Hollow carbon shell surfboard

General Discussion
81

Just think about the magic stringer for awhile… even if you don’t come up with the same solution we did, you’ll come up with one that works. The concept is to control the types, locations, and amounts of flex - independently on the deck and on the bottom.

I also found that making the deck stiffer than the bottom worked great. We made boards where the deck mostly controlled the boards overall flex. The bottoms were much more flexible - we called it “dynamic bottom technology” or something like that. You could actually see the bottom change shape in turns. The rails were stiffer so you could bury your edge and hold through turns, but the bottom of the board would adjust to the water pressure under it. I think this really helped with speed. The board could match the shape of the water beneath it to help reduce drag. The concept looked and felt like it worked. Guys said they had their best waves ever on those boards. They worked for me.

As far as your stringer goes… I think balsa would surf better than foam. Just make sure it’s not too brittle. It will get a lot of stress. When we used stringers, we made them from fiberglass - shaped I-beams. I forgot exactly what glue we used but it was made by 3M. It was flexible, super strong, resistant to salt water and UV, and really expensive. We used the same glue for joining the halves too. I think we spent about $25 on glue per board (at volume rates). The adhesive comes in a double tube - like a 2:1 ratio. You need a special gun and mixing tips to dispense it. Hand operated guns are around $30. We had pneumatic ones that were around $600 each. If you’re just gluing the stringer (and not the halves) I bet silicone would work. You’d just have to make sure air gets circulated inside the board so it will cure.

I’d really like to try some boards made with end-grain balsa. I bet they would work insane.

82

For the flexible stringer glue, consider E6000 by eclecticproducts.com, the ShoeGoo company, I 've been using it for many odd purposes, love it, similar to silicone sealer but with excellent bonding, very flexible. 3.7 oz. 4$ toothpaste tubes somewhat commonly available at hobby and craft stores, reduced size caulking tubes about 13$ sometimes found at RV supply or maybe the boat store, UV sensitive type is no good outdoors but might be ok inside your board? Don’t know about salt water exposure, rain water isn’t a problem. If you find it, buy one for testing or to have around, you won’t regret it. You can call the company 800 767 4667 to ask where to find it in your area.

83
Quote:

End-grain balsa core material:

http://www.nida-core.com/…daprod_balsalite.htm

Test section looks really good. Can’t wait to see how the complete board turns out.

More end-grain balsa products, scrimmed and otherwise. See the sections on Baltek SB and Decolite. Warning: there seems to be a plague on the internet, the symptoms of which are that every time a company revamps their web site, they succeed only in making it twice as difficult to use. Unfortunately, Baltek is no exception…

http://www.baltek.com

-Samiam

84

I made the top half of a real board. The finish is not too good. I waited too long between spraying a clear coat in the mold and laying carbon. The clear coat had nothing to stick to as it catylized and there are many holes in the finish. There are parts of the finish with no holes and it looks absolutly awesome. I decided to use carbon kevlar on the outside for looks, also I think it would be more functional on the surface. I had a few mixups during the layup and it took longer then I thought. The first layer of cloth had started to harden by the time I got it in the bag. It was difficult enough just making a test section in time, making a whole board it another story!! Im using a long cure laminating resin too.

I feel that I gained lots of knowledge about what works and what doesn’t after making the top half. I feel the bottom half will come out much better. The bottom half will have holes in the clear coat because I sprayed both molds at the same time (in order to save time). Ironic huh?? I could remove the clear coat from the bottom mold and respray it, but Im not sure if I could remove the thin layer without damaging the mold. Any suggestions?? I havn’t tried anything yet. However, I might just leave the holes in the bottom in order to match the top half!!

85

I forgot to thank you guys for all the input. What about 3M 5200 Marine Adhesive Sealant? Would that be good to adhere the stringer, and the top half to the bottom half??

Kendall, Im thinking about not connecting the top and bottom

stringers on this board. The more I think about it, the more

sense it makes. Also, a big problem that will be solved is how to

make the stringer mate properly with the top and bottom halves. I

planned on adding a independent stringer on each half, strait down the

middle. Then I would sand each one flush with the inner edge of

the board so the top and bottom stringer would match. This seems

like too much work for me.

86

I don’t think you have too much to be disappointed about! Looks like half of a very expensive surfboard to me…

I’m sure I’m not alone in the numbers of people who’ve lost sleep thinking through the steps of a project like this over the last few years. I’m just so stoked seeing someone with the time, knowledge, and budget not only putting it all together, but also sharing it with us here.

Don’t get down over small flaws…the big picture is freaking awesome. Thanks.

