What to Choose?

[dmaziuk]

There was a recent post somewhere mentioning the possibility of the body adapting to "decompression stress", quoting DIVING INCIDENT REPORTING SYSTEM (DIRS) - DAN Annual Diving Report 2017 Edition - NCBI Bookshelf as possibly supporting evidence: majority of reported DCS incidents occurred on the first day of a trip and half of those: on the first dive. It's possible that the model is right for the wrong reasons: multi-day gas accumulation is underestimated, but the body adapts and takes care of it.

Yeah, I've a little Jupyter notebook that I plan to put on GitHub someday... familiarity breeds contempt.

 

[BoltSnap]

Complete nonsense. I run an Eon Steel, as does my wife, as do quite a few people here. No problems whatsoever It's a very reliable computer. I also run a Perdix, which is Ok but IMO its only advantage over the Eon is that it can display 2 gasses simultaneously - useful for SM if you're too lazy to read the SPG's in front of your face..

I've also just completed a trip with 48 repetitive dives over 12 days - all 60min in nitrox max depths of 30m. There was No discernable difference between the NDL's given by Buhlmann and Fused RGBM.

There is a huge prejudice against Suunto here on SB, and while the company is far from perfect most of the negative comments are regurgitated nonsense.

Depending on the region of the purchaser then the pricing of different products may or may not be a greater influence rather than capability

I have been using Suunto computers since the early 90's and their choice of algorithms was never an issue for me. I have always had a Suunto computer on me while diving even if my main dive computer was a different brand. I have several models of Suunto computers now and use them in our dive school. Suunto's product quality went down the toilet since around 2005. Their customer service is even worse. Their attitude towards their customers is most terrible. They have had a consistent huge problem with the pressure sensors on their dive computers. They have computers that develop issues with rapid unjustified discharge of the batteries. When they replace a dive computer with faulty pressure sensor, they charge you an arm and leg for it only to have the replacement computer go down with the same issue and you have to pay for a replacement since the warranty the replacement for only 3 months. The replacement cost is higher than the wholesale price I usually pay for their computers. I have to pay for shipping to them in Finland which costs almost what it would cost to buy a new computer. Their response time and attitude is crap. Other than that, they are a wonderful company with great looking products.

 

[scubadada]

It more or less ignores multi day diving.
It assumes on and off gassing is symmetrical and doesn’t do anything to explicitly take into account repetitiveness dives. It relies on the left over gas from the earlier dive.
It doesn’t scale for depth.
It does nothing for sawtooth profiles.

Sorry, I don't understand anything that you are talking about. How does Buhlmann ignore multiday or repetitive dives by tracking gas accumulation over time? What is scaling for depth? Are you talking about sawtooth profiles like reverse profiles, not playing a significant role other than accurately tracking depth?

 

[stuartv]

I get paid for writing open source code, I can promise you that until you see the actual code with comments and explanations, the difference between "proprietary" RGBM and "non-proprietary" implementation of ZHL with GFs is six vs half a dozen.

How is it that you’ve had the opportunity to view the source code for a proprietary RGBM implementation? Are you working for one of the dive computer manufacturers?

 

[KenGordon]

Sorry, I don't understand anything that you are talking about. How does Buhlmann ignore multiday or repetitive dives by tracking gas accumulation over time? What is scaling for depth? Are you talking about sawtooth profiles like reverse profiles, not playing a significant role other than accurately tracking depth?

All the fast and medium compartments which will limit your dives are back to empty overnight. The longer compartments which you see mounting up are not going to get high enough to matter.

Read the source code.

ALL Bühlmann does is integrate gas uptake and release over time It then compares that gas load arrived at by that integration with some fixed (for a given depth) limits.

That is the entire algorithm.

In practice the gas load (in the compartments which count) at the start of a new day is zero. So no information survives overnight. There is no mechanism for multi day.

Between dives the off gassing rate is the same as the on gassing rate. The same time coefficients are used and the equations are the same. This is not true of all deco algorithms. There is no explicit mechanism to make a second dive extra conservative just because it is one in a series, just the gas load you start with. It is a major assumption that that is a correct means to take into account previous diving.

Because it is just integrating, there is no difference between a dive that repeatedly goes from zero to 15m and back and one that is steady at 10m (I am making up the exact numbers). I have heard proper deco scientists on stage explain why such sawtooth profiles are bad. I assume everyone agrees they are bad?

ZHL16C was tested at particular depths. It was not tested over very wide range. So while the computer manufacturers which use it started out targeting people to serious depth, the original model doesn’t do as well at serious depths.

 

[KenGordon]

There was a recent post somewhere mentioning the possibility of the body adapting to "decompression stress", quoting DIVING INCIDENT REPORTING SYSTEM (DIRS) - DAN Annual Diving Report 2017 Edition - NCBI Bookshelf as possibly supporting evidence: majority of reported DCS incidents occurred on the first day of a trip and half of those: on the first dive. It's possible that the model is right for the wrong reasons: multi-day gas accumulation is underestimated, but the body adapts and takes care of it.

Isn't this statistics for accidents in general, not bends in particular? The BSAC 2018 Incident Report has 24% of DCI incidents involving repeat diving.

 

[Diving Dubai]

What is it about Buhlmann ZH-L16C with GF that bothers you with regard to repetitive dives and multi-day diving?

My recent experience shows me that there is zero difference between Buhlmann ZH-L16C with GF, and Suunto RGBM for repetitive recreational diving.

I've just completed 48 dives over 12 days. While all were shallow (less than 33m) but all at the 60 minute length. The limiting factor was always gas in AL80's of my wife and the guide who both have exceptionally low consumption (I used SM but wasn't' much higher than them) I would suggest this is a more aggressive schedule of diving than the vast majority of AL 80 warm water divers would complete.

We had currents (sawtooth) and short SI's (1hrs sometimes 45mins) And yet the Eon and Perdix showed a similar NDL . Although the Eon uses (as you know) Fused RGBM) above 30m (according to Suunto) it uses the standard RGBM above 30m. Only once or twice did I get down to 10 mins which cleared as you rose above 18m (Perdix) or 13m Suunto)

The guide with a D4 did hit deco (4mins) a few times, but this would be more to do with the conservatism settings limitations (not having the aggressive settings available to us which are pretty much equal to 45/95.

So from my perspective there's nothing to choose from either algorithm

 

[stuartv]

So from my perspective there's nothing to choose from either algorithm

... when you're diving to a max of 33m and never diving to your NDL because you're always gas-limited.

Correct?

 

[Diving Dubai]

... when you're diving to a max of 33m and never diving to your NDL because you're always gas-limited.

Correct?

In the context of my post which refers to dives the vast majority of divers make, AND in teh context of 48 repetitive dives - which after all was the remark someone else made, then yes

I can assure you also that the same is valid on deeper dives, to 50m with Deco. No difference between Buhlmann and Suunto RGBM in respect to Deco times and total run times but my experience isn't with more than 5 repetitive dives most within the 40 - 50m range, all 1hr max

 

[scubadada]

Hi @Diving Dubai

Your Eon Steel (and the Eon Core and DX) run Fused RGBM. They run Technical RGBM down to 40 m (on air, nitrox, <20% helium) and switch over to full RGBM from 40-55 m. The P-2 setting is quite liberal, similar to 45/95 and DSAT.

The new D5 runs Fused RGBM 2, said to give shorter ascents from deep air dives and on repetitive dives using air/nitrox