The modern design of the fin was invented in 1914 by a Lieutenant Commander in the French Navy, Louis de Corlieu (source). Since then, the design of the humble swim fin has seen countless iterations, styles, and designs to suit many different kinds of activities from snorkeling to SCUBA! One design that has become especially popular in recent years is the split fin. But is this new trend legit or just a gimmick? As it turns out, split fins can be a great choice for snorkeling!
But to understand how the split fin works, we need to know how a regular (paddle) fin works first. What made Louis de Corlieu’s basic design from the early 1900s so effective?
How regular (paddle) fins work
Water pushes back against anything moving through it (resistance). That means anything moving through water has the potential to generate propulsion.
Your legs generate propulsion when you do a flutter kick, for example. Moving your legs up and down pushes the water off and around your feet, creating thrust. Thrust is the result of Newton’s Third Law, which is often simplified to the catchy phrase, “For every action, there is an equal and opposite reaction.” So, as your legs push water behind you, there is a corresponding force that pushes you forward.
However, compared to say, a frog’s webbed feet, the comparatively narrow human foot is not very good at generating thrust. So how do you generate more thrust with your kicks? Increase the surface area of your feet! Just like the webbed feet of a frog or a duck, a wider, flatter area can move greater amounts of water. Enter the swim fin!
Related post: How do SCUBA fins work?
Swim fins are designed so that the water they displace as you kick runs off the blade’s edge, generating your thrust.
How split fins work
The key innovation of the split fin is that the lengthened edge (from the split) provides a greater thrust area. On the down-stroke of the flutter kick, each wing of the split fin will twist, kind of like a foil or a propeller. This effect creates a pressure differential across the fin. Water flows from the high-pressure side (the direction of your leg’s movement) to the low-pressure side. That pressure differential funnels lots of water through the central split and off of the wing edges. Because these wings can direct displaced water in such a precise and controlled manner, they’re highly efficient at translating your kick energy into propulsion.
Split fins are designed for short, fast strokes
The split fin design also means you can generate more thrust on the up-stroke relative to a standard fin where most of the thrust comes from the down-stroke. The twisting and funneling effect from the wings occurs when you move the fin in both directions. However, this means split fins are most effective with short and fast strokes. Strokes that are too wide will disperse water outside the slipstream of your body, reducing your thrust efficiency.
Typically, split fins will also have prominent side rails and channels designed to shunt water towards the split center of the blade. This is in contrast to paddle fins, where water is encouraged to spread evenly off the edge of the blade. In fact, the design of split fins is very similar to an expert swimmer from nature: the seal. A seal’s hind flippers have evolved to exploit a similar thrust mechanism! Similar to the rails and channels on split fins, the digits in a seal’s hind flippers twist and flex to shunt water towards a soft curved center. This gives the animal a lot of propulsion for each tail stroke. Check out the relaxing video below to see these flippers in action!
Split fins vs. paddle fins
Traditional paddle fins are better at generating thrust quickly if you have a powerful kick. In other words, paddle fins have superior acceleration if your kick is strong enough. For that reason, some snorkelers and divers find that split fins are more difficult to use in areas with strong currents. However, with a sustained rapid-stroke flutter kick, split fins can still bring you to high speeds that may leave your companions struggling to keep up!
The higher resistance of the paddle fin is also better for maneuverability and precise movement. For example, many SCUBA divers will swim close to the seafloor, coral, and other rock formations to do scientific research or take underwater photos. They may also be diving in tight spaces like caves and wrecks. In these situations, a practiced diver can use subtle ankle movements and unique kicks (such as the helicopter kick and reverse kick) to precisely control their position. Split fins are much less responsive to these fine and subtle movements.
As I mentioned earlier, split fins work best with fast, low-amplitude kicks. This style contrasts the long, slow kicks with a wide range of motion that most SCUBA divers learn. As such, folks used to kicking with paddle fins may find split fins difficult to get used to. Because split fins are easier to kick, you also get less “feedback” from them (it’s harder to feel them moving through the water). Experienced snorkelers and divers who are used to this feedback may not like the feel of split fins as a result.
However, for the same reasons, split fins can be an excellent choice for beginner divers and snorkelers.
Most folks new to either sport will be used to a swimming flutter kick, which uses short fast strokes. As such, adapting to the split fin will feel more intuitive. These fins can allow beginners, folks with mobility issues (especially at the knees or hips), and anyone with a weak kick to achieve speeds comparable to their more experienced friends. Just be careful because that low feedback from the split fins may reduce your spatial awareness, causing you to accidentally kick someone or something!
One major downside to split fins is that they are quite expensive relative to paddle fins. Both the shape and the materials of the split fin must be precisely engineered to work properly. That means manufacturers must rely on more complex construction protocols and composite materials (thermoplastic elastomers) with unique chemical structures.
How to kick with split fins
Split fins work by directing the force of the kick into the water more behind the fin. This means greater propulsion and thus efficiency, so good for saving energy over longer swims. However, you must use smaller, more rapid kicks (flutter kick) to keep that backward force in your slipstream (your body’s profile). With the proper kick, you can achieve high speeds in these fins with much less effort than paddle fins.
