Chris Verstappen of Technical Dive Services, Bonaire 46m / 150 feet below the surface on the sandy bottom just outside the La Machaca Reef, Bonaire.

Opening my waterproof wet-notes wallet, I see two math problems that my Jedi-level Technical Diving Instructor Chris Verstappen has left for me to solve at this depth to see if I can feel some sort Nitrogen Narcosis effects.

What is the Best Mix for 150 feet? What is the Maximum Operating Depth (MOD) for EAN37 (Nitrox37) These are easy problems, over the last few weeks with Kyle and Max we have solved these problems dozens of times. 150 feet down with a pencil writing on waterproof paper, I start setting up the familiar equation Pg = Fg * P in the easy to arrange “T” format where Pg is on top and Fg and P are below the bar in the T.

Riiip – there goes my mask. Chris just pulled my mask off my face. It was already gloomy dark down here, and now keeping my eyes open as I have been trained, I keep my buoyancy of about 8 inches off the sandy floor while I use my right hand to put my mask back and then use air to clear my mask.

In the middle of clearing my mask my air is killed. I am breathing on the right side (short hose) after having breathed down to 2500 psi on the left side (long hose) on the way down. Chris had turned off my valve while clearing my mask so I would experience lower-case emergencies piling up on top of each other.

Breathing is priority #1, so I leave my mask slightly akimbo with some water, and reach back to the right-side first stage valve and casually re-open the tank. Chris has already done this to me (and Kyle) probably two dozen times over the last few weeks. First at 20 feet, then 30, 40, 60, 80 and 100 feet.

I am breathing again, back to the mask.

“Ho-ho-ho!” Chris booms 150 feet below like a crazy Dutch Santa Clause delivering the watery version of lumps of coal to would-be divers that want to push their limits.

The mask is in place, what is the Pressure at 150 feet again? Hmm 150/33 + 1. What is 150/33?


Chris just unsnapped my right tank’s bottom clip.

100/33 is 3, I know that. But that extra 50 feet?


Damn, he just unsnapped the top snap. Now my right-side tank is floating free and drifting away tethered to me by the thin black “necklace” bungee on the right hand regulator.

The math is going to have to wait a bit.

To get the top snap of the tank in place, I need to reach over with my left hand deep past my right armpit and find the large stainless steel ring that I will snap the top of the right cylinder to. This is plenty hard on land when using a bench to support the tank. The first time I tried it, was a solid 10 minutes of pure frustration where I started re-considering my decision to pursue side-mount. Oh, and I have to maintain that flat horizontal working position 8 inches above the floor, keep breathing smoothly, keep checking my remaining pressure, keep an eye on my computer for both keeping the depth steady and how much “bottom” time do we have left. While I clip that tank back on and get back to getting the last bit of water out of my mask, so that I can get back to solving these math problems.

Snap. The top is in place. Now, I have the easier challenge of getting the bottom snap connected to one of the two D-rings on my belt. Checking the lift on the tank I choose the middle D ring. While working to connect it, I get back to the math problem.

Hmm… if 100/33 is 3, then 50 must be half! Yes! I am a genius. Now what is half of 3? 0.5. Now that is a half. Half of 3 is 1.5. Aha! The pressure is 3 + 1.5 = 4.5 Right??* Then all I need to do is solve 1.6 (the maximum partial pressure of O2 you handle before being exposed to possible uncontrollable convulsions and start gulping down water and drowning yourself). 1.6 / 4.5 hmm…. let’s just call it 1.5 / 4.5 = 0.333 – boom! Nitrox 33 is the best mix! Woot! I write this down while Chris has moved on to demanding to know something about this dive, he is pointing to his computer and flashing the “Deco” pinky finger.

Yeah. Let me get back to you Chris. What is the MOD of Nitrox37.

I am task fixated at this point and I do not realize it.

I really want to solve the second math problem. I am good at things. I am going to be good at decompression diving…

MOD of EAN37 = PO2 = 1.6 = 0.37 * P?

P = 0.37 * 1.6 = uh… I want to multiply 1.6 by 0.37…

Chris is again asking me with his pinky finger how much time do we have left at 150. He is gesturing forcefully at his computer and then my computer.

