Past NDL. And then this???

[KeithG]

I would not run that set of GFs. It gives you deep stops and then cuts short the shallow stops.

Great thread. Thanks for the feedback. I think the OP is more aggressive than me. You think my computer is more aggressive than you want. Good info. I am trying to understand how to make sure I am conservative enough as I get older. We are here to learn. I do not push the NDLs of my computer, less than 10 minutes rarely happens...

We really do not know what gradients my computer uses. My "modelling" of the Uwatec Aladin was very limited. I did 2 extreme dives to the edge of NDL with multiple sawtooth dips and just very very slightly went beyond NDL (1 minute of deco - according to my computers - 3 different models of Aladins). I then mapped one of those computers "relatively closely" to a Subsurface Buhlmann 30/90. As a non-deco diver I ignored the GFlow setting and left it at 30 and simply fiddled the GFhigh until Subsurface gave we NDLs throughout the complete dives that where within several minutes of my real dive computer. My guess at 30/90 could be wrong. But it matches close enough?

The next claim is that my computer is more aggressive than you want to do for multiple dives. This is good info for me. How far back do you (and others) think I should dial it? Warm water dives, no current, great viz, 3,4,5 or 6 one hour dives a day.

 

[kafkaland]

We really do not know what gradients my computer uses. My "modelling" of the Uwatec Aladin was very limited. I did 2 extreme dives to the edge of NDL with multiple sawtooth dips and just very very slightly went beyond NDL (1 minute of deco - according to my computers - 3 different models of Aladins). I then mapped one of those computers "relatively closely" to a Subsurface Buhlmann 30/90. As a non-deco diver I ignored the GFlow setting and left it at 30 and simply fiddled the GFhigh until Subsurface gave we NDLs throughout the complete dives that where within several minutes of my real dive computer. My guess at 30/90 could be wrong. But it matches close enough?

The next claim is that my computer is more aggressive than you want to do for multiple dives. This is good info for me. How far back do you (and others) think I should dial it? Warm water dives, no current, great viz, 3,4,5 or 6 one hour dives a day.

I think you're not too far off for the dives and conditions that you describe. A GF High of 90 is perhaps a bit on the aggressive side when you do that many dives per day, I'd dial it back to 80 if I were in your position (I use 85 in warm water, but generally don't do more than three dives a day). And you are correct as far as I understand this, for the dives that you are doing the GF Low is pretty much irrelevant as long as you aren't diving deep and getting close to deco. But since you're doing many shallower dives, I'd avoid deep stops, as they only push nitrogen from the fast to the slow compartments, and you already have plenty of loading there. So a GF Low of 40 might be appropriate, in my opinion. But your mileage may vary.

 

[KeithG]

I think you're not too far off for the dives and conditions that you describe. A GF High of 90 is perhaps a bit on the aggressive side when you do that many dives per day, I'd dial it back to 80 if I were in your position (I use 85 in warm water, but generally don't do more than three dives a day). And you are correct as far as I understand this, for the dives that you are doing the GF Low is pretty much irrelevant as long as you aren't diving deep and getting close to deco. But since you're doing many shallower dives, I'd avoid deep stops, as they only push nitrogen from the fast to the slow compartments, and you already have plenty of loading there. So a GF Low of 40 might be appropriate, in my opinion. But your mileage may vary.

Good feedback, thank you. BUT my troglydite computer does not allow fiddling with GF settings so I currently have no idea what "dialing it back to 80" means in real life.

I will use this info as a take away and compare the NDL readings from past dives based upon Subsurface calculations at Buhlmann 30/80 and 30/90 and 30/100 and then try to figure out what NDL behaviour I want to incur.

P.S. A short while ago I started a thread asking if my dive computer was obsolete. It appears that I maybe asked the wrong question? Maybe I should have asked if it was too aggressive for a vacation diver?

 

[DevonDiver]

1) The first red flag I saw was repeated sea-saw behaviour. In many (most / all?) of your dives you did one or more 10 to 25 foot dips. I have been told this seesaw behaviour is bad. I am unaware of how this affects various algorithms or nitrogen loading.

