Is a 40cuft indefinitely useful?

[211ratsbud]

Hey guys, I'm accumulating at a reasonable, and intelligible rate some gear as I make my way into tdi adv nitrox and deco procedures. I would like to know if within the certification of that course, if the 40 would be sufficient for all dives planned under that level? That's pretty much it.. thx guys

 

[RainPilot]

Most early tec courses are going to limit the amount of deco you can do. AFAIK that is around 30 min for the early courses so a 40 should be fine for that. Every tech diver I know has at least one 40 in the mix on their dives, even if it's just a spare O2 hanging on the line.

 

[tbone1004]

Hey guys, I'm accumulating at a reasonable, and intelligible rate some gear as I make my way into tdi adv nitrox and deco procedures. I would like to know if within the certification of that course, if the 40 would be sufficient for all dives planned under that level? That's pretty much it.. thx guys

yes and no for it being sufficient for all dives. It won't cover all dives, but it should cover all OW dives that you'll be doing. In cave diving we can get to bottom times where an AL40 doesn't have sufficient capacity, but in the OW it's the tank you want. I inherited an AL30 that I use in OW and am just too lazy to sell it and get a 40 because it's fine in the OW and I use an AL80 in the caves because of our typical deco length, but if I could easily find someone to trade it for a 40 I would in a heartbeat. They are indefinitely useful. When a 40 becomes not enough for O2, it will be good for 50/50, or spare O2, etc etc. you will always have a use for it

 

[KenGordon]

I suggest you take the course, learn from that how to plan the dives, plan some typical dives and see what gas you need. Then buy the kit to match.

 

[nadwidny]

You will always find a use for a 40.

 

[Patoux01]

Here around, O2 seems to be carried in 7l tanks more often than S40s (5.7l or something).

 

[211ratsbud]

Thx guys, I have a ton of 80's I could use, and not owning a single 40, makes me wonder how useful.. Apparently it will always have a use .

I am instructed to show up to the course with a cylinder for use in that class. Easy enough.

 

[RainPilot]

Here around, O2 seems to be carried in 7l tanks more often than S40s (5.7l or something).

I think thats more to do with the metric system than anything else. A 7 liter is around 50 cf so pretty compatible, dimensionally they are quite similar to the US AL40 and you get a bit more gas. When I learned to dive you got 15L, 12L, 10L, 7L and 3L. Of those a 7 would be the closest in function to a S40. I have a 6L steel tank but its a repurposed SCBA tank from a fire department.

A lot of guys were diving 7L rec doubles or even 7L 300 bar single BM configs, made life a lot easier climbing down cliffs to get to the entries and stuff. They would have a couple of 7's lying around for deco tanks easily.

 

[Patoux01]

It's not to do with the metrics, we have both available.

I hardly know anyone using a 7l aluminium for back gas, I'd probably be the only one around that would do that because I only have aluminium tanks.

It really has to do with a choice, most explain it by doing 2 dives on the same deco tank.

 

[Jim Lapenta]

A 40 will work fine for the training dives up through Adv Nitrox and Deco Procedures. At least with the TDI courses due to the limits on deco for training. That said if you have a super high SAC rate it could be cutting it close. I own a 40 and a 30 that I use interchangeably. Depends on the dive.
What I would advise you to do now, whether you own or get a 30, 40, or even 80 is to get it rigged correctly, and start carrying it on easy, shallow dives.
Practice putting the bottle on and taking it off in the water. You don't necessarily have to deploy it the first few times but just get used to having it.
See how it affects your ability to access other items and if it has any effect on your trim, and make any adjustments before you show up for class. The instructor is likely going to make some recommendations to your set up anyway but you'll get a head start.
Once you've carried it on a few dives get with a trusted buddy and have them stay within arms reach, ready to donate a reg if necessary, and practice deploying it and getting on the stage/deco reg. Until you get your advanced training the gas in the bottle should be the same as your back gas. You still need to go through the gas verification procedure.
This helped me out a great deal before venturing into tech training.
I dived with guys who gave me tips on setting the bottle up and practiced using it. When it came time to take my NAUI Intro to Tech and Helitrox class I had close to 50 dives in doubles carrying a 40 stage bottle.
It's also why I have students carry a slung bottle in the Advanced Open Water class. Along with it being a redundant air supply, it's good practice to get divers who at some point may decide to go the tech route used to slinging a bottle.
For Advance Nitrox and Deco Procedures I want to see students show up for class with a minimum of 25 dives in the configuration they are going to use, including stage/deco bottle, dry suit, doubles or sidemount, etc.
It makes the training go a lot easier if I don't have to show one student how to mount their deco bottle.