Archive for January, 2009

How deep can you dive on SCUBA?

Wednesday, January 14th, 2009

When people first hear about SCUBA diving, many ask this question.   My standard response is “to the bottom”.   While I am joking a bit, unless you’re doing a wall dive, this is usually the case.

Part of the answer depends on the location of the dive: off the coast of New Jersey, the bottom slopes gently for the first 30-50 miles.   Shortly after this we hit the Continental shelf, commonly called the Canyon.   Here the depth drops sharply to several thousand feet.   Obviously our diving is on the gently sloping bottom.

About 3 miles off the beach, the depth averages about 60ft.  After 20-30 miles, there are some great wrecks in 130 ft.   The bottom slope does vary from place to place.   There is narrow trough cut by the Hudson river commonly called the Mud Hole. Inflatable Water Slide It is deeper than the surrounding area, but the outflow of the river makes the conditions more challenging.

The rest of the answer depends on the diver’s experience and training:

Novice divers should stay shallower than 60ft, until they develop the skills and comfort in the water necessary to go deeper.

Advanced divers go between 60 and 130 ft.  At this point they carry additional safety equipment necessary to perform these dives.

Technical divers go beyond the 130 ft range down, sometimes in excess of 300 ft. These divers have spent years training and practicing for these dives.  They carry redundant gear and practice techniques to survive equipment failures.   Many famous shipwrecks are in this range: the Andrea Doria, the U-869, the Black Sunday wrecks including the S.S. Carolina.  These all fall in this range of technical dives.

How deep do I personally go?  Well, I teach Technical Divers.  While I enjoy spearfishing and photography in the 50-130 range, we can often be found diving in the 180-250 range.

What is a Rebreather?

Tuesday, January 13th, 2009

Many people see my dive gear, and ask “What newfangled contraptions is that”? Ok, maybe they don’t use the word “newfangled”, but you get the point. I dive a Closed Circuit Rebreather (aka CCR). While people think of these as “new”, they actually predate the gear we consider standard SCUBA (also called Open Circuit or OC).

History: Early rebreathers were used not for diving, but for escape. Mines and Submarines both presented situations where a compact breathing device was needed to allow crews to escape to safety. Theses were developed back in the early 1900, and produced in quantity by 1910. Open Circuit SCUBA was not commercially available until the mid 1940s.

How do they work: Let’s start with a quick review of metabolism. Our cells take in food and Oxygen (O2). These are combined to produce energy, but have a toxic byproduct of Carbon Dioxide (CO2). Our Cardiopulmonary system takes some of the O2 from the air we breath, and distributes it to our cells. At the same time it takes the CO2 generated bouncy castle for sale by our cells, and releases it into the air that we exhale. The O2 and CO2 exchanged by our lungs is actually a small percentage of the volume of gas that we breath (about 3%-5%).

On Open Circuit, when a diver inhales, the regulator provides the diver with gas (usually air) at same pressure as the surrounding water. When we exhale, the gas is vented out into the water producing the column of bubbles associated with diving.

When a CCR diver exhales, the gas is vented into a flexible chamber called a counter lung. Within the Rebreather, O2 is added back into the gas, and it is passed through a “scrubber” which removes the CO2. We then inhale the same gas which again contains the proper O2 percentage.

With OC 95% of the gas we exhale has not been affected by our respiration. It is not used. It is wasted. On CCR, this 95% is recycled, cleaned of CO2, enriched with O2, and breathed again. This allows us to make use of smaller tanks, as our O2 consumption does not change with depth.

Monkfish, Round 1

Tuesday, January 13th, 2009

I retell this story regularly, and get a variety of responses.  As such, I thought I’d add it to the blog.    I really don’t recall the date, so let’s just say “long, long, ago in an ocean just off the beach”, I spotted my first Monkfish.  I don’t have my own picture of one, so I’ll have to reference a shot by Herb Segars. 

A little background for those of you unfamiliar with these creatures.  They are often called goose fish, or all mouth.  The latter is more a description, and an accurate one.   They are in the anglerfish family, and are mostly head and mouth.  They grow to over 5 ft in length, but 3 ft is more common.  They lie flat on the bottom with their belly down (like a skate or ray) but with the mouth facing up.   They are also well camouflaged.  When food (fish, lobster, crab, diver … ) comes within range, they quickly open their huge mouth which sucks water into their mouth and hopefully the prey comes with it. If they don’t completely swallow their prey on the first attempt, the rows of sharp teeth hold it in place for a second or third try.   Basically they are a large ugly eating machine.   The part of the fish that is not mouth, is mostly stomach.   On the other hand, the little bit of fish that remains is very good eating.

Stories are told of divers not seeing the fish, and kneeling on them, or putting their hands on them.  The shock factor having the sand come alive and try to grab you with rows of teeth, is the subject of many a dive tale.   Others tell of battles with the beast which often resulted in leaking drysuit or torn gloves.

Back to the story.   So here I am, novice diver swimming along spearfishing sea bass and totaug.  While making a pass over an old derelict lobster pot, I notice an odd shape in the sand.   It’s clearly not a fluke, and after a few seconds, I come to the conclusion that it’s a Monkfish.   Now what?  I’m not sure I want to argue with it, as it was larger than any fish I’ve encountered to date.  As I was the last in the water, and my dive is about done, I know Captain George should be down here somewhere hunting lobsters and getting ready to pull the hook.   I quickly found him and signal him over.

The ensuing conversation was all made with hand signals and gestures, but went something like this:
George:  Do you want him?
Dave:  I guess.
George:  Open your bag in front of him, and I’ll prod him into it.
Dave: OK, but I hope I don’t lose the fish in the bag.
Monkfish:   I’m not that dumb.   Stop putting that bag in my face.

