Creature Feature: Narwhal (Monodon monoceros)

While those of us in the Northern Hemisphere are now into the frigid winter season, what better topic to write about than that of a special, you might even say mythical, Arctic creature, the Narwhal. These unusual creatures are what legends are made of and the source of its horn has been the topic of a few tales.

The Inuit legend of the Narwhal
A wicked woman lived with her daughter and her son, who was born blind. As the son got older, his sight improved, even though the mother tried to convince him of his helpless state. One day a polar bear came near the house and the mother told the son to aim a bow and arrow at the bear through the window covered with seal skin and strike him down. The boy pulled back the arrow and the mother took aim from him. The arrow struck the heart of the bear and although the boy could hear the groans of the dying bear, the mother laughed scornfully at him, saying that he had missed the bear. That night the mother and the daughter had fresh polar bear meat while the mother cooked dog meat for the son. Later the boy's sister told her brother that his shot was successful and secretly gave him meat.

Time passed and an old man came to the house for a visit. Before he left, he told the young girl how she could help her brother regain his sight. In the spring, he told them to watch for a red-throated loon who would swim trustingly toward them. Once the loon was close enough, the blind brother should wrap his arms around the loon's neck and the loon would take him to the bottom of the lake. Once they came up, his sight would return. The loon told the young man not to tell about his regained sight until later in the summer when he would send a pod of belugas to their campsite.

When summer came and the ice began to break, the belugas began to move. On one occasion, a pod was closer to land than usual. The young man grabbed his harpoon and told his sister to accompany him to help him aim. They went to the shoreline and the mother, seeing the son with a harpoon, became concerned and followed them. Once she was close to them, the son gave the end of the line from the harpoon to his mother, asking her to tie it around her waist to hold the harpooned animal. The concerned mother told her daughter to make sure he was after a small animal as she was tied to the harpoon. The son instead aimed for the largest whale and harpooned him. The mother was cast into the sea. As she submerged she spiraled around the line, with her long hair twisting into a long lance. This is how the narwhal came to be.

In medieval times, Europeans believed the narwhal tusk was the horn from the legendary unicorn and it came with all the unicorn's magical powers. Believed to cure poisoning and melancholia, Vikings and other northern traders sold the horns for more than their weight in gold.

The name narwhal comes from the old Norse word "nar" which means corpse, referencing the blue-grayish, mottled pigmentation like that of a drowned sailor (calves are actually born brown, with no spots). The scientific name, Monodon monoceros, is a Greek derivative meaning "one-tooth one-horn" or "one-toothed unicorn". The narwhal, or narwhale as it is also known, is a medium-sized, toothed whale that lives year-round in the Canadian Arctic and Greenlandic waters, and whose closest relative is the beluga whale.

This fascinating horn is actually a very long tooth. All narwhals are born with 2 teeth in their upper jaw. After the first year of life, the male narwhal's left tooth grows outward in a counterclockwise spiral. The tooth can grow upwards of 7 to 10 feet long. The function of the tooth is not exactly known. It has been suggested it might be used as a display of dominance during rivalry or courtship, it may aid in obtaining food, or even be used to amplify sonar pulses emitted by the narwhal, but it has not been shown to be used as a weapon. "Tusking" is a behavior displayed by males when they rub their tusks against one another, possibly to determine dominance within the group.

Narwhals travel in pods of 4 (keeping to generally smaller groups under the winter ice cap)  up to 20 in the summer, feeding on fish, shrimp and squid. In winter, they eat benthic critters (flat fish) as deep as 4900 ft (1500 m) under the arctic ice. They are the deepest diving mammals. Their dives can last anywhere from 7 to 25 minutes. Sometimes these groups fall victim to the shifting ice pack, get trapped and are hunted by Inuit, polar bears, orcas, or walruses. In the summer they congregate in larger groups, in shallower ice-free waters.

Narwhals are very vocal creatures, making clicks, squeals and whistles to communicate and/or navigate.

