Couple questions on a pony bottle for bail out

[lowviz]

Given your concerns, you should also consider sidemount. Sidemount is more work as you have to switch regs, but it is also truly redundant. As a plus, sidemount is a much more stable configuration than backmount.

 

[Greg_Vic_Diver]

I've been on the fence in regards to a pony vs doubles with isolated manifold, and decided I would join this conversation.

I agree that the pony seems like more of an inconvenience, but it appears to offer complete redundancy. The only scenario I can see where this would fail, would be a catastrophic failure from my back gas that I did not detect. Then I go to get my pony, and apparently it has had a catastrophic failure also, and I didn't even notice it right under my left arm. This scenario however doesn't seem plausible.

My only fear with doubles is this scenario: I check my PSI every few minutes, however before I go to check my air again I go to take a breath and tanks are empty. Something catastrophic has happened behind my back, and I didn't realize I was losing air. Both tanks are empty.

Are both of these scenarios not really plausible, and I'm just being over cautious? I want doubles as I move into more advanced diving; however I feel like I almost want a pony if I went out and solo'd with doubles.

What do you think?

For the doubles scenario: If you are checking your gas every five minutes and you don't hear any big bubble leaks coming from behind your head (close to your ears) you will never have that scenario. I have had even very small leaks from a poorly connected DIN valve that I could detect just by listening. It can't just disappear without you knowing if you are properly monitoring your gas.

I won't speak about your ambitions for solo diving as that has many of its own risks/issues associated with it. I will tell you though, if you want to get into advanced diving, get some training on your doubles and get started now. You will feel more stable in the water and if you already are diving a wing and back-plate there won't be much difference in your gear. You can easily switch between the two (single tank and double tank).

Figure out your future dive goals and make sure you buy equipment and acquire training that leads you down that path - it will save you lots of $$ not buying gear and/or training you don't need.

 

[MB NZ]

if you want to get into advanced diving... Figure out your future dive goals and make sure you buy equipment and acquire training that leads you down that path - it will save you lots of $$ not buying gear and/or training you don't need.

You have to be talking about CCR here!

 

[DaleC]

Greg, you are mixing too many concepts into your replies.

If you are arguing that you want to use doubles to do two small dives I don't know what to say. Yes, you can, it's perfectly valid, but you are humping way too much weight around for my tastes. Why carry 200cuft of gas for a recreational dive you expect to use 60cuft of gas on? I can do the same with my single St72 and be neutrally buoyant with no weight belt (as I am doing in the video linked a few posts back).

If I am doing a shallow modest dive I use a single. If I am going a little deeper I use a single/pony. If I am doing an extended dive I use doubles. I suit the equipment to the task. For many applications a single/pony is an economical, workable, reliable, standardized form of redundancy that you can travel with it, use repeatedly for repetitive dives and share among friends. You can choose to take it on one dive and leave it on the next.

That you choose the same rig regardless of conditions I understand, it goes with the concept of standardization. Personally, I reject that mindset in favour of adaptability. Is one "better" than the other? Who's to say. I can only say that being adaptable works for me and I have been able to dive successfully operating that way.

But on a practical note. If weighting stays the same with your doubles, how do you compensate for all the gas expended between start of dive one and end of dive two? Are you that negative at the start, or very buoyant at the end? I think both extremes are sub optimal (I prefer to be close to neutrally weighted) and can't understand how you get around that issue without adjusting weight.

---------- Post added July 17th, 2014 at 11:01 PM ----------

I've been on the fence in regards to a pony vs doubles with isolated manifold, and decided I would join this conversation.

I agree that the pony seems like more of an inconvenience, but it appears to offer complete redundancy. The only scenario I can see where this would fail, would be a catastrophic failure from my back gas that I did not detect. Then I go to get my pony, and apparently it has had a catastrophic failure also, and I didn't even notice it right under my left arm. This scenario however doesn't seem plausible.

My only fear with doubles is this scenario: I check my PSI every few minutes, however before I go to check my air again I go to take a breath and tanks are empty. Something catastrophic has happened behind my back, and I didn't realize I was losing air. Both tanks are empty.

Are both of these scenarios not really plausible, and I'm just being over cautious? I want doubles as I move into more advanced diving; however I feel like I almost want a pony if I went out and solo'd with doubles.

What do you think?

As someone who dives both systems, doubles are more inconvenient. However, they do allow more gas. Just remember, you can get into a lot of trouble with more gas! They are heavier, require proficiency in certain skills (valve drills and not trapping hoses), and a little more attention during fills (I have received half fills because the isolator was closed). Most of all, they are heavier. How much that matters may, or may not, make a difference.

