Why do some agencies recommend using a bottom timer instead of a computer
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----------------------I wouid guess that the majority of tech divers today use computers. If I have seen a tech diver in the last two years without a computer, I missed it.
I agree with you. The OP asked why some agencies oppose them.... They do it to eliminate the dependancy of using them. I also do not see but a very few die hard DIR divers dive with out a computer. Im sure this varies area to area.
---------------------------I believe every agency teaches all levels of diving within the NDLs in their OW classes. I don't believe anyone teaches to just be above 40 feet and you'll be OK.
does not Padi have instructor standards that say no training be conducted below 40 feet during certification training? To follow the recommended "not deeper than training" leaves you shallow where it is near impossible to get into trouble in regards to exceeding NDL? Staying above 40 ft makes NDL a moot issue and keeps you in an acceptable range for CESA and no REQUIRED STOP AT 20 FT for ANY SURFACE. I dont think they teach with the premis of "just be above 40 feet and you'll be OK" It becomes an assumed byproduct of the process and perhaps IMO the reason behind teh recommended limits given inthe course. My wife had to sign a document saying she understood that she was certified to dive to depths of no deeper than (padi recommended OW limit of 60 ft.) and another line item stateting that during training she received a max depth exposure of 34 or 35 ft. Another line item saying her certification was based on the observation of skills at depths no greater than that 35 ft. and another line item saying she would not dive beyond her training or exposure limits with out further training. The instructor limit of 40 ft pretty well establishes the risk of any serious problems of dives at less than 40 ft as being minimal and to stay with in those limits should make any dive with in limits OK to do. They did impress the idea that if you stayed above the recommended 60 ft you should never be able to exceed NDL and always be in range to do a CESA.
------------------------------------ Things like the rule of 120 only apply to certain dive tables and do not work with others.
I agree 100 percent. and ,,,,,that it is an air rule , which makes if the most conservative compared to nitrox tables ect. My wifes class mentioned the 120 rule but in the context of the limited view of OW diving on air only. When she got to nitrox class it was also discussed in regards to the 120 would be greater than the intent of the 120 air rule of thumb and why. Basically to support the nitrox giving longer bottom times/ ndls.
Michael Guerrero
Contributor
I find this the most amusing part of the discussion. I'm a normoxic Trimix diver and have spent somewhere in the $20K range in training, fills, boat rides, and gear. I'm not suffering for having spent $500 on a used Petrel. In my view, it's just the opposite.
I have also never found a technical diver who only knew how to fly the computer and didn't know how to actually plan a dive with a schedule. It's a tool, just like all the others we carry. My computer doesn't plan my dives, I do. When it's necessary to deviate from the plan, my computer helps me do that safely.
Michael Guerrero
Contributor
Something about don't make generalizations seems apropos here.
I really like number six because I don't think I've ever tracked my nitrogen groups. We do a tech dive, hang out for an hour or two, jump in, and do another one. Haven't done more than three tech dives in a day and take a break after the third or fourth day if doing a lot of diving. Never...once...tracked nitrogen groups. I died a long time ago from doing things I wasn't supposed to though.
The limit is 40 feet for the firt two OW dives. It is 60 feet for the second two.
The rule of 120 makes sense with the US Navy air tables and those other tables based on them. It does not work with the PADI tables.
At least in the training I have, students must plan and execute dives using tables before they can do them with computers.
I dont see that to be true on the padid tables
http://4.bp.blogspot.com/-KFm9pYIVm...RA/s1600/dive_tables_PADI+Chikarma+Diving.jpg
from 100 ft on down to about 50 ft it rins from about 105-125 many at the 115 area.
I think the4 point of hte 120 rule is as it applies to a failed computer is that if youare at 70 ft youhave about 50 minutes to ndl per the 120 tule ( its actually about 40. and if you have been down 35 min with or with out a computer its time to start planning to start your ascent. The 120 rule is not exact or linear throught ethedepth range but is consistant enough below 60 ft to use in the event of a computer failure. If teh amount is off that much then meke it aa 110 rule and use the same process. here is how I reAD THE TABLES
DEPTH NDL TOTAL
100 20 120
90 25 115
80 30 110
70 40 110
60 55 115
50 80 130
40 130-140 170-180
the avg totals for 50-100 ft is 116 and that is close enough for me to call it a 120 rule
The 40 ft line is the one that says you can not get hurt as deco goes if you stay at 40 or shallower because you will be out of gas before you can get near to an ndl. possibly you can do back to back 50 ft dives and not get to ndl prior to taking an SI. Padi says "RECOMMENDED 60 FT, should be the limit for an OW without any further training or experience. and again you probably cant get to ndl without running out of gas first.
