Bookshelf: SEALAB

SEALAB – Ben Hellwarth


In the 1960s the US Navy developed three undersea habitats, in order to experiment with saturation diving and to explore the possibility of humans living on the ocean floor. Of necessity, any group of people engaged in this pursuit would be separated from life on the surface, in some cases by days or weeks of decompression obligations. SEALAB I, II and II were progressively deeper and more complex habitats. Developing them was a technical challenge that led to many advances that we benefit from today. The experiments also provided an opportunity to study the psychological and physiological effects of isolation, and of long periods of breathing mixed gases under pressure.

The SEALAB experiments took place during the same era as the efforts by NASA to put a person on the moon, and received far less attention. Jacques Cousteau was interested in the project, and himself experimented with underwater habitats called ConShelf I, II and II. These habitats were far better publicised than the US Navy’s efforts, even though their aims were more modest.

Author Ben Hellwarth does not confine his attention to the habitats, but also provides a fairly detailed history of decompression theory and diving history. Like Neutral BuoyancySEALAB might provide a relatively painless introduction to dive theory for Divemaster candidates. In fact, this book reads like a thriller at times! Some photographs from the SEALAB projects are available on the US Navy website, and in this slideshow. To our modern eyes, the clunky and primitive appearance of some of the gear is a reminder of how pioneering the now 60 year old work to allow humans to live and work in the sea was.

If you’re interested in the history of saturation diving, I recommend this article, which covers some of the ground that Hellwarth does in SEALAB. If you want to see it in action, check out Pioneer (fictional movie based on actual events) or the series Deep Sea SalvageYou should also check out this article by Hellwarth, entitled The Other Final Frontierand this podcast/radio show. If you are EXTREMELY interested in this subject but don’t want to read a book, try out this hour-long lecture video by Ben Hellwarth.

Experiments with underwater habitats are ongoing.

Get a copy of SEALAB here (South Africa) otherwise here or here.

Movie: Pioneer


In the late 1960s, massive oil and gas deposits were discovered in the North Sea, transforming Norway into one of Europe’s wealthiest nations. Pioneer depicts some of the early, feverish oil-related activity during the 1970s. The Norwegians needed to build a pipeline to bring the oil to land from depths of up to 500 metres. Lacking the technical expertise – particularly with respect to the underwater work that must be done by saturation divers – they bring in American assistance.

Norwegian divers (so-called “pioneer divers“) dived to depths that are now considered unsafe, even for saturation divers, and a group of them have sued the Norwegian government for compensation for damage incurred during their careers in the early days of the oil boom. Pioneer tells the story of Petter, a Norwegian diver who is present during a diving accident and embarks on a search for the cause, believing that human error was involved and that someone must take responsibility.

I enjoyed the film enormously, but most of the reviews I have read found it a bit turgid. The milieu is evoked with incredible attention to detail, including the awful 1970s moustaches and unfortunate hairstyles. The dialogue is in both Norwegian (subtitled) and English. It is beautifully filmed, with clever camera work mimicking the limited view that the divers have while working underwater and in the saturation chamber. The underwater scenes are excellent, reminiscent of those in For Your Eyes Only (I’m joking – they genuinely are extremely convincing and quite magnificent). Tension is maintained throughout, and the action takes places over a fairly short period of time.

You can get the DVD here (South Africa), here or here.

Suunto D6 in full panic mode (part II)

Yesterday I told you about a dive on Doodles, a reef in southern Mozambique, during our trip to Ponta do Ouro last month. Doodles has a maximum depth of about 14 metres. After forty five minutes’ dive time, my Suunto D6 began to register extreme depths (89 metres maximum), and to give various instructions about decompression ceilings and times, accompanied by strident warnings about exceeding my PPO2.

Suunto D6 after missed decompression
Suunto D6 after missed decompression

While annoying and potentially dangerous to lose the services of my dive computer mid-dive, it was also an excellent learning opportunity. Because I usually try quite hard to be safe and not to upset my computer, and dive within the conservative, recreational limits that I am trained for, I never get to see any of this behaviour from the instrument. (Fortunately the dive was shallow and I still had plenty of no-decompression time left so it was far from an emergency situation.)