RGBM is adaptive to certain 'red flags'. It's a well known feature of Weinke's work.

When contrary dive behaviour is evident, the algorithm reduces the permissible surfacing gradient (hence the name 'Reduced Gradient......')

Saw-tooth dive profiles are right at the top of that list of contrary behaviours; along with fast ascents, re-descents, omitted safety stops and too brief surface intervals.

In short... RGBM penalizes sloppy or dangerous diving behaviour by adding mandatory conservatism in the background.

This is one reason the algorithm gets so many complaints about being 'too conservative'..... but in many cases, seemingly extreme conservatism is just indicative of sloppy, imprudent diving.

From my experience, it can appear foolish to jump on the 'blame an algorithm' bandwagon for reasons just like this. Human factors must be considered first, before the pure math.

RGBM a very good model for novice (and some experienced!) divers... it keeps them safe when they're diving imprudently, whether by choice or through ignorance.

Predictions and Assumptions

Thanks @giffenk for running the OP's profiles through Subsurface. The results aren't unexpected at all.

As the OP (@stepfen) earlier stated "you don't know my diving style"; well, it's exactly as I'd predict for a novice; it also fits with the many 'clues' in your story and the outcome that occurred.

Certain behaviours triggered the dive computer to respond/adapt in an equally predictable and understandable manner.

The dive computer simply adapted to preserve your safety, according its programming.

Choices:

1) Replace the computer with one that won't adapt to preserve your safety.

2) Improve your diving so that a computer doesn't have to behave conservatively in the first place.

I'm surprised so many in this thread opt for the 'change the computer' solution. That's why I feel denial has an impact.... after all, it's not easy to consider that the problem stems from you.

As @doctormike has mentioned several times in this thread....human factors like 'normalization-of-deviance' should be the first possibilities examined when diving incidents and accidents occur...

A bad workman always blames his tools....as do imprudent and/or ignorant divers.

On Conservatism

5-6 dives per day, repeated over multiple days... especially for a vacation diver who doesn't normally dive frequently... is very aggressive regardless of what algorithm or conservatism is used.

Personally, I'd be increasing my conservatism setting for anything above x2 dives per day. That'd be on top of any conservatism added for other DCS susceptibility factors that may be present. Dives #3 and onwards would be on max conservatism.

I also wouldn't be doing heavy (3+ dives) diving for more than 3 day in a row. Lighter diving (1-2 dives) I'd not do more than 5-6 days consecutively without a break day.

Diving computers and their algorithms have a ridiculously high standard of safety in preventing decompression sickness.

Nonetheless, Darwin's Law accurately predicts that there'll always be a proportion of divers who'll decide to push their decompression instruments (or ignore or 'trick' them) to the extent that they'll still end up injured with decompression sickness.
Like Lemmings... It's bewildering...

There's no such thing as an undeserved bend.

 

[RainPilot]

Good feedback, thank you. BUT my troglydite computer does not allow fiddling with GF settings so I currently have no idea what "dialing it back to 80" means in real life.

I will use this info as a take away and compare the NDL readings from past dives based upon Subsurface calculations at Buhlmann 30/80 and 30/90 and 30/100 and then try to figure out what NDL behaviour I want to incur.

P.S. A short while ago I started a thread asking if my dive computer was obsolete. It appears that I maybe asked the wrong question? Maybe I should have asked if it was too aggressive for a vacation diver?

If you use your DIY pressure pot, put your computer into real deco ie a 20 min or longer obligation. If you then follow the stops it recommends, you should be able to determine a GF low comparison.
It won’t map directly and since it’s not actually Buhlmann it will vary on repetitive dives etc but you will be in the ballpark.

 

[Centrals]

Only saw it once. My wife was hanging below me at 120' and went into deco. It cleared before we hit 60'.

Point is that we were on the same dive as everyone else, not in our own limited NDL world.

