Breathing underwater

Most divers ask “how long will my air last?” There are several variables to this but primary factors are how much air you start with, the depth you intend diving to, and your rate of consumption.

Body size is important, and activity underwater and stress levels are also factors. Fitness is not necessarily an huge factor. An unfit overweight diver that moves slowly in a relaxed manner will consume less air than an elite athlete with a high stress level finning inefficiently.

A 12 litre cylinder filled to 200 bar will have 2400 litres of air. If your breathing rate is 20 litres a minute on the surface you could use the cylinder for 120 minutes. The same cylinder at 30 metres will only last 30 minutes.

Cylinders
If you decide to purchase your own cylinder, it’s critical to maintain it

The technical jargon to work out your predicted air consumption per minute is as follows:

The volume of the tank is divided by the breathing rate multiplied by the absolute pressure of the depth at which it is breathed.

Afterwards, you can calculate your realised or actual breathing rate for a particular dive. Take the amount of air you consumed on the dive in bar, and work out how many litres you used using the above information. You can work out how many litres of air you used per minute by dividing the number of litres by the dive time. You can track your air consumption, and tie it to a variety of factors – how you felt on the day, your weighting, how your gear was set up, and of course depth – if you keep proper records in your logbook for each dive.

Diving at the Two Oceans Aquarium

For Tony’s birthday in June we spent a Sunday morning at the Two Oceans Aquarium at the Waterfront, diving in the I&J Predator Exhibit and in the Kelp Forest Exhibit. These were two of the best dives I’ve ever done. You need an Open Water or equivalent qualification for the predator tank, though I think you can do a (expensive?) DSD there too. For the kelp forest you need an Advanced qualification, as even though it’s only 6 metres deep, it’s very surgy.

On both these dives, you are on view to the public. It’s fun to wave at the kids through the windows of the displays. They are very excited to see real live SCUBA DIVERS in the water with all the fish. Needless to say, the scuba divers were very excited to be there!

Youtube videos for both dives can be found here.

Kelp Forest Exhibit

We started in the kelp forest – you wind your way up to the roof of the aquarium and drop into the water off a small wooden platform. This exhibit completely is open to the air, since it’s comprised of vegetation and sea creatures found in Cape waters, and because kelp loves sunlight. Kelp also likes water movement, so there are a variety of devices to keep the water moving – dump buckets, a plunger, and some pumps. This makes it quite choppy on the surface and quite surgy below. (Fascinating fact: since kelp cleans the waste products – such as ammonia – out of the seawater by filtering it, a lot of the aquarium’s water is passed through the kelp tank on its way to other exhibits.)

The exhibit has live kelp that is actually growing, which is quite an achievement, but you’re not supposed to hang onto it the way I sometimes do in the open ocean! The tank is packed to the brim with white steenbras (my absolute favourite), red stumpnose, galjoen, zebra, roman, shysharks, fransmadam, and even a gully shark if you can spot him. The fish are huge, many of them much larger than any I’ve seen in the ocean. I was extremely fortunate to be allowed to feed them – I was given a small bag of squid pieces and sardines, and the fish gathered around me as I knelt on the bottom. It was wonderful, so busy and colourful. They weren’t shy, bumping into my legs and BCD once they’d realised I had lunch with me. There’s a hilarious finger-biting episode at around 2:45 minutes in this video:

The water is cold, and the tank isn’t actually very big. There are nice swim throughs between the rocks (made of fibreglass) and the kelp. The visibility isn’t perfect as the water is so highly aerated, and there are little bubbles of air everywhere. But it’s a thrilling dive and a very rare opportunity to get so close to so many beautiful fish.

