deep, full length double concave

Any old dudes remember who has mucked around with deep, nose to tail doubles? I’m doing it with vee between the 1/8" concaves and they have more speed and bite but are silk between turns. I’m guessing it will take over from the single within a few years…

The first ones I rode were in the last of the single fin days. Both flat bottoms with Double-barrels

and subtle vee bottoms with Double-barrels. Then the thruster came and it seems the

Double-barrels reappeared with the ‘potatoe chip’ hyper-rockered shorties of the early-90’s.

Those were fast and loose but most likely the rocker killed the whole deal, they required

continuous rail/rail motion.

When the doubles were directed properly throughout the bottom, they went unreal but if

anything was a little off, they were real boggers…

So did the concaves go to the nose, or fade out at some point?

On the single fins, both. Most just between the feet, but I do remember a few with full-length doubles

and of those a couple were exceptional…

Cool…how deep at max?

approx 1/8" (2-3mm) very gradual throughout. If I had known then what I know now

I would have placed max double in a certain spot for pivot.

Doubles seem to give good drive, as they cup under more than a single for their given

depth. I single would need to be pretty deep to have that bite near the rail edge…

I’ve had a couple of deep double concave edge boards shaped by Bob Duncan…

As far as I know they are patterned after early dual concave designs worked out by George Greenough and Mike Cundith…

The smaller of the two boards was just too small for me and has been sold. The other is a pretty decent utility board for medium to large California waves. I have had occasions in high tide backwash where it became slap-happy but what board isn’t in those conditions? Also, the forward edge has caught me by surprise a couple of times.

I know now how I would tweak the design and one thing would be to blend in more of a gradual belly forward. Another might be to add some tail rocker. This one is pretty parallel and flat in the tail.

We did them back in the 70’s when I worked at Natural Art but those were single fins.

I have a newer design that I like even better called CAT channels. Kind of a channel bottom but kind of concaves. Sort of a combination of the two. It runs full length and has even more drive and is smoother that the double … IMHO. Tricky to shape. When you divide the concaves it changes the angle of the bottom edge to the waveface creating more drive. More angles make the ride smoother. The concaves are not symetrical, deeper towards the rail adding more drive. Most of them I’ve done have 4 CAT concaves.

“If it isn’t a CAT it must be a dog.”

Started those about 10 years ago with big success. Haven’t shaped much lately though and no one else does em.