Recreational Pony Bottles, completely unnecessary? Why or why not?

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A vehicle analogy was made earlier and I would like to add one. When I talk to certain divers who keep pushing their advanced training I frequently ask what advanced driver training they have taken such as skid-pan, crash avoidance etc. Invariably then answer is none but all of them spend more time driving than diving and the death statistics can be scary.
But... There's plenty of specialist driving for which you have to take training. Racetrack driving where you need an Advanced Open Water ticket (OK, racetrack certification).

Then there's offroad driving where you may have attended some course/workshop in how to drive. Sure, just like diving, you could have worked it out for yourself.

Desert driving? How to get yourself out of trouble when you've sunk in a sandpit?

Point is, normal driving's a lot like a cattle boat dive in a resort. Technical diving is a lot of speciality skills, especially to prevent "problems" which often equate to death & injury.
 
But... There's plenty of specialist driving for which you have to take training. Racetrack driving where you need an Advanced Open Water ticket (OK, racetrack certification).

Then there's offroad driving where you may have attended some course/workshop in how to drive. Sure, just like diving, you could have worked it out for yourself.

Desert driving? How to get yourself out of trouble when you've sunk in a sandpit?

Point is, normal driving's a lot like a cattle boat dive in a resort. Technical diving is a lot of speciality skills, especially to prevent "problems" which often equate to death & injury.
I wasn't talking about tech diving I was pointing out what some people push for rec divers. How many accidents do you see on the road, my crash avoidance course saved me several times.
 
Metaphors never stand close scrutiny :)
 
I wasn't talking about tech diving I was pointing out what some people push for rec divers. How many accidents do you see on the road, my crash avoidance course saved me several times.
If GUE were to offer a crash avoidance course, I'd take it. :gas:
 
What comes to mind is the time I showed up at a dive boat for some recreational dives to depths just over 100 ft and noticed all or almost all of the divers had one of three configurations: single tank and pony, double tanks, or rebreather. It was evident that most or all divers believed there would be too much risk without a redundant air source, but it wasn't evident what their collective wisdom believed was the optimal configuration.
Optimized for what? Safety? Efficiency? Bottom time? Cost? Logistics? Each one will rate different in each category. Common local knowledge will you general indication. Same dive environment in a different country will yield different demographics on the dive boat; in a poor country, you will probably see everyone on singles diving with air. But they will probably adjust also their dive styles accordingly so that there is no carnage among divers.
 
For sidemount it's sort of 1/3ds. This should leave you with 2/3ds spread across the cylinders, i.e. 1/3 each side left at the turn point.
Typo? 2/3ds remaining of the total original volume is 2/3 each side at the turn. (One-third used from each on the way in, another third from each used on the way out.)

@Gareth J - I think your example is great at highlighting the shortcomings of penetrating to thirds on SM (or ID). There's just not much gas left for secondary issues without resorting to buddy's reserve. No argument that manifolded doubles typically leave you with more gas for the secondary issues than does SM.

I would expect, though, the SM diver considers that increased risk and plans accordingly to reduce it to acceptable levels. E.g., penetrate less than 3rds, take a buddy (or two!), exit with the current, etc. In other words, they arrange for "enough" reserve.

I think this is also why independent doubles is commonly regarded as the worst of both worlds -- they take the hit on reserve but gain none of the SM benefits in return.
 
Now you find you have a problem with cylinder B. You only have cylinder A (with 100 bar)
Would you elaborate on this problem? What kind of problem is it?
 
Optimized for what? Safety? Efficiency? Bottom time? Cost? Logistics? Each one will rate different in each category. Common local knowledge will you general indication. Same dive environment in a different country will yield different demographics on the dive boat; in a poor country, you will probably see everyone on singles diving with air. But they will probably adjust also their dive styles accordingly so that there is no carnage among divers.
I would think that in a given locality, such as the one of the dive boat in my anecdote, with divers of a similar demographic, they would seek to optimize for as many of those goals as possible. I would think the average rec/sport diver would ideally like the safest, most efficient, least expensive, logistically easiest system that will give adequate bottom time. Nevertheless, I believe some of the variation I witnessed stemmed not so much from divers' different ideas about optimization as from different goals for the dive. For example, I suspect the rebreather divers weren't using rebreathers for safety or to extend bottom time; rather, they were more likely getting in some practice/training hours in preparation for more challenging diving. Maybe some of the doubles divers, too. The next time I returned to dive there, I took my doubles, mainly for the goal of getting some experience with them. The point of my story was that it wasn't possible to determine the reason so many divers had different configurations simply by the fact they were diving different configurations.
 
Typo? 2/3ds remaining of the total original volume is 2/3 each side at the turn. (One-third used from each on the way in, another third from each used on the way out.)
No typo.

Rule of 1/3rds. Two sidemount cylinders contain half of the gas each side. Assume 210 bar each side (3 x 70 = 210) (also doing absolute thirds!)

Breathe down by 70 bar on both sides leaving 140 bar. This is 1/3 consumed and 2/3 remaining.

Boom, lost all gas on one cylinder.

Have half of 2/3 left = 1/3 remaining to get out of Dodge.
 
AIUI, the Shearwater / Suunto planners only give you the dive profile, they don't calculate your gas requirements.
I only know the Shearwater planning in tech mode, but in tech mode the planner does calculate gas requirements based on your inputted SAC/RMV.
 
https://www.shearwater.com/products/teric/

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