We love diving, whether it's technical diving to explore deep wrecks or just sport diving to search for seahorses or nudibrancs, we can't get enough. We also like to try different equipment and enjoy sharing what we have experienced and learned. We hope you find our blogs interested and that they help you make the most of your equipment and diving. If you like our blog posts, please feel free to 'like' them and share them with your friends.
Truk Lagoon claims the world’s greatest wreck diving and with over 60 ships plus aircraft, in a protected lagoon, the claim is justified. On this trip we were invited to join Max Gleeson (maxgleeson.com) and Lesley Hillyer (AquaSea) as they continued to work on Max’s second documentary on the wrecks of Truk Lagoon (more below). Martin, with his huge ‘underwater selfie stick’, also joined our group.
|Buddha, on the Oite|
We have been to Chuuk before, using different twin tank systems and although a simple back plate and harness was the better option, it still felt cumbersome in narrow doorways and corridors. This time we went side mount, I had my Stealth 2.0 Classic while Karen used a Stealth Rec wing fitted to her Classic harness.
In switching from cold water to warm, with different suits, tanks and side mount rigging, it took a couple of dives to get weight, trim and ‘boat procedures’ down pat. Operating out of the Blue Lagoon Dive Shop – our boat driver, Rhys, went from intrigued observer to expert assistant, helping to don tanks after just a few dives.
|Roller, near the San Francisco Maru|
Max’s second video will feature lesser known and deeper wrecks of Truk Lagoon. This worked well with our objectives to revisit the Oite and because I needed a better photo of a road roller lying on the sand with the silouette of the San Francisco Maru in the background. I'd taken a photo on the last trip, not thinking about the ship in the background (hence, I didn't get it right).
Cutting a long story short, these are the ships, our dive depths and some of our notes for those whom might contemplate similar (and there’s much more to see).
|Wreck||Our depth||What to see|
|Yubae Maru||30m||tableware and saki bottles, props sticking up|
|Patrol Boat||27m||limited damage, interesting valves and gauges|
|Nagano Maru||58m||trucks and road roller in the hold|
|Kiyosumi Maru||27m||torpedo holes at bow, a bicycle, coral decorated masts|
|Fujisan Maru||58m||a large tanker with fuelling pipes, signal light on sand|
|Oite||62m||one of only two destroyers in the lagoon|
|Momokawa Maru||36m||bridge telegraph and phono tubes|
|Shotan Maru||49m||vehicles in the hold, bullets, shells, pots and pans|
|Unnamed lighter||27m||(see below)|
|Amagisan Maru||38m||large forward gun, great exploring|
|San Fransisco Maru||62m||tanks, vehicles, road roller, engine room and lots more|
|Seiko Maru||41m||large decorated masts, bathrooms and mess, telegraph|
|Taiho Maru||44m||(see below)|
|Kensho Maru||27m||large engine room in excellent condition|
|Aikoku Maru||40m||manoeuvring helm and telegraph at stern, galley|
|Soporo Maru||26m||had to happen – 3m visibility, but clear inside|
Highlights for the trip were the Oite, San Francisco Maru and two wrecks that had not been visited by divers for many years.
|Tank on San Francisco Maru|
The Oite is (was) a destroyer and the speed boat in the lagoon, with a slender hull and with two large props, after the engines, fuel and munitions there must have been little space for the crew (respectfully, some are still there). With a limited run time it was exploring on a schedule (luckily, we did two dives on her), but we located a gun in the wreckage of the upturned bow that we hadn’t seen before. The stern section, upright, has a large gun and anti-aircraft guns that make for great photos. The San Francisco Maru was great, as always, and I got the photo of the roller.
The first of the two ‘new’ wrecks, was the Taiho Maru. Blown in two but Max and MacKensey (our guide) found her rear half. Rumour says it lost popularity as a dive site many years ago because the leaking aviation fuel burned divers’ exposed skin – fair enough! The water is clear now and this wreck, lying on its port side, has one of the most photogenic props in the lagoon.