Paul Nicklen/National Geographic/Getty Images

Fast Facts
Type:  Mammal
Diet:  Carnivore
Size:  13 to 20 ft
         (4 to 6.1m)
Weight:  3,500 lbs 
             (1,600 kg)
At Birth: 5 ft; 175 lbs
Max Life Span:  50 yrs

[1] http://en.wikipedia.org/wiki/Narwhal
[2] http://www.enchantedlearning.com/subjects/whales/species/Narwhal.shtml
[3] http://animals.nationalgeographic.com/animals/mammals/narwhal/
[4] http://www.narwhal.org/IntuitLegend.html

Be a Hero with a "Save-A-Dive Kit"

Ever been all set to go for a dive and at the last minute your buddy realizes he’s forgotten something, or worse, some piece of your equipment has broken, and you had to call the dive? Wasn’t that just the worst? Or even worse, what if this happened to you on your trip-of-a-lifetime in that exotic destination you had always dreamed of diving?

Recently, on a SoCal live-aboard trip I led for a weekend of diving, we had many different equipment issues pop up that could have ended diving for several people on board.  If it were a local beach dive, that might not have been such a big deal, but being stuck sitting on the boat all weekend while everyone else is diving really isn’t all that much fun. And for me, it is not an option at all.

When I pay to go on a trip to get several dives in (especially in a new location), I want to make sure I am prepared for any unexpected events, such as gear malfunctions.  So I would like to talk a bit about some of those unexpected events and what you, as a well-prepared diver, can do to save the dive.

We all know scuba is a pretty gear intensive sport, so there could be a number of things that might go wrong that you can be prepared for.  Let’s start with some of the easy fixes with basic equipment: masks, fins, mouthpieces, snorkels and streamlining clips.  Having a spare strap or two for masks and fins is always a great idea.  Extra snorkel keepers are also a good thing to have around, as well as spare gear clips for streamlining (including retractors).  For those divers who have a tendency to bite down harder on their mouthpiece than they need to, having an extra one for yourself or a dive buddy can come in handy.  It’s always nice to make sure everyone has their equipment streamlined.  Spare clips for your’s or your buddy’s hoses are an easy thing to carry extra of.  Remember it might be you that has to use your buddy’s octo.  Do you really want it dragging around in the sand because he forgot his clip?  Another simple piece of gear that is great to have on hand is a box of spare o-rings.


Now let’s move on to something that takes a little bit more thought: BCD’s and dive computers.  Even though we take care of our gear, once in a great while something is bound to break.  The bcd has many areas of concern, such as buckles, straps and weight pouches.  Of those, the one that poses the most common problem is the weight pouches.  They generally do not break, but they do fall out on occasion for different reasons.  If you lose one, there is no safe way to do the dive without proper weighting.  Having a spare pouch (or if you’re “old school”, a spare weight belt) or two will come in handy.  And if you have changed out your original bcd tank strap for maybe a quick release type, you might just want to keep the old one in your dive bag just in case.

Now to what I think is the biggest issue that might end your dive: the dive computer.  Atomic and Suunto make great computers, but remember they are just that, an electronic device.  The main reason any computer might fail is often the battery.  Make sure you check the battery status before you go on your dive, and always have a replacement battery available.  If you can’t replace the battery yourself, you might have a tech nearby that knows how to do it for you.  And while I am on the subject of batteries, make sure you have a spare one for the transmitter to your air-integrated computer.  Another great idea is to have a completely separate computer.  Yes, you should be diving with two computers on your body, just in case.  If one of your computers fails during your dive, you are still able to continue on because you you’re your backup computer.  I really don’t know too many professional divers who dive with just one dive computer.  It just makes sense to have redundancy when it comes to such important equipment. 

So to make sure you have a worry free dive, you should carry with you what we call a “Save-A-Dive Kit”.  This will help to make sure you, or your buddy, can still make the dive no matter where you are, beach or boat.  Unfortunately, we cannot fix everything in the field, but for 99 percent of the issues that may come up, we can.  It doesn't have to be anything fancy. Just make sure your kit has the spare items that will keep you from calling your dive.  If you have any questions about what to put into your kit, talk to your instructor or go to your local dive shop.  If you are one of those people who don’t think it is necessary to have a kit, I have a question for you.  Why do we carry a spare tire in our vehicles?  How often does a tire go out on us?  Better safe than sorry – right?  One last thing, the kit does not have to be just for your dive gear.  Don’t forget about your underwater camera. 

