WARNING: This post, or any on this blog for that matter, doesn’t constitute and is no subsitute for proper training and experience. We encourage you to seek the proper training before you attempt anything our posts discuss.

If you’ve spent any time on dive boats you’ve probably heard buddies or teams plan the next dive. It often goes something like this:

Buddy One: Let’s head out at 215 degrees.

Buddy Two: Okie Dokie.

*splash*

Hardly a comprehensive dive plan. At the very least they are missing a good gas plan. A solid gas plan tells us how much gas you should reserve to get you and your buddy back to the surface completing all the scheduled deco obligations. Remember, every dive is a decompression dive and we need to let our bodies off-gas the nitrogen we have built up in our tissues.

“But I have a computer! It tells me how much breathing gas I have left in terms of time! Neat huh?”

Computers are useful tools. However, letting them do all the thinking for us is not a good idea. First off, your computer is pretty dumb. You’re computer has no idea what your buddies air consumption is like. It doesn’t know what your ascent profile looks like, wether you plan to do deep stops at 75-50% of your depth or just a three minute “safety stop” at 10-20ft.  It also hasn’t the foggiest what your air consumption is like during an emergency. This is often as high as 1cf/min or 25-50% faster than your regular consumption rate. When your teammate has an out-of-gas emergency is not the time to find out you’re going through your gas twice as fast as your computer thought you were. Long story short: You are smarter than your computer. There is a fast and easy way to plan your gas usage with your buddy to make your diving safer and more enjoyable. Let’s take a look:

Proper Gas Planning In Detail

There are a few things we need to know to make a proper gas plan. Firstly, we need to know how many cubic feet there are per 100 PSI in our tanks. This number is called a “Tank Factor.” Not all tanks are the same and 1500PSI in a HP100 is not the same amount of gas as 1500 PSI in a LP85. Second, we need to know what our ascent profile looks like. Third, how much gas will we be using per minute in an emergency and lastly, what will our average ATA’s, or atmospheres absolute, be during the ascent?

What the heck is a tank factor?

Different tanks have different service pressures and volumes. So how do we come up with the PSI per cubic feet in terms of a nice round easy to work with number like 100 PSI? The answer is determining our bottles “tank factor.” Let’s do a little math. I know, I know but it’s easy I promise.

How do we calculate our tank factor? We divide the rated volume by the rated service pressure and multipy that number by 100. Boom. Easy yes?

Let’s look at my shiny new LP85′s. They have a volume or 85CF and a service pressure of 2400PSI so my tank factor would look like this:

100(85cf/2400PSI)=4 Tank Factor

So my tank factor would be 4cf/100 PSI or just “4″. Remember, this is back-of-the-cocktail-napkin math so there is no need to be super precise. Rounding up to a whole number is just fine.

How long will our ascent profile take?

We need to determine how much time it will take us to deal with an emergency and ascend to the surface. For our example lets say we are on a 100ft dive. For this example we are going to using the ascent profile that PADI recommends: A direct ascent to the surface at 33ft/min and a three minute safety stop at 10-20ft. let’s also give ourselves one minute to deal with the emergency and get everything stowed away and ready to ascend. How much time will we need to get to the surface? The calculations look like this:

1min Emergency Time+(100ft Max Depth/33min Ascent Rate)+3min Safety Stop=7min.

So, at the very least we are going to need 7 minutes of gas to get us safely to the surface.

Great, 7 minutes. But how much is that in cubic feet?

We need to know our emergency air consumption rate. Hopefully, your not the type of diver who gets into emergency situations often enough to know this figure off the top of your head so let’s use the industry standard of 1cf/min.

7min(1cf/min)=7cf

So we need 7cf to get us back to the surface? Not quite. Our gas goes faster when we are at depth and we need to factor that into our plan. We can aproximate our average depth in feet for our ascent plan by dividing our max depth by 2, or…

100fsw Max Depth/2=50′ Average depth.

Still pretty easy? Feet doesn’t do us much good here though as we need to know how many cubic feet of gas we need. To calculate that number we need the average ATA’s of our ascent plan. To find our avergage ATA’s we divide our average depth by 33 and add 1.

50ft/33+1=Average ATA’s

Average ATA’s = 3

Multiplying the minimum amount of gas we need, 7CF, by our average ATA’s will give us the amount of gas we need to get a diver home.

