BrianS
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Don't forget, if you raise your computer to view it from your side, you will get a false reading since the computer is going up faster than you are.
Chad_Ordelheide:
Ascending faster than 60ft/minute
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Please consider reading (and ask questions if you do not understand) a short DAN article on the subject: DAN
The 60-ft/min ascent rate was a compromise between the rate asked for by the Combat Swimmers (100-ft/min) and the Hard Hat Divers (30 ft/min) (SCUBA Diving Magazine Link). It was decided on by putting a diver on a stage and seeing how fast the diver could be hand cranked (as it was done then) to the surface. The 60-ft/min rate is an a priori decision that dictates the rest of the numbers in the U.S. Navy Tables.
The goal on ascent is to not bubble while maintaining a maximum permissible gradient for offgassing (thus the value of the deep stop). While there is not doubt that the slower the ascent rate (as long as you continue to offgas your controlling compartment) the better, if you want to optimize your available bottom time on a repetitive dive you need table specifically designed for the altered ascent rate.
The biggest problem with the 60-ft/min ascent rate was that divers did not follow it. Actual in water observations of sport divers (lost the reference I think it was Egstrom back in the early 80s) showed typical ascent rates rate two to three times greater.
It is a fallacy that, There have been numerous studies over the last several years showing that 60ft per minute was too fast. What is known is that when recreational divers make slower ascents (and now keep in mind that were focusing on the ascent and not rocketing up at 120 to 180 ft/min) there were fewer problems.
So what is the bottom line? Id been taught to come up ten feet on my depth gauge, check my watch, ten seconds on my watch, check my depth gauge, all the way to the surface. I did that for years and years.
When there was an initial suggestion that we drop back to 30 ft/min I did ten seconds on the watch, 5 feet on the depth gauge. When precautionary stops began to be discussed, I added a three-minute stop at 10 feet.
As I learned more about decompression theory I realized that a variable ascent rate (faster from depth and slower shallow) made more sense, especially when used in conjunction with deeper stops. So I changed my ascent to 120 ft/min to half of my dive depth with a stop of two minutes (figuring it takes about a minute for the blood to fully circulate) followed by a 30 ft/min ascent to 10 feet with a 3 minute stop. In light of what I know today, that stills seems to make sense, though I have slowed the deeper part of my ascent.
The 60-ft/min ascent rate was a compromise between the rate asked for by the Combat Swimmers (100-ft/min) and the Hard Hat Divers (30 ft/min) (SCUBA Diving Magazine Link). It was decided on by putting a diver on a stage and seeing how fast the diver could be hand cranked (as it was done then) to the surface. The 60-ft/min rate is an a priori decision that dictates the rest of the numbers in the U.S. Navy Tables.
The goal on ascent is to not bubble while maintaining a maximum permissible gradient for offgassing (thus the value of the deep stop). While there is not doubt that the slower the ascent rate (as long as you continue to offgas your controlling compartment) the better, if you want to optimize your available bottom time on a repetitive dive you need table specifically designed for the altered ascent rate.
The biggest problem with the 60-ft/min ascent rate was that divers did not follow it. Actual in water observations of sport divers (lost the reference I think it was Egstrom back in the early 80s) showed typical ascent rates rate two to three times greater.
It is a fallacy that, There have been numerous studies over the last several years showing that 60ft per minute was too fast. What is known is that when recreational divers make slower ascents (and now keep in mind that were focusing on the ascent and not rocketing up at 120 to 180 ft/min) there were fewer problems.
So what is the bottom line? Id been taught to come up ten feet on my depth gauge, check my watch, ten seconds on my watch, check my depth gauge, all the way to the surface. I did that for years and years.
When there was an initial suggestion that we drop back to 30 ft/min I did ten seconds on the watch, 5 feet on the depth gauge. When precautionary stops began to be discussed, I added a three-minute stop at 10 feet.
As I learned more about decompression theory I realized that a variable ascent rate (faster from depth and slower shallow) made more sense, especially when used in conjunction with deeper stops. So I changed my ascent to 120 ft/min to half of my dive depth with a stop of two minutes (figuring it takes about a minute for the blood to fully circulate) followed by a 30 ft/min ascent to 10 feet with a 3 minute stop. In light of what I know today, that stills seems to make sense, though I have slowed the deeper part of my ascent.
