Stage Bottle Question

[Cheekymonkey]

I am taking a tech course this coming March, in the mean time everything is just filled with O2 service air. But during the wait until then I am beginning diving with my doubles as well as a stage bottle slung to familiarize myself with the gear fully before it is time for the class. The class itself will be enough for me to worry about, without task loading from unfamiliar gear. But I certainly apprecaite your concern.

The nitrox fill the other day just got me thinking about that though, so when you say "The variance is still there in tech except also with helium as well as O2." you meant that the allowed variance remains + or - 1%?

 

[cerich]

1% never bugs me with O2 and 2% doesn't bug me with Helium.

 

[Cheekymonkey]

Ah another Hijack by me then, this is one successful thread for getting questions answered by the way Thanks everyone for that. Doc you brought up V-planner, for all the homework for the course, I have completed it using formulas and tables as requested by my instructor. When I asked about Deco software though he pointed me towards V-planner as well and I now have it. Regarding V-planner, I am absolutely lost, I have tried reworking some of my homework problems in V-planner and I wasnt able to get very far beyond setting up my profile with my name. Do you know of any very good tutorials on learning V-planner that include example dives or something (like most other computer software tutorials do) or someone I can contact for a quick lesson in using it, I can be a little bit computer slow.

 

[Cheekymonkey]

Thanks man, just had a hard time with the wording and wanted to clear that up to make sure.

In the 90's when tech diving became more mainstream there was an absolute rash of wrong gas switch diver deaths.

The method we both typed is IMHO the best one I have found and I've tried a few...

One thing that does creep up withtech divers using standard gases is the assumption that the tank actually has the standard gas for the MOD in it. I've known of a couple folks who got lax in checking every bottle before every dive and worked on assumption or trust in the content duct tape that another filled out. A bad and stupid practice.

 

[Doc Intrepid]

Do you know of any very good tutorials on learning V-planner that include example dives or something (like most other computer software tutorials do) or someone I can contact for a quick lesson in using it, I can be a little bit computer slow.

Dude, not to put too fine a point on it, but this is why you pay money to your instructor! There are a number of variables you must set, which MAY take into consideration factors such as your age, weight, physical condition, surgery you may have had, bad knee joint you may have, diabetes, other medical conditions, SAC/RMV - in other words you set the 'conservativism' factor you wish the software to use in the algorithm. There are also other issues you must consider; gases, ascent rates, descent rates - and all of these things are - especially for a beginning technical student - items that you want to discuss with your instructor.

So don't be shy. Ask your instructor to sit down with you and go over every parameter in the software, and explain the liabilities and benefits (and ancillary drawbacks) of selecting this gas, or that ascent rate, or a conservativism value, etc.

These are things that its important you go into in depth (no pun intended) with your instructor.

YMMV...

 

[Meng_Tze]

Thank you so much for the wonderful answers cerich and doc. The above checklist for switching to a stage bottle cerich was wonderful and as I begin the diving with oppotunities to practice this, I certainly will until it becomes habit as that does make perfect sense and seems to eliminate most problems right there.

Since I made the OP though, I guess i'll hijack it myself and move on towards your last post cerich about checkign the mix myself. I do habitually self check the mix since I have become a nitrox diver. But it made me wonder, my normal Open Water certification is PADI, and when we teach nitrox we teach to use the tables if the gas is within +1 or -1 percent of the gas the table was intended for. For instance the 32% mix I intended to get yesterday was actually about 31.1%, while this was exceptable for using 32% calculations through PADI, what are the feelings on this regarding beginning tech diving, is it still safe to plan with 32%. Obviously having 0.9 less O2 leaves you with a slightly deeper MOD, but will the minor loss of N2 offgassed between 31.1% and 32% cause problems in deco plans?

Deco is more of an applied art rather than an exact science.. you will hardly ever get the exact mix you want, you adapt the dive plan accordingly. When I dive trimix and do top off's to maximize my He, I always end up changing actual plans.... fact of life when diving mixed gasses. Don't get me wrong, I never jump in the water without knowing what the plan is, it is just that sometimes when sitting at home planning a dive, the actual gas changes things on site.

It is good to practice swimming doubles yes, clip on a stage (don't breathe from it yet), just carry it and practice clipping on and off. Then use stage for part of the dive (same gas as backgas), with someone who has done it too, just in case.

slow progression is the key

 

[rjack321]

Once you get vplanner up and running...

You will be able to experiment with mixes that are slightly "off" and start to understand how much they influence total deco time (not much IMO). Try going plus 5% or even 10% on He and see how its changing things and minus 2% on O2, etc etc. You'll start to see the general relationships for yourself.

Be sure to discuss how these things may or may not be important in your planning with your instructor. Ditto for plus-minus 10ft on your actual depth and plus-minus 5 mins on actual time.

There are "allowable" variances and shifts in the depth-time-mix universe. But they aren't as cut and dried as 1% good, 2% baaad.

 

[Michael Schlink]

Run the dive on a few different programs, Vplanner, Deco, Voyager, then throw in conservatism factors and then you'll really see how much it's not an exact science.
Breathing rate, temperature, physical conditon, etc. etc. etc. Pulling yourself up the ladder, hot shower, there are just too many variables to get too anal about it.

 

[matt_unique]

I read everywhere that stage bottles should be worn in an off position so that they do not freeflow, and as one extra precaution to prevent you from inadvertantly breathing from the wrong bottle. My question then is what stops the water from invading the reg, do you pressurize the hoses prior to the dive and then turn off the bottle to just prevent this issue?

If you are using Sherwood regulators they need to be on before you get wet. I personally keep my deco bottles on. Some will say the Sherwood 1st stages have a one way valve, but I don't trust that valve to work at depth under silly pressure. I also had a Sherwood tech tell me the valve is good for about 20' before it would leak.

They are slung right in front of me, I will see the bubbles if they are leaking.

--Matt