Learning Ascent Rate

[jeffsterinsf]

Other threads have covered the limitations of relying on a dive computer to judge ascent rate (lack of situational awareness, lag time, etc.) and suggested that using other cues are key to becoming a better diver, but I haven't seen any solid suggestions on how to accomplish this learning process.

A depth gauge moves far too slowly to be immediately useful in judging rate of ascent, and suffers from the same issues of lack of situational awareness.

Some have suggested not ascending any faster than your smallest exhaust bubbles, but tiny bubbles rise at rates a couple of cm/s, seemingly too slow for the suggested 3m/min ascent rate. (10^-2 cm bubble at 1.5 cm/s, Weinke, Technical Diving, 2001, giving about 1 m/min).

Motion Of Bubbles And Bubble Characteristics
http://www.seas.ucla.edu/stenstro/NewBubble.pdf
indicates that bubbles larger than about 1 mm (up to about 7 mm) rise at about 30 cm/s, or 18 m/min.

Quite a range there for trying to use bubbles as the reference point.

George Irvine states in his talk
http://www.baue.org/library/irvine_baue_talk.html
"We also would implement a slow ascent for wreck diving, stopping every 10ft consciously to get a 30ft ascent rate. Thirty-foot ascent rate is merely stopping every 10ft for 20 seconds, not counting the time to move. Consciously stopping yourself as you hit 10ft increments will give you a good clean ascent rate."

Is this a reasonable approach?

Are there other actionable suggestions for learning this critical skill?

 

[neil]

jeffsterinsf once bubbled...


George Irvine states in his talk
http://www.baue.org/library/irvine_baue_talk.html
"We also would implement a slow ascent for wreck diving, stopping every 10ft consciously to get a 30ft ascent rate. Thirty-foot ascent rate is merely stopping every 10ft for 20 seconds, not counting the time to move. Consciously stopping yourself as you hit 10ft increments will give you a good clean ascent rate."
Is this a reasonable approach?

It SEEMS like a reasonable approach, but.
stopping in this fashion is logically NOT the same as maintaining a 30fpm ascent rate. The question is: does this produce the same effect on offgassing. Can I safely zip between stops at 100fpm? If so, then the 10 ft. stops make the whole process really easy.

Neil

 

[Uncle Pug]

neil once bubbled...
stopping in this fashion is logically NOT the same as maintaining a 30fpm ascent rate. The question is: does this produce the same effect on offgassing.

Evidently the answer is no.

There was an article by Dr. Bennett discussing linear ascents vs ascents with discreet stops in the June issue of Alert Diver.

Seems discreet stops win in the goat survival department

 

[100days-a-year]

UP,I was divin' or I'd have gotten that quote out sooner.I dive with BT or computer at all times mostly for the ascent rate IF I'm somewhere that visual clues are either absent or difficult to use .I try to go less than 1/2 the speed of my slowest bubbles.This gets me a net of <30 fpm .My computer downloads show me at 60fpm til 30'-60' then I'm usually ~15fpm or less.Try setting your computer at the highest setting 1 per sec or 1 every 5 sec.Then dive several dives,download it and graph your actual ascent rates vs. your "alleged"one.If you read BRWs book it'll explain the process whereby gas pressures in bubble nuclei either help or hinder off-gassing and how ascent rates figure in to the ultimate disposition of infused gas .

 

[Uncle Pug]

100days-a-year once bubbled...
UP,I was divin' or I'd have gotten that quote out sooner.

Rub it in Tony.

 

[The Chairman]

following your bubbles are not possible... a stiff current, low vis, etc... all these things make relying on external signs a crap-shoot. You have to use a standard such as a depth guage or a computer in order to determine depth and either use the ascent gauge, or time your ten foot intervals to stay on track.

I like the ten foot/20 second rule when I only have a depth guage. I don't think that the concept is to move between stages as quickly as possible (100fpm, etc), but rather to sit for twenty seconds at every stage and then move on. This will give you an ascent somewhat slower than 30 fpm, but thats not a bad thing.

That being said, I usually will ascend from the deeper zones rather quickly (40/50fpm) until I hit 80 fsw and then slow it down to 30fpm until I hit 20, where I slow it down to 10/15 fpm (even after a 5 minute safety). The % pressure change is so much greater the shallower we get that I really take greater care the closer I get to the surface. BTW, these are MAXIMUM ascent rates for me... my downloads from my Cobra indicate that I ascend much more slowly.

 

[riddler]

Some have suggested not ascending any faster than your smallest exhaust bubbles, but tiny bubbles rise at rates a couple of cm/s, seemingly too slow for the suggested 3m/min ascent rate.

Sorry to dig up an old thread, but I'd like to revisit this. I hear mixed things about ascending no slower than your smallest bubbles. Many SSI manuals state this - that you should ascend no faster than your smallest bubbles. But I've heard very experienced divers say this is a fallacy.

So my question is, if you have no working depth guage and no buddy to follow, what is the best way to control your rate of ascent?

 

[dutch-scuba-kid]

it's not about the smallest bubbles I think... I think it's about one of thé smallest... Maybe third largest (which are smaller than they sound).
Hmm... try that. Anyway, I just use my watch. 10m/min.

 

[pipedope]

Is one way.
You can measure the time in seconds to rise 5' or 10'.
10 seconds for 5', 20 seconds for 10' is a 30fpm rate.

If you don't have a depth gage, it is broken or vis has gone to zero and you can't see it will make you do something else.

One possability is to shoot a bag and hand over hand up the line.

If you stop at each 10', think of all the practice you get at bouyancy control.

 

[MikeFerrara]

Sorry to dig up an old thread, but I'd like to revisit this. I hear mixed things about ascending no slower than your smallest bubbles. Many SSI manuals state this - that you should ascend no faster than your smallest bubbles. But I've heard very experienced divers say this is a fallacy.

So my question is, if you have no working depth guage and no buddy to follow, what is the best way to control your rate of ascent?

Forget bubbles.

First of all, I hope you don't end up with no depth gauge and no buddy. Don't do that.

but... there are a number of things you can use to estimate ascent rate. Any visual reference like a line or a wall will work. Particles suspended in the water tend to stay at a fairly constant depth if there isn't water movement to move them. You can also pay attention to your ears. They'll tell you more than you think if you pay attention and maybe practice a little.