DIVE-FINS HAVE ONE JOB TO DO, AND THAT’S TO PROVIDE PROPULSION. It’s how this is achieved that scientists and designers have worked on for years.
As the boffins look to find the holy grail of powerful performance without fatigue, one train of thought is to build a blade that is pre-angled. The latest fins from TUSA embrace this ideology and I’ve been putting them through the DIVER Test treadmill.
Imprex Duos are open-heel strap fins made from two materials. The first is a ridged polymer forming the central spine and side-rail supports, and also wraps around the foot-pocket linking it to the main blade.
The material is a black rubberised polymer. Soft, pliable and permanently bonded to the ridged frame, this also forms the main body of the blade and foot-pocket.
A reinforced side-rail tapers down from either side of the foot-pocket and extends to the fin-tip. This, along with raised guides on the upper surface of the blade, channels the water, minimising spillage over the edge to provide a claimed further increase in performance.
The blades are angled downwards at 20° from the bottom plane of the foot-pocket in the maker’s patented ABD design.
The theory behind this strategy is best summed up in TUSA’s own claims: “A standard flat fin inhibits propulsion solely by fault of design. An angle between the heel of the foot and the calf of the leg remains when the leg is extended to kick.
“This angle causes approximately 10% of the propulsion to be lost. The Angled Blade Design accommodates for this anatomical characteristic and ensures maximum efficiency throughout the kicking cycle.”
The foot-pockets feature drainage holes and internal ridges to negate suction when donning or doffing the fins. The EZ strap-and-buckle system found on all TUSA’s high-end models is used.
The fins felt pliable in my hands, so it was surprising to find that they were actually quite rigid when in use under water. They provided a lot of forward thrust when using a flutter-kick, and didn’t roll on the foot as the power was applied from my quadriceps and calf muscles.
The angled blades made the up-stokes tougher than I’m used to at first, but my body soon compensated and I stopped noticing the effect after a few dives.
The fins supplied were Medium size, equating to an 8-10 (US) foot-pocket. This proved too tight on my size 9s with drysuit boots, but a perfect match with 3mm wetsuit boots. My foot slipped in and out of the pocket when donning and doffing even under water without any signs of suction.
The straps adjusted in small increments and were held in place firmly by the EZ buckles without a hint of slippage. I’m not a huge fan of rubber fin-straps and would change them for stainless-spring versions at the earliest opportunity if I were the owner.
Walking about on the boat was made more difficult than normal by the raked blades, leaving the “backwards shuffle” as the only safe way to manoeuvre with the fins on.
I’ve been diving for more years than I care to mention with a popular and reasonably stiff-bladed Italian model of fin, and my leg muscles have built over time to cope with the increased effort needed to get around under water. This meant that I could manage easily with the Imprex Duos, but those who have been using predominantly softer-bladed or split-fins over time will no doubt find them hard work initially.
A case in point was when instructor Yvonne Tatchley took the fins for a spin prior to modelling them at Wraysbury Dive Centre.
“Wow, these are stiff and really hard work, Nige!” she proclaimed as she exited the water – her personal choice of fin is lightweight and soft-bladed.
These high-performing fins suited my physique and I enjoyed the performance they were able to deliver, but they may not be a suitable choice for everyone, especially those lacking the muscle power to get the best from them.
COlOURS: Black, Fishtail Blue and Flash Yellow
SIZE: S, M, L
STRAPS: TUSA EZ Strap and Buckle System
DIVER GUIDE 8/10
Appeared in DIVER September 2016