Are dive computers making bad divers?

[scubadada]

I wanted to make this response separately.

In an earlier post, I gave dive details of a 2-tank dive I did last week. I will repeat the challenge here: explain to me how you and your boys would handle the planning for this 2-tank dive using EANx 32:

Dive One: 103 feet for 81 minutes
Surface Interval: 1:15
Dive #2: 82 feet for 88 minutes

I assume these were two of your no stop dives in Cozumel last week. You didn't give avg depth so we would have an idea of what you did. No tables would allow you to plan these dives.

I dived Navy tables from 1970-1980. I dived PADI RDP from 1997-2002. I have dived a modern dive computer for every dive since 2002, 2145 dives. Long live the dive computer.

I use my NDL planner all the time. I do much of my diving in SE FL on charter boats, much of it with 36% nitrox. The SIs are often on the short side due to the length of my dives and the dive schedule. I often check my NDL to allow me to make my next dive, consistent with the dive schedule. Sometimes I only need a half hour, sometimes I take the whole 45-50 min.

 

[scubadada]

What are the rules of thumbs you used in the first paragraph?

Where are the 81 and 25 coming from?

Square profiles. ha

 

[boulderjohn]

Interesting challenge for rules of thumb and approximation…

103ft is 31m. At 30m it’s 30 mins on 32%, thereafter it’s 1;1 for decompression. 81-30 ~= 50, so 30+25=55mins on the bottom and 25 mins of accelerated deco.

Second dive’s shallower but there’s the short surface interval. Would plan for roughly the same timings on the second dive, 55mins bottom and 25 to 30 mins of decompression.

But I’d check it in MultiDeco and would follow the computer's TTS calculations.

Bzzzzz whrrrrrr….MultiDeco says that estimate isn’t a million miles out using 50% as the deco gas. Estimate errs on the side of caution.

Those were NDL dives--no decompression stops.

They were, of course, multi-level, which was my point. The tables can't plan or track multi-level dives like that. If you are going to use tables to plan your dives or as a backup to a computer, you will have to limit yourself to square profile dives.

 

[Centrals]

But could a modern computer cause a poor decision by presenting to much information, it's a lot easier to make a quick decision when you don't have to think about all the information a computer is displaying.

Too much information?
Some of them could not even understand the meaning of ndl. Paid no attention to alarm.

 

[BRT]

That's an interesting idea. One minor downside I discovered diving with two computers on a liveaboard is that it meant one more buckle to do and undo five times a day. It's the kind of thing that makes it very tempting to just start leaving the second one behind, because what are the odds. But then if you end up needing it, it won't have all your previous dive info. If computers came in pairs as a rule, I imagine they might come in some type of bracket to either strap them both on your wrist side by side with one strap, or to have them on two sides of the same console.

I'm a little skeptical that divers in the analog days were as attentive to their instruments and tables as some claim or imply. It would be interesting to travel back in time and secretly attach some computers to their gear, then compare the data with their logs.

I have a console attached to my regulator by a hose. So far have not forgotten it and no buckle problems. A wrist mount spare is around the hose. So far have not forgotten that one either. I have passed that one off to a dive buddy a couple of times when their computer failed and used it once when my main battery went dead. Yeah, dive buddy could not have had exactly the same profile as I did up to their failure point. But still better than going to tables.

 

[Akimbo]

True, although few rec computers these days have exactly the same algorithm unless they're the same brand.

I'm guessing that is why Stoo thinks computers should be sold in pairs. Not a bad idea but probably wouldn't work (marketing-wise) unless there was a package discount. (for other readers) The same problem is true for dive buddies using different algorithms.

I have always felt that computers should be sold in pairs... primary and backup.

However, even if computers don't match up exactly you are OK to follow one and keep the other as a backup. The one exception is if you are operating so close to the NDLs that the backup freaks out and locks up when it thinks you surfaced too early — not likely to happen on most liveaboard guided dives.

This actually happened to a guy on my last liveaboard trip in Palau. His Oceanic Pro died and lost a day of diving. I brought a Oceanic wrist watch size PDC as a spare to my 2nd PDC so loaned it to my dive buddy instead of leaving it in my cabin. Between the two of us, we had four different algorithms without a problem.

 

[Blackcrusader]

Those were NDL dives--no decompression stops.

They were, of course, multi-level, which was my point. The tables can't plan or track multi-level dives like that. If you are going to use tables to plan your dives or as a backup to a computer, you will have to limit yourself to square profile dives.

I have not once tried to use tables to plan multilevel NDL dives. That's what I have my DC for. Same as I do not do gas planning for NDL dives. I may go to my Perdix and do a gas plan for the fun of it just to see how close my actual dive is at the RMV I used.

 

[Fishdip]

I wanted to make this response separately.

In an earlier post, I gave dive details of a 2-tank dive I did last week. I will repeat the challenge here: explain to me how you and your boys would handle the planning for this 2-tank dive using EANx 32:

Dive One: 103 feet for 81 minutes
Surface Interval: 1:15
Dive #2: 82 feet for 88 minutes

Little confused what you are asking? You all ready said how long and how deep for each dive. And how long of a surface brake. What else are you looking for?

 

[Fishdip]

That's an interesting idea. One minor downside I discovered diving with two computers on a liveaboard is that it meant one more buckle to do and undo five times a day. It's the kind of thing that makes it very tempting to just start leaving the second one behind, because what are the odds. But then if you end up needing it, it won't have all your previous dive info. If computers came in pairs as a rule, I imagine they might come in some type of bracket to either strap them both on your wrist side by side with one strap, or to have them on two sides of the same console.

I'm a little skeptical that divers in the analog days were as attentive to their instruments and tables as some claim or imply. It would be interesting to travel back in time and secretly attach some computers to their gear, then compare the data with their logs.

I feel like most ppl forget the tables are made with decent safety factors. On top of that My instructor pointed out that they are/were looked at as more of a guide to help you stay safe.

 

[boulderjohn]

Little confused what you are asking? You all ready said how long and how deep for each dive. And how long of a surface brake. What else are you looking for?

You said you and your boys plan each dive with the tables. I am asking you to do that. To make it clear, just answer the first following questions in order using your tables.

1. What tables are you using?
2. The first dive is planned to 103 feet. According to your tables, what is the maximum time for a dive at that depth?
3. If you do the maximum time on that dive, what will your maximum time be for a second dive to 82 feet after a surface interval of 1:15?
4. Add your two maximum times together. How do they compare to my combined time of 169 minutes?