Carbon topcoat / build options

I'm thinking about building an open ocean rowboat in carbon fiber / aramid mixed layer hull. The boat would be covered in storage, and let’s say out in the sun and saltwater getting used maybe 30 − 50 days a year. It would be well-treated, hosed off after use, and perhaps waxed or buffed a few times a year.

I’m pretty sure I can make a plug, and a tooling gelcoat mold. For the hull, I’m leaning away from a gel coat and vinylester infusion, and toward an epoxy vacuum infusion.

I’ve done a lot of research, but haven't found further information on building techniques, specifically on my options to protect a carbon outer layer.

I’ve been impressed with what I’ve read about Resin Research Epoxy, primarily because of the toxicity / co-toxin sensitization issues. Secondarily, they say their epoxy has some U.V. stability. I’d love to hear comments on that, but don’t imagine it would be practical to leave the carbon shell exposed to sunlight and saltwater.

About the only topcoat I've found that advertises UV protection is System Three WR-LPU (Polyurethane) Topcoat (http://www.systemthree.com/store/pc/WR-LPU-Topcoat-c29.htm). If used as recommended (Dry Film Thickness recommended 2 1⁄2 - 3 mils) would that offer adequate protection? Are there others that would be better? Give me names, I can do further research.

(I assume that I’m just going to have to get used to hearing this polyurethane clear coating referred to as ‘paint,’ even in the maker’s application guide. It’s pretty confusing, however).

I’d like to be confident that the topcoat and the hull are a good match in terms of resistance to fatigue and micro cracking. I’d try to build the hull thick enough that it wouldn’t be stressed into flexing too much.

There’s a canoe builder that uses fiberglass as an outer layer over epoxy / carbon, but they don’t say what resin / polyurethane they use on the fiberglass.

Would a transparent fiberglass / epoxy outer layer offer enough (or any) UV stability? Could I do a vacuum infusion mixing PolyUrethane and fiberglass with carbon and epoxy? I'd prep the mold with mold release / wax, spray a few coats of the PolyUrethane, then lay down fiberglass, then the carbon / kevlar layers, then infuse with epoxy. If this is workable, would I let the Urethane cure completely, or lay the glass while it was still tacky?

Or would it be better to prep the mold, lay down the carbon and kevlar, infuse, cure, pull the hull, then do a hand layup of fiberglass? With what resin or material?

I'd look in to building a hot room to let it cure, but may not be able to.

Any advice most appreciated.

 

you are using Carbon and kevlar ??
They are opposites to each other carbon has no stretch and kevlar has a ton of stretch !!
Then you want to infuse and then add more by hand lay up again very confusing to say the least . Do you have trouble sleeping at night ??

 

Have you priced out these materials in the general laminate thicknesses you'll need?

 

Well, I've found three canoe builders who make production boats laying up hulls with alternating layers of these two fibers, and distributers who sell composite materials have carbon and aramid woven together, so I guess I'm confused that you're confused, and I sleep fine. First two distributors I checked sell mixed weaves:

Par, no I haven't as I've been putting off getting windows emulators on my mac, so I can run hull building PC software, so I can figure out what dimensions I'll need. I also don't know how to calculate the strength / thickness / material relationship. Once I've built my hull in software, I'll obviously know more. But there are enough youtube videos on infusion / mold hull making to give me an idea of what might work.

Since I originally posted, I found another product that might work with fiberglass over carbon: System Three SB-112 http://www.systemthree.com/store/pc/SB-112-c12.htm, but I still don't know if clear fiberglass will absorb UV, or to what extent it'll protect the carbon beneath.

 

yes kevlar is great for impact protection
Carbon will never safe your life but kevlar will

 

Engineering with these materials really takes a good grasp of the material properties you're working with. If you going to use these materials to advantage (considering their cost, there's no other reason to use them other wise), then a fairly carefull assembly of the laminate schedule, needs to be worked out. This is especially true of small, light weight craft.

 

The system 3 product is a paint, not a resin (if you define a paint as a resin in solvent).

All polyurethanes at about more than 50microns will be UV resistant - you can use Awlgrip, International etc etc. Alwgrip also do a clear 545 primer if you want to fill weave a little. Downside would be pack sizes here, Not sure if this comes in smaller packs than 2gallon set.

All the topcoats will cope with your craft flex wise. Adhesion will be more a issue.

You can apply these onto the epoxy no problem - after sanding. I know some people who have been experimenting with applying topcoat in mold and then laying up. From what I remember (it was a few years ago, sorry) they were using pigmented systems...so this doesn't really help.

The problem if you do attempt it is that you have to allow the topcoat to cure enough and the solvent escape. Is it worth risk of future delamination? No material supplier is likely to give you any recommendation due to all the ifs and buts.

I am not clear about your proposal? You want to lay "fibreglass" over the epoxy/carbon/kevlar matrix? Polyester fibreglass? Why do you want to do this?

"Assa Abloy" was a Volvo 60 from about 10years ago. This was clearcoated over carbon/kevlar. Looked very cool. But i warn you now. If you sand the epoxy layer before topcoating be sure that the resin layer on the surface is thick enough/smooth enough otherwise you will sand into the cloth...which is a nightmare for you.

Your problem may well lie here. If you bag/infuse you will be definition have a low resin thickness on outer side (this is reason to bag/infuse - you get near best resin/cloth ratio ie not overly resin rich). This is perhaps why you read that some builder 'fibreglassed" over epoxy? They were trying to provide a smooth, glassy outer surface?

All epoxies suffer from UV degradation. It's inherent in chemistry of epoxies. Some suffer more than others. The 1st problem is yellowing. After many years it will start to chalk/go milky/crack on surface. It will depend on the epoxy and how much sun it gets.

