Review: TDI Normoxic Trimix with John Chatterton, November 2019

[tmassey]

By now, you probably know the drill. This will be *LONG*. Grab a beverage and settle in...

As I wrote about in my review of Advanced Wreck with John Chatterton, his class had dramatically changed my perspective on the most fundamental aspects of diving. Before the class, my idea of technical diving was heavily colored by my (incomplete) understanding of "DIR"-style diving as the only way to dive. After the class, I was left with lots of *questions* about *why* to dive one way or another -- which is the first step to truly *understanding* what you're doing.

In the past four years since I took the class, I've continued to reflect on this. What are the underlying assumptions of what I'm being taught? Do those assumptions match up with my requirements? How does this shape the standards and procedures that this class implements? It has added a significantly deeper level of appreciation for the training I have received.

During that time, I've had a fair amount of additional training: TDI Cavern, Advanced Nitrox, Deco Procedures, Intro Cave and Full Cave. These were valuable classes that taught me numerous additional skills, but none altered my perspective the way Advanced Wreck had. Finally, in spring 2019, I took GUE Fundamentals, a class that had intimidated me for a decade. I expected this class to change my perspective on diving, and it did -- but not in the way that I expected. I wrote about this in detail in my review of my class. But in short: I found that the fundamental assumptions the GUE philosophy are valuable and effective, but if you cannot satisfy those fundamental assumptions completely, much of the value of the philosophy is lost. And, for me, the cost (on several levels) to satisfy all GUE assumptions would significantly outweigh the benefits I would practically receive. So while I would encourage *everyone* to take a Fundamentals class, for me, it was not a path forward.

I also found that for me, taking the Fundamentals class had required addressing some deep emotional issues that I hadn't even been aware of just a few short months before. This has allowed me to understand how my internal emotional expectations were not really lined up with my mental expectations -- or what the class was offering in the first place. And finally, I'm no longer looking for emotional validation from technical training! For a very non-emotional person, realizing all of this was a pretty difficult struggle. But it has helped me to understand better what training is and is not going to provide.

So with this background, I was considering what I should do to take what very well may be the last level of training I achieve: Normoxic Trimix. At this point, I was not looking for a fundamentally different way to look at diving. I've been given plenty of perspective on the spectrum of diving from total self-reliance to heavily team-reliant, and I've created my own specific requirements and expectations. In taking this class, I was not looking to change this.

However, I *was* looking for an opportunity to change my perspective. At this point in my diving career, I could not point to a single dive and state, "I was narced on that dive." I do *not* say I *wasn't* narced, but rather I did not have a clear incident where I understood what it was to be narced. I did have a general idea of one dive being harder than another, or where in retrospect I was probably not as effective as I might have been under different circumstances. But I had no real concept of a feeling of narcosis.

This bothered me. Obviously, you don't *have* to experience impairment to understand the idea that being impaired is not a good idea on a dive. And if there were something you could do to ensure that you would never experience the impairment, that might be fine. But you can't: we've all heard stories from even experienced divers where on the wrong day and under the wrong circumstances, someone states that they experience narcosis *much* shallower than they had ever experienced before. So if you can't guarantee that you'll avoid it, it's probably a good idea to understand it. And I didn't want my first "aha!" experience to be on a "real" dive to 200 feet, with who knows what resources to lean on when it happens.

Besides, by this point, I understand the importance of helium in diving mixes. I've read the lipid solubility assumptions and the gas density/WOB research. I appreciate the logic that, outside of cost and availability, there really aren't many downsides to adding helium. Without any real experience, I'm already sold on the benefits. So I don't really need a helium cheerleader. What I really want is a helium naysayer. Someone who might have a more nuanced perspective to offer.

And besides: I've spent the past couple years either surrounded by cave divers, or even more, GUE-trained cave divers. It's time for a change!

So, I decide to take TDI Normoxic Trimix with John Chatterton. From my previous class with him, I was aware of his self-reliant perspective. But it had been four years, and at the time I was an inexperienced tech diver. With a few more years of experience, I welcomed the opportunity to receive additional training from his perspective.

