Hollow Carbon Fiber Fish

thanks for all the helpfull topics past present and future, my wife on the other hand, not so thankful. let me begin. before i order my resin and blank i wanted to ask a few questions. Im not sure if anyone can help me but i am starting with sways and we’ll see where it takes me. I work with Carbon fiber, Kevlar and fiberglass in aerospace so im familiar with its workability and strength properties. I have acquired 9 yards of 12K carbon fiber plain weave and would like to build a hollow carbon board. i can shape a foam blank layup the carbon, drill a hole for the vent poor acetone in the hole and the foam melts out without hurting the carbon. I can get 7 plys out of the 9 yards, that would be 4 on top and 3 on bottom 2 each at 90 and the others at 45 with the extra scraps used for the rails nose and tail. do you think that this will be strong enough to support 180lbs in sloppy knee to rare head high great lakes surf? fin boxes would have extra internal support with balsa blocks. would it be a good idea to add extra balsa blocks in strategic areas were there is higher pressure? any help, suggestions or advice would be great. thanks in advance.

I like the idea about not wasting the eps slurry. I wonder if that would work.


Sounds like a great project.  But why must it be hollow.  Once you shape the blank and glass, why not just keep the core?  For a 5-10 fish, you’d only have about a pound of weight in the core.  Good luck an be sure and post pic’s of the whole build.


all the best

I’m familiar with 12K Carbon, but wouldn’t normally use it because it’s generally a large patterned, higher weight per sq. yard product than the more commonly used 3K glass.

It would be extemely helpful to know the weight of the cloth you have, based on  the weight per sq, yd. or meter.

If your 12 K Carbon were a common  12oz. per sq. yd. fabric and you were to require  say 1.5 sq.yd. of carbon over all to cover each side of the board.

My calculations are as follows:       (based on the hypothetical weights and dimensions suggested above)

1.5 sq. yd. of carbon = 18oz. weighed ( based on 12oz. per. sq yd fabric.)    Multiplied  by 4 layers for the deck       =   18oz. x 4 =       72oz.

 1,5 sq. yd of carbon = 18oz. weighed   (based on 12oz. per sq yd. fabric)    Multiplied by 3 layers for the bottom  =   18oz.  x 3 =   54oz.

Total Carbon fabric weight  is  126oz. or  7.875lbs.   without factoring in epoxy weight.!!   Add epoxy and you’re looking at nearly doubling that…

Even if my hypothetical example were high regarding cloth used you can see how the weight sky rockets when using this higher K carbon in that many layers.

Even with all those deck layers the board would most likely still  “oil can” when you step on it due to the composite skin not being thick enough.

You’d be better off with a 1/4" thick  HD foam like Core-Cell  and such, and only one layer of your 12 K on either side of that.

Check out Aviso hollow surfboards.  Without an internal frame or core the skins need to be thicker imho.

Your cloth might be free,  but if it’s as heavy weight as I’m thinking,  it’s too heavy duty for what you’re planning.

A lot of people think  Carbon’s  so light , Kevlar’s lighter still.

But at the end of the day.   12oz. of carbon is the same as 12oz. of fiberglass or   even  12oz. of feathers for that matter.

I belive in what you’re doing,  I really do!

I just think you’ve got the wrong material for the job … The standard 5.7oz. 3k is better suited.

12 K makes beautiful car hoods, furniture, and other cool stuff but is generally is to bulky and heavy for what we do…

Futures is using it on some of  their latest fins.   The square “box-like” weave is  very attractive.


Hey. I could be totally wrong. I need to know the weight per sq,yd to be sure…



Short cut to an Aviso ?..this process has crossed my mind more than once !..but I always end up asking myself, why ? ( as Greg said)…Being in the aerospace industry , you should have a contact with Aviso company , and they would have some good info on strength ,durability,lay-up etc…good luck Mark, it should be interesting…ps…dont waiste the melted eps , pour it into a mould and make something !..a fin maybe?

Ahmmm- I was gonna reply early on, but things bit me.

In any event, I’ll agree. Don’t waste your male mold. Instead, I’d do a couple of laminations over half, pop it off, add stanchions or what have you, then finish it, lam well around the rails. Not unlike the honeycomb board of yore, except they were two halves badly stuck together. You can do much better.

Rabbet or what have you in the deck and bottom of your male mold for a sheet foam inclusion to stiffen it up, easy-peasey. Feather edges for a nice structural transition, so you don’t get sharp stress transitions that make for breaks .

