"no fly" time

[Riger]

Posted again as the original seems to have gotten lost in the discussion.

As a Scuub Nuub with a recent PADI AOW cert, I find myself pondering this;

When I use my Computer as the yardstick for my bottom times, it gives me credit for an ascending profile, this technically violates my NDL Table limits. The reason that this is OK, is because my Comp is using a safe algorithm .... yes?

By the same logic, is it acceptable to follow the "No Fly" recommendation of my comp after single or multiple dives, even if they are lower than the DAN and/or PADI recommendations?

Best Regards
Richard (Riger)

 

[Tigerman]

Posted again as the original seems to have gotten lost in the discussion.

As a Scuub Nuub with a recent PADI AOW cert, I find myself pondering this;

When I use my Computer as the yardstick for my bottom times, it gives me credit for an ascending profile, this technically violates my NDL Table limits. The reason that this is OK, is because my Comp is using a safe algorithm .... yes?

By the same logic, is it acceptable to follow the "No Fly" recommendation of my comp after single or multiple dives, even if they are lower than the DAN and/or PADI recommendations?

Best Regards
Richard (Riger)

No, your computer dont use a "safe algorythm". It uses and averaged algorythm and diving after the computer can still get you bent.
Its referred to as "computer-rider hit"..

 

[Walter]

There are two ways to never get bent.

1. Don't dive.
2. If you do dive, don't come up.

 

[Riger]

No, your computer dont use a "safe algorythm". It uses and averaged algorythm and diving after the computer can still get you bent.
Its referred to as "computer-rider hit"..

Are you serious?

How/Why would a company like Uwatec or Suunto (and others I guess) use an "Unsafe Algorithm" and risk their users getting bent by giving them unsafe No Fly times?

I appreciate that following computer (or tables) No Stop Times (or NDL's) does not absolutely assure that you will not get bent, but not using Safe Algorithms is an entirely different matter.

Which leads to another question;

Is there a list of Algorithms (as adopted by the Computer Manufacturers) which are "sanctioned" or "considered suitable" by the Diving agencies such as DANS/PADI/NAAUI etc..?​

Best Regards
Richard (Riger)

 

[LeadTurn_SD]

Posted again as the original seems to have gotten lost in the discussion.

As a Scuub Nuub with a recent PADI AOW cert, I find myself pondering this;

When I use my Computer as the yardstick for my bottom times, it gives me credit for an ascending profile, this technically violates my NDL Table limits. The reason that this is OK, is because my Comp is using a safe algorithm .... yes?

By the same logic, is it acceptable to follow the "No Fly" recommendation of my comp after single or multiple dives, even if they are lower than the DAN and/or PADI recommendations?

Best Regards
Richard (Riger)

1.) Your computer is giving you credit for a multilevel dive. The NDL table does not, since it assumes you spent your entire time at the deepest depth of the dive. Your computer is not necessarily using a different algorithm from the PADI NDL table, it is just doing continuous calculations to credit you for time spent at shallower depths during the dive.

2.) Most computers begin a count-down after you surface, the "Time-to-fly". Refer to your owner's manual, but I believe the "Time-to-fly" countdown on most computers is quite conservative, and follows DAN recommendations. I do not think the "Time-to-fly" countdown is based on your dive profile, I think it is a pre-set value (my computer's "Time-to-fly" is 24 hours, even for shallow dives).

Again, check your owner's manual to be sure.

Safe Diving!

 

[Riger]

.....

2.) Most computers begin a count-down after you surface, the "Time-to-fly". Refer to your owner's manual, but I believe the "Time-to-fly" countdown on most computers is quite conservative, and follows DAN recommendations. I do not think the "Time-to-fly" countdown is based on your dive profile, I think it is a pre-set value (my computer's "Time-to-fly" is 24 hours, even for shallow dives).

Again, check your owner's manual to be sure.

Safe Diving!

