Carbon-Kevlar board layup

[rhorton1]

Planning a wind-sup board build this year for tackling small ocean waves. Planning on a carbon-kevlar-bamboo sandwich construction. I've done my research and think that I've found a good glassing schedule for the board to make it durable and light. I'm going to vac-bag everything, so I don't anticipate any issues with getting the kevlar to lay down correctly. However, I haven't been able to find any info on where to place the kevlar in relation to the other layers Any recommendations on where the kevlar should be placed relative to the carbon for maximum ding resistance?

I am imagining from the outside to the 2lb EPS foam core that there will be carbon, bamboo, carbon, and then kevlar. Keep highest strength stuff on the outside and the flexible stuff on the inside. Any other surfboard/SUP/windsurf board builders out there with some thoughts?

[joethewindsufa]

check with OES professional builder on seabreeze forum

http://www.seabreeze.com.au/forums/Windsurfing/General/Custom-Board-build-day-by-day/

and there is always the boardlady ...

[jingebritsen]

keep wood and kevlar deep, well away from water.

[swchandler]

It's my understanding that kevlar is not easily sanded. Given that, I would recommend burying it under your top lamination, whether it is carbon or fiberglass, or a combination of both.

[thombiz]

I've built several boards and I'm going to suggest a few changes. I've tried to build boards out of 2 lb. Styrofoam but have found 1 lb. foam to work equally well. The key is where to source the EPS. On the most recent board, I sourced the EPS from a manufacturer in Phoenix, Az. It is stronger, lighter, and stiffer than other EPS I've used and I'm going to attribute that to low humidity and better manufacturer controls of the chemicals. Personally, I would never use any wood in any composite. There are too many variables in weight, strength, density, invisible fractures, and flexural properties. My most recent boards have used Corecell at about 5 lb. density. Density has a bit to do with cell size and cell size impacts how much resin it takes to fill the voids and bond the reinforcing. Be sure to use a lot of microballoons in the resin at the coreing surfaces. Corecell is fairly easy to bend (compared to other core materials) using a heat gun. Now, reinforcing. When you are standing on a floating board, the reinforcings on the bottom of the board are in tension and the reinforcings on the top of the board are generally in compression. These layups are quite thin, maybe .015" thick. Thick layups are generally heavy because they are dense. Weight can be reduced by mixing microballoons in the layup resin. A very thin layup is not going to be especially ding resistant (but great for super light boards, (omit one of the 3 outside layers)), no matter what reinforcing is used. Kevlar, carbon, and s-glass are generally very strong in tension. S-glass is something like 30% the strength of equal weight of carbon, but s-glass is tougher and less brittle and much cheaper. A good light weight and tough layup for the bottom might be 2 layers of 4 oz s-glass with a layer of 4oz. carbon between plus 1 layer of 4oz. carbon between the between the EPS and the corecell. For the top, a 4 oz layer of carbon between EPS and coreing, and 3 layers of 4 oz s-glass or e-glass above. Kevlar should only be used if it is part of a hybrid cloth like carbon/Kevlar. With this sandwiched between the s-glass, sanding Kevlar will be minimal. To make the board easier to paint, mix white colorant in the epoxy resins of the outermost layups.

These are only suggestions. Do as you like, but try to understand the nature of the materials you plan to use and good luck.

[bred2shred]

Kevlar is generally used for impact protection. It's not going to provide much in the way of protection if it's buried beneath the carbon and core layers - needs to be on the outside to be effective (think bullet-proof vest). It's also not easily sanded and is hygroscopic as others have said. So you may want to place a glass ply over the Kevlar or just skip the Kevlar all together and go with a glass/carbon layup.

sm

[U2U2U2]

I don't see any structure material other than bamboo, this is to be used top and bottom and no core cell or other ?

If you are using Kevlar on the entire board it will be costly to say the least.

i will only use Kevlar in the nose, mast track. It would need to be covered in the nose with carbon then glass . Using this , my thought is use all the different properties to create strength.

My project does not have bamboo, I am using core cell.
The areas that need the most reinforcement are between the footstraps, nose.
From the sound of your research you are aware of this.
You will find here and elsewhere various options on materials, quantity and placement, most will not , recommend 2lb.
My board is 2lb.

Their is more than one way to bake a cake, even more ways to make a board, no reason why you have to follow what Cobra does, who are there to make money, and try to make a sound board.

Unless you are coping a board, it likely the success will be limited

[dmilovich]

Not a lot of rationale for using Kevlar at all, I'm afraid. If you're trying to limit penetration into a board from some sharp object, it could be useful, but we don't have too many bullets or knives attacking our boards (or do we?). It's always a puzzle why that stuff shows up on masts, too.

Based on a lot of work we did some years back for high-impact racing ski poles, the only benefit of Kevlar was for reduced cut resistance from ski edges. (these poles were used by a number of Olympic and Pro gold medalists, btw)

The primary way to enhance impact resistance is to use toughened epoxy that is well cured, along with the usual carbon and glass (S or regular) fiber, and some sandwich construction. Even a modest amount of heat will improve epoxy laminate properties. But you don't have much freedom to do that with an EPS foam core. If weight is the issue, then carbon wins in general. S-glass is more impact resistant in laminates than standard E-glass, but more expensive.

I would not discount the Cobra (or other reputable board builder) construction approach since part of any cost benefit is not having boards fail in use, so most likely they've thought this through already. Probably the biggest thing you can do is to figure out whether use of a double sandwich (outer thinner sandwich with higher density foam/bamboo/whatever over the eps thick low density core sandwich) makes sense in your high impact areas or not. It's tough to do given the need to shape the rails properly. Another approach is to see if you can get any kind of oriented fiberglass cloth, meaning cloth that has more strength in one direction than another. If so, it will help impact on rails if you can orient the stronger direction around the rail itself.

Of course, you will likely need a connected (top deck/bottom deck) box-type construction for your mast and fin boxes.

Good luck.

[rhorton1]

Thanks all for the suggestions.

I wanted to add a layer of kevlar to increase ding resistance against mast dings and other tumbles while wind-supping. However, after looking at videos on the seabreeze forum as well as watching some windsurf construction videos on youtube, I think that strategic carbon reinforcement would be easier. Seems to be what the pro board builders are doing. None of the videos I have seen incorporate kevlar reinforcement....I might as well just spend that money on more carbon fiber! Good note on changing the fiber orientation in the reinforcement areas... I will try for 0, 90, +45, -45 degree orientation reinforcements over the nose and rails.

Since the board is primarily a SUP, I think that a full sandwich construction with divinycel/corecell foam would be overkill. I have used bamboo sandwich construction on a couple of kiteboards to good effect, and will be sticking with that method for this wind-SUP. A double bamboo veneer will give 3mm of separation between reinforcement layers, and I plan on using that in the standing area. Yes, its thin, but better than nothing. Maybe I will go up to 3 layers of bamboo in the standing area....This paired with the 2lb EPS core and a deck pad should make the board pretty resistant to heel dents. If worse comes to worse I can add a nose pad too.

I've also got high density foam for wrapping the fin boxes and mast track. Haven't decided on whether to include foot straps or not seeing as this will be geared more toward light wind sailing...

Regardless, once the build process starts I'll keep everyone posted with pictures.

[wynsurfer]

I've given some thought to doing this as well. Where does one get the bamboo?

Divinycel improves impact resistance and does not absorb water so might be worth doing.