Do I really need a computer?

[rstofer]

I don't think there's anything wrong with it.

The problem I see is twofold: First, making a mistake. Second, any NDL you memorize only applies to the first dive and unless you can memorize every RNT versus SIT, getting the ANDL for repetitive dives takes arithmetic and the result needs to be noted somewhere. The slate comes to mind.

Then there is the problem of the table du jour. Sometimes PADI, sometimes NAUI; each has a different NDL. My family uses PADI, I prefer NAUI because it provides some deco information.

Richard

 

[CoralSeaMan]

Doesn't one of the training agencies use only computers in training? If trained that way, a computer is necessary.

 

[Rick Inman]

The problem I see is twofold: First, making a mistake.

Really? I spent a day in the chamber dong a table 6 and my computer said I was clear.

Second, any NDL you memorize only applies to the first dive and unless you can memorize every RNT versus SIT, getting the ANDL for repetitive dives takes arithmetic and the result needs to be noted somewhere.

Hypothetically, what if you came out clean and didn't deco so much on the surface?

Then there is the problem of the table du jour. Sometimes PADI, sometimes NAUI; each has a different NDL. My family uses PADI, I prefer NAUI because it provides some deco information.
Richard

How much difference is there really between the different tables? The fact that there IS a difference should tell you something..:cool2:

 

[Apollon]

I appreciate all the info, very enlightening.
What I've been doing as a rule is always do a series of stops on almost every full length dive.
If I dive to 100 feet let's say for the max ndl, then my first stop would be at half that depth at 50 feet. I hold this for 1 minute then go to 40 for a minute then 30 for 2 or 3 minutes then 20 for 4 and 10 to 15 for at least 3-5 or till my air runs down to no less than 200-300.
I do the depth averaging thing to some degree but don't push the limits on what I think is safe.
I also memorized the tables fairly easily by using the 120 rule. PADI is actually about a 110 rule (actually it's not very consistent in this regard).
There are a few glitches in there, 50 being 60 and 60 being 50 (in the 120 rule.

Once I dove of the backside of Catalina at Farnsworth. It's a deep dive if you want it to be. We went down to 130 and stayed the absolute max according to my now lost Suunto. I was planning to do a series of deep stops, the first at 70 and going up in 10 foot increments. The computer totally freaked out and wanted to send me staright up to 15 feet. I ignored it and continued on with the scheduled stops. I was diving with a GUE trained friend of mine and there isn't a dive he will do without stops and gas management. When I finally got to my 15 foot stop the computer wanted me to stay there for something like 15 minutes which was absurd. We finished our stop in 6-7 minutes, something like that, and the computer froze me out. For the next dive I my buddy loaned me a bottom timer.
The very next dive after that trip was the infamous kayak dive and I've never looked back.

I'm still pretty new at this and have lots to learn. And I'm starting to think the reason the shop said I really absolutely should have a computer is because they would have made another 200-300 hundred dollars off me. They said nobody uses tables any more, they only taught them for historical value?

For the record: I'm not DIR of GUE trained, but I do like Kool-aid.

 

[orange_diver]

Here's some information for historical value only : Some divers have been known to average their depth in their brain (they say it becomes easy with practice), then add their bottom time to there average depth, and use a total of 120 as their NDL. They often change their exit strategy from, "head straight up to 15' for 3 mins", to stopping at 10' intervals for a minute on the way up, and then spending a long time moving up the final feet. No computer, long bottom times and they come out nice and clean.

what else are you gonna spill the special herbs and spices used by KFC?

but seriously, no special sauce here but just wanna chime in in case anyone thinks they should dive like this w/o the proper training and understanding behind it -- "Rick's rule" is a tad aggressive at certain depths... i.e. just one example is we don't stay at 80' for 40 mins.

 

[DocWong]

While most divers I know do dive and follow what their computers tell them to do, I've found it quite liberating to dive with my instruments on "Guage Mode."

IMO the safety factor is about a wash between knowing your tables vrs diving a computer as there are advantages and disadvantages to both.

When I first started diving we didn't even have BCs, computers or even tank pressure gauges. We had to know what our "NDLs" were. Of course you just dived until it was hard to suck air and then you pulled this valve on the back of your tank to get the reserve air and did your ascent.

Then I dived computer for 200 or so dives. It certainly was nice to just follow the computer on those 4-6 dive multiple dive days in the caribbean.

