Ascending without a dive computer

[rjack321]

You definitely will have residual nitrogen after the safety stop. The smallest bubbles go too fast, use your depth gauge and bottom timer to go 10m per 1 min.

 

[JackD342]

Thanks for the input guys. I'm presuming, too, that the 3min @ 5m/16ft deco stop does completely purge the system of residual nitrogen so even if using the 'smallest bubble' advasc method you are still safe?

Remember that whole flying after diving rule? And calculating your RNT and pressure groups between dives? No, the 3 minute safety, not deco, stop does NOT completely purge the system...

 

[Chris Richardson]

Remember that whole flying after diving rule? And calculating your RNT and pressure groups between dives? No, the 3 minute safety, not deco, stop does NOT completely purge the system...

Apologies. Yes, of course: wrong choice of words: 'completely' and 'deco' :-(

 

[Diver0001]

There is no contradiction here.

The PADI RDP was based upon the standard ascent rate when it was created--60 FPM. All their research was based on that ascent rate, and the table they created was based on that ascent rate. That means they cannot change that recommendation when you are using the tables, because the numbers on those tables would no longer be valid.

That is not what the computer version of their course says, though. There they tell divers to ascend at the rate called for by the computer algorithm they are using, which as Diver0001 says, is almost certainly going to be 30 FPM.

Your ascent rate depends upon the system you are using to control your dives.

It should also be made clear that the 18m/min used for the RDP is a maximum for the RDP. As I said above, research done since the advent of the RDP indicates that 18m/min is generally too aggressive.

There is also a "minimum" ascent rate at which you are essentially making a multi level dive and not an ascent. The minimum ascent rate has not, to my knowledge, been the subject of research but if you play with deco models then you will probably conclude that if you are not ascending at at least 3m/min that you are still ongassing too much during the ascent.

It would have been nice if the RDP had stated that an ascent needed to be at LEAST "x" meters per min but no more than "y" meters per minute, because that is the reality. As it is, 10m/min is fast enough to account for an ascent in terms of the underlying model so it will work for the RDP as well.

Finally, for the benefit of the OP some divers will break the ascent up into phases depending on how deep they were diving, beginning a bit quicker and ending much slower. For example, assuming a diver starts at 40m on a no-stop dive. A possible strategy would be to go from 40-20m in about a min and then from 20-10m in another min and 10-5m in another min and then finally surfacing after the safety stop in 1m.

For recreational diving I just use 10m/min across the board but for some kinds of diving, particularly very deep and/or technical dives, my natural instinct is to slow down the ascent as I get shallower. YYMV.

All that said, my point was initially to inform him that he can control his ascent rate very accurately without a computer.

R..

 

[Diver0001]

Thanks for the input guys. I'm presuming, too, that the 3min @ 5m/16ft deco stop does completely purge the system of residual nitrogen so even if using the 'smallest bubble' ascent method you are still safe?

"completely purging" takes about 12hours according the RDP. Some computer models don't "completely" purge for about 3 days.

What the safety stop does is just build in a margin to account for any sloppiness during the ascent and/or for environment (cold, heavy working under current) and physiology (being tired, less than fit etc).

In a perfect world a safety stop would not be needed but decompression (table) theory is like measuring to the millimeter and then cutting with an axe. The 3 min it takes to do a safety stop is just to stack the deck in your favour.

R..

 

[Pedro Burrito]

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A ScubaBoard Staff Message...

Moved from Advanced to Basic. This is a green zone so please reduce the snark. I started diving with a dive watch, no SPG, no BCD, and a J valve and I ascended without a dive computer and actually lived!

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[Colliam7]

. . . my information equipment is only a Citizen Promaster Diver AY5000-05L, instrument console depth gauge and a PADI eRDP. Any thoughts, opinions, recommendations, etc, about this would be appreciated.

You have a great timing device. It is a classic! It will actually show you seconds, which most dive computers will not do (they only display minutes). Keeping an eye on your depth gauge, and your dive watch, you should be able to manage your ascents, to keep the rate in the 30 - 60 fpm range. As many have suggested, keeping the ascent rate closer to 30 rather than 60 is the prevalent practice these days. But, if you ascend at 45 fpm rather than 30, it is NBD. I wouldn't worry about tracking bubbles, or trying to distinguish between small bubbles and large bubbles. Ascend 15 feet, letting 30 seconds elapse. Ascend another 15 feet, and let another 30 seconds elapse. There are no data to suggest that you cannot dive safely with that approach. Just because a device gives a digital readout does not necessarily mean it will make you safer. I didn't have a DC for the first 3 years and several hundred dives I did. I just watched my depth gauge and inexpensive digital watch from Chez Target (which was nowhere near as nice as your Citizen ). Even today, while I usually dive with 2 (not inexpensive) DCs, I have a pretty good visceral sense of how fast I am ascending (developed by watching my time and depth, NOT some readout on my DC), and do most ascents with 15 foot increments, and don't assiduously watch my DC-monitored ascent rate.

