A Divers Diary of the TDI Rebreather Cave Diver Course

divers_diary

Photo credit Peter Lapin

Over the past few months, two members of the TDI training department spent their weekends assisting in the development of the Rebreather Full Cave Diver course. As CCR Advanced Mixed Gas divers with years of deep ocean experience and zero overhead environment training; they were the perfect candidates to test and challenge this course in the making as real students with one of the most experienced cave instructors in the field.

After 20+ hours underwater, a lot of lessons learned, humbling and exhilarating moments and more; they completed what is now the TDI Rebreather Full Cave Diver course. To recap on those experiences, here are some highlights from their course:

Day 1: Land Drills - After learning how to properly deploy and follow a guideline, our instructor set up a triangular course for us to follow in the woods. We tracked the guideline several times over with different variables in play each time around. The first time through the course we were able to have our eyes open and simply walk next to the line, easy enough right?  This drill eventually progressed to closing our eyes while keeping in contact with the guideline and each other. The last time around the course with these variables in play it took us well over three times as long compared to the first time around. I don’t think I will ever forget our instructor’s face when he said, “you both are dead.” Ouch!

This drill was used as an example of improper dive planning.  If we planned our bailout gas requirements based on the first time it took us to track the course (in easy conditions) and something went wrong (leading to a challenging exit), we would have exhausted our emergency bailout gas reserve before exiting the cave. First lesson of the course: Expect the unexpected and plan for the worst case scenario. Caves are an unforgiving environment; when things go wrong the potential for a continuous downward spiral is always present and you might be faced with little or no options if you do not plan your bailout accordingly.

Cavern Dives - The first few dives we made in the course were conducted in the cavern zone.  This was our first experience applying the land drills we conducted earlier that day.  Line laying, gas sharing, and zero visibility scenarios were played out extensively until our instructor was confident in our ability to handle these stressful situations.  These were possibly some of the most humbling experiences of my diving career.  Going into this course I thought I was a pretty good diver capable of handling a lot in the water. At this point, I realized I was truly a novice in this new environment with a lot to learn.  This was certainly going to be an interesting course…

First Cave Dive “I need to get in better shape.” During our first swim beyond the daylight zone of the cavern going into the darkness of the cave, I felt the outward flow of water seek to push me out as I was striving to swim in. Although this makes for an easier exit, it created a very wearing entrance. I was trying to recall all of the things our instructor said about body positioning in the water, learning the cave’s personality, and tucking behind rocks or the diver ahead to “draft” them. None of it seemed to be working; I was tired, frustrated, and my ego was about the size of a pinhead at this point.

Working hard and over-breathing is not a good recipe on a rebreather. I knew I had to take a break to collect myself and gain control of my breathing rate before progressing on at a slower pace. I spent the rest of the dive observing my instructor’s movements while trying to get a feel for moving efficiently in the water. My technique was improving but I was lacking speed and stamina.  I knew I was in need of a lot of work to keep up in this environment.

That was the last dive for the weekend and I left with a goal in mind; get in better shape! I spent the next three weeks out of the caves and in the gym. The only diving I did during that time was in shallow water practicing skills and line laying drills for the dives to come.

1st half of the course “A rebreather is a tool, utilize it!” Throughout the course, we practiced a number of skills and drills to make the most of a rebreather in the cave environment. Even though you must always properly plan your bailout requirements for the dive to allow a safe exit, with proper training and execution, diving a rebreather sometimes offers other options in adverse situations.

We spent the majority of these dives practicing and perfecting these options which include but are not limited to; flying the rebreather manually, semi-closed rebreather mode, bailout bottle swapping exercises, and more.  The first half of the course also included a lot of lost diver and lost line drills.  We exercised these drills on almost every dive until we were comfortable quickly deploying our safety reels and conducting a quick search for either a simulated lost teammate or the main line.  These drills were a good reminder of how great a rebreather is for the cave environment.  In the event you lose the mainline or a teammate, you have time to conduct an efficient search without having to worry about a quickly depleting gas supply.  While we were starting to feel comfortable in the cave, there was still a lot of work to be done.  At one point my teammate mentioned, “I feel just comfortable enough to get myself into some serious trouble.” Meaning he was comfortable in the environment, but knew he had a lot left to learn.

2nd half of the course “I am starting to get the hang of this…” After three months of a new workout routine, a fair amount of time in the caves, countless skills & drills; our overall comfort and confidence in the cave environment increased.  We were now working on complex navigation in the cave, making multiple jumps off of the main line and doing large circuits and traverses.  We were moving quickly and efficiently in the water for extended periods of time without getting tired and our skills were on target but we still didn’t quite have “it” yet…

Our instructor placed a major emphasis on situational awareness in the cave. The reoccurring question of the course was “what is your swim rate?”  If we couldn’t answer that question appropriately, we typically received a “come on guys, you have to know your swim rate” lecture. The reason why it’s important to know your swim rate is to track the amount of time it takes you to swim a certain distance given the environmental factors (i.e.; high flow, low flow, and siphon). You can track this by monitoring a timing device as you pass each line marker indicating penetration distance. On a rebreather, you don’t always have your gas supply to tell you when to turn around. A rebreather enables a diver to spend a vast amount of time in the water; this can be deceiving in the cave environment if you venture too far in without adequate bailout to exit if something goes wrong.  Often times you have to use time and distance to judge your turning points.  If you go beyond the range of your bailout you can end up in a seriously problematic situation.

Last Cave Dive“We finally figured out what “it” is…”   As we were making our way into the cave I noticed we were swimming at a rate of 80-100FT/minute. I knew we made substantial headway in swimming rates since we started the course however, 100FT/minute was not a realistic pace given the limited amount of work we were putting out. As we were nearing the point we designated as our turn around location, we decided to call the dive a little earlier and make our way out. As we were exiting the cave, we noticed our swim rate slowed down to 50-60FT/minute, meaning we were moving at half the pace and would exit in double the amount of time it took us to enter the cave.

Once we surfaced our instructor asked why we called the dive earlier and if we noticed anything different. After indicating that it was a siphon, noting our exact swim rates, and the reason why we turned sooner was to allow extra time for our exit; he finally smiled and said “you got it.”

After completing the TDI Rebreather Full Cave Diver course; experiencing some of the most challenging, humbling, and exhilarating moments in my dive career, I can honestly say I can’t wait for more. The amount of dive experience my teammate and I had prior to the course could not prepare us for this type of diving. Now it’s time for us to keep our skills fresh, stay current, and slowly gain experience in the caves.

Contact SDI TDI and ERDI
If you would like more information, please contact our World Headquarters or your Regional Office.

Tel: 888.778.9073 | 207.729.4201
Email: Worldhq@tdisdi.com
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One Response to A Divers Diary of the TDI Rebreather Cave Diver Course

  1. Jim jones says:

    Great experience for me as well!!

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