Technical Diving without Dive Computers

[Germie]

I dove till 2013 without computer and if needed I still can do.

First option:
-Make a plan with Vplanner/Multideco. Adjust it where needed (Pragmatic deco). The +5m depth or +1-3 minute bottomtime was easy (depending on depth). For example, if you go to 100m and one minute more bottomtime means about 8 minutes more deco. So do 4 minutes at 6 on ean80 or 100% and the other 4 minutes between 21m and 9m. So that will mean 1 minute 18m, 1 minute 15m, 1 minute 12 m and 1 minute 9 m. OR: 2 minutes 12m and 2 minutes 9m. Deco is no absolute science.
At 120m is 1 minute 20 minutes more deco, so 10 minutes 6 m and the other 10 minutes between 21m and 9m.
The examples above are just examples, and some of the limits are: deco is not lineair, but if you talk about 1-2 minutes more bottomtime at 100m, the results are more or less linear. If you use this, you only need plan in your wetnotes and the note: +3m =+10 minutes deco, +1 minutes=+8 minute deco (examples too).
Pragmatic deco can be used too as you know the bottomtime and the total divetime. If you forget all other things you still can make a decoplan on the fly to give you a good option to come healthy out of the water.

Second option:
-Ratio deco. Here you use more or less the same as in the example above. 40 minutes deco means 50-80% of time on the highest decogas, rest on lower decogas. But best is to prove it with software. Pragmatic deco is more or less same as ratio deco. Ratio deco is used with standardgases, but pragmatic deco can be used with every gas.

Third option:
-Average depth calculation. This is the option that is less trustable. I always said use this as last option when you forgot all other things. Average depth is tricky in caves too. On normal profiles you willl see your average depth of a trimixdive will be between 22 and 26m.

All options above work easiest on 'easy' profiles like a wreck. Average depth in a cave can be totally useless (you can reset it on a bottomtimer, but even at 20m depth you will build up nitrogen and if the way back is long time at 15m maybe your deco is not gone at the exit, but the average depth shows it is fine).
To use the first option in a cave (pragmatic deco) you need to have the map to know depths and lengths, know your swimmingspeed in and out, etc. The first option is always used by me, even if I know have 2 trimixcomputers. I always plan a new dive with software. Why? I need to know the amount of gas/bailout needed. The only difference is that during a dive I use the computer and not follow the wetnotes plan. In a course divers have to follow the wetnotes and are allowed to check it with their computers. But in my eyes every diver need to be able to plan and execute a dive without computer.
When experience grows you will see globally if a diveplan is possible or not even without software.

 

[oldschoolto]

I always get a laugh out of divers on the advanced or tech forums talking about how learning and knowing tables is so important.... But, In basic or normal forums tables are talked about like their useless and a waste of time because computers are the cats meow...
Okay, back to the reality of tables rock..

Jim....

 

[Germie]

There is no need to learn tables by head. The tables for technical diving are more or less useless if you want to use them for planning as you mostly decide to use other gases than mentioned in the tables ( I talk now about a trimixtable). They are usefull to understand runtimetables or to understand that longer bottomtimes means longer decotimes. But the plans you dive are nowadays made with a computerprogramm. If you use the gases mentioned in the tables you can still use tables safely. But if you decide to use other gases, then you cannot use the tables anymore. Then you plan your dive, you make a RUNTIMETABLE (different from the planningtables) including backup and you can dive. This is diving without computer, but based on a diveplan. If you have a table where only EAN70 is used as decogas and you want to use EAN50 and 100%, then you cannot use the EAN70 table. So you need to use another planningtool. And there are nowadays good planningtools.

The recreational sportsdiving divetables are still usefull to see the max NDL time and to learn to understand that depth means more saturation. Diving within NDL is quite easy with a computer. And if your computer fail, your buddy will have one. That is the idea of sportsdiving. There is no backup computer required. Further jump in, take a computer and turn back if you reach your gas (1/2+X bar) turnpressure or your computer says you are at limit of NDL. Tables for sportsdiving are useless is a big word, but agencies now all teach computer diving too. But the computer is never required.

 

[kensuf]

There is no need to learn tables by head. The tables for technical diving are more or less useless if you want to use them for planning as you mostly decide to use other gases than mentioned in the tables ( I talk now about a trimixtable). They are usefull to understand runtimetables or to understand that longer bottomtimes means longer decotimes. But the plans you dive are nowadays made with a computerprogramm. If you use the gases mentioned in the tables you can still use tables safely. But if you decide to use other gases, then you cannot use the tables anymore. Then you plan your dive, you make a RUNTIMETABLE (different from the planningtables) including backup and you can dive. This is diving without computer, but based on a diveplan. If you have a table where only EAN70 is used as decogas and you want to use EAN50 and 100%, then you cannot use the EAN70 table. So you need to use another planningtool. And there are nowadays good planningtools.

The recreational sportsdiving divetables are still usefull to see the max NDL time and to learn to understand that depth means more saturation. Diving within NDL is quite easy with a computer. And if your computer fail, your buddy will have one. That is the idea of sportsdiving. There is no backup computer required. Further jump in, take a computer and turn back if you reach your gas (1/2+X bar) turnpressure or your computer says you are at limit of NDL. Tables for sportsdiving are useless is a big word, but agencies now all teach computer diving too. But the computer is never required.

Computers are required by SDI, but you're also allowed to teach tables. Their feeling is more people can remember how to read the NDL on a computer versus remembering how to read tables.

On a related note, learning ratio deco helps a lot with understanding the relationship between depth, time, and decompression requirements. While I would never actually deliberately plan a decompression dive based strictly on a ratio deco schedule, I find it very useful to be able to quickly spitball 25 minutes at 200 is roughly 50-55 minutes of deco.