IT’S JUST NOT NATURAL,” I protest loudly. “Breathing under water You’re crazy!” Mr Paul Vincent Toomer gives me one of his hard stares, the sort no-one wants to receive. “Bloody freedivers!” is his response.
We’re facing off either side of a Poseidon MK V1 recreational rebreather, thanks to DIVER. The magazine has found out that I don’t scuba-dive, and Paul doesn’t freedive, and it wants to see what would happen if we taught each other.
And it has added closed-circuit diving into the mix, now that it’s possible for a complete novice to obtain a recreational CCR certification.
Here I must pause to confess that I have twice used a scuba set. Twenty years ago I did a try-dive in Indonesia. The sole instruction I was given was “don’t stop breathing”, before I was dragged unceremoniously around a reef for half an hour.
The second time was in the Blue Planet Aquarium for a film shoot, unfortunately timed for the daily shark feed. Neither experience ended particularly well, and as I started freediving and it became my career, it never crossed my mind to get back into the water with a scuba set on.
Perhaps it was the fact that my introduction had been less than ideal, but analysing my reticence, two things come up. The first is the sheer weight of a set of tanks compared to, er, nothing, and the filling, servicing and faffing about associated with it.
The second is my fear of relying on a piece of kit that could go wrong. With freediving, I am in complete control of how deep I go and for how long, and that feels very safe.
Despite all the safety checks I know go into a scuba dive, I’ve seen enough freeflows and other incidents to make me extremely nervous about tank-diving.
The Poseidon rebreather aims to take any uncertainty out of recreational diving, as it won’t play ball unless it is completely happy with all the pre-dive safety checks.
The other integral part of keeping me safe is the incredible Mr T. Paul Toomer has been there, done that and got the tattoos and hearing damage to prove it.
Rock-star and tech-diving legend, he is also a gifted teacher, making the extremely complicated very clear and never once showing any frustration about being saddled with a Luddite newbie such as myself.
Mask, snorkel and fins were the height of complication for me, so being faced with the MKV1 felt like a caveman being given a computer. Paul started off with it completely disassembled and got me to put it together, talking me through each part and the checks needed.
Despite the gadgetry, the theory is quite simple. You exhale air down the right tube which is then passed through a scrubber to remove CO2, and then inhale through the left tube, with oxygen sensors adding extra O2 when the partial pressure dips.
Diluent gas is added to the mix when you descend, to prevent the volume of gas in the loop decreasing.
The diluent also serves as a back-up system, containing enough breathable gas to get you to the surface, and a simple switch on the mouthpiece takes you from closed- to open-circuit.
It’s also lighter and smaller than a traditional open-circuit system (18kg ready to dive), has three hours’ typical dive-time with no deco stops, and the silence and lack of bubbles of closed-circuit apparatus means less disturbance of life under water.

IT MAY BE LIGHTER than a normal scuba rig, but for someone who thinks her weightbelt needs to be carried by someone else, the rig seemed to weigh a ton.
Paul has considerably more muscle power than me, so helped me in and out of it in the classroom as we went through the operation and safety checks.
The computer cycles through 55 safety checks before allowing you to use it in the water. Fail one and it’s back to the start, after sorting out the problem.
This became very frustrating for me as Paul, with the patience of a saint, changed solenoids, O-rings and batteries until we were ready to go. The upside, of course, is that you know when you step into the water that the MKV1 has your back.
Unless you do something daft, like take the mouthpiece out in closed-circuit mode (thus flooding the system, making you super-heavy and sending you down very quickly), your diving should be very safe.
The MKV1 also has a HUD (head-up display), so if it wants you to look at your computer the mouthpiece vibrates and a red light flashes in your field of vision.
With five separate warning systems, try to do what the machine deems to be unsafe and it will annoy the hell out of you until you come back into line.

