Ascent rates. Why do you choose to do it the way you do it.

[TSandM]

One agency does

 

[Charlie99]

Charlie, you're doing ratio deco!

As I noted, a lot of people focus on the differences between the various approaches and miss what they all share in common.

Sometimes you have to poke and probe a bit to see the similarities. For example, the rather arbitrary Pyle stop method is to stop a fixed amount of time halfway between the start of ascent and first mandatory (shallow Haldane) stop. Then halve that distance for the next stop, then halve it again until the distance between Pyle stops is small (20'< ??).
That doesn't sound very much like a variable ascent rate that slows when shallow unless you plot the profile and look at the plot with your eyes a bit out of focus to kind of average things out.

I kind of grew into my ascent method long before I ever heard of ratio deco, perhaps before AG developed it. But at the core of both ratio deco and my 3 step NDL/small deco ascent is that "slower and slower the closer you get to the surface" shape of deco that pops up in so many different ways.

The simple "30fpm to 15' safety stop", as you already know from the Dan Europe Marroni studies, actually is a pretty good profile, and is better than a constant 10fpm ascent that starts on the bottom. 15' for 3 minutes is very simple, yet also very effective. The next level of sophisticated would simply be to adjust the safety stop depth ---- a bit deeper( eg 20') for deep dives, a bit shallower (eg 10') for a shallow 50' dive. Most divers also intuitively will extend the length of the safety stop for dives close to limits.

Splitting the safety stop into 2 depths is a reasonable extention of a single 15' stop, and the slower-when-shallower deco curves tell us that the time should be weighted towards the shallow stop.

My 3rd, deeper stop, is sometimes nothing more than just a time-depth waypoint check ---- I know how long I should be taking to get to 40' or 50' at 30fpm, and if I'm a bit fast, then I'll hang out there until the right time. So you can see how my ascent profile can get morphed from a single 15' safety stop to something that shares some features with 5th D's ratio deco.
Indeed, my ascent profile is a lot more like 5th Dimensions's ratio deco that does the essentially linear (i.e. same time spent per every 10' stop) GUE minimum deco and extended minimum deco for repetitive dives.

 

[TSandM]

Yes, this "shape of the curve" underlies all the decompression strategies, probably in large part because of the assumption of exponential loading and unloading from the compartments. Steve Lewis (Doppler) has a lovely essay on The Deco Stop on the topic, which I think anybody interested in the topic ought to read.

 

[hutterw]

I learned to dive a long time a go. I took a long break ( 25+ years). Took another open water class. Things changed. What they taught was 60 ft/min., then 30 ft/min from your safety stop at 5M to the surface. In practice I have found divers who take at least 10 min to ascend from their safety stop to the surface. What do you do? Is this a precaution, or do you notice a difference in how you feel after a dive? I'm 50 now, and I want to be conservative, so I can keep doing this for maybe another 50 yrs or so..
Bob
PS I'm diving in the puget sound area, so relatively cold water.

Nwbobber,

Yours and my diving histories are very similar I originally was qualified in 1980 in Michigan. Got tired of diving cold water and gave up the sport. Last year my wife talked me into re-certifying and we have almost 100 dives since. We are empty nester and take every opportunity to head to warm water to dive.

Because my wife and I always travel to dive we maximize our underwater time that results in two very tired people by the end of the day and trip. When I was younger I do not believe this profile would have fatigued me half as much but life marches on.

I ascend at 30’ per minute. Why, because that’s the rate that makes my computer happy and it slower than what I was taught.

I also ascend very slowly from my safety stop. I read somewhere that if you ascend very slowly from the safety stop you will have less fatigue after the dive and I agree with that statement. There may be a physiological explanation for this or it may simply be a placebo but for me it works.

Try the slow ascent and see what effect it has on you. It’s free, about the only thing in this sport that is!!!

 

[WKenny]

It must be great being your diving buddy!

 

[Nemrod]

I still ascend at 60 fpm as long as I am within the no deco tables and not deeper than 60 to 80 feet. I still use the original Navy Tables. If I am into deco or deep (deeper than 80 feet) then I shift to a different schedule. Deep, at or into deco, I will use 60 fpm to 60 feet (or some other depth depending on factors based on my own experience). After a momentary halt I will then use 30 fpm to a safety stop. A safety stop is just that, a safety stop, an extra margin, it is not mandatory but I do believe it to be a useful and wise thing to do when possible which is most of the time. Three minutes at 10 or 15 feet should be do-able for almost any no deco dive.

I have read so much conflicting info on all of this I have to start filtering and my BS Meter starts hittting overload. I am confident that the susceptability to bends is affected by fitness, obesity, intensity, cold, multi level/multi dive, possibly hydration, age, general health (which relates to circulation and body condition). There are other things as well. The OP is 50 and is concerned with that, ho hum, that ALONE does not render him prone to bends or more prone to bends than an 18 year old, it is simply one factor to take into account. On any day an individuals susceptability may well vary.

I have my own secret methods which a number of long time divers have secret methods and I will not divulge them since they depend on a lot of experience to beef them up. Basically I use the original Navy tables as I leanrned in the 60s, I track my time and depth and apply mental calculations to arrive at a profile on the fly. Recently I aquired a new fangled Aeries Atomos computer and though I though I would hate the thing I have taken a fondness to it. It is generally more conservative at depth than I am otherwise and it does multilevel different but I sort of like the thing. I realize people get hit using computers but this one seems fairly benign and appears to remain well within the tables as I would have calculated them for a given dive.

N

 

[nwbobber]

I am not worried about the bends. I plan to dive on the conservative side. What I am more concerned about is the idea that if you slow these ascents down, and you can feel the difference, there is something going on which may have a cumulative affect on you. The lack of fatigue alone is a good enough reason to take a few extra minutes on your ascent. My BS meter has not sounded yet on any of this new information. Although there is disagreement on how to respond to it, hence all the different ascent profiles, that is understandable because of all the complexity regarding variable rates of taking on or off gassing. I believe the condition exists and I can do something about it, so why not?

I also bought a computer, it is a suunto gekko, which doesn't like ascent rates over 30fpm anyway. I haven't heard it squeak yet, so I guess my habits are not that bad anyway. I do plan to slow down even more though.
Bob

 

[Ed Hatfield]

I am finding the theory interesting but difficult to understand. I want to be as safe a diver as I can be. Not just for myself but some day I hope to dive with my grandchildren.
I was trying to understand as much of the information as possible. I do have one question with respect to the ascent rate from the deeper and/or longer dives. Is it the depth of the dive or the proximity to the no deco limit that determines if a series of stops is recommended? Or is it a combination of the two? In my PADI OW and AOW it was ascend at less than 60ft/min and 3m/15ft safety stop. I don't recall anything else and I can't seem to find anything else in the manual (I didn't look too hard so it could be there).

 

[captain]

Do whatever makes you feel good as long as it within the parameters of some table or computer. I, like Nemrod dived from the get go on the Navy tables and 6O feet per minute accents rates. Here I am 50 years later with no DCS hits or any other health problems that I could blame on anything other than being 63 years old.
None of the tables or computer programs are exact science and everyone has their own opinion that whatever decompression process they use is the best but none of it is chizzled in stone.

 

[Al Mialkovsky]

I go very slowly and never exceed what my uwatec computers tell me to do, usually quite a bit slower. After all what padi is teaching is dangerous for most of us.