OK, I'll say it...it doesn't get any more exciting that this!
(My inner mat geek...stoked!)
Of all the design elements of the surf mat, none is less important than the width of the flanges...
...and yet, the flange width, if it's extremely narrow or extremely wide, can ruin a mat. A flange that's too narrow (or non-existent) allows water to wrap around the rail in low velocity situations...which is when you most need the water to shear off the rail. A flange that's too wide will "buzz" at high speeds -- slowing the mat down, and interfering its ability to hold in.
Below is one of the earliest known photographs of a surf mat, published in 1935. It would appear that there were no flanges on this design. At first blush, it's logical...a cleaner shape should work better, right? But in practice, surf mats perform better with flanges than without. That little bit of fabric running around the perimeter of a mat cleans up the water flow immeasurably. I've made mats with the flange bonded flush to the mat's outer pontoon, creating a truly round rail...and none of them worked particularly well. Very boggy in slow/bumpy waves.
A 50's era shot of English school boys on holiday in Australia. The surfoplane-style mats they were riding had narrow flanges.
60's Hodgmans sported narrow flanges.
Two shots of 70's era surf mats...look how wide the flanges were!
Two recent eras of 4GF mats. Surf Sister on the right with a thin deck mat with patches. Val with a later canvas deck mat. The stiffer material of the canvas deck allows the flanges to be narrower and still shear off the right amount of water, without buzzing at high speed. There's a sweet spot in every mat design that allows both those elements to be in balance.
Kendog on a Neumatic. Lean flanges, but still plenty of width to allow for shearing water off the rail.
Art imitates life. JJ's inflatable hand plane mat with nicely proportioned flanges...
...while his figurine-sized mat has flanges you could land a Piper Cub on. Break out the scissors, JJ!
Tom T's surf mat art features a fastidious depiction of the flange...
..as does the work of John C. :)
The flange of an air mattress is simply the result of bonding the top and bottom layers of fabric together along the perimeter. So in truth, it's a design element born out of manufacturing need. But, as we've learned over the years, the flange is essential to a mat's performance.
Flanges Rule!!! :) :) :)