Ascending without a dive computer

[BRT]

Not everyone, especially newer divers, has the same sense of time passed while watching a gauge. I am confident in my ability to do a nice slow ascent with just a gauge now, but 25 years ago? Not so much then.

I was certified 33 years ago and had no computer. I watched my depth gauge and sometimes my smallest bubbles. I don't remember it ever being a problem except for a couple of close calls with a drysuit, but then I knew I was going too fast without looking at my computer.

 

[Rred]

IIRC the percentage of divers that got bent from improper ascent rates, back in the 70's and 80's "following your smallest bubbles", is curiously the same as the rate found in today's divers relying on an expensive and unreliable mixture of electronics and seawater held apart by mere o-rings.

As George Carlin [RIP] said TOO MUCH STUFF.

And back then, an ascent rate of 60fpm was normal. Today's 30 is way more conservative. Back then, the debate was over the "French" ascent method, where divers were taught to follow their bubbles, yes, but to ascend at a 45 degree angle, not straight up, which also slowed the effective ascent rate.

Like ABS braking systems in modern cars. ABS is mandated for safety, and in many circumstances it can stop a car faster. Except, the accident rate for ABS brakes has actually INCREASED because all those highly trained drivers now rely on the ABS system, "knowing" it will keep them safe. It doesn't.

Sometimes KISS is still a good idea. Computer, ascent rate, alarms, very nice. But like today's 14" thick mattresses...somehow, so many of us grew up with mattresses that were only 6" thick and it didn't harm us.

 

[doctormike]

IIRC the percentage of divers that got bent from improper ascent rates, back in the 70's and 80's "following your smallest bubbles", is curiously the same as the rate found in today's divers relying on an expensive and unreliable mixture of electronics and seawater held apart by mere o-rings.

Wow! You really have that data? I would be interested in that.

Of course, for that comparison to be useful, you would have to account for differences in the number of divers, physical characteristics of divers, and differences in the range of profiles and amount of inert gas loading.

 

[GJC]

IIRC the percentage of divers that got bent from improper ascent rates, back in the 70's and 80's "following your smallest bubbles", is curiously the same as the rate found in today's divers relying on an expensive and unreliable mixture of electronics and seawater held apart by mere o-rings.

As George Carlin [RIP] said TOO MUCH STUFF.

And back then, an ascent rate of 60fpm was normal. Today's 30 is way more conservative. Back then, the debate was over the "French" ascent method, where divers were taught to follow their bubbles, yes, but to ascend at a 45 degree angle, not straight up, which also slowed the effective ascent rate.

Like ABS braking systems in modern cars. ABS is mandated for safety, and in many circumstances it can stop a car faster. Except, the accident rate for ABS brakes has actually INCREASED because all those highly trained drivers now rely on the ABS system, "knowing" it will keep them safe. It doesn't.

Sometimes KISS is still a good idea. Computer, ascent rate, alarms, very nice. But like today's 14" thick mattresses...somehow, so many of us grew up with mattresses that were only 6" thick and it didn't harm us.

I'm also interested in the data comparing DCS rates with tables vs computers.

Also interested in data on ABS and non ABS accident rates.

 

[BRT]

IIRC the percentage of divers that got bent from improper ascent rates, back in the 70's and 80's "following your smallest bubbles", is curiously the same as the rate found in today's divers relying on an expensive and unreliable mixture of electronics and seawater held apart by mere o-rings.

As George Carlin [RIP] said TOO MUCH STUFF.

And back then, an ascent rate of 60fpm was normal. Today's 30 is way more conservative. Back then, the debate was over the "French" ascent method, where divers were taught to follow their bubbles, yes, but to ascend at a 45 degree angle, not straight up, which also slowed the effective ascent rate.

Like ABS braking systems in modern cars. ABS is mandated for safety, and in many circumstances it can stop a car faster. Except, the accident rate for ABS brakes has actually INCREASED because all those highly trained drivers now rely on the ABS system, "knowing" it will keep them safe. It doesn't.

