Tank sizes when diving

[FinnMom]

IMHO there are very few good reasons why not to use a bigger tank.

With 12L being the standard I own one 15L tank and I'll always put it on a single-tank diver if they want to use it. In our cold water we have to use drysuits or thick wetsuits, so there is no chance of them not needing a weightbelt. My heavier tank means a little weight off their waist & that's always a nice thing. A bigger tank also provides a little extra reserve and/or a chance for both of us to stay down a little longer if they wish, esp. since most of us buddies have double 10L or double 12L tanks.

I also feel that it's great giving a new diver less to worry about. If they have a larger tank than the old boys, or at least a larger tank than they are likely to need, they don't need to worry about running low on air or cutting their buddy's dive time or being exposed as an "air guzzler". I'm happy with anything that lets a new/otherwise unsure diver to relax and feel less task loaded.

 

[Colliam7]

IMHO there are very few good reasons why not to use a bigger tank.

Good point, especially when weight is an issue, with colder water.

 

[o2dependant]

I think anyone who decides on a bigger tank is just considerate and wanting the most out of their dive. Thanks if your part of my group. I see it as a more economical way to dive too. You get more time for your $$ to enjoy.

 

[GrimSleeper]

Theoretically, the nitrogen loading for a diver consuming 120 cf of air, at a given depth over a given bottom time, should be greater than that of a diver consuming only 80 cf of air under the same conditions. Given that a) most recreational dive tables and computer algorithms are rather conservative to begin with, and b) the incidence of DCS among recreational divers is rather low to begin with, I would not personally be concerned about a likelihood of harm. But, maybe I am just oblivious.

Not really the way it works. The diffusion of inert gas from the lungs into the blood and thence into tissues is driven by the gradient between ambient pressure and gas tension in the tissues. The actual volume of gas passing through the lungs is irrelevant, for a given depth/time profile, and the volume of gas dissolved into body tissues during a dive - even at saturation - is small. Just feels big if it all comes out of solution at once...

Bear in mind that the fast-breathing, inexperienced diver we're picturing here isn't really 'consuming' the extra gas, just moving it in and out of his/her lungs very quickly!

As for the better breathing versus more gas question, I used to fret terribly about my SAC rate. I got it down to something really quite respectable just in time to start technical diving and realise that the answer to most problems is simply to carry more gas. I don't see an issue with people using higher-volume tanks - or doubles, for that matter - if it enables them to comfortably and safely carry out the dives they want to do.

 

[MSDT476614]

Thanks all for sharing your views. Perhaps a little background helps clarify some issues.

- I'm operating in the equatorial region. Water temps @ surface hover around 85F. Thermoclines are an infrequent occurrence unless one goes to depth or dives in 'winter' in some destinations.
- Providing larger tanks costs more, more to buy, more to fill - hence the queries to solicit a response
- People here tend to be not so well built and some DMs struggle with the 100s/15Ls physically
- Maybe 0.005% of divers in this part of the world own tanks, we use tanks provided by operators at the destination mainly
- 'Naked' diving is encouraged - meaning board shorts and a rashguard mostly, in some cases a mankini ;D

Points noted about:
- more air being more comfortable for the newer divers (risk reduction)
- about more air allowing newer divers to reach NDLs (risk increase)
- about 'penalizing' divers who use less air (smaller built or less task loaded)

To be fair on the other hand we do also have requests from petite divers (usually ladies at about 5' tall and 100 lbs or less) asking for 8L/60s as well so they can handle the gear better above and under water.

Some dive profiles and consumption rates where shared, much thanks! I've constantly noted SACs, just seems these days more and more average sized folks are asking for larger tanks.

Average lead weights a diver puts on here in this part of the world is 6 to 10 lbs (in 2lb blocks) with full 3mm to 5mm wets.

 

[Tigerman]

If the staff is not so well built, 15l steel tanks is brilliant - they need to bulk up anyways

 

[MSDT476614]

Not really the way it works. The diffusion of inert gas from the lungs into the blood and thence into tissues is driven by the gradient between ambient pressure and gas tension in the tissues. The actual volume of gas passing through the lungs is irrelevant, for a given depth/time profile, and the volume of gas dissolved into body tissues during a dive - even at saturation - is small. Just feels big if it all comes out of solution at once...

Bear in mind that the fast-breathing, inexperienced diver we're picturing here isn't really 'consuming' the extra gas, just moving it in and out of his/her lungs very quickly!

Thanks Grim!

As for the better breathing versus more gas question, I used to fret terribly about my SAC rate. I got it down to something really quite respectable just in time to start technical diving and realise that the answer to most problems is simply to carry more gas. I don't see an issue with people using higher-volume tanks - or doubles, for that matter - if it enables them to comfortably and safely carry out the dives they want to do.

Issue arises when newer divers (think 25 dives) with not so excellent SACs want to do tec courses thinking that doubles will help them through their air consumption rates (more gas no problem) but still hit the tec depths and times. Issue also arises where the diver feels pressured into taking a course using doubles just to seek reprieve on air consumption. I've got no problems teaching divers how to carry up to 6 x 80s in non-overhead settings. It just costs a lot to learn to that stage?

---------- Post added December 15th, 2012 at 09:01 AM ----------

If the staff is not so well built, 15l steel tanks is brilliant - they need to bulk up anyways

yes sir! I'll inform my female DMs who average 5' tall and 100lbs to bulk up right now.

 

[Tigerman]

at 5' and 100lb they should carry ATLEAST 150lb each

 

[GrimSleeper]

Issue arises when newer divers (think 25 dives) with not so excellent SACs want to do tec courses thinking that doubles will help them through their air consumption rates (more gas no problem) but still hit the tec depths and times. Issue also arises where the diver feels pressured into taking a course using doubles just to seek reprieve on air consumption. I've got no problems teaching divers how to carry up to 6 x 80s in non-overhead settings. It just costs a lot to learn to that stage?

I'd definitely be steering divers with 25 dives away from doing anything beyond Intro to Tec courses, regardless of why they want to do them. Which brings you back to either providing higher-volume tanks, or mentoring people in ways to improve their consumption. FWIW, we do a bit of both here. We've got some C95s that we'll fill to their rated 241 bar if people really want them, but we charge extra because it's extra stress on the final stage safety on the compressor and we get through the filter quicker. If people don't want to pay more for more gas, we're happy to offer tips on ways to use less. Either works for me.

 

[NAM001]

The more expensive the boat trips become the more prevelant larger tanks wil be. $200+ for 2 20 min dives is pretty costly. 400 if you are paying for your buddy. so why not make it 2 40 min dives. As long as you can buddy up with someone with like volumn and watch your ndl, there is no problem. WE all know that does not describe all divers. I have had boats tell me i can not take a lp120 on thier boat. My lp95's have always been accepted. I also see boats calling for back on board with 1000 psi and starting accent at 1500 for a 90 ft dive and actually checking psi when getting back.