Being an idiot myself, I have found that the KISS principle is a good thing


Doc , I dont think moncoque would be a win…it would be a good idea to put some extra strength in the rails , though…something shapable, that would not get melted by the styrene…maybe

So I kept trying to post by typing in the comments section then I click post topic and the next page tells me to type something into the comment field, I may have figured it out though. And my first post was so well put together and well thought, but now I guess you get the dead part of my brain

Greg: I was hoping for a hollow board for a few reasons. I think that it would de-lam rather easy with a foam core on a hot day. I made a HWS and loved to come in avery hour of so to relieve the pressure via pressure vent and it made such a sweet swoosh sound. Hollow carbon would be sweet bragging rights. Im also in the composite field and ive been making a photographic resume so I thought this would put a little more flash on it. Im 6’3” 180lbs so I wanted to do a king fish about 6’6” whatever I do surfing related I will post here.

VanHelsing: thanks for your comment you made me think of a few things that I looked past in my excitement. Unfortunately my fabric is a massive 19.2 oz cloth. This would yield about a 20lb or so surfboard. Ouch. i know that being a 12k doesnt make it necessarily 3 times stronger than 3k but it has to be to a point much stronger, stiffer, less flex and so on. More filaments equals more strength. Unidirectional cloth is ideal for strength, given direction, layers and orientation is observed. Boeing uses unidirectional for wing spars, pressure bulkheads and many other structures in the 777 and sail masts use the same. I guess im saying that 12k has tows that act much like the uni directional fabric. 12k would be rough to contour also and without using vacuum I would most likely have way to much resin. The proper weight ratio is 60 to 40 or 70 to 30 cloth weight to resin weight. Im thinking either using it cosmetically on a board or making fins from scratch. After that I do believe a carbon bicycle may be in order.

Kayu: ive researched aviso and do like the boards they make, I just think they need to use a ton of cloth and the price adds up fast at up to 60 bucks a yard and I would guess about 15-20 yards in those boards. As a great lakes surfer its hard to ask why when it comes to surfing. Picture mid January 10 degrees outside 30 in the water, 25knt wind from the rare north east and you know that its gonna be at least head high with a few overhead. At this point we ask how not why. How do we get out there, how do we take advantage of these conditions, the ice builds up on your beard and hoodie toes froze even with 7mm booties, but you scored 2 decent waves and they might have to last you at least a month. Were addicted to surfing and we do it the hard way. we get to do it so infrequently it makes me physically ill at times. So I guess to me everything about surfing is hard, why not make a board that would be hard to make as well. Unfortunately my wifes job moved us far away from the coast.

Doc: I think your onto something. A couple light layers split the halves build structure inside put back together and poof all done. Resin makes such a great bond with carbon that I wouldn’t be worried about laying a couple plys around the rails to put the halves back together. Ill have some thought on this one. Guess I don’t sleep tonight.

Keep the ideas coming, thanks


After building hundreds (and breaking around 30 or so) carbon fiber, Kevlar, and aluminum honeycomb hollow surfboards, my advice to you is… don’t do it.  It’s way harder than you can imagine, and that’s if you were using the right materials and processes for the task.  

Do you really need a 20+ lb shortboard?  The materials may be free, but is it worth the (considerable) effort?  

From my perspective, it seems like you’ll just end up with a super-heavy crappy board and lots of toxic sludge (what are you gonna do with that?).  

Even using appropriate materials and processes, making hollow carbon boards isn’t easy.  On top of getting the shape right, constructing two halves, joining them together (I can’t describe how critical this part is)… epoxy impregnated carbon needs to be post-cured at high temperatures to realize its potential strength.  

My suggestion is make stuff with a greater likelyhood of having a successful outcome.  How about fins?  Better yet… how about an ultra-mod Alia?  That would be awesome.  You could make a bitchen Alia with a sheet of Divinycell skined with your carbon / Kevlar.  

At Hydro Epic, it took us probably a couple hundred boards before I think we got it right.  Even then, quality control issues had us churning out crap along with the gems.  So many things can go wrong, and so many have to go right to make a magic board.  

Yo Junkyard!


Just thinking, if you want a 12k finish you could always use a “spread-tow” 12k plain weave. Some of those come in pretty light at just under 6oz. We used a load for fast build kit aircraft wings but had it pre-pregged. Surface finish was a bitch initially but when we got the cure cycle nailed it came out sweet. I’ve just bought a road bike frame with 12k spread-tow plain weave over 3k plain weave and its fantastic. Okay, thats kind of irrelevant, but hey, it looks Gucci. Thats pre-preg as well and I have no idea how it hand lays. 


