Dive computer

Responsible diving during a drought part 1: Your dive gear

It is no secret that Cape Town is a little low on water. The coastal dive industry, even though we spend a lot of time in the ocean, is actually quite a heavy user of fresh water. Everything thing you learn about taking care of your equipment revolves around the phrase “rinse well with clean water.” Clearly this is not an option in Cape Town at the moment.

So how do you maintain your dive gear and keep it in safe condition during such circumstances? For a dive centre or training facility the volume of gear that needs cleaning can be overwhelming at the end of the day. Here are a few suggestions on how to manage.

No matter how well you de-kit after a shore dive, wet dive gear tends to collect sand. (You can minimise this by using something like the Wetsac, but this isn’t always an option with my students.) I take the gear back into the ocean and rinse it as well as I can in the shallows. This involves several trips as wet dive gear is heavy.

Wetsuits are rugged and don’t too much mind being left salty. They do end up being a little crispy after a while, but the most important, non-negotiable aspect is hygiene. I take a spray bottle with a mixture of Savlon or Dettol and spray the inside of the salty wet suit, then let it dry. Gloves, booties, hoodies and rash vests get the same treatment.

Regulators get a similar treatment, without the disinfectant. I give them an overall light spray with warm water in a spray bottle, with a good spray into the mouth piece. The inflator hose nipple also needs to be rinsed well as this does not handle salt build-up too well and could get stuck during a dive (at best, annoying… at worst, life-threatening).

Cameras, dive computers, torches and compasses do need a little more care, but fortunately are relatively small and have lesser water requirements. I use a narrow, tall bucket and put the bucket in the shower. While showering you can easily catch enough water to cover these items…. Seldom more than a litre is required, and you can leave them to soak.

The biggest challenge is a BCD. Again, it is a tough and rugged piece of gear, but the inflator mechanism does not like salt build up. Using the same bucket of water used for the camera and dive computers, I soak the inflators overnight. I then connect an airline and inflate and deflate the BCD to help flush out the valves behind the inflate/deflate buttons.

Whilst such basic, minimalistic care for your dive gear is not as thorough as that recommended by the manufacturer, it is a method of extending the use of your gear when the availability of fresh water is close to zero. As a rule I prefer to only have two students per class and can effectively wash three sets of gear in less than three litres of water.

It goes without saying that as soon as it rains, you should be collecting that water to give your gear the long, luxurious soak it deserves (and probably needs by that stage)!

Bookshelf: Scuba Confidential

Scuba Confidential: An Insider’s Guide to Becoming a Better Diver – Simon Pridmore

The natural sequel to Scuba Fundamental (though it was written later), this book is aimed at qualified divers who may have reached a plateau with the sport, and want to improve their skills and explore more of what diving has to offer. Author Simon Pridmore does not shy away from subjects such as solo diving, deep diving and technical diving, and offers valuable perspectives from a lifetime in the dive industry.

Pridmore begins with a subject that isn’t discussed enough (because it would supposedly scare away potential new divers): safety. He talks about why divers die, survival strategies, and the essential mental preparation that should come before diving.

Many divers who have passed the first, awkward stage of their careers on scuba seek to improve their skills. Pridmore discusses buoyancy, navigation, and the touchy subject of deco. The following section addresses some of the specialty options available to divers who wish to extend their qualifications: night diving, wreck diving, drift diving, cave diving, ice diving, and technical diving. While you may decide that some of these types of diving are definitely not for you, there is still much to learn from the techniques and thought processes required to do these types of dives safely.

Pridmore also deals extensively with equipment issues, returning to the subject of deploying an SMB, care and use of dive cylinders, mastering your BCD, and dive computers. In many instances, these items of gear are a matter of life and death, and well worth talking about. Narcosis, nitrox, rebreathers and other gas-related subjects round up the sections of the book that pertain to dive safety.

The final chapters deal with dive travel, with a section on liveaboards and a recap of some etiquette, which becomes increasingly important when one is diving with people one doesn’t know.

This book will satisfy a growing diver’s thirst for knowledge, draw attention to areas that need improvement or reflection, and prompt further exploration of dive-related subjects. It’s an excellent gift for the curious diver in your life.

Get a copy of the book here (SA), here (US) or here (UK).