7cf(3ATA)=21cf

But wait! That’s 21cf for one diver, not two. Let’s double that number.

21cf(2 Divers)=42cf.

“That’s great and all, but my gauge shows PSI not cubic feet.”

Still with me? Good. 42cf of gas minimum gets two divers safely back to the surface from 100′. But that number is not really that useful for us either. We need to know that figure in terms of PSI. How do we get that? By dividing our tank factor by minimum gas in cubic feet multiplied by 100.

(42cf minimum gas/4 Tank Factor)100=1050PSI

Well there you have it.

The magic number. 1050PSI is the bare minimum you need to leave the bottom with to get two divers safely back to the surface from 100′ on an LP85. Is it more than you thought? Keep in mind in an emergency situation, minimum gas means that you will have zero PSI in your bottle when you hit the surface. Because a tank with less than about 300 PSI may have gotten water in it, it will need a visual inspection or it might corrode. In an emergency, however, that will be the least of your worries. After some practice creating a solid gas plan shouldn’t take more than a couple of minutes to figure out in your Wetnotes.

I hope that helps even the most math phobic of you. Call or drop by the shop if you have any questions. and as always, safe diving.

Ok, let’s be honest. How good is your buoyancy? Proper buoyancy and propulsion techniques are the corner-stone of better diving. Being able to use the skills you learned in class while hovering horizontally will greatly increase you confidence and safety, lead to better air consumption and save the reef for other divers to enjoy. There are two basic building blocks to good diver trim: body positioning and propulsion techniques.

Good trim starts with proper body positioning. Arching your back slightly while keeping your head up and feet parallel with the bottom puts you in roughly the right orientation. Keep your hands folded out in front of you to counter balance your center of gravity. Keeping your hands folded also helps you fight the temptation you use your hands for stability.

There are two reasons we keep our hands relaxed and folded when diving. Firstly, your leg muscles are much stronger than your arms. Using your leg muscles to control trim is much more efficient and will lower your air consumption. Secondly, from your buddy or teams perspective, one more hand used to control your buoyancy is one less hand available to help them in an emergency.

Have you ever noticed that controlling your buoyancy while moving is much easier than holding a stationary hover? The reason is most divers fin in such a way that their thrust is directed downwards. This means you need to be slightly negative to maintain your position in the water column. So when you stop kicking, you’ll need to add air to your BC to compensate.

Frog kicking or a modified flutter kick will force the trust from your fins directly back. This means you simply glide to a halt when you stop kicking. Improper finning technique means every movment you make with your fins moves forward. Learning to use the sides of your fins by slicing outward from the frog kick position dives water forward and the diver back. Quite a handy skill to have in heavy surge over an urchin encrusted reef.

The take home is this: Continuing to develop your buoyancy skills means better air consumption, better buddy or team safety, and less environmental impact to the reef.

Check out Andrew’s demo and stop by the shop if you have any question.

As always, safe diving.

While I haven’t gotten to play with this camera and the Ikelite housing set up on paper it looks great. The SLT-A55V has a feature set that would be of interest to underwater photographers.

The big advance that makes this camera a threat is Sony’s new Translucent Mirror Technology. apparently, this lets the camera focus and shoot simultaneously. Unlike other DSLRs, the mirror in these cameras never moves. This eliminates the time needed to raise and lower the mirror. The benefit is  speeds of up to 10 fps. What’s more interesting to me is the fact that there is no optical viewfinder on the camera. Instead it boasts an electronic viewfinder that Sony claims is WYSIWYG(What You See Is What You Get.) This gives you an approximation of the white balance and exposure before you take the shot. I can envision a bright LED viewfinder with 100% coverage that I can see under a dense kelp canopy or down deep on a wreck.

The camera also shoots 1080p HD video in the easy-to-edit H264 AVCHD format. The nice thing about this is the autofocus uses phase detection which can be much faster than traditional autofocus for fast underwater subjects like sea lions.

The APS-C sized sensor is a bummer, but to be expected as a competitor to the APS-C Canon and Nikon lines. A smaller sensor contains denser packed photo sites than a full frame camera which can produce more noise. Low light performance also suffers. However, Sony touts their Sony Exmor™ APS HD CMOS technology as achieving phenomenal resolution with no penalty in low-light sensitivity or sensor noise. The sensor is a CMOS versus a CCD so it remains to be seen how Sony addressed the wobbly ”jello cam” effect that plagues Nikon’s APS-C sized sensors.