I check my computer, run-time just went from 14 minutes to 15 minutes. We are still good. 14 or 15 minutes is not a milestone for me. But I cannot bring myself to understand he wants to know 20 – 15 = 5 minutes left to go. I have a Math Problem to Solve!

I go back to 1.6 * 0.37 and I think that 0.37 is pretty close to 0.4, and 0.4 * 4 = 1.6 = woot! I am a genius again. P is 4! Going metric, the depth is 4-1 = 3 * 10 = 30m or 100 feet! That is the MOD of EAN37. I write this down with confidence.

Chris will not stop. I do not understand what he wants from me and my computer.

I know I am screwing up. I do not want to screw up. This is my final dive (hopefully) to earn my Decompression cert. I feel my frustration with myself grow. I have always been an over-achiever and take almost everything too seriously.

For this dive I had the role of the dive leader, which included stating explicitly what are the goals of the dive. Included, was for me to recognize when I was getting frustrated with myself and find a way to relax and calm down.

I recognized that I was frustrated and no longer thinking well.

I hand signaled to Chris to stop.

I was experiencing narcosis, frustrated and I needed to calm down.

We have been doing pretty much only diving and diving training since we arrived in Bonaire a month ago. We started with Rescue and Wreck diving at one of the large PADI shops. The Rescue training was something that I been especially looking forward to as Kyle, Max and I dive on our own from Ad Astra or from our dinghy Exit Strategy, and rarely pay for guided dives. If we are going to learn to dive, then well damn it – we are going to learn to be a self-reliant team.

The Rescue course did teach us new skills but it was not as challenging or rigorous as I was expecting. So then we took the Wreck course and learned to map, use lines and do a mild penetration of the Hilma Hooker down at 85 feet. To be honest, I did not feel like I learned anything specific from the Wreck course, but it was a good experience. But between the Rescue and Wreck courses for Kyle and I the bill was $1200. It did not feel like a good value. Our instructor was very cheerful and went as far as he could inside of the PADI system to teach us more, but fundamentally PADI chops up their courses into tiny bite-sized nuggets with small theory and a fixed small number of dives and everyone basically passes in the same amount of time no matter what.

Initially I went to TDS to get our 4 Aluminum 80 tanks visually inspected as is strongly recommended to be done annually. The typical charge for this service is between $40 and 75 per tank. I opened to the door to TDS and was in awe immediately with the incredible array of exotic diving gear he had on display. Also in his shop were two space-suits – I mean – two closed circuit rebreathers. Also a huge chart of training offered by TDI and SDI which I had been reading about on one of the big SCUBA forums.

He smiled and had another woman in the office who was a PADI Instructor that was in the process of crossing over to being an SDI Instructor and they were in some sort of class. He immediately included me and my family and effortlessly synthesized learnings for me and outlined a path of training for my family.

We started with all three of us in the water to do a basic buoyancy and skills review. Really? After taking Open Water, Advanced Open Water, Rescue and Wreck – he wants to check to see if we can clear our masks?

Yes. For Chris, you are never done learning. Your buoyancy and trim can never be good enough.

He took us to the house reef in front of TDS. We swam under a low rope, cleared our masks while hovering, and made ultra slow maneuvers up across and down a mooring block.

Level, barrel rolls, valves being turned off, floating with your head upside down, the final skill check was to hover just 2 inches off the bottom and glide up to a spoon deeply embedded in the sand. Take your regulator out of your mouth and pull the spoon out of the sand with your mouth and gently lift off the bottom with a breath hold and return the spoon to Chris once clear of the bottom.

We all did fairly well (considering our small number of dives) I think from his reactions as he kept pushing us to do more and more. At the end of the one hour dive in 20 feet with Chris it was by far the most intense and useful dive training I had experienced.

Back in his shop, I said I just want us to all learn what we can from him. Whatever he thought made best sense.

Back to 150 feet below on La Machaca Reef

Stop and Think.

I signaled the universal sign with two flowing hands that I am going to simply breathe for moment. I shut my eyes, enjoyed the breathe. Exhaled and then looked at my dive computer again. Aha I know what he wants! We are at 15 minutes, this dive was planned for 20 minutes. We have 5 minutes left.

