What makes us think we can trust any of them

[Charlie99]

Ok, I can dig that. And this is what Snowbear is teaching me also, yes?

But, also note this statement by Marroni, found here: "Lewis showed that the stop is in fact preferential to slowing the ascent rate. Thus, as indicated previously, a 5 min safety stop is much more effective than a reduced ascent rate..."

When Marroni contrasts stops vs. slower ascent, Marroni is usually using the context of his study, and is contrasting a linear, constant-all-the-way-to-the-surface 10fpm ascent vs a 30 or 60fpm ascent at the beginning, with stops partway up the ascent. I don't have access to the Lewis article to know in what context he makes his statement.

Snowbear will have to speak for herself, but my understanding is that what matters is the overall shape of the ascent (slower when shallow), rather than that the exact details of whether the overall shape is controlled by varying the instantaneous ascent rate or controlling it by a series of stops.

The profile StSomewhere uses, of 1@30', 1@20', 1@10' slows the average ascent rate during the last 30'. (I'm assuming he uses 30fpm ascent until 30') This is better than doing a constant rate all the way from the bottom to the surface, but it could easily be modified to what IMO is a better profile by increasing the time shallow a bit more. Interestingly, adding a bit more on the shallow end is what his Suunto computer wants him to do.

 

[Snowbear]

Snowbear will have to speak for herself, but my understanding is that what matters is the overall shape of the ascent (slower when shallow)...

You said it just fine

 

[StSomewhere]

Just wanted to add that I'm not necessarily complaining about the extra time the Suunto wants (demands?) me to do shallow. The real problem is that I need my ascent rate to match my buddies ascent rate.

 

[Charlie99]

Just wanted to add that I'm not necessarily complaining about the extra time the Suunto wants (demands?) me to do shallow. The real problem is that I need my ascent rate to match my buddies ascent rate.

I doubt that his ascent rate faster than the ascent alarm on the Suunto. If his ascent rate is slow, then what happens when you leave the Suunto in the computer mode? Suunto may have a dive simulator that you could use to check this out. This would be much better than taking as gospel some over-simplified comments of an instructor in a 2 day course.

As others have posted, the Suunto properly gives you credit for slow ascent, deep stops, and the offgassing in the faster compartments during the ascent, while continuing to properly calculate continued ongassing in the slower compartments.

I'm not trying to give you a hard time, but it does sound like you have some misconceptions about how your computer works.

 

[StSomewhere]

I doubt that his ascent rate faster than the ascent alarm on the Suunto. If his ascent rate is slow, then what happens when you leave the Suunto in the computer mode? Suunto may have a dive simulator that you could use to check this out...As others have posted, the Suunto properly gives you credit for slow ascent, deep stops, and the offgassing in the faster compartments during the ascent, while continuing to properly calculate continued ongassing in the slower compartments.

No, no it doesn't, not the ascent profile. It's been wired to demand a 3 minute stop (exactly 3 minutes) at 15 ft (+/-). I've not only spent some time with the planner and simulator (which are similar but different functions on the Vytec/Vyper/Cobra), I've looked at the pretty graphs the buggy SDM 2.x software generates from dive profiles. Violate that 3 minutes for 15 ft and the computer will cut your subsequent NDLs.

And since you have such faith in the Suunto programming, why do I feel so much better (vibrant, less tired) doing a slower, shallower, non-linear deco/safety stop than what is programmed into most dive computers and advocated by almost all agencies?

Obviously you are missing my point if you think the ascent is faster than the alarm.

 

[100days-a-year]

I prefer objective data VS. the subjective"I feel better"Having a tendency to have more bubbles post-dive as ascertained by Doppler is a serious concern for me.I'll stick to as much of a square profile as I can followed by rapid ascent to my deepstop then staged discrete stops.

My anecdotal evidence is this >3K dives mostly(75%) over 100' and 25% with a deco obligation.Not on case of clinical DCS and only 2 days of soreness that could not be attributed as easily to other causes.Rarely get headaches even...shudder...on air.

 

[StSomewhere]

This would be much better than taking as gospel some over-simplified comments of an instructor in a 2 day course.