Losing all your gas without knowing in either system is pretty unlikely. A few divers who use manifolded doubles but want complete redundancy dive with the isolator closed, but being proficient in valve drills can serve the same purpose. If you get doubles, learn the drills.

Another choice not discussed here are independent doubles, two main tanks not connected. This is an older configuration that fell out of favour when the isolation manifold came along, as it allowed more gas to be used in the event of a failure. This was important because doubles were being used by deep/cave/wreck divers and the more available gas the better. But for a solo diver they can afford a larger volume of gas with complete redundancy. Old school but still effective.

 

[rivers]

I have been out of diving for a little while (about a yearish) but I've finally decided to get a pony bottle as I hopefully get things rolling again.

I decided on a 19cf for recreational diving mostly in the 50-90ft range and I think I'm going to sling it for ease of access and the ability to pass it off if necessary. I'm currently looking for a regulator in the $200 range (Mares Rover 12, Genesis GS2000, Oceanic GT3/SP5, Cressi XS2/AC2).

Question 1 - What are your recommendations on basic slinging methods/rigs? I use a Zeagle Ranger.


I know there's continuous debate on how to store tanks and I like to keep my Worthington HP100's at 500psi if they'll be sitting for a while.

Question 2 - Since a pony tank is not used regularly, how do you store/cycle it? I intend to simply do a wet-breathe test before each dive.

Thanks a lot in advance,

Chris

I'm going to do something completely irrational and answer the OPs questions.

1. When it come to how to rig it (either backmount or sling), it's a matter of personal choice. I would try both methods and see what you like.

2. Store it with gas in it. If you have a dive that you definitely want it on, make sure to top it up before you go if you need to. Make sure to practice regularly deploying and breathing of it. If sh*t hits the fan, you want to make sure reaching for the reg, turning on the valve, etc are all second nature.

Here is the thing about diving. Everyone has an opinion and opinions will vary from person to person. No matter what kit configuration you dive, make sure you are comfortable in it. Make sure it's safe (ie AAS is easily deployable, not caught in anything, etc, everything is secure on the rig, no danglies), and make sure it's appropriate for the diving you're planning.

 

[John C. Ratliff]

What justification could you possibly have for this? The only acceptable reason I can imagine would be the first dive after flying to a destination with the empty pony that could only be filled with air immediately after arrival. Otherwise this makes no sense whatsoever.

The pony is for emergency use. That means you plan for the worst possible time. You are diving nitrox, presumably to extend your NDL. So you might very well be beyond the air NDL at the time that you need the pony. Now you grab your emergency supply and immediately go into a deco situation because you have switched to air. Of course you are also going to immediately ascend (if you can) so your deco obligation might clear on the way up. Unless, as you said, you managed to get yourself tangled in some line or something else prevents your ascent. But why risk putting yourself into a deco situation in the first place?

The gas in the pony doesn't get used in normal situations other than a breath or 2 to check the reg on each dive. It needs only an occasional top off. There is no reason for it to be filled with air. It should probably be the richest gas you carry, as long as it does not exceed your max pO2 at max depth. There is simply no justification for any nitrox diver to have a pony filled with air.
iPhone. iTypo. iApologize.
emphasis added, jcr

Okay, I've been reading through this and need to make a few comments. First, about people having a pony bottle which free flows, and de-tuning the regulator so that this doesn't occur. I would say get a Dacor Olympic or Dacor Pacer regulator, and use them as thy have engineered out free-flowing for those second stages. This is the advantage to having dived for a while--knowing how some of the "older" technology works. But in an emergency, you need the regulator to be functioning well, and not de-tuned.

Second, about the Aqualung Calypso--it isn't the same regulator that the Navy Experimental Diving Unit approved in the 1980s. That was a balanced piston regulator called the Calypso by U.S. Divers Company, and the newer Aqualung Calypso is an unbalanced piston design which will breath harder as the tank pressure drops--I don't know whether it currently has U.S. Navy approval.

Finally, to this post. Note the sentence I highlighted; you won't immediately go into a decompression situation because you switched to air--that is a fallacy. You get into a decompression situation by breathing nitrogen (or another inert gas such as helium) under pressure. This gas dissolves into the blood plasma over time, and simply switching from nitrox to air does not place further nitrogen into your system immediately. That takes time, and pressure. However, the person has begun an ascent, so this time is not counted as bottom time. So no further decompression obligation would be incurred if ascent immediately begins.

SeaRat

 

[Greg_Vic_Diver]

Greg, you are mixing too many concepts into your replies.

If you are arguing that you want to use doubles to do two small dives I don't know what to say. Yes, you can, it's perfectly valid, but you are humping way too much weight around for my tastes. Why carry 200cuft of gas for a recreational dive you expect to use 60cuft of gas on? I can do the same with my single St72 and be neutrally buoyant with no weight belt (as I am doing in the video linked a few posts back).

