Why no accurate computers?

[boulderjohn]

First dive NDLs are relatively easy to come by and compare, but they don't reflect how computers behave on repetitive dives.

Nice post!

I just want to emphasize this part because it has seemed to me that many people only pay attention to first dive NDLs and not to the rest of the algorithm, especially repetitive dives. I have seen people on ScubaBoard claim that they don't need a computer and just follow the tables, usually the Navy tables or NAUI tables (which are really the Navy tables). When you look more closely at what they are saying, what they are actually doing is following the table first dive NDLs, waiting for the same surface interval as everyone else, and then repeating the first dive table NDLs. I hope I don't have to explain what is wrong with that.

 

[Bob DBF]

The USN tables are not designed for sport diving repetitive dives.

I would like to add that the reason that the Navy Tables are brought up is that they were the only tables available to recreational divers when the sport began, and for quite a while after.

Navy divers are working divers and the tables were designed to keep the diver on the job as long as possible. If a second dive needs to be made, they have the next diver in rotation suit up and make the dive rather than do a repetitive dive. If the job takes longer, the probably would use a surface supplied diver to start with. The idea of repetitive dives is a contingency for special circumstances rather than how they normally do business.

Every decompression algorithm is a trade off depending on a divers objective. The Navy is focused on maximum initial time on the bottom, others are for multiple dives in a day, others are focused on padding safety, and so on.

Every one of the computers are extremely accurate at calculating their algorithm. Which one you choose to dive depends on what you decide is important to you, taking into account that your body may not act the same as algorithm describes. Whether using a computer or the Navy tables, I stay further away from NDL now than decades ago when I was young and fit, although the algorithm remains the same.

 

[scubadada]

Hi @Bob DBF

I used USN tables for my 1st 10 years of diving from 1970-80. When I got back into diving in 1997, I used PADI tables. I bought my 1st computer in 2002 and have never looked back

 

[Bob DBF]

Hi @Bob DBF

I used USN tables for my 1st 10 years of diving from 1970-80. When I got back into diving in 1997, I used PADI tables. I bought my 1st computer in 2002 and have never looked back

1962 - 2008 on the tables, at first because there wasn't anything else, then later because my local diving really didn't need a computer. I went to a computer because I began some some travel diving, and had the income for it. I like the computer better, and wear it even if I decide to do a table dive or two for old time sake.

 

[Belzelbub]

Nice post!

I just want to emphasize this part because it has seemed to me that many people only pay attention to first dive NDLs and not to the rest of the algorithm, especially repetitive dives. I have seen people on ScubaBoard claim that they don't need a computer and just follow the tables, usually the Navy tables or NAUI tables (which are really the Navy tablespoons). When you look more closely at what they are saying, what they are actually doing is following the table first dive NDLs, waiting for the same surface interval as everyone else, and then repeating the first dive table NDLs. I hope I don't have to explain what is wrong with that.

I’d hope you wouldn’t have to explain what’s wrong with that either. But, I wouldn’t be surprised either. With the prevalence of computers today, I could see how the use of tables could get skipped, or glossed over. When my kids were doing their checkout dives, they used computers, I was pleased to see that they also worked out their pressure groups using the tables as well.

I dove for years before I got my first computer. Way too many benefits for me to go back to just tables, though I could if needed. Main benefit for new divers is to have something along in case they get distracted and overstay, go too deep, etc. At least then the DC can guide them back up safely. Better to find out then than to work it out topside that you had a deco obligation.

 

[dberry]

@Happy Spearo
<SNIP SNIP SNIP SNIP>
Dr Richard Pyle - DCI

Very informative post mainly deleted, just to emphasize this linked story from Richard Pyle. I had never read that, or even heard much about Pyle other than his now largely discredited deep stops. Definitely an eye-opener and cautionary tale about being young and believing oneself to be immortal.

Thank you for linking that.
-DB

 

[NAM001]

What you are saying is you misread my comment.

no imsaying that your comment dies not represent what the norm considers a rec dive 60min at 100 ft is not a rec dive.

 

[tursiops]

then it would not be an 80 minute dive at 100 ft.

You need to read the posts more carefully, perhaps. He said 80 mins TO 100 ft; you are trying to change that to 80 mins AT 100 ft.
Rather different.

 

[KenGordon]

There is the family of ZHL8 algorithms for lower power processors. Uwatec Aladin Pro uses this. It has 8 compartments instead of 16 so likely takes half the power?

No, because the overhead of having a computer at all swamps the few thousand ops saved by using half the compartments. If you have less power available then the obvious thing is to reduce how often the ascent is recalculated.

 

[KenGordon]

I have dived with a few people who use two identical dive computers with two different GF setups.
Computer 1 - Normal diving, GF's
Computer 2 - Very aggressive GF's 100/100

Under normal circumstance, the dive is carried out using computer 1.
If there is an incident, gas loss, decompression gas loss, bailout, medical issue, etc. And the diver needs to exit ASAP, i.e. before running out of gas or because of some other emergency. Then computer 2 is followed, with the expectation that a bend is likely.
This follows the rule that "we can fix a bend, we can't fix drowning".
It is also known as the KYAGB (kiss your ass good bye) plan.

I do this. The idea is that in the case of a co2 hit I want out of the water ASAP and I am willing to use the fastest ascent I can reasonably expect to survive. SurfGF is no use until my last stop, mostly I am worried about getting to the last stop without running out of bottom bailout on the way. My absolute limiting factor is this bailout TTS, although I respect my non bailout TTS (Ie a shorter one).

if I had a decent primary computer it would allow for different GF numbers between CC mode and bailout mode.