Tank configuration

[swimmer_spe]

This comment seems to gloss over the fact that sidemount diving has really only come into fashion in the last several years. Many, many cave divers have used BM doubles for years. And many still do. Just my casual observation is about 50/50 SM vs BM. ...and I dive the Florida caves pretty often.

I dive SM in caves where there is advantage, but prefer BM otherwise.

Couple more points for the OP..

You can use an H valve to get full redundancy in a single tank configuration. So doubles ar not needed for that.

I also think gas consumption is just one of those things you need to work on. And will eventually get better when you start diving more frequently.

You can find many pages of debate around the relative benefits of SM vs BM. I think your bigger issue is just figuring out a way to get more time underwater and gain confidence and skills.

Gas consumption has always been an issue for me. When I first started, I could barely last 20 minutes on a steel 120. Now I am about 45 minutes. Part of it was realizing I was overweight by about 20 lbs.

What is the advantages of SM? What are the disadvantages?
Locally there is no where to dive SM.

 

[swimmer_spe]

This bothers me. It's either you are misinterpreting the singles, backmount, side mount issue or you need to change your dive op/instructor/ guide.

I dived the cenotes several times on a single tank and no one was "annoyed" with me. I've not taken the cavern course, but I have taken my mask off, rinsed and defogged it in the cavern numerous times and switched my primary to my octopus several times cause I was biting through my mouthpiece. Being able to perform these tasks inside the cavern was a learning experience for me and I'm glad I "had" to do it.

Maybe it was a misinterpretation. It just seemed that they felt it was the best way to go.

I can do all those skills. The issue is not doing the skills. The issue is that if possible, I would rather not have to constantly switch regs to keep my tanks even. Maybe I am making more of this than it is. Maybe I am not suited for it. I am just trying to sort of what the differences are, and why one is used over the other.

 

[kensuf]

The reason some prefer SM over backmount, and others prefer BM over SM really comes down to personal preference. They each have pros and cons. Some people believe BM is the best route for the majority of cave diving, others view SM as the best route for the majority of cave diving.

However, regardless of the differences between SM and BM, based on the things you have written in this thread, you are not mentally prepared to engage in cave diving. Period.

There's a thing called stress, which can lead to perceptual narrowing, which can lead to panic.

Stressors are like the layers of an onion. Things like a wet breathing regulator, being in an overhead environment, monitoring your air, monitoring your time, maintaining trim, being in unfamiliar gear, a leaking mask, having a regulator tugged out of your mouth by the wall of a cave, all add stress and build on top of each other. When you get to a point where the cumulative toll of the stressors is enough that you start focusing on those stressors -- let's use the need to clear a regulator, for example -- then you begin losing your awareness of everything else around you. You may lose attention to the guideline, you may lose awareness of which way is out, you may get separated from your buddy, you may cause a silt-out. When you start having perceptual narrowing problems, and then the fit hits the shan, you may very well wind up in full bore panic.

Once you're in full blown panic, there's no coming back. Your thinking brain shuts down and your lizard brain takes over. You become a hazard to yourself and the people you are diving with.

This really happens. I've seen people in full out panic. It's not a pretty sight.

In technical diving (and really, it should be all diving), we have the golden rule: Anyone can call any dive at any time whatsoever with no repercussions. If something as basic as taking a second stage out of your mouth, putting it back in, and clearing it causes you stress, then I strongly suggest you use the golden rule to avoid going into the overhead environment entirely. Focus on diving in the openwater and perfecting the basics.

Fact: Water filled caves can be some of the most unforgiving places. The cave doesn't care if you live or die, it is just there.

Fact: When you have a problem in a water filled cave, you cannot go straight to the surface. You have to deal with the problem in the cave and make your way out.

Fact: Remaining calm in a cave environment is MANDATORY. The first or second thing I teach brand new openwater divers is reg removal and clearing, if the idea of doing this causes you mental discomfort and stress then you have ZERO business cave diving.

Look, I'm really trying to help you here. I'll even be happy to mail you a free copy of Sheck Exley's Blueprint for Survival which outlines several of the risks and hazards in cave diving by looking at a half-dozen fatalities in detail if you PM me an address.

 

[elgoog]

Cave divers and instructors far more experienced than me have already highlighted critical points. I don't have any significant overhead experience yet but I'm going to comment on a couple of things below as I feel they are relevant to any kind of diving.

When I was there, it seemed that most were diving sidemount, with a few diving backmount. At each site, I think I saw about 10-20 divers, and I was the only one with a single tank.

Don't ever feel like you should be diving what everyone else is diving - certainly not at your level. Dive the rig you're comfortable with and get as much experience as you can with it until the needed skills become automatic. Going to doubles adds more things you need to know and be very comfortable with doing before you do any kind of more advanced diving.

Gas consumption has always been an issue for me. When I first started, I could barely last 20 minutes on a steel 120. Now I am about 45 minutes. Part of it was realizing I was overweight by about 20 lbs.

