Training for "Recreational Trimix"?

[TSandM]

Dan, that's exactly why I don't carry a pony bottle -- but if these guys want one, they do have to decide what to put in it.

Guy, why would your wife have to cope with doubles AND a pony? Once you have doubles, the pony's pretty irrelevant. I managed double Al80's on the dive boats off West Palm, and I'm not very big. (Of course, your objection to the expense for such a small number of dives is a legitimate one!)

 

[danvolker]

I have to add one point to all of this.... for a "recreational diver" with advanced skills, very squared away, in a "Real Buddy Team", it is incredibly easy to ascend from 140 to 20 feet, holding stops, holding trim and awareness and sharpness...there is nothing to it.

For the bogus diver that got on the 140 foot dive, but does not belong there, this is a bad place, where they have a huge challenge for their very lacking skillsets.

In Palm Beach on the charter boats that run to places like the Hole in the Wall, or the Hydro, you will run into a large number of very squared away advenced divers. Just rec certified, but often with greater ability to handle any likely problem on these dives, than the typical instructor in any Resort Destination. It is this kind of a diver I am thinking of, when I put out ideas way beyond anything any agency would support.
This is a place where some of the guys we are talking about, have been spearfishing places like the Hole in the Wall for over 20 years, and are really much stronger divers than 90% of the tech instructors in Florida....Stronger, meaning they will handle the currents, the potential problems, and the planning for the dives they will do, BETTER than the tech instructors...One reason for this will be many Hundreds of dives like this under their belts, compared to the tech instructors with a dozen like this, and because the tech instructor will be carrying so much gas, and so much gear, that they are actually at a major disadvantage in the deep drift environment of Palm Beach. They are like puffer fish that are all blown up, and they don't know any better...they don't see their drag issues, or what the maximum duration should be to still allow a diver to be slick instead of a semi hauling a half dozen tanks at a snails pace.....
The spearfisherman type I am talking about, with buddy skills, would be my choice every time for a buddy over 90 percent of the tech instructors in Fl.

---------- Post added January 9th, 2013 at 04:26 PM ----------

One thing about a highly skilled spearfisherman that has done the Hole in the Wall over 100 times....this will be a person with extremely good peripherol AWARENESS and vision, meaning they should have great skills for staying aware of how their buddy is doing--if this is part of their "mission" on the dive....And spearfisherman are used to "mission-oriented" dives..also good for the edge of the envelope we are talking about in this thread

Obviously the spearfisherman that don't want any part of buddy diving, are NOT included in this tangent

 

[waterpirate]

My disconnect here is that regardless of the gas choice it is a bounce dive off the hydro. I have never dove the hole so will not comment. I guess if you are going to bounce you should be clear headed, but why not seek the training to take your time and enjoy the scenery. Go to the doubles, put deco gas in your stage and go slow and easy with good technique.

For me bouncing the hydro with 100% as my next breath at 20' is non starter. A safer aproach to that pony bottle for me would be 32/20 or simmilar if I were to participate.

My other disconect is that if they are gue rigged, that shows a willingness to get it right. This plan is half baked on the rest of the gear needed to go to the next step. At a minimum they should get Y valves on those big singles and a beter gas choice for that stage. Why not seek out Chad or someone simmilar if they want to bounce on rec trimix? That would IMHO be a better choice.
Eric

 

[guyharrisonphoto]

If we trained and dove with doubles, it would be for longer bottom times calling for deco (why go through the hassle with doubles and trimix only to stay no-deco and waste a huge amount of the gas instead of enjoying the scenery) and we would carry some sort of deco mix in the pony for an added safety margin.

I know from experience that a single 130 is near the limit for my wife and adding a pony would be at the limit.

Really, what I am looking at is:

1. Formal tech training in deco, doubles, etc, with the expense of setting up the doubles and reconfiguring our gear or just buying a separate doubles set-up, the very lengthy training needed for such a course, the number of dives needed to get used to the new equipment before even taking the risk of a deep dive, even assuming my wife can handle the weight on the boat, compared to

2. Diving with equipment we know like the back of our hand, and that we are comfortable diving to depth, with a relatively shorter course of training to add the safety/enjoyment factor of trimix, only having to get used to the small pony for deco.

As for what to put in the pony, I would go with a mix suitable for deco but also useable in an emergency, maybe 28%.

 

[rjack321]

As mentioned earlier in this thread, no reputable instructor will train you for deco in a single tank. 28% is essentially useless for deco. Actually any gas which is safe to breath on the bottom or even near the bottom will not be accelerating your deco.