But the biggest reason for choosing his class was his perspective on dive gasses. This includes the role that low- or no-helium gasses play in diving, as well as the selection of deco gasses. Before the class, my perspective was heavily influenced by GUE, and that means Standard Gasses and the heavy use of helium (at 100'!). That is not Mr. Chatterton's perspective. And I wanted to understand that perspective more fully. There were some other elements that were different than my previous training: bottles on both sides, for example. I was looking forward to experiencing these as well.

Once again, John was very generous with his time leading up to the class. I discussed with him my perspective on deep dive gas selection centered on Standard Gasses. But I also stated that I was looking for an opportunity to experience narcosis in a controlled setting. That agreed with his goals for the class as well. His description was that if you haven't experienced narcosis it's a boogyman. He was very flexible with his approach to making sure that my desires were met.

One thing that made planning for this class more difficult than it needed to be was my desire to be a cheapskate – and to be prepared in advance. My goal was to bring with me the gasses that I would need for the class. It turns out that Force E's Trimix prices are pretty reasonable, and I should have simply let them take care of it. (Ironically enough, their deco O2 prices are a little less reasonable than their Trimix prices, and I needed O2 fills while I was there....) To bring my own gasses required that I knew what gasses to blend! Of course, when diving best mix, that leaves the blend open, and discussing the advantages and disadvantages is a big part of the class, plus there's a buddy with his own desires, of course, etc.

In the end, I should have simply got my fills at Force E. Don't make the same mistake I did. But we did get it worked out in advance. In fact, it looked a *lot* like the current class structure (ours was the last of the pre-2020 structure) if you combined the two Hydro Atlantic dives: slight Trimix x 2 on the Newtown Creek (Lady Luck), air on the Hydro Atlantic (with a stage of 21/35 for the middle of the dive), and 18/45 on the Lowrance. Deco gasses were 36% and 80% (only 80% on the Hydro with the 21/35 stage). Getting to that point required a lot of e-mails back and forth. (OK, it required a lot of e-mails from me: Mr. Chatterton is very patient...)

 

[tmassey]

Part two...

Starting the class by meeting at the dive boat was an interesting start. At the Trimix level, you hope you can be prepared to do a recreational-class dive without a lot of handholding. It turned out that there were a fair number of hardware issues: a failed deco reg, a missing o-ring, and other such details. Fortunately, we were able to address them all before we left the dock. The dives were extremely straightforward and skills-heavy: valve drills, gas sharing, etc. Honestly, I had never done the Lady Luck before, and sitting here now 2 months later, I literally have *zero* recollection of the wreck at *all*. The underwater time is quite busy. (That holds for the other two wrecks as well: I have only two specific memories from the Hydro, and only one from the Lowrance. I have way more memories from my Advanced Wreck four years ago!)

When the dive boat returns, things get busy. You have a *lot* of gear, and the car's pretty far from the boat. A cart is really handy to have: I happened to have one, or sometimes you could borrow someone's. There was they typical scramble of dealing with gear. At a point John would arrange a time 60 minutes in the future to meet at Force E Boca Raton. Don't relax: that's not that much time. The first day I allocated 20 minutes to cover the 11 miles to get to the class. And I was late: it took 30 minutes each day. I basically had minimal time between when the boat arrived at the dock and when I was expected at the classroom. Keep moving with a purpose.

That is one of my complaints for the class. For Advanced Wreck (four years ago), we met at Force E Pompano. For this class, we met at Force E Boca Raton. My guess is that they might not do Trimix fills in Pompano, hence going to Boca. But that cost an hour each day just getting to and from the classroom, time I would have preferred spending using for something else... While I'm on the subject: Advanced Wreck was class then dive; Trimix was dive than class. I preferred the former. Easier to focus on the classwork when not tired (or sub-clinically DCS'ed!) from the morning of diving. I'm sure there's a reason for the change, but selfishly I prefer the other way.

First day of class was straightforward. We focused on planning our dive for the next day. Because I had already worked out the gasses for the dive, I had already worked out things like bottom time and deco strategy. The way Mr. Chatterton did it in class was not the same way I had, though we were using the same numbers. I didn't really worry about it – like I said, the numbers were the same. In any case, we had a plan, we had our gasses and our strategy.