After the dive, I soaked the computer in warm fresh water, and it gradually came out of dive mode over a period of about ninety minutes. During the course of this simulated ascent, the required decompression times and depths calculated by the algorithm were not adhered to, so the computer entered an error mode, which, according to the manual, indicates that “the risk of DCI has greatly increased.” (In fact, from all the beeping and flashing, I suspect the computer thought I was dead or close to it.) This error mode does two things: it disables the dive planning capabilities of the computer, and it locks you out of dive mode for 48 hours.

The D6 in gauge mode
The D6 in gauge mode

I had never gotten the computer into this state before, so I was keen to see how it behaved when I took it on a dive in error mode. You can see in the photo above that I am wearing Tony’s Mares Nemo Wide (aka the flatscreen TV) to give me actual information about my no-decompression time, depth and dive time, but I took my D6 along for the ride. It is in gauge mode; this means it gives you only measurements, and is the setting a free diver might use.

The measurements available in gauge mode are: depth (18.4 metres in the photo above), the maximum depth you’ve been to on this dive (19.9 metres), an elapsed dive time (17 minutes), and water temperature (not shown) but it refuses to calculate a no-decompression limit for you. This would usually appear where the Er appears in the picture above.

Depth profile (with warnings)
Depth profile (with warnings)

For your enjoyment, here’s another screen shot of the dive profile from MacDive, with the warnings expanded. Click on the image to see it full size. It is clear that the first warning beeps I heard during the dive were because of elevated PPO2 levels. At 89 metres the device immediately put me in deco, and then as it “ascended” fairly rapidly, it gave a warning about oxygen toxicity (OLF or oxygen limit fraction as used in the Suunto algorithm) and an ascent rate warning. On the right, at about 10 metres, a warning is given that the depth is still below the required level to complete the decompression.

All the green circular icons appearing around the middle of my dive, where the computer thought I was at 35 metres, indicate that the computer registered that I surfaced, but not for long enough to show on the dive profile. Weird!

My D6 remained angry for 48 hours after the dive at Doodles; by this time, we had finished our diving for the week. I’m not sure whether the problem with the pressure sensor is a permanent one (requiring repairs, a service or a new dive computer), or whether it was just dirty or stuck and will have resolved itself next time I dive with the instrument. I’ll be wearing a spare dive computer when I do, just in case.

Surviving underwater in an air bubble

A news story in June resonated uncomfortably with me: a Nigerian sailor survived for two days in a pocket of air trapped beneath the tugboat he was in, which capsized in heavy seas. The tug was servicing an oil platform off the Nigerian coast.

I was immediately reminded of the Miroshga, an unseaworthy whale watching vessel that capsized in appalling conditions off Hout Bay in October 2012. The boat had its bilge pump installed UPSIDE DOWN, and was rated for over 40 passengers when it’s only five metres longer than our boat – which can take seven passengers (and when Seahorse is fully loaded, she feels full). Furthermore, the Miroshga hadn’t had a SAMSA inspection since fundamental changes were made to the vessel and its engines. The money-hungry decision to head out in a 25 knot south easterly wind and high seas was incredibly irresponsible.

Most people who go on seal cruises, whale watching or cage diving don’t spend half their lives on or near the sea, and simply don’t have the tools to assess whether conditions are safe and whether the boat is seaworthy. The passengers trusted the charter operator and SAMSA, and were badly let down. One man drowned, and three women were trapped under the boat in pockets of air for several hours, their limbs dangling in the freezing water, until rescue divers brought them out. I cannot imagine how traumatic the experience was for them. The rest of the passengers were rescued by a boat full of poachers, and by some incredible NSRI volunteers. It was a shameful day for the boat charter operators, and for those responsible for legislating and enacting maritime safety provisions in South Africa.

