Sandwich Power      

or "1 + 1 + 1 = 27"

 

sandwich

  

single-skin

For a Spanish version of this article, click here
 

Boards are stressed in many different ways: in "normal" operation, the rider's weight pushes down, the ocean pushes back up, creating a bending moment, often some torque as well, causing mostly compressive loads on deck, and tension on the bottom. All sorts of bending/ twisting loads happen during wipe-outs. And then there are encounters with hard objects, causing impacts and punctures. The most common failure mode in old-fashioned "Glass Boards", though, is denting. Single-skin construction, while strong overall, has very little panel stiffness for its weight, leading to the all-too-common creasing of glass boards over stringers, as well as deck collapse under heels and toes.

Enter the sandwich: the same fiberglass skins one would find in a comparable glass board, spaced apart by a relatively light sheet foam, increasing the panel's stiffness many-fold. With such a disproportionally large increase in panel stiffness, the core's density can then be decreased, leading to an overall decrease in weight. Weight decrease equals more float, better acceleration, and livelier turning due to lower swing weight. An altogether most excellent improvement!

(btw, the boarding industry did not invent sandwich construction - it came down to us from first the aircraft industry, later all aspects of transportation - where lighter weight means higher profits. Racing sailboats - my training ground - went sandwich in the early 70s and never looked back)

So how does it work?

Below an example, using a few bits of paper, some EPS foam, plus a couple chunks of lead:

 

two sheets of paper laid over the short span between two blocks of EPS foam. They can't even support their own weight

think of the paper as the fiberglass skins in a board

a piece of 3/4oz 1/2" EPS foam - a whole lot stiffer than those two bits of paper, but a 1.6# chunk of lead in the middle causes it to bottom out

think of this sheet of EPS foam as the Divinycell in a sandwich board

same ingredients as above, stacked on top of each other. Again, the 1.6# chunk of lead causes things to bottom out
same exact ingredients as above, but I glued the bits of paper to the bit of EPS foam with paper glue - nothing fancy, just some Elmer's Glue-All. The loose stack in the foreground, the glued one in back.

What a difference!! The glued up one hardly deflects at all, while the loose one is bottomed out.

panel weight is identical for all intents and purposes.

double the load - still no noticeable deflection in the glued-up panel
with 9.1# piled onto the glued-up panel, I start to see a deflection.

Sandwich Power!!

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