This was the dive I was looking forward to: 165' on air, with a stage of 21/35 to switch to during the dive. This was not a new idea from me: I had read about other Trimix instructors doing this, and their students were surprised by the results. I was looking forward to both parts: I wanted to know what air was like at 165', and I wanted to see how Trimix would change things. So, pack up from the classroom, and we'll meet at the boat the next morning.

Boarding the boat went better the next day: fewer (but not zero!) hardware issues. Off we go to the Hydro. So, how did an air dive to 165' go? Badly. I clearly experienced the effects of narcosis. It was clear what I was experiencing, and that I had experienced it many times before. I had a very difficult time focusing my eyes. Not like you're not wearing your glasses; it's not blurry, you just can't get your two eyes to coordinate on focusing on the same point at the same time. I understand why they call narcosis "Martini's Law": the inability to focus my eyes is the same thing I experience if I drink two martinis in quick succession. The *feeling*, though, is completely different: with martinis, there is an obvious slowing and softening and relaxing of everything, and if you have nothing to do, you can simply melt into it and enjoy it. With narcosis, I didn't get the softening and relaxing at all. I just had the inability to physically focus on things (and, certainly, the struggle *mentally* to do the same), and along with it irritation and frustration. Everything was irritating, and you just don't have that many resources to address things.

So, after about 10 minutes of this, we switched over to 21/35. The difference was enormous. The first thing I noticed was that the colors came back. I hadn't really realized that I wasn't seeing colors before. I don't *think* I was seeing black-and-white, but rather that I was so unable to focus on things that I was only comprehending the outline of things, rather than anything approaching details, and my mind was throwing away anything but the most basic information. On Trimix, everything brightened and deepened -- and widened. I also started to become less irritated. This effect was fast: within 30 seconds, I could tell the difference.

What also surprised me was how my buddy reacted. When we hit the surface, that was the first thing he said, how much better he felt with the switch to Trimix. So it wasn't just me. John, on the other had, said he couldn't tell the difference at *all*. Does that mean that he's *always* impaired when he's diving? Actually, I think it mainly comes down to his superior physical and mental state on the wreck. We discussed it in class: he's done this wreck dozens of times. He has zero mental obstacles to doing this dive. He also is much superior to us in moving through the water. That was the first thing I noticed: how darn *hard* I had to work on that dive. It really was a snowball: tension leading to physical exertion amplifying the effects of (nitrogen) narcosis, which amplifies the effect of work of breathing, which amplifies the effect of(CO2) narcosis, which increases the tension..... Break that chain, and the effects are a lot lower!

Personally, I think that's probably the reason for the difference in people's sensitivity to deep air, and why some highly-experienced divers see a role for it. In their experience, the effects are minimal -- because of their superior technique. For us mortals, we don't have the technique, so we need to remove the mitigating factors. I likened it to exceeding the speed limit. Can you exceed the speed limit safely? Certainly. Can you drive 130 MPH in a 70? Sure. And if the conditions are excellent, you'll be fine. But when all of a sudden there's a box in the middle of the road, are you as safe? Deep air is like that: when conditions are benign, you're fine. But if even a small problem develops, it can snowball quickly. I'll take the margin.

So, I got my wish. I got a narcosis experience. I could feel it building, I could see what it was doing to me mentally and emotionally. And I could see where I had experienced this many times before, just not as severely or as quickly. I clearly saw how Trimix reduces that. And I had my first experiences keeping multiple bottles with me and carrying them on both sides. (I had done cave dives with O2 and a stage before, but in caves we drop them as we go, so you drop your O2 nearly immediately, and your stage fairly quickly as well.) Successful class, skills learned, we're done, right?

Nope. Turns out the learning had just begun.

So we go back to the classroom. The first thing we do is download our computers to his notebook. (This is one of two reasons why a Petrel/Perdix is required: to download the dives to a local computer rather than Shearwater Cloud, and to change GF underwater.) So we start breaking down our dive profiles. The critique of our profiles was unique: I've never had or *heard* of a similar thought process. (I might be letting his cat out of the bag. I don't know if Mr. Chatterton *intends* for this to be a surprise, but it was a surprise.)

