Tank configuration

[WetRocks]

N..but there are accounts of fatalities where A lack of SM proficiency was a likely factor.

Really? Do tell...

 

[Caveeagle]

Really? Do tell...

I was careful not to say confirmed or cause.. and this hardly the place to re-stir that silt...

Just search for roll offs in sidemount and you will probably find what you are looking for

 

[swimmer_spe]

Then I guess I did NOT understand. If you intend to do only those guided cenote dives that every dive shop down there offers to OW divers, then stick with single tanks for that. I suspect your guide would scratch his head if you said you wanted to dive doubles for that kind of dive. If you're diving with a group--that is, unless you have a private guide--it's almost guaranteed that everyone else in the group will be diving a single Al 80.

I got confused when you mentioned having taken a cavern course and seeing others diving SM and BM.

I do have my cavern certification. To me, all that means is I know what I should be doing in an overhead environment. It does not mean I will dive in an overhead environment alone, or without a guide. I am just trying to sort out the gear.

 

[swimmer_spe]

Just a silly initial statement. The transition from BM single to BM is easier! ...period.

Especially if the diver in question was trained well and is in a Hogarthian / primary-donate configuration. (Which is a good idea, and getting more common)

Sure, some people will take to SM faster than others, but a much higher variability in gear, body types and preference is just a starting point. I know cave divers that have well over 50 dives (in SM) and are still tweaking their configuration, or swapping over to different brand/types.

I have seen well sorted out divers step into a set of doubles with minimal surface training and within 20m, look VERY good in the water.

**Now for the OP, I am not recommending either path, but getting some formal instruction is probably a good idea.

OP here. What is a Hogarthian? I do have 2 regs, one in my mouth, and the other one is the one I typically donate.

If I switch to SM or doubles, I will definitely get formal training. This fails under my theory of "I don't want to become a statistic."

 

[swimmer_spe]

@swimmer_spe
1: "back in the day" which realistically was only like 5 years ago, we all had to figure it out ourself. You can buy sidemount gear from anywhere, those of us that started diving sidemount before it became a fad had to figure it out for ourselves. Steve Martin has the online video courses that are apparently very good. Servicing sidemount gear is no different than servicing anything else. Regulators are regulators, just because they have different hose lengths on them doesn't make it witchcraft, a bcd is still a bag with some valves on it and those don't really need to be serviced anyway. You can also contact Matt et al at Dan's Dive Shop in Toronto who teach sidemount. They're still a 5 hour drive, but for something like this, it's worth it if you are committed to sidemount.

2: I think you're still missing the important point that I made in that arguably too long post. The problem you have for cenote diving is that you will not have any more gas to stay down with doubles or sidemount because of the limitations of your certification. It is not until full-cave that you are allowed to use thirds of doubles. If you have a single AL80 you are allowed to use a third of that, or about 25cf. If you have a pair of AL80's whether on your back or sides, you are only allowed to use a sixth of that, again roughly 25cf. The extra mass will usually mean less penetration on the same air volume though with your high sac rate it may not matter much. You have to learn to maximize the gas that you have with you, not just band-aid the problem by carrying more.
Going to doubles at home is one thing if you want to stay down longer, but is it worth the cost of that class and the gear?

3: Very rough numbers. 120cf tank, assuming you left 500psi behind means roughly 100cf used. You said you're at 45mins now, and at 40-60ft you're SAC rate is around 1.0cfm. That's high. Typically you'll see around .6 which is around 70-75 minutes of dive time. 1.0 is what we typically use as a SAC rate for racing around in an emergency, .6 is considered "normal" for kicking around in a thick drysuit.
For a similar amount of money as the doubles course and gear, you can go take a course similar to GUE Fundies as mentioned previously which will teach you how to move efficiently through the water.
You need to be comfortable and relaxed before you go under. Every dive should start with a cold water treatment which is you breathing on the regulator or snorkel, mask off, face in the water. In through the mouth, out through the nose until you are relaxed enough that you can slow the exhalation down and stop/start it at will. In truly cold water it will often take over a minute. If you don't do that, you have an elevated heart rate from gearing up, getting into the water, floating around trying to get situated etc. and it takes a long time for it to stop. The mammalian diving reflex is a wonderful thing but to trigger it, your whole face has to be wet.

Gas switching in sidemount can be done as frequently or infrequently as you want, but to say "switch every 500psi" is putting a pair of needless gas switches in. You switch gas in sidemount typically at the maximum delta you are comfortable with from a trim perspective, and/or whatever is convenient for you. The bigger the tanks, the more frequent the gas switches because 500psi is a lot more mass out of a 149 than it is out of an 80. If that point is 500psi, which is convenient on an al80, then there is nothing that says you have to have one tank going first and the other playing catch-up. Breathe one 500, then the other 1000. Still have a 500psi gap, then breathe the other 1000 so you never exceed a 500psi delta, but you are minimizing gas switches. Have to think and ask for the why behind the what/how instead of blindly follow things that you hear.

There is still a learning curve for doubles, while I think the curve is a bit less steep for doubles, it is still there. Valve drills are no joke to start learning, and the trim profile definitely does change vs. singles. I find it easier to get started with doubles than sidemount because there is basically a single acceptable base configuration and the adjustments that you make from there don't really change anything major. In sidemount there are basically 3 accepted "base configurations" and those three are all very different than singles so it takes a bit longer to get sorted initially

Thank you for the long reply.

