Fin Terminology

Being familiar with basic surfboard fin theory and terminology will help in deciding which fin(s) might best facilitate your style of surfing. More specifically, understanding the following concepts will help you sort through the True Ames collection of fins.

The template of a fin is the outline of the fin. Each True Ames fin model is based on a template that has been designed using decades of experience and knowledge, and has proven itself where it most counts: in the water.

AREA: ( Including Base and Height ) 
The area of a fin can be described as the amount of area inside the outline – or template – of a fin. And you might apply your geometry skills to note that the length of the fin’s base, and its height (i.e. depth) are closely related to the the area. In general, more area equates to more hold and drive, and less area equates to a faster, looser ride.

An easy way to the think about rake is how “swept back” as opposed to “upright” the stature of a fin is. The more “swept back” a fin is, the more rake it has. A more technical definition is the angle between a line that runs parallel to the base of the fin, and a line that runs through the front corner of the fin and the tip of the fin. More rake will deliver more stability and a tendency for long drawn out turns, while less rake will deliver a more sensitive ride with a tighter turning radius.

In the most basic terms, the flex of a fin is how much it will bend side-to-side. More precisely, the flex of a fin is a description of how the fin flexes perpendicular to the direction of flow. Important qualities are how much force it takes to flex the fin (i.e. how stiff the flex is), and how quickly and reliably the fin returns to center. At True Ames, our craftsmanship and materials produce fins with consistent flex that quickly and reliably return to center, and with this as our starting point, we make each fin design with the optimal amount of stiffness. A stiffer fin will have a more sensitive and quick response, while a less stiff fin (i.e. lots of flex) will often provide subtly delayed, yet increased projection.

The foil of a fin can be described as the contours of the fin when viewed from an “edge-on” perspective. Similar to how the foil of an airplane wing affects the flow of air as it passes the wing, the foil of a fin affects the flow of water. A 50/50 foil has symmetrical contours on either side, and this will be the case for all of our single fins. Within our system fin collection, you may find anything from 50/50 foils to 70/30 foils to flat inside foils. Whatever the foil ratio is, all True Ames fins feature continuous foils with the thickest section of the foil towards the center of the fin, and thinner sections at leading and trailing edges.

Relevant to all types of side fins, toe is basically how much the side fins are pointed in towards the stringer. In other words, it is the measurement of the angle between the line that runs parallel to the stringer and the line that runs parallel to the base of the fin. If these two lines are parallel, the fin has no toe, or in other words they are pointed straight forward. Often fins will be “toed-in” by a few degrees, which results in enhanced control and maneuverability, while fins with no toe maximize speed by causing the least amount of resistance to water flow.

Cant is a measurement of how much a fin leans out towards the rail of the board. Or more precisely, how many degrees away from perpendicular to the bottom of the board the fin is. As a rule of thumb, center fins have no cant, and side fins have a few degrees of cant. However, there are some side fins that feature no cant. No cant on your side fins maximizes speed by causing the least amount of resistance to water flow, while some cant on your side fins will give you more control, especially during turns.

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