Different algorithms for buddys...

[Bubbletrubble]

What do others do when diving with a buddy without a computer? I hate to have him go by MY computer, but it would prolong his bottom time. Opinions?

If I'll be diving with a buddy without a computer, then our dive profile will be compatible with whatever table he's using. In most cases, however, I'll offer to lend a dive computer to him/her. I have a couple of spares in my dive closet.

FWIW, used dive computers can be had for $100 or less. I've purchased a new air-only computer at that price point and a couple of used nitrox-capable computers for that much. You just need to be patient. Spend some time combing through Craigslist ads and Ebay.

2 divers sharing 1 computer is poor practice. It can increase DCS risk for a diver who doesn't have the best buoyancy control or doesn't pay close attention to where the other buddy is, particularly if the divers are flirting with exceeding NDLs. As you know, in order to limit DCS risk, sharing one computer demands that the diver without the computer needs to always stay at the same depth or shallower than the diver with the computer.

There's also the issue of setting a good example for your son. You want to be modeling "good" diving behavior.

 

[captndale]

You should not get too hung up on the exact numbers. Your computer is just a guide. Use whatever numbers it gives you conservatively and you will be doing as well as you can.

I once was working out a dive plan on my laptop along with two of my buddies. We were independently planning the same dive, each of us on our own computer. We were using the same dive planning software, with the same default settings. We each got slightly different decompression plans. Why? We used the same program, with the same settings and the same inputs but the decompression times at some stops differed by a minute or two. The only answer was that because we were using different computers, the math was being handled slightly differently by each machine. Things like rounding errors can accumulate and produce slightly differing results.

 

[Tortuga68]

The only answer was that because we were using different computers, the math was being handled slightly differently by each machine

Can anyone comment on this? That doesn't make any sense to me

 

[DevonDiver]

Again...the short answer remains 'no'.

It's unlikely that both divers would follow precisely identical dive profiles. Over the space of many repetitive dives, it might start to make a difference - however, the advice of most training agencies (including PADI) is that you dive to the most conservative of the computers. This adds a nice safety factor.

 

[stargost]

My son and I had been strictly diving RDP tables, but I recently got a computer...but he doesn't have one(yet). I still have him do his tables and calculate his RAT, and we never come close to decompression limits. I'm sure it is recommended for him to stick to his tables if we ever get close to limits, but it would certainly give me more bottom time than him. What do others do when diving with a buddy without a computer? I hate to have him go by MY computer, but it would prolong his bottom time. Opinions?

He's your son... I'd suggest you give him your computer, and that you dive with table ...
The BT will be very likely be limited by the tables, but at least your son (and you) will have some idea and ways to track his ascent rate.

Of course the risk is that he'll figure out he can dive longer, which may not be a great idea, but you can make sure you are both limited by the table/original plan.

 

[Akimbo]

Alberto’s (aka eDiver) post illustrates how algorithms favoring deeper stops “could” cause some confusion and inconvenience for dive partners — especially on repetitive decompression dives. Implementations of RGBM probably vary a little more than others as well.

How important this factor is are depends on your dive profiles. I can offer one argument favoring identical computers of any brand: learning curve. They all have them. I am not suggesting that these are critical or priority factors, but do justify consideration in your decision matrix.

 

[scadreau]

Can anyone comment on this? That doesn't make any sense to me

What program was being used and what operating systems were you on?

The only thing I can think of right now is different operating systems or different core libraries.

 

[Charlie99]

...., the advice of most training agencies (including PADI) is that you dive to the most conservative of the computers.

Following the more conservative of the two computers is not just a suggestion of training agencies.

If buddies stay together and each diver avoids violating his computer and avoids running low on air, then the natural result is that the two buddies dive to the most conservative of the computers.

 

[burnerking]

Cheers all for the replies. Settled my current and future questions.

 

[captndale]

Can anyone comment on this? That doesn't make any sense to me

I do not remember what computers we were using, just that they were all different. I am told (I am not a computer professional.) that PC's use separate math processors to handle numerical calculations. Those math processors are likely to be different and act slightly differently in different machines. Since decompression calculations entail several integrations, all performed simultaneously and repetitively, small rounding differences will quickly be magnified.