I digress. What happened in Nigeria? Out of the twelve crew on board the tugboat, ten bodies were recovered, one was lost, and the twelfth crewmember, Harrison Okene, was discovered alive, under the boat in 30 metres of water, surviving by breathing from an air pocket. Upon being rescued by divers sent to retrieve the crew’s bodies (can you imagine their shock at being greeted by a living person when they were expecting only corpses?), Okene had to undergo sixty hours of decompression in order to avoid being bent. He’d been breathing air at four atmospheres for two and a half days!

The incident prompted a fascinating discussion on StackExchange, a discussion forum for a variety of disciplines (I lurk in the statistics and quantitative finance forums). A user posed the question:

How large does the bubble have to be so that a person in it can have indefinite supply of breathable air?

The reason it’s even possible to have an “indefinite” supply of air is that if the bubble is large enough, oxygen will diffuse out of the surrounding water back into the bubble, and carbon dioxide won’t build up to fatal concentrations. You can read through the discussion if you want to (fun to see physicists arguing, nice if you like formulas!) or there’s a news article here about the theoretical bubble size that would be required for survival. Turns out the actual air bubble was close to the size calculated by the physicists that would allow survival for at least the time that Okene was submerged. Lucky, lucky man!

Update: Here’s the helmet cam video from one of the rescue divers who brought Mr Okene to the surface. The text at the beginning is wonky – persist. Note the South African accents! The diver’s voice is squeaky – I think because he’s breathing a gas mix with helium in it. It gets good at about 5:30 but it’s extremely interesting to watch in its entirety to see what sort of conditions these divers work in, and how the surface support talks them through their tasks and keeps them calm.

Series: Underwater Universe

Underwater Universe
Underwater Universe

The four episodes of this History Channel series cover waves, tides and currents, predators, and pressure – all powerful features of the ocean that can be sensationalised (some more easily than others) and presented for shock value and as imminent threats to human life. Full advantage is taken of this fact.

This very American offering doesn’t boast the measured, mellifluous tones of Benedict Cumberbatch or Steve Toussaint as narrator, but the line-up of (mostly in-studio) guest narrators is quite impressive. Bruce Parker (The Power of the Sea), Susan Casey (The Devil’s Teeth and The Wave), David Gallo (scientist presenter of the TED Talk I mentioned here), Scott Cassell (student of the Humboldt squid), Richard Ellis (writer of a number of ocean history, art and science books), and Neil Hammerschlag (shark scientist) were familiar to me, as was big wave surfer Ken Bradshaw, from this article. The strange, uncomfortable way in which the studio narrators were filmed, with silent close ups interspersed with talking, was very annoying and must have been incredibly embarrassing to shoot. Or perhaps the cameraman took the footage when the narrators didn’t realise they were being filmed.

Unlike BBC documentaries, which tend to rely purely on incredible photography and fluent narrative to convey information, the History Channel favours a CGI-heavy approach that we encountered in Treasure Quest, Deep Sea Salvage, and also in the National Geographic Shark Men series. For the subject matter of this series – particularly the sections on waves, tides and currents – it was very appropriate and informative. The first episode, devoted to tsunamis, rogue waves and “monster waves”, made good use of CGI to illustrate the concepts as they were explained. The series was produced shortly before the Japanese tsunami of 2011 (there is a hastily tacked on “thoughts and prayers” disclaimer) and features interviews with a survivor of a tsunami in Samoa. I am fascinated by rogue waves – the whole episode could have been devoted to them but they don’t make for good television – we only have indirect evidence of their existence. Also, I could have done with more footage of giant ships battling storms, but that’s what youtube is for…

The least interesting and most irritating episode was the one devoted to the ocean’s top predators, which suggested that orcas are a serious threat to humans. As evidence, the cases of captive killer whales drowning and injuring their trainers at marine theme parks were cited. No mention was made of the psychosis that these whales suffer from as a result of confinement in a small, barren, completely unnatural environment. An incident in which orcas inexplicably rammed and sank a yacht in the Pacific Ocean is also described and re-enacted. Whether the orcas did what they did because they wanted to kill the people on board is highly debatable. There is also a half-hearted attempt to paint whales as potentially vicious killers, recounting incidents when sperm whales rammed whaling boats in the 19th century. More power to the sperm whales, I say.

