computers and dive tables

[jeckyll]

1) you need to undertand your computer. So throw that thing into plan mode and then work through the tables. This is especially important if you dive in cold water. Remember that "add 10 feet for cold water" thing? Understand what you are using and set the safety factors accordingly (I found that my computer on safety factor 1 matches the "add 10 feet" thing very closely). As part of this, is your computer conservative or liberal? How does it compare to computers that someone else would be using (more important for regular buddies IMO, too much to keep in your head otherwise).

2) Don't let the computer dictate what you should do. I.E. it may let you do something that is dangerous and makes no sense. Don't turn off your brain just because you have a computer.

3) If your computer dies after the first dive, are you done for the day? If so, that's pretty sad. How do you work out what type of dive you can do if your computer were to pack it in after dive 1. Work out some contingencies and learn what you would typically have for NDL's after one of your standard local profiles. Again, IMO, you should not turn off your brain just because you've now got something electronic strapped to your wrist. (UnclePug had some great posts on dive profile and the shape of your profile, search and be merry )

FWIW, I always carry my tables (multiples) with me. I would be very comfortable if my computer died after doing dive 1 on of my standard profiles, to go back into the water and complete dive 2 and bet you $$ to donuts that I'd be just as safe as with the computer.

Enjoy your computer, just don't let it do the thinking for you, it's a rather stupid device

 

[Brandnew2Scuba]

I will never use a dive computer, well at least I don't plan on it. I like looking at the dive tables personally. I think it is good to use the dive tables so you get intimately aquainted with the limits, i also use the Navy dive tables, because I am very healthy, and I want to know what the limits really are. Not suggesting anyone do this, it is not a good idea, stick to what you learned in your certification course, bla bla bla etc. etc. etc.

You try and test the limits? Does that have anything to do with that joint before diving philosophy?

 

[*Floater*]

It seems a natural progression that if one really enjoys diving and plans to continue with the sport, one purchases a dive computer.

My question is after buying a computer do you ever look at your dive tables again? Why or why not?

Since I started using my Sherwood Wisdom I rarely if ever use my dive table. Am I missing a part of the post-dive process by sticking with the computer?

I don't look at them post dive, but I do sometimes write a table on my wrist slate and then I track my average depth and make sure I'm within the table limits. The computer I leave in gauge mode, or sometimes I leave it in computer mode just see how its algorithm likes my diving (but it goes in gauge mode anyway if I violate its limits too much).

 

[Charlie99]

And since many of my dives are square profiles anyway on wrecks then they line up pretty well.

The type of profile you dive makes a huge difference. If I did all of my diving in SE Florida and the Keys I probably wouldn't bother with a computer. Near square profile dives, usually on nitrox, when up in Boynton Beach. Down in the Keys it's generally either dives so shallow that decompression isn't an issue, or its one of the wrecks. While the wrecks are not pure square profile, they are close enough that simple averaging of the depth is a pretty good approximation.

OTOH, the typical dive profile in Maui or Cozumel is a lot easier to calculate with a computer. I have a lot of 100', 65 minute dives in my logbook, using just a single AL80 -- often getting back on the boat with 1000+ psi. They are nice safe multilevel profiles that are not particularly agressive, but which, if calculated using square profile tables, are waaaaaay off the charts.

Different places. Different profiles. Different tools.

-----------------------

In practice, having done a lot of single tank multilevel dives I don't have to explicitly plan them ahead of time on a decompression program on a PC or using a wheel. After a while you end up repeating more or less just 4 or 5 profiles and can tell whether what your computer is saying is correct. Initially, however, just doing a crude multilevel plan with the PADI RDP treating the different levels as repetitive dives with 0 minute SI is a pretty good sanity check. Don't forget to do some gas consumption planning at the same time.

A wise diver uses all of the available tools, while avoiding blind reliance on any one of them.

Charlie Allen

 

[plot]

I took an SSI course and never received my dive tables with it. When it was all said and done and I had my cert card, they gave me some PADI tables. If you've ever compared the two, then you'd know that the PADI tables are pretty much useless to me...

I might not be able to look at exact numbers, but I understand the theories behind the tables and how the whole progression of dives in a day work, so using some common sense, pre-planning my dives (plan mode on my computer is awesome for this), then I'm comfortable relying on my computer for the rest.

It'll do my math for me so I don't miscalculate something on my tables. It'll help me acheive longer bottom times when I go down to 100 feet for 2 minutes then finish out the dive at 30 feet, and if for some reason I carelessly go down farthur than I thought I did or stayed down to long, it'll tell me where to do safety stops and for how long to fix my own stupid human error (I've never been in this situation, I'm careful to avoid it, but I know someone who has been in this situation and realize that sometimes people can lose track of things while admiring the underwater world). It'll even beep at me if I'm ascending to fast.

If you understand it, and use it as a safety tool to aid in your dives, then I think you can get away perfectly with using only a computer. At least for recreational diving you can.

 

[jeckyll]

Charlie: I agree on the profiles being a big factor.

On many of my dives I do not check the NDL remaining on the computer. Unless I go beyond 80 fsw or am on my 2nd dive of the day, there's no point.

On dives planned beyond 90 fsw I know up front the profile I'll be diving, so I usually don't worry too much about it then either. However, it's nice to do a quick sanity check to ensure that you're well within the limits. Pretty much all my dives are multi level, so I have many dives with a BT of > 45 minutes and a max depth of over 80 feet.

I must admit that I don't have any dives past 100' that lasted over an hour. I do have a 77 feet for 61 minutes on an AL80 though

 

[RJP]

I disagree here. Both the tables and computers are based on the same thing. While there are different decompression models, lets assume that we use the same model for a table and encoded in a computer.

But look closely at a computer and a table of the same model..... you will be 'surprised' to see that they will be about the same. What basically happened is that the manufacturers have encoded the same model as you have on tables into the computers, sometimes with an even bigger safety margin.

Tables and computer models will give you the same profile given the same decompression model. (and I am not talking about a few minutes here or there)

Yes and no - you're assuming that you dive a perfect square profile. Further assuming that it takes ZERO time to descend and ascend.

Look at your computer as you ascend and watch it "give NDL back" to you.

 

[Scuba_Steve]

.........Further assuming that it takes ZERO time to descend and ascend.

Look at your computer as you ascend and watch it "give NDL back" to you.

All models rely on a given maximum ascent rate (and should minimum, but that is rarely an issue with most divers)

Told ya it'd rot your brain.

What else would you have it do while ascending, regardless of model, table, wheel or computer?

 

[David K]

It seems a natural progression that if one really enjoys diving and plans to continue with the sport, one purchases a dive computer.

Wrong grass hopper....you have it backwards.

If you dive once a year while on vacation dive computers will keep you out of trouble, otherwise they will stunt your understanding of how your body on-gasses & off-gasses. If you dive regularly & are interested in understanding how your body reacts to diving, dive computers will impede your development.

Planning & executing your dives old school requires some planning, divers with dive computers should plan as well but my experience is they just jump in the water & dive until their dive computer or SPG tell them its time to get out of the water.

Having a dive plan before you hit the water is a good thing. At first the planning will seam rigid & inflexible. Once you understand some simple principals and shortcut math diving with a dive table, depth gauge & bottom timer will be easier & more flexible than diving with a dive computer.

I dive with a dive computer in gage mode & find this less complicated than memorizing all the BS symbols on my dive computer. When my dive computer croaks I plan on replacing it with a bottom timer.

David K

 

[jeckyll]

David: I do not believe that diving a computer and using your head are mutually exclusive.

Computers rot your brain the way that radar detectors get you tickets...