MacDive – a digital dive logbook for Mac OS X

It was frustrating to discover, when I bought my Suunto D6 in 2011, that a Mac-compatible version of the native Suunto software did not exist. This has changed in the intervening years, but I don’t care – my search for software that I could download my dives into led me to MacDive, and I’ve been using it ever since. Rather than tying me to a single brand of dive computer, MacDive handles almost any dive computer you can think of. The software currently costs $25, which is approximately one million South African Rands at current exchange rates, but it is excellent value and updates frequently as support for new devices is added.

Here’s a screen shot of MacDive, with the ten dives we did in Malta in 2011 selected. The dive profile on the screen is from one of the two incredible dives we had on the wreck of the Um El Faroud. The summary information at the bottom of the screen hides a lot more detail that can be stored about each dive, including gear configuration, dive operator, the name of the boat (if used) and Divemaster, and so on.

MacDive also calculates summary statistics for the dive sites that you load, and allows you to interrogate your dives by country, by date, by the computer used, and even by diver. The software would allow you to share the logbook with another user (or users), and if you look carefully you’ll see Tony’s name on the screen. That’s because I downloaded the profile of his dive at Doodles on that fateful day when my Suunto D6 fell through the bottom of the ocean. When I did that, I specified that he was the diver, and not me.

MacDive is full-featured software that not only allows you to record a lot of detail about each dive, but to add photos if you wish. The software matches the timestamp on the photo to the dive profile, enabling one to have fairly detailed information about depth and temperature when an image was taken (assuming your dive computer and camera have SYNCHRONISED WATCHES). I have exported the data out as a .csv file, which is excellent if you want to perform some analysis of trends in your air consumption, for example, or draw pretty graphs.

MacDive is compatible with a wide range of dive computers – I’ve used it with a Suunto D6, a Suunto ZOOP, and two different Mares Nemo Wide computers – which makes it ideal for a multi-computer family where the backup dive computer may be of a different make to the primary one. A full list of the supported devices can be found here and if your device is not supported, the developers of the software are open to adding it if you submit a request. In most cases the installation of a USB driver is required to make the dive computer talk to the software, but this is a once-off requirement and hardly onerous.

The forums and FAQ have been very helpful when I have had difficulty setting up different makes of dive computer, and the entire user manual is online in wiki format. With reference to the manual I have renumbered my dives to maintain the correct sequence, and merged multiple dives that were interrupted by an interval in water shallower than 1.2 metres that was long enough that my computer decided the dive was over. The database format is very flexible and allows one to keep the sequence of dives looking as neat as they would in a paper logbook.

I have been using MacDive for four and a half years, and have been very happy with it, particularly the fact that it isn’t tied to any single type of dive computer. If you’re looking for an electronic logbook and running the Apple OS, check it out.

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.

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.

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)

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.

Suunto D6 in full panic mode (part I)

On the second dive we did at Doodles during our trip to Ponta do Ouro, something happened that caused my dive profile to look like this (click on the image to embiggen):

Profile (from MacDive) of a dive at Doodles

Fortunately that something was not me falling down an 89 metre deep hole in the ocean floor whilst breathing off a 12 litre cylinder of air, 45 minutes into a dive. It was something going wrong with (we think) the pressure sensor of my Suunto D6 dive computer. I have had the computer for a few years, and apart from the compass appearing to have packed up, it has been a fantastic device.

The first inkling of trouble that I had was when the computer started beeping at me, and when I looked down to see what was up, it said we were at 89 metres. Sunlight was falling on me, so I thought this unlikely. I checked with Christo, and he didn’t think we were that deep either. Nor did his computer. Fortunately I had been diving with a group for a few days, and we were well within our decompression limits at a depth of 14-15 metres. Losing the computer three quarters of the way through a dive wasn’t the disaster it could have been.

I took this picture shortly after the beeping started. The display at the top of the screen shows that the computer is reading 76.7 metres. The maximum depth of 89.0 metres shows at the bottom left. The bottom right shows the oxygen partial pressure, at 1.9. This is greater than the 1.2 limit that I have set for myself inside the computer. The computer thinking that I had rapidly exceeded the maximum PPO2 is probably the initial cause of the beeping I heard.