The other dangerous predators were (predictably) white sharks, Humboldt squid, saltwater crocodiles and Australian box jellyfish. There was a small environmental message at the end of this episode, mentioning that squid will probably end up the top predators in our oceans if current trends – fishing out large predatory fish and global warming in particular – continue.

The third episode, on the immense pressures that objects in the deep ocean are subjected to, was very interesting to Tony and me as divers. A confusing interview with a diver whose brother got DCS on a wreck dive leaves (I suspect) much out. Were they even qualified divers? Why was he surprised that his brother felt unwell and confused as to the cause after he popped to the surface from 30 metres after a 30 minute dive?

The bulk of the third episode, however, recounts a 1981 experiment called Atlantis III in which three volunteers were taken in a saturation system to a simulated depth of 686 metres while breathing Trimix 10 (70% helium, 20% nitrogen and 10% oxygen). It took 31 days for them to decompress. The chief of the experiment, Peter Bennett, was the founder and former CEO of DAN. There’s a more information about the project here – worth a read (download the pdf slowly), and a briefer account here.

The series concludes with an episode on tides and currents, including rip currents. The massive tidal range of Morecambe Bay in the United Kingdom,  is discussed at length. At low tide, up to 300 square kilometres of mudflats is exposed, and flooded again when the tide comes in. The guides who escort people out onto the mudflats when the tide is out seem like charming individuals – it is recommended not to wander around at low tide without local guidance. In 2004, the rising tide trapped and drowned 23 Chinese immigrants who were working the cockle beds – with such a large expanse of land to cover, the rising tide comes in at great speed. There is also a harrowing re-enactment of a father and his two sons getting washed out to sea in a rip current in Kauai that should make you think twice about swimming at beaches with warning signs on them.

You can get the DVDs here if you’re in South Africa. Foreigners, go here or here.

Movie: For Your Eyes Only

For Your Eyes Only
For Your Eyes Only

A Top Gear special about James Bond’s cars put us in a frame of mind to enjoy some vintage Bond. Tony thinks Roger Moore was the best Bond; I am torn between Sean Connery, Timothy Dalton, and Daniel Craig. For me, Roger Moore is at the bottom of the list (jostling for position with George Lazenby). Chronology, Tony’s fondness for Moore, and the fact that we only have about three James Bond DVDs swayed us towards a re-viewing of For Your Eyes Only.

For Your Eyes Only doesn’t only feature a convoluted plot, ridiculous foreign villains with hilarious accents, and a ridculous foreign Bond girl – also with an hilarious accent. It also contains extensive underwater footage that can teach us about the behaviour of sharks, what to wear when diving (yellow PVC overalls and gumboots), and how to manoeuvre a hard diving suit inside a shipwreck.

That said, the underwater scenes are surprisingly slick and well-shot for a movie made in 1981. They were filmed in the Bahamas. Carol Bouquet, the actress who plays Bond’s main squeeze, Melina, apparently had a sinus condition that prevented her from doing underwater stunt work, so the close-ups of Moore and Bouquet were filmed on a sound stage with fans blowing and special lighting. Bubbles were added afterwards. If I’d had this knowledge when I watched the film I’d have looked more closely at those sequences; without knowing they were filmed on dry land, I admit that they are very convincing.

In the screen capture below, I’ve grabbed a moment of the action as Bond and Melina take a submersible down to a shipwreck (the St Georges) lying over 100 metres under the sea, and exit at depth to penetrate the wreck and retrieve a very important computer. They run across the sand in their yellow gumboots. While inside the wreck they encounter a villain in a hard one-man diving suit, and a vigorous battle ensues. They blow him up, but are unaffected by the concussion despite being only a couple of metres away when his suit explodes. Upon returning, victorious, to their submersible, they are set upon by another villain in a one-man submersible with various pointy bits and cutting devices. There is an extended wrestling match between Bond’s submersible and the villain’s.

