Shearwater coming out with new DC?
- Thread starter Bali1
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My VT3 and Geo2 (I would imagine other Oceanic computers) would go into violation gauge mode for 24 hours for a missed deco stop. The other 2 violations are deco stops below 60 feet (nicely addressed by KenGordon) and diving deeper than 330 feet. I dive both my computers in DSAT, they run very close. I always clear both from deco and have never encountered the VGM. The no lock out of the Petrel/Perdix is fine but is not one of the main features that attract me to the Shearwater computers.
AJ
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My Suunto D4i has locked me out after three days of diving. My Petrel kept me diving during the rest of that vacation. My D4i is gaining dust since.
FYI: I did some shallow easy beach to house reef dives, not even beyond 20m. Maybe AI did not like me to drain the tank below 50 bar or something like that? Or maybe I ascended too fast too many times for it's liking (moving arm up while taking pictures)? DM 4 showed quite a lot of violations. Still don't know the exact reason, but there was no real reason as far as I can tell. Just my Suunto panicking over nothing.
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I'm always interested in what is important to other people and why.
For you, it appears to be a proper air integration feature. Let's pass on the "one less hose" argument and look at this. I'm intrigued.
Up until now (for me), an AI feature was a "nothing". However, when I used to dive with my son, that would have been a very nice option. He wasn't always at arm's reach away.
I'll add to my Shearwater wish list for a proper recreational DC: Two input AI. Perfect for ID's or buddy diving. This opens up the Pandora's box of reliability. Reliability could be a real vacation-killer.
Question: How do pressure transmitters and DC's communicate underwater? Ultrasonics is my guess. That would be interesting as first stages generate monstrous amounts of ultrasonic noise. Whatever, any good engineering effort could solve this to whatever degree of reliability.
Back to AI. I'll admit, after a bit of thought, I'd love to lose the lollipops on my sidemount rig.
How would others use AI? Rockbottom monitoring for a buddy pair, realtime SAC rate info, a reminder to switch on sidemount or independent doubles?
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I dive mostly solo. I've never monitored anyone's tank pressure but my own. I've had my VT3 for 5 1/2 years, 622 dives, flawless performance. I've never lost tank pressure for more than 30 seconds, am generally unaware but see it on the graph when downloaded. That being said, I dive with the Geo2 and a SPG as backup. I've never needed them but am loathe to lose a dive or series of dives. The VT3 does not monitor SRMV in real time, I see it after I download
My Zoop and D6 and my wife's Cobra would lock the diver out for 48 hours if the NDL is exceeded and the diver blows off the resulting mandatory stop. I'm not familiar with other computers that have a lock-out feature, so I can't comment on how that compares.
When I bought my first Suunto, I was blissfully unaware of this feature. The first time I exceeded an NDL, I did my best to do what I thought the computer was trying to tell me, but for whatever reason I exceeded the "ceiling" and got locked out. But I guess this feature had the intended effect of figuratively whacking me on the nose with a rolled-up newspaper, as I never made that mistake again. My wife and I enjoyed many (long enough and deep enough for us) dives with our Suuntos before switching to the Petrels.
The idea of a revolutionary "recreational-ONLY" dive computer that somehow softens the hard NDL number that is the foundation of all other rec DCs is intriguing, but probably quite risky for a manufacturer to try that.
I think the Liquivision computers/transmitters use ultrasonics. I think Oceanic and others use RF.
My Atom has the Buddy Check feature. I have never used it and I have never understood how it would really be useful. The range on the transmitter is short enough that, if I have the transmitter on the right side of the 1st stage and I wear my DC on my left wrist, I get occasional dropouts. It's hard to imagine that the DC would get good enough reception from a transmitter on a buddy's tank to actually be useful. If I have to swim right up to you to have my DC be able to show me your air I may as well just give you the signal to ask you.
A lockout only occurs if a mandatory decompression stop was violated. To have the computer lock means the diver did not follow the displayed decompression information. If it was intentional because you decided to follow the Petrel NDL schedule and let the D4i be violated...I can understand where an experienced diver may chose to do that. If it happened without you being aware...shame on you.
The decompression algorithm does not look at your tank pressure...that does not factor into the equation. It looks at the following dive behavior:
* Dives with short surface intervals
* Multiple ascents
* Ascent rate violations
* skipping a "Mandatory" Safety Stop (usually caused by an ascent rate violation)
All of these will affect the next dive. If you start the next dive with the "Attention" symbol, you should expect to see shorter NDL times that you expected.