Given the limitations you've posed already, your existing dives being "on the edge" but your wife not being capable (for whatever reason) of adding doubles and suitable gas reserves for deeper deco diving....

I think its time to just accept the fact that there is no magic elixer here. You can either:

a) continue to do the bounce dives on lean nitrox and be "on the edge",
b) switch to 25/25 or something like that - and do no-deco bounce dives on light trimix (which is expensive and still short dives),
c) or realize that you are asking to do technical diving on recreational gear with a minimal time/gear investment and that's just not a good idea.

Maybe its time to skip the 100+ft dives.

 

[dumpsterDiver]

A couple comments.. DanV refering to a pony bottle filed with deco gas.... I have a problem with that... For me, a pony bottle is really a bail out bottle. That means that it is safe to use on the bottom; so in this case it could be air.

To suggest that a recreational diver who is doing recreational dives (no deco) carry a bottle with a very rich deco mix is unwise. We know that breathing the wrong gas at the wrong place kills divers... Why take oxygen or 80% on a dive with no deco? I think the diver would be safer carrying something he can use on the bottom, rather than something that can easily kill them in an emergency. But hey, I NEVER took any technical courses, I just dive.

Also, Guy determined that he needs a 40 cu-ft pony bottle for a 130 ft dive? Yet he is concerned with weight? For no deco dives in 130, in a high current environment especially, I see little reason to take a bottle that large. I would choose a 13, but certainly a 19 should get you from the bottom to the top.

If you did one dive on the hole in the Wall and had trouble clicking pics in a screaming current, don't be surprised... I have done that dive many times and it can be very challenging, you are vulnerable to being swept offshore (I've hit like 154 there i think) and there can be tons of sharks and if your buddy stops up current, you probably can NOT reach them to help them. For this reason alone, I feel that you really must have your own redundancy (and 80% ain't it). It is just too easy to get separated in a 3 kt current in 125-135 feet. It is often a one-way street... there is no going back, even if your buddy is near death.

So we know that volker exaggerates, but that dive can be very tough and the current will cause you to exert yourself, if you don't just drift along. if you are pulling a float (as I often am) the dive just gets that much harder. It is a tough dive, especially for the first couple dozen times if you do more than sight see.

So I guess what I am saying is that, it is pretty normal to feel compromised on that dive. There is narcosis, but the exertion and the screaming current etc. make it a lot tougher than a calm day on the hydro Atlantic that is much deeper..

 

[TSandM]

I think we all make decisions about cost/benefit and risk assessment, and we come up with different answers. I decided to go with the doubles and the deco training for a bunch of reasons, but a big part of it was that I was determined to cave dive, which meant mastering doubles, which meant I was going to invest the money on the gear, and I was going to have to learn to cope with the weight. But I have friends in Southern California who have made a different decision, and are actually doing dives in the deeper recreational/shallower technical range on a single 130 with a 40 of O2. I don't like the risk assessment in that for myself, but they concluded that somewhere in the neighborhood of 5000 dives between them without a catastrophic gas loss was good enough odds.

Similarly, I don't see the cost/benefit of a helium mix for no-deco diving penciling out very well (and my recreational trimix class, done in doubles, included being blessed for some backgas deco), but if Guy thinks it does, I think he's far better off with a bit of training for problem-solving at depth than he is just throwing some helium in his tank and going for it.

I do very little technical diving at home, and to be honest, if it weren't for the cave diving, I'd probably just sell off my doubles.

 

[DA Aquamaster]

In terms of risk assessment there is both the probability of it occurring as well as the impact of it occurring.

I'll accept a fairly high probability of something going wrong if the impact is low - a snarled reel for example where I can just pull out another one with no threat to me or the dive (but I still prefer to pre-flight the reels to ensure the line will come off cleanly to reduce the probability of a failure). I will not however accept even a low probability of a failure if the impact is high - a total gas loss on a single tank dive with a single tank buddy who may lack adequate reserves in a situation where I have a long ascent and/or a deco obligation.

In my opinion taking a chance of getting dead or seriously hurt because you did not want to bring doubles along (side mount, back mount, independent, whatever) on a deco dive is pretty frigging stupid.

 

[Kevrumbo]

Of course, this is far outside of agency guidelines....but it does represent real world choices we know advanced divers make all the time, in spite of agency guidelines...with that disclaimer, I would say that a buddy pair as squared away as Guy and Maribi, would have each other instantly as a redundant source of gas should a failure occur at 140 feet deep. If this happened, one would pass the long hose to the other ( they are both geared DIR style by-the-way) , and they would immediately begin their ascent..using light to signal others in the group they are ascending..... The "only" use I can see for the pony bottle, is to have 100% O2 in it, that they could use at 20 feet to create a better gradient to offgas with, and to represent additional volume of gas for the final 10 minutes of deco they may want to do.

