VR3 VPM and HE RGBM: do they get along under pressure?

silent running

Hello all, I will be doing some tmix diving soon with 2 guys who use the VR3 VPM and I will be using an HE RGBM. I had forgot which comps they were using and I hope the stops/run times will not be too different. I'm not just interested in how the stops/runtimes compare, but also in the actuall performance of the 2 on dives-how they count minutes, how they respond to doing stops slightly deeper, missed stops etc... Does anybody have any experience diving the 2 side by side? I looked for a thread that had this kind of info, but couldn't find one... Thanks, -Andy

Andy Del

If you have access to V-planner, this may help...

I did a taste test comparison between V-planner VPMB/E and my VR3 VPM last night.

Using 12/55 dil, +2 on V-planner and 0 conservatism on the VR3, a 46m 45 minute dive had matching run times until the last stop @ 6m. Here, the VR3 ran an extra 3minutes.

But, taking that to:

Using 12/80 dil, +2 on V-planner and 0 conservatism on the VR3, a 96m 45 minute dive (I'm not planning this, just couldn't be bothered moving the numbers around so much) had a difference in run times of over 45 minutes, with the VR3 taking longer to 'clear'. Moving V-planner to +4 got a close match, however, most of the stops were different by a minute or so, both ways, and the run times came out, again, 3 minutes apart.

Hope this helps somewhat...

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dive2dive2000

Andy,

Are you using an explorer, GAP, Gap Lite or custom hard tables? If they are hard tables you will probably exit a lot quicker. If it is computer generated just play with the conservitism and you will come close. The most important factor with RGBM is the min of a 3hr sit and a shallower 2nd dive. I always try and remind myself that all deco is just theroy no matter what type of profile you dive, so when you are in the middle of the South Pacific remind yourself How far is the chamber, How long will it take to get me there, and who will be operating it while I am inside? After I think about that I then plan my dive. I know and see divers using GF, and I know and see divers using RGBM, so I am comfortable with both profiles, I do not personally know any VPM divers so I would not dive a VPM profile. I am not knocking VPM I am just not familiar with it.

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Safe Diving,
Martin

jradomski

3 hours isn't really necessary (its just the ideal time), latter dives are just longer by a bit (not really a bad thing), 1.5 hours is really the minimum SI I would use, but I always shoot for at least 2hrs.. (this is true for custom tables and real time calcs, for the generic published RGBM table stay within the rules as these are set up for ranges)

I have never had any issues with the explorer on repetitive dives with the second being the same depth or deeper (again the profiles are a just bit longer)

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silent running

Hi Marty, very nice to finally meet you today. You are certainly right to remind me to be conservative, I will not be pushing it. I'll be using NAUI RGBM tables for back up and diving my HE with +1 conservatism. I will see how it compares with the tables and pad them accordingly. During training, they tracked very closely with 0 conservatism on the HE and it was a little behind the tables most of the time, but not always. Joe has pointed out that the NAUI tables are a bit more aggressive than the RGBM in the HE, seems to be true. -Andy

silent running

Andy, thanks for the info. The guys I'm diving with have V planner, so it will be interesting to see how they handle the differences btw the VRs and the planner. I'ts always interesting to see how real time deco comps behave and sometimes differ from the dive planners with the same alg... -Andy

Mdemon

Joe, if the deco is "clean", which compartments are requiring the longer SI? Is this because of the extra deep stops? Just curious - I know very little about RGBM!

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JS1scuba

The 3-hr sit time goes back to the DCAP tables that Hamilton created for the Key West Consortium tables that were ranged. It's basis was two-fold. First because oxygen is belived to have a 90 minute half time a 3 hour sit time will reset the CNS clock nicely. Furthermore if the final deco gas is oxygen or something with a PO2 of 1.4 or greater a repet dive can be done with the exact same deco times as the first dive but by shortening the bottom time by 5 minutes.

This seemed to work very well as a "rule of thumb". For more than 10 years I never did a repet on gas with less than 3 hours of sit time until 2004 when we were on the USS Monitor flying the new Cochran EMC-20s and I took the risk on a 90 min sit time. The pucker factor was high but the deco was clean and efficient. Even so today I prefer a 2.5 hour sit time unless I have to make the dive for operational issues.

For a 200 fsw dive for 30 min a 90 min sit time on a set point of 1.3 with 17/50 diluent should yield a decompression for a repet of the same profile about 30 minutes longer. Whereas a 3 hour SI will only increase the deco on the repet by about 15 minutes so the longer SI will cut the deco time. The only question is do you want to sit on the boat or sit on the deco line ... Time is Time ......

cheers

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dive2dive2000

Yes, it was nice to have met. From your responce I see you already know the answers, Have a great time and hope we have the chance to splash together someday.

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Safe Diving,
Martin

dive2dive2000

Joe,

do you always teach how to push the envelope over the internet to divers who you know nothing about? I think this is pretty irresponsible, but then again you cant get bent diving the internet

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Martin