One plan down.  Now what?  George bouncy castle for sale motioned for me to hand him my bag.  I obliged.  George opened the bag, then with one motion, he picked up the fish by the tail, and dropped it into the bag and closed it, before the fish had a chance to react.   He handed me the bag, waved goodbye, and went back to hunting lobster.

I could not help but laugh after hearing stories about these beasts.   My dive time was done, so I headed up the line.   Picture if you will, I’m holding the anchor line in one hand, and a bag of fish, including a very aggravated Monkfish in the other.  He’s got his mouth wide open, and I’m looking at rows of teeth that would easily poke holes in my drysuit.   My bag was one with a metal loop around the top that acts like an old style woman’s purse.   I finally figure out that sticking one end of the metal loop in his mouth will cause him to bite down, therefore preventing him from attacking me.

With a small degree of satisfaction, I board the boat only to find that I had avoided one attack, but fell victim of another.   Another endearing property of Monkfish, they generate slime. Lots of it.  I guess It’s either part of their camouflage, or stomach secretions from having it’s mouth open during the ascent.  Either way, I’ve been slimed!  My drysuit looked as if a giant had sneezed on me.  I put my catch bag in my cooler, then jumped back in water to clean the suit.

After everyone was aboard, we discovered that no one knew how to clean a Monkfish.    Fortunately, when we returned to the dock, George was able to find a commercial fisherman with the required knowledge, and hankering for lobster.   He made quick work of the task, and several of us went home with fillets in hand. I mean cooler.

In the end, Monkfish is good eating, but I must warn you, they are not for the timid.  It was a few years before I went for another one. They are not to be trifled with. They’re a mess to bring up, and a smelly mess to fillet.

What is SCUBA?

Monday, January 12th, 2009

It’s a common question.  Many have seen SCUBA divers on TV, but don’t know what it is, or how it works.

SCUBA is an acronym for Self Contained Underwater Breathing Apparatus. As an acronym, SCUBA should always be upper case. However, the word is so common that it is often lower case, or Scuba. In it’s simplest form the “apparatus” includes:

  • a tank which contains pressurized air
  • a regulator which converts the high pressure air to a pressure we can breath
  • a Buoyancy Compensator (BC) used to adjust our buoyancy underwater

The above gear is often referred to as the “SCUBA unit”. There are other forms of SCUBA, but this is the most common.

Some other gear that we also use when SCUBA diving:

  • a mask which allows us air breathers to see underwater
  • fins that make it much easier to swim
  • an exposure suit to keep warm in cold water
  • various gauges to measure depth, time, and air pressure

We really can’t dive without this gear, but it’s not exclusive to SCUBA diving.

There is also a variety of safety gear used in SCUBA diving. As the diving conditions become more challenging, the amount of gear increases. Below I’ll cover each piece of gear in more detail.

SCUBA tanks

Sunday, January 11th, 2009

Tanks are made to hold air pressure. They come in different materials, colors, sizes, shapes and pressures. To add more confusion, they even have different types of valves. As if this weren’t bad enough, different countries have different standards for tanks, and how the sizes are measured.

Material: Let’s start with the basics. The tanks are made of either steel or aluminum. There are pros and cons to each material. While aluminum is a lighter alloy, it’s also not as strong as steel. Therefore the walls of an aluminum tank have to be thicker, thus defeating the advantage of light weight. On the other hand steel is more prone to rust damage than aluminum. Before you buy a tank, talk to divers in your area and find out what they dive and why.

Color: The color of the tank really has no meaning and is strictly a personal preference. I like the unpainted ones myself. Often the paint on tanks flakes off after a few years, and defeats the purpose. Again, it’s just personal preference.

Size:   First, what do we mean by “size”?  In the USA we measure tank size by the number of cubic feet of air it can hold when it is full.  One of the most common tanks is an aluminum 80, which holds 80 cubic foot of air when full.    How much air is 80 cf?  It’s about the size of old telephone booth.   For those of you too young to remember those, think of a full size refrigerator.   We use a compressor to squeeze that air into a tank that measures about 1/3 of a cubic foot on the outside.

I like to think of tank sizes in two categories; primary tanks, and special purpose tanks.  Primary tanks are used to hold your main air supply.  They range from 60 cf up to 130 cf.  Why such a range?  One simple reason, it’s different size tanks for different size people.   There are other considerations we will discuss later.

Special purpose tanks vary in size from 6 cf up to 50 cf.  These are commonly used in addition to the primary tank for backup, to provide inflation to other gear, or to hold other gases.

Pressure: How do we know it’s full?   The air around us is under pressure, about 14.7 pounds per square inch (psi).  This pressure is created by the gravity pulling on the atmosphere above us.   When we compress the air into a tank, we increase the pressure.  Different tank materials and construction can withstand different amounts of pressure.  Therefore different tanks have different “rated” or usage pressure.  Some are as low as 2400 psi, others as high as 4500 psi.  Most modern aluminum tanks are rated at 3000 psi.   Most modern steel tanks are either 2400 or 3446 depending on the alloy and construction.   When the pressure in the tank is equal to the rated pressure, then the tank is full, and contains the rated volume of gas.

Boyle’s law tells us that this relationship between pressure and volume is linear.    Thus half the pressure means half volume of gas.   If an 80cf tank is full at 3000 psi, then at 1500 psi it has 40 cf of gas.  While diving, we carry a pressure gauge to measure our tanks.  The gauge measures psi not cubic feet, but like the gas gauge on your car, it give you an indication of what fraction of your gas is left.