We wanted to talk briefly about the newest improvement to the Flyboy Wakesurf branded James Walker Signature board, and that is the concave deck. The top of the board is sort of dished out. Here is a picture where we are sealing the foam and you can see the deck surface is sort of dished out.
The vast majority of surf style boards have a convex shaped deck. That is the center line of the board where the stringer is, winds up being the thickest part of the board or at least the tallest of the board is laid down flat on a surface like a table. We’ve talked a gazillion times about how something THICKER becomes STIFFER. The trade off though is that it doesn’t always work well for the intended purposes. So we could make an UBER stiff board that was a foot thick, but it would suck out loud if you tried to surf it.
Skim Style boards are typically made from a sheet of high density foam, so the deck is flat, with just the rails sort of curved over. We’ve all seen them and just know by looking at them what the intended purpose of the board is.
Now way Way WAY back in the day, ocean surf boards were crazy thick. They were hollow wooden boxes and probably would reminded us of giant SUP’s at this point in time. Shapers of that era started playing around with going thinner, which improved performance of the boards, well at least they turned better. BUT, as those boards got thinner and thinner, they also started breaking and breaking and breaking! What was developed during that era was stringered blanks and then also this idea of a domed or convex deck. It made the boards GO, because when they were super thin, called potato chips or just chips, they were all floppy and they tended to break. So thicker in the middle and a vertical piece of wood was the answer!
What wasn’t fully understood at that point was that the domed shape was helping to resist compression forces from the opposite side. That is, the upward forces on the bottom of the board, were being effectively resisted by a convex or domed deck shape. We’ll demonstrate this in a moment, but we’ll offer up some anecdotal evidence that you’ve seen before and probably just ignored. If you have a modern era car, someplace on the car, hood, door, roof…some flat panel will have folds in it to create stiffer body panels on really thin sheet metal. Flat panels flex like a gymnast, those curves or bends reduce the flex in some specific direction.
So now you’re thinking convex vs concave and they actually resist forces in different directions? Yessiree bob!
Lets back up a little. Remember when we did that power of 3 post? Where we said 3 layers of whatever glued up was super stiff and would resist all manner of forces? Here is a picture of that demonstration to jog your memory.
That’s amazing! Ok, so anyway, the LAYERS glued together, create a very effective flat panel stiffness. But you’ll remember we couldn’t do squat with just a single piece of paper. We should have just glued up 2 sheets of paper, because those results are just barely better than a single layer of paper.
We can also achieve really stiff panels by creating a concave in relation to the forces being applied. We’ll call that compression or pushing downward even though the push nazis want every single force in every direction referred to as push. We have something for you to push right here! So, here is a picture, we didn’t test it to failure, but you can see we are able to resist the downward/pushing/compression forces simply by creating a concave shape that is aligned in the direction of the force being applied.
Nifty, huh? C’mon you know it is! But logically, we would expect that if we simply flipped that piece of paper over, such that the top surface of the paper now had a convex shape, similar to what our domed decks looked like, it would still resist that push/compression/downward force. Right? The stiffness increase in the picture above has to be associated with the curve and so any force applied anywhere should meet with the same resistance.
Nope. Limp as a wet noodle. WTH?! Right?
So lets talk about why…ehhh, we really don’t understand why! There is a whole huge area of study that sort of explains it, but the best we can glean is that curve in the one direction improves tensile strength of the paper BUT does NOTHING to the otherside, just sort of bypasses everything. It’s kinda of interesting, if what you WANT is to improve JUST tensile strength in one direction, or on one side. Maybe specifically for some type of breakaway panel that offered resistance in one direction, but would just fold over if some force were applied from the opposite side. We can’t imagine it, but maybe there is some safety mechanism that would make sense for. Anyway, if you try and apply push/compressive/downward forces on the convex oriented paper, it just folds over. You know we don’t need to understand why, we just need to understand the effects, right?
Ok, so lets revisit our deck scenario…concave vs convex, by looking at bottom structure! You’ve no doubt heard of bottom concave creating a faster board down the line. It’s true and there are all manner of theories as to why. We once read a comment by Mike Daniels, eons and eons ago about why concave bottoms were faster. Basically he was cryptic saying, it probably did something else other than what the theories offered up. Mike is one of the lead shapers at Coil surfboards. Ok, so all of the nonsense about water flow forward or backward and thru just aren’t really applicable. But what is applicable, is a stiffening of the board against those upward flowing forces. So bottom concave, stiffens the board against forces that are lifting the bottom up. We’ve all experienced a board with too much rocker and what happens is that it turns into a plow! So, bottom concave really helps with stiffening the board against the upward/lifting forces of the wake.
But what about the top? The bottom concave really does nothing to the forces being applied from the top down. So between our feet that bottom concave really isn’t helping at all and you can imagine as surfing shifted towards more above the lip tricks, not shuvs mind you, but aerials, landing on the deck places TONS of downward/compressive/pushing forces on the deck with nothing to help resist that! The domed decks are convex and offer very little support and when you land from an aerial, the forces being applied from the top will be LARGER than the forces when you hit the water.
So what we did, was scoop out the deck! Right? The bottom of the Flyboy Wakesurf branded James Walker signature board has concaves on both the top and bottom! It’s this rather remarkable, if we do say so ourselves, uniform stiffness all over, without any attendant increase in weight or a weird centerline stiffness that dissipates towards the rails. It creates a stiffer, stronger and MORE RESPONSIVE board. We’ll get into that in future posts.
There are some other benefits that we’ll address at a later time, but we thought we’d introduce that concept and man you have to try that whole curved paper thing at home. It’s astonishing and so counter-intuitive. You’d think the curve would increase stiffness regardless of the direction of the force, but it doesn’t.
We should say that this is a dramatic over-simplification and that you’ll never have an open end on your surfboard, where there is nothing holding the curve on one side, but still the affect is the same, as you saw with the one example picture where it didn’t matter that the one end was open the concave could still resist the forces being applied against it.
Ok, thanks so much for following along, we REALLY appreciate it!