Creature Feature: Blanket Octopus

Referred to by some as the "Caped Crusader" or the "Batman" of the underwater world, the blanket octopus is a strangely beautiful creature. This fascinating cephalopod was given the common name of blanket octopus because of its flowing webbing connected between its dorsal and dorsolateral arms, resembling a large blanket, as displayed by this adult female. As you can see in this photo, its remaining arms are much shorter and lack webbing.

These octopi are classified in the pelagic cephalopod genus tremoctopus. They are further broken down into four species Gelatinous Blanket Octopus (tremoctopus gelatus), Palmate Octopus (tremoctopus gracilis), Common Blanket Octopus or Violet Blanket Octopus (tremoctopus violaceus), and Tremoctopus Robsoni. Sightings of these elusive creatures are rare, but they are known to have been found in the subtropical and tropical waters of the Mediterranean Sea and the Atlantic Ocean, and along the northern coast of Australia,  preferring surface to mid-water depths.

This cephalopod does not use ink to defend against predators as other octopi do. Instead, it uses its blanket to intimidate predators with its size. It has also been observed to display another defense mechanism. These particular octopi are immune to the deadly sting of the Portuguese Man 'o War jelly. The males and young females who lack the enormous blanket instead rip off the poisonous tentacles of a man 'o war and use them as a weapon against their would-be attacker.

The Blanket Octopus is an extreme example of sexual dimorphism. This term refers to the differences between the size and various physical characteristics of the male and female in the same species. "Imagine if your spouse was 40,000 times heavier and a hundred times larger than you. This is reality for the male blanket octopus..." [1] A male may grow up to approximately an inch in length, whereas an adult female can reach a length of 6.5 feet. The males have a specifically modified third tentacle which it fills with sperm. During mating the male rips of this tentacle, presents it to the female, then drifts away to die. The female then stores this tentacle inside a large internal body cavity until she is ready to lay up to 100,000 tiny eggs. Interestingly enough, females have been found with multiple tentacles stored in this cavity. When the female is ready to fertilize her eggs, she will pull out this stored tentacle and squeeze it "like a tube of toothpaste" over the eggs which she will then carry at the base of her dorsal arm until they hatch.

Below is a short, albeit cheezy, video showing the fascinating beauty of a female unfurling her blanket.

This second video shows another octopus calmly cruising the depths. Watch closely around 1:40 where it appears one of her banners disconnects. I could find no explanation for this, but she appears to continue on unfazed.

To see a picture of a male blanket octopus go to :

http://www.selfishgene.org/Tom/Papers/MDNetal_NZJFMR02.pdf [2]

[1] Pickrell, John (Aug. 12, 2003)."Walnut-Size" Male Octopus Seen Alive for First Time. National Geographic News.

[2] Norman, M.D.; Paul, D.; Finn, J.; and Tregenza, T. (2002). First encounter with a live male blanket octopus: the world's most sexually size-dimorphic large animal. New Zealand Journal of Marine and Freshwater Research 36: 733-736.

The Undersea World of Jacques Cousteau

The creative juices have seemed to slow down for my fellow contributors lately so rather than just writing another Creature Feature, I have been thinking long and hard about what to write that you all might find interesting. When I write my blogs it is always because it is a subject I want to know more about myself. I research it and then I like to share what I find with you.

So what to write about this week? Well, why not write about one of the great innovators of SCUBA, Mr. Jacques Cousteau. For us over 40 folks, the name is pretty familiar, but for the younger generations, maybe not so much. Being a child of the 60's, I remember sitting in front of the TV with our dinners on our TV trays watching such great shows with my family as the forever bubbly Lawrence Welk Show, Laugh In, Hee Haw, The Wonderful World of Disney, Mutual of Omaha's Wild Kingdom, and of course, The Undersea World of Jacques Cousteau.

