Reaching Greater Depths

[Kevrumbo]

Oh, crap. Since my SCR - under my standard conditions, i.e. in a DS and cold water - normally is some 16-18 SLM, I guess I'd better hand in my AOW card. And ditch those plans for taking Nitrox.


EDIT:
To the OP, and snark aside: This is something you'll encounter regularly if you continue to read SB: Blanket statements based on the writer's own version of reality, i.e. his/her experiences. Divers are different, conditions are different and what's correct for one diver under certain conditions, will not necessarily be right for another diver or under other conditions. Remember that the advice you get here comes from anonymous strangers in the Internet, where everyone is an expert. At least in their own eyes.

---------- Post added November 11th, 2014 at 09:51 AM ----------

Now, back to the original topic, going deeper: I'm considering myself to be a fairly competent diver under the conditions I'm used to (moderate current, moderate chop, no hot-weather problems - but some cold-water challenges), and my personal depth limit is 30m/100ft. For me, there's enough cool things to see in the range from 0 to 30m, since I'm not particularly fascinated by wrecks (which often is the target for deeper dives, as deeper wrecks usually are better preserved than shallower wrecks).

Besides, for most divers, nitrogen narcosis starts to creep up on you somewhere around 30m, sometimes shallower, sometimes deeper. The problem with narcosis is that you usually don't notice it in the early stages, but it manifests itself as a form of mental impairment, decreasing mental bandwidth and generally slowing down your mind. For an inexperienced diver, that is a liability, since when we're inexperienced, we're usually task loaded to the gills just by being down there. Usually, we're just fine, but if something happens, you just might not have the necessary spare mental capacity to deal with it. Since I'm rather susceptible to narcosis, I've set my own limit on air to 30m, and quite often I even set a shallower limit. And if I ever were to plan a dive deeper than 30, I'd be doing that on trimix - after getting the appropriate training - since I'm often becoming rather stupid at those depths.

Another aspect to consider if you think about going deep, is no-stop time. Even at 30m, the maximum bottom time is just 20min, and on 40m, it's about 10min. We're talking about bounce dives unless you're deco trained and equipped. You won't have much time to really look at stuff.

Third, it's gas reserves. With my SAC and carrying a 10L 300 bar tank (about 100 cu.ft. by US notation), I have a very good fit between minimum gas and no-stop time at depths below OW limits: When I'm approaching no-stop time, I'm also down to the min pressure at that depth. If I were to dive an Al80, I'd be down below my minimum reserves before I even hit no-stop limits. And 20min isn't a very long dive...

As others have said, going deep just for the sake of going deep is generally considered as meaningless by many divers. If you want to explore deeper diving, make sure to get appropriate training (i.e. tec), carry a redundant gas supply (i.e. doubles or a large pony) and make sure you have enough gas and the training to deal with any problems that might occur.

Read the OP .Storker . . if you cannot achieve an SCR of at least 15 liters/min in a warm water tropical locale such the Andaman Islands in nominal conditions, then you yourself breath like a runaway vacuum cleaner.

First things first: get a reasonable breathing rate in the environment you'll be diving in at your current level of ability (which for the moment for the Original Poster, BOW no deeper than 18m). Now for an example using an SCR of 22 liters/min and going deep on single tank as a novice diver:

18m Beginner/Novice OW Limit

A Quick Contingency "Rock Bottom" Calculation and Gas Plan Estimate for Open Water. . .

For a single 11 litre tank (AL80), a total of 11 litres/bar metric tank rating and a volume Surface Consumption Rate (SCR) of 22 litres/min -same as a pressure SCR of 2 bar/min*ATA (divide 22 litres/min by 11 litres/bar)- using an example NDL air dive to 30m (4 ATA) depth in Open Water.