The second ‘rediscovery’ was an unnamed lighter, a maintenance vessel and water pump. It also has a pretty prop, partly buried, with a huge coral fan nearby. The pump control room near the bow was fascinating, full of gauges, valves, and pipes going in every direction. We found navigation lanterns and much of the compass, including brass gimbals and the large glass dome.
Side mount proved a great choice for exploring. With much of the wooden decks rotted away it was easier to slip between the steel framework than it had been before with twins, or to roll 90 degrees and just swim through narrow doorways. Sometimes it was the camera arms that were more difficult to get through windows, when you don’t really want to touch the wreck – to preserve both it and yourself. Both Stealth rigs are very streamlined, meaning minimal exertion and less air consumption at depth – I’ll use it again next time.
Back to Max’s videos. The first video (volume 1), includes some history on Operation Hailstone (why the wrecks are there) and features 15 of the more famous and popular ship wrecks in the lagoon, plus a chapter on aircraft. It is a great video and it might also be the best ‘dive trip planning tool’ that you’ll ever see. Max and Lesley have done an amazing job organising, filming and putting the video together. I’m looking forward to volume 2, and Max has already offered a teaser on Vimeo.
With 7-metre high swells this weekend, I’ve had time to put a few words together about Nitrox Analyser Mark 2. When unable to source a PM128A panel meter for my first Nitrox analyser, I adapted another smaller LED panel meter. For this analyser I sourced a CX101A panel meter with LCD display. Here’s a quick explanation for anyone wishing to build the same.
The meter sits inside a plastic case, needing a wider project box that the LED meter. The small plastic case also holds the circuit card against the contacts to drive the display. They’re not soldered, so if you use this meter take note of the orientation of the parts and make sure that the circuit card is centered when you put it back together.
The CX101A has the same chipset but on a different circuit card to the CX102A (LED). However, the modification is similar and the first step is to find and unsolder a 910 ohm resistor from the circuit card. An advantage of this LCD panel meter is that the contacts that you need to connect to are the risers that protrude from the circuit card through the case and, by using connector plugs, the soldering can be performed on plugs instead of the circuit card.
A number of the risers / connector leads must be joined, including to set the decimal point, as per the diagram that comes with the meter (for 9v independent ground). Hook-up wires are then connected for power, the sensor and the reference voltage. The reference voltage is set using the same resistors and trimmer circuit used with the LED analyser (see previous blog).
On this analyser I added a press button switch and resistor, which bypasses the on/off switch, as a battery test button. If pressing the button shows a reduced reading compared to turning the unit on, then the voltage is starting to drop and it’s time for a new battery.
The next step is to test the analyser with air and adjust the internal trimmer pot so that the display reads around 21, before closing the case. The large pot, with the knob on the front of the box, is used to adjust to 20.9. I also tested using a cylinder of oxygen (reading 99.4% which is close, given 1 bar of air before filling).
So if you want to build your own economical Nitrox Analyser, here's an option with an LCD display. The sensor was again the biggest cost and it does take a couple of hours of cutting out and drilling holes, unsoldering, soldering and calibrating. If you do build a Nitrox analyser like this, please post to our facebook page - good luck!
With such a topic there will be opposing views and I don’t aim to convert the unconvertable. This story is about my experience to find ‘the right BCD for me’.
I learned to dive in a simple jacket-style BCD. Dive shops like these for training, simple with not much to explain. My first BCD was a jacket with integrated weights, slightly more complex but otherwise much like I had learned with.
Technical diving introduced me to the backplate, harness and wing (BP&W) BCD. Initially I didn’t think much about it, probably because I was so busy with procedures and safety drills that I didn’t give it a thought. The only thing I recall being inconvenient was a lack of pockets, but my jacket pockets had mostly been taken up by the integrated weights anyway, and I soon got some leg pockets.
My first tec BCD was a harness and wing without a metal backplate, but I soon added a stainless steel one. It was very well made but with back-mounted twins, a pony, reel, and leg pockets I accepted that there was just too much stuff to be streamlined.
