Are Suunto Zoops super conservative?

[Lorenzoid]

Yes, the Suunto is on the conservative end of the spectrum, but keep in mind that divers all over the world have been diving them for decades, so it isn't like they are off the charts.

The Suunto manual (last time I looked) lists several factors that the algorithm considers to add risk and therefore places a lot of weight on. Stated less generously, the Suunto penalizes your no-deco time for doing these things. As I recall (but you should look it up), the Suunto places great weight on a slow ascent. If you violate its preferred ascent rate, the computer shaves no-deco time off the subsequent dive. Spend an extended safety stop in the shallows if you can. If you're doing deep wall dives in Cayman with nowhere to spend an extended safety stop, consider whether the Suunto is not a good choice for you. As I also recall, the Suunto places great weight on a long surface interval. Unless you give yourself at least an hour of surface interval between two deep dives--and I would give it even more--the computer will shave no-deco time off the subsequent dive. It also keeps track of multi-day diving. So if you do multiple days of aggressive diving in a row--who knows, maybe as few as two--you might find yourself penalized the next day. On a week-long vacation, I often took a day off from diving in the middle, which my Suunto seemed to love me for. If I also recall, it prefers you follow the old (perhaps debunked) advice that each dive should be shallower than the preceding dive. Also, alhough I don't recall seeing this specifically, since Suunto's algorithm is nominally based on a bubble model, it may also penalize you for sawtooth dive profiles.

By keeping those factors in mind, I used a Suunto for easy (that is, maybe up to 100 feet) Caribbean dives for many years without issue. Many of the divemasters on those boats used Suuntos, too. If you, as many do, believe Suunto is mistaken in their belief that those factors increase the risk of DCS, then go with a different computer. There isn't much publicly known about Suunto's algorithm because it is a proprietary version of the RGBM algorithm, so you have to make a decision based on what you're able to find published. Read some of the discussions on SB regarding the merits of various algorithms and decide for yourself.

 

[DavidFL]

One thing that has been implied but not explicitly stated is this: decisions related to comparing your computer with others need to be made on the surface. Once you have made your surface decisions about what computer to use and what conservatism setting to make, the best advice, repeated in various forms above, is to follow the computer's information about NDL's, and if you exceed the NDL's, then follow the computer's recommendations about decompression stops and times. Otherwise, there is no point in carrying your own dive computer.

For your consideration in your future surface decisions: my first dive computer was a Suunto Gekko (pretty sure it's the predecessor to the Zoop). My second dive computer was a Suunto Cobra 2. For about 8 years and several hundred dives I used both of those computers. My dive buddy has computers of a different model. Most of the time, the end of our dives aren't based on hitting NDL's, but when that occurs sometimes it's me and sometimes it's her.

Today my primary dive computer is a Shearwater Perdix.

When I began to try to have a better understanding of what was going on in the Suunto computers, I became aware that the underlying algorithm they use is the proprietary Reduced Gradient Bubble Model (RGBM), and there is a lot of information around that Suunto's implementation of RGBM has some additional 'conservatism'. The anecdotal/rumor information says that Suunto's RGBM 'penalizes' a diver (that is, makes the recommendations more conservative) if he/she exceeds some ascent rate, and also 'penalizes' a diver for reverse profiles (subsequent dive deeper than the previous dive), and there may be other similar additional variables taken into consideration in the software algorithm. Since both the underlying RGBM algorithm and Suunto's implementation are proprietary, you can't actually find information that gets to the objective content of the source code to the software or even a complete software description document, so only those with access to Suunto's intellectual property are in a position to objectively answer questions about "what's going on inside" a Suunto Zoop with regard to conservatism.

If this experience, or the responses you get here pique your curiosity and you want to invest some time in understanding why some of the responses are verging on shouting, and why a moderator immediately posted the rules of the forum after your post, I highly recommend Deco for Divers, a book by Mark Powell, and "Decompression Controversies", a video by Dr. Simon Mitchell. A google search will take you to those and tons of other related information.

