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Old 08-30-2022, 06:23 PM   #16
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Re: Elbow trip 8/27/22

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Question 1, it assumes you will use the initially programmed gas, but it highlights when a better programmed gas is available, and you'd have to manually accept that better gas on way up.

Question 2, yes.

Question 3, yes. A single pony won't be able to be a panacea for all considerations. I was not using the rationale of a Bail Out Bottle (BOB). I wanted the higher mix on way up. 35% was selected because that is what I had in the pony that's been sitting in the garage for 2 years since hydro unused and that is what I had in a steel 100 HP I could use on the boat to whip the pony with. I use about 1000 pounds of pony on way up. Started with 3100, so had to whip it 2x for the 6 dives. If I was planning to do it again, would use some rationale and go with about 60% and start hitting it at about 60' for a better wash out effect. Or another individual may use a BOB pony and a higher mix pony if they want to cover more areas of concern.

I have no training beyond my initial Nitrox cert in 1999, but read a little and have access to great mentors that routinely dive deeper than most. So please don't take what I say as gospel. Much smarter folks out there than me, but enjoy the dialogue as I love diving.
Thanks for the detailed response. Although I have no training, I have, in the past done a lot of short dives in that depth range.

You seem to be going in the opposite direction compared to what I would probably do.

Here is my logic. (for using a pony with air in it).
I want to be able to survive a catastrophic failure of the main tank, Primary consideration. I've only ever had this happen once, so it is rather unlikely.

I am willing to incur a little more hang time and maybe a little more residual nitrogen associated with foregoing the enriched decompression.

If you have a failure at 180 and are negatively buoyant at the time, you might take a while to get off the bottom and you might be forced to go to the pony. I really don't understand how dangerous that is to use a very rich mix, for a very short time, under a strenuous situation. Maybe the danger of toxing out is relatively low? I wish I knew.

Sometimes on dives like that, we would send up a marker float from 20 feet and the boat would motor over to us and drop down some oxygen for deco or a safety stop. that was always nice but not something you could count on. Then again, guys driving boats that cost more than my house probably have the room and resources to do that sort of thing without too much trouble.

As you mention, if you want to carry three bottles, that might give you the safest all around solution. If all goes well (in a catastrophic emergency) it won't take more than a tiny pony (of air) to get you from 190 to 70 feet (in a hurry) and from there you could safely switch to the deco/pony bottle and possibly offset any accelerated ascent rate from the deep.

Maybe I sound paranoid, but this dive scared the crap out of me.

https://youtu.be/JO642vPEaaM

Last edited by jfjf; 08-30-2022 at 06:46 PM.
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Old 08-30-2022, 06:32 PM   #17
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Re: Elbow trip 8/27/22

Yes, this is one of the more interesting threads I’ve read on SB in the last several years.
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Old 08-30-2022, 06:43 PM   #18
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Re: Elbow trip 8/27/22

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I will let Dave answer your questions as they are based on his decisions and experience, but I will add a little general knowledge.

A 6 minute dive to 170' is not a "very short bounce dive", especially if they are repetitive dives. Off the top of my head, I can't give you a direct time comparison, but doing a 6 minute dive to 170' could be compared in terms of nitrogen loading to doing an hour plus long dive at 60-70' on air. In my opinion, switching from 25% to 35% is not to shorten your ascent time, it is to increase your bottom time on subsequent dives without going into deco.
I short deep bounce dive to the deco limit at 175, (or a little over) is different than a long shallow dive to the deco limit with respect to the types of tissue loading. Plus if you do over an hour on air at 60-70, your computer will spank you hard, not a 3 min deco.

I bet someone could run some software and run a 170 ft dive for 8 minutes or so on air versus same dive with a deco on 35% and the residual supersaturation after those two dives would probably be VERY similar after an hour long surface interval, unless the diver did a very extended stop on 35% .. and of course the idea is (I assume) NOT do an extended (lengthy) hang.

