RGBM vs Buhlmann table cutting?

[keith_henson]

morning all,

I have to admit that i have been diving on pre cut tables for the last couple of years using proplanner to cut the tables, adding in my own deep stops if necessary.

Now since i shifted to XP pro from win2k, proplanner refuses to work, so I resorted to my backup software by GAP. I noticed that there was a new version a few months back, so downloaded it, and ran a few dives on it. I was very supried at how much less time you spend in the water using the RGBM model instead of the standard buhlmann tables.

I used the program for the last 6 dives on RGBM +1 conservatism, as a JIC, but have not noticed any ill effects *touch wood*.

Now I have a dive on sunday out of dover. We have all agreed that as its a one dive day, we are going to sh*g the hell out of the deco (not scubajay) and run a 40-50min bottom time.

I put this in GAP this morning, with the 31% back gas in twin 12s and a 51% stage mix (dont ask, blame it on colinicky ) The RGBM is 0 conservatism, the Haldane is 85/20 gradient factor.

This is for a 40min bottom time. Can i have thoughts about what is going on here. I know i studied this intensly on my MSc on dive science, but im still a little "funny" about getting out of the water so soon. The tables direct off GAP are:

RGBM factor 0
Bottom time 40mins
stop depth, Time at depth, gas
40m, 40 mins, 31%
30m, 1 min, 31%
21m, 5min, 51%
9m, 1min, 51%
6m, 5min, 51%
3m, 6min, 51%
Total runtime: 61mins

but buhlmann style:
40m, 40min, 31%
30m, 1min, 31%
21m, 5min, 51%
18m, 1min, 51%
15m, 1min, 51%
12m, 2min, 51%
9m, 3min, 51%
6m, 5min, 51%
3m, 11min, 51%
Total runtime: 71mins

I have calculated that I have more than enough gas for this time just incase jonah strikes (or team cluster fcuk ). The 3m stop will be incorporated into the 6m stop as 3m out of dover aint a good idea (99% of the time).

My RGBM table that I will dive (and buhlmann as a comparison below):
RGBM Factor 0
Bottom time 40mins
stop depth, Time at depth, gas
40m, 40 mins, 31%
30m, 1 min, 31%
21m, 5min, 51%
15m, 1min, 51% (added this due to not liking a 1.2ata pressure gradient change)
9m, 1min, 51%
6m, 11min, 51%
Total runtime: 62mins

Buhlmann style:
40m, 40min, 31%
30m, 1min, 31%
21m, 5min, 51%
18m, 1min, 51%
15m, 1min, 51%
12m, 2min, 51%
9m, 3min, 51%
6m, 16min, 51%
Total runtime: 71mins

9 mins more on on the buhlmann method, should I be worried?

Keith

[wreckweasel]

I presume sir isnt concerned about running a hot mix at depth? (personally I'd be draining a bit and air topping it to say 28%)

Anyway, if you're bothered about the deco, add time in, either on your last stop or factored across the shallow stuff. For the sake of 10 mins, does it really matter

[Okeanos]

Depth Arrive Stop Leave Mix -EAN 31 -EAN 51
-----------------------------------------------------------
40 00:02 00:00 00:02 EAN 31
40 00:40 EAN 31
21 00:42 00:01 00:43 EAN 51
9 00:44 00:03 00:47 EAN 51 00:46
6 00:48 00:08 00:56 EAN 51 00:53
3 00:57 00:14 01:11 EAN 51 01:06
0 01:12 EAN 51 01:29

The above is done with Decochek with a 10mpm ascent rate. I know I prefer(need) longer stop in the shallows due to my physiology, I've never liked deep stops. Runtimes are similar to Buhlmann though.

[milldog]

There are no hard and fast rules to deco after all it's just theory and if it works for you with no ill effects why worry? Deco is different for every person.

what you could get out of the water in, I might not be able to. I could have had one of my homemade milkshakes and lost 8 stone before getting on the boat (and believe me i looked like skelitor last time i had one )

If this is working fine for you but would like some other deco software pm me your email address and i'll send you over Deco Planner 3

Graham

[keith_henson]

single dive, OTU's are not a problem. If it was two dives then i might consider a lesser mix. I know im not going to be using any effort on this dive at all. And if a whole world of hurt does hit me smack on like a run away train ill be off that wreck faster than jay with a port hole and a bell.

A hot mix for some people i know is 1.6ppO2 and sometimes upto a 1.8!

I would rather not myself, have got something of a niggling feeling of self preservation kicking in now

[aquaholic]

I would also alway do at least 1min at all shallow stops from 21m i.e. 18m, 15m, 12m, 9m as this is the range most critical for the avoidance of skin bents and niggles...

[PBrown]

Originally Posted by keith_henson

The RGBM is 0 conservatism, the Haldane is 85/20 gradient factor.

I don't use RGBM, so I can't say what the differences between these conservatism factors are, but if you run a GF of 20/100 it will give a runtime & curve very similar to the RGBM one you have posted. So I'd suspect that the conservatism is having a large effect.

Personally I would be happy to run with a 20/100 profile on this dive, although as already mentioned I'd probably reduce the bottom mix down from 31%.

cheers,
Paul

[Okeanos]

Originally Posted by aquaholic

I would also alway do at least 1min at all shallow stops from 21m i.e. 18m, 15m, 12m, 9m as this is the range most critical for the avoidance of skin bents and niggles...

By stopping at those depths you are likely to increase your deco obligation in the shallows as you will still be on-gassing the slow tissues. I know this is only a relatively shallow dive and the deco is minimal and whatever you do deco wise probably won't cause you any major problem, but the principles are still the same.

Skin bends - now that opens a whole new can of worms!

Unless you're crawling along the sand at 40m for an hour or so 31% isn't a problem.

[keith_henson]

Originally Posted by Okeanos

By stopping at those depths you are likely to increase your deco obligation in the shallows as you will still be on-gassing the slow tissues. I know this is only a relatively shallow dive and the deco is minimal and whatever you do deco wise probably won't cause you any major problem, but the principles are still the same.

Skin bends - now that opens a whole new can of worms!

mmmmmm, that crispy feeling, like someone who was operating on you, ate a bag of crisps and left that bag in there when stitching you up

mmmmmmm

[wilbo]

Originally Posted by Okeanos

By stopping at those depths you are likely to increase your deco obligation in the shallows as you will still be on-gassing the slow tissues. I know this is only a relatively shallow dive and the deco is minimal and whatever you do deco wise probably won't cause you any major problem, but the principles are still the same.

Skin bends - now that opens a whole new can of worms!

Interesting. (My limited understanding of) Ratio Reco has divers switching at 21m to 50% and then stopping at exactly those depths - 18m, 15, 12 and 9 for half the deco obligation - with the rest at 6m..

So are you saying that at roughly half the depth or less - you are still on gassing the slow tissues?

Sorry for the mini hijack Keith. Or should I call you the 'Badger man'?