n00b question..

[TheMotrCty]

Okay, so I have an SSI Total DiveLog packet.

On the DiveLog pages where you record dives, the last section "Post-Dive" indicates that if you are not diving the Dive Tables, but using only computer information, "fill in the colored items only". Ergo, it instructs the user to fill in "Depth", "Bottom Time" and "Surface" interval. RG, RT and TT are left blank.

Okay, easy enough, but if I do that then how am I supposed to know what my repetitive dive group designator is for repetitive dives?

Totally confusing.

Hope I don't die. (j/k)

Ron

 

[seiff]

Ron,

This is why alot of people will use a computer only as backup (if at all) and still use tables primarily. The trend now is to only rely on the computer, and I have over heard SEVERAL conversations on boats and in shops that end with "does anyone even use dive tables anymore?" Well, yeah, we do.

Most "advanced" (technical, decompression, etc) divers, as far as I understand, use tables primarily. NOW YOU KNOW WHY!! You personally don't feel safe not being able to understand your pressure group and repetive dive profile on your own. This simply means that you are a sane person and have a safe attitude.

In reality, you aren't going to die with just a computer because the computer is based on the same tables for the most part, and it knows how long since your last dive and how long you are on the surface, so when you hit the water again it will give you a different "maximum time left on dive" then if you were a fresh diver. The computer keeps working on the surface. It's doing the repetitive dive calculations for you and shortening your dives as needed to keep you safe.

Keep your tables. Use the computer as a backup, not the other way around, like is so popular now.

Hope this helps. -tadd

edit- P.S. I don't like that a training organization would encourage leaving ANYTHING blank on a dive log, especially when it comes to blood gas and decompression limits. Doesn't SSI teach you to use tables, and even give you a free table with the class?

 

[Brainscramble]

Ron,
edit- P.S. I don't like that a training organization would encourage leaving ANYTHING blank on a dive log, especially when it comes to blood gas and decompression limits. Doesn't SSI teach you to use tables, and even give you a free table with the class?

SSI does teach the tables and does give you them as well, one thing you forgot to mention is what happens if your computer fails, then your left guessing, unless you know your tables.
My stand is; use your computer but don't rely on it, have a back-up and know your dive (depth, BT, SI, etc.) before you even get wet. I have had battery failers and floods at depths of 140' + and if you don't have some sort of back-up, you could get yourself into serious trouble, quickly.

 

[AbyssalPlains]

I do not recommend using tables primarily and computers as a backup. This is like saying "When traveling, use carriages for primary transportation, but have a car in the garage as a backup." I do keep tables as backup, but IMHO, relying on tables precludes you from diving the way that the vast majority of divers is doing it, every day, all around the world. Do those folks get bent every day by the thousands? Not that I've heard. Just as an example, one of the few times I actually wanted to use my tables was on a trip to the Florida Keys recently. After our first (wreck) dive to about 100 feet, I wanted to figure out how long our surface interval should be before we went on to a shallow reef dive. Guess what? According to my table, we shouldn't even have DONE the first dive in the first place! My buddy and I did nothing out of the ordinary, we descended last, went shallower than most of the other divers and ascended first, so if anything, our dive was more within the safety margins than what everybody else was doing. Had we gone by the table, we would have not made a second dive AT ALL, while everybody else made a perfectly safe, shallow reef dive. If you can live with paying for a two-tank dive but being the only person on the boat not doing a second dive, that's perfectly fine, but not very good value for the money, don't you think? Tables are not intrinsically safer than computers, they simply are a crude crutch to be on the safe side because the necessary calculations can't be made by a static table nor by a human brain in real-time while diving. They are a relic from times when people didn't have the tools to handle the task more appropriately. Put it this way: Would you undergo surgery without anesthesia, just because a hundred and fifty years ago that was the way surgery was done?

 

[AbyssalPlains]

R

Most "advanced" (technical, decompression, etc) divers, as far as I understand, use tables primarily. NOW YOU KNOW WHY!!

