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

[tursiops]

That's partly true, and after this conversation, I think you are right, and my apologies for making this thread ridiculous. The best way to state my position is with the dive plan, which I will list below. Of course, ascent rates can be changed and recalculated. But, the thought process is there. Why use a pony bottle, when the reserve gas is already there in the first place? If you cannot find your buddy during an OOG emergency, revert back to your open water training and head for the surface.

Dive Plan:

A critical goal in planning a dive in open water is determining how much gas is necessary for an emergency scenario; With that in mind, we want to plan for one diver to suffer an out-of-gas emergency during the deepest part of the dive, which provides sufficient reserves for any range of potential problems within the buddy group.


Let's make a few educated assumptions that leave us all with a bit of room for conservatism.

1. Let's assume that our average surface consumption rate is ~ 20 L/ 0.75 cuft per minute.

2. The assumed ascent speed will be on average 3m/10 ft per minute.

3. The average depth of the ascent is used for all calculations. Divers should attempt to maintain a controlled ascent of between 20 to 30 feet per minute and follow minimum deco (MDL/NDL) profiles. This is based on a slow but foreseeable ascent rate that provides some wiggle room for safety. Also, the 20 L/ 0.75 cuft per minute SCR is approximate based on the outcome of an average diver in most situations.

• MG should never be less than 40 bar/600psi to account for inaccuracy and/or readability in SPG's.

Let's determine our minimum gas for the dive.


Minimum Gas:

Consumption= 0.75 SCR x 2 divers= 1.5 cuft /min

ATA: (80ft / 2 = 40ft); (40 ft / 33 +1 = 2.2 ATA

Time: 9 minutes (10ft/min ascent rate plus one minute at depth to resolve the problem and initiate an ascent (8 + 1= 9).

1.5 x 2.2 x 9 = 29.7 cuft of gas or (29.7 / Tank Factor 2.5 ) x 100 = 1,188PSI or to make it easier on the SPG 1200 Psi Minimum Gas to be conservitive.


To keep this dive easy and fun, this will be an all-gas usable dive in the Caribbean of the Midwest, Haigh Quarry. Our plan states that if we share gas from the deepest point of the dive, we require at least 1200 psi in our AL80 to reach the surface while safely transferring from one cylinder. As soon as we get 1200 psi, we would have to call the dive and begin our ascent. With that said, let's determine our usable gas with our MG and SCR examples.


Usable Gas:

1200 MG subtracted from the fill pressure of an AL 80 3000 psi

1200 psi – 3000 psi = 1800 psi usable gas


Now, with that information, let's determine our bottom time:


Bottom Time:

80 cuft tank with 1800 psi = 45 cuft usable (1800 psi / 100) x 2.5 TF = 45 cuft

0.75 cuft/ min SCR x 2.2 ATA = 1.65 cuft / min @ 80ft

45 cuft / 1.65 cuft/ min = ~ 27-minute bottom time.


Now, we are ready to dive and have fun on a single tank without a need for a pony bottle.


However, this does give us some wiggle room if we want to go for a more extended dive, right? According to the MDL for Standard Gas 32% (My agency), we have up to 50 minutes at 80ft. So let's do this dive in the AL 80s.


Minimum Gas:

Consumption= 0.75 SCR x 2 divers= 1.5 cuft /min


ATA: (80ft / 2 = 40ft); (40 ft / 33 +1 = 2.2 ATA


Time: 9 minutes (10ft/min ascent rate plus one minute at depth to resolve the problem and initiate an ascent. 8 + 1= 9)


1.5 x 2.2 x 9 = 29.7 cuft of gas or (29.7 / Tank Factor 5 ) x 100 = 594 PSI or make it easier on the SPG 600 PSI Minimum Gas to be conservative.


Usable Gas:

600 MG subtracted from the fill pressure of an AL 80 3000 psi

600 psi – 3000 psi = 2400 psi usable gas


Bottom Time:

Double 80 cuft tank with 2400 psi = 120 cuft usable (2400 psi / 100) x 5 TF = 120 cuft


0.75 cuft/ min SCR x 2.2 ATA = 1.65 cuft / min @ 80ft


120 cuft / 1.65 cuft/ min = ~ 72-minute bottom time which goes over our 50 minute MDL time. So, as a buddy team, you would have to be watching your depth and time throughout the dive if you decided to use doubles.


let's go over our pre-dive check:


Goal: Have fun at Haigh Quarry and see some catfish.


Unified Team: Diver 1, Diver 2, etc.


Equipment Check: Does all of our equipment work properly, valves, regs, inflators, valve dumps, primary light, backup light, what's in our pockets? Computers on and working? Do we have a cutting device?

Modified S-drill to make sure the primary hose is free from obstructions.

Exposure: (depth and time) 80 ft for 27 minutes (Single Tank) 50 (Doubles)

Deco: Minimum Deco or MDL procedures. 50 Minutes on 32% EANX @ 80 ft.

Gas strategies:

AL 80: 3000 psi, MG 1200, 1800 UG.

AL 80 x 2 3000 PSI, 600 MG, 2400 UG.

Environment: Haigh Quarry, viz is about 30 ft, water temp 55 at depth.


So, before we "ok" each other as a buddy team to descend, after planning the dive and checking all of our gear, what do you think the likelihood of a catastrophic failure or the need for a pony bottle would be?

Sticking with the single tank example -- which is appropriate for this forum (you really ought to say the second example is for doubles) -- and using a more likely and sensible ascent rate, i.e. 30 ft/min as the OW agencies train and the computers provide -- you only need 400 psi, not 1200. Given that most recreational dives at most resorts and most dive boats say to leave the bottom at 700 psi, and be back on the boat with 500 psi, I see no conflicts with current practice. Now let's consider the lost buddy, and the failed regulator. It is an OOA emergency, and the basic training says CESA. I submit a pony is safer (and easier to learn) than a CESA.