Emergency Reserve/Rock Bottom pressure calculation, from 30 meters with one minute stops every 3 meters to the surface,
-->Just "tally the ATA's":
4.0
3.7
3.4
3.1
2.8
2.5
2.2
1.9
1.6
1.3

Sum Total: 26.5

Multiplied by 2 bar/min*ATA equals 53 bar Rock Bottom absolute reading remaining on your SPG. --this also happens to be the pressure in bar needed for one person in an emergency contingency to reach the surface with the above minimum decompression ascent profile.

So ideally for a two person buddy team, multiply 53 by 2 which is 106 bar for both to reach the surface (sharing in a buddy Out-ot-Gas contingency).

But realistically, for two experienced divers stressed: 106 bar plus 30% of 106 bar equals 138 bar Rock Bottom SPG reading.

For two novice divers stressed: 106 bar plus 100% of 106 bar equals 212 bar (!!!) -a full 11L (AL80) cylinder is 207 bar!
--->obviously then, two novice divers on single 11L tanks should not be diving to 30m for any significant length of time. . .​

 

[Storker]

Read the OP

I didn't take exeption to the OP. I took exception to your blanket statement:

If you're not at that breathing rate now, then you're not ready for any further training to go deeper for longer . .

Aaaand then came the qualifier:

if you cannot achieve an SCR of at least 15 liters/min in a warm water tropical locale such the Andaman Islands in nominal conditions, then you yourself breath like a runaway vacuum cleaner.

There's quite a difference between "If your SCR is more than 15 SLM, you're not ready to go beyond OW" and "If your SCR is more than 15 SLM in warm water and under benign conditions, you're not ready to go beyond OW". Anyway, I still don't agree with you.

SCR (or, as it's often called, SAC) value isn't the crux. Knowing how to calculate gas reserves and being able to bring enough gas is. If your SCR mandates more gas than the standard cylinder in your neck of the woods carries, the answer is simple: Bring more gas. Or learn to calculate min gas and limit your time at depth to what your gas reserves allow.

 

[Bagster]

Don't jump right into AOW. Best thing you can do is just dive a lot - especially with more experienced divers who are good role models. Sounds boring, but it's true. You'll be surprised at all the things you thought you were doing right, which you really weren't.

The o.p. seems like a strong argument for exactly the opposite. Tom went to 40m on his own with a very incomplete education. He would have been far better off taking the Advanced course immediately after OW.

In AOW, one gets educated about the differences between 20m and 30m. In the (typical?) OW course, time is limited and very little is said about going beyond 20m, except, "don't do it". Obviously, that admonition failed to get through to Tom.

 

[Lopez116]

The o.p. seems like a strong argument for exactly the opposite. Tom went to 40m on his own with a very incomplete education. He would have been far better off taking the Advanced course immediately after OW.

In AOW, one gets educated about the differences between 20m and 30m. In the (typical?) OW course, time is limited and very little is said about going beyond 20m, except, "don't do it". Obviously, that admonition failed to get through to Tom.

Good point. I assumed the op would not be doing dives like the blue hole with his experience level. The point is to get lots of experience under appropriate conditions and preferably with a good role model.

Hopefully the OP isn't discouraged by the criticism of these posts. The purpose isn't to discourage you from being ambitious - it is to give you a reality check. Being a newly minted diver, you truly don't know what you don't know. Take it slow and really enjoy the learning process.

 

[Bagster]

In my perception, many fresh OW certs (myself recently included) make a nebulous assumption that the principle and most important difference between 18m/60ft and 30m/100ft is that "the surface is farther away and harder to reach in case of emergency". One is not taught about increased gas consumption or nitrogen narcosis in OW. Such things may be mentioned in passing, but not sufficiently reinforced to be learned.

Having just finished AOW, I am now educated about narcosis and gas consumption, from the required reading, repeated explanations and warnings from the instructor, and actual practice on the deep dive, where we planned a limited stay based on our gas supply., and performed dexterity exercises at surface and at depth. The seriousness of going to 30m was hammered home by checking our depth and time on the rdp table, and noting that the dive could not be done as a no stop without a computer; sobering information that, I think, many divers forget, if they ever understand it to begin with.

