Bottom Contours Part 2

Stu Nettle picture
Stu Nettle (stunet)
Design Outline

By Cory Russell

In the last instalment of Boarding School we discussed the various types of vee bottom designs. Over time the importance of vee has changed, from being a magic ingredient at the birth of the Shortboard Revolution to one that's only used in retro designs, as it is today.

The reason for the shift is that in the late-80s and early-90s surfers began to demand more out of their equipment, which in turn forced shapers had to evolve their knowledge of design. Rocker had begun to increase on the back of Kelly Slater and the Momentum generation who were taking surfing above the lip and doing controlled sliding turns. The boards they were riding had become highly refined and tuned. Concaves were introduced to provide lift as well as giving the surfer more control.

This was a tough time in surfboard design and many experts identified it as the first time in the history of surfing that the average surfer couldn't ride the same equipment as the pros. Over time, the dimensions would change but the importance of concave in the modern performance surfboard would remain.

The following instalment will decipher concaves and channels.


The purpose of concave in a surfboard is to contain the flowing water and its energy as it passes along the bottom. The increased energy created by a concave pushes the board up, increasing lift and decreasing drag. When concaves became standard on pro equipment, around 1992 and 1993, surfing took a turbocharged leap into the future.

There are two types of concave used on surfboards: single concave and double concave. Various combinations as well as depths can be applied to a surfboard to achieve the desired outcome.  

Single Concave

Single concave is best described as a single curve from rail to rail. The deepest part of the curve is along the stringer or centre of the surfboard – similar to a shallow ‘U’ shape. The depth of single concave can vary but it is usually deeper than double concave. As such, a single concave contains more water or energy which will create more lift. A single concave provides the board with a greater difference between the rail rocker and centre rocker. Longitudinally, the board is straighter through the centre than it is on the rails.

It is this difference that allows the rail to pierce the wave face rapidly as well as enable more water to pass under the board when pressure is applied to the rails. A board with a single concave performs best in quality waves and/or surfing made up of committed turns.

Single concave viewed in profile

Double Concave

Double concave is a set of curves from each rail to the stringer or centre of the board. The deepest part of the curves is between the rails and the stringer – similar to a ‘W’ shape. The depth of a double concave can also vary but it is usually shallower than a single concave. The difference between the rail rocker and centre rocker is reduced which enables the board to have more of a neutral feel.

A board with double concave is more versatile and forgiving as well as performs in a wide range of conditions.

Double concave viewed in profile

Twin Vee Concave

Twin vee concave first got my attention in the early nineties after I saw a design article featuring Mitchell Rae of Outer Island surfboards. Mitchell told me he had been experimenting with deep concaves since the late-60s and the twin vee concave was a progression of that.

The twin vee concave places a double concave from nose to tail in a vee bottom board. It balances the lift created by concave with the smooth rail to rail surfing a vee bottom provides. The result is a really efficient, versatile bottom contour. The original design had around two inches of flat panel leading into the rail, all the way around the board.

Many shapers have used this design in current models but allow the double concaves to go all the way to the rail.  


Channels have an interesting history as described in a previous Swellnet article and the theory behind them is equally thought provoking. Channels are wedge shaped grooves sanded into the last 24 inches of the tail, usually 5-10 millimetres deep and varying widths to suit the board’s tail width (the length and depth can also be altered to suit the board). The number of channels can vary between two and ten depending on the surfer or desired outcome.  

Channels are designed to assist the direction of water flow from nose to tail and generate speed down the line as well as provide drive through turns. By adding channels to the bottom of a surfboard you are increasing the wetted surface area which provides extra lift as well as creating small corridors of increased rocker which provides greater release for the water passing along the bottom of the board. Also, the vertical walls created by the channels provide a level of resistance that can allow for smaller fins to be used.

Six channel swallow tail as shaped by Dale Wilson at Byrning Spears

When done properly channel bottoms are a work of art. A few years ago I was working with Jamie Byrne (son of the late Al Byrne) and I would ask him for any insights or tips he had been taught by his father, who was one of the biggest exponents of channel bottoms. Jamie told me his dad would simply look down the rocker of the board, identify the sweet spot and get to work!