ONCE WE MOVED from the classroom to the pool, putting the MKV1 on felt very alien. I immediately felt that I was floundering. Used to feeling in control and sometimes even graceful, to have equipment on my back took quite some getting used to, with seemingly no ability to control my movement and buoyancy.
This was coupled with having to exchange my freediving fins for short, heavy scuba fins which, despite the reduced size, felt difficult to use.
One major difference between open- and closed-circuit diving is in buoyancy control. With open circuit you can control your movement with your lungs, but with closed circuit this goes out of the window.
Part of the rebreather set-up are the counter-lungs that inflate and deflate in opposition to what your lungs are currently doing.
This means that there is never more than one breath in the loop, and that this breath doesn’t go up or down, because everything you breathe out stays in the system. You can add more gas in, but it doesn’t affect buoyancy the same way as in scuba.
You therefore control your buoyancy primarily with the BC which, in a shallow pool, had me bouncing up and down like an ungainly yoyo. In shallow water it became a matter of tiny amounts of air in and out affecting buoyancy, which was very difficult to control.
When I was firmly anchored at the bottom of the pool doing safety skills, I didn’t have to worry about moving, just breathing. This was strange enough for a freediver, but then my mask had to come off completely, stay off for a minute and then be put back on and cleared.
This may be a standard skill, but it’s one that’s no fun. On a freediving course we do mask-off skills, but they are at depth, include coming back to the surface, and you can keep your eyes closed.
Here I was in one place, feeling the water against my face, checking the computer and trying (against my better judgment) to breathe!
With breathing, to my mind a closed-circuit system has pros and cons. One huge advantage is that the air you breathe is warm. I remember, even two decades ago, the cold and dry air of the scuba tank.
Another massive advantage is extended dive time and an absence of bubbles that might scare away fish.

FOR ME THE DISADVANTAGE lies in the short supply of gas available to breathe in and out. When we get ready for a freedive, our breathing patterns change, depending on what we’re doing. So when we prepare at the line, our breathing is very soft and gentle, as if we’re falling asleep.
Just before we go, however, we are completely emptying and then filling our lungs. And even within that, sometimes I yawn during the breathe-up, so the volume of my lungs varies considerably.
In addition, being a freediver and yoga teacher, I have a very flexible diaphragm and rib-cage and am used to taking in large volumes of air easily and freely.
This is just not possible with a closed-circuit system, as you are limited to an extent by the volume of the counter-lungs.
When you descend, and increased pressure causes the volume in the loop to decrease, you take a breath in and uh, where has the gas gone
To get more diluent into the loop you then have to strongly inhale. This pulls in more gas, but never as much as a full inhale. Paul explained to me that I had to regulate my breathing to a small amount in and out, and being unable to expand my lungs fully whenever I wanted was a massive adjustment for me.
At the other end of the scale, on the ascent, when the volume in the loop expands there has to be a way of venting the gas, so now you exhale through the nose until you once again have a manageable amount of gas in the system.
Despite my being a self-confessed technophobe who once failed a computer skills exam at the first hurdle after spending an hour failing to find the on-switch, the MKV1 is a thing of beauty.
And despite the simplicity of freediving equipment, I can see the attraction of shiny, clever kit, and it is testament to the incredible power of the human mind that machines such as this exist.
Freedivers may use physiology honed over millions of years, but the MKV1 elevates us from aquatic apes to masters of the underwater world.

AFTER MY LESSONS FROM GURU TOOMER, it was time for him to become the Padawan as I took his toys off him and introduced him to a new world, via the SSI Level 1 Freediving course.
“I feel naked!” he roared. “Where’s my stuff!” I mollified him slightly with a pair of long fins, and got him in the water to see what I was dealing with.
The advantage of teaching someone who has so much in-water experience to freedive is that they are supremely comfortable in and under the water.
The disadvantage is that their water skills, perfectly suited for scuba or rebreathers but not for freediving, have become so instinctive that it is very difficult to get them to unlearn them and try something new.
Paul found the breathing easy to master and had no issues at all with confidence or equalisation, hurdles that most novice freedivers battle to overcome.

THE FIRST ISSUE to arise was with his finning. The classic “trim” of a scuba or CCR diver is to have the head up to look at computers and see where they are going, the arms held in front of the body, and the knees bent with the fins out of the way. The finning style is also gentle, with no real forward stroke because it would affect the line of the body.
Comparing the trim of such a diver to a freediver, one is a banana and the other
a cucumber, and Paul had to be slowly straightened out…
With freediving, the body position is all about hydrodynamics and ease of equalisation. Unless specifically looking for or at something, the head is always tucked in. This not only helps with profile in the water, but makes fast and efficient equalisation much easier, as there is less strain on the eustachian tubes.
The arms are usually flush with the sides of the body, and the finning has an equal forward- and back-stroke.
When finning for freediving, the legs should move as if you are walking, with almost straight legs and an equal movement forward and back.
The difficulty people find is that when you put long fins on, you suddenly have to use a lot more strength on the forward stroke, which is usually weak or non-existent. As a result, you descend at a sharp angle, rather than straight down.