Dive date: 6 June 2010

Air temperature: 18 degrees

Water temperature: 14 degrees

Maximum depth: 5.7 metres

Visibility: 10 metres

Dive duration: 27 minutes

I&J Predator Exhibit

The second dive we did was in the predator tank, which is a lot warmer than the kelp forest. On this dive, the Divemaster was armed with a piece of broomstick to “guide” the sharks away if they were to bother us. There are five ragged toothed sharks in the exhibit, none more than two and a half metres long. I think they’re all female. They cruise round and round in circles, looking completely awesome. I spent a long time just sitting on the floor of the tank watching them.

The other magnificent inhabitants of this tank are the sting rays. There’s Olive, a giant (and I mean GIANT) short-tailed sting ray like we see at Long Beach and Miller’s Point in summer, and a whole host of small (the sort of size that makes you want to take them home as pets) devil rays. Tony spent a significant part of the dive (while I was sitting watching sharks) chasing tiny rays around with his camera set on video.

In the corner of the tank we met the loggerhead turtle. She was lying next to a water vent, with her head in the corner. I was allowed to touch her on her neck (it felt really soft, and I felt lucky). I wasn’t convinced that she was a happy girl – she looked kind of depressed. Our DM said she gets more active when the water temperature increases, and sure enough I saw her swimming happily past the glass in the predator tank two weeks ago, when I went for my Saturday morning training at the aquarium.

The tank also contains musselcrackers, garrick, yellowtail, and (at the moment, but not when we dived in it) the remains of a sardine baitball.

The only moment when I got a bit of a fright was when we were surfacing against the rocks in the middle of the tank, and I omitted to look where I was going: straight into the path of a raggie. And sharks don’t generally get out of the way! Fortunately our DM had seen me behaving like a space cadet and “guided” the shark off to the side (since I wasn’t able to interrupt my ascent quickly enough).

Dive date: 6 June 2010

Air temperature: 16 degrees

Water temperature: 18 degrees

Maximum depth: 5 metres

Visibility: 25  metres

Dive duration: 35 minutes

Bookshelf: Ocean: An Illustrated Atlas

Ocean: An Illustrated Atlas – Sylvia Earle & Linda Glover

Ocean: An Illustrated Atlas
Ocean: An Illustrated Atlas

I eyed this book for weeks and weeks before finally succumbing and placing an order online (get it here). It’s a National Geographic publication, and – as one would expect – absolutely magnificent. It’s mainly about the detailed ocean maps, but there are articles on each ocean, and on topics such as the impact of climate change, conservation and deep sea exploration.

Sylvia Earle is incredibly impressive – a living legend (according to both the US Library of Congress, and yours truly).  She has a long history of work in and on behalf of the world’s oceans, holds several diving records (she’s hardcore) and is a world-renowned scientist and explorer. She’s an expert on the subject of oil spills, and is – I think – soon set to release a book on the latest BP-led fiasco in the Gulf of Mexico.  She also holds the designation of Explorer-in-Residence at National Geographic, which sounds both like a contradiction in terms and like the coolest job in the world.

I spent most of my time in this book poring over the maps, and picking up nuggets of (potentially) useful information about where the sea is deep, where it’s shallow, and what the bottom profile of a whole host of international dive sites is like. There are water temperature maps (myriad rainbow shades showing the spectrum from freezing cold water in indigo, to lovely warm water in red). There are fascinating charts showing the position of the various (and multitudinous) information collecting devices (buoys and others) all over the world’s oceans. I also learned, thanks to one of the detailed double-page maps, that the ocean’s currents are far more complex than primary school geography led me to believe… The update on the state of oceanography and deep sea exploration was also fascinating. I was awed to discover that the average – that’s AVERAGE – depth of the world’s oceans is about 4 kilometres. As recreational open-circuit scuba divers, we can go to 40 metres with the appropriate qualification. That’s hardly scratching the surface.

This is a magnificent coffee table book, but not just one that you’ll leave lying about and not return to over and over. The impression it left me with was twofold: one, how vast and varied our oceans are. The second impression was of how little we know about what’s under the waves. That is kind of thrilling!

You can obtain a copy here if you’re in South Africa, otherwise click here.