Born June 11, 1910, Jacques Cousteau entered the École Navale (the French Naval Academy) in 1930 and graduated as a gunnery officer. Unfortunately (however fortunate for us) a car accident cut short his dreams of a a career in naval aviation, so during his time of rehabilitation from this accident he turned his interests to what lay under the sea. 

In 1936 Cousteau began his diving career with a pair of Fernez underwater goggles. (As a little side note, Maurice Fernez was a pioneer in the field of underwater breathing apparati. He was elemental in the transition from the tethered diving helmet of the 19th century to the invention of the self contained equipment of the 20th century.) The actual self contained underwater breathing apparatus (SCUBA) used by Jacques Cousteau in the 40's was invented by Commander Yves le Prieur in 1926. Dissatisfied with the length of time this unit allowed him to stay under water, Cousteau improved the design by adding a demand regulator invented by Émile Gagnan in 1942. In 1943 Cousteau tried out the first prototype aqua-lung which finally made extended underwater exploration possible and opened the door to the open-circuit scuba technology we use today. With that Cousteau embarked on a long career of ocean exploration and underwater film-making.

In the late 1940's, he took part on a small team assigned to explore the Roman wreck of Mahdia (Tunisia). It was the first underwater archaeology operation using autonomous diving, opening the way for scientific underwater archaeology. In 1950 Cousteau founded the French Oceanographic Campaigns and leased a ship called Calypso which he had refitted as a mobile laboratory for field research and the principal vessel for his diving and filming. For his 1956 film "Silent World", Cousteau, assisted by Jean Mollard, constructed the experimental underwater vehicle SP-350, the "diving saucer", which was able to transport the researcher to depths of 1150 feet. In 1965 Cousteau repeated his success with 2 more experimental vehicles which could now reach depths of 1640 feet.

To recite Jacques Cousteau's numerous achievements and accolades would take longer than this blog's depth. Suffice it to say, Cousteau influenced abundant changes in the perception of our oceans. Cousteau believed in sharing his scientific concepts with the world and regularly referred to himself as an "oceanographic technician". The legacy of his life's work includes more than 120 television documentaries, over 50 books, and an environmental protection foundation with an astounding membership of over 300,000 (http://cousteau.org/).

Jacques-Yves Cousteau died unexpectedly in Paris on June 25, 1997, at the age of 87. To this day, he is one of the most famous undersea explorers of the 20th century. If I have piqued your interest in this passionate visionary of the underwater world, you might find one of these other websites interesting:

http://www.biography.com/people/jacques-cousteau-9259496

http://news.nationalgeographic.com/news/2010/06/100611-jacques-cousteau-100th-anniversary-birthday-legacy-google/

Creature Feature: Rosy-lipped Batfish (Ogcocephalus porrectus)

By request, today I present you with the rosy-lipped batfish (scientific name: ogcocephalus porrectus). Found in the waters of Cocos Island off the coast of Costa Rica, this odd looking fish looks like it is ready for its "maybe it's Maybelline" close-up for smear-proof lipstick, but it definitely needs a shave.

This bottom-dwelling fish can be found at depths ranging from 90 to 450 feet. Seen from above, it has been said to resemble more of a "frog fish roadkill" than a bat. Full-grown it is about the size of your open hand, nearly flat on top, and spreads its pectoral fins out to its sides. A slow and clumsy character, the rosy-lipped batfish uses its pectoral and pelvic fins like legs to crawl on the ocean floor rather than swim. Ichthyologist and batfish expert John McCosker says they prefer to “sit upright, like old tail-dragging airplanes.”

It has a leathery skin that feels like sand paper and large spiny knobs covering its back. To add to its bizarre appearance, this fish has a unicorn-like horn protruding from its head. According to McCosker, this rostrum (a Latin word meaning "beak") is "firm - sort of like chicken gristle, and it protects a thin, retractable appendage that the batfish deploys to lure small edible fishes".

Ogcocephalus corniger is found in the waters of the southeastern
United States and the eastern Gulf of Mexico. 

Rosy-lipped batfish are voracious, carnivorous eaters who prefer a diet consisting mainly of small fish, shrimps, mollusks and crabs. An interesting x-ray of a close relative to the rosy-lipped batfish shows just what they enjoy eating. Another close relative is the red-lipped batfish, also called the Galapagos batfish (Ogcocephalus darwini), so aptly named for its choice of residence.

