Composite sandwich, alternative fabrics

Following up on the surftech build, I want to duplicate that concept, but without relying on the external resin or thick fabrics to achieve rigidity at the expense of weight.

There are some lightweight CF fabric's, but they are super expensive. I found a 2 oz CF, but it was almost $90 a foot. The more common 5.7 oz is almost reasonable at around $20 a foot. 5.7 is way more than I would need. That's similar to a 10 oz e or s glass.

Interestingly though, the Young's Modulous of that 5.7 oz carbon is almost identical to 1/8" basswood. So I decided to use some CF for stringers.

Rudimentary drawing of the blank design.

The EPS core and D-cell rails set up. I painted a light layer of epoxy on both to be sure that I got a good glue up.

I cut the CF to shape as best I could. The bottom contour will be a slight issue. I'll need to shape the bottom and the CF will resist shaping compared to the EPS. One issue I will have is over-shaping the EPS close to the CF stringers.

The CF awaiting wetout.

Once wet, the CF stayed vertical on the EPS without much effort. I smoothed it and then aligned the d-cell rails.

Finally, into the bag to pull everything tight.

Jeff i am using a 27" bag now and have you tried the tent trick i use

I did! It's raining outside pretty good, so I have the shop doors rolled down. I taped a piece if kite string to the bottom of the door and the center of the open end of the bag. Then rolled it up! Worked like a champ. Thanks again for sharing that.

So your CF will act as your stringers and then a layer of 1.7 oz CF on the top right. Wasn't that $90 a foot, ooooooooouch. Looking good and I love the the CF stringers. How did the shape up?

Hey Kona,

I apologize if I confused you, it's 1.7 oz Kevlar, not CF, as the sandwich layer. Not that the Kevlar is cheap, but it's about 1/2 the price of a similar weight CF.

Yeah...the theory is that the CF laid up on the rails will give me some stiffening effect, hopefully similar to basswood. We did the first build with just e-glass and s-glass and it's plenty solid and stiff - enough to hold Dennis up at 270'ish. A 3 pound some-odd oz board for a 270 pound guy is pretty amazing in my book. On this new build, trying to find the right balance to reduce some weight and increase stiffness may prove a challenge.

I'll get back to the build over the weekend and will post up more details and pic's. Thanks for following along.

Good job SD and Merry Christmas

I have this board built and I'm working on the paint. Zylon exterior, Kevlar sandwich layer.

This is the paint scheme I am stealing! I want to wrap it from bottom to top around the rails.

White base coat down and I am beginning to cut out the masking tape.

I really like to see that your now working on art as well as technology.

Thanks Show, the art is actually harder than the build, IMO!

Jeff, thats the re-issue Powell board I ride! CF stringers, kevlar sandwich, custom classic graphic, dude,... I may be developing a little envy...very sweet! As always, you out did yourself once again Jeff!

Thanks Dimitri. You have that skate deck? Such a small world. I love the look.

White stripes masked out.

The white base coat is down, now I am masking the black stripes leaving just a tad for the red pins. I should have this part done by June ('10)

This image gives an idea of what the final paint will look like, only inverse.

Crappy picture - it's a good thing I don't do this for a living! You can sort of see the two masking tape lines - I'll lay down red on the gap in between.

First couple of coats of red.

Your garage or shop must be full of boards! Looks sweet!

Definately filled with "stuff". Thanks Duffy. How is your boat selection coming along? You're doing a TON of due diligence. Good for you!

The first few "stripes" unmasked. I think I'm going to let it bake a little more, before proceeding.

Unmasked. I'm happy with the look, although undecided about doing the deck to match.

Nice

Looks great Jeff , man thats alot of work , good for you . alot more time then i will ever spend in one.

Thanks Guys. Yeah, it's becoming a career rather than just a single board!

thats cool Jeff - from shape shop to paint shop

Hey Petr long time no hear! How are things in CZ? I am rapidly NOT becoming a fan of graphics on boards. Serious PITA.

Hey Mark have you seen that WO.com, the poor cousin of the overly emotional DD.com, is reorganizing to include a board building forum? A mini-sways!

Boat selection is hard, I have it narrowed down to Tige 22v or 24v, Avalanche, Enzo or Sanger v237, but thats not really narrowed down I don't like making mistakes. When are you riding the board?

LOL Yeah, that's like 6 different boats. It's a big investment, I do applaud all the work you're doing.

When will I ride that board? I'll probably die of a coronary before it's complete! I decided to paint the deck so that the bottom flowed around the rail to the deck. I laid down the black, so I need to do the red pins and then hit the whole thing with clear. Maybe another month, if the weather is good.

Yeah, my buds 22v is prob the biggest wave I have seen, it's just short compared to other wakes. I think I will wait and find the best deal. They are all pretty similar, and I will be happy with any of them. Your new board has a similar design to my 09 bullet.

Best deal is always good. The outline of the two boards are very similar. Yours no doubt has a fuller nose and a slightly different tail.

Yeah they said they changed the 09 a little. It has a slightly wider nose area and more rocker. I wont get to ride it till april or later, it just stares and me!
Duffy

I hate when boards do that! I swear when I am working at night mine call my name. More rocker? Wow, it was pretty significant to begin with. Do you have the dimensions?

I could measure it, what would you like to know? The info came from Mike Walker himself, I don't know how much dif it really is.

That's very kind of you Duffy. Don't worry about it. Accurately measuring tail and nose rocker is a pain. I just thought you might know off the top of your head.

This paper has been peer reviewed and has been found free of conflicts-of-interest.

When I've built the composite sandwiches with a 1 pound core, I've found it necessary to insert high density foam to seat the boxes. The HD foam prevented the fin boxes from twisting or deflecting. That solution tended to cause a few issues. One is that the final weight was increased to just about that of a 1.5 pound density foam blank, which was rigid enough that it didn't require said HD inserts. Another issue is that upon failure, the boards tended to
crease at the end of the HD foam inserts. I didn't have many failures, but enough to make
me want to change that area. Additionally, the inserts were prone to taking on water and I
had at least one separation failure.

In the design of a board there are a number of ways to "tune" flex. One is with the thickness of the core. The thicker the core material, the stiffer the board will turn out, all other factors remaining he same. The formula that describes the increase in stiffness returns an exponential increase. Another, though, is by changing the flexural modulous of the core itself...a stiffer core makes for a stiffer board, without requiring an increase in the thickness of the board.

Stiffness, though, doesn't necessarily equate to stronger, as the ability of a core material to absorb shear stresses and thus not bend or break, is technically stronger in the context of a board.

My current project will attempt to duplicate the above build, but with the following changes:

1) Core material is 1.5# EPS
2) External HD foam is 3 pound H-45 Divinycell (pretty blue color )
3) Elimination of the HD foam inserts.

I decided to wrap the graphics over the rails and on to the deck. The picture shows the black stripes laid down and the masking for the red pins. I'm not confident that I did a good job matching the red top to bottom, we'll see when I unmask.

Done! Awaiting traction this week.

Deck




Bottom

We're heading out tomorrow, so I traction'ed up this build. The painted board weighs in at 4 pounds, 5 oz with fins and traction. The other board which is 1/8" basswood stringers in 1.5# EPS and 4/4 top by 4 bottom weights 3 pounds 15 oz with fins and traction. It was a 2 pound some odd ounces naked. It will dent horribly, but won't break, I'm confident of that.

We'll see how they ride tomorrow!