In recent times, the manufacturers of some shaping machines have made it possible to cut channels into a pre-shape. Previously this wasn't possible and the big surfboard companies did everything they could not to do channel bottoms. It will be interesting to see if the number of channel bottom boards will increase when the technology becomes available in the future.

Torus Channel

In 2010, Gary McNeill of Gary McNeill Concepts had an idea for a new bottom contour on the boards he was making for Dave ‘Rasta’ Rastovich.  The idea was to apply a wide channel that almost ran the length of the board within a concave.

The torus channel provides the surfer with another level of engagement under their front foot. In the past most of the control elements of a surfboard were centred on the tail with its sharp edges and fins, however this bottom contour allows a similar feeling under your front foot as well. The channel engages in a way that can make the board hold in at high speeds such as barrel riding or deep turns when other boards would blow out.

By having the edge go right up to the shoulders in the board it also means it needs less fin area to keep the board holding in. Less fin area equals less drag and less drag equals more speed.

I recently contacted Gary about this design and he told me he's in the process of taking the design even further, adding deep concave panels either side of the channel. Gary assured me the early feedback has been great.

The torus channel, a product of Gary McNeill's creative mind

Rail Channels

About 18 months ago, a guy brought a board in to me that he'd been riding. The board had been shaped by Mark Rabbidge. It was a traditional looking fish with a more modern rocker, yet it was only when he handed it to me that I discovered it had rail channels. The rail channels are parallel to the stringer, they start about twelve inches from the nose and run all the way to the fins.

Recently I had the opportunity to ask Mark about his rail channels and he couldn't contain his excitement. Mark told me he's been shaping them for years and couldn't believe how much faster the board was when it was laid on rail.

Not long after I saw Mark’s rail channel design I noticed the boards George Greenough had made for Rasta to take to Fiji - coined the 'edge boards'. Since then there's been an abundance of shapers with similar designs. If applied correctly the rail channel theory has plenty of merit. The channel reduces the rail’s buoyancy and also provides a more direct path for the water to follow when the board is on rail.

A traditional fish with rail channels as shaped by Mark Rabbidge


It was 1989 when Phil Myers came up with a design called the vent system, essentially a deep double concave with forward vee and channel. I recently contacted Phil about the vent system and he told me this was one of numerous designs he'd created but many of the other designs were difficult to manufacture. A relentless innovator, Phil also created the hydro channel which is the basis for Tommy Peterson's acclaimed Fireball.

The vent system proved itself under the feet of a young Danny Wills and 1988 world champion Barton Lynch. Phil explained the design was different to other boards on the market at the time and he received some backlash from other shapers. However, the boards were fast, they performed on rail, and were suitable for all levels of surfing in all conditions.

I asked Phil if he still has people ordering them? "Yes," said Phil. "The design has a lot of merit, especially in good strong waves such as reef or point breaks." 

"The feedback I get is that the bigger it is, the better the board goes!"

Prodigious channel shaper Phil Myers and his vent system


The eternally creative Erle Pederson came up with the jet bottom design in the mid-70s. Originally called the ‘Kewarra Jet Bottom’, it was a series of curved channels that would crisscross and exit the sides as well as the end of the tail. The idea was to "bust all forms of water tension" and were theoretically similar to rapids in a river. They also increase the amount of air on the bottom of the board.

This design was first applied to vee bottom boards and would provide the lift a vee bottom does not possess. Similar hydrodynamic principles are applied in boats designed for speed.

I shaped my first version of a jet bottom a few months ago and it was a mighty challenge. I marked it out a few times but once that was complete it was a lot easier than I thought to shape.

Erle is still creating boards under the Surf 1770 brand and pushing the boundaries with his unique design theories.

Erle Pedersen and the intricate concentric channels of his jet bottom


When I design a board I don't focus on the specific amount of vee or concave it will have, but prefer to concentrate on the rail rocker and how it will combine/complement the centre rocker of the board. To simply focus on the amount of vee or concave in a board alienates the other elements of design and can create a design with big limitations.