So, I seriously doubt the 35% makes much difference at all for subsequent dives. But hey, maybe my guesstimates are wrong.
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Old 08-30-2022, 07:22 PM   #19
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Re: Elbow trip 8/27/22

Interesting video. You just have to love modern photography and especially GoPro video. You handled things like a man. Especially staying in the water to see after the fouled prop. It shows how calm and collected you were.
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Old 08-31-2022, 09:04 AM   #20
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Re: Elbow trip 8/27/22

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Thanks for the detailed response. Although I have no training, I have, in the past done a lot of short dives in that depth range.

You seem to be going in the opposite direction compared to what I would probably do.

Here is my logic. (for using a pony with air in it).
I want to be able to survive a catastrophic failure of the main tank, Primary consideration. I've only ever had this happen once, so it is rather unlikely.

I am willing to incur a little more hang time and maybe a little more residual nitrogen associated with foregoing the enriched decompression.

If you have a failure at 180 and are negatively buoyant at the time, you might take a while to get off the bottom and you might be forced to go to the pony. I really don't understand how dangerous that is to use a very rich mix, for a very short time, under a strenuous situation. Maybe the danger of toxing out is relatively low? I wish I knew.

Sometimes on dives like that, we would send up a marker float from 20 feet and the boat would motor over to us and drop down some oxygen for deco or a safety stop. that was always nice but not something you could count on. Then again, guys driving boats that cost more than my house probably have the room and resources to do that sort of thing without too much trouble.

As you mention, if you want to carry three bottles, that might give you the safest all around solution. If all goes well (in a catastrophic emergency) it won't take more than a tiny pony (of air) to get you from 190 to 70 feet (in a hurry) and from there you could safely switch to the deco/pony bottle and possibly offset any accelerated ascent rate from the deep.

Maybe I sound paranoid, but this dive scared the crap out of me.

https://youtu.be/JO642vPEaaM
Two things I’ll put out there for discussion.

1) O2 toxicity is nothing to mess with. You don’t want to exceed the depth limit of your mixture, the danger of “toxing out” as you put it, is extremely high. Unlike nitrogen narcosis where you feel the effects of it come on and can alleviate them by ascending, O2 toxicity hits without warning, causes you to black out and it’s deadly. If nothing else is drilled into your head during a Nitrox course, let the one piece of info that sticks with you is that you NEVER exceed the depth limit of your mixture.

2) Personally, I don’t want to depend on the boat to hang bottles for me. Ultimately, my safety is my responsibility. I hope there is never an emergency or problem, but if there is, I want the boat to be able to focus on the situation. Common scenario……two divers are drift diving and come up a couple hundred feet from each other, how is the boat supposed to hang bottles for both divers?
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Old 08-31-2022, 09:15 AM   #21
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Re: Elbow trip 8/27/22

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I short deep bounce dive to the deco limit at 175, (or a little over) is different than a long shallow dive to the deco limit with respect to the types of tissue loading. Plus if you do over an hour on air at 60-70, your computer will spank you hard, not a 3 min deco.

I bet someone could run some software and run a 170 ft dive for 8 minutes or so on air versus same dive with a deco on 35% and the residual supersaturation after those two dives would probably be VERY similar after an hour long surface interval, unless the diver did a very extended stop on 35% .. and of course the idea is (I assume) NOT do an extended (lengthy) hang.

So, I seriously doubt the 35% makes much difference at all for subsequent dives. But hey, maybe my guesstimates are wrong.

From Dave’s post, he was not going into deco on his dives. He was going to the no deco limit, ascending and using the higher mix above 100’.