In contrast, paddle fins rely more on water resistance, rather than water flow, to generate propulsion. As such, slow high-amplitude kicks are necessary for moving the large amounts of water that will create your thrust. Slow kicks also allow time for the fluid motion of the fin to “snap”.
So in short, split fins are designed for short, fast kicks, but paddle fins are designed for long, slow kicks. Obviously, there is a lot of variation across different models, but this is the general rule. Most folks who don’t like split fins either don’t like the lack of feedback and/or have trouble adapting their kicking style.
Ultimately, it comes down to personal preference!
If you’re in the market for a split fin, check out my overview of some of the top-rated models at Leisure Pro (my preferred online dive shop for US/Canada shipping) below!
Top 5 split fins for snorkelers and divers
1. Best overall: Atomic Aquatics Split Fins
- Price category: High-end $$$$ (over US $200)
- Foot pocket: Open-heel
- Stiffness: Flexible, but prominent rails add rigidity
- Sizes: Small (US Women’s 6-7, US Men’s 5.5) to X-Large (US Women’s 13-14, US Men’s 11.5-13)
- Color options: Black with multiple color accents
- Special features: Open-toe adds comfort and allows water to flow through the foot pocket; durable quick-release buckle can be swapped for a spring-strap; power rails add some rigidity that makes the fin more adaptable to alternative kicks (e.g. frog kick)
- Other notes: Considered to be the “definitive” split fin, has won multiple awards, and is a great choice for both snorkelers and SCUBA divers (provided your wallet can handle it!)
2. Best for the wallet: Atomic Full Foot Split Fins
- Price category: Standard $$ (under US $100)
- Foot pocket: Full-foot
- Stiffness: Flexible, but prominent rails add rigidity
- Sizes: Small (US Women’s 5.5-7, US Men’s 4.5-5.5) to X-Large (US Women’s 12-14, US Men’s 10.5-11.5)
- Color options: All black, Black with yellow accents
- Special features: Soft, ergonomic foot pocket is comfortable barefoot; open-toe adds comfort and allows water to flow through the foot pocket; power rails add some rigidity that makes the fin more adaptable to alternative kicks (e.g. frog kick)
- Other notes: This split fin is the perfect option for someone on more of a budget, or who will primarily be using them in tropical water. Versatile enough for both snorkeling and SCUBA. Some users report needing to size up.
3. Best for SCUBA: TUSA X-Pert Zoom Z3 Open Heel Split Fins
- Price category: Premium $$$ (US $100-$200)
- Foot pocket: Open-heel
- Stiffness: Flexible, but stiff enough for open water SCUBA activity
- Sizes: Small (US Women’s 6-8, US Men’s 5-7) to Large (US Women’s 13+, US Men’s 10-14)
- Color options: Black with silver, blue, or yellow accents
- Special features: Blade is angled at the foot pocket to compensate for the natural angle of the human foot when fully extended; comes with stainless steel spring straps
- Other notes: On the heavier side (~4 lbs with variation depending on size). The angled blade helps to maintain horizontal movement, a great choice for those who tend to drift downwards while kicking. However, this feature is not great for surface activity due to slapping/splashing.
4. Best for versatility: Scubapro Twin Jet Open Heel Split Fins
- Price category: Premium $$$ (US $100-$200)
- Foot pocket: Open-heel
- Stiffness: Soft/flexible (the black colored fins are more rigid than the yellow/blue fins)
- Sizes: Small (US Women’s 5-6, US Men’s 5-7) to X-Large (US Women’s 11-12, US Men’s 12-13)
- Color options: Black (stiffer), Yellow (soft, highly visible), Blue (soft)
- Special features: Vents at the base of the blade help to reduce drag; open-toe adds comfort and allows water to flow through the foot pocket; wide foot pockets can accommodate 5 mm booties for cold water activity
- Other notes: These durable fins have been on the market for decades and are versatile enough for both snorkeling and recreational SCUBA. Shorter blades make them easy to fit in luggage!
5. Best for wide kicks: Scubapro Twin Jet Max Open Heel Split Fins
- Price category: Premium $$$ (US $100-$200)
- Foot pocket: Open-heel
- Stiffness: Flexible but stiff enough for SCUBA activity in mild currents
- Sizes: Small (US Women’s 5-6, US Men’s 5-7) to X-Large (US Women’s 11-12, US Men’s 12-13)
- Color options: Black with white, yellow, blue, or grey accents
- Special features: Vents at the base of the blade help to reduce drag; open-toe adds comfort and allows water to flow through the foot pocket; wide foot pockets can accommodate 5 mm booties for cold water activity; spring-strap allows for one-time adjustment and compensation for depth compression
- Other notes: A slightly longer and higher-performance alternative to the regular Twin Jet. The length and stiffness are a great option for folks who want the thrust efficiency of a split fin but prefer a traditional kicking style (wide range of motion).
Have you had any snorkeling or SCUBA experience with split fins? Let me know in the comments whether you love or hate this trend!
Still not convinced that split fins are for you? Check out some of my other articles on fins instead!
Related Posts:
Ideal snorkeling fins for beginners
Short vs. long fins, which is best?
SCUBA vs. snorkeling fins, what’s the difference?
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