Deep Diving Gas Planning

[OldFNG]

I'm going to apologize in advance for what may be a long winded question, but I consider this part of super advance planning for my new years gear purchase and dive plans.

Background:
I've got about 19 dives under my belt, PADI [OW,AOW,DS,DEEP] most of which were in the tropics. Of those dives about a half dozen were deep dives (between 80 and 130 feet) During my deep dives I've always had some sort of boat surface support with dangling AL80 Tank with Air and about 10 Lbs of weight just in case.


Gear Owned: Cressi Backjac BCD, Hollis FX 100 Biodry Drysuit, Delta 4 regulator Package, Mares Nemo Wide Computer, 2 x AL80 Tanks + fins snorkel mask etc.

Question:
I'm now doing my diving in altitude mountain cold water lakes, so I'll have to tow out a float. Theres some nice dives I'm looking at in the 100 to 130 foot range and I'm trying to plan my gass appropriately. In an effort to avoid the Spare Air vs Pony bottle vs doubles with manifold discussion lets assume that I will have a Pony bottle with enough air to get myself to the surface (probably an AL40 or so pony bottle with air) and I will not be diving with doubles with isolator manifold until I do deco/tech training when I have about 70 dives under my belt.

My question is mostly about gear / procedures for my backup plan in the event of catastrophic gas loss and I have to switch to the pony bottle near the end of my dive. Would it be in my best interests to get another first & second stage and attach to my second AL80 tank to dangle from my float with a lift bag in case I need to bail out. I know in most cases the pony bottle should save me, but I'm wondering about those cases where I'm close to NDL and I have an emergency for whatever reason. What kind of decompression load can I get put into in that sort of situation and how much deco time should I plan for in my gas management. Also would I be fine just dangling the gear from a float, or would a lift bag and weights clipped to my descent line be a better option. Also what depth would you clip it at, I'm assuming 20 feet would be ok, but maybe 25/30 depending ont he deco algo might be a better choice.

Like I said sorry for the long winded post but I'm mostly looking for some advice as I start planning for my dives in the new year.

 

[gcs118]

This isn't an answer to your question, but be sure to consider actual vs. theoretical depths at altitude. 100-130 ft. dives, depending on the altitude, could put you well out of recreational diving limits.

 

[LiteHedded]

reserve enough gas to get you and your buddy to the surface and you dont need this pony tank.

 

[OldFNG]

The pony tank is only there in the event of complete systems failure, first stage freezes, something breaks etc. I just believe in planning for contingencies. Also yes good reminder about actual vs theoretical.

 

[LiteHedded]

The pony tank is only there in the event of complete systems failure, first stage freezes, something breaks etc. I just believe in planning for contingencies. Also yes good reminder about actual vs theoretical.

your buddy will be there as well. with enough reserve gas to get you to the surface.

 

[Cave Diver]

My question is mostly about gear / procedures for my backup plan in the event of catastrophic gas loss and I have to switch to the pony bottle near the end of my dive. Would it be in my best interests to get another first & second stage and attach to my second AL80 tank to dangle from my float with a lift bag in case I need to bail out. I know in most cases the pony bottle should save me, but I'm wondering about those cases where I'm close to NDL and I have an emergency for whatever reason. What kind of decompression load can I get put into in that sort of situation and how much deco time should I plan for in my gas management. Also would I be fine just dangling the gear from a float, or would a lift bag and weights clipped to my descent line be a better option. Also what depth would you clip it at, I'm assuming 20 feet would be ok, but maybe 25/30 depending ont he deco algo might be a better choice.

Like I said sorry for the long winded post but I'm mostly looking for some advice as I start planning for my dives in the new year.

If you're diving within NDL's and you have a catastrophic gas loss causing you to head to the surface, you shouldn't be incurring any mandatory deco time.

I would also personally be *highly* reluctant to count a tank strapped to my float into my emergency gas plan. If you do so and surface to find that it's somehow come unclipped and no longer there, you're facing a much worse situation than if you carried all the gas you need and just planned the dive properly.

Are you doing these dives solo, or with a buddy?

 

[lowtech]

As a new diver as well here's my opinion.

Pony bottles are for trained solo divers. Since I'm not trained to dive solo, I'm gonna bring a buddy instead of a pony bottle.
If I felt the need to bring a pony bottle, I wouldn't factor it into my gas plan. I'd just make sure it can get me safely to the surface.

As for hanging a bottle on a float is your failure scenario catastrophic gas failure at max depth, can't use a buddy, and CESA to the hung bottle and try to work off the damage done by the fast accent? It's probably my limited experience, but I think you'd already be in deco when the failure occurred, and in that case I'd follow whatever training you received, for violating NDLs.

I feel very hesitant on commenting about placement/position or hanging bottles on lines as it "sounds" like flirting with decompression diving. I just thought it might help so see how another diver might view this type of dive, with around the same level of experience.

 

[OldFNG]

Thats typically what I was thinking, my plan is take enough gas to support both in the event of an emergency, resort to buddy if fit hits the shan, follow procedures for violate NDL and make sure all safety stops can be maintained.

Where the idea of an extra suspended tank comes from mostly stems from my deep dive training which in all cases had surface support "just in case" I'm mostly trying to emulate that as much as possible but from what I'm hearing is that isn't needed as long as the plans are being followed with regards to gas planning. I'm just anal and love to plan, check the plan and plan for contingencies again just in case.

 

[Garth]

Wow. To start... A pony bottle is for anyone who would like additional redundant air source in the event of a failure. This is directed at response posted about pony only being for solo divers.. I.e that's ridiculous.

To the OP. You did protect yourself from the spare air doubles argument but let's discuss the ... Only 19 dives thinking of slinging a pony as well as an al80 to a float all while incurring no mandatory deco argument. Or let's not.

 

[Garth]

With 19 dives were they all instructional dives? Or did you miss a 1 in front of all this?