The divers race across the ocean floor from their submersible
The divers race across the ocean floor from their submersible

Curiously, although both Bond and Melina are breathing a mixture of helium and oxygen (because they’re diving so deep), their voices are unaffected by the helium, and sound completely normal. They also move through the water with remarkable ease, and – mysteriously – a large amount of light penetrates down to the shipwreck at 100 metres. No mention is made of the decompression obligation they’d have after their underwater high jinks.

If you want to combine a love of diving with a fondness (or love) for James Bond, you could do a lot worse than For Your Eyes Only. You can also check out Thunderball. You can get the DVD here if you’re in South Africa, otherwise here or here.

Bookshelf: The Last Dive

The Last Dive – Bernie Chowdhury

The Last Dive
The Last Dive

The Last Dive is a number of things: a history of how cave diving techniques came to be applied to advanced wreck diving (use of lines for wreck penetration, for example), the story of the early days of mixed gas diving in the United States, the chronicle of the close-knit bands of divers who risked their lives to explore the cold, deep waters off the north Atlantic seaboard of the USA and retrieve trinkets from the many vessels wrecked there, and a biography of Chris and son Chrissy Rouse, who were involved in all of the aforementioned threads of the tale. The central subject of the book is the Rouses’ death while (or just after) diving on the German U-boat discovered by a local dive boat skipper.

I first encountered the Rouses in Robert Kurson’s book Shadow Divers, a gripping read about the efforts to identify the same mysterious German U-boat that the Rouses perished on, off the coast of the US, and Deep Descent, which describes diving on the wreck of the Andrea Doria and features many of the same divers and dive charter operators. Their relationship is (perhaps too) sympathetically portrayed by author Bernie Chowdhury, a friend of the family.

The Rouses were extremely technically proficient divers, but their downfall seems to have been their fraught and fractious relationship that was characterised by vicious bickering and name-calling that stopped only when they put regulators in their mouths to descend into a cave or onto a wreck. Chowdhury shows how their difficult (but ultimately loving) relationship led them to doing a dive (their final one) onto the U-boat when the conditions were decidely sub par. Their choice to dive to over 80 metres on air, when they were proficient in mixed gas use, as well as what seemed to be the firm conviction of Chrissy (the younger) Rouse that he was immortal, also appears to have contributed greatly to their deaths.

Both Chris and Chrissy Rouse died of DCS – Chris died in the water within minutes of surfacing, and his son Chrissy hours later in a recompression chamber. They had both ascended rapidly without any decompression stops, from a longer than planned dive to over 80 metres, having lost their stage cylinders in their disorientation after emerging from a disastrous penetration of the submarine during which Chrissy became trapped under a fallen book shelf and a self-inflating life raft.

Earlier in the book, Chowdhury describes his own experience of very serious decompression sickness, which gives great insight into how debilitating (if not fatal) the experience of being bent can be. His enumeration at the end of The Last Dive of the serious physical conditions now prevalent among divers of his generation who have persistently pushed the envelope and, in many instances, been bent and recovered, serves as a cautionary tale to those who believe that no-decompression limits are for wussies.

As I expressed in my review of Deep Descent, I strongly disapprove of the macho cowboy attitude that seems to be (have been?) disturbingly prevalent among the divers and charters of this generation (and not limited to the United States). But Chowdhury’s book is more than an ode to the glory days of artifact retrieval and experimentation with trimix. As a history of cave diving, mixed gas diving and advanced wreck diving it’s invaluable. As a diver himself, conversant with all these disciplines, Chowdhury is able to explain in simple terms concepts that would slow down someone who hasn’t done a dive course. The book is very readable despite the technical subjects covered.