There were two items of special attention: hitting (and not exceeding) stops, and total runtime. Hitting stops properly is not that unique. The level of pickiness was -- and appropriately so. The last time I had a class focused on stops was AN/DP. At that time, stops were new to us: it was a skill we were learning. It was expected that our stops would be bobbled -- so much so that the stops we were doing were usually *simulated*, not required. If you messed up, no harm. Well, this is the next level. We're supposed to be experienced deco divers at this point. We're executing dives where those stops are *not* simulated. And with the addition of helium, we're adding more gas faster and to more tissue. So you better be hitting your stops -- and not exceeding them. After all, the deep stops are limited by the fastest tissues, and screwing up there means Type 2 DCS. So don't screw this up.

Of course, for all of us, by the time we got to the shallow stops, things were *much* cleaner. The stops are farther apart, and there's less to do on them. Unfortunately, those stops are a lot less sensitive: it's slower tissues, for example. So the ones to be sharp on are the hardest ones to do! This point was brought home very clearly when we compared our profile to John's. All I can say is, he knows how to hit a stop.

The other part, and the part that blew me away, was the focus on runtime. So once we covered how well (or not) we hit our stops, we then looked at how our actual runtime compared to our predicted runtime. Look at the TTS when you begin your ascent. Then look at how long it took you to *actually* surface. How do they compare?

 

[tmassey]

Part three...

Here's my numbers: we left the bottom at 30 min. My TTS at that moment was 39 minutes. That means that I should have cleared my last ceiling at 69 minutes (or really, 68, with a minute to surface from 10'). Did I? Nope: my 10' ceiling cleared at 75 minutes. That's an additional 6 or 7 minutes, or a runtime that exceeds the plan by 10%.

Normally, I would not have considered this as a problem. In all of my training, there was very little emphasis on a machine-like focus on hitting stops. Yes, you want to get to the next stop at a reasonable pace. Deco will be more effective at that shallower depth. But what's the rush? 1 minute between stops, two minutes, whatever! The important part is that you're safe, right?

Not here. The emphasis was: hit your stops. Get to the stop depth. Not higher, not lower, your stop depth. Stay there, not higher, not lower. And be focused on getting to that next stop. For example, pay attention to your *actual* ceiling. That number in the top-right is *not* your ceiling. It's your stop depth, and it rounds down in 10' increments. But your ceiling could be much higher. We were not encouraged to ride the ceiling (moving up foot by foot as the ceiling changes), but to at least 'cut the corner': by the time you've got, say, 1 minute left of a multi-minute stop, your ceiling is probably just a foot or so below the next stop. So get going! Your goal is to execute your plan, and that means hitting your runtime.

That focus on runtime extends throughout the execution of the dive. For example, you'll need to switch gasses. That means getting ready for that gas switch and executing it on the fly. In our case, we needed to deploy an SMB for our ascent. Once again, that means doing it on the fly. It extends to *how* those gas switches and SMB deployments are done, how the gear is stowed and rigged, what order things are done in, etc. The entire dive becomes an integrated ballet focused on executing the runtime plan.

This was unexpected for me. From previous experience, I knew some of the differences in what gear Mr. Chatterton uses and how he uses it. I understood that his reason for doing this was "efficiency". But I didn't fully understand the *why* of the focus on efficiency. It wasn't simply an end to itself, but rather steps that all lead to a central goal: plan your dive and dive your plan. I was surprised how deeply that goal spread throughout the entire process. It's as central as "Start with the end in mind" for GUE, and just as wide-ranging.

Once I made this realization, I finally understood the dive planning I had seen previously. For me, a dive plan starts as a static profile. You know, something that you punch into your planner: 25 minute bottom time, 165' depth, 21/35, EAN50, EAN100. Out comes an ascent profile. You write that into your wetnotes. Of course, you have some contingency plans: what happens if I exceed my depth by 10', or my bottom time by 5 minutes? You put some alternatives in your wetnotes.

If you're like me, you've got those in your notes as a last-ditch backup. You don't *plan* on actually diving that profile. If you were, all you'd need is a depth gauge and a bottom timer -- you know, GUE-style. No, you're going to dive your computer -- it's why you have it, after all. And why? Because we're not diving a square profile. There's no need to limit ourself to that: the dive computer will figure it all out for us as we go. But if it were to fail, you know that fictional written profile will get you home safely, if not efficiently. And that's because that profile really isn't that close to the dive you plan on doing. It's probably planned a little deeper, and a little longer, than you actually plan on hitting. Which is fine: it'll work out. If the fictional profile can be done safely, you're probably OK for your actual profile.

