Recreational Pony Bottles, completely unnecessary? Why or why not?
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On @boulderjohn's point about standardization and "diving on the edge of technical diving," I try to keep a reasonably bright line between technical and recreational. In the interest of standardization of equipment and procedures, a decision is made in advance whether to plan the dive as a technical dive or a recreational dive. Sometimes, the doubles and the extra gas will be overkill, but the idea is to err on the side of caution. Sometimes, gas calculations will reveal that diving a single tank with enough reserved gas for both divers to surface calmly in the event of a catastrophic failure does not give enough bottom time for the dive to be worth it, and the question becomes whether doubles are worth the hassle. In this school of thought, where standardization in gear and procedures is paramount, there's really no middle ground for a pony. I may be sitting out some dives that others do routinely with their pony bottles for backup.
Also, I am prepared for one major failure on a dive, not two, as the probability of two concurrent major failures is too low to be worth being ready with the gear and procedures to handle on every dive. If there is buddy separation on a recreational dive, the procedure is to look around for no more than one minute, then surface if the buddies don't find each other. If a diver is out of gas on a rec dive due to a catastrophic reg failure, the buddy is presumed to be there to donate, and we have reserved enough gas to surface calmly. If I were to find myself regularly diving where vis is poor and buddy separation more likely, I would consider planning all those dives as tech dives, where the gear and procedures are different.
Also, I am prepared for one major failure on a dive, not two, as the probability of two concurrent major failures is too low to be worth being ready with the gear and procedures to handle on every dive. If there is buddy separation on a recreational dive, the procedure is to look around for no more than one minute, then surface if the buddies don't find each other. If a diver is out of gas on a rec dive due to a catastrophic reg failure, the buddy is presumed to be there to donate, and we have reserved enough gas to surface calmly. If I were to find myself regularly diving where vis is poor and buddy separation more likely, I would consider planning all those dives as tech dives, where the gear and procedures are different.
I do, too. If I am planning to go into deco on a dive, I treat it as a technical dive from the start. If I am thinking I might be close to deco on the dive, depending upon the situation, I may bring along redundant gas just in case something unexpected happens.
jadairiii
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If I'm in that range were an "unexpected event" may require more gas, then I am in doubles to begin and it also is a good bet I'm in 90' of water or deeper. IMHO, doubles are simpler, more streamlined and balanced and gives me way more gas than even a 40 bottle.
There are deeper reefs in our area that are great for lobstering, but on the edge of "recreational", we dive doubles, often one dive on scooters, start deep and end up a mile from our drop point, on the first reef, with no deco. But lots of places for the "unexpected event" to occur, better to have more gas than less, and a "pony" would not cut it.
OP
I'm going to come back to this one last time. If you look back at the thread, I never once said redundancy was not necessary. I showed that if the diver would like more bottom time within MDL and a redundant gas source—manifolded doubles would be the best option. This example is stated in the lower portion of my dive plan here:
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 and see what happens. (Doubles)
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.
Clarification: My argument is NOT about ascent profiles, catastrophic failures, buddy separation, or any other hypothetical problem someone on this thread comes up with to somehow detract from my original recommendation/point. However, please debate those all if you choose to; I, on the other hand, will stay out of those conversations. I am giving my example of why I do not use a pony bottle, nor do I recommend them.
My argument, in my opinion: Pony bottles for recreational divers are not needed if instructors are teaching their divers how to calculate and monitor their gas effectively, and in that calculation, you add an equation for something called minimum gas or AKA rock bottom, etc. (shown above). The thought process for this type of instruction is to lead your divers by beginning with the end goal in mind. In my agency, most come to achieve their dreams of becoming cave and technical divers. Starting them out on the right dive planning foot (Fin) is crucial. Moreover, learning how to calculate reserve gases is a building block method that allows them to calculate further their Surface Consumption Rate, Rule of Halves, Thirds, and All-Gas Available Dive scenarios. In addition, one can now have the ability to calculate gas consumption in the team with different size tanks. With that said, this starts in what we call fundamentals and is a recreational skill. One could choose to never go into technical diving, and they would still learn how to do this in the Recreational 1/2 and, level 3 courses in my agency. Adding a pony bottle, as some others have said, can be a crutch, and in my humble opinion, are not needed if you:
- Know how to calculate a reserve on back gas to safely get you and your buddy to the surface or nearest available gas source in an emergency. (Minimum Gas)
- Dive as a team.
Sidebar: I have added pictures from the book Fundamentals of Better Diving as a citation for Min Gas Calculations and also finding "T" for the ascent profile.