Compared to what??? The agency that teaches dive skills to divers on their knees? Who spend almost no time teaching decompression to OW students beyond "stay away from those black squares on your RDP"? The same people who proclaimed from the rooftops that nitrox was a voodoo gas, before figuring out how much extra cash they could generate with their Nitrox-for-Dummies class? Who swore tech diving was the spawn of Satan until they developed their own program that advocates teaching students to dive air down to 170 ft (with instructors also on air)? Sure, those guys have to be a real bellwether of decompression knowledge. :06:

There are a lot of people who no longer think Modified Haldane is the correct way to design a dive profile. Not just GUE and 5thd-x either, but divers from a lot of tech agencies. But if history is any gauge, I suppose PADI and the recreational dive computer manufacturers won't catch up for about the same number of years as they spent vilifying Nitrox. I've invested some time analyzing my recreational dive profiles with bubble model decompression software, and I've also read the same PADI DM materials as you have, I'm just not convinced PADI and the recreational dive computer manufacturers (Suunto, Uwatec, Pelagic) hold the patent on decompression knowledge.

 

[Charlie99]

And since you have such faith in the Suunto programming, why do I feel so much better (vibrant, less tired) doing a slower, shallower, non-linear deco/safety stop than what is programmed into most dive computers and advocated by almost all agencies?

My point is that the Suunto gives a limit that you should not exceed. Nothing in the Suunto programming requires you to immediately pop up to that limit. Take that "slower, shallower, non-linear deco/safety stop" that makes you feel vibrant and run it through the Suunto planner/simulator. My bet is that it's perfectly happy with it.

Somehow, a myth has developed that improved profiles (aka bubble-friendly) are incompatible with dive computers. A related myth is that a dive computer determines your profile.

Don't just take my word for it. Take your desired profile and run it on the simulator.
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edit: you will have to spend the time shallow that the Suunto wants to clear the 3 minute safety stop requirement, but we should easily agree that this requirement adds more margin, i.e. is more conservative, than only spending 1 minute at 20' and 1 at 10'.

, I'm just not convinced PADI and the recreational dive computer manufacturers (Suunto, Uwatec, Pelagic) hold the patent on decompression knowledge.

I don't either. OTOH, the recreational dive computers don't force you to follow any particular dive profile.

I'm not advocating isn't anything complex or black magic. Figure out how you want to dive, then dive it. If it's a good profile your computer will be happy.

 

[StSomewhere]

Well that's 1 minute at 20', 1 minute at 10', and as slow as I can manage from 10' to the surface (depending on conditions).

But, fair enough, you are right that you don't *have* to do exactly the stops that it asks for, but if you ride your dive computer to the NDL (like most recreational divers are taught to do) you'll be doing the stops it recommends. Probably at the exact time when your deco profile (and it is a deco profile IMUO) should be the most conservative.

The question is, besides on SB, how many people are taught to dive the computer any differently than the NDL number on their Suunto or maybe to the yellow bars on their Pelagic? And how many do any stops beyond what their computers tell them to? Not me, not before I did that silly 2-1/2 day class (and the related followup).

 

[Scuba]

But, fair enough, you are right that you don't *have* to do exactly the stops that it asks for, but if you ride your dive computer to the NDL (like most recreational divers are taught to do) you'll be doing the stops it recommends. Probably at the exact time when your deco profile (and it is a deco profile IMUO) should be the most conservative.

The question is, besides on SB, how many people are taught to dive the computer any differently than the NDL number on their Suunto or maybe to the yellow bars on their Pelagic? And how many do any stops beyond what their computers tell them to? Not me, not before I did that silly 2-1/2 day class (and the related followup)

These are good points. However, I don't think it's so much a case, although in some cases it is, of being taught to ride the limits as it is a case of being taught to stay within those limits, whether using a computer or a table as a reference. Decompression is often not effectively taught except for its dangers, or even realistically recognized. Note the training agency term "No Decompression Limits" - that is the problem.

Another problem is the continual propagation of false information regarding deco computers and computer users.