Apr 23

Test panel resonance

We had some fun over the weekend, despite the continued stereo issue. It’s got to be something screwed up in the head unit, it comes on all by itself even though all the switches to it are off and then the on/off button on the head unit won’t turn the unit off, the only way is for the batteries to drain or to disconnect the head unit from the batteries!

Ok, so that isn’t what we had slated to talk about this morning. We wanted to talk about our test panel resonance and tie that to the buoyancy discussions we’ve had over the last week or so.

Do you remember the picture of Drew boosting on his skimmer? Most high end skimmers are made with a core of Divinycell. It’s a cross linked PVC foam. Closed cell and it comes in a variety of densities. Lots of skim style boards were made with H80, which is a 5 pound density, but some also used H100, which is a 6 pound density foam. As our loyal followers you’ll remember we tore up the whole “volume” garbage as a meaningful measurement, instead pointing out that density was the key metric because it took into consideration both volume and weight.

Skim style boards tend to have some standard thicknesses. Now that excludes the recent introduction of EPS and center stringered entries into the market, that are following on the path of the now defunct Skim Stixx. The common thicknesses are 1/2″, 5/8″, 3/4″ and 1″. There are others, but those four are the most common. Those thicknesses come from the dimensions of the core foam. That is you can buy Divinycell H80 or H100 in thicknesses of 1/2″, 5/8″, etc.

When we did those buoyancy tests it really got us thinking. We heard a spammers comment about buoyancy being the factor for projection out of turns. That’s crap, buoyancy just isn’t the factor. Pushing against a 7 pound force isn’t going to result in some rocket engine thrust out of a bottom turn. It’ll rebound with 7 pounds of thrust thanks to Newton’s laws we know this. How far do you think 7 pounds of force is going to push your 150 pound body? Right, it’s not. Well that’s not true, it will, but it’s probably not going to even disturb your balance.

Why is there significant buoyancy in ocean surfboards and not ocean skimboards? Origins of ocean skimming started from round wooden disks. They were heavy and certainly not very buoyant, but when riders ran along the beach and tossed them their density carried them along in the super shallow water along the beach. They evolved from there, having a need for that momentum or follow along which mostly came from a specific amount of weight.

Ocean surfboards on the other hand don’t really need that momentum from being run and tossed. Tow-in surfboards have some weight added to aid with the chop in huge wave, but mostly ocean surfboards were light and larger than skimboards to create a lower density for paddling in and out and also to help increase the combined buoyancy of surfers plus surfboards as they would wait in the lineup.

Did you pick up on that? Tow-in surfboards are tiny and heavy, because? They are towed in. Current tow-in boards will range between 5’5″ and 6’2″ (a typical shortboard is 6’2″!) and they can range upwards of 10 pounds, a 20 pound tow-in boared is not uncommon. Now they basically just blast down the face of really huge waves, the extra weight provides that momentum and also helps calm down some of the bounce as the riders go hurtling down the face of the waves.

They don’t paddle in or out and density then changes for those boards. Skim style boards have very little buoyancy and really talented riders boost them. Buoyancy then, is probably an unneeded attribute carried over from ocean surfing and we are fed it as NEEDED by snake oil salesmen and also the spammers and talking heads that mostly do more harm than anything else.

Let’s ask a question, before moving on. Can you guess why there is a surge in skim style boards made with EPS and center stringers? Well, commerce is one thing, folks want a share of that skim style market. But when the high end skimmers are made from Divinycell and we’ve seen boards made this way come and go, why would others pursue it? It’s easy and known, right? We mean if you utilize that sort of construction for all of your products, of course you’d continue to use it, because there is no learning curve.

Let’s flip that over now. Why would we use light weight EPS for surf style boards? Same reason.

If we eliminate buoyancy as a necessary factor and we say, an optimum weight is probably 5 pounds ready to ride. That gives us a lot of freedom doesn’t it? Skimmers use Divinycell because it allowed the follow along weight, but also could get hammered with folks jumping on them repeatedly without being destroyed.  Surfboard manufacturers wouldn’t because, it would reduce needed buoyancy for paddling plus they didn’t know how to use it, right?  They would have been using Poly U and EPS with center stringers.  But why don’t WE use it for surf style construction?  The wakesurf board manufacturers?  It’s probably mostly because we’ve always done it this way which wasn’t the use of high density foams.

Buoyancy isn’t the factor we’ve been thinking it is, nor is it really providing an improvement in our performance. There seems to be a optimum weight of around 5 pounds and then THAT will effect density based upon the size of the board folks ride. Weight is definately a factor, especially in the air, being able to manipulate a lower weight board is helpful. Although that seems to be tempered by momentum, where we need to board to follow the rider, so the average wakesurfer of 150 pounds seems to like a 5 pound ready to ride weight. BUT volume and density are less a factor than we have been led to believe.

We want to show you a quick video that we won’t really delve into until tomorrow, but listen to the different tones as we twang them. That resonance is coming from the test panels vibrating or flexing under the load and springing back. Fiberlass only first has the lowest resonance, the carbon fiber, bamboo veneer and fiberglass panel is a medium resonance and the divinycell wrapped in fiberglass has the highest resonance. You hopefully can hear the change in pitch.

If you prefer to watch the Flyboy Wakesurf test panels video in your Youtube Console there is the link.

Next, we weighed our test panels. The lightest was the divinycell laminated between two layers of 4 oz fiberglass and the heaviest was the 8 layers of oriented fiberglass.

8 layers of fiberglass at 0.6 oz


Carbon fiber, bamboo veneer and 4 oz fiberglass at 0.4 oz, is 1/3 lighter than the fiberglass only panel


Divinycell wrapped in 4 oz fiberglass at 0.4 oz, same as the carbon fiber, bamboo and fiberglass test panel.


We’ll pick up there tomorrow as we continue on with this discussion with bouyancy and this concept of resonace and possibly post some more of James Walker wakesurfing. Thanks so much for following along!


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