 

[KenGordon]

Yes, the Suunto is on the conservative end of the spectrum, but keep in mind that divers all over the world have been diving them for decades, so it isn't like they are off the charts.

The Suunto manual (last time I looked) lists several factors that the algorithm considers to add risk and therefore places a lot of weight on. Stated less generously, the Suunto penalizes your no-deco time for doing these things. As I recall (but you should look it up), the Suunto places great weight on a slow ascent. If you violate its preferred ascent rate, the computer shaves no-deco time off the subsequent dive. Spend an extended safety stop in the shallows if you can. If you're doing deep wall dives in Cayman with nowhere to spend an extended safety stop, consider whether the Suunto is not a good choice for you. As I also recall, the Suunto places great weight on a long surface interval. Unless you give yourself at least an hour of surface interval between two deep dives--and I would give it even more--the computer will shave no-deco time off the subsequent dive. It also keeps track of multi-day diving. So if you do multiple days of aggressive diving in a row--who knows, maybe as few as two--you might find yourself penalized the next day. On a week-long vacation, I often took a day off from diving in the middle, which my Suunto seemed to love me for. If I also recall, it prefers you follow the old (perhaps debunked) advice that each dive should be shallower than the preceding dive. Also, alhough I don't recall seeing this specifically, since Suunto's algorithm is nominally based on a bubble model, it may also penalize you for sawtooth dive profiles.

By keeping those factors in mind, I used a Suunto for easy (that is, maybe up to 100 feet) Caribbean dives for many years without issue. Many of the divemasters on those boats used Suuntos, too. If you, as many do, believe Suunto is mistaken in their belief that those factors increase the risk of DCS, then go with a different computer. There isn't much publicly known about Suunto's algorithm because it is a proprietary version of the RGBM algorithm, so you have to make a decision based on what you're able to find published. Read some of the discussions on SB regarding the merits of various algorithms and decide for yourself.

Is there any controversy about sawtooth profiles, short surface intervals and repeat diving increasing the chances of DCS?

 

[Lorenzoid]

Is there any controversy about sawtooth profiles, short surface intervals and repeat diving increasing the chances of DCS?

I'm not sure about sawtooth, but I suppose there is no controversy over "short" surface intervals between repetitive dives. (But how "short" does Suunto consider too short?) Here's what I found in the Zoop manual:

"Some patterns of diving cumulatively add a higher risk of DCI, e.g. dives with short
surface intervals, repetitive dives deeper than earlier ones, multiple ascents, substantial
multiday diving. When this is detected in addition to adapting the decompression
algorithm the Suunto RGBM model will in some circumstances also advise, with the
Diver Attention Symbol (review chapter 3.6) that the diver extend the surface interval."

It isn't clear what all of this means. "Patterns" and "cumulatively" are sort of cryptic. Is one hour close to a magic number for the surface interval? If you have a pattern of two successive 55-minute surface intervals, does it penalize you on the fourth dive of the day more than other algorithms would?

 

[DavidFL]

Is there any controversy about sawtooth profiles, short surface intervals and repeat diving increasing the chances of DCS?

At the "Basic SCUBA Discussions" forum level, the OP's question seems to be whether a Suunto Zoop is more conservative (than his friends' "watches") in general, and hence also more conservative dealing with sawtooth profiles, short surface intervals, and repetitive diving, and all the other independent variables in decompression algorithms. Seems to me the answer is maybe yes at this level, and otherwise the discussion is probably not at this level.

 

[KenGordon]

Was it on here that someone posted getting bent having nipped down to recover a dropped camera at he end of a dive?

 

[Streydog]

I started using a Vyper Novo in October. I have been using it on the same arm as a Geo 2.0 (Dsat) for 65 dives so far. I always have more NDL time on the Geo but I have not put the Vyper in Deco yet.

In Roatan I did 19 dives in 6 days averaging 55 minutes, using air except 4 dives on 32% and the Suunto was fine. The lowest NDL I saw towards the end of the trip on a 106' dive was 3 minutes, the Geo was at 8'.