Anyway, diving has always been about exploring and finding something new; there were wrecks in Truk Lagoon and all this equipment was accepted as the price of admission.
Later, when using the BP&W with a single tank, it became obvious that this configuration really was more streamlined. Experiments ensued: a complex harness versus simple webbing, moving the tank position, relocating weights for trim, and so on. Unexpectedly, the simpler the system the better it performed. Then came a home-made sidemount experiment – not perfect (far from it) and a challenge for the (then) untrained, but the result was astounding, real streamlining did exist and gliding was fun!
Sidemount diving is another story but I still do a lot of single tank backmount dives, teaching courses, or just drifting around the shallows taking photos. However, even for simple dives I want the best trim, buoyancy and streamlining that I can get, so I achieve lower air consumption, better distance and longer bottom times (enabled by Nitrox if need be).
My original jacket BCD is of good quality and it looks like new even after years of use, but it now feels like a parachute underwater and it only gets wet for open water courses. All other backmount dives are now with a BP&W system, and these are the main reasons why:
I also use a modern wing design that’s narrower across the top and bottom and shaped down the sides, in contrast to my first ‘old style’ wing (an oval shape with even thickness all round). For about 3 to 4 litres of buoyancy, the old style wing leaves much of air between my head and the tank valve, so the weight at my waist drags my feet down. The narrow top of the new wing forces the same amount of air into the sculpted side sections, moving the buoyancy closer to the centre of gravity and making trim easy. I like easy, and I have no desire to fight my BCD for decent trim.
But what about those missing pockets? I now use a dive pouch that I can fit more into and clip onto a shoulder strap D-ring and have a good look inside – try doing that with jacket BCD pockets!
Building an inexpensive Oxygen Analyser is an achievable home project thanks to the Oxygen Hacker’s Companion by Vance Harlow. The analyser I built is a variation with one major difference – the panel meter.
WARNING: From here on this blog gets seriously nerdy - you have been warned!
Aside from the O2 sensor, the panel meter is the major component of the analyser. After waiting three weeks for a PMA128A panel meter, my order arrived with the panel meter and a few other items cancelled. I also ordered a CX101A panel meter for a future more-compact analyser (but a CX102A was delivered instead - LED display instead of LCD). So my future project became my only choice.
As background, these 3.5 digit panel meters measure 0 to 200 millivolts (mV) (actually 199.9mV) using a 7106 chip or 7107 chip (basically the same chip but it drives LEDs directly). Electronic components are manufactured to a tolerance (e.g. + or – 5%), so to get an accurate reading the panel meter has a fixed resistor and potentiometer or ‘pot’ so that the builder can compensate for component variations. This works by using the pot to adjust a reference voltage (Vref), which is then used by the chip for comparison to the voltage being measured.
Adjusting the pot changes Vref and the display by a few percent. However, an Oxygen sensor won’t create 20.9mV for air, so a more drastic change is needed to Vref by replacing the fixed resistor. I tested my O2 sensor (a PSR 11-39-MNB from TFM Engineering) and it read 12.2mV in air and close to 59mV for my test O2 cylinder. So in this case the panel meter Vref needs to be adjusted so that 12.2mV is displayed as 20.9. In addition, the voltage from the sensor can vary with age and so too will Vref as the analyser’s battery gets low – so on-going calibration is needed. For further information refer to the Oxygen Hacker’s Companion.
As the CX102A uses the same chip as the PMA128A, so I figured I could apply the same theory and a bit of experimentation. After tracing the circuit, the resistor I needed was located near the on-board pot, it’s the surface mount resistor 'R3', labelled 9100 (910 ohm). R3 was removed using a soldering iron, tweezers and a magnifier – it’s only about 2mm in length. Tip: don’t have the soldering iron on the board any longer than necessary as heat will damage the circuit card and chip.
Next I soldered hook-up wires to the circuit pads either side of where R3 was – one on an original pad and the other to the side of the on-board pot as this was easier. As the soldered connections are small I glued the wires to the board with a hot glue gun.
