Does anyone dive with tables anymore?
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I dive with tables often. I dive with computers often. They are the same thing, a way to represent, in a useable form, a mathematical model. The table is a series of snapshots, the computer is an animated cartoon, both work if understood and used properly.
I had to dust off the tables on Monday when my computer crapped out on my first dive.
I use them every time I dive with a simple bottom timer. No need for a fancy computer unless you're doing a ton of diving.
SlicerDicer
Contributor
I base all my dives off tables and use the computer to be there as a companion. I do not rely on the computer to do my dives.
To answer your question, I think not very many people dive tables any more. But that doesn't make them invalid. It's just that computers, because they can continuously calculate nitrogen loading based on the real depth where you spend your time during the dive, tend to give you much more no-decompression time.
If you are shore diving with a buddy who is also using tables, there is NOTHING wrong with diving profiles determined by them. But if you are going out on the kind of charter boat where the group goes with a guide, the other divers will be very unhappy with you for using tables . . . because you will have to surface long before anyone else, and on some boats, that means the whole group goes up.
You see, the issue, as already stated, is that tables assume you spend the entire dive at your maximum depth. Many sites aren't like that; you can multi-level the dive, moving upwards as you go, and not incurring nearly the nitrogen loading that the tables assume you have. There ARE multi-level table tools, but even they can't account for a dive where you descend to maximum depth, and spend the whole dive working your way up a wall. In such a case, the tables are extremely conservative and undoubtedly very safe, but really curtail your dive.
To give you a real example from our local diving: A very typical dive for us is to do a shore entry at the site, and swim down a rope line. It will take us about 15 minutes to reach 70 feet, and at that point, we work our way across the site, coming up to 60 at about 25 or 30 minutes. We then work our way up the pilings that form that part of the site, taking another 15 minutes or so to get to 30 feet. After we've checked out that portion of the site, we swim across to our original line, taking 15 to 20 minutes to return to the vicinity of our entry. So, we have a 60 minute dive to 70 feet, according to the tables . . . and the PADI RDP has you well into deco -- even on 32%, you're in deco by tables. But really, you aren't -- because you spent half of the dive shallower than 30 feet.
When I first started diving, I had a computer, but I tried to log my dives using the PADI sheets, which assume you are using tables. I was profoundly confused by the fact that every single dive I did put me horrendously into deco by tables, but was fine according to my computer. I eventually learned why, and realized why almost no one dives tables any more. They are a good tool to stay safe, when you have nothing else. But they are punishingly conservative for many very acceptable terrain-based dives.
If you are shore diving with a buddy who is also using tables, there is NOTHING wrong with diving profiles determined by them. But if you are going out on the kind of charter boat where the group goes with a guide, the other divers will be very unhappy with you for using tables . . . because you will have to surface long before anyone else, and on some boats, that means the whole group goes up.
You see, the issue, as already stated, is that tables assume you spend the entire dive at your maximum depth. Many sites aren't like that; you can multi-level the dive, moving upwards as you go, and not incurring nearly the nitrogen loading that the tables assume you have. There ARE multi-level table tools, but even they can't account for a dive where you descend to maximum depth, and spend the whole dive working your way up a wall. In such a case, the tables are extremely conservative and undoubtedly very safe, but really curtail your dive.
To give you a real example from our local diving: A very typical dive for us is to do a shore entry at the site, and swim down a rope line. It will take us about 15 minutes to reach 70 feet, and at that point, we work our way across the site, coming up to 60 at about 25 or 30 minutes. We then work our way up the pilings that form that part of the site, taking another 15 minutes or so to get to 30 feet. After we've checked out that portion of the site, we swim across to our original line, taking 15 to 20 minutes to return to the vicinity of our entry. So, we have a 60 minute dive to 70 feet, according to the tables . . . and the PADI RDP has you well into deco -- even on 32%, you're in deco by tables. But really, you aren't -- because you spent half of the dive shallower than 30 feet.
When I first started diving, I had a computer, but I tried to log my dives using the PADI sheets, which assume you are using tables. I was profoundly confused by the fact that every single dive I did put me horrendously into deco by tables, but was fine according to my computer. I eventually learned why, and realized why almost no one dives tables any more. They are a good tool to stay safe, when you have nothing else. But they are punishingly conservative for many very acceptable terrain-based dives.
Osric
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You've had lots of great answers already. I thought I'd throw one more opinion into the mix.
If your buddy will dive with a computer, you will want one too. You can't dive off of their computer and assume you'll be fine, and you won't want to cut their dive short all the time.
If you'll mainly dive with strangers on trips, mostly shallow dives, then I think it's personal preference. In those situations there will always be others out of air before you are anyway, you can surface with them.
A computer is a very small expense in the scheme of diving costs. It will allow you to dive longer on typical profiles and alert you to some basic mistakes you might be making (like rapid ascent, low air, etc). You don't need one, but I believe that for the reasons I have just given most people have one.
Osric
If your buddy will dive with a computer, you will want one too. You can't dive off of their computer and assume you'll be fine, and you won't want to cut their dive short all the time.
If you'll mainly dive with strangers on trips, mostly shallow dives, then I think it's personal preference. In those situations there will always be others out of air before you are anyway, you can surface with them.
A computer is a very small expense in the scheme of diving costs. It will allow you to dive longer on typical profiles and alert you to some basic mistakes you might be making (like rapid ascent, low air, etc). You don't need one, but I believe that for the reasons I have just given most people have one.
Osric
A lot of people are vacation divers, myself included. When spending big dollars for a week at your chosen warm, clear water tropical, world class diving destination a dive computer is a wonderful thing. Diving tables will cut into your underwater time, what you spent all that money to do. If you look at it on as time underwater per dollar, a computer can decrease the cost per time spent underwater. One trip to paradise and it is paid for. Most (if not all) dive computers can be used to plan your dive. They also consider residual nitrogen levels from repetitive dives. I use mine for planning and executing dives. I can only think of 1 person on the dive trips I have been on that didn't have a computer.
Mr Carcharodon
Contributor
No they are not a need, and really not that much of a plus for dives shallower 40 or 50 feet where the NDLs are long and you will likely be limited by gas supply. So if you were only doing shallow dives a strong case could be made to spend your money on other aspects of diving like going on trips. Of course you do need a depth gauge and a timing device of some sort and a computer is certainly one way to do that. At the 80 feet you mentioned a computer would be a plus unless you knew you were always going to dive square profiles. One thing to know is that there can be significant differences computer to computer on calculated no decompression time. It is not correct that all computers use the same algorithm as the tables. For that matter there are many tables and not all the tables use the same algorithm. One way to get around the discrepancies from computer to computer is to dive the same computer (or table) that your buddies do. Then there are $1500 dive computers out that no one really needs just like no one really needs a Ferrari but they both might be nice to have.
windapp
Contributor
Although they are wonderful for multi-dive, multi-level tracking, a lot of dive computers suck for dive planning more than one dive. I find that tables are much quicker for multi-dive planning than trying to use my computer.
One thing that you can do is use the tables to plan a multi-level dive as a series of square dives. While this would be a clear violation of the rules for using the tables, it doesn't hurt if you use your computer to actually execute the dive. The whole idea is to use the tables to give you a rough idea of how much time your computer is going to give you.
One thing that you can do is use the tables to plan a multi-level dive as a series of square dives. While this would be a clear violation of the rules for using the tables, it doesn't hurt if you use your computer to actually execute the dive. The whole idea is to use the tables to give you a rough idea of how much time your computer is going to give you.
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