Suunto D6 showing 76.7 metres' depth — Suunto D6 showing 76.7 metres’ depth

In the middle of the screen you can see a large number 8.0, which is the depth to which the computer wants me to ascend in order to do a decompression stop. Next to that number is an arrow below two horizontal lines, and the number 35. This is how long I should stop at 8 metres in order to fulfil the calculated decompression obligation.

The D6 thinks we have ascended to 47 metres now

After a few minutes (I was actually busy ending my dive with a 5 metre safety stop) the computer believed I had ascended to 47.3 metres. By that stage it wanted me to go to 11 metres for a 45 minute stop. When I surfaced after about 60 minutes of dive time, the computer stayed in dive mode, thinking that I was still at a depth of about 35 metres. It continued registering a slow, quite smooth ascent for another hour and a half, as seen in the dive profile above.

The computer was still very grumpy when it took itself out of dive mode in a mug of warm water in the bathroom of Planet Scuba, while we were eating a post-dive lunch. The ascent profile it registered did not fulfil the calculated decompression obligations, and it showed that I had violated my decompression ceiling (either by taking too long to ascend to start the stops, or by not spending enough time at the stop depth).

I have put myself briefly into deco a few times (usually during days of repetitive diving during dive trips, and once or twice in Cape Town with two relatively deep and long dives in a day), so the readouts from the D6 on this dive are not unfamiliar to me. I have never before, however, seen such large numbers or heard so much beeping! I have always corrected the situation by ascending a little way, which removed the decompression obligation and returned the display to what I am familiar with as a religiously recreational, no-decompression diver. In this case, the D6 was doing its own thing and nothing I did seemed to influence the depth reading it gave.

I found this to be an excellent opportunity to re-familiarise myself with the behaviour of the Suunto D6, and also to see what all the error messages look like on the dive profile when I downloaded the computer into the MacDive software I use for electronic dive logging. The story does not end here – if the computer did not think I was dead from DCI, it wasn’t going to let me dive any time soon – check back tomorrow (or the day after).

Long term test of the Suunto D6

I’ve had my Suunto D6 dive computer for three years, and while wearing it I’ve done 150 dives for a total of 90 hours underwater. I’ve also been a remarkably good girl, diving within my qualifications (PADI Deep Specialty) for a maximum depth of 38.6 metres.

I discovered that my Suunto D6 needed a new battery while waiting at the airport to board a flight to Durban, on the way to Sodwana for three days of warm water diving. Tony had suggested more than once that I check it prior to our departure, but NO, I was too busy and important to do THAT! Fortunately a spare dive computer was on hand, so I dived with one of Tony’s Suunto Zoops on the trip.

(As an aside, the D6 won’t download dives from the computer into the MacDive software when it has low battery. It goes into data transfer mode when you plug it in, but refuses to download – I got error code -7. Once the battery is changed, downloading is again possible.)

Changing the battery on a dive computer can be a fearsome experience – at least in South Africa. Unless you can change it yourself (like the Mares Nemo Wide), it often entails sending the computer to Johannesburg to the agent who imports that particular brand. Then, in a kind of awful lottery, you wait for one of three possible outcomes, all seemingly equally likely:

after the agent acknowledges the safe arrival of your dive computer, a few weeks pass and the agent swears blind he hasn’t seen one of that make for the last five years (this happened to Tony in January)
the battery is changed, the computer comes back, the first time you use it it floods, and you have no recourse to anyone
the battery is changed and the computer works just fine (phew!)

The odds are never in your favour.

Fortunately Duncan at Orca Industries in Claremont is able to change Suunto D6 (and other) batteries. I think he’s the only person in Cape Town who can do the Suunto D series. (It’s a ten minute process, but mine took five days because the computer ended up under a shelf somewhere for four and a half days before Duncan was told about it!)

Overall I am extremely pleased with my D6. I have minor quibbles. These are chiefly related to the intricacies of doing an air dive after a Nitrox dive, and the fact that it weighs as much as a fully grown labrador retriever, so isn’t suitable for most ladies to wear as a watch. I also don’t trust the compass very much, for no particular reason other than it’s digital. It’s great to dive with, though, and I wouldn’t hesitate to recommend it to others.

Underwater selfies

Tony got a new 5 millimetre Mares Pioneer wetsuit to replace his Flexa 8-6-5, which was getting a bit long in the tooth. When I was clearing photos off my old underwater camera, I found this little photo shoot, in which he appears to have been testing his gear in our swimming pool… Under the pool cover.

