Why not go to 100' ?

[noj3333]

Thanks for all the replies. Just to put it in context, I'll be diving in Grand Cayman, as a couple of you mentioned, and with one of the top rated dive ops - so temps, visibility, and safety should be OK. And I always discuss my experience level with any of the outfits I dive with. But I I think you've convinced me that taking a deep dive course or at least personally guided deep dives makes sense. I know my SAC down to 60' but no experience below that. I've never undergone narcosis. It can't hurt to be cautious, and a couple of instructional deep dives will allow me to calibrate my performance at 100' .

As a new diver myself, money spent on a private DM is pretty much always worth it...

 

[DevonDiver]

I’ve actually been to a bit over 70’ on a couple of dives, and really did not notice any difference.

First things first... you can't rely on any type of sensory feedback to feel 'risk' at depth.

With the exception of narcosis, the majority of which is sub-symptomatic anyway... it feels the just same at 190' as it does at 30'.

Hence the massive complacency that exists in people diving much deeper than their training. This doesn't occur in other activities, like climbing or motorcycle racing, where risk (speed, height) is clearly recognized by our land-dwelling instincts...

By sub-symptomatic; I mean that you can be heavily degraded by narcosis without noticing a tangible effect (see Nitrogen Narcosis - Perceptions of Susceptibility )

I wrote this article last year to help advise on exactly the kind of question you're asking:
Deep Diver: What You Really Need To Learn

But other than faster air consumption, shorter NDL, and possibly some narcosis (I don’t know how I’d be affected having not gone that deep yet, but feel nothing at 60’) why not go to 100’ with the DM?

The deeper you go, the less forgiving your dives become. It's as simple as that.

The concept of requiring further training to venture into deep depth reflects that the consequences of error become much more significant. What you 'get away with' at 60' is more likely to bite you in the ass at 100'... and more so again at 130'.

Training and experience reduces error.

1. Faster Air Consumption: A loss in situational awareness can much more easily/swiftly result in an out-of-air situation.

2. Deep Depth: If out-of-air, it takes much longer to reach the surface. How confident are you to CESA effectively from 60'? 90'? 100'?

3. Shorter NDL: Is a naive way to describe accelerate saturation. You absorb more nitrogen into your tissues. More nitrogen equals higher risk of DCS. It means more significant DCS injury in the event of an incorrect ascent. Be scared of DCS... it's not a fairy story.

4. Increased Narcosis: Reduced mental capacity leads to reduced situational awareness, increased risk of making errors, less effective problem solving and crisis management.... more inclination to panic and stress to less severe stressors.

As land-dwelling mammals, our instinctive capacity to identify risks underwater is critically limited. In fact, the only instinctive risk stimulus we can experience is that of air depletion. We are not instinctively or physiologically evolved to identify/react to other risks present when diving underwater. This can mean that many risks in deeper diving remain as 'theoreticals'... numbers on a computer screen... and don't provoke any kind of fear or prudent response.

I tend to be very relaxed when I dive, not at all anxious, check my air and NDL frequently, have pretty good buoyancy control, and a fairly low rate of air consumption

Relaxed when? If everything is uneventful? What about when an emergency occurs?

Good buoyancy control, awareness and low air consumption are the minimum requirement for more advanced recreational dives.

But... time to consider...what about your other skills?

When did you last practice air-sharing? How current and reliable is that skill? What about your capacity to CESA? What's the deepest proven depth you could safely ascend from without gas? How is your ability to diagnose and rectify fixable equipment problems in-water? Your knowledge of what to do if you exceed an NDL? Did you ever use a computer in emergency DECO mode yet? Would you recognize CO2 retention, if it happened? When did you last practice free-flow regulator breathing?

So why not go for it? I suppose I could arrange for some deep dive instruction first, but really don't want to spend the money if going to 100' is not that a big deal.

It's not a big deal if you presume nothing will go wrong.

Does it become a bigger deal if you entered the water in the assumption that things would, or could, go wrong at that depth?

It should...

Don't assess risk based on a best case scenario.... consider the worst case situations and determine what you know (not assume) your capability to deal with them is...

See what you think to this article: Technical vs Recreational Scuba Diving: Boundaries and Limitations -

Caveat: I am not saying that a course will necessarily improve any of this. Many courses are junk.