 

[KenGordon]

The assumed ascent speed will be on average 3m/10 ft per minute.

I was on a course once and when asked to plan a dive the other student struggled. He was extremely rusty. After some polite cross examination (and a lot of lip biting on my part) it turned out he just dived the plan developed on his previous course over and over.

BTW I checked my copy of the Fundamentals book and it doesn’t mention ascent rates as far as I can tell. More modern books warn about people on the internet though.

 

[Lorenzoid]

They are. What's the "must surface with 50 bar / 750 psi" rule all about?

That's not "gas planning"; that's winging it and hoping, by making adjustments on the fly, to hit the target.

There was a thread here that discussed various ideas in gas planning: Rock bottom, 500 PSI, or something else?

If I'm not mistaken, simple gas planning is getting more attention in basic OW courses than it used to. "Rock bottom" (also known as "Minimum Gas") need not be intimidating to a new diver. A simple way to think about it is that each buddy reserves enough gas to get both of them to the surface in the event one is out of gas. It need not involve any calculations at all if one is math-phobic or just lazy (and there's nothing wrong with some degree of laziness; diving is supposed to be enjoyable). There are cheat sheets that show you the minimum your gauge should read for any depth. Bring the cheat sheet on a wrist slate, or better yet, memorize a few depth and pressure combinations, and you're all set.

To address some other things mentioned in recent comments, I believe proper buddy procedures need not be burdensome. I believe most OW divers are taught that if they lose their buddy, standard procedure is to look around for one minute and then surface if you haven't found your buddy. That should work fine for the average diver, especially if they adhere to the recommended depth limits for their experience level. If you are paired with an insta-buddy who wanders off and you can't or don't wish to follow, then request a different buddy. If you are the one who wants the freedom to wander off and do your own thing, then by all means learn to solo dive, use a pony bottle, and treat your dive as the solo dive that it is.

I haven't been reading this thread since Thursday, but it looks like the same points raised 100+ posts ago are being re-hashed. I'll try to limit my re-hashing of my own points.

I'm a believer in the value of keeping one's gear set consistent, so one develops familiarity and muscle memory with it. If one chooses to make a pony a part of their normal gear, then make it a practice to bring it on every dive. Keep it in proper condition, keep it full, and keep your muscle memory in deploying the pony fresh through regular practice. To me, all that seems like more effort than justifies the return on effort; the probability of a catastrophic regulator failure is very low, and the buddy system is intended as a way for the average diver to deal with that. In their daily lives most people don't carry around safety equipment to protect themselves from low probability events. Rhetorical side query: Is there is psychological component that makes us more fearful of drowning than other modes of death and therefore more accepting of extra safety gear? I suspect it has been mentioned upthread, but if you make it a practice to carry a pony yet don't make a practice to, for example, test tanks for carbon monoxide contamination, are you behaving logically? (I don't know if the risks of catastrophic regulator failure and carbon monoxide poisoning have been quantified--just an example off the top of my head.) Maybe others are more disciplined than I am, but I could see myself getting complacent: "This will be an easy dive; I don't need the pony on this one."

With normal buddy procedures and some simple pre-dive gas planning, I would say the average diver can dive as safely without a pony as with a pony.

Divers doing advanced or more complex diving might use a pony for various reasons, but I suspect there are divers who buy a pony for the wrong reasons--maybe a safety blanket, or to look "tech" (none of us here, of course), or to do a dive that they may not realize is as advanced as it really is and for which the better choice would be the true redundancy provided by doubles or sidemount and the training that generally goes along with those configurations. As for the last point, I'm sure people have long since brought up in this thread the possibility that carrying a pony might make some people feel more confident or brave than they otherwise would and perhaps push their envelope when they otherwise wouldn't have.

 

[Hartattack]

Delete

 

[KenGordon]

I think the disconnect here is the assumption that the "back gas" will always be available

It feels like he is deliberately ignoring being unable to access it.

We should probably stop feeding him now.

 

[elan]

BTW I checked my copy of the Fundamentals book and it doesn’t mention ascent rates as far as I can tell. More modern books warn about people on the internet though.

They are specified in SOP Part 1 Accent Rates.

 

[Hartattack]

Delete

 

[Lorenzoid]

How many dive accidents have been posted here this year with the same scenario where a group of folks go diving and they only notice when one of the group is missing when it's time to return to the boat or they don't see them on the surface after a dive. While we would all like to say that they stay within a few feet of their buddy at all times, this is not the reality of what is actually going on.

I would ask why we as divers are simply accepting this as "the reality of what is actually going on" rather than reminding ourselves to fall back on our training and also doing our best to remind others. Diving in a group where individuals don't have a particular buddy to keep track of (or feel they can slack off their duty as a buddy because there is a divemaster in front) is not wise, and I don't think any training agency teaches OW divers it is acceptable. Outside of low-vis diving, which I would say is an advanced kind of diving, how hard is it to keep track of one other person? Even before I had a regular buddy, and I often found myself paired with an insta-buddy, I would stay within a few feet of my buddy.

 

[Hartattack]

delete

 

[Hartattack]

Last post for me on this topic:

I let the internet and my ego get the best of me the past few days on here. I dive a certain way that I love, and I would be happy to show anyone how to dive that way if they are interested. The ideas and procedures in this sport can be very passionate, and sometimes one can get carried away, and with that said, I apologize. I do not mean to offend anyone on here.

Nevertheless, I would love a chance to dive with any of you, even if we disagree on how to do that because no matter how we do it—we all enjoy it, and that's what it is all about. Thanks again for reading my ramblings and the spirited debate.