Ascent Rate - Deep Dives

[gcbryan]

Exactly the point of my original question. Would be nice if there developed a concensus on the best ascent profile, described in terms a bit easier to understand than Erik Baker's papers on M values and deep stops. Gotta confess I've tried a few times to get thru those papers, and both times I got stuck in the mud.

My PADI manual says less than 60fpm, my NAUI manual says less than 30fpm, and the Navy Dive Manual says "Always ascend at a rate of 30fpm (20 seconds per 10fsw). Minor variations in the rate of travel between 20 and 40 fsw/min are acceptable". My computer wants me to stay away from 30fpm, although apparently a lot of divers shoot for 30fpm when they need to minimize ongassing. And the latest research seems to favor some type of deep stops.

Sounds like there isn't a clear concensus in the dive industry on ascents...

I know this isn't exactly your point but if you've got your computer set so conservatively that you only have 11 minutes at 100 fsw then you're not going to have any problems regardless of ascent rate (within reason). You can pick 30 fpm and you will not be having any problems. Turning your dive and following the slope back up is a great idea as well just don't do it 1 minute before NDL.

 

[jonnythan]

If you're getting into a variable rate ascent, you're already WAY past what 99% of OW divers understand and practice.

Just sticking to 30 fpm is way beyond most OW divers.

 

[Don Burke]

I've seen this somewhere else before too and frankly I was quite surprised that the 3m/min ascent faired so badly. We're drilled in the blanket statement that slow is better but the evidence suggests quite a different picture. It had me looking for the logic.

R..

With the benefit of 20-20 hindsight, it seems obvious.

An ascent rate of 0.1 fpm would plant a diver coming up from 20 minutes at 100 feet deeply into a staged decompression profile. It follows that slower would not be better and faster (within limits) would indeed be better than 0.1 fpm.

My take on the situation is that percentage of volume change per minute is a more accurate choice if one is looking for a linear way to express a safe ascent rate. In the real world, a velocity is the only thing that we have to work with.

Many divers held for years that fast ascent rates deep reduced decompression obligation. While not the whole answer, there is some merit to it.

It certainly appears that 60 fpm to the first deep stop and 30 fpm from there to 20 feet is favored by some algorithms. The simulator for my Oceanic sure seems to think so. From there on up, it would be difficult to go too slowly.

Perhaps the next generation of computer algorithms need to express ascent rate by volume change.

 

[Bwanar]

There are tons of variables here including your definetion of deep, but as a general guideline....45-60ft a min. to 100' and 30ft. thereon. I have read and use to practice up to 60fpm to 60ft. and 30ft. there after, but I prefer the more conservative approach. Many times even when I have gotten into deco by a minute or two, using the former assenct I am out of mandatory deco by the time I hit my 20ft. safety stop. This is using a Cochran Commander nitrox. As a caution, this personal experience of over 32yrs diving should in no way be construde as safe for all divers.

I've always figured when it comes to ascents, slower is better. Well, except for deep dives, in which you may still be ongassing even while ascending, and your remaining NDL time may keep ticking down.

What I'm trying to figure is this: is there a goal, an ideal ascent rate? Of course, too fast (over 30ft/min) is bad, and my computer will throw in a mandatory stop if I exceed 33 fpm continuously or 39 fpm momentarily. But too slow is also bad, cause you may suddenly run out of NDL time.

So if you are deep, and need to start offgassing, is the goal to ascend at around 30fpm, or is slower really better?

 

[Azza]

This is a related question in a way. I am new to diving but everything that I have read and been taught says that a proper ascent rate is 60fpm or slower. Yet I see people all over the boards spitting out the proper ascent rate as 30fpm or slower. I know slower is better but what is the truth in this? My dive computer book, the OW dive book, the PADI dive tables and the PADI OW dive video all state the 60fpm rule and nowhere mention the 30fpm rule.

If you read your book a little closer it will say that 60fpm is the "maximum" ascent rate. 30 fpm is the recommended.

 

[Spoon]

I generally do a 1 minute at each of 30 ft, 20 ft, and 10 ft.

i do the exact same thing. i was taught this in dir, got into a lot of trouble doing these when the other folks were doing 3 mins at 20ft.

 

[boomx5]

i do the exact same thing. i was taught this in dir, got into a lot of trouble doing these when the other folks were doing 3 mins at 20ft.

Remember, those are only the minimum deco limits. There is nothing wrong with extending them a bit. Also, if I had no option of diving Nitrox and had to dive air like if I was on a trip, I would indeed extend them by a minute or two at each stop from 30' to the surface, or just do a real slow ascent from 30'.

 

[WaterDawg]

i do the exact same thing. i was taught this in dir, got into a lot of trouble doing these when the other folks were doing 3 mins at 20ft.

Spoon, is that what you did on the dives you got skin bends? The 3 below 100ft?

 

[rockjock3]

If you read your book a little closer it will say that 60fpm is the "maximum" ascent rate. 30 fpm is the recommended.

I read the open water book from cover to cover 4 times already and watched the DVD 3 times and on my fourth time (I want to be as prepared as possible before I start my class in three weeks). There is no mention of 30fpm anwhere. If you look at the definitions in the back it states on page 239. "ASCENT RATE - the proper speed for ascending, which is no faster than 18m/60 feet per minute. A rate slower is acceptable, and appropriate." It does say that an slower ascent rate is appropriate, I was just trying to see where the 30fpm comes from because none of PADI's materials mention a "30fpm" ascent rate.

I was wrong on my computer however. The manual actually states that the computer will adjust my ideal ascent rate between 7 and 18 meters per minute depending on what is appropriate for my current dive profile.

 

[jonnythan]

Guess the different agencies make different recommendations.