Why this drag-queen-looking fish looks like it does, I don't know if anyone really knows. I didn't find any answers in my research. But does the rosy-lipped batfish remind you of anyone in your family?

Creature Feature: The Blue Dragon (Glaucus atlanticus)

The first time I saw a picture of this little guy I thought it had to be a photoshop thing; some little creature made up by some talented artist. It made me want to delve deeper, and you know what I found - It really does exist!

Believe it or not, this little sea slug or nudibranch, is pelagic (lives in the open water). It is often found floating upside down on the surface of the ocean in temperate and tropical waters in such regions as the east and south coasts of South Africa, Mozambique, European waters, the east coast of Australia, and the islands of Hawaii. They also have been spotted in the waters of Bermuda. Its average size when fully grown is a whopping 3-4cm. The blue dragon's floating abilities are due to a gas-filled sac located in its stomach. Because of its location, this sac causes the slug to float upside down exposing its blue-white foot to the surface of the water, leaving the silver-gray dorsal surface facing downward into the water. This is an example of counter shading, where the coloration helps to protect the organism from it predators both below and above. These slugs spend most of their lives drifting along, directed by currents and winds. They are generally not observed by humans except on those occasions when strong onshore winds bring masses of them (often called the "blue fleet") to beaches, causing much pain for swimmers and beach-goers.

Common names for this beautiful slug are blue dragon, blue glaucus, blue sea slug, blue ocean slug, and sea swallow. G. atlanticus is carnivorous and preys on other, larger pelagic organisms such as the venomous Portuguese Man o' War, the by-the-wind sailor, the blue button, and the violet snail. They have also been know to become cannibalistic.

The blue dragon is immune to the venomous nematocysts of the Portuguese Man o' War, and when consuming this animal, appears to select and store the most venomous nematocysts in specialized sacs called cnidosacs on the tip of its feather-like fingers. Because it is able to store up this venom for future use, ironically it can produce a more powerful and deadly sting than the man 'o war upon which it feeds.

Blue dragons are hermaphrodites (have both male and female reproductive organs). After mating, both animals produce 4-6 egg strings within an hour that float freely in the water or are placed on the remains of prey. These busy little slugs can produce from 3300-8900 eggs per day.

References:

1. Glaucus atlanticus Forster, 1777. World Register of Marine Species, accessed 3 April 2010.
2. "Marine Species Identification Portal : Glaucus atlanticus". Species-identification.org. http://species-identification.org/species.php?species_group=pelagic_molluscs&id=189. Retrieved 2011-11-21. 
3. Rudman, W. B. (6 November 1998). "Glaucus atlanticus Forster, 1777". Sea Slug Forum. http://www.seaslugforum.net/factsheet.cfm?base=glauatla. Retrieved 26 February 2011. 
4. Debelius, H.; Kuiter, R. H. (2007). Nudibranchs of the world. IKAN-Unterwasserarchiv. ISBN 978-3-939767-06-0. 
5. http://seaslugsofhawaii.com/species/Glaucus-atlanticus-a.html
6. http://www.thecephalopodpage.org/marineinvertebratezoology/glaucusatlanticus.html

Chris’ Dive Experiences: Unlock A Passion For Sharks And Shark Diving

 If you hang around anybody that was diving in the 70’s to early 80’s in Southern California chances are you’ve heard the stories of how healthy our ocean was back then. From just snorkeling in a few feet of water off La Jolla and pulling up trophy sized abalone with little time and effort, to sitting at the face of an overhang underwater and trying to decide how many trophy sized California Spiny Lobster you were going to take, to being on a local SoCal dive boat and getting bored at seeing more blue sharks on the way to your dive site off Catalina Island because it basically always happened. 

Unfortunately, gone are days of any of the above experiences happening without a lot of time, money, and effort. But if you are willing to spend a couple hundred bucks and a full day on a small boat you just may unlock something you didn’t even realize was buried deep inside you, a passion for sharks and shark diving.

