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.
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.
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.
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 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.
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 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.
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.
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.
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.