Do I really need a computer?

[halocline]

I really like the wheel. I especially like that it does not use a battery, it can get wet, stepped on, etc, and still works. I always take it on a trip.

DA aquamaster's post about tables providing some basic deco info for unintentional deco obligations has a lot of good info. It's also easy to remember that almost always the initial deco requirement for those who "slip" over the NDL line is an extended stop at 10ft. Since the NDL line is theoretical anyway, I routinely extend the safety stop regardless of whether I'm using a computer or not, on any dive in which I am anywhere near NDL. What's the hurry to get out of the water?

 

[Apollon]

11- 14 min? I think you are actually spending way too much time on your safety stops.

I don't think so, personally.
Of course you probably know a hell of a lot more than I do about it (with my crappy little 0-24 dives), but even somebody who reads a lot and has both eyes and ears open all the time, like me, knows that shooting straight to 15 feet after a deep cold dive is an extremely risky proceedure. A DAN study showed that no matter how long you spend at 15 feet it will do you no good if you are already bent because you bypassed all the deep stops.
From what I've heard, many of the computer algorithms are based on this 15 foot stop only theory and do not allow for deep stops. Maybe since the study and findings came out they have changed, I don't know.
Original padi tables are flawed science now too because according to the newest technology there is no such thing as a dive that you can just come up from at 60 ft per minute and blow off your stop. I was using the bottom times as a reference and doing my own deco proceedure. I dive with big tanks so the added stops don't affect my bottom time. I know how much air I need to do alll my stops according to my max depth and I always am able to complete the stops and have a little reserve air left in the tank after I come up.
I don't really know how I can improve on that.

 

[TSandM]

11- 14 min? I think you are actually spending way too much time on your safety stops.

As long as you have appropriate amounts of gas, you really can't spend too much time in the shallows (30 feet and up). And if you do dives where there's good stuff to look at there, why NOT spend that much time? All it means is that you get out of the water with less dissolved nitrogen.

Where stops get trickier is with the deep ones, and especially if you are diving to max recreational depths. There, if you decide to prolong your 70' stop, you are not doing yourself a favor. But above 30 feet, you're offgassing, and there's no reason not to stay there as long as you're warm, amused, and have adequate gas.

 

[Scared Silly]

Before computers I used a simple rule for diving with AL80s where the conventional wisdom is that you do not dive deeper than the volume of the cylinder (this only works for the north american system of measuring the air volume). So an 80 is good to 80 feet. That said my rule was my depth in feet plus my bottom time when added together could not exceed 100.

80 feet 20 minutes
70 feet 30 minutes
60 feet 40 minutes
50 feet 50 minutes.

These a some quick and dirty rules that follow the PADI tables. I also had several std mutli level profiles written down.

Not matter what system you are using - the key is fully understanding it and where it works and more importantly where it does not.

 

[Rhone Man]

Two comments occur to me:

I always remember that the old US Navy tables, NDL + depth = 120 (60 ft and 60 mins, 90 feet and 30 mins), but you need to recall that the US Navy tables should be regarded as the edge of the cliff. You don't want to find yourself getting close. And of course it only works for depths between 60 and 110 feet.

The other thing I never forget was advice in Gary Gentile's 1990 classic Advanced Wreck Diving, he says if all else fails: as a rule of thumb, spend 2 minutes at 15 feet for every 1 minute you go over your NDL. It is pretty unscientific - but if you have to guess, at least have a basis for your guess.

But given I dive with two computers, I am pretty hopeful I'll never need to rely on either.

 

[rstofer]

First of all, those Naui tables seem to be based on navy tables. Let's examine the navy subjects used to determine those NDL limits. Young, incredibly fit men with excellent cardio. Is that your normal diver? not that i've seen. Therefore those tables can be a little aggressive for most. Given that, at 80' for 40 min, the Naui table is basically saying "you are 5 minutes over what your NDL is, and you must do 5 minutes of deco". It's a fallacy to think you can blow that off. Will it bite you in the ass? Maybe not. But maybe yes.

Yes NAUI tables are, or at least were, based on the Navy tables - a long time ago. But they are as valid today for recreational divers as any other and a lot more conservative than PADI's (see below). They have been used for many years as have the PADI or SSI tables. There is no basis in comparing them to the current Navy tables and they ARE intended for recreational diving. They just make different assumptions for NDL versus depth. The NDLs are longer at some depths and shorter at others when compared to PADI and always less than the Navy's.

Depth...NAUI..PADI..NAVY
.............NDL....NDL...NDL

40..........130....140.....200
50............80.....80.....100
60............55.....55.......60
70............45.....40.......50
80............35.....30.......40
90............25.....25.......30
100..........22.....20.......25
110..........15.....16.......20
120..........12.....13.......15
130............8.....10.......10


When the NAUI table says there is a MANDATORY stop, it is not optional. You can't blow past it and, if you do, it will very probably result in an injury. But at least NAUI is willing to formalize a way to recover from busting the NDL.