Then getting back into diving cold water in Northern California, I drank the Kool-Aid and never looked back. (joke referring to taking GUE's (Global Underwater Explorers | Global Underwater Explorers) Fundamentals of Diving, training with preset equipment configuration, high level of in water skills and dive knowledge, planning, etc and controversy over some overzealous adherents )

I already had a computer, it was a SUUNTO Stinger that I just put in gauge mode. At first it was a bit awkward for me, but after awhile I began to see the advantages of diving that way. For me, it gives me a better sense of time and depth, how long I can stay down, etc. And it makes planning much easier for the dive.

Here's a table that pulled it all together for me:

DIR-diver.com - Using the min deco table

The table is useable for diving AIR or EAN 32 (32% oxygen, 68% nitrogen), though in the DIR world diving on air is rare, except when you're practicing in the pool on skills.

It also means that withoug exception you're doing at least a 3 minute stop at 20' and a 3 minute stop at 10'.

 

[White Knight]

Let's make this really simple: Technology baby!! Go with it.

 

[rstofer]

but seriously, no special sauce here but just wanna chime in in case anyone thinks they should dive like this w/o the proper training and understanding behind it -- "Rick's rule" is a tad aggressive at certain depths... i.e. just one example is we don't stay at 80' for 40 mins.

I guess I'm a little uncomfortable discussing deco strategies in a basic scuba forum. Mostly because I don't understand them and have no training in the black arts. Of the 'ad hoc' methods recently described, where is it written that they have been tested on thousands of divers over decades of use? In fact, I thought recreational diving, by definition, didn't use deco. The idea was that you could, at any time, make a direct ascent to the surface without stopping.

However, 80' for 40 minutes is a legitimate table dive using the NAUI tables but it does have a mandatory 5 minute deco stop at 15'. NAUI Dive Table 1 I prefer to think of the mandatory stops as an 'oops' strategy, not something I would plan.

I think it is pretty well established that computers tend to be conservative. I also think you need to have both feet on one side of the river. Either dive your computer or dive the tables. I'm not sure mixing and matching is a good strategy.

Richard

 

[orange_diver]

I guess I'm a little uncomfortable discussing deco strategies in a basic scuba forum. Mostly because I don't understand them and have no training in the black arts.

Agree that these "black arts" are best not learned on the internet. There's a lot left unsaid here and on all the DIR websites and papers that need to be learned in person from an expert in the theory and application.

Of the 'ad hoc' methods recently described, where is it written that they have been tested on thousands of divers over decades of use?

Can't speak for other "ad hoc" methods to use your term, but in my opinion ratio deco takes the best parts from all the working models and latest theories: Buhlmann, VPM, RGBM, bubble mechanics, oxygen windows, etc and discards what doesn't work.

It has been tested by hundreds of divers doing all sorts of recreational and technical diving on thousands or tens of thousands of dives. That being said, all decompression theory is fuzzy at best. You may be surprised to learn that all decompression models (including those used in computers) are based to some degree on initial experiments using goats to decompress and bubbles in snake's eyes. I'm not joking.

In fact, I thought recreational diving, by definition, didn't use deco. The idea was that you could, at any time, make a direct ascent to the surface without stopping.

We believe that all diving is decompression diving. And stops at certain depths are mandatory. Yes, in an emergency a nice controlled 30 fpm ascent should be fine, but i wouldn't want to test it out if i've been at 100' for 20 min on air, especially in cold water. Have people done it and walked away? Sure. But others like rick have been bent on perfectly fine computer profiles.

However, 80' for 40 minutes is a legitimate table dive using the NAUI tables but it does have a mandatory 5 minute deco stop at 15'. NAUI Dive Table 1 I prefer to think of the mandatory stops as an 'oops' strategy, not something I would plan.

First of all, those Naui tables seem to be based on navy tables. Let's examine the navy subjects used to determine those NDL limits. Young, incredibly fit men with excellent cardio. Is that your normal diver? not that i've seen. Therefore those tables can be a little aggressive for most. Given that, at 80' for 40 min, the Naui table is basically saying "you are 5 minutes over what your NDL is, and you must do 5 minutes of deco". It's a fallacy to think you can blow that off. Will it bite you in the ass? Maybe not. But maybe yes.

I think it is pretty well established that computers tend to be conservative. I also think you need to have both feet on one side of the river. Either dive your computer or dive the tables. I'm not sure mixing and matching is a good strategy.

Well...we dive neither.

 

[orange_diver]

I appreciate all the info, very enlightening.
What I've been doing as a rule is always do a series of stops on almost every full length dive.
If I dive to 100 feet let's say for the max ndl, then my first stop would be at half that depth at 50 feet. I hold this for 1 minute then go to 40 for a minute then 30 for 2 or 3 minutes then 20 for 4 and 10 to 15 for at least 3-5 or till my air runs down to no less than 200-300.

11- 14 min? I think you are actually spending way too much time on your safety stops.