Wisdom of trusting one's dive computer?

[Eric Sedletzky]

How do you plan a dive when you are doing an exploration somewhere that has never been dived or charted with possible sheer walls, sawtooth profiles, and the unknown?
We have many such places in my area. Computers have really opened up many more possibilities than running tables and square profiles.
Not trusting computers is so 20 years ago.

 

[Eric Sedletzky]

...go to your backup computer or ascend, do your safety-stop, and surface. The "table in your pocket" doesn't know how deep you've been nor for how long, and your backup watch doesn't know when you entered the water unless you set the bezel.

Chances are that if your computer craps out you might already be way past your welcome on tables simply because how talented computers are at milking every bit of no deco BT out of your dive.
At the most, a watch will give you real time minutes so you can ascend at a slow rate and to time your three minute stop. A manual depth gauge will give you a clue as to your depth, but the dive IS over.
A back up computer is obviously the best solution, and an identical model the ultimate solution.
To think anybody can switch from a computer to tables mid stream during a dive and finish it out is just assinine.

 

[tursiops]

Chances are that if your computer craps out you might already be way past your welcome on tables simply because how talented computers are at milking every bit of no deco BT out of your dive.

Concur.

 

[PfcAJ]

How do you plan a dive when you are doing an exploration somewhere that has never been dived or charted with possible sheer walls, sawtooth profiles, and the unknown?
We have many such places in my area. Computers have really opened up many more possibilities than running tables and square profiles.
Not trusting computers is so 20 years ago.

I did a fair bit of cave exploration between 80 and 200ft with runtimes between 2 and 5hrs before I started using a computer. I’d have no problems doing an exploration dive of any magnitude without one.

Average depth, awareness of your available gases, knowledge of the relationship between depth and deco time, prior experience to anticipate what to expect.

 

[broncobowsher]

But you have much experience with running without a computer. You lived and breathed it so long. That complete knowledge just isn't around anymore. To a few, yes. To the masses, no. You are the unicorn in the room.

For the rest of us mere mortals that dive sometimes, you use a computer. You get a basic understanding of what the computer is doing for you, basic ideas of what reasonable run times at depths will be. But a computer or two is how the world works these days. Grabbing a set of tables out of your pocket is keeping a couple quarters for a pay phone, out of date. Potentially functional to someone who grew up with it. But you are just showing your age more than your wisdom.

 

[PfcAJ]

But you have much experience with running without a computer. You lived and breathed it so long. That complete knowledge just isn't around anymore. To a few, yes. To the masses, no. You are the unicorn in the room.

For the rest of us mere mortals that dive sometimes, you use a computer. You get a basic understanding of what the computer is doing for you, basic ideas of what reasonable run times at depths will be. But a computer or two is how the world works these days. Grabbing a set of tables out of your pocket is keeping a couple quarters for a pay phone, out of date. Potentially functional to someone who grew up with it. But you are just showing your age more than your wisdom.

well I’m 33... probably on the younger side of the bell curve for this forum.

this isn’t some mysterious and arcane knowledge passed down from master to apprentice. It’s just paying attention and learning the techniques. Things like “read the tables” and “pay attention to your depth” are OW class skills. The trick is to keep doing it.

 

[Eric Sedletzky]

I did a fair bit of cave exploration between 80 and 200ft with runtimes between 2 and 5hrs before I started using a computer. I’d have no problems doing an exploration dive of any magnitude without one.

Average depth, awareness of your available gases, knowledge of the relationship between depth and deco time, prior experience to anticipate what to expect.

Please keep in mind this is the basic forum, so discussions about 200’ dives on mix and depth averaging should not be discussed here.
Depth averaging from info based on tables is not something that should be attempted by recreational divers. Every table I’ve ever seen was developed for square profiles except for the wheel which was a pain to use and never really took off (side point). I doubt the top scientists of the world who came up with the tables did not plan for people to start adjusting and averaging depths and times trying to outsmart something that has taken many years of research to get right and were never designed to be monkeyed with.
It would take a mathematical genius, a freak of nature, to even begin to come close to how accurately a computer can adjust NDL time every second of the dive at any given depth. Dive times at different depths are not all the same in regards to gas uptake therefore are never linear, and therefore a straight average for all the different depths during a dive doesn’t work.
For someone to think that they can mentally keep track if every minute of their dive at every depth and do the fine math during a dive on the fly equal to a computer is insane.

 

[PfcAJ]

Please keep in mind this is the basic forum, so discussions about 200’ dives on mix and depth averaging should not be discussed here.
Depth averaging from info based on tables is not something that should be attempted by recreational divers. Every table I’ve ever seen was developed for square profiles except for the wheel which was a pain to use and never really took off (side point). I doubt the top scientists of the world who came up with the tables did not plan for people to start adjusting and averaging depths and times trying to outsmart something that has taken many years of research to get right and were never designed to be monkeyed with.
It would take a mathematical genius, a freak of nature, to even begin to come close to how accurately a computer can adjust NDL time every second of the dive at any given depth. Dive times at different depths are not all the same in regards to gas uptake therefore are never linear, and therefore a straight average for all the different depths during a dive doesn’t work.
For someone to think that they can mentally keep track if every minute of their dive at every depth and do the fine math during a dive on the fly equal to a computer is insane.

^this is why people think it’s forbidden knowledge only to be possessed by a select few.

“That shouldn’t be discussed here”.

Top Secret! Everyone close your browser immediately!

20’ or 200’ the principles remain the same. Avg depth works for everything except the most extreme of hypothetical cases, and even then it’s incredibly close to what any computer or deco software will spit out.

Paying attention works. Monitor your depth and time. Practice. Compare with the avg depth calculated via another source (buddy, computer, depth graph).

studying tables works. “Hey if I’m at this depth my NDL is x. If I stay 10’ deeper for the same my NDL is y minutes less. Neat!” Study those relationships.

none of this is crazy talk, dude. It might be “crazy” in the context of an OW class designed to pump out divers that can jjuusstt barely not drown themselves unsupervised, but i think that’s a very poor standard to aspire to, and even worse to suggest that we not talk about something better.

 

[ChuckP]

^this is why people think it’s forbidden knowledge only to be possessed by a select few.

“That shouldn’t be discussed here”.

Top Secret! Everyone close your browser immediately!

Curious to how conservative you played dives like that - OW is one thing because you can control the depth but the cave unknown depth thing - Ugghh

I gots to think lots of conservatism and progressive entries??

Diving today with the tools we have and the lessons learned from before - we got it pretty easy - maybe too easy

 

[PfcAJ]

Curious to how conservative you played dives like that - OW is one thing because you can control the depth but the cave unknown depth thing - Ugghh

I gots to think lots of conservatism and progressive entries??

Diving today with the tools we have and the lessons learned from before - we got it pretty easy - maybe too easy

You come up with limits as a starting point. A max depth, a max time. I can anticipate the avg depth and plan a ballpark dive time.

Shallower? Dive can be a lil longer. Deeper? A lil shorter.

An OW analog would be knowing your NDLs for 60,70, and 80ft. 3 numbers to remember. You go on a wall dive and enjoy while paying attention to your depth. You knew before you got in the water what your plan was (to enjoy the reef between 60 and 80’), your minimum gas volume, and you max allowable dive time(s). Avg depth (since you’re payin attention) will tell your your NDL time.

I don’t think we “pushed it” on any of those dives. Even as I transitioned into computer usage the times are always within a couple minutes from what I would have done without it.