The pot on the panel meter itself was set at 200 ohm, while the resistor R3 was replaced with a 500 ohm trimmer pot (a small blue square pot) and second larger pot for on-going calibration (with a knob on the front of the analyser) - see circuit diagram. The large pot should have been 100 ohm but I couldn’t find one, so I used a 1000 (1k) ohm logarithmic pot with a 120 ohm resistor soldered across two terminals (one in the middle and on one side) as this creates a fairly linear 120 ohm pot - close enough.
With a 9V battery, switch and some hook up wire, this was all tested on a project board using a separate circuit to simulate the sensor output range to be measured. The battery leads were soldered to pins 1 and 2 on the circuit card, and a join was made from pin 3 to 4 for the decimal point. The sensor leads connect to pins 7 (+) and 8 (-).
Once tested, everything was soldered together and assembled inside a plastic project box. With the goal of a ‘compact O2 analyser’ I used a project box for a TV remote control from Jaycar. A mono headphone socked was added to the box, and a headphone plug to the wires from the sensor, so that the sensor could be connected and disconnected as required.
I tested the complete unit, adjusting the blue internal trimmer pot to calibrate the analyser before closing up the box – minor adjustments are now made using the larger pot with the green knob on the front of the analyser.
All up the analyser cost about $150, with the sensor being $115 and the panel meter and project box about $10 each. It took about 20 hours in research, prototyping and assembly but the next one will be quicker.
A final note of thanks goes to Stephen from TFM Engineering for the sensor, sensor holder and Oxy Hacker’s Companion.
This blog is part 3 of a three-part blog about experiences from adventures in Eua, Tonga. Go to the previous blogs for the introduction and Experience #1: Pod of Five, and Experience #2: Cathedral Cave.
Experience #3: Mother and Calf
Humpbacks come to Tonga to breed and give birth and while more common in the protected waters of Vava'u and Ha'apai a couple find sheltered spots along the west side of Eua. Boat captains follow a simple rule, if the mother stays between the boat and calf, and starts to move the calf on, you leave – don’t stress the mother or a calf that is yet to gain its strength.
In three previous visits to Tonga we have swam with a couple of cow and calf pairs, mother and baby, Humpbacks before. The calf can be playful, curious and fast, and the mother lets it investigate snorkelers under her watchful eye. On each occasion the mother had come 'out of hiding' and had a hopeful bull as an escort. However, this time was different.
'Slipping under the waves' is an overused cliché but in this instance it was a necessity, the last thing you want to do is to upset a 30-something tonne mother. So, in our small group of five we quietly lowered ourselves into the water and swam, floated slowly towards the two whales, avoiding sudden movements and any splashing.
As soon I could see them under the surface I hesitated. At less than 2 metres long this was easily the smallest Humpback calf I'd ever seen, it was so young. I immediately thought that the mother isn't going to let us near them but, keeping together, we approached. The mother became aware of us and we waited. We were spread out with a few metres between each snorkeler. She descended a bit with the calf beneath her but did not move off. How do you tell a whale that you mean no harm? I tried a slow roll on the surface - like when interacting with young adult whales – we’re here to play?
Then the calf came up for air, my rolling seemed to attract its attention and it came towards me, took a breath, did a head-down tail-up twirl, gave me a stare, and went down again. The mother didn’t move and the calf resumed its position nestled under her chin – it seemed that they were comfortable with us being there.
Every five minutes or so the calf surfaced to breathe, it did a roll or twirl, checked out a snorkeler or two and then returned to mum. Often the calf would rest under its mother’s chin but on another occasion it moved alongside. A giant five-metre long pectoral fin swung out and gently guided the calf beneath the mother where it was embraced in both arms – it was a beautiful sight.
After a while the mother rose to breathe, did so and then descended about a metre but did not move off. The pattern repeated, each time the calf surfaced it would roll or twirl, take a look at a visitor and return to mum. Over time it came closer, to within a few metres of each person – even though it was very young we could never out-swim it and the best option was to avoid any sudden movement, relax and enjoy.