This is a real "buddy team", so planning for separation at 140 feet deep is not of any value. If one lost gas at 140, the other would have plenty of gas to get them up safely to 20 feet, where they would have an O2 stop. They would need to plan their max duration of dive at this depth, based on the amount of gas the two would go through on ascent with stops, to 20 feet.

Agree & concur . . .that "pony bottle" should be a slung deco cylinder of Oxygen.

Note: Shallow depth NDL's on Helium can be less than Nitrox, or even Air diving:

From Bruce Wienke, Technical Diving in Depth, Reduced Gradient Bubble Model (RGBM) In Depth:

Helium NDLs are actually shorter than nitrogen for shallow exposures . . . Reasons for this stem from kinetic versus solubility properties of helium and nitrogen, and go away as exposures extend beyond 150 fsw, and times extend beyond 40 min or so.

Helium ingasses and outgasses 2.7 times faster than nitrogen, but nitrogen is 1.5 to 3.3 times more soluble in body aqueous and lipid tissue than helium. For short exposures (bounce and shallow), the faster diffusion rate of helium is more important in gas buildup than solubility, and shorter NDLs than nitrogen result. For long bottom times (deco and extended range), the lesser solubility of helium is a dominant factor in gas buildup, and helium outperforms nitrogen for staging. Thus, deep implies helium bottom and stage gas. Said another way, transient diving favors nitrogen while steady state diving favors helium as a breathing gas.

Helium offgassing rate

The greater diffusivity of Helium from a free phase bubble model perspective (i.e. RGBM) means possibly loading idiopathic bubble seeds/bubble nuclei and having a Boyle expansion pathology resulting in DCS upon ascent --even if you were diving trimix within air or nitrox NDL's. . .

Attached are the comparative NDL's for Eanx 32 and Helitrox; and example deco profiles for bottom times at 30m and 33m, for Ean 32 and Helitrox w/ or w/o O2 deco. . .

As you can see, the NDL's for even a light triox like NAUI-Tec's are less than Eanx32, within the RGBM paradigm. . . Point is you shouldn't dive trimix as "NDL" prescribed to an Air or Nitrox Table --IMHO the "Rule-of-Thumb" should be always do Oxygen deco on a trimix dive, or even at the very least, an O2 deco clean-up on your last dive in a repetitive "NDL" recreational series of trimix dives. . .

 

[rivers]

If we trained and dove with doubles, it would be for longer bottom times calling for deco (why go through the hassle with doubles and trimix only to stay no-deco and waste a huge amount of the gas instead of enjoying the scenery) and we would carry some sort of deco mix in the pony for an added safety margin.

I know from experience that a single 130 is near the limit for my wife and adding a pony would be at the limit.

Really, what I am looking at is:

1. Formal tech training in deco, doubles, etc, with the expense of setting up the doubles and reconfiguring our gear or just buying a separate doubles set-up, the very lengthy training needed for such a course, the number of dives needed to get used to the new equipment before even taking the risk of a deep dive, even assuming my wife can handle the weight on the boat, compared to

2. Diving with equipment we know like the back of our hand, and that we are comfortable diving to depth, with a relatively shorter course of training to add the safety/enjoyment factor of trimix, only having to get used to the small pony for deco.

As for what to put in the pony, I would go with a mix suitable for deco but also useable in an emergency, maybe 28%.

I can't comment on any trimix training at the moment as I haven't taken a trimix course yet. I can comment on the use of doubles though. If you are already diving in a single tank bp/w set-up, nothing really changes besides the amount of weight on your back, which isn't noticeable in the water. The only thing you need to learn how to do is a shutdown/valve drill, which is relatively easy if you can reach your valves.
i just moved to doubles back in October. Very easy switch and comfortable in them almost immediately. I use Faber twin steel 12L tanks, which are equivalent to twin 95 ft3 (I think). I'm also 5'3 and a 125lbs. I carry my own tanks without much issue, and also have a trolley to wheel them around a bit easier. Don't completely write off doubles for you and your wife. They weren't a cheap outlay, but it wasn't massively expensive either. My twinset was £220 (bought used), found a used halcyon explorer for £100, and bought one new reg for £130. I don't have a great deal of money and luckily had friends who could loan me a wing or regs until I could afford to buy one.