The reason for this is the depth of vee or concave reaches a certain point of influence on a board before experiencing a form of ‘neutral velocity’. After that any additional vee or concave will have a minimal effect on the design. This neutral velocity varies for each board depending on its construction, weight, and the surfer riding it. The reality is that concave can only generate so much lift and vee can only reduce it to a maximum amount before it is neutralised.

In my experience, boards with extreme vee or concave are a solution for a design flaw in the rocker. The radical increase/decrease in rail rocker will momentarily hide a faulty design but the problem will remain.  

By now you should be either well informed or overwhelmed about the bottom contours of a surfboard and how they work.

I always encourage people to try different types of boards and see what works for them.  The most important thing you can do is to start a conversation with a shaper and learn how he applies these principles to your surfing.

In the next instalment we will discuss volume.

Cory Russell
Cory Surfboards / Stretch Boards Australia

Wanna read past articles of the Boarding School?
Bottom Curves Part 1


GuySmiley's picture
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GuySmiley Friday, 17 Mar 2017 at 9:07pm

That Torus channel thingie, old mate had an Alan Oke single fin from back in the day like that, narrower but nose to tail.

PCS PeterPan's picture
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PCS PeterPan Saturday, 18 Mar 2017 at 12:01am

Interesting to see more experiments in board design going down.
Those extreme takes ,ie:jet bottoms must be fun to glass and sand eh ?
Reckon I'll stick to my basic singles and slight doubles though . . . water doesn't like getting too many questions asked of it IMO.
Surfed in Fiji late 2016 with some retired pros and up and coming juniors . Checked out their boards during the trip , all pretty basic single concaves and flattish battoms with slight v doubles in their step up boards. Totally inspiring surfing by these folk on basic equipment.
Anyway , whatever flicks yer switch !

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cory Saturday, 18 Mar 2017 at 11:32am

Hi Guy and PCS,
Just so you know... Gary McNeil is one of the nicest guys in the industry and does not claim to be the first person to have a single channel running through the board. I would love to see a pic of the old Alan Oke board if you had one? The time in surfboards was super creative!

I understand what you are saying about subtlety in design. Shapers love to test theory, push boundaries and inspire surfers to travel on different parts of waves. Often they take what they learn in the extreme and apply it in a subtle way. Cheers

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GuySmiley Saturday, 18 Mar 2017 at 2:11pm

Hi Cory, no offence was intended just pointed out what old mate had. Its all heritage today -yesterday. I ask, old mate might come good with a pic.

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cory Saturday, 18 Mar 2017 at 2:43pm

Hey Guy,
No offense taken... I will take any opportunity to tell people what a bunch of legends we have shaping boards in Australia. :)

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lostdoggy Saturday, 18 Mar 2017 at 11:45am

The number of channel bottoms is increasing already from what I can see.
Thanks for the articles Cory.

cory's picture
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cory Saturday, 18 Mar 2017 at 2:46pm

They are very popular at the moment. The biggest disappointing thing for me is both fin companies refuse to develop their products so they could be used easier in channels. Cheers for the support

Clam's picture
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Clam Saturday, 18 Mar 2017 at 4:54pm

That's a shame about fin boxes . It must cause compromise of the design making things fit different brand fin systems ?

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cory Sunday, 19 Mar 2017 at 8:29am

It's true... hopefully they figure it out and support the shaper/glassers.

udo's picture
udo's picture
udo Tuesday, 21 Mar 2017 at 10:16am

Cory do you have ideas in mind for the diff type of plugs for Channel bottoms ?

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cory Tuesday, 21 Mar 2017 at 11:05am

Hey Udo,
The major fin/fin box companies only need to make small changes to their existing plugs. The way I install FCSII is reverse the bearing and locking device to give the cutter extra depth and maintain the bearing contact with the jig. I chok the jig parallel to the channel and route it. This means I use 3 degree plugs for the sides and zero degree for rear quad plugs. The problem with this is FCS only make zero degree plugs with the click in device on one side so customers have to screw the fin in on one rear quad fin. If FCS manufactured a zero degree plug with the locking device on the other side it would resolve this.
As for futures... it's a lot harder. I modify the boxes so the top of the box matches the angle of the channel. Installation is a little tricky to as you have to use there old method and do it in two parts. I shown the Futures guys my plug last Easter but heard nothing from them. Small changes could make a big difference to manufacturers.

linez's picture
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linez Saturday, 18 Mar 2017 at 5:17pm

Love these articles, thanks Cory. You mention both single and double concaves separately, but most boards I have had for a long time now have combined both. A single with double in the back 1/2 or 1/3rd. Best of both worlds?