After an hour in the water with the mother and calf we all felt particularly privileged, grateful to have had such an experience, and that it was our time to leave them be.
Diving and snorkelling adventures provide awesome experiences and, according to that study, happiness (see In-water Adventures = Happiness Part 1) – I can't disagree. These were just three such experiences that Karen and I enjoyed, and we can't wait for more! We hope that you too have some amazing adventures.
Want to join us next year?
Thanks to my fearless travelling companions: Karen, Felicity, Linda, Carson, Geoff and Harry. Great adventures are always best when shared.
Special thanks to the Deep Blue Tonga team at Ovava Tree Lodge, Eua: Finau, Grant, Aneesh, Aaron, Harris and most especially to Wolfgang. Great food, great service and amazing adventures are their specialty.
More photos: Tonga - Eua - 2015
Experience #2: Cathedral Cave
Eua is quite different to the other islands in Tonga, it has been formed from up-lifted limestone with impressions of ancient coral often clearly visible in the rocks. It is also the oldest island in Tonga, and the highest.
The island also has a surrounding plateau, much of which sits between low and high tide. A number of underwater caves have formed in this plateau, many of which are waiting to be fully explored. The most well-known is the Cathedral Cave, reportedly the largest of its kind in the southern hemisphere.
Entry to the Cathedral is from the ocean through a wide arch at a depth of 20 - 25m. Once inside, the cave opens up into a large cavern with several ‘skylights’ in the roof, which appear like ‘blue holes’ when viewed from the cliffs above.
Although there is light inside the cave it is a true overhead environment with no safe entry or exit through the skylights.
Despite any swell and ocean noise outside the cave, inside the water is calm and silent and light streams down from the roof in beams as if coming through blue stained-glass windows. When passing under the first few skylights no imagination is required to work out how this cave got its name.
In the main cavern area the waves roll over the skylights in a fascinating display, it’s like watching thunder clouds rolling across the sky in a dramatic time-lapse video. Then with each cycle of ebb and flow of the waves above mini-tornado whirlpools reach down into the cave – it’s best to stay below all of the turbulence and just enjoy the show.
This was our fourth trip to Eua and fourth dive into the Cathedral Cave but this time we had no dive-leader responsibilities. It was a chance to enjoy, to photograph the beams of light and to float on my back in mid-water, face-up tank-down, watching the mesmerising display in the skylights above.
It's a happy place.
Words can never capture the feeling of being there, so I'll let the photos help in explaining.
It doesn’t matter if you believe in simple geology or something more, the Cathedral Cave in Eua is a truly special place that will only ever be known to divers.
I recently read a study about happiness. In essence, material things we want and obtain soon become 'stuff' but experiences can make us truly happy and, ultimately, define us as individuals. In diving we need the equipment but it’s the adventure and experiences that we seek. That’s why Karen and I enjoy technical diving, sport diving and in this instance I’ll include snorkelling in the list – it's all about the experience.
With that in mind I'd like to share three experiences from a recent holiday to Tonga. I know that words won't do them justice but I'll try my best. First of all, to set the scene.
Eua (pronounced "A-wa") is three hours by ferry or seven minutes by plane (yep, just seven) east of Tongatapu, which is the main island of Tonga. With large areas of forest and national parks it has a population of about 3000 friendly locals, scattered in a handful of villages, who are devout Christians and serious rugby fanatics. If you’re looking for an air-conditioned villa and a choice of restaurants then Eua is not for you, Eua is for Adventure tourism with a capital 'A'.
Experience #1: Pod of Five
Each year Humpback Whales migrate up from the Antarctic to Tonga, to give birth, breed and relax in warmer water. The waters around Eua are not as protected as other islands where tourists swim with Humpbacks. Snorkelling in deep open water means dealing with swell but it also allows for a different level of interaction with the whales. Young adult Humpbacks visit Eua and they can be both curious and playful.