Chowdhury does not conclude that the risks taken to achieve what this particular group of divers did were unreasonable, and does not overtly criticise the Rouses for the attitudes and behaviour that – I think most sensible people would agree – contributed to their deaths instead of just a scare that might have forced an adjustment to the dive plan. While he admits to having experienced times of ambivalence about diving, particularly when he describes the strain it placed on his relationship with his wife and son and the long road to rehabilitation that followed his episode of the bends, his equilibrium surprisingly undisturbed by the loss of several friends and acquaintances to the sport he loves, and his own health difficulties.

For some more perspectives on this book and the perceived accuracy of the descriptions of the events it covers, you can read this review and this discussion.

You can purchase the book here if you’re in South Africa, and here if you’re not. The Kindle edition is available here and here.

Oh, and go sign up for some DAN insurance, please?

National Hyperbarics

Exterior of the hyperbaric chamber
Exterior of the hyperbaric chamber

Clare and I took a tour of the National Hyperbarics facility at Kingsbury Hospital earlier this year. This is a specialised clinical hyperbarics facility, where they use a recompression chamber to treat diving injuries as well as to provide wound care. Breathing oxygen at an elevated pressure (higher than atmospheric pressure) is beneficial to healing of wounds, and also part of the first aid for decompression sickness.

In contrast to the chamber we did our chamber dive in at UCT, the National Hyperbarics chamber is for medical purposes. It’s equipped with comfortable seats for eight patients, and oxygen masks and monitoring equipment for each patient. It’s rated to 30 metres so actually wouldn’t provide a very exciting chamber dive experience despite the creature comforts!

Interior of the chamber
Interior of the chamber

The team at National Hyperbarics are almost all (I think) scuba divers, and on occasion I have referred my students to them for assessment before signing up for a dive course. In addition to providing and monitoring hyperbaric oxygen therapy, the doctors are able to advise and prescribe treatment for divers with asthma and other concerns which may require medical clearance before getting in the water.

Control panel for the hyperbaric chamber
Control panel for the hyperbaric chamber

In the event that you have a diving accident in Cape Town, this is probably the chamber you’ll end up in. If you’re a DAN member (which you should be), DAN will arrange transfer to National Hyperbarics for you. If you’re not, you’ll have to contact them yourself to arrange for a medical technician to meet you at their Claremont facility should you require recompression treatment. So if you aren’t a member of DAN, visit the National Hyperbarics website immediately and save their contact number in your cellphone.

Update (February 2012): National Hyperbarics is moving from Claremont to Tokai. Their new facility is currently not open, so you can’t use their chamber in the event of an accident. Dive safely!

Update (March 2014): It doesn’t look as though National Hyperbarics is going to open for business again. If you’re concerned about which hyperbaric chamber you’ll go to if you have a diving accident in Cape Town, read this post.

Suunto D6 dive computer

I’ve been using the Suunto D6 dive computer for about eight months now, having finally got my grubby paws on it just after returning from our last trip to Sodwana. I think it’s about time I write a little review of it, because Suunto have just released the D6i and before you know it my computer will be a museum relic.

Specifications and appearance

The D6 is near the upper end of the range of Suunto dive computers – the model I have will now set you back in the region of R10,000 and there are several cheaper but no less effective offerings. The USB interface cable that will enable your dive computer to talk to your computer will set you back up to a further R1,500 – although this item is frequently advertised on special by Suunto stockists and occasionally as a special bundled with the dive computer, so keep your eyes open. It’s far more usual, however, to have to buy this innocuous-looking cable separately, and gasp at the price.

You can choose an elastomer strap or a metal strap (for about R2,000 more). Although the metal strap looks really cool, it’s not really practical if you dive in varying water temperatures and change the amount of neoprene on your wrist frequently. The computer functions as a dress watch if you want to use it as one – it displays the time constantly when not in dive or memory mode – but it weighs more than a slab of chocolate (130g) and is far too large for the average lady’s wrist, so I don’t use it for this purpose except when travelling (to deny the baggage handlers at OR Tambo Airport the privilege of stealing it).

