using a pony bottle to extend bottom times?

[Yoyoguy]

All,
This may be a really dumb question but what are the views or thoughts on using a 40cf pony slung on the side to extend bottom times but staying safely within recreational limits? Here is the reason I ask. As of right now, I am a gas hog. I definitely have been working on my breathing, maintaining better buoyancy throughout the dive...etc. to help BUT I never seem to come even remotely close to NDLs. For example, 100ft dive on air NDL is 20min per tables and 16min per my dive computer. Any time I have dove to 100ft I have started my accent at 11-13min into the dive (about when my aluminum 80 is at 1100psi) and I reach the surface with 600psi (this includes a 50ft 3min stop and a 15ft 3min safety stop). So instead of buying a larger tank or doubles...etc, why not use the 40cf pony I already have? I tow this pony for safety anytime I dive deeper than 60ft. Why not use the air at the end of the dive to slightly extend bottom times? just curious, not that I would actually do this. Please don't make this a bashing thread and yes I am saving for doubles and continued training. Again just curious.

 

[CAPTAIN SINBAD]

AL-80 is a bad tank for deep dives. Try AL-100 or steel 100.

 

[Basking Ridge Diver]

So if you would not actually do this - why ask?

I would not get in this habit of using a pony to extend your dive - you are using the pony as training wheels for your dive. Learn to use the air you have by slowing down and learning to bring your RMV/SAC down first. Do you even know your RMV - if not why not? This is the advanced section - find out how and start tracking it so you can begin to understand how to get it under control.

Find out if you are over weighted or if your buoyancy is the issue - then re-evaluate the need for a larger tank. Find out if you are out of shape and if needed - get into shape - run a couple miles a week - swim if needed but get in shape...

My two cents...

 

[Yoyoguy]

So if you would not actually do this - why ask?

I would not get in this habit of using a pony to extend your dive - you are using the pony as training wheels for your dive. Learn to use the air you have by slowing down and learning to bring your RMV/SAC down first. Do you even know your RMV - if not why not? This is the advanced section - find out how and start tracking it so you can begin to understand how to get it under control.

Find out if you are over weighted or if your buoyancy is the issue - then re-evaluate the need for a larger tank. Find out if you are out of shape and if needed - get into shape - run a couple miles a week - swim if needed but get in shape...

My two cents...

I never have used my pony as extra gas so it is not going to be a habit. buoyancy is spot on...I did all the checks with my rig in a pool and myself plus weight checking before and after dive. I am at the point where at the end of the dive with my wing completely deflated at 15 feet I neither sink nor float. Also, my trim is pretty much perfect as well. I am able to hover a couple feet off the bottom (slowly sinking and rising with breath with out hands/legs moving and pretty much horizontal). I have been practicing frog kicks but im not great at it. I will admit I NEED to SLOW WAY DOWN!!! That is definitely my number one issue. I have been tracking my gas before and after each dive but I have not sat down and actually calculated my RMV/SAC yet. I need to do that one of these nights. Sorry I am at work and this question just popped in my head so I thought id ask.

P.S. I would say im average shape. I am pretty active but I don't go to the gym.

 

[tbone1004]

first off, it is no longer a pony bottle if you're intending to use it, it is a stage bottle. If you want to dive with a stage bottle, then that is perfectly fine, just understand how to use them and proper gas management.

I agree with 100ft on an al80 may not be the smartest idea, but such is life.

Why are you doing a 3 minute stop at 50ft? You are still ongassing with that profile btw, certainly not helping your offgassing and wasting about 150-200psi/4-5cf of gas for nothing. I'm not getting into a deep stop discussion, but half depth is idiotic especially when you are well within NDL's since you are still ongassing. Half pressure is fine, but half pressure of 100ft is 30ft ish, not 50.

Other than that, listen to what was written by the above posters about making your sac rate better by being more efficient. Quick mental math puts your SAC rate at 0.8 give or take, which is very high. If you can get your SAC rate down to 0.6, you will hit your NDL's on an AL80. 0.6 is still pretty high unless you're kicking around all over the place in which case it is "normal". If your computer tracks average depth you need to be tracking your sac rate from every dive. The 0.8 comes from 12 minutes at 100ft, burning approximately 1500psi which gives you 400psi for descent which is a little conservative so it very well may be 0.9cfm. Point still stands that slowing down and learning to be efficient is going to fix most of this problem for you.

I would recommend doing a modified breast stroke kick as your only kick. Does two things, prevents you from silting the place up, but more importantly it uses small muscles. When you flutter kick you use the 3 biggest muscles in your body, glutes/hamstrings/quads, with a frogkick, you use your calves, and the small muscles in your hip. Smaller muscles burn less oxygen, so combine a more efficient kick with using more efficient muscles, and your breathing rate goes down.

 

[redacted]

Some dive ops may frown on using a pony in such a manner so talk to the op first.

If you need more gas, get a bigger tank.

 

[Michael Guerrero]

If you breathe down your pony and then you have a neck o-ring failure, regulator failure (first or second), or lose a burst disc in your AL80, what's your plan? If you end up being distracted or getting in a situation that takes a little time to get you out and accidentally go into deco, while breathing down your pony, will you have enough gas to complete deco and get back to the surface? If you run into a panicked diver who pulls your reg out of your mouth because they're OOA, but you've already breathed down your pony, what's your plan?

It's your call if you think you can deal with these and any number of other possible contingencies. I don't know anything about you personally, but if you match the typical diver demographic, then losing some weight and taking up a cardio routine will probably do more for your gas consumption than anything else. At least until you get to elite athlete status .

Mike

 

[CptTightPants21]

Yeah, an Al80 is not the best tank for deeper dives. If you routinely go to those depths you might want to look at an HP100 or 120. That would give you the additional air you need to enjoy your dives.

Would not recommend making the pony bottle use as part of my dive plan. I have used one in a lake or quarry with benign conditions so I wouldn't have to surface swim, but it should never be "part of the plan".

 

[uncfnp]

I have never understood why anyone uses a 40 for a pony on recreational depth dives but that is another thread, in fact several. But if I were carrying a 40 on dives and routinely running out of air before NDL's then yes, I would consider using it as a stage.

But first, I agree with others that you need to make some changes. Get a bigger tank if that is an option and stop doing those 3 mins at 50. At most do a brief 30 second to one minute stop but at your dive time I don't even recommend that. If you want that extra margin, do a 5 minute SS between 20 to 15.

Remember too, if you breathe down your pony only do it to the level that keeps a safety reserve for emergencies. After all, that's why you carry a pony. And this will also mean that you are going to have to fill that "pony" with each use.

 

[KevinNM]

Those people who believe in stops at 50% of depth for min deco dives advocate 60 second stops, not 3 minute stops (thought it's more complex then that...).

You should do a 10 minute swim at your normal speed at ~33 feet one day, writing down the pressure at the start and end and see what your measured SAC is. Then try it again going a lot slower. None of the dive pros you see are racing anywhere unless there is an emergency, they move slowly and glide between kicks.