After being delayed a day (the ferry broke) our first whale swim in Eua began slowly. After some brief encounters we came across a pod of five young adult whales, each weighing about ten to twelve tonnes. With a couple of tail strokes a whale can disappear from sight in quite clear water, so a trick is to appeal to their curiosity – it’s as much about whales swimming with people as the other way around. With ten snorkelers in a group the whales came in to eyeball us, then began to show-off – we were in luck.
To keep the whale pod’s curiosity, one or two of our group (myself included) would do a shallow duck dive where we could be seen and do a roll underwater, or just roll on the surface. In many instances, as I’ve experienced in the past, the Humpbacks will watch and respond in kind. This time I tried to copy them, when a whale rolled and could see me, I responded, as did other snorkelers. Another Humpback seeing those rolls (by either human or whale) would do the same. In one moment we had three whales and a couple of snorkelers all rolling, with arms, legs, fins and tails in all directions!
After an hour the pod decided to move on and we climbed back onto the boat, exhilarated but now tired from the ocean swell. But after a few minutes the pod returned with surface rolls, fin slaps and general 'fooling around'. We all watched, enjoying the show – did they still want to play? I took the camera and got back in the water, alone.
I swam towards the pod as they moved towards me, a great opportunity for head-on photos. I focussed on a couple of whales, turning 180 degrees to drift / swim in the same direction. Swimming on my right side and concentrating the viewfinder on a whale coming closer to me, I adjusted the camera lens to its widest but couldn’t fit in half a whale, or a third, or…. Looking out from behind the camera the whale was barely 2m from me, with another on the other side of it (obviously they didn’t know about the 5m rule). I decided on a slow roll onto my back and away to the left but found there were two more whales on that side, even closer! Looking straight down I saw the fifth whale in the pod.
As a reflex action I made a few quick kicks to 'get away', which is completely futile when you have time to think about it. How this was interpreted by the pod I'll never know (did we startle the little boat-creature?) but in any case they moved apart and gave me more space – I wish I hadn’t kicked. For a brief moment I was in the middle of a tightly packed pod of five Humpback Whales – I was happy for the experience and I will never forget it.
This is part 1 of a three part blog. Keep reading for more adventures from Eua, Tonga:
Experience #2: Cathedral Cave.
Experience #3: Mother and Calf.
More photos: Tonga - Eua - 2015
Here I am, out of the water with a torn leg muscle - so to fill in time I thought I'd sort out out my save-a-dive tool kit. Regular equipment servicing maintains warranties and reduces the chance of missing a dive but even so ‘stuff just happens’, so I always carry a small plastic tool box of bits, which goes in the car for each local dive trip. At one time or another each item has proven to be useful. So, based on the contents of my tool box, here are some ideas that will hopefully help you to also "save a dive".
The contents of a save-a-dive kit will depend on what you’re doing. If going on holiday to a resort with a well-stocked dive store there may be little to worry about, if you’re out with your buddy for a weekend dive you’ll want a 'few things just in case', and for a major expedition you’ll want to be well equipped. The list below fits in the 'few things just in case' category of save-a-dive kits.
When making a save-a-dive kit it’s useful to think about two groups of items – spare parts and tools. You can start with some ready-made save-a-dive kits or start from scratch, either way here’s some things to consider.
I’m a fan of cable ties – they are handy for so many things. Use them to hold broken plastic clips together, secure a corrugated inflator hose if it comes off (rare) and secure a fin strap if a side clip is lost. They have many uses and not limited to dive equipment. On a dive holiday three years ago I had to fix a strap on one of my Crocs – I still wear the Crocs, complete with cable ties! On our last holiday my wife also used cable ties as light-weight D-rings.
If you’re away for a while or just want to be prepared for more eventualities, consider adding the following to your save-a-dive kit:
The above lists of tools and spare parts should help you out in most situations.
Occasionally you’ll find a need something extra, and add it to your kit. On a recent holiday we had ‘an urgent need’ for a 1.5mm hex key to tighten a hex bolt on a camera housing – it has now been added to my kit. Of course, if you have upgraded your regulators or mask, it can be handy to take the old ones along as spares (I've lent mine to friends a couple of times).
