Suunto: how conservative is the algorithm?
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dschonbrun
Contributor
Mason,
The SUUNTO RGBM is on the conservative side at "100%" setting. It says so very clearly in the user's manual. There is a setting for "50%" on some advanced models that allows you to increase your nitrogen exposure (essentially increasing your NDL Limits). But, it's only for divers who have a good enough amount of experience and know that their bodies can handle this amount of nitrogen and are able to bleed it off safely.
Also, keep in mind that the conservatism doesn't necessary preclude you from diving, it just means that you are required to perform DECO stops. Anyone who doesn't understand this shouldn't be pushing their limits.
I've just done 3 dives in a row in St. Kitts for 2 days straight on Air using a VIPER 2. Here are the numbers for today:
Dive 1: MOD 81 ft, BT 45 min
Dive 2: MOD 66 ft, BT 67 min
Dive 3: MOD 41 ft, BT 66 min
On the second dive, when the computer was set on the conservative "100%" RGBM, I was penalized and had to do a 12 minute Deco stop, and had a 10ft ceiling. Based on the multi-level profile we executed and other diver's computers, I found this a bit conservative.
When I switched to the "50%" advanced setting, I was able to execute the last dive with no DECO stops, only a 3 minutes safety.
I think it is sensible to gradually increase your level of risk as you feel comfortable, but this has a lot to do with fitness. Very fit bodies can often adjust to increased nitrogen and oxygen saturation levels better than individuals who have greater adipose tissue.
The whole point of the computer is to keep you safe, just remember that.
D
The SUUNTO RGBM is on the conservative side at "100%" setting. It says so very clearly in the user's manual. There is a setting for "50%" on some advanced models that allows you to increase your nitrogen exposure (essentially increasing your NDL Limits). But, it's only for divers who have a good enough amount of experience and know that their bodies can handle this amount of nitrogen and are able to bleed it off safely.
Also, keep in mind that the conservatism doesn't necessary preclude you from diving, it just means that you are required to perform DECO stops. Anyone who doesn't understand this shouldn't be pushing their limits.
I've just done 3 dives in a row in St. Kitts for 2 days straight on Air using a VIPER 2. Here are the numbers for today:
Dive 1: MOD 81 ft, BT 45 min
Dive 2: MOD 66 ft, BT 67 min
Dive 3: MOD 41 ft, BT 66 min
On the second dive, when the computer was set on the conservative "100%" RGBM, I was penalized and had to do a 12 minute Deco stop, and had a 10ft ceiling. Based on the multi-level profile we executed and other diver's computers, I found this a bit conservative.
When I switched to the "50%" advanced setting, I was able to execute the last dive with no DECO stops, only a 3 minutes safety.
I think it is sensible to gradually increase your level of risk as you feel comfortable, but this has a lot to do with fitness. Very fit bodies can often adjust to increased nitrogen and oxygen saturation levels better than individuals who have greater adipose tissue.
The whole point of the computer is to keep you safe, just remember that.
D
Thankyou, thats make more sense to me now. You mentioned on air...you dont use Nitox? Also a 12 mintue deco stop, thats a long time. if you didnt do the whole 12 and started to ascend againe will the unit lock you out?
Mason, think about why you carry a computer. You carry a computer because excessive nitrogen loading, when not countered with adequate decompression, causes decompression sickness. Since none of us wants to do multi-level dives according to strict tables (because of the short bottom times), we carry computers that can do the iterative calculations necessary to figure nitrogen loading in the various compartments, and warn us of when we are approaching the point where a direct ascent to the surface is no longer safe.
But the truth is that no computer knows what is going on in YOUR body -- No computer knows how fit you are, how well hydrated you are, how good your circulation is, how hard you have worked at depth . . . There are a lot of variables that go into figuring how long you can stay down and where. So, if you are going to follow a computer, you are making a risk assessment. Saying that you want to buy a more liberal computer to maximize your bottom times is simply saying you are willing to undertake more risk of DCS. Now, by "more", I may not mean "high", because frankly, the risk of DCS in any recreational profile approved by any computer is low.