The computer has a four button interface that I find very intuitive, and I could figure it out to a large degree without reading the manual. That said, if you buy a dive computer, YOU MUST READ THE MANUAL! Don’t be a fool – you want to know EXACTLY why the thing is beeping at you, what it looks like when you go into deco, and be very sure (as one clown – who was buddied with us once because he didn’t know anyone on the boat – wasn’t) whether the “3” you see on the screen indicates a time in minutes, your current depth, or the number of brain cells you have. Read the manual!

Air integration and the D6i

The D6 has actually been replaced by the D6i, which is functionally identical but has more internal memory, and is capable of air integration with an optional (heart-stoppingly expensive) dongle that you attach to your cylinder and reads remaining air. The computer will then give you an estimate of remaing dive time based on air consumption to date. I have no interest in this (at the time I bought the D6, air integration was the main distinguishing feature from the D9) – I’d use a pressure gauge regardless, and wouldn’t feel comfortable trusting what I see as an physical, analogue process (displaying the air remaining in my cylinder) to a potentially failure-prone piece of electronics.

I know I may sound like a luddite here, but an experience Tony had on the boat a few months ago confirmed my reservations. Another instructor’s student had an air integrated computer and no pressure gauge (why bother with redundancy?). The air integration with the computer wouldn’t work, but they only discovered this on the boat when they were parked over the dive site, and – after toying with the idea of cancelling the dive, and then swapping kit so the instructor, who should have an excellent feel for his air consumption, had the set up with no pressure gauge – did a very short dive. As a mathematician I can see that having snapshots of your remaining air at 20 second intervals to look at in the dive manager software might be appealing though…

Decompression algorithm

The D6 uses the Suunto Deep Stop RGBM (Reduced Gradient Bubble Model), and allows for continuous decompression as you ascend (instead of forcing you to do stops at particular depths). It also allows you to complete your safety stops at depth – something I haven’t experimented with much, but will be using next time we dive the Lusitania. The computer recommends a safety stop once you exceed 10 metres on a dive, and if you violate the recommended ascent rate it will advise a mandatory safety stop between 3 and 6 metres. I tried to photograph the D6 during a dive where I’d switched on deep stops, but there was a 20 metre layer of green plankton blocking out the light from above, and my flash kept reflecting off the screen protector. Hence the dubious results you see here. I have 28 minutes of no-decompression time remaining, dive time is 11 minutes, depth is 20.9 metres, and my first deep stop will be at 13 metres. Maximum depth (bottom left) so far has been 23.8 metres.

Suunto D6 during a dive - first deep stop is due at 13 metres
Suunto D6 during a dive – first deep stop is due at 13 metres

You’re most likely aware of this, but a dive computer does not measure anything that is going on in your body with respect to dissolved gases. Dive computers use mathematical models – based on the original dive tables, only more sophisticated – that approximate, for the average person, how much nitrogen has gone into solution in the body’s tissues, and how fast it is being released, based on your dive profile. They measure depth temperature, and time, that’s all. For this reason many dive computers, including the D6, have an option for you to set a more conservative calculation algorithm if you’re at higher risk of DCS – for reasons of increased age, high body fat percentage, or any of the other DCS-predisposing risk factors. You can also adjust the partial pressure settings up and down if you so desire, but anything higher than 1.4 bar (ata) strikes me as reckless.

Nitrox and no-fly time

It goes without saying that the D6 is Nitrox capable, and it’s very straightforward to set the Nitrox mix. After one dive on Nitrox, the option to do a repetitive air dive disappears, and you have to manually set the oxygen percentage of your mix back down to 21%. I think this is to force you to think about what gas is in your cylinder. The D6 also handles switching to a richer mix for decompression, and this optional second mix may be set through the same menu system as the primary nitrox mix.

The D6, again like most dive computers, gives a no-fly time after you’re done with diving for the day. This time is usually well under 18 hours, but you’d do well to follow DAN guidelines for flying after diving (usually 18 hours after your last dive) and not bank on the reading given by your computer. Do not be like Gerard, who shall remain nameless, and mistake the time display on your computer for the no-fly time. After a dive on the Aster that ended at about 3.30pm, he announced that his no-fly time was “fifteen hours and twenty nine minutes.” A few minutes later, to his puzzlement, it was “fifteen hours and thirty four minutes!”