I turn to him, crisply indicate “Deco-5” meaning we have 5 minutes left.

I realize for the first time that I am under the influence of Nitrogen narcosis.

I grab the wet notes and write down “N2 – Slow” (no way that I was going to be able to spell Nitrogen Narcosis) and show to Chris.

He smiles and laughs, and affectionately clubs me in the head.

I stuff the wet notes back into my thigh pocket and relax a bit and enjoy the relatively chilly water of 76F / 25C vs the normal surface water temperature of 86F / 30C, looking around in the twilight gloom I was hoping to see an Eagle Ray like I did the day before on my first trip down to 150 feet. No Eagle Ray. There is a discarded mooring and a vague oil-drum that was filled with cement and a cowfish. But overall pretty desolate compared to the reef.

Chris asks me to point to the way back. I helicopter around and point confidently the way back to the wreck of the Hesper a Venezuelan tug that is at the very bottom of the reef at 115 feet (35m). He shakes his head no, and points about 30 to 40 degrees to left of my direction. I stubbornly maintain my belief in my bearing. With Chris you have to have conviction in your answers as he is constantly trolling you to be sure you really know your stuff. After firmly disagreeing with me, he guides me correctly back to the Hesper. We confirm that we are headed to 21m / 70 feet to our first deco stop and more significantly this is where we will switch to our planned deco gas of Nitrox 50.

As the dive lead, I will be the one directing Chris to switch his to his deco gas first. My job is to watch that he uses the correct protocol of showing me the tank he will switch to, holding the dedicated regulator for that gas in his other hand he traces the low-pressure hose back to the chosen deco gas cylinder. I signal okay, and he confirms his depth and does the switch. After watching him for 15 seconds to be sure he is good with the dec gas, I then reciprocate the deco procedure and perform my gas switch.

Next stop? 7M / 20 feet. Chris is using 2 Shearwater dive computers and I am using a Shearwater that I just purchased from him. As we swim up to 20 feet, I show him I am confused on its current gas setting and he shows me that despite its automatic planning of using deco gas if it has been setup for planning purposes you need to manually set that you have switched gases on the computer. Between all 3 Shearwater computers each has a different deco schedule. The procedure in that case is to follow the most conservative computer. With Chris’s two computers – one on each arm showing different schedules – I joke with him that he must have been swimming rotated 90 degrees.

We finish the last deco stop at 3M / 10 feet, clip the side tanks to my butt rail and we head to the oceanside locker room of Captain Ron’s Habitat where TDS is located.

I am feeling good. I know I had some mistakes and I knew I was experiencing narcosis at depth, but I was maintaining my buddy position so much better during the dive, and was not nearly as task saturated on the way back up. I did push it too far the day before and mildly damaged my right ear attempting to equalize too quickly and I aggravated it again on this dive, but I have enough experience to know that it will be fine if I just take it easy on my equalization for the next few weeks.

Later, back at the surface we reviewed my math: There were two errors with my calculation of the Best Mix for 150 feet. First, I should have used a maximum partial pressure of 1.4 and not 1.6. 1.6 is used only for when you are resting at your decompression stops sucking down special mixes with 50%, 70% or even 100% O2 accelerating the off-gassing of Nitrogen from your tissues due to the lower partial-pressure of Nitrogen in these mixes relative to compressed air. My second error was more serious. The equation for finding the Pressure at a given depth is P = D(ft)/33 + 1 or P = D(m)/10 + 1 in the problem above, I failed to add another +1, it should have been P = 3 + 1.5 + 1 = 5.5, and the target PPO2 should have been 1.4, so I should have solved for 1.4 / 5.5 = 0.25 or Nitrox 25 is the best mix. With Nitrox 33 at 150 feet, the PPO2 would have been = PPO2 = MixO2 * P = 0.33 * 5.5 = 1.815 or 1.8. 1.8 >> 1.6 !!