It's not about the certification card you hold... it's about the skills, knowledge and competency you possess. You can teach yourself a lot... and get informal mentoring in many instances.

Experience counts for something... but your experience is limited only to what you've experienced... 50 uneventful dives is very little experience. 10 eventful dives is valuable experience. In general... doing more dives results in more exposure to incidents occurring. THAT is what is meant by gaining experience..

Read more: The Experience Paradox and The Biggest Risk in Diving (and how to avoid it)

There's no point doing an Advanced Open Water or Deep Diver course unless the instructor is genuinely going to increase your skill, knowledge and competency to mitigate risks involved with deeper diving. To assure that result, you need to carefully select an instructor who will train you.... and not just one who will tick a few skills boxes to meet a basic requirement.

If you find a good instructor to develop your capacity for deeper diving, you'll know automatically why that training was incredibly valuable.

If you've done a few dozen dives and nothing has yet gone wrong... then it's easy to fall foul of complacency. A mistaken belief that either (1) nothing will ever go wrong.... or (2) that your success on those past dives equates to high competency. That's when you start questioning the need for further training. Why do it, right?

One thing to be aware of is the Dunning-Kruger effect. It's worth 'Googling'....

 

[diver0008]

You will be diving in a group and with a guide. If you are told that the dive will be to 100' and you don't want to go that deep, don't go on the dive.

Remember: Plan your dive and dive your plan. If the dive is planned by the DM to 100, that's where it's going.

Or, go on afternoon dives, which are often shallower.

Or, do the deep dive, stick with the guide, and follow his or her instructions.

 

[DevonDiver]

I know my SAC down to 60' but no experience below that.

If you know your SAC, you can extrapolate that to calculate your air consumption at any depth.

What you wrote, sounds like you don't know your SAC.

I've never undergone narcosis.

The narcotic (anesthetic) effect of nitrogen begins as soon as partial pressure is raised. i.e. as soon as you dip below the surface. It doesn't become significant until you reach depths ~100ft and below. Feeling the symptoms of narcosis is not the same as being effected by narcosis. Narcosis can be very much in effect without the diver noticing any obvious effect.

Too many divers (and a few instructors) are under the illusion that narcosis is akin to 'feeling intoxicated'... that's just one obvious symptom amongst a plethora of more insidious symptoms. The so-called 'martini rule' has a lot to answer for.

It can't hurt to be cautious, and a couple of instructional deep dives will allow me to calibrate my performance at 100' .

Good attitude. Push your boundaries under supervision. It's better to make your mistakes under the care and scrutiny of an experienced diver, than to learn the same lessons in real scenarios where there are real repercussions for getting it wrong.

From the perspective of a more experienced diver, you realize that the Open Water course really is the very bare minimum training needed to get underwater safely. The safety stems from the fact that the minimum training has to be linked with reasonable limitations on the scope of diving conducted. There's a balance between training, experience and the level of diving conducted. Risk occurs when diver's overstretch themselves... and this is quite common with novice divers, who've yet to gain the experience necessary to prove their limitations.

It's wise to dive with Divemasters... because their local knowledge goes a long way to enabling an enjoyable and satisfying dive. However, the Divemaster is not there to act as a substitute for a divers' lack of competency or skill on the given dive.

This is often called a "Trust Me Dive". It's never advocated, but it's done far too often - some dive centers just won't turn down a few $$ or are reluctant to disappoint customers... even at the expense of customer safety. When dive centers do show willingness to short-cut on customer safety with regards training/experience... you have to wonder what else they'll short-cut on... for the sake of a few bucks.

You aren't paying a Divemaster for the 'convenience' of abdicating personal responsibility for your own safety. Relying on another diver to compensate for personal inability sometimes goes badly wrong...

 

[admikar]

After finishing my OW, I never went bellow the "limit". During my AOW (under CMAS) we went down to 30m. After finishing that course, we planed one dive down to 40 m. Before people start screaming that I am an idiot, there were two of us newly minted AOW's and eight instructors in two teams. Two of us were in single tank rigs, instructors were all doubles. Point of this dive is to experience narcosis and its effects, being as safe as possible with four instructors watching over each of us. I was given a slate with instruction to write my signature on surface and every 10 m after that. After completing that (feeling quite fine), one out of air situation was thrown at me to see my response. After completing that, I was put in charge of leading "my" team, including tracking NDL, team members and navigating (that was easy part, since we were diving a wall) and ascent to the top.
Everything went OK,or at least I thought so. And......I took a look at my slate........WTH?! First signatures were fine, but those at 30 and 40 m looked like I wrote them with my foot, and left one on top of that. What scared crap out of me is not that I got narced, I expected that, but the fact that I felt nothing at all. I did complete that dive safely, but would I do it again, without safety net of a pro looking over me.NO!
So, next dives are strictly down to AOW "limit", if I feel up to it.

