The Basics- Rake, Height and Base Length
The base of the fin is simply what it implies. That is, the distance from the tip of the front of the fin-base to the tip of the back of the fin-base. For the basis of this article we shall simplify things. As a good rule of thumb the wider base will usually create a looser feel to the board while a narrow base will sometimes be create a tighter, stable board. As an example of this, a Liz Twin Fin (a type of loose board small wave board) will have an extremely wide base length to heighten its pivoting and maneuverability characteristics. On the other hand a traditional California Noserider will have a narrower based fin which will help stabilize and stiffen the board during critical noserides.
Fin Rake and Height
Fin rake is the distance from the tip of the rear base to the tip of the extreme top end of the fin measured at a 90 degree right angle. This sounds complex but it is easy to measure. To find your rake, take a ruler to the tip of the top of your fin (the closet point possible to the tail). At a right angle to the fin base follow the ruler down to the bottom of the board. Mark this point with an x with an erasable pen. Measure the distance from the bottom rear tip of your fin to this point. It is usually just a few inches yet this design feature has large ramifications in the performance of your board. A fin which has a longer rake is more “swept”. These fins are great for larger, hollow waves as their swept aspect holds the tail in the wave in critical sections. Swept fins with high rake are used also on noseriders as this type of tail is less likely to spin out in high and critical noserides. Despite this, swept fins can make a board to tight and sluggish in small mushy waves. For these types of waves a less swept or more “upright” fin with a wider base is more feasible. They help you pivot in tighter arcs and have more release (the ability to quickly re-set the trajectory of your board).
Fin height is also very important. Obviously a 9 inch high fin will sit deeper in the water and have more holding power. The deeper fin has less chance of spinning out in bowling sections as it holds the tail of the board down. The disadvantage to this is you will have a little more drag and fin to deal with. This is great if you want to noseride but if you are a hot-dogger a high fin may hamper your style. On the other hand a fin with lower height (4.5 + inches) may be looser. Many small wave short boards have smaller up right fins to maximize their maneuverability and shorten their turning arc. Shorter fins may also have more release than deep higher fins. Despite this when the waves get big and hollow a shorter fin may “pop” out of the water and cease to hold your tail in the water. This is called a spin out
The above rules are only very broad generalizations. Many surfers have their theories which they will die by. Keep in mind that creativity is part of the fun of our sport. Anything may work therefore don’t be narrow minded. Mark Richards rode virtually horizontal twin fins at Hawaiian 10’ foot sunset and won numerous times. They were not supposed to work but he made them work. Kelly Slater gets away with riding small wave fins at gigantic Margret River Australia. It is truly amazing at how fin performance stereotypes can be completely incorrect.
Len Barrow, July 2011.