Transitioning from Open Circuit to CCR for Cave Diving.

I wrote the following in response to someone asking about my experience in making the transition from Open Circuit (OC) Cave Diving to Close Circuit (CCR or eCCR) Cave Diving.

When I decided to take my Megalodon cave diving, I had about 50 OC cave dives and about 40.5 hours doing open water deco and wreck penetrations in New Jersey and the Saint Lawrence Sea Way. By this time, I felt very comfortable in my unit and had dived it in some very demanding environments. I was OC Cave Certified from NACD and IANTD certified on the Meg for Open Water to 145'.

When I moved to Mexico, I was very committed to getting Cave CCR trained. However, draw was just to great to wait for the instructor I wanted to be available. Plus, I was starstruck with my eCCR. I thought it was the perfect solution for everything and I just didn't want to wait to dive it. So, I talked to a handful of people here and made the decision to go cave diving with it. I started off slow. I did dives I could on a single 80 bailout. Luckily, most of the diving I do here is shallow, less then 50-60 feet, so you can do a lot of diving on a single 80. I dove in very forgiving systems and really put a lot of time and effort into it. I spoke to people who were diving their rebreathers in the caves and came up with my own procedures. Slowly, I progressed into ever more difficult and demanding dives. I discovered that what I thought was reasonable level of buoyancy control was crap when the cave magnified it. I also discovered that as the dives grew in length, my ability to dive the unit degraded as I got tired and my concentration weakened. At this point, I was diving the Meg exclusively and had abandoned OC.

Then I went for OC Side Mount training and my eyes opened up again. I learned my Meg is not the best tool for every job. Really, it is a horrible tool for many many of the jobs. For instance, diving Taj Mahal on the Meg sucks; it is shallow and there is a lot of up and down. Or Joe's line at Ponderosa, another horrible ride. Or Minotauro, too tight to take the CCR and appropriate BO and be comfortable.

I started to split my time between OC and CCR. Today, I spend more time in OC then I do CCR. It is just easier for me. I try to choose the right tool for the right job. For instance, today I went for a nice 2:40 dive at Naharon on the Meg.  I dove a 1.2 set point and plumbed my 80cuft BO into my manifold to drive my BOV, wing and diluent.  At a 1.2 you get an amazing amount of no stop time.  That place is perfect, the passages are larger and the depth is pretty much constant 50-65ffw. This is one of the places that makes me love my unit. The eCCR is the right tool for that job. I could see a lot of dive sites in Florida being perfect for a rebreather, like Little Rivers.

The short of the story is that I am still up in the air on whether I am going to go for the training. I have a bunch of people around me who have a lot experience and I am learning from them. I get to dive with some really committed folks. Unfortunately, I know that you don't know what you don't know, until you learn it. So, I am really torn, normally I am all over getting the training, here I am having trouble seeing the value.

I guess there are some other points:

1. Everything is more complicated with a rebreather. There is more equipment and more checks. If you dive 3-4 times a week, this can be a burden. I like to throw my regs in a basket, pickup the tanks and go for a dive. The rebreather takes prep and breakdown and care onsite. I had to plan accordingly; I had to build in more time into all my budgets.
2. I had to become very conscious of mixed team diving. I dive with open circuit divers, like my wife. I need to be aware of that when doing my risk analysis and preparation. She needs to be aware of it and know the procedures. I now mostly dive OC when I am with other OC divers, unless it is a big dive that is eCCR appropriate. If you have to donate your bailout, it is gone. You can't get it back. You need to think about a solution for that. Are you going to make everyone carry a buddy bottle, or are you not going to be part of the team? Your team needs to decide.
3. I dive open circuit pretty regularly, so I am maintaining my SAC rate. I monitor it continually to ensure my gas planning is correct. If you abandon OC totally, your SAC rate will suffer and you need to take that into account when gas planning. Plus, diving a location OC, gives you a very clear picture for BO planning.
4. I have to be willing to pick the best tool for the job. Some times it is OC, sometimes it is CCR.
5. There is a fine art to loop volume/buoyancy management. I haven't mastered it yet. I am still working on how much dil or o2 to add given a change in the loop volume. I hate hearing the solenoid fire all the time. You can't just dump dil in, it will drive down the PO2, you can just dump O2 in, it will drive the PO2 up.
6. Sometimes air isn't the best diluent. A little Nitrox can dampen the swings in the PO2 when you have to adjust the loop volume because of the ups and downs in the cave.
7. If you are a solo diver or reject the idea of team bailout; Diluent/BO is the limiting factor. Every dive turns into effectively a stage dive. You have the CCR on plus you have a bunch of BO tanks. What a pita. Sometimes I can go just as far on my 80's side mounted.
8. Your rebreather's open water configuration may not work in the cave. If you don't live in cave country, plan on spending the first couple of days figuring out how to trim yourself out. I loved my tanks inverted when diving open water; with two SS backplates my trim was perfect. Recently, I had to deinvert them to fix my trim in the cave. I needed to change the balance point and I didn't want to add any weight. I am still looking for way to remove weight from the system. I am still working on my bailout mounting. The rails on the butt plate suck and are in the way and don't work well with 80's. I need something more like the original Nomad buttplate with the d-rings. Plus, fighting even the slightest problem in trim will wear you down. The loop really magnifies any energy you put into the system when finning to compensate. The change between cold water and warm fresh water can play havoc on your configuration.

Rebreathers are amazing tools, sometimes I want to sell mine and sometimes I want to hug it. I always have to respect it! It is like any high performance piece of equipment, it can harm you much faster then you can imagine.