Bruce Herold
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What is considered safer, repetitive diving conservatively (4 dives per day for 5 days)with USN tables within the NDL range or letting a computer do it all for you?
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USN Tables vs computers
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What do you mean by "letting the computer do it all for you"?
You still dive conservatively staying within your NDL whether you use tables (whoever's) or a personal dive computer.
You still dive conservatively staying within your NDL whether you use tables (whoever's) or a personal dive computer.
To me, "conservative" using tables includes diving two times, or at most three times per day, and, if the dives involve significant nitrogen loading, taking the third day off. I describe one approach here: http://www.scubaboard.com/forums/ne...first-time-ocean-post7375577.html#post7375577. Don't forget to allow for factors such as cold water, cold weather, degree of exhaustion, driving home over mountains, etc.
I'm not sure whether this approach is *safer* than following a computer, but I feel perfectly safe with this approach. (I don't use a dive computer.)
Safe Diving,
rx7diver
Mr Carcharodon
Contributor
The Navy tables were not really set up for a long string of repetitive dives. By their nature tables have to pick one, or a few, compartments to set the limits. At least a dive computer will track multiple compartments and let you know if you are getting limited by slower compartment which could happen for the described dives. That said you are likely comparing small differences in risk. And those small differences are likely are not quantified for most dive computers.
It's a good question but the answer is somewhat academic - an analogy might be asking if it's better to use a measuring device on which every centimetre is marked, or is it better to use one that has millimetres also.
The fundamental difference between any table and a dive computer is that the mathematics involved in designing a table are inherently limited by the size of the table that is practical. When they were first developed, there were no computers as we know them today so the calculations were long and involved. It would - in theory - be possible to design a table which calculates your dive profile as accurately as a computer but it would stretch from here to the next available solar system and your pressure calculations would take about the same time as it would to get there!
Computers effectively re-write the tables as they go, based on the same fundamental mathematical models and so therefore one could say that the tables are far more conservative than dive computers, which therefore might make them "safer" but only in the same way that it might be considered "safer" to drive at 30mph rather than 40mph in a 55mph zone... if that makes sense.
Also - many computers take into account research that tables don't and can't - such as the "Reduced Gradient Bubble Model" (RGBM) used by Suunto and Mares which - whilst the mathematics is waaaaay beyond basic scuba, takes into account bubble formation in the body that was not even part of the research behind the tables, and would be impossible to integrate into them.
Which is a very long winded way of saying that as long as you stay within the limits of either your tables or your computer, your dive will be as safe as the tables or computer allow, but you will find that a computer gives you (in general) longer repetitive dive times with shorter surface intervals and therefore makes your holiday just that bit more enjoyable!
Hope that helps
C.
The fundamental difference between any table and a dive computer is that the mathematics involved in designing a table are inherently limited by the size of the table that is practical. When they were first developed, there were no computers as we know them today so the calculations were long and involved. It would - in theory - be possible to design a table which calculates your dive profile as accurately as a computer but it would stretch from here to the next available solar system and your pressure calculations would take about the same time as it would to get there!
Computers effectively re-write the tables as they go, based on the same fundamental mathematical models and so therefore one could say that the tables are far more conservative than dive computers, which therefore might make them "safer" but only in the same way that it might be considered "safer" to drive at 30mph rather than 40mph in a 55mph zone... if that makes sense.
Also - many computers take into account research that tables don't and can't - such as the "Reduced Gradient Bubble Model" (RGBM) used by Suunto and Mares which - whilst the mathematics is waaaaay beyond basic scuba, takes into account bubble formation in the body that was not even part of the research behind the tables, and would be impossible to integrate into them.
Which is a very long winded way of saying that as long as you stay within the limits of either your tables or your computer, your dive will be as safe as the tables or computer allow, but you will find that a computer gives you (in general) longer repetitive dive times with shorter surface intervals and therefore makes your holiday just that bit more enjoyable!
Hope that helps
C.
I'd like to see the plans based on tables that allow you to do this..... following the rules, tables will likely keep you out of the water for repetitive dives, as well as limit dive time on any you can string together. Essentially being "more conservative". Is that safer compared to some of the "new" concepts integrated into current PDC algorithms? IDK...
