The fin of your standup paddleboard plays a big role in your on-water comfort, speed and overall performance. It’s the one replaceable part of your board that can dramatically change its performance–but understanding them can be tricky. But that’s why we’re here.
Having a fin that's well matched for the conditions and discipline–flatwater, downwind, surf, river, technical racing or distance racing–can make all the difference with tracking, stability, speed and maneuverability of your SUP.
Here's a breakdown of what fin type works best for each discipline.
Typically flatwater touring involves a bigger (10 to 14-feet), more stable (higher volume) board and and a longer, straighter fin to help cover distances as straight as possible.
Even for beginners stability is normally no concern on these boards, and since it doesn't require much turning, maneuverability also isn't an issue. The key in a good touring fin is the ability to track straight. Look for a longer model (10+ inches) that acts as a keel, with more surface area and a fairly aggressive rake (the angle at which it slopes backward; helps with speed and shedding debris such as kelp or grass).
For downwinding, SUP mimics a design resembling of the traditional longboard fin--a narrower, medium sized fin (seven to 10 inches) with an arched rake and a "shark fin” profile.
Featuring less surface area and a more aggressive taper, this design loosens up the tail of the board for quicker directional changes, which are critical to connecting bumps downwind, and allows for smoother transitions between rails going down the line.
Most SUP surfboards come equipped with at least three fin boxes. Unless it's an aggressive SUP shortboard, in which case you'll likely prefer three fins more akin to those of a traditional shortboard "thruster," the middle fin box usually fits a different fin type than the side fins. The center box will work with most longboard surf fins, so play around with a variety and dial in the design that works for you. A longer center fin will add more drive and hold but will slow down rail-to-rail transitions and overall maneuverability. For more control and grab in the wave face, add in two smaller surf fins on the sides. Changing up the length of the center fin in conjunction with the side fins will change the board’s performance characteristics more than you might think.
Inflatable SUPs are the indisputable best option for river paddling. They usually come with their own fins, whether they're permanently fixed to the board or pop-in attachments. Most inflatables come with rubber, flexible fins so they don't get damaged on rocks or by scraping the bottom. These fins bend and tend to perform much worse than fiberglass or plastic fins, but they're definitely better than no fins at all. The key is to find something that performs for what you’ll be doing the most of: will you mostly be running rapids (short and rubbery will be fine)? Have a lot of flatwater between whitewater sections (longer fins for better tracking)?
Technical racing--that is, racing on short courses with surf and/or lots of buoy turns--calls for a fin similar to the downwind design. For this you want something stable but also surfable and quickly maneuverable around buoys. Tracking is less important. Look for something in the eight to 11-inch range with a narrower profile, a sloped rake and a tapered posterior margin (the back of the fin) that will surf and maneuver well without sacrificing too much stability.
Straight and stable is the name of the game for paddling long distances, so here we return to a similar design to what we'd use in flatwater. A deeper-sitting fin works best both to keep the board tracking straight and to help with balance. With distance you're also less concerned with surf ability and turning, so look for a SUP fin with less rake (straighter up and down) but be aware of what kind of debris you'll be paddling through. The less rake, the easier it is to catch an annoying piece of trash or sea weed.
Now that you know what fin will work best for your SUP, get out there and see for yourself!