I was recently asked a question about why I showed one of my students a modification that isn't normally done in backmount. This question came up as a result of a discussion on one of the Internet forums. Here is a slightly modified ( ;-D ) version of my response:
I received an e-mail asking about the reason I have my inflator and dump valve swapped and why I showed one of my students that modification. As my students has already stated, his intention is to transition to sidemount eventually. One of the common modifications in sidemount rigs is swapping the inflator and dump. There are a few reasons for this. In the standard wing, the butt dump is located on what is the underside of the wing when it is mounted properly. Air rises, so when dumping air from here it is necessary to change from a horizontal position to a head down position so the air bubble can rise to the bottom of the wing and release from the exhaust. This change in position isn't always possible when diving some sidemount passages. Also, with the inflator hose on the top of the wing, the only way to get all of the air out of the wing, short of inverting and using the butt dump, is to go into a head up position and raise the inflator hose up. It's physics. Also, in a sidemount rig if the inflator hose is on top, the elbow is exposed and unprotected and subject to damage.
Okay, so with that aside, I also had a student in the course that was in sidemount configuration. When looking over his rig I spoke with him about the two different ways of configuring the inflator and dump valve. I explained to both students the advantages and disadvantages of both and gave them the option of configuring their rigs either way. One thing I never do in my courses is tell my students how they must configure their gear, unless it's a safety issue! I let them know all the different ways I have seen rigs configured and allow them to make the choice.
One of the more important things about overhead diving, both real and virtual overhead, is to build up muscle memory. It's absolutely necessary that divers know where the inflator is, the dump valve, d-rings, cutting tools, etc. I started my cave and tech instructor internships about a year after having gone to sidemount. I hadn't been in my backmount rig in over a year and one of the issues I found I had was reaching for the inflator and dump without thinking about it. They were both in different locations on my backmount wing and I found myself constantly going to the locations where my sidemount inflator and dump are. I teach students in backmount and sidemount. I also feel it's a disservice to my students if I don't demonstrate skills, such as valve drills, in the configuration they are in. So I dive in backmount when I have students in backmount. Somewhere along the line I decided to mount a set of manifolded doubles to my sidemount rig. This left the inflator and dump in the same locations as I'm used to and reinforced the muscle memory I have built up over the years. I also found that dumping from the top was much easier , even in backmount! Because the dump valve is on the back of the wing (or the top when it's on), there is no need to change orientation in the water. There's no need to go head down or head up. Just reach up and dump. The air, as per the law of physics, exhausts up like it's supposed to. Because my student is intending on eventually diving sidemount (before he takes a cavern course), it also made sense to start building that muscle memory now in his current rig. While the inflator and dump may be in slightly different locations, they will be close enough that the transition should be fairly easy. I presented him with the information and he made the decision. While I see some benefit to some of the DIR philosophies, I don't agree that everything needs to be one way. I believe doing what works for one's own diving is the way it should be, as long as safety is not compromised.
And as for technical v. recreational courses... According to many agencies, cavern and intro/basic cave are recreational, but so are cave and advanced nitrox and decompression procedures. IANTD even considers Advanced Recreational Trimix as a recreational sport diver course (max depth of 160'). The technical courses begin with Technical or Extended Range Diver (max depth of 180') and continue with normoxic trimix and above. While some may disagree, the skills learned in ITT are an excellent foundation for cavern. The cavern diving course involves a lot of task loading. There is a lot of line running and doing multiple skills at the same time. Rather than learning to multitask in an overhead environment, it's beneficial to learn how to maintain neutral buoyancy and horizontal trim while task loading prior to that. This is where ITT comes into play.
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