The old tables vs computer argument

[redacted]

No more tables and no computer
My current evolution is no more tables and no computer. I use a methodology called "Ratio Decompression" in which I can extrapolate my ascent schedule in my head based on a ratio of 1:1 - 1 minute of deco for every 1 minute of bottom time for nitrox and trimix once the Rule of 120 or Rule of 130 has been exceeded and we are no longer on a slide-pause "direct" ascent schedule called "minimum deco."

What do you do for subsequent dives?

How would you conduct 4 or 5 dives a day to a depth of 80 to 100 FSW on EAN32?

 

[Trace Malinowski]

The thing is Blackwood and I, never having met nor dove together, could hit the water right now and be on the exact same page. I'm fine with S-curving the deco. I just used a pragmatic deco in my example, so he and I could agree to a plan for depth and bottom time, agree who leads, who follows, what are the responsibilities of each diver. We could agree how to handle a push to extend the time if we were having too good a time. All we'd have to do is show up with the same gas (within a range) ... in fact, he could have Trimix 18/45 in his tanks and I could have Triox 21/35 and we could still do the same dive as long as we matched deco gas. If we lose deco gas, we just double the stops. If we make a second, repetitive dive, we just double the stops. After a thorough dive plan that can be discussed within a few minutes, we'd be on the same page for equipment and safety checks. There is a very high probability we could do a major dive together with precision never having met due to our training, but we'd be smart enough to make one or two practice dives together before going full tilt.

We both capable of doing the dive independently, but the strength of team is that we can back one another up. If Blackwood was leading and it was his job to recheck the deco prior to ascent, after we decided on 10 extra minutes on the bottom during the dive, and 15 extra minutes inside a structure at the top of the wreck, and his gauge/timer failed, I could take over. At the gas switch, I'd pull out my notebook, scribble a new plan quickly, and show him. If we agreed, then we would move together signaling the time to move and the time to level off and deco simultaneously. If we needed to deploy a DSMB, he could pull it out and launch it while I calculated our ascent. We would probably have decided on a minimum of 3 minutes at the gas switch, so out of an entire dive, we could do whatever we wanted, more or less, and take just a minute or two to plan an ascent. Deco just isn't hovering motionless bored out of your mind. On one my my favorite 150 foot wreck dives, we usually spend an hour on the wreck between 150 and 60 feet beginning deco as we explore the forward hatches and bow, then we swim or scooter over to a shoal, ascend up the wall of the shoal, swim or scooter as if making a wall dive, and ride a wicked cool current on a fast druft dive on top of the shoal back to our anchor line. We play on the shoal under the boat for a while, then complete our 20 and/or 10 foot stops hanging mid-water and back to the warmth of the deck.

 

[Trace Malinowski]

What do you do for subsequent dives?

How would you conduct 4 or 5 dives a day to a depth of 80 to 100 FSW on EAN32?

Those are good questions. Normally, for a repetitive dive we would simply double the stop times.

For decompression or technical dives, we would also probably only make one or two dives per day.

Suppose we were teaching and making dives all day in those depths, or diving off a liveaboard and making multiple dives, on nitrox 32, our Rule of 120 tells us that for minimum deco (direct ascent) with deep safety stops for one minute, if our depth and bottom time are not greater than 130 we can follow our recreational plans of pausing at 50% of depth. So, we can stay at 80 feet for 50 minutes and 100 feet for 30 minutes and still do a recreational schedule. If we are doing a multi-level dive, we can depth/time average. Anyway, stopping at 1 minute from 50 feet to the surface or 40 feet to the surface could be fine if our surface intervals were 1 hour between dives. However, we'd probably double the second dive and keep it 2 minute stops for the 3rd, 4th or 5th dives.

To back up that thinking, I checked my logic with V-Planner software (have it on PC, notebook, and blackberry) anmd the stops required for the first dive are 2 minutes, then between 6:20, 7:20 or 8:20 for each subsequent dive. Doubling our stops will be adequate giving us 10 minutes of safety stops every dive.

Making so many dives is something I prefer not to do, but it is possible. I do it as an instructor, but not in my geberal diving.

 

[Puffer Fish]

It's actually quite simple in application, though reading it for the first time can be a lot to digest. I have the advantage of being taught it by Andrew Georgitsis, who basically formalized the system.



RD obligations are essentially envelopes of a few models (Buhlmann and VPM). By only using a select set of gases, one is able to recognize trends and apply them. Diving "best mix" or something won't necessarily work, and is outside of the scope of this simplification.



As Trace mentioned, often the team will give the hand signals at the same time. It's everyone's responsibility to keep up. It's the deco captains responsibility to make sure everyone is on board.

If the deco captain starts making ridiculous calls, you can say "no", discuss it, or even take over if you want to. It's not like you just turn off your brain and start blindly following him (doing so can get you hurt, to which kevrumbo can attest).