I do agree that if going to the no deco limit and ascending on the same mixture vs going into deco and then using the higher mixture for the deco stop, the nitrogen load would be similar. However, doing a no deco dive dive and switching to the higher mix does make a difference for subsequent dives.
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Old 08-31-2022, 07:18 PM   #22
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Re: Elbow trip 8/27/22

Very nice to see so much interest and conversation.
Diving regular depths to 100' on Sunday, so likely no pony, but will play around with breathing off mix I put into my BC bladder to prepare/simulate something I may have to do into the case of a catastrophic Equipment failure at depth. (As jfjf graciously presented)

Totally agree with Diverboy on the Do Not play around with oxygen toxicity at depth. I was mentored early DO NOT do that. I remember my friend telling me, "I"ll do the deco, but I will not mess with oxygen toxicity."

Respectfully differ on opinion with jfjf, but that's really fine. We have a different rationale. If his rationale is a BOB, and will do the deco, that is fine. Still safer than a singular cylinder and is a full redundancy. My pony is not a BOB, but a richer mix gas to breathe at a shallower and appropriate depth. If jfjf does not feel that the 35 is that much more different than the 25, fine by me. Entitled to his opinion, but not his own facts. The fact is it does make a difference. Science is science and partial pressures and wash out effects, whether small or large, make a difference. I did 5 repetitive dives from 157 to 178 followed by a dive to 135 with the mixes and actions I described and never had so much as a minimal headache. I was hyper focused on hydration the previous day and day of, and also took some breathes of pure O2 on the boat. It was rewarding to plan and have a good outcome. Also enjoyable to debrief with many knowledgeable folks after both on and off of Spearboard.
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Old 08-31-2022, 08:33 PM   #23
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Re: Elbow trip 8/27/22

Hmmm.....good stuff. I've been down to 180' fighting a big fish. Shit gets creepy. Better have your S in order.
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Old 09-01-2022, 08:55 PM   #24
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Re: Elbow trip 8/27/22

I’m not sure this “argument” is winnable.

Perhaps my assumption that: "a little nitrox on ascent is not going to matter much", is rather weak. In my defense, I did ask if anyone was interested in actually crunching the numbers with some software, but we never got that kind of objective analysis.

Maybe my position could be defined simply as saying: diving 180 feet with no redundancy is not a good game to play.

In my mind, a thinking diver would have to balance the likelihood (and the consequences) of a scuba failure at 180 versus the decompression benefit of having 35% (or something a little richer) for a portion of the ascent in order to reduce nitrogen. In other words, is the reduction in actual nitrogen loading (although probably “small”), which occurs on EVERY dive, worth the risk of not making it to the surface if in the VERY unlikely event, a regulator fails???

It really is a discussion of priorities and statistics. My priorities are a little different than DBrown’s and nobody has really shown us the numbers.

It is entirely reasonable to expect that two people, who have different objectives (or priorities), are going to reach different conclusions when they attempt to solve the same complicated problem (particularly when all the relevant data is unknowable).

Makes for an interesting discussion, I sure hope it remains a hypothetical discussion on the internet for everyone involved.

Perhaps a 6 cuft pony bottle of air tucked in somewhere nice and tight would not be too obtrusive and would help ensure everybody gets to collect social security?

Last edited by jfjf; 09-01-2022 at 09:04 PM.
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Old 09-02-2022, 07:51 AM   #25
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Re: Elbow trip 8/27/22

Team Head Hunter that regularly dives that depth and deeper with all their years of experience would be the perfect ones to answer your questions. For me, with a main bottle and a single pony at that depth. I'd take regular air in the pony in case of a major equipment malfunction. I once had a high pressure seat go when I got down to about 143' on the "Pipes" in the MG. Regulator just kept free flowing. I switched over to my pony and shut down my main tank on the way up. I'll say it again. That would be "my" choice. If I had 2 pony bottles. Then, one would be air and the other about 60%.

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Old 09-02-2022, 04:08 PM   #26
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Re: Elbow trip 8/27/22

143'? Scary and unexpected. Reliability is supposed get better under pressure when it comes to seals. I had a HP hose break whilst diving in the Tampa Bay shipping lane, 50' for about an hour. Luckily, I wasn't diving alone....that time...and was able to use my partners 2nd reg.
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