Suunto computer are particularly conservative with regards to repetitive dives, or reverse profiles; my husband was once given 20 minutes of mandatory deco on a dive where my friend's Aeris computer had none, and my depth-averaging tables had none, either. But the real question is whether my husband's computer was sensible and we were not, or the reverse. And I don't have a good answer for that question, and neither does anyone else. Deco is not a science. Decompression algorithms do NOT model what actually occurs in the body, but follow a mathematical model of gas loading and diffusion. People get hit when they "shouldn't", and people get away with profiles that would give one cold chills to see.
Choose your computer according to your risk tolerance; but realize that if you buy a "liberal" one, you are taking greater chances -- but you really don't know how much greater.
But the truth is that no computer knows what is going on in YOUR body -- No computer knows how fit you are, how well hydrated you are, how good your circulation is, how hard you have worked at depth . . . There are a lot of variables that go into figuring how long you can stay down and where. So, if you are going to follow a computer, you are making a risk assessment. Saying that you want to buy a more liberal computer to maximize your bottom times is simply saying you are willing to undertake more risk of DCS. Now, by "more", I may not mean "high", because frankly, the risk of DCS in any recreational profile approved by any computer is low.
Suunto computer are particularly conservative with regards to repetitive dives, or reverse profiles; my husband was once given 20 minutes of mandatory deco on a dive where my friend's Aeris computer had none, and my depth-averaging tables had none, either. But the real question is whether my husband's computer was sensible and we were not, or the reverse. And I don't have a good answer for that question, and neither does anyone else. Deco is not a science. Decompression algorithms do NOT model what actually occurs in the body, but follow a mathematical model of gas loading and diffusion. People get hit when they "shouldn't", and people get away with profiles that would give one cold chills to see.
Choose your computer according to your risk tolerance; but realize that if you buy a "liberal" one, you are taking greater chances -- but you really don't know how much greater.
scubafanatic
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...you might review a copy of the June 2008 'Scubadiving' mag......they just tested/compared 14 new dive computers...and there are some pretty significant differences between them!
halocline
Contributor
In general, I think this was a well thought out and insightful post, until this comment. There simply is no evidence that a "liberal" dive computer user is more likely to get DCS than a conservative computer user. Consequently, using a liberal computer is NOT taking a greater chance. You may assume that "conservative algorithm means less risk" and it's a sensible assumption, but it is not supported by any sort of data whatsoever.
IMO, computer use is not about "keeping you safe" as someone else posted, (not TS&M) it's about convenience; with one exception, the ascent rate alarms are certainly a safety feature for new divers who are still mastering buoyancy control. Aside from that, computers allow you to dive safely with less rigid profile planning, which is a convenience, and can certainly result in longer "safe" bottom times, which is an attractive convenience.
The only thing "keeping you safe" while diving is your own dive behavior, regardless of whether you use tables, the wheel, (which is a pretty useful gadget) or a computer.
I'm sorry, but I'll stick with the statement that the more nitrogen loading you experience, the greater your risk of DCS is, everything else being equal. A computer that allows you to be deeper, longer, is tolerating more nitrogen loading, and therefore more risk.
The problem is that, as David Sawatzky wrote in a column in Diver magazine a year or so ago, the biggest reductions in DCS occurred as a result of Haldane's original observations. Everything that's been done since is nibbling away at the edges, and the differences between approaches can often be hard to see.
The problem is that, as David Sawatzky wrote in a column in Diver magazine a year or so ago, the biggest reductions in DCS occurred as a result of Haldane's original observations. Everything that's been done since is nibbling away at the edges, and the differences between approaches can often be hard to see.
I used to get mandatory deco on my suunto all the time whereas my Oceanic (using the same model as the padi tables) still had me way clear.
To be honest this never bothered me as I like to dive relatively conservatively. I did the deco and treated it like a multilevel dive but what I do really really like about suunto is it gets cranky if you ascend faster than 9 metres per minute. Diving a suunto computer really trained me to ascend very slowly (without me really realizing it) and I didn't realise how slow until I dived with others not using them and they got all funny about me ascending too slow
Excellent. Couldn't have said this better myself.TSandM:
Since the objective of decompression theory, as applied to/by/with dive computers or tables (counting PADI's wheel as a special case of a table) is to manage absorbed nitrogen, and greater restrictions are incurred when more nitrogen has been absorbed, I don't see how anyone can maintain that using a more liberal computer is not taking a greater chance. Logic doesn't support that statement, any more than it supports PADI's assertion in their Nitrox manual that using nitrox has no effect on safety.
