Anatomy of the Tunnel Bottom
A Unique Surfboard Design by Bryan Bates
25 September 2019
Significant innovations in surfboard design don’t come around very often. Since the Thruster inception, surfboards have largely been more refined versions of older designs. As we cycle through the discard bin of prior designs in search of points of difference, most of what we learn we’re only remembering. So it is with a serious mind that I present for your consideration my Tunnel Bottom as an innovative and effective new bottom contour.
What is it?
The Tunnel Bottom is a specific bottom shape applicable to any surfboard. It employs design elements and effects similar to a catamaran. Essentially it is a vee bottom with a deep V shaped concave ripped through the guts of it. In the past 30 years, two bottom shapes have dominated the surfboard marketplace: the Vee Bottom and the Concave (and variants: ie double concave). The Tunnel Bottom draws from the best part of both of these designs and eliminates their inherent drawbacks. Vee bottoms, while quick rail to rail and steady underfoot are panned for their lack of lift and sit down in the water like a boat hull. Concaves create lift by directing water flow through the centre of the board and have a more lively, sparky feel, but lack stability at higher speeds and that rail to rail feel. The Tunnel Bottom has the rail to rail feel of a vee with the crisp, quick, up-on-top of the water feel of the concave.
A 5’9” Tunnel Bottom Twinzer shape in the shaping room ready to glass.
How does it work?
The vee panels of the design allow the board to be quickly transitioned from rail to rail. Vee directs water flow off to the sides of the board, and lowers the rail line rocker with respect to the centreline, making it faster on rail and having a more “open” feel, so turning becomes easier. Meanwhile, the deep V shaped concave creates lift and reduces the wetted surface area, thereby reducing drag and allowing the board to go faster, specifically at lower speeds. The deep V concave is lined up with the side fins of the board design. The execution of the concave is done with a distinct edge. Water can’t stick to a hard edge as it can with a round or soft edge, so it allows the water to release and that effect translates to speed. When the board is in a turning attitude, you’re engaging the vee panels, and water sheets off the edge of the concave. It’s open and free with low drag. When the board is flat, as in just riding down the line, the concave is engaged and you can feel the benefit of the lift and natural speed created by the water being squeezed and directed beneath your feet.
Another important design element I employ is the use of the “tucked edge” on the rails. Where the bottom of the board meets the underside of the rail I make that edge as strong as possible tip to tail while making sure there’s an appropriate amount of radius to the bottom of the rail for the type of board and to suit the rider. The effect is to “fool the water” into seeing a forgiving rail while providing a hard edge where it meets the bottom of the board allowing water to release, and not cling to the rail. This results in a more engaged rail feeling and a noticable increase in speed due to the lack of drag from water not being able to stick to the rail overly long. A 90 degree rail would be the fastest thing possible but impossible to control as it would be severe and prone to diving under when turned. A fully soft rail is forgiving and easy to turn but lacks precision and crispness. This form of tucked edge is both forgiving and crisp, and much like the Tunnel Bottom takes the best aspects of both (soft and hard rails) and fuses them into something better than either individually.
11’ ICBM (Inter Continental Ballistic Missile) Tunnel Bottom for Gio in EPS/epoxy
How did you come to discover and develop it?
In 2012, I was introduced to finless surfboards. I began working with Derek Hynd making his Far Field Free Friction boards. My task was to handshape, glass and finish a series of his seven specific models. I began riding these boards and loved the effortless speed afforded by the lack of dragging fins and the generous application of hard edges and channels which freed the water and added grip. Lost among the visual interest of the creative channels in the boards was a deep concave in the back half of the board that was critical to the design performance. It kept the board up on top of the water, skimming along. I saw the use and effectiveness of this in Alaia designs as well.
7’1” Drifter for Jason. The bulk of the Tunnel Bottom design came from my Drifter design. Tunnel Bottoms delete the drifter channels and add concaves into the vee panels.
Down the rabbit hole I went and spent 3 years just shaping and riding finless and semi-finless designs constantly feeling that there was ways to improve the performance and control. I developed my semi-finless “Drifter” design out of this and was constantly surfing and reworking boards to get the feeling I was after. I’m a big believer in the scientific method of eliminating variables to isolate and understand a particular design component. So in doing this, I would only change one aspect of the design at a time to make sure what I was feeling was true, and coming from the change made and not another, less obvious design difference.
Initially, I felt the flat bottom through the middle of the board was a hinderance. To do a boardslide, you’d have to put the board flat against the face. I tried a vee panel instead to correct this problem and it worked a treat. The board had more feel and control and could be tilted into a boardslide across the face of a wave rather than having to fully place the board flat on the face. This allowed for quicker transitions from one move to the next and more rail engagement. Then I thought about that concave in the back and decided to run it all the way up, and lined up the lines of the concave with the fins, the vee panels being on the outside of that concave. It worked straight away: great feel rail to rail and positive engagement with a crisp, fast feel while the board was flat and just driving down the line. The Drifter was a hit and I made and rode loads of them for a period.