Hi Dale, I'm not mixing additional concepts, just answering your question on how you can have more gas when using doubles for reserve than if using a single tank + pony. If comparing, you'd have to compare equal dives to equal dives...right?

But on a practical note. If weighting stays the same with your doubles, how do you compensate for all the gas expended between start of dive one and end of dive two? Are you that negative at the start, or very buoyant at the end? I think both extremes are sub optimal (I prefer to be close to neutrally weighted) and can't understand how you get around that issue without adjusting weight.

If properly weighted this is not an issue. Properly weighted means diving a "balanced rig". A balanced rig means three things:
(1) With full exposure protection and minimal gas in the tanks (~500 PSI) one can hover and be neutrally buoyant at 20' with no gas in your wing/BCD
(2) The rig without you in it will float on its own with full tanks of gas (using the wing/BCD to float)
(3) You can swim up off the bottom with full tanks of gas and no gas in your wing/BCD

Now number (3) can be an issue if diving a thick wetsuit as it will compress and loose buoyancy as you descend further. Is the case of a thick wetsuit, the test would have to extend to the maximum depth one wanted to dive and you would need to have enough ditch-able weight to ensure you can still swim off the bottom with no gas in your wing/BCD. Shell/trilam drysuits are best in this regard as they don't compress and have a static buoyancy characteristic regardless of depth.


---------- Post added July 17th, 2014 at 11:01 PM ----------

As someone who dives both systems, doubles are more inconvenient. However, they do allow more gas. Just remember, you can get into a lot of trouble with more gas! They are heavier, require proficiency in certain skills (valve drills and not trapping hoses), and a little more attention during fills (I have received half fills because the isolator was closed). Most of all, they are heavier. How much that matters may, or may not, make a difference.

I actually think they are more convenient as I can leave the tanks on the shore for the second dive and not have to switch out any tanks....but I know everyone is entitled to their own opinion. It's true own should always check the valves before the dive, check your gas before leaving the diveshop and learn how to check them properly during the dive.

If you get doubles, learn the drills.

Good advice!

---------- Post added July 21st, 2014 at 08:18 PM ----------

Finally, to this post. Note the sentence I highlighted; you won't immediately go into a decompression situation because you switched to air--that is a fallacy. You get into a decompression situation by breathing nitrogen (or another inert gas such as helium) under pressure. This gas dissolves into the blood plasma over time, and simply switching from nitrox to air does not place further nitrogen into your system immediately. That takes time, and pressure. However, the person has begun an ascent, so this time is not counted as bottom time. So no further decompression obligation would be incurred if ascent immediately begins.

This is not true and dangerous.
Grab any decompression software, plug in a long deep dive to the end of recreational limits using 32% nitrox and note the decompression time to the surface. Now do the same thing but set your deco gas to 21% nitrox and switch deco gases at just above the maximum depth (will simulate using it as the gas for ascent). You will now have a decompression obligation.

As you ascend you have a gas gradient and a pressure gradient you can use to to help you decompress. If you actually increase the nitrogen/gas gradient going into your tissues (instead of reversing it out like is done in accelerated decompression) you increase the decompression time required to offgas the nitrogen in your tissues during ascent. Nitrox tables calculate the NDL assuming you are using the same gas the entire time. Use the same gas in your "reserve" as your bottom gas if you diving within NDL - if not get the proper training for decompression diving (and learn what gases to properly use).

 

[dumpsterDiver]

Okay, I've been reading through this and need to make a few comments. First, about people having a pony bottle which free flows, and de-tuning the regulator so that this doesn't occur. I would say get a Dacor Olympic or Dacor Pacer regulator, and use them as thy have engineered out free-flowing for those second stages. This is the advantage to having dived for a while--knowing how some of the "older" technology works. But in an emergency, you need the regulator to be functioning well, and not de-tuned.

Second, about the Aqualung Calypso--it isn't the same regulator that the Navy Experimental Diving Unit approved in the 1980s. That was a balanced piston regulator called the Calypso by U.S. Divers Company, and the newer Aqualung Calypso is an unbalanced piston design which will breath harder as the tank pressure drops--I don't know whether it currently has U.S. Navy approval.

Finally, to this post. Note the sentence I highlighted; you won't immediately go into a decompression situation because you switched to air--that is a fallacy. You get into a decompression situation by breathing nitrogen (or another inert gas such as helium) under pressure. This gas dissolves into the blood plasma over time, and simply switching from nitrox to air does not place further nitrogen into your system immediately. That takes time, and pressure. However, the person has begun an ascent, so this time is not counted as bottom time. So no further decompression obligation would be incurred if ascent immediately begins.