That is a deadly amount of O2 that would have had a good chance to cause those uncontrollable convulsions and drowning especially a diver working and not at rest. What does that mean friends? Do NOT buy a Nitrox labelled tank off of Ebay or a fellow cruiser and then get it filled up at your local gas dealer with the “best Nitrox” he is willing to put in your tank and go “down deeper and longer!” (I have run into two cruisers who were diving without any idea of the math and physics behind mixed gasses, and another two speculating how they could get their hands on Nitrox tanks without having to take a course.) Most people have heard of the bends, and so they think you would get some warning signs before something Really Bad happens. First off all, waiting to feel the onset of the bends while still down in the water is a fantastically fucking poor idea, because as you come up that last 10m to the surface your body will mimic a 2-liter soda bottle on a hot 4th of July picnic after the 10-year old bored kid shook the bottle for 10 minutes and then rapidly twisted off the top to get everyone soaked in corn syrup. But the corn syrup is your blood and the bubbles are all throughout your body. In your joints. In your spine. In your organs. Skin. And your body treats these bubbles as foreign invaders and immediately treats these bubbles as foreign bodies and immediately starts to coagulate your blood, likely setting up your blood vessels to have blockages. And when the blood vessels are the special ones bring blood to your brain – stroke and death are common.

But that is Decompression Sickness (DCS) – the bends. Oxygen Toxicity from breathing > 1.6 PPO2. Again no warning, you just lose control of your jaw and throat and start convulsions and slurp down water. Have a great buddy with you? That is great. Will not help much. You drown underwater at a depth great enough to run into Oxygen Toxicity on low-mix Nitrox (if you can get your hands on high-mix O2, then you have probably taken Advanced Nitrox and know better) then you are below 100 feet and are likely in a Decompression Dive. What does that mean? It means your buddy has to make stops at say 60/70 feet for X1 minutes, 40/50 feet for X2 minutes, 20/30 feet for X3 minutes and at 10 minutes for X4 minutes. How long are these stops? For a very short, mild decompression dive maybe 3-5 minutes, for a serious tech/deep/long/wreck/cave these decompression stops can be hours long. So even if you have a world-class instructor-trainer as your diving buddy, if you go into Oxygen convulsions below 100 feet, your buddy as absolutely existential decompression stop obligations herself and besides swimming your dumbass to the surface, she needs to do her deco stops, and then she needs to swim your ass to the boat or shore. You are brain dead after 10 minutes for sure. Do the math, there is almost no scenario where you go into Oxygen convulsions and can be recovered. Even if you are at 10 feet and sucking pure Oxygen, if you lose track of what you are doing, or have few emergencies pile up and drift down to the very shallow 25 feet you are now at 1.6 PPO2. Again, you drown at 25 feet. Your buddy takes 15 seconds to notice. 15 seconds to grab you and swim you to the surface. They can not effectively get the water out of your lungs and CPR until you are on a hard surface. After taking my rescue course in controlled conditions of shallow water right on the beach, it is still long minutes of work to swim an unresponsive diver to shore while you divest their gear and your gear while attempting rescue breathes (all the while while their lungs are full of water). 6-10 minutes after sucking water into your lungs and passing out your are dead. OMG! I am never going to dive!! Well that might be your reaction, and maybe even a good idea. But the real point is do not be a dumbass and start diving with Nitrox without understanding throughly how to dive with mixed gas and all of the dangers – and all the math.

Back in Chris’s shop, after a the regular thorough and hours long debriefing he handed me my TDI Decompression Procedures Diver certification card. It was the first certification card he did not hand to me on the last dive of each course. Despite not getting the card in the water at the end of the dive, I was serene and it was not a thing I was thinking about – I just liked the dive – it was a good dive – and I felt like I was a better diver. It reminded me of being in training at Elite Martial Arts back in Austin and doing the belt tests – you know if you did a good belt test and it did not (really) matter to you if you got the belt.

So what was all the training under Chris Verstappen at TDS?

His plan was that I would be the tent-pole for the family with learning to wear a side-mount setup of twin Aluminum 80s with two regulators. I would have the ultimate safety as a father in the water with two separate tanks, and two separate cylinders as I dove with Kyle and Max.

Runaway regulator? No problem, shut down the offending tank and breathe off the other one.

O-Ring burst? Cannot happen, these tech-side mount rigs are DIN valves.

Catastrophic first-stage failure? Whatever, again, I have another tank.