Ben

87

Hi Ben - Agreed. The big picture is awesome. I know he was going for a finished look right out of the mold but this looks like an easy fix… maybe some sanding and a gloss coat? That’s what most of us have been doing for years anyway.

88

5200 is great glue, no first hand experience here but the boat builders constantly rave about how strong it is, it is slightly flexible, it takes up to 7 days to dry! I might have seen a speedier type in the marine store, still 3M and in the same family as 5200. I didn’t follow your stringer idea but was thinking how touph it would be to mate top and bottom surfaces with single piece stringer, one idea is to “make the shape” for one half keeping the stringer height purposely low, put modeling clay on top of unmated surface of stringer, assemble both halves, the modeling clay should smash down to the correct mating height. Thats the way engine builders measure valve clearance to head surface.

89

Here is the bottom half. I installed the fin boxes. I tried a new method for creating the flange to glue the two halves together. It created a sharper edge in general. However I had a major flaw in the tail of the board where the flange folded over incorectly and never contacted the flange mold. Also I had a mojor problem with print through from the foam stiffeners. I placed them in the lamination and pulled a vacuum too early before the outer layer cured enough to stay put. I will sand the entire board down after the halves are joined. I will do a quick resin cheater coat to fill the flaws on the top and bottom, then glass the whole board with 2 oz. I think this will dramaticly improve the finish. I have thought of new techniques in the glass schedule to correct these flaws. I also have a new design for the removable portion of the mold which forms the interior gluing flange. I feel that board #2 will be much higher quality.

90

here are a few pics of the flaw in the tail.

91

Love the whole thread, a man after my own heart. In the last pics you appear to be using a kevlar / carbon hybrid cloth. Why? Isn’t it a pig to sand, what structural benefits do you perceive??

Keep it up, it’s great

Rik

92

Carbon / kevlar cloth. I bought it on a whim ant the fiberglass shop. Ive never used it and was curious to see how it would come out. The surface finish will make you go crazy if you stare at it too long!! I dont plan on sanding enough to penetrate the cloth. Also If I have a massive deck failure the kevlar may help hold the deck in tact so shards of carbon fiber don’t go through my feet. I was reading up on the internet about carbon fiber cockpits in experimental aircraft. Overall it is a very bad idea because in the case of a crash, the carbon fiber splinters and the cockpit becoms an “Iron Maiden.” For this reason, it has become common practice to use a layer of kevlar on the surface to hold the broken carbon in tact.

93

Yep, we use kevlar for impact damage control in boats. I built a long board from a glass kevlar hybrid cloth. Deck failed in compression so I beefed it up with some unidirectional carbon and all well now. A whizz kid embedded the nose of his short board in the deck of mine. Snapped his board and left the nose sticking out of my deck! If mine had been all glass it would have broken as well. BUT YOU CANNOT SAND THE STUFF!!

Keep up the great work

Rik

94

Man… I just wrote a very detailed post, then my computer crashed and I lost it. I’ll try one more time…

You’re bringing back some Hydro Epic memories… Kevlar is a bitch to sand or cut, but it adds a lot of strength to the board. We used it on the deck to keep our boards from exploding under extreme stress. Our soultion to exposed edges was to not have any. I designed the deck of the board to have an integrated flange. That way the Kevlar wrapped to the inside of the bottom and didn’t leave an exposed edge.

The integrated flange requied a separate mold section that was added during the layup process. It’s kind of a pain to get the material and bag under the flange section - especially on swallow tails and small boards - but it saved us some work later.

Our layup went something like this… first we’d apply a topcoat. Early boards used polyester “Duratek” (spelling?), but we switched to epoxy later. We’d spread a thin layer of topcoat into the mold and let it cure just past tacky. Then we’d drop whatever laminates we wanted and wet out our outer layer of cloth. After that we’d drop in the honeycomb. We wet out the inner layer of cloth on a sheet of peel-ply on a separate table - we layed the inner layer at 45* to add strength. We’d flip that onto the honeycomb, add some breather and bag the thing. We’d then let it cure in an oven.

If you want to build a simple glue flange, here’s an (relatively) easy way… Lay up a single layer of carbon into your deck and bottom molds. Let the cloth lap over the mold’s flange by a few inches. Make sure there are no folds, wrinkles, or imperfections around the edges. When you get the parts out, glue them together along the excess that overlapped the flange. cut out the center sections of the deck and bottom, leaving around two inches of rail intact. Now add the same materials you’ll use on the final boards to the inside of the rails. Keep the finish as smooth as you can. Build up the outside of this contraption to add stiffness - if you’re going to cure parts in an oven, use the same materials and resin you’ll use on the board to prevent issues with expansion and contraction. You’ll have to split the flange mold at the nose and tail, and have a way to reconnect the parts - you want a single mold for making flanges, but you’ll need a way to get them out later.