PEOPLE OFTEN THINK OF FREEDIVING as simply being about diving up and down
a line. However, the point of being able to dive up and down a line is that it makes your leisure diving much more efficient. If you can get straight down easily, you have longer under the water to pootle about.
Freedivers also learn an equalisation technique known as the frenzel, for quick and efficient equalisation, and this was yet another thing with which Paul had to become familiar.
Most of his equipment we ditched for freediving, but the equipment he did use was very different to scuba or CCR.
Apart from the long foot-fins, the masks have a much lower volume, snorkels are simpler, and weight is worn on a rubber belt, tightly fixed to the hips so as not to inhibit breathing.
Paul’s biggest issues came with his head and arm position and his finning, which
I corrected at the surface and also under the water by swimming down behind him and encouraging his head to tuck in, and attempting to straighten his legs.
He was a fantastic student and determined to get things right, with most dives ending with a roar of frustration at himself and a few words that reminded me of the ducks that were bobbing about.
Apart from trim, another wholly natural and sensible habit for scuba or CCR divers is to look constantly at their computers. With freediving we teach that for most dives you never look at it. We know how deep the students are diving, and we want them to keep the body position and concentrate on equalisation and technique rather than be distracted.
Freediving computers can have depth alarms set, and these alert you as to when you need to do your mouth-fill for deep diving, but this is an aural alarm – you don’t need to look at a screen.
Paul kept instinctively looking at his computer and forgetting to fin correctly, tuck his head in, or take his snorkel out of his mouth, a safety no-no for freedivers.
However, thanks to his perseverance and determination to get it right, he was soon diving naturally down the line and executing the safety drills and skills for the Level 1 course.

KEEN TO GO DEEPER and explore more that Vobster had to offer, I took him to the sections of the aircraft that start at around 10m. This is often a challenging experience for scuba or CCR divers who are familiar with Vobster, because they are used to breathing under the water while swimming around the plane.
First I took Paul to the top of the mid-section, then again to look through it, then to swim along the outside, and finally to swim through.
He was as cool as the cucumber I had turned him into, and was soon swimming down to the front section, in through the side door and out the back, making it look as if he had been freediving for years!
Finally out of the water after our epic exchange of skills, we discussed the differences between CCR and freediving. Both underwater activities, the differences massively outweighed the similarities.
It wasn’t just a case of choosing whether or not to breathe under water – there were also different equalisation skills freedivers needed to learn, different kit, different breathing techniques, finning style and body position.
What I found so gratifying was the effect a freediving course had on Paul. Walking round Vobster enduring the taunts of “Lost your tank”, he replied with: “Mate, you’ve got to do this!” before turning to his phone to enthuse to his friends about how freediving would improve their tech diving.
For my part, it only increased the respect I have for people who have the patience, knowledge and skill to use equipment under the water.
The MKV1 is an incredible piece of kit, and for a total novice to now be able to enjoy the benefits of CCR diving, it can only be a good thing.
Freediving and CCR diving are poles apart, but being able to do one certainly makes learning the other easier!

Emma Farrell is a freediving instructor-trainer with AIDA and SSI who has taught in the UK and worldwide since 2003.
A founding member of the AIDA education commission, she helped write its freediving education system. She has also written her own courses for scuba-diving “gas guzzlers”, monofin and spearfishing safety courses, and a book, One Breath, a Reflection on Freediving.
Emma has worked with Olympic medalling athletes to improve performance through freediving and yoga techniques. She has competed internationally, coming second in one competition despite being the only female entrant, and is a competition judge.
Based in Somerset, Emma runs Go Freediving (www.gofreediving. with a team of instructors, teaching in the UK and abroad.

Emma Farrell is a freediving instructor-trainer with AIDA and SSI who has taught in the UK and worldwide since 2003.
A founding member of the AIDA education commission, she helped write its freediving education system. She has also written her own courses for scuba-diving “gas guzzlers”, monofin and spearfishing safety courses, and a book, One Breath, a Reflection on Freediving.
Emma has worked with Olympic medalling athletes to improve performance through freediving and yoga techniques. She has competed internationally, coming second in one competition despite being the only female entrant, and is a competition judge.
Based in Somerset, Emma runs Go Freediving (www.gofreediving. with a team of instructors, teaching in the UK and abroad.