Maybe someone could suggest a well accepted sarcasm emoji as I am sure it would be quite useful.
I think you and I may have missed something like "subtle irony" again.
This thread begain in the Basic Forum and was moved to the Advanced Forum but was started in reference to "recreational" divers. I do not understand why it is drifting off into the world of tech and planned deco and twinsets. Many recreational divers ride their computers, right or wrong, another discussion, drifting into deco perhaps momentarily while still early in the dive and with still plenty of air on hand via themselves or their buddy. I have rarely seen manifolded twinsets or independent twinsets used for recreational, sport SCUBA diving and that is the intent of the OP to discuss.
In a recent misadventure, from approximately 100 feet, with a small deco obligation that cleared during ascent, I used 1,000 psi from an aluminum 80 to make my ascent to the surface including a five minute (?) safety stop and retained my reg (mostly) while waiting for pick up. The 1,000 psi of an aluminum 80 is 27 cf so had I had a total back gas failure, not just a primary failure at the second stage equivalent (I switched to my octo to complete the dive) my missing buddy(ies) would have needed 2,000 psi onboard or I would have needed a 30 cf pony. In normal circumstances it is not unusual for me or my usual dive mates to complete one hour dives as deep as 100 feet plus (and then much more shallow) and be back on deck with nearly 1,000 psi on the spg. Are auxillary bottles wise for some recreational profiles, I guess my thoguht is a qualified yes and a qualified no, I am going to split the fence. It depends upon the dive. I dive basically Hogarthian single tank rigs for recreational level dives as defined by most abc agencies, no deco, less than 130 feet (for me and wife 100 feet) and a buddy (usually my wife unless solo). I would not typically use a pony for such a dive, especially with max depth above 80 feet and benign conditions. I am not discussing solo diving, which borders IMO upon technical diving and at the minimum very advanced level diving beyond the scope of the OP's intent of discussion.
James
In a recent misadventure, from approximately 100 feet, with a small deco obligation that cleared during ascent, I used 1,000 psi from an aluminum 80 to make my ascent to the surface including a five minute (?) safety stop and retained my reg (mostly) while waiting for pick up. The 1,000 psi of an aluminum 80 is 27 cf so had I had a total back gas failure, not just a primary failure at the second stage equivalent (I switched to my octo to complete the dive) my missing buddy(ies) would have needed 2,000 psi onboard or I would have needed a 30 cf pony. In normal circumstances it is not unusual for me or my usual dive mates to complete one hour dives as deep as 100 feet plus (and then much more shallow) and be back on deck with nearly 1,000 psi on the spg. Are auxillary bottles wise for some recreational profiles, I guess my thoguht is a qualified yes and a qualified no, I am going to split the fence. It depends upon the dive. I dive basically Hogarthian single tank rigs for recreational level dives as defined by most abc agencies, no deco, less than 130 feet (for me and wife 100 feet) and a buddy (usually my wife unless solo). I would not typically use a pony for such a dive, especially with max depth above 80 feet and benign conditions. I am not discussing solo diving, which borders IMO upon technical diving and at the minimum very advanced level diving beyond the scope of the OP's intent of discussion.
James
Increasing bottom time is not why divers use pony bottles. They are not used for dive planning. There are scenarios where having redundancy with a pony bottle is superior to manifolded doubles, such as 3-tank boat trips. Swapping out the primary cylinder in between dives is more practical that having two sets of doubles.
Let's not pound a square peg into a round hole.
You have to look at the forest, not just the trees of your choice if you are going to have a meaningful conversation.
While I teach min gas in open water courses and detailed dive planning, given the poor viz, sometimes currents, and realities of not having a dive buddy in view at all times, redundant air sources have their place.
I don't think the data supports this. Bret Gilliam presented at DEMA a long time ago that the number of recreational divers far eclipse the number of technical divers, and they also keep diving for a lot longer.
When I started diving, I never thought I'd get into technical diving, nor rebreathers. But I'm in the minority here.
You need to accept the reality that the vast majority of divers are not interested in team based diving. They want to look at pretty fish (one of my favorite activities). And the largest agencies focus on meeting this market demand. Most just wanted to be herded like cats while they follow a dive guide. That's reality.
Calculdating min gas is irrelevant if catastrophic gas loss occurs. If a first stage fails shut like happened to Graham: My Own Out of GAS Experience, you better be right next to your buddy (unlikely) or have a pony (more reliable than any buddy). Burst disks failing (which I've seen), hoses bursting, etc. do happen. Just rarely.
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