From what you suggest I might be tempted to skip the topcoat and just wax with UV resistant wax (they exist - think of it like suntan lotion for paint). Get a canvas cover made, and only uncover when you are actually out in sun. If it starts to get damaged, lacquer it. (sorry if this is actually loads of work to strip hull back to paintable. Then again it is time you would need to budget in at a build stage if you go that way)

ps screw the technical reasons for using carbon/kevlar weave. It looks cool when clearcoated. This is almost good enough reason to use it for your dreamboat. The only reason I am not married yet is that I said I want a carbon/kevlar/titanium ring from the wife. She's still saving

 

the RC44's are clear finished I wonder what they used?

 

If you use epoxy resin (such as your "low toxicity" resin research brand) you will need to wetsand the finished hull and spray 2 pack PU (and that stuff is plenty toxic!!) be careful that kevlar strands are not on the outside surface as they will "fluff up" when abraded. I would suggest a clear PE or VE gelcoat (They offer UV protection) and then VE infusion of your laminate. Epoxy resin both yellows and seems to get degraded "eaten " by UV as well as needing that postcure.

ps Carbon /Kevlar weve has more wow/**** factor than carbon alone IMO

 

If going to the trouble of using these fabrics and taking full advantage of what they bring to the table, using polyester resin systems is just folly, as the resin's modulus of elongation isn't well matched with the abilities of the fabrics. Vinylester is a closer match, though still not most advantageous, compared to epoxy.

The wise thing to do is use an LPU topcoat to protect both the resin and the fabrics. This will need renewal from time to time, but is the most durable of the possibilities. Of course, the clear coat is purely an aesthetic consideration and absolutely the most difficult thing you can ask of a coating of any type or resin on any substrate.

 

From what I've seen the carbon fiber will start to break down if not protected from the sun's UV rays. Case in point many newbies to sailing think it is cool to have clear coated carbon masts, looks cool right. Well what happens after a few years in the sun then the mast will start to break and get brittle from the exposure to the sun. The problem with carbon fiber it is strong and stiff up to the point of failure, then it does not bend it just fails. Also from what I've read the custom mixed fiber cloths are not the best either, again looks very cool, but are more for the wow factor not the best for marine applications.
Having said that in the laminate schedule in the boat I’m building I will use 200 gram carbon fiber cloth, 6 oz. Kevlar, and 6 oz. E-glass (white cloth). The general layup from the inside skin out is 200 g carbon x 2, 3/8” foam, 200 g carbon x 2, with one layer of 6 oz E-glass on the outside using west system epoxy and vacuum bagging the laminates. The boat will then be painted with a UV type paint. There are some stress points that will have up to 6 layers of carbon on each side of the foam. The outside layer of E-glass is to protect the carbon from scratches and blunt force that may fracture the carbon. Along the keel and point of the bow I will have some Kevlar buried under the carbon next to the foam to prevent punctures for beaching the boat. Also the bow sprit has a layer of Kevlar in the layup to add the strength properties of Kevlar to the tube. The boat is a light weight 20’ racing trimaran the planned weight is approximately 500 pounds.

 

Thanks Par, I couldn't agree more, which is why I'm researching laminates before doing hull design. I want to understand this stuff, and have a complete and well-researched strategy worked out for the build. I really can’t afford to waste either time or money.

 

Colin, thanks very much, that’s immensely useful information. Just what I was looking for (I was hoping someone would say just that about flex).

 

Yes, that’s the trick. How to best give a vacuum smooth epoxy / carbon layer a protective topcoat. Ideally, with a chemical bond. You’ve restated my problem well. I’m looking for protective outer layer that will also guard against UV. There’s a canoe maker that uses fiberglass over oven-cured epoxy carbon, but they guard their process (and don't tell). They do show that a fiberglass outer layer could also be sanded and re-epoxied, or re-urethaned for repairs, which is a plus.

I’m thinking of using an outer layer of fiberglass into the mold, then carbon, infuse with RR, then pull from mold which should give a nice hull. Between the Resin Research UV protection, and the fiberglass, UV hopefully won’t be an issue. I'm also not sure whether to build up hull thickness, maybe with glass. I’d love to find out more about clear fiberglass as a UV barrier. Anyone?

If inadequate, I can then lightly sand and coat with PolyUrethane.

But I guess I don’t understand why the car guys can skip this. They spray clearcoat over carbon without seeming to sand their vacuum carbon parts, so what’s the difference?

I tend to agree!

 

Me too! Though I think they'd be obsessed much more with weight than me, and those boats are on the water so little, that they probably get a waxed buffing every time they go out to compete. But I'd love to know their process.

Yeah, I’m starting to see that too, and getting less interested in Kevlar. I'm really not worried about puncture resistance in my use of the boat, and need to find more information, but I'm under the impression that while the kevlar fiber's coating chemically bonds with an epoxy matrix, the fibers themselves can still (and want to) absorb water. I don't know if one unnoticed but deep scratch could then lead to swelling or other delamination problems, but it's a concern.

The kevlar would still be lighter than fiberglass, but perhaps not worth the cost as I’d like a light boat, but I just don’t need it superlight. Ocean rowing rewards some mass and momentum, so I may not loose sleep over a carbon / fiberglass mix.

I agree with you, and with PAR, but you guys aren’t giving me solutions. We’re all in agreement that a good vacuum infusion of carbon is wonderful material. And that it’s hard / impossible to sand it. So how do you protect it from UV?

To my understanding, a thin outer fiberglass layer which can then be sanded and coated with PU makes the most sense. If there's something I'm not getting, or there are better solutions, I'd love to hear.