The stringer is a stiff, thin, vertical component, usually of wood but sometimes of carbon fiber, running from nose to tail down the center of the board. The stringer serves to increase the board's overall strength and reduce its flexibility. Some boards have multiple stringers while others have none.
The stringer is one of the central areas of surfboard design to which the shaping community is paying increased attention. While it has always been commonplace to see wooden stringers running down the center of a foam blank, shapers have reevaluated the stringer’s function to further advance the sport.
When Clark Foam ceased operations in December 2005 it signaled the beginning of a revolution in surfboard design and technology. While many pioneers ventured into the unknown waters of different materials and design before Grubby Clark shut his company’s doors, it took this large splash to send ripples into every corner of the sport. This revolution has produced an era of accepted innovation. Never in the history of modern surfing have we seen such a consistent effort to improve board performance and strength through design and material experimentation. The following are common stringer designs.
The stringer is the thin strip of wood that traditionally runs down the middle of the surfboard. The wood is typically made of balsa and the thickness increases the strength and rigidity of the board. Some boards have multiple stringers for added stiffness.
The stringer system in which two stringers wrap the perimeter of the rails. They are typically made with balsa material, but shapers recently introduced carbon fiber as a new material used for parabolic stringers. The desired function behind parabolic stringers is memory flex, which dictates how quickly the shape can bend and bounce back to its original shape. A balance of strength and flex must be found because flex is useless without the element of strength. In traditional center stringers, there is torsion flex, meaning the perimeters flex and twist. This will cause the board to slow and fatigue. With a strengthened perimeter, the surfer can apply a more controlled weight to the board’s rail, thus gaining more controlled buoyancy. This enhances drive, improves wave face penetration and increases speed. The added flexibility on the perimeter of the board allows you to lean into the stringer in turns as apposed to the foam. This bends the stringer and shoots you out of the turn as it flexes back. That means more speed, acceleration and torque through each turn.
Often times, longboards have multiple stringers for the purpose of adding strength. This is sometimes needed because the larger surface area of a longboard can flex and wobble too much. Additional stringers will minimize this effect.
Some surfboards have no stringers. Epoxy and Carbon Fiber boards often have a stringerless design. Their materials and sandwich construction give the board added stiffness so a stringer is not needed.
Wood used for stringers
Surfboard shapers are experimenting with stringers more than ever before. But still, the tried and true standard is the wooden stringer. These wooden stringers offer strength and controlled flex to the relatively weak foam and fiberglass material most commonly used in surfboard construction. We can see stringers down the middle, near the rails, and now even on the rails, but regardless of placement, the materials used play a big part in determining how the surfboard will flex. So, which stringers offer the best strength to weight ratios, increasing the lifespan of our boards?
Common Wood Types For Stringers
Four of the most common wood stringers used to strengthen our boards are Balsa, Basswood, Western Red Cedar, and Englemann Spruce. As with all surfboard materials, desirable stringers are lightweight, meaning low density. When taking this into consideration it becomes clear why Balsa became a favored material. According to WaveEquation.com, Balsa is .16 as dense as water, making it very buoyant and half as dense as the other three woods.
Flex vs. Strength
One extremely important aspect to the art of surfboard shaping is balancing flex with rigidity. Flex allows a material to bend without breaking, store energy, return to its original shape, and release the stored energy. This sequence has captured the attention of those interested in surfboard design over the past couple of years. We mention this because a common downside to low density is low stiffness, or increased flex. A flexible stringer is OK as long as it plays by the rules and doesn’t bend far enough to damage a surfboard’s fiberglass. Freshly cut Western Red Cedar has the next lowest density relative to water at .31, but it is almost twice as stiff as Balsa. This strength may offer design advantages to your shaper or glasser that would be worth a conversation.
In an effort to find the lightest and strongest stringers, WaveEquation.com created its own measurement of pound for pound strength, which it calls “Specific Stiffness”. This measurement, which divided the woods’ densities relative to water by their stiffness, suggests that Basswood, Englemann Spruce, and Western Cedar (in that order) all combine low density with increasingly higher strength. If your shaper uses blanks with these stringers then he must appreciate the stiffness and buoyancy of these woods. As a surfer looking for the strongest and lightest board available you should, too.