PADI Ascent Rate

[Charlie99]

If you are properly weighted, then you won't have much air in your BC and it is easy to maintain neutral buoyancy / zero ascent rate by varying your lung volume. Once you have found that neutral spot, then you get used to how much you have to expand your lungs to get the right amount of lift to get the desired ascent rate. After a while, ascent rate control becomes automatic.

YMMV, but I found that following just the ascent rate indicator on the computer was almost impossible. The indication lags a bit and isn't all that precise.

The smallest bubbles work pretty good, but as others have noted, you have to keep going back to new bubbles.

I found that simply watching various bits of little particulates / junk in the water works best and easiest for me. Kind of the same as watching bubbles, but the junk is stationary (provided there aren't vertical currents) and are good references for very slow ascents.

The depth reading on the computer works as a good backup on ascent control, and it's a good practice to note the time you start an ascent and mentally pick out a couple depth/time waypoints that you want to hit. For example, coming up from a square profile at 80', I'll note the times I intend to finish 40', 25', and 15' stops (roughly 2,3, and 6 minutes from what is currently showing on computer as elapsed dive time).

Instantaneous ascent rate is not as important as the overall total time of ascent. In other words, you could bolt between 10' levels at high speed, as long as you wait at each 10' increment the appropriate time. Dan Europe has a good article on this.

 

[Scubafroo]

Looks like this thread needs to be revitalized with current article in SCUBA Diving magazine and online article
10 Rules of Scuba Diving

 

[NAM001]

Isnt 60 fpm treated ilke 1.6 PPO2 1.4 is the recommended limit like 30 fpm but not to exceed.....

 

[TMHeimer]

Yes, PADI does recommend that slower than 60'/min. is better, but there are a couple of things to consider. One is that, like the official 130' depth limit for rec. diving, the ascent rates are numbers that are just agreed upon. I don't know if there have been any tests done such as 30' vs. 60' per minute, but I kinda doubt it. There was a time when 100'/min. was the "norm" I believe. Another thing -- regarding lawsuits/liability-- is how can anyone really prove beyond a doubt exactly how fast someone ascended? There's no record of it (even on a DC I would guess), so it would be a buddy's word on how fast he thought his injured buddy ascended? And the incident may have occurred years ago before an ascent rate was changed by the agency?

 

[Bob DBF]

Yes, PADI does recommend that slower than 60'/min. is better, but there are a couple of things to consider. One is that, like the official 130' depth limit for rec. diving, the ascent rates are numbers that are just agreed upon.

When I started diving you were trained for NDL diving. 190' was and is the deepest you can go without going into deco, so that was the limit of your training. Recreational diving which includes technical diving (term invented in the '90's) has no limit as such, but NDL diving does and the agencies agree that their training now is limited a depth as well. I have seen it referred to as 120' as well as 130' on a number of occasions.

I don't know if there have been any tests done such as 30' vs. 60' per minute, but I kinda doubt it.

Since the US Navy changed their tables to 30fpm, I would bet their records show a large enough difference to justify the change. They have a long history of revising their dive manual according to their research into diving and the data from the logs of dives being made.

There was a time when 100'/min. was the "norm" I believe.

That was well before my time. As I heard there was a difference of opinion in the USN that the SCUBA divers wanted 120fpm and hardhat divers wanted 30fpm, the compromise for a standard, after working with their Deco experts was 60fpm. This happened well before recreational SCUBA started, which relied on the Navy tables to dive. What went on in other countries, I have no idea.


Bob

 

[tursiops]

Bubbles of different sizes rise at different rates. The bubble that rises at 30 ft/min is about 1.6 mm in diameter. Of course, as soon as it rises it gets bigger, and so goes faster; the speed goes as the square of the diameter, so the speed changes pretty quickly.
Alert Diver | Ascent Rates
Re: How fast does an air bubble ascend underwater?
Scuba Diving Bubble Mechanics

 

[boulderjohn]

When the PADI tables Were created, 60 FPM was the standard ascent rate, established by the U.S. navy in the 1950s using a less than scientific methodology. PADI did extensive research to create its tables, all the time using the 60 FPM ascent rate for all the dives. It established its tables that way, with its mass of numbers and letters. Eventually, well after that time, research started to indicate that 30 FPM was a better ascent rate. OK, then. The problem for PADI is that the mass of numbers and letters that constituted its dive table were all experimentally derived using 60 FPM. Those numbers were proven by research to be safe guidelines for diving when using that ascent rate. If you are using a different ascent rate, they have no experimental validity. Those tables were established with that ascent rate, so there is no way to change it.

Most people today take the PADI courses using computers, not the tables. When they do, they are NOT told to ascend at 60 FPM. They are told to ascend at the rate specified by the computer. In most cases that will be 30 FPM.

 

[boulderjohn]

"Slower is better" is not universally true. Take it to an extreme, and you will see what that means. Ascend at 1 foot per minute, and you are just adding bottom time with no benefit for off-gassing. A study done about 15 years ago compared ascent rates of 10 FPM, 30 FPM, and 60 FPM. They determined that 30 FPM was best, and 60 FPM was second best. Last place went to 10 FPM. At that rate, to oversimplify the explanation, the amount of gas you are still taking on exceeds the benefit of the gas you are letting off.

 

[Steve_C]

I just glance at my computer from time to time as I go up the anchor line. May stop from time to time to look at something. If I see the little bars on the side of the computer I stop for a few seconds until they clear. Do the safety stop. Definitely computerize the last 15 ft which is off the anchor line.

 

[gfaith]

-- is how can anyone really prove beyond a doubt exactly how fast someone ascended? There's no record of it (even on a DC I would guess), so it would be a buddy's word on how fast he thought his injured buddy ascended? And the incident may have occurred years ago before an ascent rate was changed by the agency?

You would be wrong nearly all computers will provide that ascent rate if logged in Subsurface, and most DCs record an ascent level exceeded which also shows up on the graph of the dive.

Example provided if needed.