All my other dives have been in Cozumel using HP120's and nitrox, many over 80 minutes. I have not seen the dreaded Suunto penalty...yet.

 

[boulderjohn]

I'm not sure about sawtooth, but I suppose there is no controversy over "short" surface intervals between repetitive dives. (But how "short" does Suunto consider too short?) Here's what I found in the Zoop manual:

"Some patterns of diving cumulatively add a higher risk of DCI, e.g. dives with short
surface intervals, repetitive dives deeper than earlier ones, multiple ascents, substantial
multiday diving. When this is detected in addition to adapting the decompression
algorithm the Suunto RGBM model will in some circumstances also advise, with the
Diver Attention Symbol (review chapter 3.6) that the diver extend the surface interval."

Note that I put one phrase above in bold.

More than 15 years ago (2001, IIRC), a major workshop was conducted to try to determine the origins and the reasons for the standard rule against reverse profiles--making later dives deeper than earlier dives. The workshop determined that the very first instance in which this "rule" was mentioned was a 1972 PADI OW student manual, in which it was merely a suggestion, with no reason given. PADI was part of the workshop, and they did not know who made that suggestion or why it was made. In subsequent manuals, the suggestion became worded more and more strongly, until it eventually became a rule. No reason was ever given.

Many people, including especially me, are convinced that the reason for the original suggestion was related to practicality and not to physiology. In 1972, diving was based on the U.S. Navy tables, which had a very conservative design for surface intervals--you had to stay out of the water a long time between dives. With any tables, if you do two dives to different depths, doing the deepest dive first gives you a much shorter surface interval before the second dive. If you were using the Navy tables and did the shallower dive first, you could be out of the water for a very, very long time before being allowed to do the second dive. Once you had the required surface interval completed, though, there was no physiological problem related to doing that second, deeper dive.

The workshop ended with the NEAR consensus that doing second dives deeper than the first was perfectly fine, as long as you had given yourself a sufficient surface interval. I put the word "near" in bold for a reason. There was one notable person disagreeing with that conclusion--Bruce Weinke. Weinke insisted that doing deeper dives after shallower dives led to "bubble pumping"--bubbles formed on the first dive could be crushed by the second to the degree that they could pass from the venous side to the arterial side and potentially cause DCS problems. This was particularly true with deeper dives, he insisted. As a result, the workshop said that the deeper dive first recommendation would still stand for technical diving.

Bruce Weinke is the designer of the RGBM system used by Suunto and others, and that system is, to the best of anyone knowledge, unchanged since he created it before that workshop. It would not be surprising if doing a deeper dive after a shallower one would be severely penalized in that program.

 

[Diver0001]

Bruce Weinke is the designer of the RGBM system used by Suunto and others, and that system is, to the best of anyone knowledge, unchanged since he created it before that workshop. It would not be surprising if doing a deeper dive after a shallower one would be severely penalized in that program.

Just to add to this, the wording of the conclusions at the time was that "reverse profiles" of 12m/40ft or less do not appear to be a concern with respect to increased DCS risk. If I'm not mistaken I believe they also indicated the need for additional research.

It should also be noted that Bruce Wienke in addition to dissenting on the reverse profiles discussion also dissented on the NEDU study that basically showed that bubble models, including RGBM, are broken (I'm paraphrasing for brevity here).

Wienke has a HUGE stake in these things because RGBM is his ticket to significant wealth through licencing. To my way of thinking he has let his judgement become clouded by "what's good for Bruce" and is no longer someone I see as a reliable source of scientific information, nor do I see him as someone who has the best interests of divers at heart.

 

[boulderjohn]

It should also be noted that Bruce Wienke in addition to dissenting on the reverse profiles discussion also dissented on the NEDU study that basically showed that bubble models, including RGBM, are broken (I'm paraphrasing for brevity here).

He participated to that effect briefly (but only briefly) in the discussion about deep stops on ScubaBoard. After a few comments he was through.