The same methodology is easily applied to "recreational" diving via the 120/130 rules (that Trace mentioned), or by counting back from the 150' setpoint. In fact, as long as you stay within the Deco Limit, it's exceedingly simple: 30FPM to 1/2 max depth, and 10FPM thereon, stay out for 90 minutes and do it again. No pressure groups, RNTs, adjusted NDLs etc. to worry about.

Interesting method... would not work for a large portion of the diving done in Florida, but it is an interesting mental exersize. It does, in fact, produce a reasonable dive profile...

It's down side is that it is a static system...but computer technology is changing as more is learned about bubble generation (acutual measurements, not theory). They are not "there" yet, but are moving fairly quickly.

We know now that slow accent rates from deeper depths increases, not decrease your nitrogen loading..we know that breathing rates effect nitrogen absorption..that going from warm to cold and back to warm are major issues.

I would guess we are about two generations away from having all the major factors accounted for that are outside the specific human.

If you look at the latest and greatest, you get work load NDL adjustments, temperature adjustments, and optimized accent rate changes with depth...

Is all this safer? Time will tell, and looking at a few people will not answer that.

At some point, it still comes down to trusting what it says and following it or not following it. So far, I have been impressed with having around 30% more bottom time and the ability to have shorter surface intervals. And modeling the dives afterwards would seem to indicate it is at least as safe as any other method.

 

[Trace Malinowski]

Interesting method... would not work for a large portion of the diving done in Florida, but it is an interesting mental exersize. It does, in fact, produce a reasonable dive profile...

It's down side is that it is a static system...but computer technology is changing as more is learned about bubble generation (acutual measurements, not theory). They are not "there" yet, but are moving fairly quickly.

We know now that slow accent rates from deeper depths increases, not decrease your nitrogen loading..we know that breathing rates effect nitrogen absorption..that going from warm to cold and back to warm are major issues.

I would guess we are about two generations away from having all the major factors accounted for that are outside the specific human.

If you look at the latest and greatest, you get work load NDL adjustments, temperature adjustments, and optimized accent rate changes with depth...

Is all this safer? Time will tell, and looking at a few people will not answer that.

At some point, it still comes down to trusting what it says and following it or not following it. So far, I have been impressed with having around 30% more bottom time and the ability to have shorter surface intervals. And modeling the dives afterwards would seem to indicate it is at least as safe as any other method.

It's employed by the best divers in the world and was developed by them in the state of Florida. Many of us have used it in both the caves and the Keys. My last trip to Florida found me in a long penetration of the Spiegel Grove. Silent World Dive Center is the best operator for those of us who are DIR, IMHO.

The fact that you do load at depth is why we "Get out of Dodge" at 30 feet per minute and pause at 80% of ATA's/75% of depth where off-gassing begins (50% of depth for recreational dives).

Breathing lighter gases such as Trimix reduces breathing resistance. Increased breathing resistance increases CO2. Increased CO2 increases stress. Stress produces catecholomines. Catecholomines produce hydrogen peroxide. Hydrogen peroxide can trigger seizure. The harder one works during a dive, the more energy is required, the more energy is required, the more oxygen is needed. As the diver breathes a heavier gas like air, the more work is required to get oxygen from it and the more CO2 is produced. The more CO2, the more stress ... the process continues. CO2 is the sneaky culprit that may be responsible for more diverr deaths than originally thought. Divers who are better trained and who are physically fit produce 50% less CO2. Divers with proper training wear the right exposure suits to stay warm - often this may be a drysuit even in warm water depending upon the parameters of the dive.

One thing about bubble mechanics, if you keep the tension on the bubbles longer, if you do take a DCS hit, it is likely to produce smaller bubbles at shallower depths than big bubbles possibly decreasing the severity of the injury.

The greatest advantages is that buddy teams can remain together and they won't have different ascent schedules being given to them by different computers. There is no computer to lock you out and you can always check this method with Deco-Planner or V-Planner. If the software tells you a variable that you think is more conservative, then great. However, those of us who do ratio deco are usually anywhere between a +2 or a +5 (possibly greater) conservation factor of safety when compared to the software and we can stay as long as we have gas reserves.

 

[Peter Guy]

Back to the OPs question:

How do table divers manage "real life" diving? As far as I can tell, not so well! Which is why the switch to computers of one form or another (either on your wrist or on your laptop).

Ratio Deco and its first cousin, Minimum Deco are amazingly simple to learn and use -- honest. If I can use them safely, and I can and do, anyone can -- in fact it is a lot easier to use them than to use those god-forsaken tables.

As far as doing depth averaging, especially during a recreational dive, it is pretty trivial -- and really not all that hard (or perhaps not all that important) at all. You know what your max depth was (see, it's right there somewhere on your computer/bottom timer), you know if you stayed down around there for the whole dive or if you wandered up to where you are when you decide to ascend -- then just guestimate it (is it half-way between max depth and where you are or closer to max depth?). Start your stops at the 50% point and do 1 minute per 10 foot ascents from there. It is truly NOT "rocket science" and, as Trace mentioned, when you dive with people who use the same "program" the dive is easy.

