Freediving with Monofins
Geschrieben von: Sarah Whitcher
All spear fishermen, recreational and competition freedivers seek the most efficient way to move through water and will generally look to the animals already inhabiting our oceans for clues on how to accomplish this. When comparing human physiology to marine animals the nearest we get to mimicking the biomechanical movement is that of Dolphins, Whales and Manatees. For us to emulate these splendid creatures we have to adapt our own body with the use of a prosthetic tail, the monofin.
One needs only to look at our fascination with mermaids/men and their tail fins to realise that the half human half fish has captivated our imaginations for centuries.
A short history of the Monofin
When we think of being streamlined and graceful in the water we picture how, with ease, dolphins and whales effortlessly cruise through the depths. Our human physiology enables us to try to mimic this gracefulness, but to really gain speed and efficiency we need to make a few adaptations to our bodies. It is most likely that throughout the history of humans we have tried to recreate a fish’s propulsion by increasing the surface area of our feet. This has lead to some unusual designs of fins. In Polynesia spear fishermen developed fins made of large leaves and after the World War 2 the British public made their fins from gluing marine plywood to their plimsolls.
One of the very first monofins to be worn was in the sport of fin swimming and was homemade and formed from two titanium rods connected by a sail cloth. Monofins were then developed using plastic and rubber and used in fin swimming competitions from the early 1970’s.
For freedivers to use the monofin it had to be designed to perform at depth, to withstand the pressure changes without deforming its shape. It was not until 1992, when Rossana Maiorca wore one to a new record depth of 58 metres in 1’48’’ that a monofin was formally welcomed into freediving. Nowadays most of the constant weight records are made wearing a monofin which gives further credence that it is both faster and more economical to monofin than to bi-fin. The freediving monofin has continued to evolve and today is manufactured using modern technology and materials.
Construction
With modern materials and the advances in building technology, monofins have developed considerably from the plywood and plimsoll days. Today’s monofins are made from plastic, glass fibre, carbon fibre, carbon composite (carbon and glass fibre) and usually bound together using epoxy resin.
The monofin is made up of two sections; the foot pocket and the blade. The foot pocket is formed from a thick rubber and can be an ‘open’ or ‘closed’ pocket design.
Currently freediving monofins are still only made by very few manufacturers and generally are made to order. As a result of this small market the monofin can be expensive.
To reduce the cost for monofin novices cheaper plastic blades have been produced. However as the monofin freediver develops their action and power the progression will be towards purchasing the glass fibre and carbon blades which are both lightweight and flexible. The carbon composite is the most popular blade offering the same mechanical properties of that of carbon fibre and glass fibre but without the expense.
Carbon composite material is a weave and when cut into pieces it can be layered into a 3D mould at varying angles fixed by epoxy resin and cured in an autoclave at a temperature of 300°C.
The degree of angle that the material is placed on top of each other will result in different flexibility. A large mix of angled material will be more rigid than that of material that has fewer angles. Since the material can be positioned in such a way to produce various flexes, it can also be positioned differently throughout the blade to enable certain parts of the fin to flex more or less. This is particularly useful in creating a blade that will flex in a spoon shape when pressure is exerted on it. This spoon shape has been proven to be beneficial in generating greater propulsion through water. Spars can also be laid over the edges or at the junction of the foot pocket to help prevent the monofin from skidding or sliding sideways. The lay up and moulds of different blades are closely guarded secrets by the manufacturers as this is what defines the characteristics of the different blades.
Monofin Technique
Research has shown that the torpedo shape of the Dolphin is the most streamlined and produces the least drag moving through water. For a freediver to achieve a similar torpedo shape both arms need to stretch above the head, the palm of one hand on top of the other hand, elbows straight with the top of the arms behind the ears. The head is straight with the chin tucked in slightly, lengthen through the spine and the legs kept together.
The dolphin kick is an undulating action of the lower body and to perform it well there needs to be a substantial amount of flexibility in the lower spine. In order to use this technique efficiently, the movement needs to originate in the lower back above the pelvis and transfer the movement all the way to the end of the fin, causing it to "whip" the water and propel the freediver forward.
The diagram below shows the pelvis and lower back as it oscillates throughout the kick.
[to be included]
Movement is generated from the lower back and the legs start to rise upwards.
The shoulders, head and arms are static throughout the stroke.
The upper leg then starts to fall while the lower leg continues upwards.
It is important to only flex the knees a little to produce the downbeat kick.
The lower leg accelerates downwards until it comes back in line with the upper leg.
The proper sequential motion down to the monofin must be done without any undue contraction of muscles; the body must be kept completely loose.