That is *not* how John Chatterton plans a dive. If you're going to use a dive computer, then *USE* a dive computer. Of course, it's equipment, so it can fail, so you need a backup. No problem: wear a second computer. Want a non-technology backup? No problem: carry a written dive plan. But that's real simple: bottom time, first stop depth, TTS. With that, you can then re-create a profile (at *least* as effectively as ratio deco... ). There's not much that that information (and maybe an extra 10-15 minutes at 20') won't do to get you home.

Of course, this only works if you actually *execute* the dive plan you say you're going to execute. Hence the focus on being able to actually execute the dive plan you're *saying* you're going to execute.

Once again, this was a total game-changer for me. I had never really thought about the disconnect between what I was claiming to do (that is, execute a specific runtime) and what I was actually doing. I had also never thought about how, once you are going to depend on a computer, your entire approach to decompression diving could change. Bottom time is no longer the defining dive characteristic: first stop depth and TTS are. With proper use of @5, ceiling, SurfGF, etc. you have powerful information at your fingertips. The flexibility this allows is enormous, yet still keeps you within your pre-defined and pre-analyzed envelope.

This was *completely* unexpected. It was as fundamental a shift as the idea of never sharing gas. "How does diving look if you never share gas?" was the unexpected question of Advanced Wreck for me. "How does diving look if your computer is deliberately and intentionally the central arbiter of your dive?" was the unexpected question of Trimix for me.

Now, for me personally, I have some reservations about jumping into the deep end of this pool. For example, the idea of being so aggressive about leaving and hitting stops, *and* hitting the exact ascent rate that your computer is using. To paraphrase Dr. Simon Mitchell, maybe we're ascending at the right rate but for the wrong reason. But you don't address this by lying to yourself about your Time to Surface. If you want a slower ascent rate, then work that deliberately into your plan. Truly plan your dive, and truly dive your plan. If your plan says get to a stop at a certain time, do it. Either move faster, or slow down the plan. But don't lie to yourself.

 

[tmassey]

And now part four!

So, for that last dive, I had a *lot* going through my head. In fact, I literally spent about three *hours* walking moment by moment through that entire next dive. What would the descent look like? What state would all of my gear be in? How would we progress through the dive? What would I be seeing on my computer as we proceeded? As we approached the time to leave the bottom, what would I need to do? But most of the time got spent on what came next: once we left the bottom, how would I execute the plan?

That first ascent was going to be the hard part. We were using 36% for our first deco gas, with a MOD of 110'. My goal was to execute the gas switch at 110', on the way up. Unfortunately, our first stop was at 90', and our goal was to deploy our SMB's 20' before that first stop. So I was going to have a *lot* going on: gas switch, SMB deploy, hitting -- and not exceeding -- that 90' stop. I literally spent probably 90 minutes thinking and visualizing -- and I'm *not* a visualizer... What do I do first? What do I do next? What's exactly in each hand? How do I move through the steps for each item simultaneously?

So, on to the next morning. This time we had some fun with the boat: we moved from one to the other, of course after I had all my gear fully set up... But not much else in the way of difficulty. I was looking forward to this dive: no deliberate narcosis to start the process! The dive itself went fairly straightforwardly. We had some skills out in the sand, and a bit of a tour on the wreck. We ended up having to go back out (deep) into the sand, mainly to make our runtime similar to our plan. And then it was time to head up.

How did it go? It was interesting. Of course, making it hard on myself made it hard on my self. I started with the SMB and got it deployed relatively smoothly -- right up until the point when the spool slipped out of my hands... The spool ended up heading its way upward just out of reach. I started to chase it and decided not to and started my gas switch. Later, John laughed: he said as *soon* as I took my eye off it, it came right down. I looked back for the spool, and all I saw was a line plummeting to the bottom.... I started to bring the line up (*knowing* all I was going to do was creating a massive mess) when John waved me off. He showed me a neat trick I didn't know: bring the line up with your hand to create a U and clip a light off at the bottom of the U. Let the light go: it will pull the line down, and the spool up right to your hand. Wind up the line and retrieve your light. No mess. So stupid mistake, but the opportunity to learn!

