Suunto Tech RGBM vs Fused RGBM

[3dfx]

Hello everyone!
Probably something that was discussed numerous times, but I really want to read the opinion of the experienced users here.
I decided to change my old Suunto HelO2 for a new Suunto Eon Steel - despite the controversial Suunto implementation of the RGBM, I felt very well with my HelO2 and the new Eon sounded like a reasonable upgrade.
Before I ordered the Eon I briefly read Suunto's superlatives about the Fused RGBM, but never actually tried to compare the two algorithms through Suunto's DM5 Planner.
Last week I went for some scuba diving and I was extremely surprised about the deco time I received after accomplishing a brief 65m touchdown on air. Please take a look at the profile at movescout: Slav_Landov's 0:51 h Scuba diving Move (you can see the ceiling by clicking on the button below the graph). I've got 30 minutes of decompression for what should be a quick no deco dive!

After the dive I tried to compare one an the same diving profile with Suunto DM5, but using the two different algorithms. The dive time with the Fused RGBM is indeed more than twice longer than with the Tech or regular RGBM!
Am I missing something?!

 

[KenGordon]

Was your SI 1h35?

What was the previous dive like?

 

[Diver0001]

Hello everyone!
Probably something that was discussed numerous times, but I really want to read the opinion of the experienced users here.
I decided to change my old Suunto HelO2 for a new Suunto Eon Steel - despite the controversial Suunto implementation of the RGBM, I felt very well with my HelO2 and the new Eon sounded like a reasonable upgrade.
Before I ordered the Eon I briefly read Suunto's superlatives about the Fused RGBM, but never actually tried to compare the two algorithms through Suunto's DM5 Planner.
Last week I went for some scuba diving and I was extremely surprised about the deco time I received after accomplishing a brief 65m touchdown on air. Please take a look at the profile at movescout: Slav_Landov's 0:51 h Scuba diving Move (you can see the ceiling by clicking on the button below the graph). I've got 30 minutes of decompression for what should be a quick no deco dive!

After the dive I tried to compare one an the same diving profile with Suunto DM5, but using the two different algorithms. The dive time with the Fused RGBM is indeed more than twice longer than with the Tech or regular RGBM!
Am I missing something?!

Well.... it would be good for you to look into the NEDU study comparing bubble models and Buhlmann models.

In short you can conclude from that study that the current bubble models all make ascent lines that start too deep and stay too deep for too long which needs to be compensated for by longer shallow stops. The algorithms are not "efficient" in the sense that they do not allocate your deco time at depths where it does you the most good.

Most informed technical divers have already stopped using bubble models for this reason. 10 years ago a lot of people would have told you that deep ascent lines protected you from getting DCS by avoiding the formation of bubbles but it's now clear that deep ascents actually increase risk unless the shallow stops are extended to compensate for the extra on-gassing. The good news seems to be that your Suunto computer is adding the extra shallow time. Be thankful for that.

That said, there are more suitable computers for technical diving on the market right now. Are you in a position to return/exchange this computer?

R..

 

[mmadiver]

Well.... it would be good for you to look into the NEDU study comparing bubble models and Buhlmann models.

In short you can conclude from that study that the current bubble models all make ascent lines that start too deep and stay too deep for too long which needs to be compensated for by longer shallow stops. The algorithms are not "efficient" in the sense that they do not allocate your deco time at depths where it does you the most good.

Most informed technical divers have already stopped using bubble models for this reason. 10 years ago a lot of people would have told you that deep ascent lines protected you from getting DCS by avoiding the formation of bubbles but it's now clear that deep ascents actually increase risk unless the shallow stops are extended to compensate for the extra on-gassing. The good news seems to be that your Suunto computer is adding the extra shallow time. Be thankful for that.

That said, there are more suitable computers for technical diving on the market right now. Are you in a position to return/exchange this computer?

R..

Diving 90/90 myself but usually adding 10-20mins additional time at 20 and 10ft.
Just did a 400ft dive, both my buddy and I did 90/90 and we're just fine.

 

[Diver0001]

Diving 90/90 myself but usually adding 10-20mins additional time at 20 and 10ft.
Just did a 400ft dive, both my buddy and I did 90/90 and we're just fine.

Do you remember what Simon said he was using?

R..

 

[divezonescuba]

The guy from the Phillapines? has a website with an article assessing tech capable computers. Well worth looking at in your case.

A guy in my TEC 40 class had an eon steel, I heard him say a lot of things about it when he had difficulty in getting it to do what he needed during the course.

At a manufacturers seminar (not suunto), I asked if their top of the line computer could be used to tech diving. They gave me a funny look and said it used an RGBM variant. End of discussion.

 

[3dfx]

Thank you for the inputs! I'll indeed read in more detail about the difference between the RGBM and Buhlmann models. I understand that using different models will result in different dive plan.
What is extremely surprising for me is the great difference between Suunto's old Tech RGBM and new Fused RGBM - I expected some differences, but not more than twice longer dive time!
Please take a look at two absolutely identical simulations - descent to 62m with 12m/s, one additional minute at the same depth and then ascending according to the algorithm. Both plans are made with the same settings with deepstops turned off! Surface time is not taken into consideration.
The results are: 15 minutes for Tech RGBM and 34 minutes for Fused RGBM.
If that is the case I'd better post this computer on eBay... Is someone able to check the same profile on another model?

 

[Diver0001]

Thank you for the inputs! I'll indeed read in more detail about the difference between the RGBM and Buhlmann models. I understand that using different models will result in different dive plan.
What is extremely surprising for me is the great difference between Suunto's old Tech RGBM and new Fused RGBM - I expected some differences, but not more than twice longer dive time!
Please take a look at two absolutely identical simulations - descent to 62m with 12m/s, one additional minute at the same depth and then ascending according to the algorithm. Both plans are made with the same settings with deepstops turned off! Surface time is not taken into consideration.
The results are: 15 minutes for Tech RGBM and 34 minutes for Fused RGBM.
If that is the case I'd better post this computer on eBay... Is someone able to check the same profile on another model?

Check the users manual and see if you can turn off the deep stop functionality and the run the simulation again.

At any rate, what you are seeing is exactly what I was explaining above. All those deep stops on the the Fused RGBM are the reason you are getting such a long run time. If you make a deep ascent line then you have to pay the price in shallow stops to compensate.

R..

 

[3dfx]

Deepstops are already turned off for both plans...
I found a document with more information about Suunto's Fused RGBM - http://ns.suunto.com/pdf/Suunto_Dive_Fused_RGBM_brochure_EN.pdf
On page 12 you can find a graph comparing a diving profile to 80m with Fused RGBM and Buhlmann. Suunto claim that their algorithm gives shorter ascent time than Buhlmann's!

 

[scubadada]

wow, 10/100 and 20/80 are interesting comparisons, guess they wanted the deep stops to look similar. One might want to see a profile that reflects more recent thinking. Of course the shallow time is shorter, and the supersatuation of slower compartments greater.