This way, that way, both ways, no way... Rocker in mats is a tricky subject.
Since first starting to build mats I've been really interested in bottom shapes. Curves across the bottom have a huge impact on the performance of mats, affecting hold, lift, rail to rail transition, etc. But what about end to end?
In the past I have built a few mats with rocker built in to them by shaping the I-beams. This gives a curve for sure, but also leaves excess material when the mat at low inflation is flattened which causes form drag and cavitation so slows the mat down. No more of that then!
Dale Solomonson experimented extensively with "elastic rockers." This is where one skin (usually the bottom) and the I-beams have an ability to stretch and the other skin doesn't. I have moved into using this technique for some time now too when putting rocker into mats. The advantage is that at rest at low inflation the mat is flat. As inflation is increased (ie by squeezing the rail) the rocker comes in to effect.
So, on to the types of rocker.
FLAT ROCKER (ROCKERLESS)
One option of course is no rocker at all.
A mat with flat rocker basically has no elasticity in either the top or bottom skins. This means that the mat's default position is flat and flat means fast. Minimal drag. What this also means is that the mat has a wider turning circle so flat rocker is best suited to people who want to get down the line at speed.
Of course, with mats being mats it is possible for the surfer to bend the mat into any shape they want (I am a builder. The rider is the shaper). That said, mats seem to "remember" their dimensions even at low inflation. It is important point to remember is that when bending a rockerless mat, the lack of elasticity in the skins means that there will be a small excess of material on the shorter side (ie on the deck on bottom turns and on the bottom when bending the mat the other way.)
Rockerless mats are best suited to surfers who want to get down the line and have complete control over what the mat does. The lack of elasticity end to end makes the mat far more predictable in the way it behaves. As predictable as you can get with mats anyway!
Positive rocker (what people generally mean when they say rocker) gives increased maneuverability when turning off the rail by introducing a curve.
The elasticity of the bottom skin gives a smooth, progressive curve, rather than a bend so turns such as bottom turns and cutbacks can be tighter but still smooth, maintaining and even generating speed.
The downside is that rocker slows the mat down. That's not to say that rocker results in a slow mat. Just slowER than a flat one. With an elastic rocker, you are able to flatten the mat so that the elastic bottom skin returns to a flatter plane, but that magical surfmat memory will still remember and act accordingly. Also keep in mind that, unless you are almost totally deflated, at least some of the mat will be at full inflation as the rider's weight pushes air into other parts of the mat. On a flat plane, this is the nose so the rocker still has an affect.
Positive rocker is great in steeper, peaky waves needing a more maneuverable mat.
Negative rocker basically means that the mat is built to "bend the wrong way." A lot of people find it aesthetically displeasing to the eye but function should always win out over form.
The idea of negative rocker can seem counter intuitive and it is certainly a rare build but it gives a very quick mat by producing additional lift. What's more, the rocker profile helps when catching waves so mats with negative rocker can get going earlier.
The potential problems with the design are clear of course. Mats with negative rocker are less inclined to naturally want to turn up on the rail and there is always the risk of catching a rail and unexpected instantaneous pearling is far from unheard of! Rounding front corners can help with that but they can become sticky, negating the point of having a negative rocker in the first place. The advantage of surfmats over other craft is their malleability of course and surfers can manage the outer front corners to deal with these issues.
It's certainly not a design for everyone, but is an interesting, fast option for those who are happy to put the work in.
Saving the best 'til last? Maybe...
I've coined the name "free rocker" after some reflection on the characteristics of mats that I've built over the years. Free rocker is essentially a flat rockered mat but with elastic top and bottom skins. The majority of mats that I have built have had elastic decks and bottoms because I have not always restricted the elasticity. I'll be honest, this was incidental initially, rather than a deliberate decision on my part.
As I have said, at rest a mat with a free elastic rocker will be flat, even at higher inflations. The difference between free and flat rocker though, is that free rocker can stretch either way to produce a smooth positive or negative rocker when needed. At times this will be because the surfer has chosen to put it in, eg on a bottom turn or pressing down on the nose to get into a wave or over a flat spot. At other times, the mat will develop a positive/negative rocker (or both) of it's own accord because it just needs to. The wave and mat kinda get together and agree!
The more I think about free rocker, the more I think it is probably more "surfmat" than any of the above three because it is the only one that is completely unrestricted. That is not to say that it's always the best bet but fans of surfmat magic just have to dig it, right?!
At the end of the day, the decision on what's best will be down to the surfer, the waves they ride and where the mat sits in a quiver.
Lots to think about though.