Performed my guess switch. Once the SMB was squared away (after several minutes...), things went pretty smoothly. Sticking to the dive profile went much better, except where I was distracted by dealing with the reel, which made me miss my need to depart from a stop for one minute. The profile looked a lot more crisp: straighter vertical lines getting to the stop and horizontal lines at the stop. Not exactly *straight*, but straight-er. First time I'd ever had twice as much deco as bottom time -- I'm glad it was in clear 80 degree water... Not looking forward for that in our Great Lakes.....

We went over a bunch of computer information during the long stops: what's your SurfGF? What's your ceiling? What's your GF99? Change your GFHi to 85. Now what does your computer show? That kind of stuff. Helped to fill the time, and get a feeling for how changes to GF's change the information (or *don't*, as it may be).

Finally, back to class. A word about the class time: as I mentioned in the Advanced Wreck class, the material assigned before class and the material covered *in* class are only somewhat related. We probably reviewed 20% or less of the assigned material. This makes sense: I spent a lot more time going over the information before class than we spent in the class, so of *course* we couldn't cover it all. What that means is, like most advanced classes, you will get out of this class what you put into this class. The more and better you prepare, the more you'll get. Make sure if there's something you don't understand or you'd like additional information on you note this down. There may not be an opportunity to have it brought up to you -- you will want to bring it up. And if you bring something up, it will get covered. But given the amount of information involved, if you don't bring something up it might not get covered.

In this final session, we completed the paperwork, including the final exam. This was reviewed, so you have an opportunity to make sure that everything is clear. But by then, there's not a lot of time left -- get those questions in earlier! For me, end of class meant it was time for me to start driving home, back to the frozen north.

Once again, this class unexpectedly questioned fundamental assumptions I had unwittingly made. I had never contemplated such a central focus on a dive plan driven by computers and TTS. It also questioned fundamental assumptions I had *wittingly* made. For example, Standard Gasses vs. Best Mix. SMB deployment process. Gas switch process. I certainly had a good amount of things to think about on my long drive home.

Once again, this is a class I would recommend -- if you have the right expectations. You are not going to get a lot of hand-holding on the basics, whether that's dive mechanics or decompression theory. Well, maybe unless you ask for it. We didn't ask for it, so we didn't get it. I picked up lots of specific tips for smoothly executing a dive -- not just the light/spool trick. But that's not why you take this class.

I got a solid experience in the use of air below 150'. I was able to see the differences that Trimix makes in a dive. I have a new way of looking at dive planning and execution. I have a different perspective on gas choices and how they relate to -- and change -- dive execution. We did get a very different perspective on technical diving.

I mentioned a few critiques of the class as I went along above. I really only have one other item: as a student, it was difficult to know what the expectations for different elements of the process were before we started. I mentioned the surprise of the way the dive profile was broken down. There were other items that cropped up as we went along: areas where my understanding were different than the expectations. At one point I mentioned this. The answer was along the lines of, "at this level, you are expected to be able to execute at a certain level." I don't necessarily disagree with this, and at no point did I think the expectations were too high, or that not meeting expectations was handled in anything but a constructive manner. But it did contribute a certain level of uncomfortableness.

One reason why this may have been an issue for me was that my training was largely *not* by Mr. Chattterton. If I had taken AN/DP with him, I doubt there would have been as many surprises. I'm a pretty big proponent of variety in your instruction, but the cost of that is that there are going to be surprises as you move from one instructor to another. For me, it's that variety that brings value. But it can be uncomfortable, too.

Logistically, these tend to be long days. Class wrapped up near or even after 7 PM., plus the drive back to Pompano, and we needed to be at the boat by 7 AM. It doesn't leave a lot of time: make sure you've got your logistics in place, and don't plan on a lot of gear maintenance (or family maintenance, for that matter). And do what you can to make sure your equipment is in good shape. The save-a-dive kits got hit pretty heavily during this class. Try to avoid that...