An AOW cert may not be ideally trained and qualified to dive independently to 30m, but will at least be conscious of the important considerations if he/she chooses to do so.

 

[tursiops]

If you have a nominal Surface Consumption Rate (SCR) of 15 liters/min or better, then you are ready to matriculate to Adv Open Water, Nitrox and Intro to Tech for starters. At 15 liters/min, your depth gauge in meters will indicate how much in bar you will consume in 5min (for a single 11 L/bar [AL80] stage cylinder) or in 10min (double 11L/bar for a total cylinder rating of 22L/bar). So for example, at 30m depth you will consume 30 bar of gas in 5min on a single 11L tank, or 30 bar in 10min on a manifolded twinset of 11L tanks. This is IMHO/IME is the easy base reference SCR for a warm water deep/tech diver in Gas Consumption Planning & Deco Profiling, both Pre-Dive and on-the-fly real time.

If you're not at that breathing rate now, then you're not ready for any further training to go deeper for longer . .

To quote Lecter....this is BS.
Following this logic, a small lady who uses no gas will be ready for Intro to Tech on dive 5.

---------- Post added November 11th, 2014 at 10:57 AM ----------

Having just finished AOW, I am now educated about narcosis and gas consumption, from the required reading, repeated explanations and warnings from the instructor, and actual practice on the deep dive, where we planned a limited stay based on our gas supply., and performed dexterity exercises at surface and at depth.

I agree with the gist of your post, but am sad to see this statement about dexterity exercise for your recent AOW, which I assume was PADI since that is their term. The AOW Deep dive no longer has dexterity exercises; they went away in early 2009, replaced by looking at color changes at depth. The dexterity stuff moved to dive 3 of the full specialty course. So your instructor was badly out of date.

 

[Bagster]

Tursiops, we did the color chart as well. Is it possible our instructor chose to have us do dexterity exercises based on his own discretion, and is adding an activity a serious dereliction on his part?

It would seem that so long as the minimum requirements are met, additional information is useful.

 

[boulderjohn]

DAN has stopped publishing their annual report on dive accidents and fatalities, but their past reports indicate that the idea that is the basis of this thread is not remotely true.

The last report (2008) is typical of those that went before. Pages 62-63 deal with the experience level of the fatalities. Of the cases in which they know something about the diver's experience, 39% of all fatalities were to divers with more than 10 years experience, and 19% had fewer than 2 years experience.

Page 62 goes into the limits of their knowledge of the deaths. One thing they really don't know in most cases is the number of dives they had. In some cases (a small minority), they know the certification levels.

"The cases with known information included three student divers, six with open water certification, six with an advanced or specialty certification, six with technical certifications, and four instructors."

Those were out of a total of 138 deaths, so you can see how limited their information is.

I used to read and analyze all of their reports when they were published, and they regularly said that the only two truly consistent factors associated with dive fatalities were age (tend to be older divers) and obesity.

 

[EFX]

Tom, I would suggest doing both. If you are sure about taking AOW then get the materials and read through the book before you take the class. PADI requires you take deep and navigation. The other three specialties are up to you. Experience is important but you need to work on skills. I would suggest taking Peak Performance Buoyancy and work on this skill. The AOW book gives you the basics on most of the specialties. When I started back up I took my scuba review and AOW in one weekend. This worked well for me. After the class I continued to work on my buoyancy until I had my weight dialed in. The only thing left was trim and we fixed that when I took the PPB class. Hopefully, you can dive with someone more experienced and once you're comfortable, practice the OOA (out of air) drill. Good luck and have fun.

 

[boulderjohn]

One is not taught about increased gas consumption or nitrogen narcosis in OW. Such things may be mentioned in passing, but not sufficiently reinforced to be learned.

For PADI, both are covered in the course, and both are included on the final exam. I suppose the degree to which they are reinforced would depend upon the individual instructor.