Practise
There is only one Monofin technique (dolphin kick) however each freediver will have a different monofin style. Everyone has varying degrees of flexibility in the lower back, shoulders and ankles and this is what determines their style. Some find it easier to monofin with arms down by the sides if the shoulder flexibility is poor, while others may have more knee bend if the ankles aren’t very flexible. Flexibility can be improved through regular stretching and the more time practising with the monofin the better the technique will become.
It is advised that practises wearing a monofin are first performed in a pool so to enable the freediver to learn to manoeuvre and adapt to the sensations of having the feet bound together.
Lengths can be swum on the back, sides and front (a front mounted snorkel is helpful). To monofin on the back is advantageous due to the fact that breathing can be performed without breaking the stroke. Whilst to monofin on the sides in a roped lane can determine if the kick has equal velocities of downbeat kick to upbeat kick, if either is more pronounced then the freediver will be propelled at an angle and collide with the lane rope.
It is important that during the different practises concentration is on the movement of the lower back and pelvis whilst keeping the upper torso relaxed as possible. When swum at speed, a well performed monofin stroke will create ripples along exposed flesh of the swimmer.
With practise, patience and disciplined movements the body can develop a powerful and rhythmical sequential motion.
Choosing a Monofin
There are plenty of different designs of blades; assorted lengths and widths, angled at the foot pocket junction, scalloped bottom edge. Foot pockets can be of varying designs too. An ‘open’ footpocket is where the foot pocket is flat or bullet shaped and the foot is secured by a heel strap. ‘Closed’ foot pockets tend to be when heel is sealed in, the same as in bi-fins. Each design has its own merits and it is only through trial and error that a freediver will find the most comfortable monofin for them. Foot pockets can be sized using shoe sizes or small, medium, large and extra large. If used for recreational and training freediving then it is advisable to have foot pockets slightly bigger than the foot so that neoprene socks can be worn to protect the feet from rubbing and the cold. If you want a monofin to perform well at depth then the foot pockets must be very tight at the surface so that at depth; when they compress, they do not become too loose. This then means that these monofins are only worn in short intervals.
How much the blade bends is dependant on how much force is applied and so the blade stiffness is important when purchasing a monofin. The stronger the force applied the more rigid the blade needs to be so that it does not become deformed under propulsion. Most manufacturers class blades as soft, medium, hard or extra hard.
Monofins in the disciplines
The current male and female records of DYN (Dynamic with Fins) and CWT (Constant Weight with Fins) were achieved wearing monofins and each discipline involves using different styles of dolphin kick.
Dynamic’s are performed in pools where there is little water movement and so the propulsion that is produced in one kick enables the freediver to pause and glide a short distance before needing to kick again. This style uses up less oxygen than performing a continuous kick and so helps to increase distance.
Constant Weight is an open water event and the different environmental factors will mean different monofin styles. On the initial descent of the dive where the freediver is positively buoyant the monofin stroke will need to be continuous and strong. If needed, one hand can be moved to the nose for equalisation but as a result the freediver is less streamlined. As compensation the action of the monofin stroke in Constant Weight can help in equalisation because the undulation of the abdominals help to flex the diaphragm and push air into the mouth or Eustachian tubes. As the freediver continues the descent the monofin stroke can be slowed until reaching negative buoyancy and begins to free fall. After turning to ascend the freediver will again need to have a continuous stroke, however this can now be performed streamlined with both arms held above the head to reduce drag. As the freediver nears the surface the stroke will slow and stop completely upon reaching positive buoyancy.
Conclusion
There is still very little research of the freediving monofin especially its performance at depth. New designs of monofins are already being developed and undergoing experimentation and will continue to evolve along with technological advances.
What is apparent is that when there is good technique, the monofin is faster and more efficient than bi-fins. To view a well performed and disciplined monofin stroke of a top freediver is a mesmerising sight and may be a glimpse to our past before we evolved to walk on land.
Bibliography
Book: ‘Manual of Freediving’
Author: U. Pelizzari & S. Tovaglieri
Paper: ‘Functional model of monofin swimming technique based on the construction of
Neural networks’
From: Journal of Sports Science and Medicine’
Author: B. Ochmann & M. Rejman
Web Sites
http://www.leaderfins.com/cgi-bin/form.cgi/63eng?id=202&tm=1181163402
http://www.tochingoinc.com/monopalme-ang.html#historique
http://en.wikipedia.org/wiki/Composite_material
http://www.leaderfins.com/cgi-bin/form.cgi/63eng?id=202&tm=1181163402
http://www.akasha.be/dolphins-place/monofin.html
http://www.tropol.cz/index_en.php?id=sport_tech_info_en
http://www.wind-water.nl/dolph_0.htm
http://www.auf.com.au/PDF%20Files/Monofins%20For%20Freedivers%20Article%20for%20web%20site.pdf
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