Sometimes KISS is still a good idea. Computer, ascent rate, alarms, very nice. But like today's 14" thick mattresses...somehow, so many of us grew up with mattresses that were only 6" thick and it didn't harm us.

Following your bubbles up at a 45 deg angle will make you swim faster but it won't slow your ascent rate.

 

[BRT]

I'm also interested in the data comparing DCS rates with tables vs computers.

Also interested in data on ABS and non ABS accident rates.

iMobility Effects Database

 

[JackD342]

Following your bubbles up at a 45 deg angle will make you swim faster but it won't slow your ascent rate.

Is that maybe while leaning back a 45° angle, so you can better see your bubbles? Because if swimming forward at a 45° angle, I don't see how you could even tell whether or not you are matching their rate. They're behind you, right?

 

[txgoose]

Is that maybe while leaning back a 45° angle, so you can better see your bubbles? Because if swimming forward at a 45° angle, I don't see how you could even tell whether or not you are matching their rate. They're behind you, right?

Seems spot on. In the Keys I watched a DM for another group to a slow steady ascent in the perfect Lazy-boy trim position. Now he could watch his bubbles.

 

[KenGordon]

I don’t want to belabor the point. The discussion was about a stated minimum limit. I probably have beaten my curiosity on this one. I’ll call it three feet for impractical practical purposes. You and Doc and Bluetrin have been great. I appreciate your contributions here and all over SB.

I am clearly late to this party.

From your questions I suspect your are missing a piece in the jigsaw puzzle of the model being used to control an ascent.

You sound like you expect to be offgassing as soon as you start to ascend.

Actually you will only be off gassing in tissues (if any) which have a sufficient N2 loading. It maybe that none have, especially for a bounce dive to depth. With a 4 minute half time it takes a while for even the fast tissues to catch up with ambient and really a while for the slower ones. So the slower ones will almost certainly be on gassing through the entire dive,

This means that slow is NOT necessarily safer. It depends.

At the extreme end of slow you have full saturation dives. For those the ascent is always offgassing because all the tissues reached equilibrium. So slower is safer. But the dives done by recreational divers are almost the exact opposite of these.

This is why there are tables, computers and so forth.

(Ps don’t forget these are only models, not the real thing)

 

[txgoose]

I am clearly late to this party.

Maybe.

I do believe that you discounted a lot of what I've already written. I understand on and off gassing at at least an amateurish level. Post 56 and 53 of The Computer Between the Ears were instrumental in my knowledge. @doctormike and @boulderjohn were great resources in that thread as well. I don't claim expertise, just a claim to be perusing knowledge. I didn't understand a stated minimum of 9ft/min ascent rate. I still think that it is a high number. We already beat up how tissues are loading and unloading.

At the extreme end of slow you have full saturation dives. For those the ascent is always offgassing because all the tissues reached equilibrium. So slower is safer. But the dives done by recreational divers are almost the exact opposite of these.

But we are always taught that ascending too quickly is dangerous. You can't make the claim that faster is safer. At least not as a blanket statement. As you quoted me, the discussion was about a stated minimum ascent rate of nine feet/min. I still believe that is faster than is required to stay out of NDL on rec dives. Using the tables that you mention (at least the SSI versions), and some back of the napkin math, I proposed a two foot minimum. I agree with boulderjohn that this is probably unrealistically close to NDL and discounting of previously accumulated nitrogen. So I tossed out three feet per minimum. Is that too slow for you? If so, we can belabor it a bit. I'm open to it being 2-3-4-5. I don't know. Nine just seems high, still does. If 3 ft/min is at least in a ballpark, we're probably good.

In reality, unless someone was ascending an incline slope, etc, most of us would probably struggle to hold an ascent rate that slow anyway. Eventually most folks are going to hit turn pressure anyway.

This is why there are tables, computers and so forth.

Don't act like mentioning computers is going to get us back on topic. Digression is what we do.

(Ps don’t forget these are only models, not the real thing)

One thing I have learned here is that no one is actually sure what reality is. All the agencies and computer programmers are making their best educated guesses. People being responsible, which I hope to be, are just trying to find rules of thumb that work for the vast portions of our population.