Apeks RK3 Scuba Diving Fins

Apeks RK3 Fins: Open-Heel Rubber Fins Built for Cold Water, Dry Suits, and Hard Use

The Apeks RK3 is a heavy-duty, open-heel fin made from thermoplastic rubber, designed for divers who work in demanding conditions: cold water, dry suits, thick boots, rough entries, and environments where gear takes a beating.

If you dive in a drysuit, regularly wade across rocky beaches, or simply want a fin that was developed alongside military and public safety divers and has been standard-issue kit for that community for decades, the RK3 is worth your serious attention.

If you dive in warm water with lightweight booties and want a light, fast-kicking travel fin, this is probably not your fin.

What Makes This Fin Different

Most fins are sized by shoe size. The RK3 is not, and that is a deliberate choice.

Apeks makes the foot pocket deliberately oversized to fit the full range of diving footwear, from thin wetsuit boots to rigid drysuit boots. A size 9 foot in a thin wetsuit boot and a size 9 foot in a bulky drysuit boot occupy very different amounts of space inside a fin pocket. Sizing by shoe number would be misleading here.

The RK3 comes in three sizes: Medium, Large, and Super. Apeks strongly recommends you try the fins on in-store with the actual boots you dive in. That is genuinely the only reliable way to get the fit right with this design.

Blade Design and How It Works Underwater

The blade is short and wide, which gives you strong forward thrust without the long lever arm of a full-length blade. That matters in confined spaces, on the surface in chop, or when you need to change direction quickly.

The blade is also vented. The vents do two things: they reduce resistance on the upstroke so your legs do less work on the recovery, and they increase thrust on the downstroke by letting water move through in a controlled way. As a secondary benefit, the vents break up the vortexes that can form along the back of a solid blade, which is the same problem split fins address through a different approach.

The result is a fin that rewards a steady, powerful kick rather than a fast flutter. It suits the kind of deliberate, efficient kicking that experienced cold-water divers tend to develop anyway.

Spring Straps and Ease of Use with Gloves

The RK3 comes with spring straps as standard. These replace the traditional buckle-and-strap system with a steel spring loop that stretches over your heel and snaps back into place.

If you have ever tried to fasten a conventional fin buckle while wearing thick dry gloves in cold water, you understand why this matters. Spring straps let you get fins on and off with one hand, in seconds, with no fine motor skill required.

The buckle on the RK3 is custom-designed to hold the spring strap in the correct position rather than letting it shift around. If a spring ever breaks or wears out, a simple push-pin mechanism allows you to replace it without tools or sending the fins anywhere.

Durability and Field Use

The thermoplastic rubber construction is built to tolerate the kind of treatment that would destroy lighter fins: dragging across rocks, stuffing into kit bags, exposure to cold that would stiffen softer materials, and the general abuse of working dives.

Two large grommet holes are built into the blade. These fit most standard carabiners, so you can clip the fins to your kit or a line while you manage an entry, rather than trying to hold them under your arm on a slippery surface.

The fins are available in multiple colors.

Dimensions and Weight

These are not lightweight fins. The Large pair weighs over a kilogram each, and the Super more still. In the water that weight is largely neutralized by buoyancy, but it is worth knowing if you are packing for a liveaboard or carrying kit a long distance.

Who Should Look Elsewhere

The RK3 is a purpose-built tool for a specific kind of diving. If your diving is mostly warm-water reef dives in thin booties, the oversized foot pocket will feel sloppy and the weight is unnecessary. A lighter, full-foot or slim open-heel fin will serve you better in that environment.

Similarly, if you travel frequently by air and count every kilogram in your bag, the RK3's weight will work against you.

The Bottom Line

The RK3 has earned its reputation in the hardest diving environments, not through marketing, but through decades of use by military, coast guard, and public safety divers who depend on their gear.

If you dive dry, work in cold water, or need a fin that will genuinely hold up over years of demanding use, the Apeks RK3 is one of the most proven options available. Just make sure you try them on with your actual boots before you commit to a size.