The Design
Built from rugged thermoplastic rubber, RK3 fins feature oversized foot-pockets to accommodate either bulky drysuit or robust Rock-boots.
The solid construction and dense materials result in a fin that weighs substantially more than standard plastic models. The super-sized white RK3s we had on test weighed in at nearly 1.5kg each, making them negatively buoyant, an advantage for drysuit divers with buoyant feet who, by using these fins, could do away with strap-on ankle weights.
The blades are short and wide with a vented strip across the middle to eliminate, according to the maker, the vortices that can occur at the back of the blade.
The fins are fitted with stainless-steel spring-straps and plasticised rubber heel-pads with pull-tabs to assist donning and doffing.
The straps are held in position by custom-designed buckles, with push-pin retainers allowing for easy removal if the straps ever need to be replaced.
A hole at each blade-tip and heel allows the fins to be clipped together by a single karabiner for stowage or carrying to remote dive-sites.
Apeks also makes a stiffer and slightly heavier version of this fin called the RK3 HD.

In the Water
The large foot-pockets ate my bulky drysuit boots and were a bit big for me. Apeks had sent me size Super, when Large would have been more suited to my modest size nines.
That said, the fins were still useable and the extra space didn’t seem to affect performance. The RK3s outshone nearly all the modern fins I’ve tried out in recent years. Using flutter-, frog-, scissor- or back-kicks with both relaxed and power strokes, the easy-going blades remained stable, showing no signs of twisting on either the up- or down-strokes.
A few years ago we put a range of fins through the now-familiar digital-scale tests to compare performance, and included were a pair of retro-design rubber Trident fins from the Poseidon stables, which pulled the scales round to a very creditable 22kg.
I took the RK3s for the same set of pool tests and wasn’t surprised to see that they did an even better job, dragging the scales to a whopping 22.4kg.
Now that’s impressive, especially when taken into the context of the 2014 group tests, where the best performance measured was from a pair of Mares Plana Avanti Quattros at 23kg.

Conclusion
My late father often said to me: “If it isn’t broken, why bother to fix it?” The original design of these military-grade fins hasn’t had to be altered even slightly, because it wasn’t flawed in the first place.
It’s been brought into the 21st century with the use of thermoplastic rubber and stainless spring-straps as opposed to the original solid-rubber blades and straps, but that’s it – nothing else needed to change on a fin that, nearly half a century later, is still taking on the young pretenders and tanning their backsides.

SPECS
PRICE: £120
MATERIALS: Thermoplastic rubber
STRAPS: Integrated stainless spring
COLOURS: Black, white
FOOT POCKETS: Wide-fit
SIZES: M, L, Super
WEIGHT: 2.6kg (size Super, pair)
CONTACT: www.apeksdiving.com/uk
DIVER GUIDE 9/10