Our day started before the sun rose, meeting with the group and loading up our gear on the boat before it was backed into the water in Mission Bay. Once outside of the Mission Bay channel the Captain hammered the throttle and we arrived off Torrey Pines to start chumming in no time flat. As we sat and waited stories were shared of past diving trips and future plans of travel and diving. The hours passed and we all wondered if we were going to get skunked and not see any sharks. 

As the clock neared 1:30pm the single word that everyone was waiting to hear was screamed, “SHARK”! Some of us started scrambling into gear while others got up to get their first view of a pelagic shark outside of an aquarium. As the young Blue Shark circled the chum bucket behind the boat we started to gently slide into the water, one by one, in our snorkel gear. The first time a Blue shark approaches you to see what you are, you are instantly in awe of its huge inquisitive eyes, sleek powerful body, and last but not least, the eye popping iridescence of its skin as the sun rays dance upon it.

Close encounters continued throughout the afternoon, with the Blues swimming to and from the chum bucket and weaving in and out of the snorkelers, gently checking each of them out. Blues tend to investigate by bumping, and as they would swim by to check snorkelers out, these sharks would usually turn in toward the snorkeler. If you ever find yourself in this situation, just keep your cool and remember all that is needed is a little redirection with your hand to steer them away from you. This kind of shark diving provides a truly intimate experience between you and the shark, leaving you with a lasting impression of the beauty, power, and elegance of diving with Blue Sharks.

As the remaining hours of sunlight burned off, we enjoyed the experience of 3 different Blue Sharks coming to check the chum and the snorkelers out, giving each snorkeler ample time to shoot pictures and video of the sharks. Each and every person had a cheek to cheek smile when describing their encounter with the Blue sharks on this day.  As we pulled back into the Mission Bay Channel, the sun disappeared below the horizon ending a very special, intimate day diving with the majestic Blue Sharks of San Diego.

What do you think? Do you have a passion for sharks? Do you have a hidden passion for shark diving waiting to be found? Will you join the ranks of the few that chase sharks around the world seeking out special, sometimes mere seconds worth, of an encounter that will always remain in the shark divers memory? Maybe, maybe not. Let me know if you would like to experience this for yourself.

Chris' Dive Experiences: Mola Mola Bonanza Diving The Eureka Oil Rig, Long Beach

Diving in southern California and reading the local diving publications has long put diving the Eureka oil rig on my radar. It’s not too often a dive site offers a man-made reef sitting in over 600 feet of salt water. Being surrounded by open ocean, you also have a chance to see pelagic species. Diving the oil rigs may conjure up video of the military doing parachute jumps with everyone geared-up in a line, jumping in one after the other. This is called a “live boat”, meaning the boat is never moored and is under power at all times; divers line up and jump in all at the same time.

We awoke on the day of the trip to beautiful clear skies and flat seas as we motored out on the Sundiver Express. It only took us 20 minutes to reach the Eureka rig. I was surprised by just how big the rig was when we got close; it rose to around 10 stories tall. We were briefed on the diving procedure and told to gear up and get in line. Once ready, the boat backed right up to the rig pilings and two by two all of us did a giant stride in.

Photo courtesy of Lesley Alstrand

As I descended, I was instantly struck by the explosion of life. Every single inch of the pilings were covered with strawberry anemones, white anemones, brittle stars, sea stars, scallops, muscles, nudibranchs, and urchins. As we continued down to 130 feet, we were also mesmerized by some of the pelagic jellies and salps that we passed by, many of which just defy logic of how they look and move. The life on the piling at 130 feet was just as dense as the life near the surface no matter which direction you looked. It could keep you occupied for hours instead of the mere minutes that we had. As we worked our way back toward the surface I couldn’t believe it when I saw in the corner of intersecting beams a group of lobsters inching out to see what I was. Thinking of the journey that these lobsters made to end up this high on the pilings and crossbeams, with the sea floor more than 500 feet below, was amazing to me.

