Smart Strokes
An essential guide to buying fins, by Matt Crowther.

From holiday snorkellers to the seasoned diving instructor to the most prominent underwater explorers, fins are one of the most essential items of equipment. Without them movement through water, especially when wearing scuba, becomes slow and awkward. While most fins will perform adequately most of the time, for those who need to rely on performance to remain safe, careful choices should be made. For this reason fin styles vary to suit different activities.

Foot power

Any fin kick can be split into two stages. The downward ‘thrust’ kick, if executed correctly, produces forward momentum from the quadriceps or thigh muscles (the largest in the body). The upward ‘return’ kick should require minimal effort as it uses the weaker calf muscles and is carried out simply to prepare for the next thrust. Therefore, a good quality fin will improve power on the thrust and reduce resistance of the return stroke.

Surface action

For once-a-year snorkellers, who prefer to spend time on the surface in calm waters, low-cost full-foot or ‘slipper’ fins are a good choice. Small blades allow light, easy finning action and provide a slow, forward propulsion. Those intending to ‘duck dive’ down and swim along underwater might consider a higher-quality slipper fin similar to that designed for scuba. Strong plastics and often softer foot pockets add to enjoyment for the keen snorkeller.

Diving choices

Although a relatively inexpensive buy when compared with regulators, the importance of correct fin choice should not be lost in the price. What should be remembered for diving is that your additional weight, your larger surface area, and consequently, your greater resistance when moving through water, require a fin capable of creating more power with each stroke. Open-heel style fins are used with a wetsuit boot and are adjustable to suit varying foot sizes. These are the best choice for scuba divers as they have larger blades, which create more power with each kick. Warm-water divers who prefer to use full-foot designs should take care to choose a high quality fin capable of providing enough forward thrust for swimming into currents. Cheaper full-foot fins are not suitable for scuba diving.

Free-diving

Free-diving is typically undertaken by those in peak physical condition. Each descent, although to depths usually in excess of 20m, is over relatively quickly and requires ‘bursts’ of strength and power. Free-diving fin design therefore aims to produce maximum power with both stages of kick as a priority over comfort. Long rigid blades give a larger surface area and ensure that forward propulsion stays constant. It is more common that both legs travel up and down together, using leg and stomach muscles with each stroke.

Cramp points

Unlike swimmers, divers are at little risk when experiencing cramp in water. All agencies teach cramp alleviation and it is a skill that has been standardised across the globe. Avoiding cramp altogether is a better solution and can often be accomplished. Maintaining a reasonable level of fitness and making the correct choice of fin are two important factors, but even when this is done some divers still experience regular cramping. It would not be unfair to suggest that 50 per cent of recreational divers have an incorrect finning action. The most common place for divers to feel cramp is in the calf muscles. As explained earlier, the thigh muscles should be working harder, and yet quadricep cramping is an uncommon ailment. For harsher environments it is imperative that a high-quality fin is used to ease personal work loads. Finally, a poor attitude in the water, often apparent in new divers, creates a larger surface area and requires more energy to maintain a good forward momentum.

Ten Dos and Donts

  • Fins are designed to provide momentum, not lift. Buoyancy control and neutral trim will make your finning more efficient, reducing effort and air consumption.
  • Fins have no senses. You can kick coral without ever being aware of it. Practice fin control regularly. Awareness of possible obstructions above, below and behind you is imperative.
  • If you find yourself sinking into coral or silt, don’t kick any more! Use breath control or your BCD to gently raise yourself above it.
  • Know when not to fin. Finger walking and hand over hand methods are sometimes better ways to propel yourself.
  • A modified flutter kick, using the lower fin to disperse downward thrust from the upper kicking fin, can help reduce disturbance. You don’t have to actually touch coral or silt to create a problem, thrust is enough. Throw some coins in a pool and fin over them. You’ll see our point.
  • Penetration lines used in wreck or cave diving are easily caught up around fins. Proper line skills will help you avoid these problems. Tape down your fin strap ends or run the strap end under the buckle..
  • Young divers have to work harder than adults. Their muscle mass is smaller and less developed. The bulk of a scuba set is proportionately larger than for an adult. Finning is more tiring for them. They and other divers with them should make allowances, especially in currents and on long distance swims.
  • You must be able to remove your fins unaided. If you can’t, exiting the water can be very difficult. The longer you hang on a boat ladder on a pitching boat removing your fins, the more chance you have of being injured.
  • Finning to keep your head above water can quickly lead to exhaustion and drowning. Proper weighting and self-rescue skills including BCD inflation and weight ditching should be practised.
  • A skilled diver can use precision buoyancy control to ascend and descend, avoiding finning altogether, which requires energy and saps air.

What to Look For

Ribs

Ribs are incorporated into the design of virtually every fin on the market. Most commonly they run down the sides of the foot pocket and flare outwards along the edges of the blade. The ribs add rigidity and act as vertical stabilisers to prevent ‘rocking’ from side to side with each stroke. They also channel water down the fin, helping to create maximum thrust from the blade’s natural surface area. Some fins have additional ribs for strength running down the centre, from the end of the foot pocket to the tip of the blade.

Vents, channels

Popularised by the Beauchat Jet Fin, vents are designed to work on either the up stroke or down stroke, depending on design. Their purpose is to reduce resistance to movement while increasing blade efficiency. Another method to have been adopted allows the fin blade to change shape during both the up and down strokes. The addition of flexible channels running down the blade increases the power created. The blade distorts to a ‘U’ shape, giving less resistance on the upward stroke due to a smaller surface area. On the downward stroke, power is increased as water is ‘forced’ out of the end. Many other innovative designs, including angled blades, are available.

Foot pockets

In both full-foot and open-heel styles, foot pockets are usually neoprene rubber for user comfort. It is important in all cases that energy is transferred efficiently from diver to blade. To achieve this, foot pockets are normally reinforced with thermoplastic ribs and a thermoplastic panel across the top. Drain holes in the sole allow water to flush through during the dive, reduce suction when taking them off and avoid bubbles of air gathering and venting off.

Clips and buckles

Early open-heel foot pocket designs simply involved a self-adjustment strap system at the back that would tighten or loosen accordingly. Essentially, this still exists, although many manufacturers now incorporate a quick-release device. Most commonly used is the simple pinch clip (similar to that used on BCDs). Others use a style that can be activated without detaching either side of the strap. Usually the straps are made of rubber or silicone, while clips are of a tough thermoplastic construction.

Blades

Early fins featured injection-moulded neoprene rubber blades. Although relatively inexpensive they were by today’s standards heavy, negatively buoyant and required strong legs to work them effectively. Modern fin blades overcome these drawbacks and are usually comprised of compounds called thermoplastics which, depending on the design, may be rigid or extremely flexible. With most styles it is usual that the blade is tapered from top to bottom, starting thick at the foot to create a good thrust. For increased efficiency and performance, sometimes graphite fibres are moulded into the blade. Some serious snorkelling fins use a single blade with a double-foot pocket.

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