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cory Sunday, 19 Mar 2017 at 8:32am

The short answer is yes. The long answer is I try to concentrate on centre rocker and rail rocker complimenting each other and being functional. I also prefer the way a double concave blends into vee.

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linez Sunday, 19 Mar 2017 at 11:24am

Ok thanks

stunet's picture
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stunet Monday, 20 Mar 2017 at 12:06pm

In the comments of the last article, 'Spuddups' was talking about bottom curves being overstated. I was almost gonna comment then but figured I'd wait till this instalment - i.e concaves - went up.

A few years ago I had the oppportunity to ride two boards that were identical except one was a flat bottom and one had a single to double concave. The concave was only subtle, a few mm at deepest point running into two shallow concaves. Barely noticeable. In all other respects the boards were the same so any difference in performace had to be, or was most likely to be, due to the bottom curves.

The board with concave(s) had noticeably more lift and drive. It wasn't a stringent test, placebo effect was possible, but I've ridden enough board to know the feeling.

I'm always facinated by how much effect a shallow concave can have; just a millimetre or so makes a massive change in my eyes.

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Terminal Sunday, 26 Mar 2017 at 6:07pm

That was a great opportunity (would love to do that) and you raise a really important point about controls when comparing a board designs under natural conditions, where every wave is different and placebo effect can also creep in. I live in academia, in science specifically, so pretty much live and breathe hypothesis testing and experimental design. As such, while everyone was on about Kelly's wave pool and its implications for surfing in the mainstream spotlight (not that it isn't already), I was thinking jackpot, we now have a facility that provides us with the closest thing to a standardized testing environment to empirically test board design as a whole. For example, with the appropriate technology (keep that bit to myself), we can now actually measure how water is interacting with a board (i.e., different bottom contours, flex, fins; everything!) in real-time while a surfer rides a wave that can be replicated infinitely! To me, having this capability is one of the single most important things to ever happen in surfing, the possibilities in R & D are limitless, right up there with any innovation that has ever happened (actually surprised Webber and Slater haven't clicked yet, but maybe they have and keeping it on the sly).

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Lanky Dean Monday, 27 Mar 2017 at 3:34pm

For me that's what hawaii is for terminal. You don't need a wave pool....Hawaii is the best place to test boards. So is the beach closest to your home. If you test two or more boards in the same time/ conditions you can really start breaking down , understanding different characteristics.
For me the wave pool is a vacuum, it's not real, so a board that works in a wave pool won't show the same traits anywhere else.

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Terminal Saturday, 1 Apr 2017 at 8:17am

Totally agree Lanky Dean, the type of board you would test and develop in a 2-3 foot wave pool is obviously totally different to what would be ridden at sunset or pipeline. But a large portion of surfers don't/won't ever surf waves like that and will be hitting their local which is going to be 2-3 foot 90% of the time (sorry, that's what I had in mind when writing my previous comment: average joe surfer, average wave). In terms of collecting good empirical data on anything though, you need to control for as much as you can, otherwise each datapoint collected is not comparable with the last one and it makes it very difficult to tease out and build a picture on what it is you actually want to measure (and then make statements on). In surfing for example, natural waves are different every time and this presents a serious limitation (from a scientific perspective) in collecting good comparable data on something such as board performance (I think it would be very difficult to get your work published using data collected under natural conditions). Here, Jimmy Slades' wave pool fills that gap by providing a controlled, "vacuum" environment (perfect word for it), were board performance can be tested on identical waves an infinite number of times. I suppose you could think of Jimmys' wave pool as analogous to a wind tunnel where white coats test plane wings or friction coefficients for cars. By the way, really not trying to offend anyone and have the utmost respect for all shapers out there, you guys provide the interface between us and the wave. I can just see low hanging fruit with that wave pool and some surfing scientist is gonna make some amazing contributions to surfing there sooner or later (wish it was me).