SeaRat

That's funny .. about the Dacor Pacer regulator. i have been using one for my octopus second stage now for maybe 15 year (or 25)???? I like it because it is rugged, solid metal. Any other plastic second stage would have been cracked and gone after all the abuse I have put the second stage through.

This is the first I have heard that it is a good choice for this application for reasons other than robustness...in fact I always assume an adjustable second stage might make more sense, because you could tighten it up making it less likely to freeflow and then when you deploy it, you could crank the knob and make it easier to breath? But of course those plastic knobs would get snapped off ever 5 or dozen years with my abuse..

---------- Post added July 21st, 2014 at 11:31 PM ----------

Hi Dale, I'm not mixing additional concepts, just answering your question on how you can have more gas when using doubles for reserve than if using a single tank + pony. If comparing, you'd have to compare equal dives to equal dives...right?




If properly weighted this is not an issue. Properly weighted means diving a "balanced rig". A balanced rig means three things:
(1) With full exposure protection and minimal gas in the tanks (~500 PSI) one can hover and be neutrally buoyant at 20' with no gas in your wing/BCD
(2) The rig without you in it will float on its own with full tanks of gas (using the wing/BCD to float)
(3) You can swim up off the bottom with full tanks of gas and no gas in your wing/BCD

Now number (3) can be an issue if diving a thick wetsuit as it will compress and loose buoyancy as you descend further. Is the case of a thick wetsuit, the test would have to extend to the maximum depth one wanted to dive and you would need to have enough ditch-able weight to ensure you can still swim off the bottom with no gas in your wing/BCD. Shell/trilam drysuits are best in this regard as they don't compress and have a static buoyancy characteristic regardless of depth.


---------- Post added July 17th, 2014 at 11:01 PM ----------



I actually think they are more convenient as I can leave the tanks on the shore for the second dive and not have to switch out any tanks....but I know everyone is entitled to their own opinion. It's true own should always check the valves before the dive, check your gas before leaving the diveshop and learn how to check them properly during the dive.




Good advice!

---------- Post added July 21st, 2014 at 08:18 PM ----------



This is not true and dangerous.
Grab any decompression software, plug in a long deep dive to the end of recreational limits using 32% nitrox and note the decompression time to the surface. Now do the same thing but set your deco gas to 21% nitrox and switch deco gases at just above the maximum depth (will simulate using it as the gas for ascent). You will now have a decompression obligation.

As you ascend you have a gas gradient and a pressure gradient you can use to to help you decompress. If you actually increase the nitrogen/gas gradient going into your tissues (instead of reversing it out like is done in accelerated decompression) you increase the decompression time required to offgas the nitrogen in your tissues during ascent. Nitrox tables calculate the NDL assuming you are using the same gas the entire time. Use the same gas in your "reserve" as your bottom gas if you diving within NDL - if not get the proper training for decompression diving (and learn what gases to properly use).

I am sure that in theory it is better to ascend on nitrox than air, but what is the MAGNITUDE of the difference when we are talking a non-deco, recreational dive? THAT is the difference I am curious to see.. I don't have the software to do it.

I'm still gonna put mostly air in my pony, but I am curious to see a quantification of the effects of switching the ascent gas from say 32% (at 130 ft) to air for the direct assent. Is the numerical difference really "dangerous"??

 

[Greg_Vic_Diver]

I am sure that in theory it is better to ascend on nitrox than air, but what is the MAGNITUDE of the difference when we are talking a non-deco, recreational dive? THAT is the difference I am curious to see.. I don't have the software to do it.

I'm still gonna put mostly air in my pony, but I am curious to see a quantification of the effects of switching the ascent gas from say 32% (at 130 ft) to air for the direct assent. Is the numerical difference really "dangerous"??

Yea, I'd say so.

First, the most important part of the dive to avoid DCI/AGE/CAGE is the the ascent. That is where you need to be the most careful.

Did you plan for a deco obligation in your gas calcs for the reserve? Do you wish to further exasperate an already bad situation (you had to bail out to your reserve) and now blow away some deco? You like to roll the dice?

Now diving doubles makes this easy as the reserve is always the same as your backgas! how bout that.....

 

[dumpsterDiver]

Yea, I'd say so.

First, the most important part of the dive to avoid DCI/AGE/CAGE is the the ascent. That is where you need to be the most careful.

Did you plan for a deco obligation in your gas calcs for the reserve? Do you wish to further exasperate an already bad situation (you had to bail out to your reserve) and now blow away some deco? You like to roll the dice?

Now diving doubles makes this easy as the reserve is always the same as your backgas! how bout that.....

You support your contention that the practice is dangerous by repeating that it is dangerous...

You must be a great father... "Because I said so... that's why!!!!"