Apeks RK4 Dive Fins: Compact Technical Fin For Precision Diving

Technical divers and instructors looking for a fin that handles tight spaces and overhead environments should take a close look at the Apeks RK4. This compact, wide-blade fin is built for frog-kicking and back-finning, with features designed specifically for divers who prioritise control over raw power. The adjustable spring straps work well with both wetsuit and drysuit boots. The price sits around £176-260 depending on where you shop, positioning it as a mid-to-premium technical fin that competes directly with the older RK3 model.

What You Get

The RK4 has a one-piece rubber construction. The blade is slightly stiffer than the standard RK3 but not as rigid as the RK3 HD. Weight sits between these two models at approximately 1.3 kg per fin in size Large. The fins come in four sizes from Small to Extra Large. Available colours include black, white, grey, and orange. The stainless-steel spring straps have two adjustment points that can be moved forward or back by about 2 cm on each side. The foot pocket is designed for use with dive boots. Integrated stainless-steel buckles keep snag hazards low. A large pull tab at the back helps with donning and doffing, though it can be removed if preferred. The RK4 is designed for recreational and technical divers who need precise movements in confined spaces while maintaining good performance in open water.

How They Perform

Many of my colleagues who dive the RK4 say the fins excel at frog-kicking and back-finning. The shorter blade gives excellent control in wrecks and caves where you need to make small adjustments without kicking up silt. One instructor friend who switched from RK3s told me the performance underwater feels nearly identical, though the RK4 has slightly more stiffness. For photographers and videographers, the compact blade length is a real advantage. You can hold position and make fine movements without disturbing the environment.

The spring straps are easy to use, even with thick drysuit gloves. However, some divers report issues with the pull tab. It’s made from hard rubber with an embossed Apeks logo, and a few customers mentioned it rubbed uncomfortably against their ankles through boots. You need a 5.5 mm Allen key to adjust the spring strap positions, which isn’t commonly found in most dive kits. One divemaster I know solved this by swapping in the softer pull tab from his old RK3s.

The foot pocket runs slightly larger than the RK3. Some divers find their boots feel a bit loose in the same size they wore for RK3s. Others report the opposite problem – the foot pocket feeling tight on the top of the foot, particularly with thicker boots. Trying before buying is important, especially if you’re switching from another fin model.

The RK4 has negative buoyancy in fresh water. They sink fairly quickly when not on your feet, though they don’t feel heavy underwater. This can be an advantage for drysuit divers who need help with trim, but it’s worth noting if you’re used to neutral or positively buoyant fins.

For current performance, the RK4 works well in moderate conditions but won’t give you the same thrust as longer, more powerful fins. The vented blade design reduces drag on the upstroke and increases efficiency on the downstroke, but this is a fin built for finesse rather than power. If you regularly dive in strong currents, you might want more blade area.

The one-piece rubber construction is durable. The fins are made in Italy by Technisub, which also produces equipment for other major brands. The material hasn’t shown issues with cracking or delamination based on feedback from dive centres using them regularly.

How They Compare

The RK4 sits between the standard RK3 and the RK3 HD in terms of stiffness and weight. If you already own RK3s and like them, the RK4 offers a similar underwater feel with slightly more rigidity and adjustability in the spring straps. The new design looks more modern, but performance-wise they’re very close. Several divers on forums have said the RK4 doesn’t feel like enough of an upgrade to justify replacing working RK3s.

Compared to the Fourth Element Tech Fin, the RK4 is lighter and less rigid. The Fourth Element fins have more thrust power and are also negatively buoyant, but they cost more and some divers find them too stiff for all-day diving. The RK4 offers a middle ground – enough stiffness for control without excessive fatigue.

For value, you’re paying a premium price for the Apeks name and build quality. The fins work well, but they’re not cheap. If budget is a concern, the standard RK3 offers similar performance at a lower price point in many markets.

Our Take

The main strengths are manoeuvrability and build quality. These fins handle tight spaces exceptionally well, and the stainless-steel spring straps with dual adjustment points make switching between wetsuit and drysuit configurations straightforward. The one-piece construction is solid and should last for years of regular diving.

The limitations are the hard pull tab, which bothers some divers, and the foot pocket sizing, which seems inconsistent compared to the RK3. You’ll likely need to try them on with your actual dive boots before buying. The negative buoyancy is worth considering if you’re used to neutral fins – it changes your trim and weighting.

These fins work best for technical divers, wreck and cave divers, and underwater photographers who need precise control. They’re also good for divemasters and instructors who want a versatile fin that handles both pool sessions and open water dives with heavy equipment.

Final Recommendation

Buy these fins if you’re a technical diver or instructor who values manoeuvrability and control in confined spaces. They’re excellent for frog-kicking, back-finning, and situations where you need to make small, precise movements without disturbing sediment. The adjustable spring straps make them practical for divers who switch between wetsuits and drysuits regularly.

They’re also a solid choice for underwater photographers and videographers who need stable positioning and fine control over their movements. The compact blade design excels in tight spaces like wrecks and caves.

Skip them if you mainly dive in strong currents where you need maximum thrust. The RK4 prioritises control over power, so divers who regularly battle heavy water movement would benefit from longer, more powerful fins.

Also reconsider if you already own RK3s that work well for you – the performance improvement isn’t significant enough to justify an upgrade unless you specifically want the adjustable spring strap system. And if you prefer neutral or positively buoyant fins, the RK4’s negative buoyancy might require changes to your weighting and trim.