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You're right: "emergency decompression" on page 218 of my "in-between" OW Diver manual does indeed tell you what to do if you exceed the NDL by under/over 5 minutes "using RDP". For "using the computer" it just says "follow the computer". So I stand corrected, just learning the procedure is not sufficient: a daring leap of logic is also required to apply the "RDP" procedure to the case of computer malfunction.
Rred
Contributor
Games? Considering that no one really has a solid grasp on the entire question of what safety is and what personal factors change that?
Many years ago I got accused of playing games because I split a 85' dive with a long stop at 40' (to see some things) and not using the 85' profile. My logic was that really, the time spent at 40' was NOT AN 85' BOTTOM TIME, it was a prolonged deco stop.
Erring on the side of conservative numbers doesn't meaning gaming the system, and gaming the system isn't always wrong. Product liability concerns will significantly determine how every product is built. When the engineers design it, nothing goes to market until a legal team review it, and they've got the authority to say "Not yet".
The fact that every company hollers "trade secret!" and refuses to say just what they are doing....that in itself is likely to wind up in court one day. Having a dive computer without knowing what it is really doing, is something akin to having dive tables that were generated by a random number generator.
The one really good thing about using tables instead of a computer? You dive with two numbers, confirm them from two gauges (depth & timer) and that's it. Most of the dive computers that I have seen have lots of poorly laid out, poorly labeled, screens just begging for confusion and pilot error. My instructor told us he'd once gotten thoroughly narcossed, and the only reason he was alive, was because he'd been rally curious about why his bubbles were going sideways [sic] so he decided to follow them.
Get confused, misread computer...bigger opportunity for pilot error.
Many years ago I got accused of playing games because I split a 85' dive with a long stop at 40' (to see some things) and not using the 85' profile. My logic was that really, the time spent at 40' was NOT AN 85' BOTTOM TIME, it was a prolonged deco stop.
Erring on the side of conservative numbers doesn't meaning gaming the system, and gaming the system isn't always wrong. Product liability concerns will significantly determine how every product is built. When the engineers design it, nothing goes to market until a legal team review it, and they've got the authority to say "Not yet".
The fact that every company hollers "trade secret!" and refuses to say just what they are doing....that in itself is likely to wind up in court one day. Having a dive computer without knowing what it is really doing, is something akin to having dive tables that were generated by a random number generator.
The one really good thing about using tables instead of a computer? You dive with two numbers, confirm them from two gauges (depth & timer) and that's it. Most of the dive computers that I have seen have lots of poorly laid out, poorly labeled, screens just begging for confusion and pilot error. My instructor told us he'd once gotten thoroughly narcossed, and the only reason he was alive, was because he'd been rally curious about why his bubbles were going sideways [sic] so he decided to follow them.
Get confused, misread computer...bigger opportunity for pilot error.
I believe you are referring to what most would call a multi-level dive, something basic tables can't do but which computer handle with no difficulty.
Not all computer companies do that. I can't tell the ratio, but many and perhaps most computer algorithms are completely open to scrutiny.
so this thoroughly narced instructor who couldn't tell which way was up would have been better off diving tables than a computer? Please explain why that would.have been a benefit.
No question about it. If you are that thoroughly confused, it is better to have no information at all coming to you and have top make your own decisions in that confused state than to try to read a computer screen.
Of course, the difficulty of reading a computer screen is more the function of the individual reading it than the screen itself. Reading those numbers and trying to decide what it all means is apparently a real problem for you, so I strongly suggest you stay away from it. Other people may have more ability to decipher that information, so for them it might not be so much of a problem.
Dan_P
Contributor
Blow the whistle, ref.
It's less like this;
...and this...
...and more like this;
....which I think a lot of organizations that do promote using computers, ought to learn from. That's only a personal opinion, of course.
Sure, there's the "it's about the instructor, not the agency"-excuse.... but that really only holds true for agencies that do a pretty poor job of assuring a consistently high level of training quality, doesn't it.
It's less like this;
...and this...
...and more like this;
....which I think a lot of organizations that do promote using computers, ought to learn from. That's only a personal opinion, of course.
Sure, there's the "it's about the instructor, not the agency"-excuse.... but that really only holds true for agencies that do a pretty poor job of assuring a consistently high level of training quality, doesn't it.
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