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.
So let’s break this down by starting at the base.
Depth and Base
Base and Depth relate to drive and hold in the water, which is why you’ll often find inside concave near the base, channeling water! Generally a greater base will increase drive and longer fins will hold better than shorter fins, which may slip or allow the board to break free.
Sweep and/or Rake
Sweep is a measure of how far the fin curves backwards – you’ll hear people talk about “raked fins” or “swept back”. Sweep influences the turning arc of the SUP, with greater sweep best for longer, carving turns and less sweep for tight pivots and snaps.
Area is the overall face or surface area of the fin, and contributes with Depth and Base to hold and stability. Largest fin areas are often found in twin-fin setups where “keels” (50/50 or flat side fins with large surfaces/sweeps) are used on the side boxes to compensate “hold” power for no middle or back fins.
Flex or Stiffness
Flex is directly tied to the type of materials fins are made of and are one of the first things you may “feel” in your fins – and the last you may find you can control! Stiffer fins tend to be forgiving in that they’ll drive but won’t “respond” where more flexible fins will almost ‘talk’ to you through the turns with what seems a mind of their own. That’s the lively feel and responsiveness that can add real fun to board – and is often found in the single fin cutaway or cutaway center fins of the larger boards. FIND and FEEL the flex, and you’re in for a new world of fin selection!
Larger, stiffer fins will provide stability/consistency due to the surface area, base width and responsiveness, but may impact overall maneuverability/control for beginners on smaller SUP models. This is why many new boards come with larger, plastic fins. They’re outfitting the “everyman”. When in doubt, go medium and stiff to start – usually what comes with the board is great. Note – Small flexible fins may provide slip or drift and break free! Avoid them in the beginning.