As a final note, when looking to buy tools think about what they’ll be exposed too – especially if you dive in salt water. Cheaper tools may not be made from marine grade stainless or suitably coated chrome-vanadium steel. Remember to wash and dry your tools if they’ve been used on equipment that was exposed tosalt water.
Be prepared and don’t miss a dive!
One of the advantages of a backplate, harness and wing system is the ability to choose your own wing and change wings when you need to. BCD jackets are fitted by diver size with no way to change the buoyancy for the diving that they will actually do. But if a harness and wing system is being considered for its advantages, a common questions is: which wing do I need?
While they look simple, wing design is somewhat more complex and minor changes in shape affect the diver’s trim and streamlining. Materials and construction are important – a single fabric layer is light weight and great for travel BCDs and many jacket BCDs, but if you plan to penetrate wrecks or caves you’ll want double-layered construction with a tough outer shell to protect the inner bladder.
However, let’s just consider the most basic factor and purpose – buoyancy.
The lift capacity of buoyancy compensators may be specified in litres, kgs, lbs and/or even Newton-metres, but how much is enough lift? Unless you dive with no weights, the answer depends on how your buoyancy changes during a dive. The function of a BCD is to compensate for those changes with a safety margin, not to carry weight unnecessarily.
Sadly, many divers dive over-weighted and lift from their BCD is used to compensate for lead ballast that they don’t need. When did you last do a buoyancy check? At the end of a dive with minimum gas in the cylinder (approx. 50 bar), can you hover at 3 metres with almost no air in your BCD? If you sink, take out some lead and try again next dive.
Now, assuming that a diver is correctly weighted, how much does buoyancy change during a dive?
As you use air / gas during a dive your cylinder gets lighter (the aluminium or steel cylinder itself does not change weight, only the air inside it). For an average size (10.5L) cylinder I allow for 2.5kg of change (allow 3kg for a 12.2L). Some manufacturers list empty and full weights on their website – note that it’s the difference that is important here (and you shouldn't plan to breathe a tank to empty!).
Another factor is wetsuit crush – in a dry suit you can add and remove air and keep buoyancy constant. The amount of crush depends on the thickness and type of neoprene and the depth of the diver (i.e. water pressure). This is hard to measure but allowing up to 2kg change is probably more than enough for a 7mm suit. So for 2.5kg of gas used and 2kg for wetsuit crush – that’s only 4.5kg or about 10lb.
Even small BCDs have 12kg (26lbs) of lift, so what’s all of that additional buoyancy for?
Firstly there’s safety, as we’ve already discussed many divers are over-weighted, but we also change configurations and suits, and often add some lead (just a couple) to be sure that we don’t float.
Secondly, what else might you carry that changes your buoyancy? For example, if you have a deco cylinder that you will leave at a stop then your BCD needs to carry that extra weight, but if it’s weight you keep for the whole dive, you should reduce the lead that you carry. As your dives become more technical, with more cylinders, the greater the possible change in the weight of gas.
However, the reason for extra buoyancy could be as simple as recovering a weight belt lost over the side of a boat – do you have enough lift to carry a second weight belt without fining up? Let’s say that you work out that you would need 6kg (13lbs). Do you have enough buoyancy to lift a weight belt from the bottom (potentially up to 25lbs where I dive) – or will you use an SMB instead?
What if your buddy’s BCD fails, can you lift the both of you on a slow (non-emergency) ascent to the surface? You may need to double your lift, or more – and that’s for single tank diving!
Note that this is a simple explanation and does not consider factors like salt versus fresh water.
Finally, if we consider a larger wing may be more bulky and possibly less streamlined (so small can be better), what size wing do you need? It depends on how much your buoyancy will change and an added margin for safety.
In summary, you need to find your end of dive weight (almost no air in the BCD and neutrally buoyant), and then for the BCD capacity work out:
Then find the wing size to suit.
Hopefully this will help you to determine what wing size you need. And as your diving skills grow and you progress from sport to technical diving, you only need change the wing to meet your new requirements.