For example, the end of June I was on a boat with 20+ others who all had similar, but not the same, training backgrounds. We mixed and matched buddies/teammates at will and it was easy because everyone was on the same program. Having had to "soothe" my poor Suunto a time or two, I can attest to this being a much better way to dive. (BTW, I did 10? dives in 2 1/2 days, as did most of the others -- no problem with repetitive dives, we either had a good SI or doubled our stops.)

 

[Puffer Fish]

As agreed, it does produce a very conservative dive profile... problem is, that level of conservative diving is not always available to the average diver. Bluntly, many could not use it, even if they wanted to.

Remember, we are in "basic scuba".

You get on a boat going out diving... the boat plans to go to a specific site.. but when they get there, someone is already there, the wind is blowing the wrong direction.. something stops them.. so they go to another site...this one is deeper...you now make your dive.. with say 33% nitrox to around 90 ft....but they used up time going to this new site, so you want the maximum bottom time, and they want to get back for the afternoon run...which leaves a problem.. you can take longer, but your surface interval will be shorter.. or you can dive shorter and have that one hour (but no longer) surface interval. I choose to have the longer dive, with a shorter surface interval...your system does not allow that.

Situation two.. you are a spear fisherman... you see a really large fish and shoot it.. but you get into a major physical battle...you loose track of how deep you got.. you are worn out...what to do now? The computer actually knows that you have been working and greatly reduced your NDL, so you don't add a chamber ride to being tired.

Note: Increased circulation increases your nitrogen absorption.. several laws of physics involved here, backed up by actual bubble measurements...

Your system hopes that it so conservative that you cover this event.. computers can actually adjust for it.

You plan a dive for say 80 degree water, but when you actually do the dive, the temperature at the bottom is 74 (that actually happen last July in the northern gulf)..suddenly, your three mil is not so warm...

The computers can be made to adjust for sudden, unexpected changes in a way that doing math in your head cannot. However, if you have lots of time, are on no schedule, it still works well. Trouble is, that is not the majority of the diving being done..

And diving very conservatively ends up meaning a lot of missed bottom time and lost dives.

I don't think anyone want to get a case of DCS (at least I hope not), but doing every dive with a huge extra safety margin over what is already hugely safe, does not work that well in a lot of places.

Nor are the majority of divers ever going to be doing team diving...nothing wrong with it, just that it will never be more than a small percentage of people.

It's employed by the best divers in the world and was developed by them in the state of Florida. Many of us have used it in both the caves and the Keys. My last trip to Florida found me in a long penetration of the Spiegel Grove. Silent World Dive Center is the best operator for those of us who are DIR, IMHO.

The fact that you do load at depth is why we "Get out of Dodge" at 30 feet per minute and pause at 80% of ATA's/75% of depth where off-gassing begins (50% of depth for recreational dives).

Breathing lighter gases such as Trimix reduces breathing resistance. Increased breathing resistance increases CO2. Increased CO2 increases stress. Stress produces catecholomines. Catecholomines produce hydrogen peroxide. Hydrogen peroxide can trigger seizure. The harder one works during a dive, the more energy is required, the more energy is required, the more oxygen is needed. As the diver breathes a heavier gas like air, the more work is required to get oxygen from it and the more CO2 is produced. The more CO2, the more stress ... the process continues. CO2 is the sneaky culprit that may be responsible for more diverr deaths than originally thought. Divers who are better trained and who are physically fit produce 50% less CO2. Divers with proper training wear the right exposure suits to stay warm - often this may be a drysuit even in warm water depending upon the parameters of the dive.

One thing about bubble mechanics, if you keep the tension on the bubbles longer, if you do take a DCS hit, it is likely to produce smaller bubbles at shallower depths than big bubbles possibly decreasing the severity of the injury.

The greatest advantages is that buddy teams can remain together and they won't have different ascent schedules being given to them by different computers. There is no computer to lock you out and you can always check this method with Deco-Planner or V-Planner. If the software tells you a variable that you think is more conservative, then great. However, those of us who do ratio deco are usually anywhere between a +2 or a +5 (possibly greater) conservation factor of safety when compared to the software and we can stay as long as we have gas reserves.

 

[RJP]

Treatment table 6 calls for 3 20min pressurizations. If they did a table 6 and followed up with another table 6 sometime later, perhaps they interpreted that as "6 chamber rides".

That makes more sense, and would be called "two rides" in my book.

 

[caseybird]

Nice, clear discussion of the often mysterious ratio deco. Thanks.

 

[MagicChicken]

@ Trace + Blackwood : very instructive posts.

Which agency(ies) offer "ratio decompression" training? Are there any training requirements?