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Vast differences in tables

19K views 141 replies 30 participants last post by  BenL 
#1 · (Edited)
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#2 · (Edited)
You are comparing apples and oranges. Dissolved gas models such as those behind the Buhlmann tables, the Suunto RGBM, the US Navy tables and indeed the PADI tables, work on a completely different underlying basis to v-planner, which is based on a dual phase model. You cannot compare the, and specifically their respective conservatism, using only the amount of time spent in the water, as they are trying to achieve different things.
 
#24 ·
You cannot compare the ........... using only the amount of time spent in the water, as they are trying to achieve different things.
My recommendation would be to take a course on decompression, or read Deco for Divers by Mark Powell, which is an excellent introduction to the subject.
Phooey. I've read Mark's book twice. And I've done a few courses on decompression. It is still interesting to compare how long each algorithm keeps you in the water, for a defined dive e.g. 30 for 30, or 50 for 50. Agreed understanding why they do this, is more complex, and involves different models. However they are not trying to achieve different things - they are trying to achieve helping you avoid getting bent.
 
#8 ·
Also the 6m last stop on air.. Bubble models don't care for that because their is no benefit to doing air stops at 6m. If you set a normal 3m last stop, it will come down by 10 minutes or more.

Regards
 
#15 ·
Ya but PADIs ascent rate is 18m / min which is a super fast.

Also PADI only mandate you complete safety stops on all dives deeper than 30m or if you come within 3 pressure groups of their NDL
There still decompressing on the ascent just coz they don't have a lot of inert loading doesn't mean they don't have any :D
 
#20 ·
Of course, PADI does a different table for over-weight ex-squaddies probably a little dehydrated from drinking too much beer and living in the desert. On the other hand the new kid on the block is the combination table that uses both Buhlmann AND VPM together. (Dive System Orca and some other notables arriving early next year.) Still best to do a safety stop (formerly called a Jesus stop about 30 years ago), eh?
 
#39 ·
It is a while since my open water (12 years - blimey!) But I recall being told it was 'no stop' diving rather than 'no deco'. I also recall being taught about ascent rates and that you could still have a problem if you ascend to quickly. I remember some mnemonic 'ascend safely from every dive' or suchlike.
 
#44 ·
Sadly this has descended into the usual crap.

The OP asked why different tables gave different results. Different NDL's, different decompression schedules for the same dive. It is impossible to discuss this question without addressing on gassing, off gassing, decompression stops and ascent rates. It is important to define your terms in such a discussion. It makes it a lot easier if you consider that all dives require decompression. The discussion then becomes about how much and what form it takes.

Now, do you want to discuss, or score cheap points?

Rich
 
#46 ·
Cheap points thanks.

Decompression carried out on the surface having a sandwich and a *** just confuses the issue.

If you can safely ascend directly to the surface (at a safe max rate) and climb out of the water and get changed, I think it is not confusing to call that a no deco dive.

All the talk about you are still off-gassing as you walk around so you are decompressing and technically are at a deco stop at 0m is not as helpful as is being suggested. It's a no deco dive, within the no deco limit.

Tb.
 
#49 · (Edited)
Every diver is taught that the human body can accept a certain level of N2 before saturation becomes
too much, hence a drawn line or NDL (No Decompression Limit) beyond which mandatory stops are needed.

If your demographic are 18 year old US Navy that line will be in a different place to that used by your average
middle-aged tourist which naturally needs to be more conservative and why the NDL on tables can differ from
one agency to the next.

Soon as you go over that NDL line into deco it get's far more complicated as it's no longer a single line and
more a series of lines, decided on by each agency depending again on what they consider to be the safest
option and again why inevitably tables tend to differ.
 
#51 ·
Every baby diver is taught that the human body can accept a certain level of N2 before saturation becomes
too much, hence a drawn line or NDL (No Decompression Limit) beyond which mandatory stops are needed.
The sooner you stop referring to grown adults as babies, and treating them as such, the easier life gets.

If your demographic are 18 year old US Navy that line will be in a different place to that used by your average
middle-aged tourist which naturally needs to be more conservative and why the NDL on tables can differ from
one agency to the next.

Soon as you go over that NDL line into deco it get's far more complicated as it's no longer a single line and
more a series of lines, decided on by each agency depending again on what they consider to be the safest
option and again why inevitably tables tend to differ.
So, you say that one table may have a NDL of, lets say 20 minutes, and another has an NDL of 25 minutes. That would make a 23 minute dive a deco dive on table one, and a Non-deco dive on table two. Can you explain to me:

1. How this might happen?
2. What dive profile I should follow?

Rich
 
#63 ·
I know quibbling about words is fun but is somebody going to explain to me why being fit, young and healthy or otherwise effects your deco profile?
I'm not sure I can see it.
 
#64 ·
Today I have been playing around a little with different air tables I have and noticed significant differences between them.

Take for example a 30 meter, 30 minute dive planned on air with deco on air:

Buehlmann : 2 mins @6m & 7mins @3m {total 9 mins}
US Navy : 3mins @ 3m {total 3 mins}
V-Planner (VPM B+1) : 1min @12m, 4mins @9m, 21mins @6m {total 26mins}
Suuntos RGBM conservative 0 : 1min@16m & 23mins @6m {total 24 mins}
PADI: NDL of 20mins so irrelevant

I accept that USN tables are aggressive due to the fact that they are developed for very fit men that are diving professionally, I also accept that PADIs tables are ultra conservative or obvious reasons.

Buelhmann seem to be more conservative than USN but are still quite aggressive compared to V-Planner and Suuntos RGBM which both seem to be ULTRA conservative, to the point where I had to rerun my details as I could not believe the difference but they are so close to each other they have to be running some similar sort algorithms

Anyone have any observations or comments on this? Which ones if any would people be most willing to follow?



I use a Shearwater dive computer running GF deco.

I cant get many many diferent numbers for a 30min 30m dive even using this one piece of equipmnet.

If i run lets say 10/70 deco i get 31mins deco

Same computer same software running 100/100gf I get 6mins deco

So you pick the one you want.


GUE don't do air so they would do a 30m dive on 32% Nitrox with an EAD of 25m

Using their 7min deco ascent and trying to get GF deco to mimic it I get a profile of 10/80GF


ATB

Mark
 
#100 ·
RichW; said:
It makes it a lot easier if you consider that all dives require decompression
It may make it easier but it doesn't make it true. Is the one foot dive Garf referred to a decompression dive? If so, how about a one inch dive? If that's a deco dive then what about running up the stairs really quickly?

Now, do you want to discuss, or score cheap points?
Yes, and that involves pointing out when seductive soundbites are actually sloblocks.

Janos
 
#103 ·
we all seem to think usn table are for the young a fit. well form what iv read it seem even them young and so called fit divers , did not for the most part dive the table as set out .. it seem each dive supervisor would add in some fudge , for each dive ..maybe use the next depth or run a table for a 30m 30min dive as (30m 35min) usn table s my have been well used . but we dont know how thay were used, maybe them young fit divers only got by on the fudge ,, maybe then didnt need the fudge ,, lol pick me a dive and ill be out on the boat be4 you ,, young /old

iv seen 2 of my young dive buddys ( 20 years younger no smokers soft ase southen drinkers ) get bent on the same dive with me , i was in and first out first ,, tables .. lol

deep stops . and 6mind for 6m to 0m all stuff i never bother about ,, as long as iv air im happy ,,
 
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