Now that the class is done, I'm excited for this dive season. There's a bunch of new wrecks that are open to me now and I'm looking forward to diving them. And if this truly is the last level of diving I achieve, I am satisfied with the experience.

 

[grantctobin]

Thorough write up. Congrats on completing a normoxic class.
Why non-standard deco gasses? 36% as a deco gas?
What was your deepest depth on air during the course?
Were you and Chatterton on the same mix at all times?

 

[tmassey]

Why non-standard deco gasses? 36% as a deco gas?

That's a deep philosophical question: there's not a simple answer. There are advantages and disadvantages, and to hopefully avoid the total derailment of this thread, I'm not going to go into detail. Suffice it to say there are reasons that are more important to some than to others, and intelligent people have legitimate arguments on both sides.

What was your deepest depth on air during the course?
Were you and Chatterton on the same mix at all times?

I'd have to look, but I'm pretty sure it was 165' on air. He was on air at the same point as us. I'm not certain exactly when and how he switched to trimix during the dive. Too narced to notice anything but (barely) myself...

 

[rongoodman]

I'd have to look, but I'm pretty sure it was 165' on air. He was on air at the same point as us. I'm not certain exactly when and how he switched to trimix during the dive. Too narced to notice anything but (barely) myself...

Do you really think this was a good idea?

 

[ChuckP]

Interesting, my Tri mix class in the spring was slightly different but you’d expect classes to evolve. Not going to get into the difference other than to say I like the change.

Were you riding smb’s up off the bottom? It sorta sounded like you were deploying as you went up or were you releasing as you came to that first stop? That’s a complicated madness on the way to the first stop!!!

I too question the need for the haste on the ascent, at least for the way I currently dive - I understand the gotta get going and he really stresses that.

Great write up

 

[tmassey]

We were drifting for our deco. SMB was to be deployed 20’ before our first stop. Bottom was at 200, first stop was at 90. Deploying SMB was to be at 110, which was also the MOD of our lean deco gas. I complicated things by trying to deploy gas *and* SMB at 110. All of this was to be done on the fly.

From a practicality standpoint, I should have (and would normally) wait for the gas switch at the first stop, given that it was only 20’ higher, and done so with the assistance of a reference from my deployed SMB. Or, deployed gas at 110 with a specific pause, and then deployed the SMB and make my way to 90. But what is class for if not to challenge yourself with new things?

 

[Manatee Diver]

And I had my first experiences keeping multiple bottles with me and carrying them on both sides. (I had done cave dives with O2 and a stage before, but in caves we drop them as we go, so you drop your O2 nearly immediately, and your stage fairly quickly as well.)

Part of the reason why I am doing AN/DP in open water, despite my cave instructor offering it in the cave.

If you're like me, you've got those in your notes as a last-ditch backup. You don't *plan* on actually diving that profile. If you were, all you'd need is a depth gauge and a bottom timer -- you know, GUE-style. No, you're going to dive your computer -- it's why you have it, after all. And why? Because we're not diving a square profile. There's no need to limit ourself to that: the dive computer will figure it all out for us as we go. But if it were to fail, you know that fictional written profile will get you home safely, if not efficiently. And that's because that profile really isn't that close to the dive you plan on doing. It's probably planned a little deeper, and a little longer, than you actually plan on hitting. Which is fine: it'll work out. If the fictional profile can be done safely, you're probably OK for your actual profile.

That is *not* how John Chatterton plans a dive. If you're going to use a dive computer, then *USE* a dive computer. Of course, it's equipment, so it can fail, so you need a backup. No problem: wear a second computer. Want a non-technology backup? No problem: carry a written dive plan. But that's real simple: bottom time, first stop depth, TTS. With that, you can then re-create a profile (at *least* as effectively as ratio deco... ). There's not much that that information (and maybe an extra 10-15 minutes at 20') won't do to get you home.

I actually had this conversation recently. If I am carrying two dive computers, and they both fail and then because we are super unlucky both of my buddy's computers fail at the same time how am I supposed to know how deep I am and how long I am at a stop? Am I supposed to carry a third bottom timer or watch/depth gauge combo? No that isn't realistic. The best I can come up with for a complete team computer failure is to get to 10-20feet (in open water using knots in a SMB line to tell) and breath my O2 bottle as far as possible