Exploring: North Battery Pipeline

Tony has been eyeing the pipeline just south of the Lower North Battery (that collection of navy buildings with gun turrets on the Main Road just before you get into Simon’s Town) for some time. It’s north of Long Beach and further north than the wreck of the Brunswick. Even though I was coming down with what turned out to be a vicious bout of flu, I was determined to get in the water (I reckoned I was getting sick anyway…) so we went exploring one Sunday morning in midwinter.

We parked the cars on the southern side of the North Battery – there’s a little driveway and we pulled them out of the way onto the grass (here it is on Google Maps). There’s also space for just one car, pulled right off the road, right above the entry point. From there it’s a bit of a walk along the pavement, down a slope, over the railway line and then down to where the pipeline starts. You can see the single-car space next to the piece of fence, and below it the start of the pipeline to the left of the rocky outcrop in this image from Google Maps.

The entry isn’t too bad. There’s a barnacle-encrusted concrete promontory that we sat on to put our fins on, and then (theoretically) dropped forwards into the water, which was just over waist deep. While putting on my fins I got washed over backwards onto the wrong side of the promontory (thank you for my thick wetsuit!) but that turned out to be fine, as it was sheltered, and eventually I managed to get clear of the swell and kelp with a little bit of effort.

North Battery Pipeline entry point
North Battery Pipeline entry point

We followed the pipeline straight out to sea. It’s not very long, but quite undisturbed, with lots of abalone and rock lobsters. There are one or two leaks in the pipeline, emitting a brownish liquid whose origins we preferred not to speculate on… it looked warm, or oily, because it shimmered a bit before mixing with the surrounding water. Tony thought it might be mountain water (tannins causing the brown colour). Hope so. Right at the end of the pipeline the visibility got really poor from all the stuff flowing out, so we turned south.

It’s all sand south of the pipeline, with lots of beautiful anemones and countless sluggish puffer fish buried in the sand. We turned after a hundred metres or so, and swam back closer in to shore. There we found what looks like the remains of a ship – four or five big rusty bits of iron sticking out of the sand in relatively shallow water. I don’t think it’s part of the Brunswick – I think we were too far north – but it could be.

Verdict: Glad we checked it out. Lots to see on the pipeline (good for macro photography) but be careful about the poor visibility at places. Curious about the bits of ship (I assume) inshore, south of the pipeline.

Dive date: 18 July 2010

Air temperature: 17 degrees

Water temperature: 12 degrees

Maximum depth: 6.5 metres

Visibility: 5 metres

Dive duration: 30 minutes

Plan your dive and dive your plan

Three divers approached me at the dive centre one day, requesting I take them to a dive site where they could dive to 60 metres. They wanted to test some new equipment configurations. Two were certified advanced Nitrox divers, qualified deep technical divers and had made several dives to over a hundred metres… in a lake. The third diver, like myself, was qualified to dive to 40 metres.

So we draw up a plan: they will dive to 60 metres, spend 6 minutes at that depth, ascend to 50 metres and spend 5 minutes there, then ascend to 40 metres 5 minutes thereafter and so on until the reached 6 metres where they would switch to pure oxygen to reduce the deco stop time as the current at this site is strong. The third diver and myself would meet them at 40metres.

Using a software program called V Planner we calculated that including the descent time and ascent times for each stage, at a controlled rate, we would enter the water precisely 16 minutes after they started their dive and we would meet them at 40 metres. We would then all be together for the next 30 minutes, ascending with them to their 6 metre safety stop, ensure they had both switched to pure oxygen and then leave them and return to the boat.

The plan was that we would spend 6 minutes on our descent to 40 metres and all four of us would reach 40 metres together. They were made to clearly understand that should they have a problem at any depth deeper than 40 metres we would not be able to help them as we were diving 12 litre steel cylinders on a Nitrox 32% mix, limiting our depth – and what’s more we did not have the qualifications to go to 60 metres.

