Hollow carbon shell surfboard

General Discussion
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Unfortunatly, we had problems with the computer and measuring equipment in the lab yesterday. The test was unable to be conducted. It will be postponed to a later date. I am going to start making a full board now. I feel confident in my technique.

On tuesday everything was settled with the lab equipment. I am taking a mechanical lab class. I thought it would be neat if my group and I crushed some of my test sections and recorded the force and deflection as they were crushed. The data which was collected is not useful in future surfboard design. However, it was a fun way to learn how to use the lab equipment while incorperating something which Im intrested in.

I don’t have any pics of what went on in the lab, but here are a few pics of the calibration set-up at home. There is a potentiometer which is turned when the test section is crushed. 12v is sent to the pot. The deflection can be mesured by reading the change in voltage on the voltmeter. This circut was hooked up to a computer which read the voltages from the deflection pot, and the force pot (not shown in pics). The voltages were recorded to a spreadsheet at 20 samples/second. The board was crushed over a period of 5 seconds. During the crushing, the test section resisted up to 300 lbs.

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Check back to the end of page 4 on the thread for some more pics. I did 2 posts back to back and it bumped to the next page after the second post.

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Hi -

Such an impressive project! Sorry to hear about the accident. Regarding the ride and dropping in issues… does the original board that the mold was taken from behave the same way? Kind of hard to decipher why the change in materials would cause that to happen. Maybe the waves?

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It would be interesting to see if a larger section combining the top and bottom would withstand higher loads.

Maybe when the whole board is put together it will be stronger but that measurement of 300lbs is basically one 150lb rider on one foot applying 2 Gs pressure (sort of along the lines of what I’m thinking)

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Interesting stuff and cool that you have ridden the board after all that work. Clear finished kevlar isn’t a good idea though, after a couple of years the light will break it down and it will become as weak as tissue paper, so best to cover it up really.

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Beautiful project lpcdefg, Have you got a total weight yet? Did you say how you joined the two halves?

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Yeah, UV can really kill aramide (kevlar) quickly. clear coat polyurethane paint should help prevent degradation. Or a gel coat like this:

http://www.fibreglast.com/showproducts-category-Gel+Coats+&+Hardener-10.html

Make sure you have a decent layer of “hot coat/sanding coat” so you can sand it, the bond with the gelcoat will be mechanical not chemical so you need maximum adhesion.

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It would be interesting to see if a larger section combining the top and bottom would withstand higher loads.

Maybe when the whole board is put together it will be stronger but that measurement of 300lbs is basically one 150lb rider on one foot applying 2 Gs pressure (sort of along the lines of what I’m thinking)

The 300 lbs measurement is irrelevent because it only acounts for the strength from the rail to rail dimention. A lot of strenth comes from the nose to tail dimention too. By the way. 300 pounds was (about) the maximum force measured as we were hearing violent cracking sounds!!! 300 pounds is a guess because we have not converted the voltage readings into acutal forces. Based on some calibration data I guessed the highest voltage read would equate to 300 pounds.

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Beautiful project lpcdefg, Have you got a total weight yet? Did you say how you joined the two halves?

total weight = 9.25 lbs. This includes fins, leash, wax, and a little water that has yet to drip out. The two halves where butt glued together along a 1/2" wide horizontal, internal flange that is paralell with the deck. My next board will have a vertical flange, parallel to the rail. The two halves will overlap. This type of joint maximizes the gluing area. The current method only relies on the glue closest to the rail’s edge. The halves were joined with a slurry of epoxy adhesive resin and fine chopped carbon/kevlar fibers. After the sandbar accident, there is no evidence of damage to the glue joint.

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On future boards I will make an all black carbon finish. I will keep a layer of kevlar directly below the carbon. I did not know that kevlar will break down over time.

By the way, I plan on only keeping this board until #2 is finished. Once #2 is finished, This one is going strait to Ebay. I have to recover as much material cost as possible.

As for now, I need a few weeks off. I need to brainstorm and make some money. I have many new Ideas for the next board and I am confident that there will be many improvements compared to this board.

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i try not to sell boards that have faults

sounds like the rails seam will be a future problem for new owners

my wife is always hassling me to sell my older boards that have faults

i suggest that you do the rail joint on a pvc perimeter stringer

it will add improved strength without much weight

9 pounds seems excessive for a thruster shape

but very interesting project none the less!

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In a month or two after board #2 is made, this board will be useless to me. I don’t have space to hoard old boards, and I need to recoup as much of the cost as possible for future projects. I plan to link this thread directly to the ebay page so the buyer can see exactly what this board is all about. Im not going to hide anything when I sell it. I’d like to keep this as ethical as possible. It is what it is and that is that. Hopefully, one man’s junk is another’s treasure…

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I don’t have space to hoard old boards, and I need to recoup as much of the cost as possible for future projects. It is what it is and that is that. Hopefully, one man’s junk is another’s treasure…

KENDALL it seems like someone needs your storage solutions!

as I understand, this guy has about half a million boards or so…maybe he can help u…

:wink:

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hahaha… I’ve got all the old hollow carbon/Kevlar boards I need. I haven’t mentioned the stack of broken ones in my basement. When I left Hydro Epic and they moved from Nor Cal to So Cal we must have thrown away 100 old boards. I saw a couple of them for sale on craigslist a few weeks later. I pitty the suckers who bought them.

