Bubble Model (RGBM) Emphasizing Shallow Stops?

[Divetech99]

I typically dive 45 meters for 30 minutes on Air and 50% for deco starting at 21 meters. On VPM or ZHL16c, my first stop would be within 24 meters or 21 meters depending on conservatism/GF setting.

In actual Deco dives, my Suunto D9 would show a ceiling of 7 meters after 30 min at 45 meters while the Petrel displays 21 meters as the first stop.

RGBM is a bubble model and the nature of Bubble models is to emphasize deeper first stops as in the case of VPM. Right? Why then is the Suunto making me do my first stop at 7 meters?

 

[JohnnyC]

The D9 isn't a technical computer. It's just showing you your ceiling, not actually planning a staged decompression. It will happily put you at 7 meters for 3 hours. Your Petrel will actually design a "proper" decompression profile.

Using RGBM for actual staged decompression, it will favor deep stops. This is not how Suunto implements RGBM on their recreational computers.

 

[Centrals]

But D9 can handle up to 3 different nitrox mixes so it should be able to handle deco dive(non trimix).

 

[BoltSnap]

D9 has an option for deep stops also.

 

[rongoodman]

RGBM is a bubble model and the nature of Bubble models is to emphasize deeper first stops as in the case of VPM. Right? Why then is the Suunto making me do my first stop at 7 meters?

Your Suunto isn't really running RGBM, but a proprietary algorithm(Suunto RGBM) to which they have attached the name. It has been described here at various times as "folded RGBM", a compartment model with some tweaks added to make it act a little more like a bubble model.

 

[DevonDiver]

Yep..... it's important to recognize the difference between 'RGBM' and 'Suunto RGBM'. Implementation of the algorithm makes a big difference.

IMHO... very few 'recreational' computers do much more than provide 'emergency decompression' that is simplified for recreational divers. i.e. get them shallow to the ceiling and hold them there. It's a liability/damage limitation exercise.

The 'Deep Stop' option on Suunto computers is, I believe (?) nothing more than a unilateral Pyle stop.... not the implementation of a bubble model for a true staged deco ascent.

Putting multiple gasses onto a recreational computer doesn't make it a technical computer. It makes it a gimmick...

 

[Mr Carcharodon]

'emergency decompression' that is simplified for recreational divers. i.e. get them shallow to the ceiling and hold them there. It's a liability/damage limitation exercise.

So if they run out of gas and drown who has the liability then? Not that I am defending RGBM. Random or unpredictable plans seem like no plan at all. Still seems like a dubious legal approach.

 

[DevonDiver]

I don't get your point. The liability lies with the muppet who blundered into emergency (unplanned and unprepared) decompression and didn't have enough gas to complete it.

RGBM is a bubble model.... and should perform closely to VPM. But Suunto RGBM (ignoring the comical Pyle stops) seems almost Haldanian... loooonnnggg stops at 3m.

My presumption is that the seeming strategy is based on consideration of Boyle's Law... and aims to maximize time under the ceiling by reducing air consumption at minimal depth/pressure (and maybe keeping them reassuringly close to the surface for when their gas does run out...).... and it looks like a safety stop... so it's familiar.

 

[Mr Carcharodon]

The "muppet" who followed RGBM/Suunto's plan is at fault? As Michael Corleone said who's naive now.

 

[DevonDiver]

I'm still missing your point. What does RGBM/Suunto have to do with running out of gas?

The issue, I thought, was where Suunto RGBM gives stops... not for how long those stops are.

If we're talking tech diving... then the Suunto RGBM should be predictable for dive planning, and allow an effective gas plan to be calculated..... deep stops or shallow stops....it's an algorithm... and that same algorithm must feature on their planning software.

If we're talking rec diving... then it's considerable muppetry for ignoring Suunto RGBM no-stop display, then all the warnings... and incurring deco that you can't obligate. But at least Suunto RGBM puts those divers in the shallows, just below the ceiling, where their gas lasts the longest and they can most easily CESA if it doesn't last quite long enough...