Surfing Explained: Ep7 Tail Outline Shape

In Episode 7 of Surf Simply's animated exploration of surf science, we conclude the 2 episode run on outline with the decoding of the tail shape, and its performance characteristics.

This episode was written and animated by Surf Simply Coach Will Forster.

Transcript:

Using the front half, we have paddled into and caught an unbroken wave. Then, as we move through our pop up, the front foot is going to land close to the halfway point between the nose and the tail.

This means that the majority of our body is positioned over the midpoint and behind. And so we can safely say, with the exception of nose riding, that the rear half of the surfboard is most in use after the pop-up, and during every other maneuver or action, the surfer might make.

So if you want to do a cutback, or get barreled, then we need to understanding how this portion of the board is impacting us.

We highlighted in previous episodes that we generate speed using both gravity and water flow. And since it is our surfboard that controls water flow, that’s where we will start.
First, we need to understand 2 things.

The larger the surfboard area, the less drag we are likely to produce. And the lower our drag, the less energy is required for the board to lift up onto the plane where it is most efficient.
Firstly, the back half of a board works like a wing, creating lift as the water moves across it. The more surface area a surfboard has, the more lift it will create, and this lowers the speed that is required for the board to lift up onto the plane where it skims across the water and is most efficient.

So when we widen the back half of a surfboard we have the maximum potential for speed and reduced drag. This becomes most apparent when looking at the design of small wave boards. Where maximizing the efficient use of what little energy the wave may provide is integral to the design of the board. These boards, or grovelers as they’re commonly called, have a wide nose, and wide tail, for the reasons mentioned above and in our previous episode.

So why aren’t all boards like this? Well, lift is not always a good thing. The faster a board goes, the more lift the tail will create, and at high speeds, a wide tail could actually lose traction on the wave. Therefore, in situations where we might expect the board to be going faster, like big waves or barrels, we normally use boards with narrower tails as the wave itself will provide all the speed we need, and we’re probably more concerned with controlling the board on waves like this.

Additionally, speed is only one side of the coin. We also want maneuverability. And speed and maneuverability are opposite ends of the scale, whereby improving one, you generally compromise the other.

We can encourage maneuverability by riding a narrower board that is easier to roll from one rail to the other, or by looking at the second feature of the tail; the outline curve. By drawing the outline of the board away from the wave face through the tail, it makes it much easier for the surfer to release the engaged rail, encouraging smooth transitions between turns. At the other end of the spectrum, the consistent width in our small wave groveller connects the wide nose and tail with a straight line, and what we see here is an exceptionally efficient outline not only for generating lift, but also rail engagement creating maximum speed, but severely limiting our ability to pull the rail out of the water and turn.

Where we place this curve will determine how soon the rail can disengage or how responsive the board is during a change of direction, and this can be represented by the sliding scale between speed and maneuverability. Where a designer might choose speed, the rider will have to compensate with techniques such as a further back back foot, or more weight in the back foot to maintain the same maneuverability response. Where a designer might choose maneuverability, the rider will have to compensate with techniques such as pumping and surfing closer to the pocket of the wave to maintain the same speed.

To complicate things, let’s go through some configurations that we have only touched on above. Imagine a wide board with a curved outline, a wide board with a straight outline, then a narrow board with a curved outline, and a narrow board with a straight outline.
In which conditions is one more suitable, or how might the rider expect the board to perform? And for analysis’s sake, lets assume all the other variables like length, thickness and rocker profile are the same.

A wide board with a straight outline? The best configuration where wave power or steepness is not in abundance. With A very straight rail for down the line speed this board will be very fast, but probably harder to turn.

A wide board with a rounded outline? The extra width will provide extra lift that might benefit the rider in soft or small waves, and the curved outline will transition rail to rail smoothly during turns...(character limit met).