This sentence is confirming for me that the main reason you want to dive double tanks so you have extra gas and, hence, longer dives. This is not at all going to work the way you are expecting in cavern diving. The gas limits at cavern (and intro to cave) are 1/6 of double tanks which is the exact same amount of gas you are currently diving .i.e. 1/3 of single tank. If anything, your gas consumption may increase when you dive a new setup, be it backmount doubles or sidemount.

 

[swimmer_spe]

Cave divers and instructors far more experienced than me have already highlighted critical points. I don't have any significant overhead experience yet but I'm going to comment on a couple of things below as I feel they are relevant to any kind of diving.


Don't ever feel like you should be diving what everyone else is diving - certainly not at your level. Dive the rig you're comfortable with and get as much experience as you can with it until the needed skills become automatic. Going to doubles adds more things you need to know and be very comfortable with doing before you do any kind of more advanced diving.


This sentence is confirming for me that the main reason you want to dive double tanks so you have extra gas and, hence, longer dives. This is not at all going to work the way you are expecting in cavern diving. The gas limits at cavern (and intro to cave) are 1/6 of double tanks which is the exact same amount of gas you are currently diving .i.e. 1/3 of single tank. If anything, your gas consumption may increase when you dive a new setup, be it backmount doubles or sidemount.

I am quite happy to stay singles. It lasts long enough for me.

Sounds like its not worth it to switch.

 

[Lorenzoid]

When I was there, it seemed that most were diving sidemount, with a few diving backmount. At each site, I think I saw about 10-20 divers, and I was the only one with a single tank.

Are you talking about the guided cenote (cavern) dives, or are you saying that you were there diving on your own (presumably showing the operator a Cavern card)? Just about every one of the dozens if not hundreds of divers doing those guided cenote dives every day of the year is on a single tank. Now, if you're referring to divers who are not doing the guided cenote dives but rather are there on their own, either to do the cavern line or a cave dive, then sure, they are not using single tanks.

 

[Johanan]

I don't like having to clear regs. I never have. I can, but if I can avoid it, I will.

If you are sure about it, then perhaps the UTD Z-system is an option for you. Otherwise your question, which configuration, seems to be answered.

 

[leadduck]

Neither is really better or worse because a set of side mounted 85's carries just as much gas as a set of back mounted 85's. Are they different? Yes! The way that you manage your gas supply will be different between the two because in side mount you have to manage two independent tanks, maintain an emergency reserve, be able to adequately donate to other members of you team, etc.... However, ultimately volume is volume and you'll end up seeing the same cave as your buddy no matter the configuration.

I think you're missing one difference between backmount indy and sidemount, that is being able to visually inspect and manipulate all your valves, first stages and LP hoses.

I once had the inflator hose not properly screwed in and come loose at the first stage while in sidemount. One quick look told me it's me who's bubbling and which stage and which hose it was; easy to shut down that valve, screw in the hose, open again. And even if I hadn't noticed and had lost all gas in that tank, I would've had enough reserve gas in the other independent tank to get out by myself. Coincidentally, on another dive, an other team member in backmount doubles had a similar problem close to the end of the dive, being low on gas already, but didn't notice until it was too late. He ran out of gas and needed his buddy's long hose.

So for many divers going sidemount is not so much about supertight places where you can't go backmount, but about having redundant independent gas and easy access to your gear in overhead environments.

 

[swimmer_spe]

Are you talking about the guided cenote (cavern) dives, or are you saying that you were there diving on your own (presumably showing the operator a Cavern card)? Just about every one of the dozens if not hundreds of divers doing those guided cenote dives every day of the year is on a single tank. Now, if you're referring to divers who are not doing the guided cenote dives but rather are there on their own, either to do the cavern line or a cave dive, then sure, they are not using single tanks.

I was doing the TDI Cavern course.

 

[Lorenzoid]

I was doing the TDI Cavern course.

Then I would guess the "10-20 divers" you saw doing mostly SM with a few BM were not doing those guided cavern tours but rather were cave divers. You were fortunate to have avoided encountering the hordes of guided cavern divers (of which I have counted myself among). From my perspective, having been taken by my guide to some of the more popular cenotes for that, I saw a whole lot of single-tank divers with guides and a smaller number of dual-tank (I don't recall whether SM or BM) cave divers.

I have heard there are at least some cenotes that will allow you to do the cavern line without a guide if you show a cavern c-card, and I get the impression that's what you're considering trying. I don't know if they have other requirements for cavern divers, such as redundant tanks--whether BM or SM--but that seems like it would be prudent. As you may have observed, it's debatable whether every bit of the cavern line in every cenote even qualifies as cavern under TDI's definition without a bit of a stretch. I believe the guides are required to have the full cave gear, presumably as a safety net for their customers in single tanks. If some cenote will allow you to do the cavern line with your TDI cavern card, I have to believe redundant tanks--whether BM or SM--would be a given. So, if I now understand the situation correctly, I disagree with those who are advising you to stick with single tanks for self-guided cenote cavern dives.