Yes, even as just an 'occasional diver', you can dive safely with basic equipment, and you will fare better with good skills than by reliance on technology-managed ascents.

Learn to use a watch and your depth gauge.

Practice and master your equipment. Strong basic skills are valuable.

Excellent advice!

 

[TrimixToo]

You have a great timing device. It is a classic! It will actually show you seconds, which most dive computers will not do (they only display minutes). Keeping an eye on your depth gauge, and your dive watch, you should be able to manage your ascents, to keep the rate in the 30 - 60 fpm range. As many have suggested, keeping the ascent rate closer to 30 rather than 60 is the prevalent practice these days. But, if you ascend at 45 fpm rather than 30, it is NBD. I wouldn't worry about tracking bubbles, or trying to distinguish between small bubbles and large bubbles. Ascend 15 feet, letting 30 seconds elapse. Ascend another 15 feet, and let another 30 seconds elapse. There are no data to suggest that you cannot dive safely with that approach. Just because a device gives a digital readout does not necessarily mean it will make you safer. I didn't have a DC for the first 3 years and several hundred dives I did. I just watched my depth gauge and inexpensive digital watch from Chez Target (which was nowhere near as nice as your Citizen ). Even today, while I usually dive with 2 (not inexpensive) DCs, I have a pretty good visceral sense of how fast I am ascending (developed by watching my time and depth, NOT some readout on my DC), and do most ascents with 15 foot increments, and don't assiduously watch my DC-monitored ascent rate.

Yes, even as just an 'occasional diver', you can dive safely with basic equipment, and you will fare better with good skills than by reliance on technology-managed ascents.Excellent advice!

My Petrels actually have a seconds bar under TIME. You can't read it to the second, but you can definitely read it to see how far along in the computer's minute you are before it clicks over to the next minute. The seconds bar gradually underlines TIME until it goes blank and starts over.

It took me forever to notice this. I usually read my computers in glances!

To get more on topic, I will agree here with what some others have said: (a) Get a dive computer. They're cheap and useful. (b) Ascend, if you must, at the rate of the very smallest bubbles you can see at first (and no faster!) and crosscheck your rate with your depth gauge and watch. You'll get a feel for it eventually and automagically ascend at about the right rate.

 

[Colliam7]

My Petrels actually have a seconds bar under TIME. You can't read it to the second, but you can definitely read it to see how far along in the computer's minute you are before it clicks over to the next minute. The seconds bar gradually underlines TIME until it goes blank and starts over. It took me forever to notice this. I usually read my computers in glances!

My Perdix does as well. And, it took me a while to realize what the advancing bar meant. (Of course, when I actually went back and read the manual, it was an 'Aha!' moment. ) I prefer my (sadly, no longer made) Liquivision X1, which does show seconds. And, I like the 'seconds' feature for deco stops.

For ascent rate in recreational diving, I actually don't pay much attention to my DC displays, as I noted - even though my DCs are my depth gauge(s). But, the OP's Divemaster Pro is really an great unit. Sure, he can buy an inexpensive DC. But, what I see too much of - and admittedly this colors my recommendations a bit - is a slavish technology-dependence among some divers, and I believe that basic instrumentation works well, when used appropriately. I am not opposed to DCs by any means, and have never been mistaken for a diving Luddite. But, I do shy away from suggesting that an inexpensive DC is the simple answer to the OPs question, although it would be better than tracking bubbles. He already has the equipment necessary to manage his ascent rate. Why not use it?

 

[doctormike]

Thanks for the input guys. I'm presuming, too, that the 3min @ 5m/16ft deco stop does completely purge the system of residual nitrogen so even if using the 'smallest bubble' ascent method you are still safe?

Two different things.

While you don't completely purge your system of residual nitrogen no matter how slow you ascend (google "residual nitrogen time"), if you stay within non-deco limits then even without the safety stop you will offgass enough N2 to reduce your risk of decompression sickness on surfacing to an acceptably low degree.

On the other hand, an excessively rapid ascent can put you at risk for bubble formation and decompression stress even if you are within NDLs. Furthermore, a very rapid ascent can cause barotrauma if the gas containing spaces in the body aren't adequately ventilated (e.g. breathholding, reverse ear block, etc..)