Taking the Xdeep Ghost on holidays over a year ago I loved it so much that I’ve been using it at every opportunity where a single-tank backmount system is called for. It still looks like new after use in some tough conditions, but by being so good it delayed me from trying the Zeos – but the time has now come.
The Xdeep Zeos is promoted as an “out of the box” system, suitable for the new diver and able to ‘grow’ with their needs. I was after the benefits of a backplate, harness and wing system, and tough enough to handle rough entries and exits, being knocked around by breaking surf and able to withstand getting washed up onto rocks …yes, OK, conditions do need to be quite bad to keep me out of the water.
I chose to keep it simple, a basic harness without the optional deluxe set shoulder or back pads. A steel backplate would mean less lead to carry, but rather than be rational I chose a vibrant blue aluminium backplate with matching single tank adapter (STA), for a bit of bling. I moved the Xdeep weight pockets from my Ghost to the Zeos (interchangeable); why wear a weight belt if you can transfer the weight to a backplate? The left weight pocket has a D-ring, so I shifted the existing D-ring to the right side for another attachment point. I also chose the 28lb / 13kg wing, instead of the 38lb / 17kg wing, with the idea of a smaller wing being more streamlined; I don’t see the need to exert any more effort than necessary!
My test dives were a couple of boat dives with the aim of finding grey nurse sharks just off the NSW South Coast. Although I had a couple of new divers to keep an eye on, it seemed like my first pleasure dive in a very long time.
I’d adjusted the shoulder straps the night before so had no problem slipping into the harness. In the water the fit was secure and comfortable – a 7mm semi-dry wetsuit gave me enough padding, and the backplate is a good comfortable shape with well positioned slots for the harness. The Zeos trimmed to a near-horizontal position but I found my head hitting the first stage regulator – my error by fitting the STA by the top bolt hole of the backplate, it needed to be lower, an easy adjustment (after diving).
The double-layered wing construction of the Zeos is similar to the Xdeep Hydros technical BCD, making it a very rugged unit – you don’t normally see this kind of construction in sport BCDs. The double layer adds a little bulk compared to the Ghost, however the Zeos was nicely streamlined when pushing into a gentle current - my old jacket BCD now feels like a sea anchor.
28lb / 13kg lift is similar to a small - medium jacket BCD, but it's a lot of lift when correctly weighted and the weight of gas in my tank will only change about 5lb during a dive. The less weight the less lift needed. At the end of the first dive, bringing the newer divers to the surface, another diver lost his weight belt climbing on board. So back down to 20m to pick up a 24lb weight belt, being deliberately 2lb overweight for this test dive and with half a tank of gas – that’s about 28lb of lift needed, the same as the wing! At maximum inflation I was neutrally buoyant but with all the lift in the wing sitting behind me I was comfortable and trimmed, unlike a jacket where full inflation feels like being crushed to the point of restricting blood flow. (I had an Xdeep closed SMB if extra lift was needed.)
Some other notes. Some divers worry a back inflation BCD will push them face down on the surface; the Zeos had an upright surface position - the wing shape is well designed for streamlining and when on the surface. The Zeos wing has a large-toothed zip making it easily to unzip and wash out salt between the inner bladder and outer shell. Jacket BCDs have pockets (often half filled with integrated weights); however, more D-rings can be added to the Zeos harness and the Xdeep pouch is also a more versatile option rather than pockets. The Zeos is offered “out-of-the-box” in a couple of configurations, but it can be customised to individual needs. The wing and STA can be swapped for a Hydros wing and twin tank configuration, providing an upgrade path.
In summary, the Zeos appears simple, as a harness back plate and wing, but the attention to detail in its design means that it performs brilliantly and, as a sport diving BCD, it is very rugged. I also think it is a great BCD for new divers - forget the jacket and go straight to the benefits of a tec-style BCD.
Finally, we saw crested horn sharks, Port Jackson sharks and Wobbegong's but no grey nurses. They were enjoyable dives nonetheless because of the gear I was using.