Fish_Whisperer:
The slower your acsent rate the more time you have to offgas and the less likely you'll have a bubble to expand and cause a DCS hit. I think that is most important from 15 feet to the surface. I sometimes spend 3 or 4 minutes hovering at around 5 feet to make sure I'm free of bubbles.
We were diving with a guy in Coz last week who got bent and went for 3 rides in the chamber. We basically dove the same dives but I noticed he was a fast ascender. You cannot ascend too slowly.
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You can ascend too slowly. You can ascend too fast. The length and depth of your dive determines the controlling compartment.
For most recreational dives the faster compartments are in control. Even for a relatively slow ascent, say 20 ft/min, N2 will not have enough time to offgas without producing bubbles. These bubbles are most likely to occur in the blood (and be filtered out in the lungs) and possibly in the spinal cord, leading to neurological symptoms.
It has been shown (and experience dictates) that a deep stop combined with a rapid ascent rate promotes better offgasing than does a very slow ascent rate. For deep dives, a shallow stop is too late, the cap is most ways off the bottle. However, a deep stop may reduce the possibility of bubbles in the faster compartments. Take a couple of minutes at half your max depth.
I suspect that things would be much better today if the training agencies had added such a stop instead of cutting back the pressure exposure for a given residual group by one step.
For most recreational dives the faster compartments are in control. Even for a relatively slow ascent, say 20 ft/min, N2 will not have enough time to offgas without producing bubbles. These bubbles are most likely to occur in the blood (and be filtered out in the lungs) and possibly in the spinal cord, leading to neurological symptoms.
It has been shown (and experience dictates) that a deep stop combined with a rapid ascent rate promotes better offgasing than does a very slow ascent rate. For deep dives, a shallow stop is too late, the cap is most ways off the bottle. However, a deep stop may reduce the possibility of bubbles in the faster compartments. Take a couple of minutes at half your max depth.
I suspect that things would be much better today if the training agencies had added such a stop instead of cutting back the pressure exposure for a given residual group by one step.
Fish_Whisperer
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Thanks, RedHatMama and TS&M. Good stuff. (God, I love this board...) 
Thalassamania:
Well, yes, you can ascend too slowly from depth. And if your plan calls for deep stops, you had best be following the plan on your slate. My point was that from 15 feet to the surface, there is no reason not to take a lot of time to offgass as that is where the fastest rate of offgassing will occur.
Charlie99
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Do you have links to any study with actual data showing 60fpm was too fast?japan-diver:
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Dan Europe has some interesting articles about ascent rates and came to the conclusion that instantaneous rate of ascent isn't all that important, while the average ascent rate / total time to surface is.
In a series of studies, it was quite common for the 60fpm ascent rate profile to have better performance (less bubbling) than the 10fpm ascent rate, depending upon what stops were included. In general, though, 30fpm rates came out pretty good.
If you research things a bit deeper, you will find that a constant rate of ascent ---- whatever that rate is --- is NOT the optimum. The optimum appears to be an ascent which slow more and more the closer you get to the surface.
It also appears that what counts is NOT the instantaneous ascent rate, but instead the average ascent rate averaged over a few minutes.
https://www.daneurope.org/eng/lettmed1.htm has a whole series of interesting, informative articles --- I believe my comments above are a reasonable summary, with just a bit of extrapolation, of what is reported in the multiple articles at this link.
My wife and I did a Padi course in January, books stated 60 ft/min max ascent rate. One person in class had to wait a session to receive her books, as a fresh batch was coming in. Her's used 60 ft/ min also. Our instructor made a point of saying that was a "max", and slower was better. Safety stops were also "strongly urged", and simulated at 5' inthe pool. OW dives with another PADI shop always used a safety stop @ 15' partly to instill it in us, and partly to send up a marker, and check for boat traffic before finishing ascent.
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redhatmama:
You may spend as much time as you wish above 22 ft with no penalty other than reduced no-D limits on repetitive dives. But, as I pointed out, it's too late. You've already bubbled, with luck the bubbles have been filtered at the lung, but all your doing now is keeping them small until you ascend (the bubbles are not going to reabsorb in the timeframe we're using here).
A routine stop for 3 minutes at half your dive depth (plan or no plan, slate or no slate) will do you much more good than blowing off everything that's left in your tank at 15 feet or less.
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