We discussed the plan in great detail and everyone was set. A red SMB would be hoisted if they experienced any difficulty and a yellow would be released once we met at 40 metres.

Mistakes happen

We started our descent on time, and watching my dive computer and timer I descended at the agreed rate. My buddy, however, did not. He descended way too fast. Believing that they would be in control of their dive he descended very fast and joined them, ahead of schedule at a depth of 55 metres. They were 3 minutes behind schedule as they had struggled to come to terms with the ocean current. Now we had a problem. I waited at 40 metres, but they arrived late, and this meant I would risk going into deco before we left for the 30 metre stop.

At this point my buddy ran out of air. He was closer to the deep divers as he was reading their slates, so he grabbed the first regulator he could see: the deco tank regulator, filled with pure oxygen. At depth oxygen is toxic and can kill you in a matter of minutes. I grabbed it out of his mouth, so he grabbed my regulator out of my mouth as he was now starting to panic. He was holding onto me so tight I could not reach my octo so I reached for the octo of another diver. So here we were three divers locked together at 40 metres, each with a regulator in our mouths that belonged to someone else. I managed to get him calmed and off my cylinder and onto the octo of the deep diver with the most air. Now back to normal, we started our ascent and did the required safety stops, reached the 6 metre stop for them to switch to oxygen and headed for the surface. I reached the surface with 10 bar in my tank.

Deep dive
Ascending from the almost disastrous deep dive on Atlantis in Ponta do Ouro. Note the hang tank of pure oxygen.

My buddy had been to 55 m on a Nitrox mix of 32%. The maximum safe depth for this blend is 40 metres. He had almost sucked on a cylinder of oxygen at 40 metres, this is a lethal dose at depth. Mistakes happen. Be meticulous with dive planning, rehearse your incident scenarios and make sure you dive your plan.

Wreck penetration

Once you embark on the Wreck Specialty Diver course you can choose to include wreck penetration if you wish.

Wreck penetration
Wreck penetration

There is more to this aspect than just having a big torch! Passages deigned for walking along become very tight spaces if the ship is lying on its side and a once narrow walk way will have you crawling along the bottom of it while your tank scrapes the top, dislodging rust from above and silt from below – reducing visibility to zero despite your huge light.

Wreck penetration
Take care not to swim into overhead environments without a reel, line and a light

Once in a wreck you need to move very slowly as the diver behind you will not have a good time swimming in the silt cloud you create. Your bubbles are also enough to create a cascade of flaked rust in some instances. It is extremely important to use a reel and line, tied off at the entrance. You belay the line at various points to prevent the line following a route you can’t navigate on your return. If you don’t do this, the line will find the shortest route through the wreck behind you – not necessarily person-sized! Cyalumes attached to the line are useful just as a back up torch or three is also an essential requirement.

Wreck penetration
Orient yourself using daylight when penetrating a wreck

Always ensure you have studied a drawing of the layout of the sections you plan to penetrate. The MV Aster wreck just outside Hout Bay Harbour was purposely scuttled by divers, for divers. As a result detailed drawings of the interior of the wreck exist, and it is an ideal site for training in wreck penetration.

Finning

Not getting anywhere

Often divers find that the hi-tech latest fins they bought for a packet are not giving them the pleasure and speed they thought. The slightest current has them finning as fast as possible, consuming air rapidly and not keeping up with the other divers.

A decent pair of fins allows you to use your most powerful muscle, your thigh muscles. If you fin like you ride a bicycle you will go nowhere.

The downward stroke delivers the most propulsion. Keep your leg straight and kick down slowly, bending the knee slightly on the upward stroke. You will find long leisurely fin strokes will use little energy and give you exceptional forward movement.

It is also important you have a good horizontal profile in the water because if you are swimming almost upright across the bottom you create a huge amount of resistance. Stay streamlined, keep your arms at your side and ensure all your gear is tucked and clipped close to your body.

