I took my PADI Deep Diver class in the winter, in frigid water. It was not, however, briny water as all my diving at this point has been in freshwater lakes. My first intentional dive below 60 feet was in water that was around 41° Fahrenheit (that’s 5° Celsius). Yes, I said intentional – in all three previous times I dropped below 60, I was following an instructor, and they all knew I hadn’t had the class yet, so they were keeping an eye on me. Oh, and it was three DIFFERENT instructors.
Carl from Diver’s Oasis taught the class for my dive buddy Nathan and me. We spent a lot of time over the winter diving at a site by the Table Rock Lake Dam. They had some bathrooms there that were publicly available and heated, so there was a warm spot to change.
Exposure Gear
I wore a 7mm Henderson Thermoprene wetsuit with a Sharkskin Chillproof vest. Carl wore a drysuit and Nathan had a semi-dry suit. They were both better insulated than I, but I have more natural insulation (excess fat).
Class Basics
This class is pretty straightforward and not complicated. Depth changes stuff. Colors change because the water absorbs certain frequencies as you go deeper (red first). Items that are normal on the surface will compress with pressure (like neoprene in your wetsuit). In fact, that neoprene compression will impact your buoyancy and warmth if you dive deep enough. The air in your BC will compress, requiring you to add air as you descend to maintain neutral buoyancy.
The class is to familiarize you with those changes, make sure you understand that your safety stop (always important) is even more important on a deep dive, and make sure you understand the difference in your air consumption at depth. It increases, surprisingly fast.
Air Consumption
I’m an air hog at the best of times. It’s improving as my cardiovascular fitness improves, but I can burn through a tank in a ridiculously fast amount of time. At 99 feet, it’s three times faster than at 33 feet. So, if you can do a 50-minute dive at 33 feet, that same dive profile at 99 feet will only last about 17 minutes. That’s OK because your NDL (No Decompression Limit) is not very much at that depth.
No Decompression Limits (NDL)
I should define NDL. This is the amount of time at a given depth you can stay before you will be required to make a decompression stop. That’s a seriously dangerous thing for a recreational diver to do. There’s an entire series of classes on tech diving to learn about doing decompression safely. Before the advent of dive computers, a diver had to have a timer to watch to know when they needed to surface. Now, your computer will tell you. Pay attention to it. Failure to keep this in mind can be fatal for a diver (and has been for some in the past).
Your NDL (no decompression limit) time is a LOT less at the deeper end of the recreational limits. When I dive at shallow depths, my dive computer (Shearwater Peregrine TX) shows NDL and usually has a 99 next to it. That’s the largest number it can show. When I drop below 100, that number gets a LOT smaller really fast. Heading down to 120 feet – it’s usually under 10 minutes by the time I get there.
You can’t just stay till it’s at 0 and head up. You need to start up with a few minutes left or you will still exceed the NDL on the way up. If you do, your dive computer can literally save your life. It will automatically show the mandatory decompression stop – both the time of the stop and the depth at which it should occur. It’s like a safety stop but NOT optional.
Do You Know How Deep You Are?
Pay attention to your dive computer on deep dives. In our local lakes, it’s easy to tell when you’re deep. It’s dark and murky. It feels like a haunted forest on Halloween (and that’s complete with leafless trees still there 60 years after they create the lakes). I’ve heard that in the open ocean, you can drop very deep without realizing it if you don’t pay attention to both visual cues and your gauges or dive computer.
Tasks on the Dives
We practiced assembling a little puzzle at depth. Why? Because you start feeling some signs of narcosis at depth as well. It helps you to see it in a tangible way how it can affect you (we practiced the puzzle on the surface with our gloves on for comparison).
Carl also had a card to show how colors disappeared at depth, and a few items so we could see the compression effect on them – an empty water bottle, a neoprene gloves, and a ping pong ball.
Pressure Impact
Pressure at depth is a weird thing when you don’t usually really “feel” it. I was on a dive for another class where the instructor had a dive flag buoy on a 25-foot two rope. She didn’t expect us to go much deeper than that, but we did a little – down to 35 or so. Because of that, the flag itself (and buoy) got pulled below the water deep enough that the foam that made it float got compressed and it dropped to the bottom.
Final Thoughts
Was this class good and useful? Absolutely. I knew most of this stuff theoretically but experiencing it for the first time with an instructor there telling us what to expect was, in my opinion, vital to my future safety diving. Carl did an excellent job and most of my deep dives since this class have been with him or my fellow student Nathan, including my deepest dive, right to the recreational limit at 128 feet.