The water temperature was a sweet 25 degrees, according to the Mares Nemo Wide.

Article: Wired on biometric monitoring of navy divers

Wired.com published an article in their Danger Room section, all about defence, concerning proposed DARPA research on biometric monitoring of navy divers. DARPA, the United States Defense Advanced Research Projects Agency, is the organisation that commissions advanced (and sometimes wildly unrealistic… until it’s realised) research for the US Department of Defense.

One of their latest research proposals is to come up with some kind of device that could monitor a diver’s vital signs while he’s in the water. One of the vital signs that the device should be able to read is the presence of nitric oxide, which works to prevent the bends (decompression sickness: the presence of excessive nitrogen in the blood after breathing compressed air at depth). Nitric oxide would then be added to the diver’s body if the levels of this gas fell too low. There’s a lot more to it…

(As an aside, it would be wonderful if modern dive computers could do this, but they can’t.)

The brief for the required research reads like an excerpt from the script of a James Bond movie. I actually laughed out loud reading the article, but that’s the reason I’m not doing cutting edge research: lack of imagination. It’ll seem ridiculous until someone actually invents it, and you can be sure that it’ll be used in military applications before us civilians get our grubby paws on it.

Read the article here.

Tips on shopping for dive gear

I’ve been diving for a while, owned a lot of dive gear. Here are some tips on shopping for gear, some learned through painful experience!

General rules for buying gear

Try it on before you buy it. Wetsuits, booties, hoodie, you name it.
Try on your BCD and weight belt OVER your wetsuit – two layers of 5 millimetre neoprene adds a LOT of waistline!
Make sure you understand the returns policy of the shop you’re using.
Get acquainted with the Consumer Protection Act (if you’re in South Africa).
Shop around! Don’t let sales people sweet talk you. They are more interested (generally) in making a sale than in making you a happy diver.
Don’t cut the strap of your dive computer shorter unless you’re VERY sure you’re never going to dive in cold water (wearing lots of wetsuit and gloves to make your wrist thicker).

Second hand gear

When purchasing second hand cylinders: get them viz’d first (at the expense of the seller) before agreeing to purchase.
Try and get the seller to allow you to “test dive” expensive items such as dive computers before agreeing to purchase them.
It’s a good idea to check BCDs for leaks before purchasing, unless you plan to use the BCD only for shallow dives, and even then it’s iffy.

Gear to avoid

Don’t purchase based purely on colour (ladies, I know it can be very tempting).
Be realistic about what you will use the gear for. (Do you really plan to dive to 100 metres, under ice with that regulator?)
Don’t fall for wrap around face masks with 3 glass panels (here’s an example) without trying one first – they give rise to very confusing visual phenomena and distort things hugely as they pass across the join in the panes of glass!
Avoid BCDs with inflate/deflate handle handles (example here) – I have never yet seen a beginner diver (and even some divers who have done over 100 dives) using one who was in proper control of their buoyancy.
Neoprene covers on mask straps (example here) usually only work without a hoodie. They have a tendency to slip off your head during a backward roll off the boat when worn over a hoodie (although some people swear by them!).
Smaller volume masks are usually better for beginner divers than huge five litre models! They are much easier to clear.
Do you really need a three foot dive cutlass, as opposed to a small knife?

Repairs

Get a second opinion on extensive repairs.

Dive gear maintenance: Wrist mount gauges

I have a range of different wrist mount gauges as I teach a range of courses. Whether it’s a compass, dive computer, or timing device the same rules apply when it comes to maintenance.

They must all be soaked in warm fresh water after a dive.

Compasses

The bevel on the compass must be rotated several times in both directions whilst in the warm water. This prevents salt from building up underneath it.

Dive computers

Dive computers must have the buttons depressed several times while swirling the instrument in the warm water. This will ensure no salt crystals can build up behind the buttons. I have a Suunto Mosquito that has done over 1000 dives and has never given me a day’s trouble whereas many people have had button trouble with these units. If you have delicate water contacts brushing them with a soft toothbrush keeps them clear of build up.

I also take a soft cloth and wipe silicone over everything, pour it in behind the buttons and then wipe it all off with a clean cloth.