We threw them out for a reason.

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cool

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As a non believer of carbon-fibre.

I would like to see you building the same board in GLASSFIBRES.

My proposal:

6oz deck fibres parrallel (and perpendicular) with stringer

4oz inside deck fibres 45° with stringer (because it reduces twist and the inside fibres have to take the shocs of your feet)

4oz inside bottom fibres 45°

6 or 4oz (you can choose) fibres parrallel (and perpendicular) with stringer

And make a foamstringer

try it, and compare ;).

I think it will work surprisingly good. It is not that much work, you’ve already made the moulds ;).

I’m a non believer in carbon fibres because they are not as strong as everybody thinks. The are just super stiff.

If you knock on your board carbon will fail, glass will flex!

The strongest fibres are Aramide, they are really strong! But you need vacuum laminating because they suck tons of resin.

Glass will just be fine. I’d like to see a comparison :D.

my carbon experiences:

In windsurfing carbon is commonly used.

Carbon wishbooms break like nothing. Thier advantage is that they are super responsive, but when you come out of the water you have to be super careful with them. The aluminium booms last much longer.

I have a board with a carbon laminate on the outside, everytime that board gets hit by something I have to repair it. With my other boards I don’t have to.

If you use carbon it is best used on the inside (under the sandwich skin or on the inside of a hollow board) and only use it for stiffness, not for strength!

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On future boards I will make an all black carbon finish. I will keep a layer of kevlar directly below the carbon. I did not know that kevlar will break down over time.

By the way, I plan on only keeping this board until #2 is finished. Once #2 is finished, This one is going strait to Ebay. I have to recover as much material cost as possible.

BAD IDEA!!!

useing carbon and Kevlar in the same fibredirection in the same laminate is useless!!

Because carbon is way stiffer it will take almost all of the load until it breaks, then the kevlar takes over and you lose the stiffness.

So they won’t work together it will just make your board heavier and more expensive.

Carbon breaks easily on impact! Kevlar will take the impact AFTER the carbon has broken!

Want to save money? Don’t use carbon on the outside

Want a carbon look? Paint your fibres black

Want to be able to use surfwax on your board? Dont give your board a carbon look, the lightness of your board is “cool” enough!

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Hey Hans.

I’ve built at least 10 kite boards using a combination of carbon and Kevlar in each and I have 5 of the ten in my basement at this moment, hang on I’ll go see if they’re broken, No, not yet,???

I’ve been riding my three favorite kite boards I built 4 years ago, and there’s barely a scratch on the paint of each…

These boards were built using Core-cell A 550 foam and a layer of 5.7oz. Carbon- Kevlar hybrid on both top and bottom, with a couple of layers of 4oz. S2 on top of that…

  These board are a maximum of 5/8" or 15mm. thick (under feet) tapering off to 1/4" or 6mm. (at the tips)

I weigh 245 lbs, and I land these board from jumps of 15’ to 30’ on a regular basis…

 I found that the key to mixing these two materials was to use the hybrid cloth, where the carbon ran the length of the board for longitudinal stiffness and the Kevlar ran out from center line to  the rails for impact strength reasons only...

I have stopped using this cloth for these 3 reasons only :

1: Cost, $60 per meter @ 50" wide… .

2: Stiffness : The carbon adds a little too much stiffness to the boards especially when using S-glass over the hybrid, but that’s just a “taste thing”, not a mechanical property issue…

3: Kevlar is harder to work with, I own 2 pair of Kevlar scissors that cost $40 each… Believe me you need these things if you want to cut Kevlar neatly… Also you can’t sand Kevlar, it just ends up like a fluffy wool-like mess when sanded…

This summer, I hit the shallow rock bottom of my favorite kite-surf spot with the tail of my board , the area of the board I hit is only 10mm. thick , and I really whacked it! Thanks to the Kevlar the damage never made it past the cloth and near the foam…

On a final note : Check the specific gravity (or weight) of woven carbon, woven Kevlar , and woven E-glass, Kevlar IS the lightest of these three materials, so your comment about a heavier board holds no weight…:wink:

The main reason not to use Carbon OR Kevlar is “the bang( as in impact resistance) for the buck” , and excess stiffness ,nothing more,imho…

Carbon and Kevlar in the same fiber direction is redundant, I agree, but at 90 deg. to each other they can compliment each other quite well…

Kiterider…:slight_smile:

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Oh, I forgot to mention the core;

Core-Cell ; the best hard foam out there, bar none, I’ve been preaching the virtues of this foam over that of D-cell for the last 6 or 7 years, it’s all about shear strength (shear elongation before failure), not weather you can’t dent it when you squeeze it between your fingers…

All my compsand kite-surfboards will be skinned with Core-Cell. or a combination of Core-Cell and balsa. I have no vested interests in this product other than being a “more than satisfied customer”… Good products promote themselves…

Kiterider…:slight_smile: