Computer vs tables

[Leisure Pro Brett]

I would say that over your standard multi level dive a computer would edge out the tables slightly. For me the nice thing about the computers is that it removes the human error factor and most importantly is just so much easier to use. Computers are easy, just look at them and they tell you what you need to know.

 

[amascuba]

Yes it is easy but not for most. 100 ft dive to 20 min, ascend to 60 ft for 20 minutes is not 80 ft for 40 min as some think. They should stick to a computer.

Run the numbers through a dive planning application such as V-Planner or MV Plan and it will give you a run time of 45 minutes and give a similar profile that I suggested by doing the numbers in my head.

Here is what MV Plan has for the profile:

MV-Plan 1.4.2
Settings: GF=10-85 ppH2O=2.041 ftsw
===================================================
DESC:100ft for 01:30 [ 2] on Nitrox 32, SP: 1.3, END: 81ft
DIVE:100ft for 18:29 [ 20] on Nitrox 32, SP: 1.3, END: 81ft
ASC : 60ft for 01:12 [ 21] on Nitrox 32, SP: 1.3, END: 30ft
DIVE: 60ft for 20:00 [ 41] on Nitrox 32, SP: 0.0, END: 47ft
ASC : 30ft for 00:54 [ 42] on Nitrox 32, SP: 0.0, END: 21ft
DECO: 30ft for 00:52 [ 43] on Nitrox 32, SP: 0.0, END: 21ft M-Value: 57% [03], GF: 35%
DECO: 20ft for 01:00 [ 44] on Nitrox 32, SP: 0.0, END: 13ft M-Value: 64% [04], GF: 60%
DECO: 10ft for 01:00 [ 45] on Nitrox 32, SP: 0.0, END: 4ft M-Value: 73% [04], GF: 85%

 

[diver 85]

Because of an ongoing thread on dive computers, here are my questions.

For those of you who strictly use tables...what's your bottom time when compared to someone using their computer instead?

For those using the computer while diving...do you find that you get more bottom time?

I've never put a pencil to it but for multilevel diving, @ times it's @ least 3 to 4x+ longer ie computers vs. tables--- really depends on your max. depth ie the deeper the dive(ex. 100 ft vs 30 feet) the longer the dive.......

 

[lamont]

Because of an ongoing thread on dive computers, here are my questions.

For those of you who strictly use tables...what's your bottom time when compared to someone using their computer instead?

For those using the computer while diving...do you find that you get more bottom time?

I can get 70 minutes at 100 fsw without using a computer...

 

[lamont]

Let's say I'm diving 32% and did 100ft for 20 minutes, rise to 60ft for 20 minutes, and then made my ascent including minimum deco stops and surfaced. I would calculate my average depth of 80 during the dive which would give me 40minutes of MDL/NDL bottom time. My total run/dive time would be 44 - 48 minutes depending on how I felt on my 20 and 10 foot stops. That's pretty close to the same profile that many of the commercial computers will give you. It's not really rocket science, but does require some thinking.

If you do 32% to 100 fsw for 30 minutes you will just about hit your NDL. If you promptly ascend to 60 you will halt the accrual of deco time. If you then spend 15-20 minutes moving up to 30 fsw (not spend it all at 60) you will be offgassing in your fast tissues and ongassing in your slow tissues and not accruing any more deco time but shifting your compartment loading to slower tissues. Then if you spend 15-20 minutes coming up from 30 fsw you will be very, very clean when you get out, and even if you had an emergency at that point you should be very near the NDLs. If you are trained enough to be able to effecitively share gas, not lose your buddy, not lose your buoyancy control and be able to plan your gas, then you should be able to always complete at least a 3 minute ascent to the surface.

If you are still at the stage where you feel that "blow and go" is something that you may need to do, then you should dive a computer. When you've gotten enough experience so that you feel that you will always[*] be able to make 3-5 minutes of deco time at 10-20 fsw every single dive, then the excessive amounts of precision in determining your NDLs that computers give you are not required...


[*] or at least the probability of failure here must be low enough to be combined with the probability of DCS at or near the NDLs by a blow-and-go (which is actually fairly low) to produce a sufficiently low lifetime risk of DCS to suit you.

 

[MurkyRockDiver]

Run the numbers through a dive planning application such as V-Planner or MV Plan and it will give you a run time of 45 minutes and give a similar profile that I suggested by doing the numbers in my head.

Well if you use the v planner I believe that runs on a COMPUTER :mooner:

The nice thing about having a computer with you is being able to have the ability to know exactly what time you have left even if you go deeper or shallower than planned. Let say the wreck was a bit deeper than planned and you stayed just a few minutes longer then the trusty old computer gives you a nice new NDL. Plus being able to switch gas on the new ones also makes life easier on the deco line.

 

[amascuba]

If you do 32% to 100 fsw for 30 minutes you will just about hit your NDL. If you promptly ascend to 60 you will halt the accrual of deco time. If you then spend 15-20 minutes moving up to 30 fsw (not spend it all at 60) you will be offgassing in your fast tissues and ongassing in your slow tissues and not accruing any more deco time but shifting your compartment loading to slower tissues. Then if you spend 15-20 minutes coming up from 30 fsw you will be very, very clean when you get out, and even if you had an emergency at that point you should be very near the NDLs. If you are trained enough to be able to effecitively share gas, not lose your buddy, not lose your buoyancy control and be able to plan your gas, then you should be able to always complete at least a 3 minute ascent to the surface.

If you are still at the stage where you feel that "blow and go" is something that you may need to do, then you should dive a computer. When you've gotten enough experience so that you feel that you will always[*] be able to make 3-5 minutes of deco time at 10-20 fsw every single dive, then the excessive amounts of precision in determining your NDLs that computers give you are not required...


[*] or at least the probability of failure here must be low enough to be combined with the probability of DCS at or near the NDLs by a blow-and-go (which is actually fairly low) to produce a sufficiently low lifetime risk of DCS to suit you.

I did a dive a few weeks ago where I spent 40 minutes at 80 feet, did the 1 min stops at 40ft and 30ft, then spent another 28 minutes playing around with the fish in 20 - 10ft (most of it within the 10ft range) of water and surfaced at 70minutes feeling great. My computer was in gauge mode. All at 4600ft above sea-level and totally violating all concepts of altitude diving.

 

[Charlie99]

Yes it is easy but not for most. 100 ft dive to 20 min, ascend to 60 ft for 20 minutes is not 80 ft for 40 min as some think. They should stick to a computer.

Actually in the case that you describe, averaging depth is conservative. In other words after you do 20 min @100' then 20 minutes at 60', the loading in all compartments are less than if you had done 40 minutes at 80'. In the faster compartments, you will have signficantly less loading. For the slower compartments, the loading will be very similar.

OTOH, 60' for 20 minutes and then 100' for 20minutes very definitely is much heavier loading than 80' for 40 minutes.

DIR-diver.com - Average depth for deco? has some good info on this, although it is oriented towards dives with significant mandatory decompression. The ratio deco and depth averaging techniques do pay a penalty on repetitive dives of either requiring very long surface intervals, or exceeding NDL and then adding additional mandatory decompression stops to get back within limits.

=========================

As to the original poster's question --- I find that the value of a computer is very signficant in locations that lend themselves to very multilevel dives. An extreme example is Molokini islet near Maui. If often do 100' or 120' dives of 60+ minutes on a single AL80 tank of air, while never going outside NDL limits. Obviously, this is way outside of table limits. OTOH, when diving in SE Florida, the low profile reefs lead to dives where almost all of the time is spent near the same depth. Using a table there would cost very little bottom time when using the PADI RDP which is optimized for recreational diving. Using the NAUI/YMCI/SSI or other table based upon the USN tables will be fine for the 1st dive, but will have signficantly shorter allowable 2nd dive due to the method that table uses for tracking residual N2 loading.

Charlie Allen

 

[Meng_Tze]

This is not an 'ether this or that' principle. A computer will not 'give you more bottom time'. Tables are not exclusively square profiles. Neither is more conservative than the other by definition.

This is an issue of practical application.

Many people run tables exclusively and very successfully across all sorts of profiles. Many people run computers successfully across all sorts of profiles.

But here is the catch. With computers, the manufacturers have decided what algorithm they run and how much conservatism they use. Even though there is a '0' conservatism in many computers, you will fined that if you run them along side a set of tables with 0 conservatism, the tables will usually be more aggressive. So there is a potentially limiting factor there.

On the other hand, computers are superb at tracking second by second profile data and computing gas loading, deco times and a nice ascend profile. This can be done many across a hectic or square dive profile. Combined with the in bedded conservatism, you would be hard pressed to get bent; all things being equal. But it still is gas loading and deco data suggestions, you should never blindly trust a computer or leave your brain at home. This is especially true for long deco dives.

Tables on the other hand can use the same algorithms and if self generated (on PC at home) you have control over conservatism managing stops etc, etc. Forecast multi level dives become slightly more tricky, but not undoable. Tracking time and depth is essential especially when you have a runtime based on average depth.

Bottom line is that you should be able to manage your diving based on your training. A computer should never replace thinking, understanding and practice with tables. Use a computer when you want, but pls make sure you do not put your life's eggs all in that basket.

 

[captain]

If you do 32% to 100 fsw for 30 minutes you will just about hit your NDL. If you promptly ascend to 60 you will halt the accrual of deco time. If you then spend 15-20 minutes moving up to 30 fsw (not spend it all at 60) you will be offgassing in your fast tissues and ongassing in your slow tissues and not accruing any more deco time but shifting your compartment loading to slower tissues. Then if you spend 15-20 minutes coming up from 30 fsw you will be very, very clean when you get out, and even if you had an emergency at that point you should be very near the NDLs. If you are trained enough to be able to effecitively share gas, not lose your buddy, not lose your buoyancy control and be able to plan your gas, then you should be able to always complete at least a 3 minute ascent to the surface.

If you are still at the stage where you feel that "blow and go" is something that you may need to do, then you should dive a computer. When you've gotten enough experience so that you feel that you will always[*] be able to make 3-5 minutes of deco time at 10-20 fsw every single dive, then the excessive amounts of precision in determining your NDLs that computers give you are not required...


[*] or at least the probability of failure here must be low enough to be combined with the probability of DCS at or near the NDLs by a blow-and-go (which is actually fairly low) to produce a sufficiently low lifetime risk of DCS to suit you.

I understand your example perfectly but if I am making that dive and if whatever it is at 100 feet is the only objective of the dive and the only thing to see between the objective and the surface is water why would I really want it spend another 30 to 40 minutes basicly hanging around in mid water bored. Your example works well if there is reason to prolong the dive along the way to the surface but other than exiting the water with maybe less gas loading and surface interval obligation I fail to see a great advantage. I have done many dives based on your example but I wouldn't do it just to prolong run time. I also wouldn't lable it a 70 minute 100 foot NDL dive.