So let’s continue to Part Two with a definition (part One of this article is here):
A foil is a solid object that has a specific shape designed to produce force when passed through a gas or liquid. For instance, when air or water move past it (or it moves through air or water as in surfing) force is produced as “lift” and “drag” (or thrust). Ask most people about foils and they will mention an airplane wing and the lift produced by the shape of the wing that allows flight when you thrust the wings through the air with a jet engine. When talking surf fins, the ‘foils’ attached as fins on the bottom of a surfboard are given a specific angle of attack relative to the stringer (center line of the board).
Shape is combined with foil and flexibility (materials) to produce the performance characteristics of each fin or fin set. Shapes vary widely, but the terms below are constant and in general the rules around them hold true to most fins. Single fins may have the “template” (shown in blue outlines below) severely “cut away” and “raked” to change the performance and ride characteristics of the board. Quads use combinations of upright and swept sets. In ALL cases the fins work with the shape/rails of the board to produce the final outcomes/capabilities of the board.
No fins can fix a poorly shaped board, and a great board may suffer from miss-matched fins. Learn the terms so you can dig for information at the shop or with your SUP outfitter, and get the right setup(s) for your goals/conditions on the water.
You want a performance SUP experience but let’s face it – none of us want to battle a sinking board while paddling out, no matter how great it may surf once it’s finally up to speed and riding. During a recent conversation with an experienced SUP surfer who’s riding boards in the upper 8 foot to 9 foot range – he confided as we chatted opinions on surf SUPs in ‘volumes’ and shapes that he hasn’t really understood volume well enough to apply it when considering a new board.