single to double concave...

Hi, I need tips or suggestions of how to shape a single to double concave bottom. I have shaped single concaves and double concaves but never single to double… Should I shape first a full single concave and then add the other two concaves to it… Or should I shape first the double concaves and then blend the single concave… Also does the stringer on the double concave area has to be leveled to the rail edges (as on top image) or should it be below the rail edges (as on bottom image) ?

I will greatly appreciate any tips or suggestions…


  • Pura Vida

When I shape a single to double concave (when the stringer line is below the rail line), I shape the single first, then I carve out the double. That seems the best way for me to keep a flowing bottom curve, but there is no wrong way to do it. For a single to double with the stringer level with the rail line, I just kind of shape it all at the same time. You are making your own board, there are no rules to how it has to be or how you do it, but that is how I do it…

thanks for the tip… I’ll shape it tonight…

There are many ways single to doubles are shaped.

My favorite, deep single under the front foot only. The stringer line is brought back up well in front of the fins. The doubles carve an increasingly shallow path parallel to, and just inside of, the rail fins.

As it goes to the tail, it all goes flat.

This works under the assumptions that

  1. a flat tail is fastest, and with anything but a singlefin, the angled fins generate the drive, and rolled vee is slow and unnecessary

  2. deep concave for “trackiness” is desirable under the front foot. The rails bite more, and prevent front end slide-outs on more critical turns (which lets you move the wide point back).

There are others that carry deep concaves through the tail that argue the rocker line through the concaves is flatter than that at the rails, so this speeds you up. I doubt this is correct under almost all surfing circumstances - I think flat tails are noticably faster AND turn better because fins are more efficient at re-directing the tail than bottom contours.

Thanks blakestah, I agree with you…flat tail = speed. I’ve heard that (flats and straigt = speed and stiffer), and (curves and concaves = loose and slower)…is that right?

Thanks blakestah, I agree with you...flat tail = speed. I've heard that (flats and straigt = speed and stiffer), and (curves and concaves = loose and slower) that right?

Single concaves tend to be a little tracky if they run through the tail.

The double concave is angled near the rails at the tail, this complements the drive through turns nicely (ie: loosens the tail).

Flat is almost always faster. But there is something real nice about the front foot concave through harder turns.

Good tips. I start with single and work my way towards the double, but it is definitely more challenging to do.

One nice thing I have learned is to develop is feel…when shaping concaves its easy to leave subtle lumps, particularly in the tail area. I use my other hand and slide it up and down the bottom feeling for lumps and I only finish when the concave is right and lumps are all gone. Its amazing how easy those lumps appear…probably my technique.

I dont like to over-shape concaves…too much of a good thing.

Also the rail laps tend to add to the concave after the board is fully completed.

I like the small vee to be even with the rail.