Around this time I started looking and moving out into the blue that surrounded us, hoping to see something special. After only a few minutes of slowly ascending and moving back and forth along the pilings, I saw something coming toward the piling. I couldn’t quite figure out what it was. Once it got closer I couldn’t believe my eyes. I was finally getting to dive with a mola mola! The mola mola came very close, checking us out with one of its big eyes as it passed very calmly. At this point everyone in the water was very excited at what we just got to see. Little did any of us know this experience would be trumped in less than a minute. I had my eyes peeled, hoping to see the mola mola coming back and trying to be in the right place to film it on its return. As I looked into the blue I saw the shape of the mola mola coming towards us and then another, and another and another. No less than ten mola molas coming right up to the pilings and divers this time; not only checking us out but also playing in the bubbles from the divers. The mola molas stayed with us for the rest of the dive, calmly making close passes by us. It was very exciting to see this unique and hard to find species and get loads of time interacting with them.

The mola molas seemed to enjoy us as much as we enjoyed them.

Photo courtesy of Lesley Alstrand

Scuba Cylinders - Misconceptions & Maintenance

There are a few things I would like to cover in this installment of the equipment blog.  First would be the big misunderstanding between cubic feet and psi. Then I will go over the different types of bottles, (metals and sizes).  Finally, I will cover safety and maintenance as well.


CUBIC FEET vs PSI  

Which tank holds more air:  1) aluminum 80 at 3000 psi, or 2) steel 65 at 3442 psi?  Most people would pick the steel tank because of the higher pressure at 3442 psi.  Well, if you are one of them, I am sorry to say you have been misinformed.  So let’s cover the difference between cubic feet and psi.  I have heard people say they want a tank a greater psi because it means it holds more air.  In a way they are correct.  An aluminum 80 with 3000 psi has more air than an aluminum 80 with 2000 psi, but a steel low pressure 120 at 2400 psi has more air than the aluminum 80 at 3000 psi.  It comes down to this, the cubic feet (cu ft) tells you how much air the tank will hold or the capacity of the cylinder while the pounds per square inch (psi) tells you the pressure (how full the bottle is).  So when you talk about an aluminum 80, this tank has a storage capacity of 80 cu ft which is less than a steel 120 (a storage capacity of 120 cu ft) regardless of the pressure.

So when picking out a tank, you need to know how much air you want to take with you.   If you are someone who uses a lot of air while diving and are tired of being the one who makes the group turn around due to air consumption, then you may want a bigger tank.  When I say bigger I mean a bottle with a greater storage capacity (cu ft) and not worry about the psi.

ALUMINUM vs STEEL

So what bottle do you get?  You basically have two options aluminum cylinders or steel cylinders.  From there you can break down the steel ones into two more categories; low pressure (2400) or high pressure (3442 or 3500 psi).  Here is a chart on the differences on the tanks:

LOW PRESSURE Steel

In sea water with valve	LP77	LP85	LP95	LP108	LP121
Service Pressure	2400+ psi	2400+ psi	2400+ psi	2400+ psi	2400+ psi
True Capacity @ 2640 psi	77.0 cuft	82.9 cuft	93.3 cuft	108.6 cuft	120.0 cuft
Buoyancy *FULL	- 6.8 lbs	- 7.1 lbs	- 10.1 lbs	- 10.7 lbs	- 11.1 lbs
Buoyancy *EMPTY	-1.0 lbs	- 0.7 lbs	- 3.0 lbs	- 2.6 lbs	- 2.0 lbs
Weight Empty	32.5 lbs	36.8 lbs	41.9 lbs	45.95 lbs	49.9 lbs
Outside Diameter	7.25 in	7.25 in	8.0 in	8.0 in	8.0 in
Length +/- 0.125”	23.2 in	24.7 in	23.7 in	26.5 in	29.2 in

