Go deep, stay long

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.  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.

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.

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.