Best choice for most conservative rec diving

[uncfnp]

I hesitate to ask but given all the recent controversy on decompression algorithms I am confused on the best choice for my recreational diving. And before you say they all are safe let me give a little personal history.

For health reason I have to dive very conservatively. I already do prolonged safety stops and when diving "locally" I even use O2. I have a Cressi as backup but my primary DC is a Petrel 2. Since my Cressi is RGBM I bought the VPM add on and set it at + 3 but had some problems so changed to + 5. I admit I will occassionlly do a little "lite deco" on the Cressi settings but have never had the Petrel in deco.

Now I know that most of the controversy with the VPM is with deep stops and with recreational diving this isn't really an issue but its got me wondering if there is a better choice. I know its all very complicated with SI, BT, repetitive dives and gosh knows what else all playing a roll. The problem is that I don't know which algorithm best accounts for all these "recreational" factors.

So, I guess my question is how does all this decompression controversy translate to recreational diving and should I dive Buhlmann or VPM for the most conservative diving. If it helps, slow tissue off gassing seems to be my achilles heel.

 

[tbone1004]

read up on Buhlman, learn how the GF-lo works, and set that to whatever you want. Personally I'd chuck the Cressi because it isn't going to be doing much for you unless you just want it as a backup for the sake of having a backup, and set the Petrel for whatever you want. In recreational Nitrox mode the "high" is 35/75 which is quite conservative especially for NDL diving and if you feel good, stick with that. If you want to be even more conservative, then go to OC-Tec and the default there is 30/70.

That all being said, I would highly recommend you bite the bullet and do a decompression class so you can do your stops on O2, and I would also pay very close attention to the last 15 feet of your ascent proile where you experience a huge change in pressure on your body, but most people make a super super fast ascent rate. Try to take at least 45 seconds to get up from 15 feet, and/or go up to 6-7ft and stay there for a minute, then take 30 seconds to make the final ascent

 

[Akimbo]

It is hard for me to imagine a more conservative approach than decompressing on pure O2 instead of air or Nitrox... in your scenario. Hang an extra 10-20 minutes if you want to play in the 10-20' zone. You can play with the O2 clock but I doubt you will ever get close.

 

[Storker]

Have you had many DCS-like issues on dives within the NDLs of your computer?

 

[DevonDiver]

For recreational, no-stop, diving the complexities of X, Y or Z algorithms are largely irrelevant... because all you are concerned with is no-stop time. Ascent rate is a constant (9-10mpm) and you can do a safety stop. You can extend that safety stop for as long as you like to clear things up.

A tech computer like the Petrel is useful when it comes to adding conservatism, because you can use the GF99 display to see your current state of tissue gradient... and hang in the shallows until it drops to somewhere you are comfortable to surface at. You could also use the saturation graph.... but I like GF99.

For recreational diving with ZHL... I'll use something like 45/85.... ti enable decent bottom time. Sometimes I'll tweak the GF Hi to mimick what my student's computer is providing...compare computer NDLs when we hit depth... and adjust mine.... so I can better track their NDL times over that dive.

But I'll often hang around in the shallows until I see the GF is down to 20-30 for surfacing. Best of both worlds... decent no-stop bottom time plus oodles of off-gassing (none of which is mandatory).

 

[scubadada]

I believe Cressi-Wienke RGBM is the most conservative of the commonly used decompression algorithms.
http://ads.bonniercorp.com/scuba/PDF/ScubaLab-Computer-Test-September-2014-data.pdf

My primary computer is an Oceanic VT 3, running DSAT. I run my backup, a Nitek Q at a GF hi of 95-100 to match DSAT. As pointed out, only GF hi pertains to no-stop diving, GF lo only kicks in when you go into deco, it dictates the depth of your 1st stop.

If you want to continue to dive as conservatively as your Cressi, it would be easy to find the GF hi that matches it for no-stop diving. Put your Petral in ZHL and in tec mode and keep dialing down the GF hi until if matches your Cressi pretty well. You can then choose a reasonable GF lo for your encounters with light deco.

 

[uncfnp]

Thanks for your understanding and help guys.

@tbone1004 I have done AN and use O2 locally but trips out of the country this has not been a feasible option. I do use nitrox, highest available and within my MOD. I currently dive in OC tec mode on the Petrel.

@Akimbo The dives that I typically do with O2 are drift and the Capt works with me as much as possible. I even have my DSMB marked so he knows it will be a while till I surface but much over 5 minutes isn't an option, especially if the dive conditions are less then ideal. Out of the country O2 hasn't been an option.

@Storker Sadly yes. Skin and lymphatic. Especially when I don't have O2 available. On a typical week dive trip I will rash once. Could be first, middle or last day of diving. I have never had a problem in Bonaire where I often do 4 dives a day of more then an hour each for 6 days. No O2 but half the shore dive is typically in the 30 foot range. Never sought treatment or had a chamber ride. And yes, I have been checked twice for a PFO with conflicting results. No one recommends surgery at present. Just conservative diving.

@DevonDiver I had considered the GF99 but was not sure how to apply it to my dives. I will have to give it some thought with in the limitations set with the dive ops.

@scubadada I know that RGBM factors in SI, ascent etc that all pertain to rec diving but curious if the other models including recreational ZHL do so as well. I was diving DSAT when I had my first "event" at around dive 130.

 

[DevonDiver]

@DevonDiver I had considered the GF99 but was not sure how to apply it to my dives. I will have to give it some thought with in the limitations set with the dive ops.

GF99 is what I am looking at once my stops have cleared. It can mean a longer stay at 3m... and/or a slower crawl up from 3m to the surface.

I might set GF-Hi 85, or higher, for a nice no-stop time - but damn sure I won't actually surface anywhere near that high (except in emergency).

It has a myriad of other uses also... deciding optimum depths for multi-levelling 'on-the-fly'; making use of gradients for better off-gassing opportunities... and as a bail-out option in-extremis.

 

[DevonDiver]

I know that RGBM factors in SI, ascent etc that all pertain to rec diving but curious if the other models including recreational ZHL do so as well. I was diving DSAT when I had my first "event" at around dive 130.

As far as I understand it...

The Reduced Gradient of RGBM concerns those algorithm adjustments that occur when certain 'extra' microbubble triggering parameters are met.

ZHL doesn't concern itself with Critical Bubble Radii... it merely on-gasses and off-gasses in line with half-time calculations.

VPM works to track/control via Critical Bubble Radii... but it doesn't reduce the gradient based on the unilateral factors that RGBM incorporates.

 

[uncfnp]

As far as I understand it...

The Reduced Gradient of RGBM concerns those algorithm adjustments that occur when certain 'extra' microbubble triggering parameters are met.

ZHL doesn't concern itself with Critical Bubble Radii... it merely on-gasses and off-gasses in line with half-time calculations.

VPM works to track/control via Critical Bubble Radii... but it doesn't reduce the gradient based on the unilateral factors that RGBM incorporates.

Ok. Sounds like my best bet is to use the Cressi and RGBM to set dive parameters then the Petrel GF99 to fine tune and manage lite deco mandated by the Cressi.

Oy vey!