Another problematic area is the camera uses the Sony A lens mount. Sony optics are nothing to balk at but, let’s face facts here, Canon and Nikon make better DSLR glass. You are also a little limited in your lens A mount choices too. You can opt for a camera lens package that includes a 18mm fixed lens that equates to about a 28mm on a full frame sensor.

Bottom line here is that for a camera and housing package that comes in at under $2,500, it’s worth a serious look. If you get one in your hot little hands shoot us a review in the comments and let us know how you like it.

Channel Islands Scuba is starting a Photoshop and Lightroom  for Underwater Photographers course, January 11th, 2010. Here is an excerpt from the class on how to use curves to color correct your images. Enjoy.

A favorite of macro photographers, these critters are a beautiful, vibrant pinkish red invertebrate. They live on rocky substrate in colder waters. This “anemone” is not an anemone at all, but rather they are more closely related to the corals of the tropics. because they reproduce by fission, each colony is composed of genetically identical clones. These groups of clones don’t play well with others though and the outer edges of the colony develop club like tentacles they use to battle other colony’s for control of the reef. You can look for them on pilings, and rocky reefs all the way up to the intertidal zone. Interesting, if antisocial, little critters.

CO2 is a byproduct of our metabolism and we make more of it when we excercise. Kicking against a current, a badly tuned regulator and skip breathing can all boost your PPCO2. A high PPCO2 or partial pressure of CO2 can cause all sorts of problems, some with deadly consequences. 

 Because the our breathing gas gets denser the deeper we go it gets harder for our bodies to get rid of excess CO2. Since CO2 is four times more narcotic than nitrogen, diver with elevated levels of CO2 is going to be more impaired at depth, less able to deal with an emergency or monitor his depth, time and SPG. The second problem with excess CO2 build up is that our bodies don’t like it and will try to will try to get rid of it before it addresses the other dissolved gases in our tissues. So a diver with excess CO2 on a safety stop is actually spending a good portion of that time getting rid of the CO2 before their body starts to offgass the nitrogen in their tissues. Additionally, a diver at depth can simply black out if their PPCO2 is high enough.

Fortunately there are a few simple things we can do to minimize the risk from high partial pressures of CO2. First, the deeper you go, the less you should be exerting yourself. Keep your movements slow and deliberate and breath from your diaphragm. Choosing a regulator with a high ease of breathing and keeping it properly tuned and serviced is vital to keeping your PPCO2 down as well.

CO2 is yet another gas to keep track of, but fortunately it’s fairly easy to keep its negative effects at bay.

This is shear madness. Looks fun though.

Yelloweye Rockfish live to be well over a 100 years old.

If you’ve spent any time diving some of the deeper reefs off the Channel Islands, you’ve probably come across a Yelloweye Rockfish hovering motionless over a boulder pile. What you might not realize is that fish is probably older than you. In fact, it’s probably older than your grandparents. We’re talking Al-Roker-reads-your-name-on-the-Morning-Show old. The lifespan of a Yelloweye Rockfish averages between 114-120 years.

So respect your elders. Maybe even visit. They live on deeper reefs so if do you plan to drop by a Nitrox certification wouldn’t hurt.

And would it kill you to call once in a while?

We’re really looking forward to getting our hands on Atomic’s new Cobalt dive computer. Buried in the other features such as an OLED display, easy navigation, integrated compass, and magnetic switches is it’s RBGM algorithm. Fair warning: from here on out this post gets pretty nerdy.

Each computer manufacturer uses a different algorithm, or mathematical model, to calculate how much dissolved nitrogen is in your body during a dive. However, each is derived from only a handful theories namely; Haldanian, Bühlmann, reduced bubble gradient(RGBM) and variable permeability model.  The former favor taking the diver into shallower water to decompress as fast as possible while not exceeding the M value(more on this in another post.) RGBM and variable permeability based algorithms take into account smaller “seed” bubbles that occur much deeper than previously thought. They address these by stopping the diver deeper, thus reducing the possibility that those seed bubbles will form larger ones. This results in a much “cleaner” decompression. It’s great to see newer research making it’s way into the dive community with better and better products. For more on the Cobalt and other Atomic products keep checking out homepage.