Big fins
Ensure you have a good horizontal profile in the water (hint: this isn't good)

Entry techniques

It is common for similar dive sites to have a completely different entry styles, and shore diving is no different.

Boat diving will in most instances involve either a backward roll or a giant stride depending on the size of the boat and the bottom contours. A giant stride off a jetty onto a submerged object is no fun.

Giant stride
Preparing to do a giant stride off the boat in Aqaba, Jordan
Giant stride
Doing a giant stride - note the inflated BCD, and hand over regulator and mask to hold them in place.

A giant stride can be a long drop to the water on a large boat that does not have a dive platform and it is important to ensure the area is clear before you leap.

Giant stride
Hitting the water, still holding mask and regulator in place

Doing a backward roll off an inflatable has its hazards. Ensure everyone rolls at the same time to avoid landing on the person next to you. Even the slightest hesitation can result in the boat drifting slightly and you landing on a diver. Ensure that your BCD is inflated, and that you have your hand over your regulator with your fingers on your mask to hold them in place. If someone does land on you, don’t panic – just relax, remember to breathe, and wait to pop to the surface.

Underwater below the boat
It can get crowded around the boat, which is why it's important to roll off exactly when the skipper tells you to

Shore entries may have you walking through the surf to get some depth and even a small wave can knock you off your feet. Clambering over rocks at some dive sites will find you slipping and sliding about so watch the waves and time your entry and exits.

If you aren’t already wearing your mask, make sure it’s around your neck or with the strap pushed well up over your forearm, NOT on top of your head or inside a fin! Or preferably on your face already. Ensure you have your fins clipped correctly and slide the straps up over your forearm so that if you stumble and place your hands instinctively in front of you they shouldn’t get lost. As soon as you are waist deep don your fins and swim away from the shore.

Irrespective of the style of entry, before committing to enter the water ensure your gear is clipped, weight belt tight,  zipped up suits and gloves are on. Ensure your mask is on and secure and your regulator firmly in your mouth, This will ensure that should you be toppled over by a wave you will be able to see and breathe. Likewise when doing a giant stride or backward roll, place one hand on your weight belt, the other over your face with the palm holding your regulator in and the fingers holding your mask firmly on your face.

Bookshelf: Marine outposts and shipping

There’s a romance and fascination to the structures that we build to try to tame the ocean, and a sense of awe demanded by the scale and industry that modern harbours project. Learn about the development of modern shipping, about lighthouses, and more with this list of book recommendations for the shipping buff.

Lighthouses

Harbours and shipping

Sailing

  • The Complete Yachtmaster

Bookshelf: Two Oceans

Two Oceans: A Guide to the Marine Life of Southern Africa – George & Margo Branch et al

Two Oceans (original edition)
The original edition of G & M Branch's Two Oceans

Two Oceans is one of the better known guides to South African marine life, and rightly so. Tony is on his second copy – the first is so dog-eared that the covers have fallen off and the spine has split in multiple places. That’s the sign of a much-loved and well-used book!

It is extremely comprehensive and illustrated with photographs of the creatures and plants in their natural habitats, which is how you’d see them as a diver.

I’ve used the book after dives, but also as part of the volunteer training course I’m doing at the Two Oceans Aquarium, to identify sea plants and animals in rock pools and in the aquarium exhibits. It’s useful for the whole family, even if you’re not all divers, because it covers shore creatures as well as those found only at depth.

Two Oceans (updated edition)
Two Oceans (updated edition)

The book has been through several editions. The latest one (see the cover below) is greatly expanded, with more user-friendly contents pages (it’s arranged a lot like bird books, with colour-coded pages).

I use this book a lot; I would recommend it as a first or second purchase for a local diver. It covers the entire coast of southern Africa, so you may not find as much regional detail as you need, but that’s where the SURG publications step in and fill the gap! (More on those later.)

You can buy the book here if you’re in South Africa. Otherwise go here.