I began to think that there was some real scope for the bottom shape that I’d been putting on the Drifter outside of finless or semi-finless applications. So I set about on a 4 year period of trying every fin configuration and board shape variations I could think of, and in a systematic way, trying to find a place where it failed to be an improvement. I was hesitant to tout it as an exciting new design for finned boards until I’d gone through all the testing and in the end, I couldn’t fault it. In everything from 11’ gliders to 5’9” Twinzers and all manner of craft in between and the feeling has been the same: fast and lively like a concave, with the great open, easy-turning feel of the vee.
7’10” “Baroness” for Erin. A Tunnel Bottom, Diamond Tail, Stringerless Wing model. Top shelf all-rounder.
And this is where I’m at today, having put the Tunnel Bottom through as many variations as I could imagine, I’ve come away feeling like its a genuine innovation and advancement in surfboard design.
How can it be applied?
The Tunnel Bottom will readily accept any fin configuration: Single fin, 2+1, Twin Fin, Twinzer, Thruster, Quad. The key to working with the fin setup in mind is to align the side fins with the deep V concave. This way the fins work together with the concave in a directional manner. The concave follows the toe in of the fins in other words.
Any shape will also work with the Tunnel Bottom. Tail width, overall width of the board and outline variations do not have a measurable effect on the effectiveness of the bottom shape. I’ve had great luck with very long boards, 9’ ish longboards, 7-8’ midlength 2+1 and widowmaker setups, sub 7’ Single fin outlines, Twin fin Shortboards, and a variety of other shapes and designs.
Similar designs?
There’s some common ground with Edge boards which employ an interior raised surface in the bottom shape. Edge boards have an outline inside of the board’s planshape which has a distinct hard edge, and on the outside of that, theres a dropped surface going out to the rail. Inside the interior outline of the Edge board is a standard concave bottom. Both the Tunnel and Edge have a distinct crisp edge to their bottom shape features that clears water and reduces the wetted surface area, though they achieve this in different ways. I find the Edge board to be clunky in how it transitions from rail to rail due to the fact that the surface is dropped from that interior outline. When you put the edge board on rail, it then is working on a secondary surface from when the board is in a flat, down the line attitude. I can see how this would be effective for a Kneeboard, as the rider’s centre of gravity is low and won’t be thrown off by this dropped surface transition. It makes sense that the Edge design is the brainchild of George Greenough, the most innovative of Kneeboarders. I think for a stand up surfer that having two distinct surfaces is a drawback due to the delay caused by working from the interior surface to the rail in transitioning from one rail to the other. What I see as being the success of the edge design is that it taps into what the Tunnel Bottom does in reducing the wetted surface area for more natural speed while it simultaneously clears water off the edged surfaces, again creating more speed and a freer feeling in the board. Essentially both the Edge and Tunnel Bottom are employing similar design elements to achieve a fast, free feeling but the Tunnel is more smooth and elegant in how it accomplishes this.
The Catamaran Effect
One of the most efficient designs in the nautical world is the Catamaran. It’s essentially two hulls rather than one and because the two hulls have less wetted surface than a monohull does, they have less resistance and require less propulsive power (through sails or motors) and can achieve higher speeds on the water.
The Tunnel bottom mimics this catamaran design in that the deep V concave or “Tunnel” is deep enough as to have no water touching the interior deepest part a good deal of the time. Reduce the amount of water sticking to the bottom of the craft and you instantly increase the speed at which you can travel over the water. You might think that the removal of the material in the Tunnel would decrease the volume of the board and reduce the floatation and buoyancy of the board. In actuality, because the area of the board and the foil of the board remain in tact, there is no noticeable decrease in the floatation or paddling ability of the board, and in fact due to that lack of resistance, the paddling speed is increased.
7’6” Widowmaker Tunnel Bottom. Just a fabulous board!
Outlook
In the past 30-plus years, I think that surfboard design has largely stagnated due to the demands of rapid, inexpensive production and the effect of professional surfing and marketing. A majority of surfers have been conditioned to believe that the surfboards that the Pros are riding are the pinnacle of what is known or can be known about surfboard design. The truth is that a Pro’s board is a very refined object today, developed for a certain type of surfing and waves that have very little in common with the everyday surfer’s experience. Large surfboard manufacturers depend on the perception that their designs are cutting edge and the best in order to ensure that what they produce will sell in the marketplace to justify their levels of production. For large manufacturers to pivot and adopt new and creative designs which fail to achieve uptake costs them dearly, so risk taking is kept to a minimum.
Recently we’ve seen more surfers shift to looking at what alternative designs can do for their surfing experiences and begin to look away from the performance shortboard as the ultimate ideal. I think that right now is an expansive and interesting time in surfboards and it’s my hope that the Tunnel Bottom can be both different and effective enough to jar our thinking further away from what corporate marketing would have you believe regarding innovative surfboard design.
I won’t be patenting my design; I’m here to share it. I would enjoy it much more if others were to try it, make their own and find their own ways to interpret it, leading to greater and greater discoveries. It’s my belief that surfboards are at their best when made for the individual, as everyone does it a little differently. So let’s take some risks, be brave and keep pushing the edges of our understanding of surfboard design.
Bryan Bates
The board that really proved the concept of the Tunnel Bottom. I thought that if it would work in an 11 footer it ought to go on anything and this board is the fastest, freest big board I’ve ever ridden. EPS/epoxy