All the best Junkyard! 

Uhmmm- Kayu, I think you have a Really Good Idea.

Let’s think in terms of something like Paul Jensen’s HWS boards- with the cork rails, very shapable. So, you do up the male mold with what are essentially square rails. Do it in two halves, top and bottom, run the lamination down the sides a little more than half way. Laminate it together, but not a lot of laminations. You might even kinda slide the halves together like the two halves of a cardboard box with some slightly thickend epoxy brushed on to get it just right- a lot easier than trying to match up two compound curved surfaces at thin edges. .

Then, on go some outboard strips of a relatively high density aircraft-spec foam, Divinycell or similar, shape as desired, laminate over and there you have it.

The one thing that concerns me is the square-ish edges at the deck and bottom of the original off-the-mold stuff, you might have some weakness there, but a fairly dense foam plus a lamination or several might just deal with that adequately.

As a bonus, JYD has already built a HWS, so this kinda hybrid Carbon/HWS arrangement could be a good thing for him, the familiar blended with the new. Easier to do a transition than a whole new thing.

Again, Really Good Idea


Doc ,   we overthink…Junkyards concept,as I understand it , is to shape the board , glass it , then remove the core , to end up with a hollow board…if the blank was built with a perimiter of rail , in a material that wouldnt melt with the eps , it seems quite feasable without too much complication…the rail material ?..take your pick ,there’s a few that come to mind…maybe balsa ,with  a barrier stringer to prevent soaking up the styrene ?..it’s experimental , and to waiste a good core and turn it to sludge is not  an attractive thing to do…to me , it’s one of those things you would do , “just to see what happens”…the use of carbon fibre in surfboards is total overkill,and as the Aviso boards have proved , you don’t need a heavy layup of fibre to far exceed the reqired strength of a durable ,lightweight surfboard…particularly on the rails…if anything , I think the deck may need some stregthening , for impact from the foot traffic…one  interesting advantage here, would be the re-coil of a hollow a hollow carbon board…something the Avisos are renowned for

I’m not a fan of the toxic waste you are going to make, either.


I once thought of making a hollow foam board the following way:

  • Shape XPS or EPS blank

  • bag on top skin with inner lam.

  • Cut out pieces of foam from the bottom side (leave some sort of deck supporting stringers in)

  • lam on a bottom skin using clamps


This seems way less toxic than your idea.

well the toxic sludge is more toxic water then sludge.  did a test chunck.  making anything out of it will be useless.  tried some foam core 12k fins,  looks wise theyrs great but the foil turned rough and not useable.  12k is a hard material to work with.


lots of good ideas here guys. thanks.  i got the 12k from an Epic aircraft that i did a firewall repair on.  min order was 10 yds and i used maybe 1 so i feel i have to make good use of the rest.  not sure where im even gonna get the time with a new house, baby, and wife but ill keep you posted with the surf related builds


howdy mark,

glad to see other folks here pushing the materials science part of boardbuilding! other folks have tried building hollow boards from woven stuff, with mixed results. i went the path you plan to take a couple years back thinking i could get away with woven plant fiber as principal raw material, bonding different layers of woven grass, rattan, etc into deck & bottom panels using wood glue, contact cement and roof sealant. the resulting 20kg weight alone made the 9’ finished-but-half-laminated board a safety risk in the lineup, at which point i decided to stop throwing good money after bad, learn from my mistakes, and stick with woodstrips to make my next boards which i’m finishing now. 

i may not have the proper science & engineering background to dissuade you from what you’re about to do, but conceptually the idea of forming a composite hollow monocoque using multiple layers of a high tensile strength material such as woven carbon fiber (or bamboo for that matter) with a resin polymer acting as binding agent ultimately depends on the strength of the bond to withstand the typical forces a surfboard is subjected to underfoot. over time the raw material itself may not fail but when the resin that binds the woven layers loses its strength from too much flex, impact stress and/or the usual surf wear & tear, material fatigue of that matrix sets in. but i may be wrong, that’s why it would be good to hear from the engineers & scientists in sways so they can recommend processes to ensure the worst doesn’t happen. if only mike torres (camplus) could give us feedback on his project posted here a couple years back, a wood-framed, ballistic nylon-skinned, resin-sealed HWS, he could give us plenty of insight on how such boards perform in actual surf conditions.