Dive Manager software

The Suunto dive manager software, that allows you to examine the details of your dives on your computer screen at home, is not compatible with Apple Macs, so I had to find another solution. I’ll review the software I do use, MacDive, in a separate post. Apparently from “fall 2011”, whenever that rolls (rolled) around, the Suunto software – DM4 – will also be compatible with Apple computers. I’ll test it when I get a chance, and let you know what it’s like… As is apparently wildly popular these days, one can also share one’s sporting activities on the Suunto Movescount site via an automatic link-up from within the software interface. And, no doubt, publish them to facebook.

Electronic compass

Suunto D6 with elastomer strap (right) and titanium strap (left)
Suunto D6 with elastomer strap (right) and titanium strap (left)

One of the major appeals for me of the D6 – and I think the feature that bumps its price up so much higher than the D4 – was the integrated electronic compass, which can be accessed at (almost) any time by holding down the top left (Select) button. In the picture at right, the D6 with the elastomer strap is on the compass display (the one on the right is in the memory log display mode which can’t be accessed during a dive). If you’re not on a dive when you use the compass, obviously the depth and dive time won’t show.

The D6i has updated the compass to allow accurate readings when your wrist is tilted; the old D6 (the one I have) is not as tolerant and you’ll need to keep your arm level as with a standard dive compass. Unfortunately the D6 doesn’t record the compass heading along with the temperature, depth and other dive statistics during the dive – or, if it does, the download software I use doesn’t access it. I suspect the former is true, since I installed Suunto’s own dive manager software on Tony’s PC to check, and there was no sign of compass headings. Boo.

What’s in the box

In the box was the computer, a strap extender, the instruction manual, a disc with the Windows-compatible dive manager software on it, and two or three scratch guards which are trimmed to fit the D6’s screen. I’ve done close to 70 dives with my D6 so far, and the scratch guard is scratched and still doing its job well. Tony’s computer, the Mares Nemo Wide, is protected with some cheap cellphone screen protectors we got from Look ‘n Listen. You can buy a generic size, and then trim it down to fit your phone (or dive computer, as the case may be). We didn’t expect this makeshift scratch guard – which is NOT designed for regular immersion in salt water – to last beyond five or ten dives, but over 100 dives and it’s going strong. I think I paid R60 for the pack of screen protector stickers, and we’ll get nine Nemo Wide-sized ones out of the package.

Buying it

Continuing with the subject of good value, one more tip for the bargain hunters. I actually bought my D6 from Cape Union Mart. They stock Suunto sports watches, and were able to order me a D6 from Suunto in Finland. I had to wait six weeks for it to arrive, and it cost R8,700. What made the deal very sweet was that by buying it on my Discovery Card which gives me a 20% discount at Cape Union Mart (thanks to my years in the Vitality program and points status), the computer ended up costing just under R7,000. I paid a further R1,200 for the download cable (I got that at a dive centre). If you have a few weeks before you need the computer, or are prepared to wait in exchange for some savings, it’s worth getting a quote from Cape Union Mart as to what they’ll charge you. If you’ve got a Discovery Card it’s a no-brainer. Email them via the website for a quotation, and they’ll tell you to print that and take it to your nearest Cape Union Mart to place the order. I had to pay a 50% deposit.

Update (late 2012): Based on feedback from other divers who have shopped for Suunto computers lately, it seems that Cape Union Mart isn’t doing this any more, unfortunately – but it’s worth asking anyway!

Maintaining it

Finally – if you have a dive computer and live in Cape Town, take it to Orca in Claremont to get the battery changed when necessary, and ask for Chris the “worship manager” (that’s autocorrect gone wild on “workshop manager”) to do it for you. Tony’s students have had baaaaad experiences (a hair across the seal, anyone?!) at other locations. There’s usually not much you can do if the service centre doesn’t seal the computer properly and it floods – your only recourse will possibly be to your insurance company.