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.

Concave

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

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

Vent

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

Jet

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
Shaper
Cory Surfboards / Stretch Boards Australia

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