The other HUGE difference with the NAUI tables is that the NDL includes the ascent to the surface (but not the safety stop). They were never based on 30 fpm ascent but even at 60 fpm, a dive to 120 feet has 2 minutes for descent, 2 minutes for ascent and 8 minutes on the bottom. PADI doesn't count the ascent so 2 minutes for descent and 11 minutes on the bottom. Hm...

How is it we consider PADI tables more conservative?

Richard

 

[orange_diver]

I don't think so, personally.
Of course you probably know a hell of a lot more than I do about it (with my crappy little 0-24 dives), but even somebody who reads a lot and has both eyes and ears open all the time, like me, knows that shooting straight to 15 feet after a deep cold dive is an extremely risky proceedure. A DAN study showed that no matter how long you spend at 15 feet it will do you no good if you are already bent because you bypassed all the deep stops.
From what I've heard, many of the computer algorithms are based on this 15 foot stop only theory and do not allow for deep stops. Maybe since the study and findings came out they have changed, I don't know.
Original padi tables are flawed science now too because according to the newest technology there is no such thing as a dive that you can just come up from at 60 ft per minute and blow off your stop. I was using the bottom times as a reference and doing my own deco proceedure. I dive with big tanks so the added stops don't affect my bottom time. I know how much air I need to do alll my stops according to my max depth and I always am able to complete the stops and have a little reserve air left in the tank after I come up.
I don't really know how I can improve on that.

of course stops should be started deeper. i never recommended you go straight to 15. thing is, once you are clean you are clean, and prolonging the dive strictly for a sense of "safety" COULD hamper you in other ways, to list just 4:

-- water is cold, you are cold and getting colder every minute you stay down
-- open ocean boat dive, surface conditions are getting worse by the minute
-- big swells are sloshing you around and you could get sick underwater
-- crappy viz and strong current the longer you stay down the more risk you lose sight of the anchor line or your buddies.

In all cases, it would benefit you to get out of the water as quickly as possible. It's not that its bad that you do 14 min safety stops, if you want to do them that's fine in good conditions. But i think you should also know that they don't have to be so long if you need to surface.

Do you know the minimum you should do? Let's put it that way...

 

[orange_diver]

As long as you have appropriate amounts of gas, you really can't spend too much time in the shallows (30 feet and up). And if you do dives where there's good stuff to look at there, why NOT spend that much time? All it means is that you get out of the water with less dissolved nitrogen.

Where stops get trickier is with the deep ones, and especially if you are diving to max recreational depths. There, if you decide to prolong your 70' stop, you are not doing yourself a favor. But above 30 feet, you're offgassing, and there's no reason not to stay there as long as you're warm, amused, and have adequate gas.

given those conditions absolutely. the safety stops just become a longer, shallow part of a nice dive. just want to make sure Apollon knows he doesn't NEED to stay down that long if the fit hits the shan.

 

[orange_diver]

Yes NAUI tables are, or at least were, based on the Navy tables - a long time ago. But they are as valid today for recreational divers as any other and a lot more conservative than PADI's (see below). They have been used for many years as have the PADI or SSI tables. There is no basis in comparing them to the current Navy tables and they ARE intended for recreational diving. They just make different assumptions for NDL versus depth. The NDLs are longer at some depths and shorter at others when compared to PADI and always less than the Navy's.

Depth...NAUI..PADI..NAVY
.............NDL....NDL...NDL

40..........130....140.....200
50............80.....80.....100
60............55.....55.......60
70............45.....40.......50
80............35.....30.......40
90............25.....25.......30
100..........22.....20.......25
110..........15.....16.......20
120..........12.....13.......15
130............8.....10.......10


When the NAUI table says there is a MANDATORY stop, it is not optional. You can't blow past it and, if you do, it will very probably result in an injury. But at least NAUI is willing to formalize a way to recover from busting the NDL.

The other HUGE difference with the NAUI tables is that the NDL includes the ascent to the surface (but not the safety stop). They were never based on 30 fpm ascent but even at 60 fpm, a dive to 120 feet has 2 minutes for descent, 2 minutes for ascent and 8 minutes on the bottom. PADI doesn't count the ascent so 2 minutes for descent and 11 minutes on the bottom. Hm...

How is it we consider PADI tables more conservative?

Richard

thank you for the comparison and the info -- it validates the point i was making.

regarding your PADI table question i hope this isn't directed at me because i never claimed that and i don't dive using PADI, NAUI or NAVY tables.

 

[goodive]

This thread developed to a quite discussion. I think we all agree, that you don't need computer but if you prefer to use one, make sure you fully understand all functions, options, what all those different screens, numbers, beeps, presets, settings, modes mean. How many times you've heard this: "I got this new computer, do you know how it works?" from someone ready to jump in the water. Of course if you use any form of tables/wheel/e-RDP make sure that you know what you doing and account for diving conditions. There isn't a different table for the warm, clear water, diving in 3mm shorty and a different table for the cold, rough ocean, diving a drysuit, more equipment and more weights.
So again, dive conservatively, within limits of your training and experience.
Plan your dive, dive your plan. Stay safe.