Computers & Tables

I have been searching for a new computer and have found a couple that are more conservitive that dive tables. It is hard to understand that Padi's tables are that far off as they to are more conservative than they use to be when I first started diving. Can anyone tell me why they are going in this direction and what computers are more liberal. I have a Orca Phenox that I purchased new and it is hard for me to give up when I will be sitting on the line while they drink my beer.:11: I am considering a new hoseless oceanic from Scubatoys but my LDS is trying to sell me on a Suunto Vytec. I already dive with a stinger also but would like to have a newer Main computer. I just purchased a used Uwatec for my daughter that was exchanged for a new one from Uwatec on the recall. But it to is to conservative for me. Please give some guideance.

The reason you will find that Suunto computers are more conservative than others is because they are based on the RGBM algorithm. Most other computers are based on Haldane models which do not track factors in the production of microbubbles. Whatever number your computer is showing you, i.e. X minutes at Y depth, is not a guarantee that you'll be okay within those No-D limits. That's why all computers and tables will tell you not to push the limits. Your body's risk for DCS on any given day and dive profile exists outside of whatever computer or table you happen to be carrying, which is why most people would say that looking for a computer that flashes larger numbers at you is an unsafe attitude and provides a false sense of security. If you have some reason to overstay a No-D limit, my suggestion is simply to do so, but then follow the deco profile which your Suunto computer will automatically switch over to.

For Suunto's summary of their computer model see here:

http://www.aqualung.com/technical_library/Microbubble.pdf

For a more technical discussion of RGBM see here:

http://www.rgbmdiving.com/

ps- if you usually don't do repetitive dives, or multi-day diving, or reverse profiles, which are all things that RGBM specifcally addresses, then you're more likely to be fine with just the Haldane models.

I will disagree slightly with your assessment that models other than RGBM are not suitable for repetitive or multi day dives. Now if you said the RGBM model is safer for those types of dives I would agree with you, but I can't agree with the belief that if you don't do those types of dives then the other models are fine.

What I would say is that in general you need to be aware of the tradeoff's and risk's involved with using various computers and tables. Looking for longer dive times only is not the way to go. A computer will give you credit for times at shallow depths where tables are based on the max depth unless you use the wheel or similar.

Computers differ in how much credit they give you. That said, I like the RGBM model myself and my next computer will have it.

cummings66:

I will disagree slightly with your assessment that models other than RGBM are not suitable for repetitive or multi day dives. Now if you said the RGBM model is safer for those types of dives I would agree with you, but I can't agree with the belief that if you don't do those types of dives then the other models are fine.

What I would say is that in general you need to be aware of the tradeoff's and risk's involved with using various computers and tables. Looking for longer dive times only is not the way to go. A computer will give you credit for times at shallow depths where tables are based on the max depth unless you use the wheel or similar.

Computers differ in how much credit they give you. That said, I like the RGBM model myself and my next computer will have it.

Click to expand...

I didn't mean to give the idea that non-RGBM computers can't be used for repetitive/multi-day diving...people use them all the time of course. RGBM is safer, to the extent that being more conservative is safer under any circumstances, but also because it was developed to predict the production of free gas in exactly those situations. The main point for the OP though is that simply looking for the computer that will give you the biggest number might not be the best approach to this.

cummings66:

...Looking for longer dive times only is not the way to go. A computer will give you credit for times at shallow depths where tables are based on the max depth unless you use the wheel or similar. Computers differ in how much credit they give you....

Click to expand...

Yes, particularly in the way they calculate washout during surface intervals which, of course, is what we're talking about with repetitive/multi-day diving.

I still have a problem with the understanding of these computers in regards to the dive tables. Are the dive tables obsolete or are the computers too conservative? As far as I understand the tables have already been adjusted from when I first started diving to be more conservitive to the navy tables. As far as the Uwatec that I have it is 60" for 48 min on the least conservitive and on level 5 it is 60' for 8 min. Why all this consevitiveness when we are still taught the tables?

So many people think that a conservative computer is a "better" computer. If that's the case, I got the best computer for you. My wife bought one of those pool alarms so when kids come visit, if one falls in the pool, the alarm goes off. Now that would make that the best computer right? Alarm as soon as it gets wet.

I've got a car and the speedometer goes to 150... but guess what... I'm allowed to drive 60 if I choose. I dive an oceanic computer that allows me to do a 60 ft dive for 57 minutes on air. I have pushed the limits, gone into deco, done stops to get out and surfaced without ever having a problem. Dan stats show about 1 in 28,000 dives ends up in a bends case, and then it's normally brought on by too fast of an ascent.

So me... I'll take the liberal computer. But I'm a rebel... I also cut off my mattress tags, and at least once a week I run with scissors. If you're not a big risk taker like me... guess what? Diving with a computer is easy. Jump in the water and don't let the big number hit zero. Want to be more conservative? Just like my car... just back off... don't let the big number hit 5... or 10. It's up to you.

But I've been on too many a live aboard with folks diving the oceanic computers (and others with the same algo) for a week at a time, knocking out 5 dives a day with no problems, and other people on the boat would have to skip one or 2 dives per day due to their computers algorithm. I didn't take off 2 weeks of work and fly half way around the world to read a book while the boat I'm on is parked above a WWII wreck.

But this is a personal choice - do what you think is right for you.

Broadly speaking, computers and tables are the same, one is not more conservative than the other. (Meaning, they are based on the same mathematical models.) The main difference being that computers continuously recalculate your N2 loading throughout your dive. Since you rarely dive anything even close to a square profile (which is what your basic table assumes) any computer is going to give you more time than a table because it eliminates all the rounding up. Recreational dive tables do differ from the navy tables significantly in how they calculate off-gassing during SIs. They base washout times on faster tissue compartments (the logic being navy is deco diving while recreational is no-deco, so your slow tissues will be less saturated). What that means is the navy tables give you more time on your initial dives, but rec tables actually give you shorter surface intervals and more time on repetitive dives. One of the main differences between computers is also how they calculate these washout rates.

What I just said is generalized and oversimplified, but a comlete answer would be very long and I'm not sure how interested you are....

Wow Larry, I'm surprised. My previous post was in response to Gamehunter's questions, but after it posted I saw your reply. What surprises me is not your opinion, but how flippantly you make your case in a legitimate debate. If you're such a "rebel" I'm surprised you bother to use a computer at all. Do you also dive to 300' on air just because the navy tables say you can? I'm giving you the benefit of the doubt and assuming your response was written because you really are that annoyed by proponents of diving conservatively, and not because your shop sells Oceanic computers instead of Suunto. As you say, do what you think is right.