Ascent rate monitoring using air bubbles?

[DevonDiver]

As you gain more experience, stuff like ascent rate control become an instinctive 'sub-conscious' function.

 

[pea45]

Having dived more years on PADI tables than dive computers and using the smallest bubble rule. I was shocked how slow a rate you should surface when I used my first dive computer. My dive profile was full of red lines lines. I would say depending on my dive depth, time and number of dives in that day what type of dives I have done i.e no decompression or decompression dives this would be my main concern on surface rate. I guess I was lucky pre computer days as most of the dives were shallow 14m or less so I got away with to rapid a rate. All things equal i.e. plenty of air and no great whites nibbling at my fins I would ascent as slowly as possible watching my depth gauge and bubbles. As long as I can see my depth gauge slowly going up and not down (very easy to happen in open water) I would be happy, my bubbles can leave me behind so long as I am ascending and have plenty of air

 

[Sealdl]

Interesting tread. I started diving before we had a SPG and we were taught to come up slower than our smallest bubbles which we were always told was app. 60 ft./min. My concern with your ice dive is tying the rope around your arm. Why are you not wearing a harness.

 

[Izzysan]

Japan Diver is correct.
The smallest bubbles you can usually see on a dive are about the size of a pinhead, they travel at approximately 18m per minute to the surface. Ashe mentioned, back before computers we used to use them as a gauge of ascent speed. So long as you go no faster than those you, like us would live. But then again, why the completely daft dive scenario?

 

[kaerius]

Having dived more years on PADI tables than dive computers and using the smallest bubble rule. I was shocked how slow a rate you should surface when I used my first dive computer.

Smallest bubble rule is fast, and knowing that, you can go slower than your smallest(pinhead) bubbles, to stay conservative.

Dive computers typically restrict you to a 30-33fpm ascent rate, check your manual. This is quite conservative, and my computer tends to beep at me when I do the open water checkout practice of the CESA with my students(though obviously I stop them if they go too fast).

I've heard course directors talk about the no smallest bubbles rule even as recent as last year, though at least one who taught me to be an instructor told me it was useless in training open water divers, as it's much too imprecise(how big is a smallest bubble, how fast do they go anyway?), so I tend to impress that upon my students if asked(I think the book mentions it actually).

And I always carry at least dive computer+watch, and have a depth gauge on my spg. So even if my computer fails, at least I can do it manually, and I would suggest that while the scenario is bad, if you have at least a depth gauge, you can still do a rough count in your head "one thousand and one, one thousand and two, etc" and it will be more precise than the bubble method.

 

[JKPAO]

I remember reading somewhere or was it a dream???? CRS Navy Dive Tenders where originally required to pull up the divers at 100'/min. Which I'm told was so difficult they swithed to 60'/min.
Time changes all!
See you topside! John

 

[Bob DBF]

Smallest bubble rule is fast, and knowing that, you can go slower than your smallest(pinhead) bubbles, to stay conservative.

Dive computers typically restrict you to a 30-33fpm ascent rate, check your manual. This is quite conservative, and my computer tends to beep at me when I do the open water checkout practice of the CESA with my students(though obviously I stop them if they go too fast).

You have to realize that the rate of ascent and the dive tables have been changed recently, for me anyway, and when this practice was quite common the ascent rate was 60'/min, the tables gave you 60' for 60 min, there was no safety stop, and the tables gave you decompression stops should you overstay your depth a little.

My computer is training me to slow down on the way up now, and it gives me times on a safety stop if I am in the mind to do one.

Bob
--------------------------------
I may be old, but I’m not dead yet.

 

[LenC]

I'm not an ice diver, so perhaps I am missing something. The scenario is that you are in an overhead environment, extreme water conditions, zero visibility and either going deep enough or staying long enough so that your ascent rate is of serious concern to you - which means your gas is low. If you are diving this solo, that means the one piece of equipment which is going to allow you to find the only exit has no redundancy. If the tender drops it, it comes undone from your harness or somehow breaks or is cut does it matter how fast you come up?

