Underwater Exploration

I met up with some of my dive buddies this weekend for some dives at the Blue Hole. This is my last chance to get into the water before my GUE fundamentals class. Besides the wind, it was a very nice weekend. By the time we got into the water most of the open water classes were leaving for the weekend. The only thing that sucked was the people who stirred up the silt on the bottom. We did three dives. For a few of my buddies it ended up being their first dives in drysuits. That’s always a fun experience! I had two interesting experiences during our dives.

On the first dive I got a nose bleed, which was made worse by me trying to clear my mask. After I signaled my buddies, we made a controlled ascent to the surface, and we talked about it for a couple minutes and made sure that the bleeding stopped.

On the third dive, I had an experience, which validated the need to be able to reach and turn off and on your valve knobs, particularly while wearing doubles. We were practicing valve drills, so I started by purging my bungied second stage and proceeded to turn my right post off. Once the right post was off, I breathed down the primary second stage and then switched to the bungied second stage. Then I gave the OK signal to my buddy, who was supervising the drill, and began to turn my right post back on. That’s when I started to hear bubbles escape from my manifold. I signaled my buddy and he signaled back with bubbles coming from my right post. I then turned the post back off and grabbed my regulator to make sure it was seated correctly. After that I started to turn the post back on and I didn’t notice any bubbles. My buddy gave me the OK signal and we proceeded to finish the drill. The only thing that I can think that happened was the DIN o-ring was not properly seated.

Beyond that the dives were pretty normal other than the guys getting used to their new drysuits. The surface intervals were fun as well. They were filled with great company and more food than could be consumed in a single afternoon. Next stop, GUE Fundamentals class in March.

Dive Statistics:

1. Depth: 36feet – Run Time: 40min.
2. Depth: 61feet – Run Time: 31min.
3. Depth: 32feet – Run Time: 24min.

During one of my blogs you may have recalled my blog entitled “Diving at Altitude – Compensate or not to Compensate?“. In the blog I stated my argument of why Altitude Compensation may not be necessary. Well, I made an interesting observation over my last trip to the Blue Hole with an Open Water Class that may in the very least change that argument some.

The shop that I currently work with uses old, analog, console mounted depth guages for their Open Water classes. For one of our dives we had briefed the class that during our swim around we would swim around at a depth between 20 – 25 feet. To my amazement the students in the class immediately shot down to around 30-35 feet and maintained depth there. I signaled everybody and even wrote in my wet notes to swim up to 25 feet, level off and swim around. All the students looked at their gauges, gave me an OK signal and kept on swimming. I was puzzled at this, so next I swam up to one of the students and looked at their depth gauge and noticed that their depth gauge noted 23 feet. So it hit’s me that my digital gauge is automatically compensating for altitude by displaying what the altitude corrected depth is instead of an actual depth. This actually can make a big difference in the future for my dive planning.

The Blue Hole is roughtly 4600 feet above sea-level, which going by altitude correction rules makes the pressure on the body 20% less (.8ATA instead of 1 ATA) then it would be at sea-level. Going by this we can determine that the altitude corrected depth at 23ffw is 27.6ffw. (23 * (1+20%) = 27.6)

That can also make a big difference for people who manually figure their tables for recreational diving and add the altitude correction formula or tables into the mix. It appears that if you are using a depth gauge that automatically corrects for altitude adds some additional convervatism by adding additional altitude correction into the mix.

I don’t know why I’ve never caught on to this before. My depth gauge’s manual say’s that it compensates for altitude when it’s in computer mode, but doesn’t say the same thing when in gauge mode, which mine is. I always thought that the computer just compensated by taking away some of the bottom time. I never thought that it actually compensated by displaying a deeper depth then what you are actually at. It’s perfectly logical for the computer to do this, but it never dawned on me that it worked that way until this last class. Good to know…