She did not hang around and cleared it by ascending instead of letting the deco penalty built up.
But the OP did it the other way ie. by increasing the deco obligation on a very slow ascend. So why would a change of computer be beneficial in this case?

BTW, I don't share my ndl with anyone!!

 

[boulderjohn]

I am trying to understand how to make sure I am conservative enough as I get older.

When you get into true decompression algorithms, where your computer is recommending multiple stops at varying depths, the word "conservative" begins to lose meaning because different people differ on what it means to be conservative. For some, keeping you deeper longer is more conservative, and to a degree that is correct, but only to a degree. At some point staying deeper longer becomes counter-productive, for your the on-gassing of the slower tissues more than makes up for any benefit of the deeper longer stops. If you are doing those deeper longer stops, you need to compensate for that further on-gassing by doing longer shallow stops. A low number on the first GF setting gives you deeper stops; a high number on the second gives you shorter shallow stops. Is that what you want? Would you consider it to be more conservative?

 

[stepfen]

To be honest to you guys right now I am not that much interested to learn/compare/duplicate different algorithms - all these fall way too much outside my current level and to be frank I don't see the point as my target is no deco dives.

If you can try switching Subsurface to VPM + 5 and see if the two "dives" are a closer match. If you do this let me know the result.

My subsurface has VPM only up to +4 as discussed by others earlier.
VPM+4 went to deco much earlier i.e. at about 7minutes (25m) in my dive compared to my computer that went to deco at 26minutes (20m). BUT by the time I reached 3-4 meters (remember my slow "ascent") with VPM+4 I had "only" 7 minutes deco to go compared to 30+ minutes with my computer.

 

[DevonDiver]

BUT by the time I reached 3-4 meters (remember my slow "ascent") with VPM+4 I had "only" 7 minutes deco to go compared to 30+ minutes with my computer.

RGBM was kinda spawned from VPM. Bruce Weinke, the author of RGBM, worked on the VPM team originally.

What Weinke did with RGBM was to construct adaptive gradients (automatic conservatism) where certain behaviours (theorised to produce ^ bubbles) were present.

In a nutshell, your computer automatically dialled up the conservatism to max after it identified some of those bubble-promoting behaviours occurring.

Fast ascents, saw-tooth profiles and re-descents are hypothesised to have a profound effect on potential bubble formation.

VPM-B +4 isn't hugely conservative. Most divers would be using +3 as 'standard' baseline... or +2 for those with a very good grasp of their DCS susceptibility. +1 is considered hyper-aggresive... a setting only Navy SEALs should be using.

The +1/+2/+3 etc between VPM-B and RGBM (as implemented on most recreational computers) are NOT comparative.

With RGBM, 0 is standard.
1-5 reflects increasing conservatism.

With VPM-B, 3 is standard.
4+ adds conservatism.
2- goes more aggressive.

Assuming some 'red flag' behaviourals triggering the 'reduced gradient' implementation on RGBM... in addition to an aggressive multi-day mission.. I'd expect RGBM to obligate substantially more deco than VPM-B at a moderate conservatism setting...

 

[KenGordon]

For a laugh try entering some horrible bouncy dives into a vpm or GF planner. You will find that they get the same deco as a sensible profile. The commercial dive computers, as described by DevonDiver above, try to mitigate such diver mistakes. This means you cannot compare them with vpm or GF at all really.

Is there planning software for your computer? If not maybe try entering an equivalent series into the Suunto planner and see how the ceiling looks on the last dive.

Your main takeaway from this should be that slow ascents are not always appropriate. Ascent rates should be different at different depths, quicker to begin with and slow shallow, and especially the last few metres.

Even without the slow ascents you are close to the edge, try planning the dive with whatever planning feature your computer has just before the dive and have an idea of how long you can stay down.

Also understand that as you get close to the NDL the actual remaining time becomes very sensitive to depth. Moving up a few metres may double or triple the apparent time available, similarly going deeper will shorten or eliminate it. This means that 'flying' the NDL is impractical towards the end of a dive.