Ran out of gas? Hard, with twin 80s I had a 105 minute night dive last night and still had 50% gas remaining.

As a catamaran sailor, the redundancy of everything made so much sense to me. I would be my own buddy, and thus a better buddy for Kyle and Max.

Kyle is also very much interested in learning all he can as a diver, so Chris setup up gear for Kyle to learn how to handle “Doubles” – the classic two tanks on your back as his introduction to tech diving. In addition to the gear, I agreed with Chris that I should learn decompression diving. How could I be a good diver without knowing how a basic decompression dive works? All dives after-all are actually decompression dives, just most recreational divers stick with dive profiles where you can get away with just a 3 minute safety stop at 15 feet.

All of the SCUBA training post WW2 starting in Los Angeles and spreading around the world was based on formalized military training with much more theory and assumed that decompression diving would be the bulk of the dive profiles for the divers career. Thus Chris, created a course for me to get to Deco Procedures that would involve Kyle and Max into as much of the training as possible.

The first class? Visual Inspection of High Pressure Cylinders! He understood exactly that we wanted to be a well-trained, safe family of divers. Being able to inspect our own cylinders would not only be more knowledge and independence (and savings over the years) but most importantly we would intimately know our tanks, their cleanliness, how to breakdown and rebuild the valves and how to prepare our tanks for compressed air, nitrox and even what does oxygen clean mean. Now I am a certified High-Pressure Cylinder Inspector and Kaiwen is picking up my tools and 100 inspection stickers so I dabble on the side helping other cruising divers keep their tanks up to date.

To learn Decompression Procedures, I would need to learn how to decompress on high mix gas, so I would be taking Advanced Nitrox – and so I needed Nitrox to start. Previously, I was not interested Nitrox because the compressor I have on Ad Astra is just a compressed air device. Chris being awesome, had all three of us study the TDI Nitrox class together, although being 12 years old, Max officially could only accept the sport version from SDI of Computer Nitrox. (SDI Computer Nitrox skips the math, which was funny as when we did the round robin testing of Nitrox theory and math along with the PADI cross-over instructor, Max was simply the fastest in the room, quick to point out typos in the manuals and tests. Max is now fairly along in creating his own dive planning tool in Python and solves these Nirtox problems as part of the initial conditions and data gathering.)

On Advanced Nitrox, Chris included Max and Kyle in the theory and book testing even though they would not be able to receive cards, at least they had a full grasp of the theory and math of the diving conditions I would be experiencing when doing decompression dives. The same with the Decompression Procedures class, they would not be doing the deep dives or getting cert cards, but Chris insisted they understood all the theory.

Kyle picked up his Intro to Tech cert and we both received our Side-mount Certs after struggling with clipping and unclipping our tanks on many dives.

Next week, the focus is on Max, as he undergoes his Advanced Open Water course with Buoyancy, Underwater Navigation, Deep Diving, Wreck and Night Diving dives, theory and skills. Kyle and I will accompany Max and Chris on these dives with Kyle and I to watch carefully how Chris performs the skills to demonstration quality.

The week after, the focus is on Kyle to get his Deep Diving training with Chris.

Again, with Chris, besides getting these fun cards, the level of instruction from him is far more rigorous than we have experienced, and I have confirmed it with the number of PADI instructors that have come to him for continuing training.

Kyle will get down to 130 feet with true confidence of skill after Chris’ work, and Max will have a much more fleshed out skill set.

It was wonderful that he went way out of his spend dozens of extra hours to include my sons including making available to us a lot of gear to practice with outside of his class. He has been incredibly generous with his time and gear and I can say he is a warm friend of our family.

As for myself, what is next? I will spend the next two weeks diving with Chris as he instructs Max and Kyle and I will polish up all these new skills. Looking forward to getting Lionfish hunting certified for Bonaire (they are incredibly strict) and Chris says I have already fulfilled the requirements for the Solo certification.

But you know what?

Despite all these courses and certs, and being a much, much better diver than when I arrived in Bonaire a month ago, I feel like a true beginner. I feel like I finally have a basic introduction to how to dive.

And, of course, how incredible is that I get to learn all these skills alongside of Kyle and Max?

Ad Astra,