LeadTurn, thank you for the response. I checked the manual as per your guidance and;

Ref Page 9/10 of the Galileo Sol Computer Manual/Guide;

The no-fly time (NO FLY) is the time during which an exposure to the reduced pressure inside the cabin .......(snip)....... as calculated by the decompression model in the computer.

Which comes back to my question, is it safe to follow the guidance of the Computer?

The value of this discussion/thread cannot be underestimated.

Best Regards
Richard (Riger)

 

[lowwall]

By the same logic, is it acceptable to follow the "No Fly" recommendation of my comp after single or multiple dives, even if they are lower than the DAN and/or PADI recommendations?

As safe as any other data from your computer Seriously the current DAN/PADI recommendations are based on a limited set of dive profiles chosen mostly because they were right on the edge of the PADI tables, running a bunch of volunteers through the profiles in a hyperbaric chamber, seeing how long it took until no one got bent and then adding 2 hours to the longest safe time they found. BTW, they did not use a safety stop on the "dives." At the conference where they came up with the recs, they did state it would be reasonable to derive an algorithmic approach, but they declined to endorse any specific model. The US Navy did derive a mathematical model, which they tweaked to incorporate the DAN results. The computer makers that use a calculated countdown (instead of a fixed 18 or 24 hour countdown) likely did the same.

 

[LeadTurn_SD]

LeadTurn, thank you for the response. I checked the manual as per your guidance and;

Ref Page 9/10 of the Galileo Sol Computer Manual/Guide;

The no-fly time (NO FLY) is the time during which an exposure to the reduced pressure inside the cabin .......(snip)....... as calculated by the decompression model in the computer.

Which comes back to my question, is it safe to follow the guidance of the Computer?

The value of this discussion/thread cannot be underestimated.

Best Regards
Richard (Riger)

Hi Riger,

I have a different computer, and I'm not sure how the Galileo performs the calculation, but my guess is that it is still using a pre-set "time-to-fly" value that is independent of the dive profile (but maybe not, maybe another Galileo owner will chime in).

There is so much liability involved I'd say it is a safe bet that the Galileo is erring on the side of caution, so I'd say yes, you can probably fly safely when you computer says fly "ok". What I would do is use the most conservative "time-to-fly" value possible, either your computer or DAN recommendations. If there is an urgent need to fly sooner than that, I'd refer to the Navy tables referred to earlier in this thread.

Hope this helps.

 

[Tigerman]

The thing with computers - quick and dirty;
- Not all computers calculate your NDL the same. One computer could say youre fine, another that you have a deco obligation.
- The algorythms are based on averages. Your hydration, physical fitness and so on at any given day is not. A profile thats ok one day can be bad the next.
- Since the computers are based on averages, youre in most cases safe by following them, however they are less conservative than tables so they leave less room for error.

 

[Damselfish]

A computer isn't necessarily more or less safe than your table, it's just one of many ways of going about the same general thing. It's not like any of this is an exact science. There are other ways of getting more time on multilevel dives, such as using the PADI "wheel" which is sort of a fancy table. (Which hardly anyone uses since computers are a lot more convenient.)

As far as following time to fly on your computer, I don't have a problem with it. But using the DAN guidelines or whatever variation you feel comfortable with is more practical for planning purposes. I mean, if I've flown someplace, I've got a plane ticket back at a set time, and my dives are usually at scheduled times, so it's a much cruder plan like "if I do the afternoon dives the last day it's not enough time, if I stop with the morning boat it is." The thing about a computer is, if you're using it in the typical fashion you may not know what the time to fly it will show until after you're done diving, which is a bit late to decide you don't have enough time before your flight. I suppose I could do the math and squeeze in a shore dive at the last possible moment that will fit. But whatever scheme you use, it generally doesn't make sense to push it to the last minutes.

(The Suuntos I've had calculate a time-to-fly time based on your profiles, it's not always the same.)