Ascent rate monitoring using air bubbles?

[redacted]

Yeah, but that line is tied around my waist, and the line is made of floating polyprophylene. Any slack line is pulled to the surface, too. There is no rope to climb along. It just moves with me. And yes, I have two cutting tools...

If you stay negative, the line need not float up.

 

[DevonDiver]

I got training from a qualified instructor on how to do the dives

....But then I started asking myself the what-ifs.

Comprehensive training then?

 

[Blackwood]

This is an interesting science experiment, but completely unnecessary. Just go up the line. You can probably estimate 1 foot pretty closely. Watch the line, and take at least a couple seconds for each foot you cross.

That's assuming it's hanging vertically. As you stated it is not, so moving along it at 2 seconds per foot will be slower than 30fpm in the vertical direction.

That "not faster than your smallest bubbles" seems to me as a simple controlled solution.

It doesn't seem simple to me (why isn't it phrased "not faster than your slowest bubbles"?), and it's unequivocally not controlled.

 

[knotical]

Figure 4 in this paper:
http://www.waset.org/journals/waset/v28/v28-48.pdf
indicates that tiny bubbles rise at about 20 cm/sec and 2 cm diameter bubbles rise at about 30 cm/sec.
This converts to about 12-18 m/min or 40-60 ft/min. So small bubbles could be (and have been) used as a rough guide. But as we're probably all aware, in general slower is better, especially nearer the surface.

 

[fnfalman]

That "not faster than your smallest bubbles" seems to me as a simple controlled solution. Do we have any idea of the actual speed? Is it closer to 60ft/min or 15ft/min? I haven't really paid attention to such things yet...

There was an empirical experiment done by students at a university that I can't remember top off my head but they figured on an average, the smallest bubbles's speed was about 50-something feet per minute.

 

[Doubler]

Was taught and used the "smallest bubble" for years prior to computers (cert 1972), no problem . There are a lot of things we did back in the day that have been replaced by modern technology and methods. I feel I sometimes have an advantage over new divers because of the "old timers" instruction I received.

I can do long division using a pen and paper and figure out proper change without a cash register also.

 

[String]

A big problem with "smallest bubbles" if people dont practice is is remembering to always move bubbles to the next smallest. As bubbles rise they expand so if you don't do this you get faster and faster.

 

[Charlie99]

Question

How do I control my ascent rate?

(yes, with a secondary computer, but let's assume they both failed or got lost)

Use your buddy's computer to control your ascent.

 

[flots am]

I prefer to prepare for the worst case scenario, so that when an incident finally happens, I have a backup plan, and a backup to that. This is really helpfull when things start to fail big time.

Scenario

Night time ice dive, clear silt-free water, wide sea, no reference points, safety line to surface, I'm diving alone as my buddy is at the surface keeping the safety line. My computers fail. The only usable reference is the safety line. It gives me direction but no speed indication, as the rope *floats* as it should.

If you're doing an ice dive in the ocean, you're diving in some very unforgiving water and shouldn't be relying on internet advice to save your life.

That said, your rope should not be slack, since a slack line cuts off communications with your buddy.

 

[rjack321]

Look ma a tornado!!!

Seriously - with all your hypothetical problems (no buddy, no gauges, no line, no vis, whatever else you are throwing into the mix now...) who cares about ascent rate, just get back to the dang ice hole. Even 100fpm is better than dinking around much longer with all your broken gear and buddies.