure the kevlar fabric stays buried?

Alan

 

[charlie wilson]

Allan and Jim;

Jim is laminating on a Male mold, so the first, Kevlar, layer down will be inside when the initial three layer laminate comes off the mold. With core and inner glass layer it will be more or less a four layer hull, all five parts, including the core, everything pretty much where they should be. It is instructive that Colden Canoe uses ~ 30 fabric parts, three full blankets and 27 partials to strategically reinforce the hull at the bottom, stems and up the center sidewall where the paddlers weight is born by the rail system.

Foam cores replace several partials, but the foam needs be bent to shape in an oven or scored to flex into full contact with the hull. Then it needs be bedded in a putty of micro-sphere thickened resin and held in contact with the hull until the resin gels. We usually use a vacuum pump, release film a breather layer and nylon bag with sticky tape to achieve that. Voids between core and hull are a very bad thing. It is Std Op Procedure to have two layers of resinated fabric under and over foam cores. The quality of the foam is another important consideration, Airex and Divinyacell being the two best known fabricators.

The folk lore concerning glass, Kevlar and carbon is pretty inaccurate. S glass, Kevlar 49 and std modulus carbon have similar tensile strengths, ~ 600 ksi, the S elongating ~6% at breakage, Kevlar ~3% and carbon 1.5%. Tensile modulus, stiffness in msi, is 12 for S glass, 19 for Kev. 49 and 33 for std modulus carbon. Who'd a thunk? Glass is used because it is inexpensive if heavy. Kevlar is pretty neat stuff, but carbon is stiffer and hydrophobic while Kev absorbs 7% it's weight in H20. Intermediate modulus carbon, while hard find and harder to pay for, is ~800ksi/40msi/2% to breakage. We do not have data on the various Innegra combinations as used by Bic, Nova and Swift yet. It may be instructive that folks who don't care about cost, aero-space and race car folks, use carbon and Innegra but not Kevlar or glass.

Innegra is another data set. it's Tensile strength and modulus are low; 100ksi/2msi with 10% break elongation. It currently is woven in combination with glass, basalt or carbon for lamination. Nova uses co-mingled Innegra/basaslt, Swift used the same and quad woven Innegra in combination with carbon. Surely Mad River and WeNoNah are working on Innegra based composites as well. Lighter than water, Innegra floats in resin, so users need vacuum bagging to laminate. Innegra is not currently available on the retail market at Express Composites, Jamestown Dist, Noah boatbuilders or Sweet Composites.

 

[Jim Dodd]

Alan, that is how I have it planned, for now.
I'm a little concerned that it might not be stiff enough.

The Innegra that Charlie writes about, is worthy of investigation ! But for us, one off male mold guys, I'm leery. It seems better suited for the female, infusion molds. Rugged though.

Jim

 

[Jim Dodd]

Thanks Charlie !

You slipped in while my one finger was pounding away with my above message !

You brought up many important aspects ! Bonding the foam to the hull, as well as the type of foam.

For my first build, I supported the hull with heavy planking, to reduce sag in the hull. I scuffed the interior, and poured mixed epoxy with some Cab-o-sill, and ground glass down, down the inside keel line.
Spread it out, and layed in the prefit Pink 1/4" foam. The foam conformed pretty well. But I'm still worried about the foam failing with flexing of the hull!
Covered the foam with plastic, and then weighted it down with sand. Lots of sand !

It seemed to work, but I have no way of really telling. Further testing is in order !.

Vacuum bagging will be used on the next one.

Thanks Guys ! For your input !


Jim

 

[Muskrat]

No Title

Hi. New to the forum. I've built a couple kevlar and glass boats on male plugs and thought I could add to the discussion. I used the 9 oz kevlar from raka too, and they still have it for sale. The last time I talked to them they said as long as I wasn't building a battleship they would have it around.

http://store.raka.com/13ozx64in-45x90x45.aspx

As far as cutting the Kevlar goes I highly recommend buying a dedicated pair of shears and not using them for anything else. I got some from Amazon that are cheap relatively and work just as well as the $60-70 pair I originally bought.

http://www.amazon.com/Clauss-Carbon-Shears-Kevlar-Materials/dp/B000XB9X7W

I don't think I would try to do a full foam core in any boat made off a male plug. Seems like a huge pain. Ribs are much easier and have worked out well for me so far. I used lantor coremat for my ribs. It's as simple as wetting them out and dropping them in the bottom and then applying kevlar over the top. I'm at that point in the guideboat I'm building now. This time I'll use peel ply over the top so I have less sanding to do afterwords. If you make your ribs go most of the way up to the gunwales it will be plenty stiff. That's actually the only reason I'm adding them to the guideboat. It is a very thick layup with 12 oz of s glass and 18 oz of kevlar. There is no worry about oil canning but it twists a little more than I like right now.

 

[Jim Dodd]

Thanks Muskrat ! And Welcome aboard ! Nice to find builders with similar experiences !!!

I called RAKA, awhile back, and they said they were out. They may have some in now though.

Yeah, that's the stuff. I've tried a lot of different scissors, and the best I could do was chew my way through. Once I applied resin, a cutting blade on an angle grinder worked pretty good.

How spendy is the core mat, and where did you get it ?

Jim

 

[Alan Gage]

Express composites out of Minneapolis has Lantor Coremat, along with other core materials, and seem to be great people to deal with. They have an online catalog but no online ordering so you have to call to order. Knowledgeable people and they seem happy to answer questions. Their regular shipping gets to me overnight, don't know if that would apply to you or not. Sure makes it handy when I want something in a hurry, which always seems to be the case.

http://www.expresscomposites.com/foamcore.html

Alan

 

[Muskrat]

I got the coremat from here…

http://fiberglasssupplydepot.com/Coremat-4mm-39.37-width.html

I have quite a bit left over, enough for a whole canoe, but I think the 4mm was a little too thick. It really doesn't take much thickness to build a much stiffer section. I'll use 2 or 3mm next time. The 4mm made it difficult to get the kevlar down around the edges without any bubbles. So far the ribs have held up nicely with two layers of kevlar over the top. It is scary the first time you slide over a sandbar in a ribbed canoe. You can see the wave of the hull flexing as you slide along.

The special kevlar shears make all the difference. They cut the Kevlar just like regular scissors cut glass, but don't cut fiberglass with the Kevlar shears. It will dull them very quickly. I used a coping saw for the trimming once the resin was cured. There are many unpleasant parts to one off Kevlar canoes, and using a coping saw the entire length of the gunwales is up there for the worst.

 

[Jim Dodd]

Express composites out of Minneapolis has Lantor Coremat, along with other core materials, and seem to be great people to deal with. They have an online catalog but no online ordering so you have to call to order. Knowledgeable people and they seem happy to answer questions. Their regular shipping gets to me overnight, don't know if that would apply to you or not. Sure makes it handy when I want something in a hurry, which always seems to be the case.

http://www.expresscomposites.com/foamcore.html

Alan

I've been there years ago. It was a one man operation, and the guy was very knowledgeable. I'll plan to stop there when I go up to Midwest Mountaineerings Spring event and auction.

Muskrat
Does the coremat suck up resin ?
The pink foam was easy to feather the edge, I just cover the bottom, and glassed. Right now it seems stiff, but still ugly ! I'd think it would work good as a rib, and covered with Kevlar.

And speaking of resin ! Muskrat. What did you wet out your RAKA Kevlar with, and how ?

I need to get some shears !

Thanks Guys !!

Jim