Is a Computer essential kit?

[boulderjohn]

But they do work well don't they?

According to whom?

Tables were created as a result of research, sometimes years and years of research. The goal was to find the most reliable algorithm, something as close to the middle of the range of possibilities between absurdly conservative and probably going to get DCS. If you follow the results of that research carefully, the odds of your getting bent are extremely slim. The more you stray from them, the closer you get to the edge of safety, the greater your chance of getting bent.

My own personal research into NDL diving practices indicates that divers who begin their ascent prior to NDLs have a wide range of possible safe ascent strategies. For example, the PADI RDP was created using the 60 FPM ascent rate then in common use. I was told by someone at PADI headquarters that their research did indeed show that ascending at that rate from these limits was safe, but it was OK to ascend at slower rates, too. That is why the language they use says to ascend at a rate no faster than 60 FPM--meaning slower is OK. If you look at DAN language on ascents, you see that same vagueness--they tell you not to ascend too quickly, but they don't tell you what would be too slow.

People who use the methods some advocate for planning multi-level dives with tables are not using valid processes, but there is a good chance they are OK doing it because they have not moved close enough to the edge of safety. They might be darn close to that edge, but they have no way of knowing how close because the tables cannot be used to calculate that. In contrast, a computer can be used for that, because it does make those calculations. If your ascent is too slow, it will tell you. The tables will not tell you that, even if you think they do. You're really just guessing.

We will never have good data on those guess, because the percentage of divers using tables is tiny to begin with, and the percentage using them incorrectly to plan multi-level dives is undoubtedly only a tiny percentage of that tiny percentage.

 

[Eric Sedletzky]

Examples?

The only procedures I know that have been used with standard tables are not approved by the people who made the tables and other decompression experts.

Those same people that claim they can use a table and make a multi level dive out of it by depth averaging also claim that all their dives are now “decompression” dives.
What does that tell you?

 

[Hoag]

I agree with you; on the last sentence that is. One thought though... If the answer to all these (kinds of) questions is 'whatever YOU prefer', then why ask questions at all?

I think that in a case such as this one, the comments about really cheap computers (the price of which will probably even be lower than the separate components of the alternative) might inspire the OP to look for a cheap basic computer and take advantage of the added safety. No one suggests the Shearwater Perdix AI here, but a basic Suunto Zoop or Mares Puck Pro or Cressi something. A console that has a bottom timer, or a waterproof Casio watch might be more expensive, to begin with. And that's not even considering all the brainpower, dive table user mistakes, and what have you.

And that sir is the Dive and let dive philosophy in a nutshell. You don't have to agree with me nor do I expect everyone to agree with me. That is totally OK.

As to "then why ask questions at all", seeking out advice is a good way to increase your knowledge so that you are better equipped to make an informed decision.

 

[Wibble]

Those same people that claim they can use a table and make a multi level dive out of it by depth averaging also claim that all their dives are now “decompression” dives.
What does that tell you?

That decompression algorithms are just that, algorithms.

People dived with tables -- as in literally using tables + timer + depth gauge -- because they'd not been integrated together into a "dive computer". More importantly a "dive computer" that worked, was easy to use and was reliable.

Tables are still used today for learning the patterns; dives are "generally" dived against the computer; when computer says ascend, you ascend.

Now the $64k question: are we nowadays doing far more deeper dives running for longer run times AND not getting bent than, say, 30 years ago?

(Can't help thinking about everything I've read about the Andrea Doria wreck. Something like 70m/230ft which is easily done nowadays with hardly any risk (stupidity aside). In other words it's pretty easy and risk free to do a dive like that and is certainly not considered a highly specialised pinnacle dive pushing boundaries.)

Ooops, slipped way outside of basic scuba again...

 

[AfterDark]

According to whom?

I heard it thru the grapevine.

 

[AfterDark]

Those same people that claim they can use a table and make a multi level dive out of it by depth averaging also claim that all their dives are now “decompression” dives.
What does that tell you?

Every dive is a cause for decompression. Do they mean decompression stops are required? That is the question.

 

[Eric Sedletzky]

That decompression algorithms are just that, algorithms.

People dived with tables -- as in literally using tables + timer + depth gauge -- because they'd not been integrated together into a "dive computer". More importantly a "dive computer" that worked, was easy to use and was reliable.

Tables are still used today for learning the patterns; dives are "generally" dived against the computer; when computer says ascend, you ascend.

Now the $64k question: are we nowadays doing far more deeper dives running for longer run times AND not getting bent than, say, 30 years ago?

(Can't help thinking about everything I've read about the Andrea Doria wreck. Something like 70m/230ft which is easily done nowadays with hardly any risk (stupidity aside). In other words it's pretty easy and risk free to do a dive like that and is certainly not considered a highly specialised pinnacle dive pushing boundaries.)

Ooops, slipped way outside of basic scuba again...

I don’t know if you missed my point.
If they were so convinced that they could outsmart the table and turn it into a multi level tool by depth averaging then why not leave it as an NDL dive?
Turning all their dives into deco dives (however light they are) none the less, deco dives. Stops at 30 20 10 on each and every dive as protocol leads me to believe that they really don’t know and it’s a built in safety margin.
So no, you can’t make a table into a multi level dive tool and think you can take it to the max of NDL. If you want to do that get a computer.
For the dives the OP wants to do, it is shallow enough that he will not get anywhere close to NDL on a table or computer, so a square table is fine.

 

[Gareth J]

Examples?

The only procedures I know that have been used with standard tables are not approved by the people who made the tables and other decompression experts.

The BSAC88 tables work for multilevel dives. They are also designed for altitude divings.

Whilst we still teach the 88's, and the Nitrox variant. We don't teach multilevel diving using the tables because it is thought a pointless exercise. Tables are really taught because they are the easiest way of demonstrating the effects of depth (pressure), time, surface intervals and the effects of altitude.

Most students are using PDC's, their own, or a loan item from the branch or buddy/instructor.
If I'm diving with a student or an Ocean Diver, and they don't have a computer. I just lend them a Zoop, I've normally got one kicking around in the bottom of my bag.

 

[Cheizz]

I'll just drop this here:

 

[boulderjohn]

Every dive is a cause for decompression. Do they mean decompression stops are required? That is the question.

As some know, a few years ago I wrote an article (with a lot of help from Simon Mitchell) on the current state of research on ascent strategies for decompression diving. I then did research with the goal of doing the same for NDL dives. I never wrote the second article because I could not find anything close to enough of the research necessary to form an opinion. The common slow-ascent-to-safety-stop-depth has been studied forever, but there is next to nothing on alternative approaches. The few studies that have been done are flawed and not highly regarded.

The one true takeaway from my research is that there is a definite difference between true NDL dives and true decompression dives, with a fuzzy transition in between (the realm of required safety stops and so-called "lite deco"). Once you have incurred a decompression obligation, your ascent rate matters--go too slowly and you will pay for that slow ascent with added decompression time in shallow water. With an NDL dive, it does not seem to matter how slowly you ascend, as long as you don't linger deep enough and long enough to get into the decompression zone. That is what makes multi-level diving possible--if you leave 100 feet with even only a few minutes of NDL left, you can linger at various depths and end up being just fine with a total dive time as much as an hour beyond the limits of the tables.