Now you can experiment with laminate schedules for your flanges. Ours were (mostly) 8oz carbon/Kevlar, 8oz carbon, and two 4oz Kevlar. Carbon is stiffer. Kevlar isn’t stiff, but it’s strong. Glass is flexible and works for some applications. Finished flanges should connect 3/4" to 1" of the edge of each half of the board - trim them accordingly.

Now you can glue a finished flange into either the deck or bottom half of your board. Linning it up visually should work OK. When that cures, add more adhesive, and put the two halfs together. You should probably use the mold at thes point to insure exact alienment.

When the board is glued together, you’ll need to clean up the seam and fill voids. If you want, you can add a layer of carbon or glass over the seam, just as insurance (and to cover any exposed Kevlar). I wouldn’t glass the whole board, since that defeats the purpose of the mold. Parts should come out perfect already. No need to add more work… you’ve already got plenty of that.

95

So you’re saying that I need to make 2 seprate molds, to reflect each rail profile (left and right). Will these be male or female molds? These molds will make a small, but long part (rail shaped flange) which will be later glued into one half of the board and will mate with the internals of the other half. Is this flange glued to the inside of the board or the outside? Will the deck and bottom will have a flange hanging on the outside which must be trimmed off after they are joined? Im still trying to visualize all this in my head. Do you think I will have any catastrophic failures with the method I’m using?

96

Yes… two separate molds - left and right rail. Make it as one… cut it in half (at the nose and tail)… Then make it so you can put it together and take it apart easily. Put it together to make the part… take it apart to release the part.

You want to end up with what looks like just the rail of your board. It shouldn’t be more than a couple inches from edge to edge of the material. You will end up gluing this inside the rails of the board. You want to end up with between about 3/4" and 1" of gluing surface on each half of the board - all the way around.

Make the shells by lapping the excess material over the flange of your molds. When you pop your cured shells from the molds, trim the excess material from them - one easy way to do this is to take some 60 grit paper on a block and sand the bend from the inside. Be careful not to oversand. Sand until you break through the material at the edge of the flange. The flange will just fall off, and you’ll have a nicely trimed shell.

The most critical part of your entire deal is how well you execute the joining of the two shells. You want to use the right adhesive. You have to use the right amounts, and make sure the parts fit perfectly. Don’t think using more glue will solve any problems… it will just make them worse. If in doubt, add glass to the outside after you glue the thing together.

97

Well… I joined the two halves. I did not use a stringer to connect the top to the bottom. Rather, I made a few stiffening structures to the insides of the top and bottom. The board is much stiffer than I thought. Hopefully it will ride ok. I anticipate board #2 coming out much better than this one. I sanded out all the ugly parts. I glassed over the whole board with some 2 oz. I still need to finish the surface to get some of the small bumps out. I should have it ready to swim by next week. I cant wait to ride it.

98

Today there are some nasty waves on the gulf. It should start to clean up by the evening. Im gonna go out and try this thing out. I realized I still never posted a pic of the final board. I will take a pic when I go to the beach to ride it. I will post it tonight when I give the “riding report”.

99

How did it turn out???

100

Sorry guys, ive been very busy this week. Finally I have some time to talk about the performance of the board. I took the board out for the first time on sunday afternoon. The waves were about chest high and mostly disorganized. My first ride was a fast right (Im goofy). I ended up way out in front of the wave very quickly. The board seemed to float very well. I rode a few more rights and noticed that the board seemed like it was getting stuck while dropping into waves. I tried a few lefts (my prefered direction). I had a lot of trouble dropping in. The board seemed like it stalled out right before droping in and left me hanging on the edge of a breaking wave. I managed to get a few good lefts. Once again, while riding the wave the board was super fast. It seems like the board needs to get in a “groove” before it starts riding well. I did not get the opertuninty to try many turns because the waves were quick and closing out.

On monday I found some decently formed waves around chest +. It was at a spot with a hard beach break and a shallow sandbar. Unfortunatly on my second ride, I bailed on a closed out section and the wave drove the board nose first into the sandbar. The front of the board was stressed and a small pinhole leak developed in the rail about 15" from the nose. I did not notice the leak until a few minutes after the incident. I saw small bubbles in the water. I had to take the board in for the day. Repair will be simple. Just a small carbon/kevlar patch.

Here are a few pics of the finished board.