One thing to keep in mind, though, is that more often than not tech divers have utterly different profiles than recreational divers. They pretty much descend to target depth (a wreck, for example), stay there and come straight up. Rec divers rarely do that - rather, we descend, explore a reef on several depth levels, swimming down to explore a crevice, coming up to take a closer look at an anemone and so on. Toward the end of the dive, we gradually make our ascent, exploring more places in the reef and working our way back to the surface, rather doing than a straight-line ascent. A tech profile is usually much closer to the kind of profile tables were based on (straight descend to max depth, stay at max depth, straight ascent from max depth).

Just to add some perspective: In my 13-plus years of diving, I have yet to meet a recreational diver who prefers tables and uses a computer only as a backup...

 

[RadRob]

I plan my dive an have a rough idea what group I will be when I return. I use a computer as a quick reference to make sure I am within limits. About every five minutes or so, I verify with the computer.

 

[nereas]

Okay, so I have an SSI Total DiveLog packet.

On the DiveLog pages where you record dives, the last section "Post-Dive" indicates that if you are not diving the Dive Tables, but using only computer information, "fill in the colored items only". Ergo, it instructs the user to fill in "Depth", "Bottom Time" and "Surface" interval. RG, RT and TT are left blank.

Okay, easy enough, but if I do that then how am I supposed to know what my repetitive dive group designator is for repetitive dives?

Totally confusing.

Hope I don't die. (j/k)

Ron

The computer will have a dive planning feature in it. So you don't need tables, if you have a dive computer.

Just like you don't need a computer if you have a good algorithm, either on the fly or embedded software in your P/C.

Dive tables are sort of like the stone age. They work, but they are slow and clumsy.

A dive computer is a modern solution to the problem of determining inert gas saturation and required surface interval time in conjunction with your no-decompression-limit dive times and depths.

An algorithm on the fly would free you from both. There are several quick algorithms for NDL diving that can do this for you. Here is one mentioned by NAUI in their basic open water manual: dive with nitrox / sum to 115 / keep a 1 hour or longer surface interval. [50 fsw + 65 mins = 115; 80 fsw + 35 mins = 115; 100 fsw + 15 mins = 115].

And decompression software represents the most complex and detailed algorithm for NDL and decompression determinations.

Besides MOD, B/T, and S/I you should also record your average depth. This will allow you to compute most on the fly algorithms and also your RMV breathing rate.

What are on the fly algorithms? You will probably learn that someday, but not this year.

 

[jon m]

to the OP
you still can figure your pressure group using a table and the info provided by your comp. if your computer fails, you can always use your tables. for a rec. diver your computer should be sufficient. if it does fail, your dive is over. but, if you check your computer assisted multiple dives (run them on the tables)you will find that on most of them, if not all of them , your dive would be over anyway, because the tables will show you well beyond your NDL.
of course there is the wheel....

 

[John_B]

Guess what? According to my table, we shouldn't even have DONE the first dive in the first place! My buddy and I did nothing out of the ordinary, we descended last, went shallower than most of the other divers and ascended first, so if anything, our dive was more within the safety margins than what everybody else was doing. Had we gone by the table, we would have not made a second dive AT ALL, while everybody else made a perfectly safe, shallow reef dive.

It would be interesting to see the profile to see if you could've used a multilevel table (ie. the infamous PADI wheel) to track more accurate NDLs than the square profile you get with regular tables. Somebody here has even de-wheeled the wheel, creating a table format for doing multi-level dives.

Tables are not intrinsically safer than computers, they simply are a crude crutch to be on the safe side because the necessary calculations can't be made by a static table nor by a human brain in real-time while diving. They are a relic from times when people didn't have the tools to handle the task more appropriately.

People do track their profiles with their brains in real-time, using average depth and some other rules I won't go into here.

A question for you, why do you think your computer is safer? What if it was incorrectly programmed? What if you were diving nitrox and the the computer was programmed to calculate that you were breathing nitrox -- and not air -- on your surface interval? You don't have to imagine it, since it actually happened about a dozen years ago.

Just because you turn on your computer doesn't mean you have to turn off your brain. :no

John

 

[KCIREVAM]

There R dive tables that R E-Z 2 read and will keep U out of trouble with repitive dives.