 

[EricTheDood]

I have only the basic OW certification and have avoided doing dives much deeper than 60’ on all of my 25 previous dives, and that’s worked out fine with the other divers.

The 60' depth isn't a hard limit for an OW cert. With 25 dives under your belt you, it's quite possible that you're familiar enough with your equipment and comfortable enough in the water to head down to 100' under supervision. In the end, it's your call.

 

[EricTheDood]

I know my SAC down to 60' but no experience below that.

SAC stands for surface air consumption (ambient pressure = 1 bar at sea level). Add 1 bar of pressure per 10m/33ft depth of seawater and your air consumption is multiplied accordingly.

 

[RyanT]

I know my SAC down to 60' but no experience below that.

SAC is your (Surface Air Consumption). SAC is influenced by lots of different things, so knowing your personal rate is important. The beauty of knowing your SAC is that you can calculate your consumption rate for any depth. This is a useful bit of planning for any dive, but it becomes increasingly more important the deeper you go.

Just a quick example. Let's say your SAC is 0.7 cf/min. If you dive to 100' you would be at 4 atm of pressure. 4* 0.7 = 2.8 cf/min. So at 100', you're burning gas 4 times faster than at the surface. If you have an 80 cf tank, then that tank will last you 80/2.8 = 28.5 min on the bottom. Of course, you need to plan for having plenty of gas reserves for: descent, ascent, safety stop, and some "just in case." So obviously no one would plan to stay at 100' for 28 minutes with that gas volume and sac rate.

Whatever dives you do, I recommend that you start to figure out your SAC. To do this, spend some times on your next dives with a slate. When you reach the bottom, on your slate write down your: Depth, bottom time, and tank pressure. When you finish the bottom portion of your dive, just before you begin to ascend, write down those three pieces of information again. After the dive you can use this information to calculate your SAC. Use your average depth for the bottom portion of the dive, and then see how much gas (pressure) you consumed for the time you were on the bottom. You can convert pressure to volume long-hand or you can use the nifty little app (SAC rate by Elliot apps).

Do this on multiple dives as your SAC will be influenced by work load, stress, temperature, etc. After doing this for a while, you'll start to get a good sense of your average rate.

 

[scubadada]

After a diving hiatus, I was recertified with my newly certified son on Grand Cayman. Our 1st dive post certification was to 95 feet off the North wall, the 3rd was to 105 feet. Not that this was the wisest thing to do but it was reasonably standard at the time. This was 1997, on air, total dive time only about a half hour.

I would suggest getting nitrox certified before your trip. You can do this online and then go to your LDS to review your test and analyze a couple of tanks. Most of the divers in your group will likely be certified, might be best if your dive time was not considerably shorter than most or all of the others.

On Grand Cayman, consider doing your AOW, this will include a supervised deep dive. You may even want to do the Deep specialty. You could do this early in visit and reap the benefits for the rest of your stay. I'm sure your operator will work with you to devise an acceptable strategy. Having your AOW might be advantageous to you in future trips for more restricted dives, very common in some locations.

Enjoy Grand Cayman, a fantastic dive destination

 

[mainedvr]

Does the op offer certs? Why not take advantage of the book material and diving under instruction/supervision of a pro for the deep dive? I can't imagine it would cost that much more... Agency fee and card? Maybe a couple bucks to the instructor? You're doing the dive anyway.

This is a great suggestion my wife and I got certified originally to dive in Maui on our honeymoon. When we got there we thought about it and decided to spend the time doing our AOW, we got to do some awsome dives and rode scooters out to a small wreck from the shore. Sure we spent a little time in the class room but did six dives under the watch of a professional. Then we did several days of guided shore dives with others feeling more confident and actually got a great bang for our buck. But that has to be up to you and how you want to spend your vacation. Have fun