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It also depends on the dives. What is the max depth you plan to see? I could dive four dives a day easy in Bonaire and have a great time with tables. Just need to restrict my depth to 35-40 feet. In some of our local quarries/lakes you need a shovel to get below 30 feet. Easily do 4 dives a day. 45 min each. I've done one 3 hour dive along a lake shore just playing around with my doubles. Max depth 20 feet with avg of 15 and had a great time. Alone, no one to bother me, nowhere to be at a certain time. May do something similar at the same site this weekend. Depends on if I decide to dive wet or dry.
My own opinion and what I pass on to my new students is that it is better in the beginning to dive the tables and develop the discipline to plan a dive and stick to the plan. No matter what cool thing you may see 10 or 20 feet deeper. Work on your buoyancy and trim by staying at a planned depth. Once you get those things nailed then start using a computer to extend your dives and add some variables. I know this is not a popular view. But my students typically don't want to buy computers and I see no need to force them to do so. As cheap as they are now I'd rather see them spend that couple hundred bucks on renting gear/tanks for several weekends and dive locally.
My own opinion and what I pass on to my new students is that it is better in the beginning to dive the tables and develop the discipline to plan a dive and stick to the plan. No matter what cool thing you may see 10 or 20 feet deeper. Work on your buoyancy and trim by staying at a planned depth. Once you get those things nailed then start using a computer to extend your dives and add some variables. I know this is not a popular view. But my students typically don't want to buy computers and I see no need to force them to do so. As cheap as they are now I'd rather see them spend that couple hundred bucks on renting gear/tanks for several weekends and dive locally.
Belzelbub
Contributor
Way too many factors to consider in order to provide a good answer.
However, I will add that you shouldn't really "let the computer do it all for you."
As you can see on the table above, the USN tables are quite a bit more liberal at shallow depths, and they more or less even out at greater depths, but there are lots of different algorithms, so it really depends.
The benefit of using a computer is for real-time tracking, and for non-square profiles. You can apply conservative factors on the computer rather easily, so you could make the computer dive more conservative rather easily. Bottom line, though, the computer is primarily a convenience tool, that offers additional real-time tracking benefits.
However, I will add that you shouldn't really "let the computer do it all for you."
As you can see on the table above, the USN tables are quite a bit more liberal at shallow depths, and they more or less even out at greater depths, but there are lots of different algorithms, so it really depends.
The benefit of using a computer is for real-time tracking, and for non-square profiles. You can apply conservative factors on the computer rather easily, so you could make the computer dive more conservative rather easily. Bottom line, though, the computer is primarily a convenience tool, that offers additional real-time tracking benefits.
KevinNM
Contributor
If you are male, age 20-28, able to run 2 miles in 12 minutes and do 15+ pullups, and always have a deco chamber on your dive boat, then the Navy tables are probably a good match for you. If these are not true than I'd suggest you use significant caution in using the Navy tables.
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ok so here's the quick answer
If you're diving tables, the NAUI tables are probably most conservative, they are basically the USN tables with NDL one stop shorter. USN does one long dive per day and that's about it. First dive of the day you'll have quite a bit of bottom time, moreso than PADI tables, but still less than most computers because they are working off of your average depth essentially *much more complicated than that, but it's easiest to explain that way*. PADI had their tables written with repetitive diving in mind, so they have generally shorter NDL's on the first dive, but generally longer NDL's on the subsequent dives.
Depending on the computer, you may or may not have issues, Suunto's for example could very well keep you out of the water if you have fast ascents, short SIT's, etc etc.
So, which is most conservative? NAUI tables, then USN tables, then PADI tables, then depending on which model your computer is running off of and which conservatism factor it is set on. Need a bit more information on the computer you have first.
If you're diving tables, the NAUI tables are probably most conservative, they are basically the USN tables with NDL one stop shorter. USN does one long dive per day and that's about it. First dive of the day you'll have quite a bit of bottom time, moreso than PADI tables, but still less than most computers because they are working off of your average depth essentially *much more complicated than that, but it's easiest to explain that way*. PADI had their tables written with repetitive diving in mind, so they have generally shorter NDL's on the first dive, but generally longer NDL's on the subsequent dives.
Depending on the computer, you may or may not have issues, Suunto's for example could very well keep you out of the water if you have fast ascents, short SIT's, etc etc.
So, which is most conservative? NAUI tables, then USN tables, then PADI tables, then depending on which model your computer is running off of and which conservatism factor it is set on. Need a bit more information on the computer you have first.
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