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Jan 08

Composite sandwich wakesurf test panel

We’ll admit it, we’ve been slacking over the last few weeks, cold weather and the holidays, plus…well…here:

zsnow

Amazing snowboarding conditions! We’ve been up to the slopes something like 5 times in the last 10 days! Doesn’t leave much time for working in the shop. But now that the holidays are over, we have some time to NOT snowboard!

We wanted to share with you a test panel we created and share the process we go through. We do a LOT of test panels, to see how a concept works and we ALMOST always create a baseline test panel with it, so that we can test specific components before applying them to a full size board. Often times we can tell with the test panel if the concept works or not, mostly not. :) But that allows us to quickly combine a number of changes and develop a working wakesurf board. The testing is done individually. Sometimes we wind up with unexpected results, other times it’s right on target. So we’ll skip forward to the end of the process and show a picture.

test panel 019

Two test panels that look identical, they aren’t however. It’s a little hard to see, but the panel on the left has two “keys” that run the length of the surface skin and if you look closely at the surface skin, you can see them just below. The other panel is identical in terms of size and shape, but omits the two “keys”.

Some background, there have been some advances in composite sandwich construction, that use theys “keys” or a more pronounced stringer, inserted into the core and co-cured with the application of the skin. Aircraft wings with composite skins almost always have stiffening stringers, but they are different than this application in that the FAA doesn’t allow them to be ONLY co-cured, they must be riveted or bolted down also. Not something that we’d ever do, plus this isn’t commercial air traffic, it’s wakesurfing! :)

The function of the keys is to increase the bonding strength of the skin to the core, but it also does one additional thing, it creates a sort of corrugation with the sandwich layer of reinforcement. If you look closely at the picture above, you’ll see that both test panels have fiberglass between the skin and the core. For the panel with the keys, the fiberglass runs down below the key, creating that corrugation.

We’re all familiar with the stiffening of our cars door panels with folds and curves, this keys process does that same thing, while leaving the surface smooth. Possibly, this process could reduce the requirement for expensive fabrics like carbon fiber and allow the development of thinner composite sandwich structures for wakesurfing.

So we started with a trued up section of Divinycell H45

test panel 002

We then cut that section into two equal sized pieces to act as a core for the two test panels. Next we scrounged up a section of Divinycell H80 to act as a skin. This is 3MM thick.

test panel 004

…and we cut out two sections to make up our test panel skins.

test panel 006

We didn’t test the full on stringer at this point, because there is some tricky math involved, plus we’d need a different bit for our router!!!! The composite sandwich stringers that are co-cured, are a trapezoid shape, with specific angles of the sides. Instead we marked out two sections where we want the keys to go and we mark them for routing.

test panel 006

We didn’t take any good pictures, but we cut and fitted the keys using a 6mm piece of Divinycell H80. You can see that we’ve routed the slot for one of the keys and tested it for a good fit.

test panel 008

Now this next picture is important and we’ll try and explain what’s going on.

test panel 009

We’ve cut a section of 4 oz e-glass slightly oversize from our core. If you look closely at the picture you can see that we’ve pressed the fiberglass INTO the two slots that we’ve routed for the keys. When this test panel is cured, the fiberglass will run UNDERNEATH the key, between the key and the core. In effect making that corrugated effect with the fiberglass reinforcement.

We know from our car door examples that this has a stiffening effect on that flat panel. This is also what happens on wakesurf boards with bottom channeles and rail channels.

We prepare two test panels, as mentioned above, the first is our baseline without the keys and the second is the test panel with the keys.

test panel 010

For assembly, we we out the fiberglass and then inserted the keys into the slots with the fiberglass under the keys. Next we wet out the top of the keys to make sure they bonded to the skin and finally aligned the skin. After that we taped the pieces together so that we could slide them into the vacuum bag.

Returning to the first picture, the two test panels are pressed inside the vacuum bag until cured.

test panel 019

We’ll use both panels to test for stiffness and weight and compare the results. AND that folks is typically what we do when we test different ideas. Honestly, the vast majority of these tests turn out to be junk. We know, We know, only super sparkly things are supposed to be mentioned in wakesurfing! We prefer to be honest and you may have noticed, not 100% of everything in life is super sparkly. We don’t have to hide behind a super  sparkly facade.

Oh! One more picture, this is a ressurected wakesurf board that we made…somewhere around 4 or so years ago, maybe longer. Anyway, if we can ever get the tower of that boat in the background fixed, we’ll get back out on the water! We’ll talk about our plans for that wakesurf board in a future post.

test panel 013

Thanks so much for following along, we really appreciate it.

 

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