Using a computer instead of tables is indeed about convenience, but using any of these as opposed to just guessing is most certainly a matter of safety.
On the specifics of particular computers, I frequently make long and deep repetitive dives and have never in many years had a "near DCS" experience. But I have several times "bent" my Suunto Stinger while my DiveRite Nitek+ was clear. So for me (and this is only for me, in the state of health, fitness and hydration I was on those dives) the DiveRite algorithm works and the Suunto one in the Stinger (somewhat modified in later models such as the D9/6) is excessively conservative. It's useful for me to know that I am infringing the Stinger, though, as it makes me that much more conservative relative to the Nitek.
But as TS&M points out, a computer isn't plugged into YOUR body and has no knowledge of how you relate to the "average" person it is modelled on. Until you know from experience how far you can push your diving it pays to be conservative. In other words, the very fact that you have asked the question suggests that you should dive conservatively, and for you a Suunto would seem to be a wise and safe choice.
Going beyond the scope of this question, I wonder why so many people choose integrated computers, ie. those that also show your available breathing gas. I started out with one of these myself, but sold it when I started using multiple tanks and I've never missed it since. I regard the burden of having to look at two gauges (computer and SPG) as so slight as to be totally insignificant. Some computers attempt an estimate of your remaining dive time based on available gas, but in practice I find this useless and I know no-one who takes much notice of it. A hose-integrated system means your computer must be on a console, hardly convenient when you're ascending, and I haven't come across any wireless-integrated system that doesn't periodically lose the link, generating most of the annoying "beeps" I hear on dives.
I also wonder why people pay an enormous amount of money for a mask that has an integrated computer. A cute toy for sure, but one that IMO adds very little to diving convenience. I have a guest with us right now who uses one, and he has conceded that if he were to lose it he wouldn't buy another. In this as with so many things to do with diving, I've also experimented with expensive and complicated toys in the past, but now I firmly believe that simplicity is best.
Using a computer instead of tables is indeed about convenience, but using any of these as opposed to just guessing is most certainly a matter of safety.
On the specifics of particular computers, I frequently make long and deep repetitive dives and have never in many years had a "near DCS" experience. But I have several times "bent" my Suunto Stinger while my DiveRite Nitek+ was clear. So for me (and this is only for me, in the state of health, fitness and hydration I was on those dives) the DiveRite algorithm works and the Suunto one in the Stinger (somewhat modified in later models such as the D9/6) is excessively conservative. It's useful for me to know that I am infringing the Stinger, though, as it makes me that much more conservative relative to the Nitek.
But as TS&M points out, a computer isn't plugged into YOUR body and has no knowledge of how you relate to the "average" person it is modelled on. Until you know from experience how far you can push your diving it pays to be conservative. In other words, the very fact that you have asked the question suggests that you should dive conservatively, and for you a Suunto would seem to be a wise and safe choice.
Going beyond the scope of this question, I wonder why so many people choose integrated computers, ie. those that also show your available breathing gas. I started out with one of these myself, but sold it when I started using multiple tanks and I've never missed it since. I regard the burden of having to look at two gauges (computer and SPG) as so slight as to be totally insignificant. Some computers attempt an estimate of your remaining dive time based on available gas, but in practice I find this useless and I know no-one who takes much notice of it. A hose-integrated system means your computer must be on a console, hardly convenient when you're ascending, and I haven't come across any wireless-integrated system that doesn't periodically lose the link, generating most of the annoying "beeps" I hear on dives.
I also wonder why people pay an enormous amount of money for a mask that has an integrated computer. A cute toy for sure, but one that IMO adds very little to diving convenience. I have a guest with us right now who uses one, and he has conceded that if he were to lose it he wouldn't buy another. In this as with so many things to do with diving, I've also experimented with expensive and complicated toys in the past, but now I firmly believe that simplicity is best.
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