HIGH PRESSURE Steel

In sea water with valve	X7-65	X7-80	X7-100	X7-120	X8-119	X8-130
Service Pressure	3442 psi	3442 psi	3442 psi	3442 psi	3442 psi	3442 psi
True Capacity @ 2640 psi	66.4 cuft	81.0 cuft	99.5 cuft	120.6 cuft	123.0 cuft	131.4 cuft
Buoyancy *FULL	- 8.7 lbs	- 9.0 lbs	- 10.0 lbs	- 11.0 lbs	- 10.9 lbs	- 11.7 lbs
Buoyancy *EMPTY	- 3.9 lbs	- 3.0 lbs	- 2.5 lbs	- 2.0 lbs	- 2.0 lbs	- 2.0 lbs
Weight Empty	25.1 lbs	29.9 lbs	33.1 lbs	39.7 lbs	42.5 lbs	44.7 lbs
Outside Diameter	7.25 in	7.25 in	7.25 in	7.25 in	8.0 in	8.0 in
Length +/- 0.125”	16.7 in	19.8 in	22.7 in	27.7 in	23.9 in	25.3 in

Now the nice thing about steel tanks as compared to the aluminum, is that they are more negative buoyant (Most people can take off about 6-8 lbs of lead when diving) and the high pressure tanks are also a bit shorter.

ALUMINUM

In Sea water with valve	AL50	AL63	AL80	ALN80	AL100
Service Pressure	3000 psi	3000 psi	3000 psi	3300 psi	3300 psi
True Capacity	48.4 cu ft	63.0 cu ft	77.4 cu ft	77.4 cu ft	98.8 cu ft
Buoyancy* FULL	- 2.3 lbs.	- 2.2 lbs.	- 1.4 lbs.	- 5.7 lbs.	- 4.3 lbs.
Buoyancy* HALF	- 0.5 lbs.	+ 0.2 lbs.	+ 1.5 lbs.	- 2.8 lbs.	- 0.6 lbs.
Buoyancy* 500 psi	+ 0.8 lbs.	+ 1.7 lbs.	+ 3.4 lbs.	- 0.9 lbs.	+ 1.9 lbs.
Weight EMPTY	21.2 lbs.	26.7 lbs.	31.4 lbs.	35.4 lbs.	41.0 lbs.
Outside Diameter	6.90 in.	7.25 in.	7.25 in.	7.25 in.	8.00 in.
Cylinder Length	19.0 in.	21.9 in.	26.1 in.	25.8 in.	26.2 in.

As you compare the charts you can see which bottle is going to be the best for you.  Aluminum tanks are less expensive but the steels have more benefits.

MAINTENANCE & SAFETY

Both Rod & Chris are certified
by PSI to perform visual inspections 

Once you get your cylinder you need to make sure you are safe with it and you properly maintain it. It is fairly easy to take care of the bottles; you just need to make sure you follow through. You can rinse off the bottle - this will help keep the salt away from the coating.  If you do choose to rinse your tanks, make sure you do not get water into the valve.  Make sure you always leave some air in the tank as well.  Never bring an empty bottle to the shop for air. If you do, a visual inspection will have to be conducted prior to any air fill to assess the condition of the tank.

The big maintenance exams for scuba cylinders are what are called a visual inspection and a hydrostatic test.  "Visuals" should be performed on your tanks annually, while "hydros", at least here in the U.S., should be performed every 5 years.  There are other times this maintenance has to be preformed: if there looks to be damage to the bottle, as if it appears to have been dropped; if the air inside has an odor; noise is made from inside the tank; increased weight; or if the valve has been removed.  In most cases though, under normal usage, just the basic visual will be done once a year and the hydro every 5 years in order for your tanks to be filled by a certified air station.

Now here is a little bit on safety.  Everyone should know not to leave tanks standing, especially with gear is attached. "Why is this?" you ask. Because if the tank falls, it could damage the valve or other equipment like your regulator or mask, or worse, could roll down the driveway or into the street. Strange how round things tend to roll down hill.  Another nice little safety tip is how to carry your tank properly.  When you grab the valve you should have the air outlet pointing away from the palm of the hand.  This will make sure the pressurized stream of air does not blow into your hand, and holding the knob in this manner will turn it into the off position ensuring air will not leak from the valve.

So remember, when you are ready to buy a tank make sure you are getting what fits your diving. Do you want small and compact, or do you want all the air possible?  No matter what one you get, make sure you are safe with it and take the proper measures to ensure the bottle will last a lifetime.  That is about it for cylinders, maybe next time I will talk about the valves. Or is there something you want to know a bit more about? Just let me know.