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Lanky Dean Saturday, 1 Apr 2017 at 4:35pm

"For me the wave pool is a vacuum, it's not real, so a board that works in a wave pool won't show the same traits anywhere else."
Plus the wave pool is broken. I will stick to the beach, well actually the waves in the ocean at the beach to test the equipment .

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Lanky Dean Saturday, 1 Apr 2017 at 4:54pm

You'd probably be interested in an article @stunet did on Greg Webber last year. it involved shaping a board with one design element missing. Pretty darn interesting really.

The funny thing about testing boards is any good shaper will tell you every board will be different. From blank / glassing / material strength/ temperature at time of production/
boards just have too many variables. Then every surfer's stance is different/ most surfers have different body type. Every time you surf you have a different amount of energy/ flexibility /awareness.

The one board fits all, just doesn't work with surfing.

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Lanky Dean Monday, 27 Mar 2017 at 3:35pm

did you ride the two boards in the same session on the same time, tide, wind and swell. Did both boards have the same leashes?

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PCS PeterPan Tuesday, 21 Mar 2017 at 9:51am

Cory , I did not intend to sound negative but my comment does read a little that way.
Im grateful there are dedicated craftsmen/designers such as you that offer valuable info
and craft for us surfers to ride. . . all the best PCS.

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cory Tuesday, 21 Mar 2017 at 11:08am

I didn't think you were being negative at al it was a good observationl. I just wanted to share with you why shapers often push design ideas to the extreme but release them with a bit more subtlety to the market. Cheers ;)

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Lanky Dean Thursday, 30 Mar 2017 at 10:45pm

Remember seeing a gerry Lopez short board around 2001, that had a ridiculous amount of single concave, board was a five ten. The thing must have flown.
A buddy had a Maurice Cole tow board that had an even crazier amount of single concave. That thing was/went crazy .

Noticed in Hawaii a few year ago local shapers using single or double concaves then using vee behind the back fin of thrusters.

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gcuts Thursday, 30 Mar 2017 at 8:46am

OK, so let's use an an example, a shortboard, for average joe.

Bottom contours going from a flattish nose into a single concave with double concave inside the single starting just under the chest / front foot, getting deeper in both single and double concave into the fins and then flow into a slight vee from back fin out.

Pretty standard board?

What makes or breaks one board from another? Is it the depth and transition of the changes in bottom contour?

I think it is related to the rocker impacts, both stringer rocker and rail rocker.

Getting that stringer rocker curve smooth and consistent flow would be key?

So, for example the vee in the last 3 inches, would kick the rail rocker so it looks like it has a flick in the tail at the rail, while the stringer rocker is flatter?

The deepening of the single concave from say chest into fins would flatten the stringer rocker, while the rail rocker stays more curved?

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Lanky Dean Saturday, 1 Apr 2017 at 4:39pm

" The deepening of the single concave from say chest into fins would flatten the stringer rocker, while the rail rocker stays more curved?" - centre of board would have a decreased radius.

udo's picture
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udo Saturday, 14 Oct 2017 at 9:55am

Jim Banks - FLV
Jims has a write up on his site experimenting with Full length nose to tail V bottoms.

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udo Friday, 13 Jul 2018 at 6:47pm

mateo and brittany insta - 12 channels.

stunet's picture
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stunet Friday, 13 Jul 2018 at 6:48pm

Copying Richo.

udo's picture
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udo Friday, 13 Jul 2018 at 6:49pm

Nose to Tail

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stunet Friday, 13 Jul 2018 at 6:52pm

Not much plain white in that IG feed.

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Fliplid Friday, 13 Jul 2018 at 9:45pm

Earle showing how its done

udo's picture
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udo Friday, 23 Jul 2021 at 7:18pm

A bit of Classic Phil Myers Vent footage - Glenn Curtis on a 8'0 Vent