1) Sounds like the next time I am down in the Toronto area, I will go see them. And it is a 4 hour drive. 5 hours only in bad weather.

2) Early on in this thread, I was told that, and now understand that. On the first dive, I should come up on half the gas I went down with. With the second dive, do I still use the 1/6 or do I do the 1/3s? As far as the cost, I have well over $5k in diving gear. Right now, I could go OW diving without needing a thing. Eventually, I want to be able to dive in overhead environments the same. Also, for the first few dives, I will rent until I learn enough. I learned that the hard way with OW.

3) That sounds about right for my SAC. I know it is horrible. It was much worse, and it is getting better. I will not do GUE. Everything I have learned about them has told me that they are not for me.

Just from this thread, I am learning lots.

 

[Caveeagle]

OP here. What is a Hogarthian? I do have 2 regs, one in my mouth, and the other one is the one I typically donate.

Start here
William Hogarth Main - Wikipedia

I think you have been given some pretty sound advice here re progressing into overhead diving considering your current comfort level with basic skills. ..so I will not repeat those warnings.

I will say that some people pursue advanced diving more for the challenge or just some need to "level up".

I appreciate your transparency and think you could benifit from thinking through a few things.

It's kind of hard for me to imagine being cavern certified withought exposure to some of the most basic concepts. Read up on the Hogartian principles for gear rigging. Get yourself used to the idea of "primary donate". This is consistent with all cavern/cave/tech training that I have seen. So if you want to play in this sandbox, you should gain comfort with it.

If you run into an OOA diver in a cavern, you should expect them to go for the reg in your mouth and be prepared to quickly offer this reg and THEN switch to your backup. This is a fundamental skill. If you are incapable of getting comfortable with this, ....please stay out of caverns and caves.

 

[Johanan]

Cons
The tanks are not manifolded so if you have a regulator failure, you lose access to the gas in that tank

Did you mean a regulator shutdown? Because if a free flow occurs, the air is still accessible by feathering the valve.

 

[leadduck]

@Caveeagle 50? Try 500 or more. Edd still tweaks his gear on a pretty regular basis and I'd bet he's over 5000 sidemount dives... I don't know anyone who is actually truly "happy" with their stage configuration yet...

These guys are high end perfectionists and wouldn't consider backmount an alternative. There are also sidemount beginners who spend every minute fine tuning their setup by the millimeter for perfect trim and streamlining and gain aesthetic pleasure from that. Hogarthian/DIR is just a bulky mess in their view and no alternative at all. Anyway, that's all unnecessary. If you're pragmatic and the main reason for sidemounting is about lower back pain and being more self-reliant, then an open water sidemount instructor worth the money will get you weighted and in trim and that'll do.

 

[WetRocks]

2) Early on in this thread, I was told that, and now understand that. On the first dive, I should come up on half the gas I went down with. With the second dive, do I still use the 1/6 or do I do the 1/3s?

Can you explain what you were taught about gas management? I'm confused about your mention if coming up with "half the gas I went down with"

Your cavern cert, and best practice, limit you to using 1/3 of a single tank volume for penetration, and 1/3 for exit, meaning you should surface with at least 1/3 remaining. With doubles, it is 1/6 in, 1/6 out, leaving 2/3 remaining. It makes no difference whether it is the first or second dive.

 

[tbone1004]

@swimmer_spe what is your objection to GUE? I'm not a GUE diver, but the point of taking fundamentals in your situation is to learn how to move efficiently through the water. Whether or not you choose to subscribe to their methodologies after the fact is up to you, but the point is to go to an instructor who knows how to get you to move efficiently through the water to help you get your sac down to normal.

The point of the cost is a used set of doubles is going to put you back roughly $2k. That's doubles, backplate, wing, set of regulators, and add another roughly $500 for training. What that will not do is give you any sort of increased time in the cavern. The cost of this equipment, plus the cost of the course will not buy you the added time that you are looking for. Something like an Intro to Tech/Fundies course will by teaching you to be more efficient and lowering your sac rate.
Making the assumption of going to doubles, you are adding that cost and still breathing at a 1cfm rate which will double the time you get. Conversely, you can spend something around $500-$700 to take a course like ITT/Fundies and do it in singles where you limit the added skills required to be taught *mainly valve drills*, and you can focus that time with the instructor on moving efficiently in the water. This should be able to get your SAC rate down to around .6cfm which will give you a 60-70% increase in your dive time while not adding the cost/complexity of doubles. When you then are ready to take full cave training, you go to doubles/sidemount and then get the true benefits of doubling your available gas supply.

Unfortunately your assumption about cavern certification meaning you know what you're doing in an overhead environment is incorrect. The cavern cert is a recreational cert meant more for "overhangs" than "overheads" meaning you can still see the surface at any time because the sun is your primary source of light. That is why there is no cavern diving at night or in real low visibility. It does not adequately train you to dive in a true overhead where you have no reference to where the surface is outside of the line. Mexico tends to stretch the definition of cavern quite a bit but it does not change the training.

@Johanan I have had 2 first stage failures, one in a cave, where the gas was not accessible