 

[captain]

I remember reading somewhere or was it a dream???? CRS Navy Dive Tenders where originally required to pull up the divers at 100'/min. Which I'm told was so difficult they swithed to 60'/min.
Time changes all!
See you topside! John

US Navy hard hat divers were hauled up at 30 fpm, seems that was the speed of the winch that hualed up the stage they were on. When UDT scuba divers came along they wanted 100 fpm, they settled on 60 fpm. I believe now the Navy uses 60 fpm up to 60 feet and 30 fpm from 60 feet to the surface.

 

[Doriadiver11]

In fact, the best ascent rate is one that is not linear. Remember, that as you near the surface during ascent, the proportional ratio of gas volume increases more rapidly the closer you get to the surface; so physics dictates that for optimal risk mitigation, you should ascend progressively slower as you get nearer and nearer to the surface (assuming you have the same rate of exhalation throughout). Furthermore, your computer or your upline might tell you how fast you're ascending, but neither of these devices knows how quickly you're exhaling at any given moment.

I learned in the old Navy tables 60fpm days, but.... ALL of these "rules of thumb", (including the most recent rule of 30 feet per minute; regardless if it's indicated by your computer or hand-over hand on an upline), are just that....."rules of thumb". These, along with visually simple references such as the "smallest bubble rule" were all created arbitrarily simply to make it easy for any diver to comply with a relatively safe rate of ascent (operative word there is RELATIVELY). In fact, the safest rate of ascent depeneds upon from what depth you start your ascent, how fast you're exhaling, and your rate should slow substantially as you near the surface (especially the last 20 feet).

I've been a commercial and recreational diver for more than 35 years, and after over 5000+ dives in all sorts of conditions, gas mixes, and depths, I've just about seen it all. I've seen people violate deco-stops and other people "blow and go" from 90 feet without injury; while other times I've seen people adhere to the hard and fast recreational "rules" and get themselves paralyzed or embolized from a "too rapid ascent" (even going 30fpm according to their computers).

In the old days (1960s, and 1970s), practically every ascent was conducted as though it was an emergency ascent; and I rarely saw an injury back then. In those days, even recreational divers were actually taught PHYSICS, and PHYSIOLOGY during an entry level course, (as opposed to the bogus crap weekend courses they are giving to 10-year olds nowadays -- Thanks PADI).

Divers back then understood how to conduct every dive, and every ascent in terms of RISK MANAGEMENT (which is about "probabilities".....ie maximize the probability of success....minimize the probablility of injury). The "smallest bubble" rule of thumb MIGHT work, depending upon what depth you reached, how long you stayed, from what depth you started doing an emergency ascent, etc..

In such a scenario as you describe, you need to get to the underside of the ice canopy asap (to minimize your depth and thus air consumption) before you make your way back to the hole following your rope (I'm assuming the rope tied to your waist is the "drag-out line" your tender will use to pull you to the hole .... right ?)., but anyway; knowing the PHYSICS, will serve you a lot better than a bunch of arbitrary rules of thumb. So sure, use the smallest bubble rule from depth to around 20 feet, and from there, slow down substantially until you hit the bottom of the ice...that should maximize your probability of success.

In any case however, I have to say this as well.....that the real moral of this story is this: in the scenario you describe (solo night-ice dive with no functional computer, ... qua..... 'how do I know how fast I'm ascending " ?.... answer is... you don't )....

Sorry, but that is a ridiculous question. If you're conducting a dive like that and find yourself in such a situation; sorry, but you have not managed your risk properly, and your ascent rate control should be the least of your issues. Anyone who actually gets themselves into that situation, if they live through it; should quit diving immediately and take up golf...because you don't belong in the water....and certainly not under the ice alone at night.

No offense, but no demonstration of bravado is worth losing your life over. Good Luck and I hope you never find yourself in this situation.