The ascent rate has to exceed 10m/Minute continuously for more than 5 seconds to get an ascent rate warning. I see a lot of people state the issue was caused by moving their arms or lifting their console to read. This is usually not the case. The most common ascent rate violation I see is that a large number of divers do not think about the ascent rate when completing their safety stop. Once the countdown from three is complete, they come straight to the surface and often much too quickly. That can trigger a violation and the diver gets the "Attention" symbol displayed on the surface. When everybody else decides the surface interval is over, the Suunto diver may still have the "Attention" symbol showing when they start the next dive. That action will affect the NDL levels on the dive.
I am not trying to defend the Suunto algorithm (I have a Petrel also) or say that you did any of these things. Understanding what can cause increased conservatism is key to using the computer and I see a lot of "it's the computer, not the way I dive" excuses from students or past students when I saw exactly what the diver was doing to cause the ascent rate warning...and it was appropriate. Deciding if the penalty for bad behavior (as determined by the computer) and how it affects the NDL of the next dive is another discussion, but the manuals do describe the dive patterns that cause increased conservatism.
An example...22 dives over six days with a Suunto DX (P0, A0) and a Petrel in REC mode on medium conservatism. Both computers tracked NDL fairly closely. The DX does use a different algorithm (Suunto Fused RGBM) than the D4i, so this is not a "like to like" comparison, but the DX will penalize bad behavior like the D4i and make adjustments on the next dive if needed.
Since Shearwater is watching this thread, I will add my perspective as a recreational diving photographer. I use a "two handed" DSLR photo rig. I also dive a hogarthian long hose rig with a clipped off spg, along with my AI computer (Galileo Sol). Having gas info on my wrist is invaluable, as compared to holding my heavy camera rig in one hand, unclipping the spg, checking it, and re-clipping it. That sounds like no big deal but before I hear "equipment solution to a skill problem", try it at 130' in a strong current dealing with the photo rig! In fact, I view AI as a valuable safety factor in that regard, and more than just a convenience. It is a real, tangible, valuable benefit that I desire and why I have not taken the step of buying a Shearwater yet.
As for your other questions, I dont (and don't know anyone and I dive with an advanced crowd including some tech divers) who uses "rock bottom" for rec diving. That being said, my computer allows me to set a "surface reserve" which is the amount of gas that will be in my tank when I reach the surface. It also has a predictive gas usage algorithm, which will tell me to begin my ascent at the pressure which will assure I arrive at the surface with the set reserve, including my predicted gas consumption through the ascent and safety stop. I have found this to be very accurate at least the way Scubapro has implemented it. Thus, my "surface reserve" is the amount of gas available for my buddy if needed during an ascent at the end of a dive. While not as formal as "rock bottom" I can set the reserve at whatever I want, so if I want a cushion, I can set it at 1000, say, on a deep dive. Of course, I will get sent up early by doing this. For dives up to 90' I leave it set for 600, which is enough to get a buddy to the surface in a true emergency OOG situation (which will be faster that usual and not include the safety stop).
If you do "rock bottom" you can set the computer to give a warning at your calculated surfacing pressure or any other turn pressure you want.
As for real time SAC, my remaining gas time is all calculated in real time based on change in tank pressure over time. So, it is, effectively, "real time" SAC calculation during the dive, but translated and displayed as useful information regarding remaining dive time. If you are working hard, the computer automatically takes this into account in its prediction. No mental calculation necessary during the dive.
Such a feature would be essential on any computer I get. I was going to look at the Liquvision Omnix, but posters here have indicated it does not have this feature. That makes it a no-go for me.
My computer also offers buddy air monitoring. My buddy and I can program our computers to read each other's transmitters. A button push during the dive brings up your buddy's gas supply. However, I don't use this much as we usually do a mutual gas check 2 or three times during the dive. Also, because my computer (like most) uses rf transmission, you have to be within 4 or 5 feet of your buddy's transmitter to get the reading from them. So, it is a handy feature, but not necessary.
However, Liquivision uses ultrasonic transmission, which they say is good over pretty long distances, and offers an option to display buddy gas on the main dive screen. This would greatly increase the utility of this feature if it is effective, but I would not trade buddy air monitoring for an effective predictive gas use algorithm.
So, that is my take on why AI is a desirable feature for both basic and advanced rec divers. Hopefully, it offers tech divers some insight into why this feature is so popular and so useful to their rec compadres.
AJ
Contributor
Did not do deco. Nowhere near it. Multiple ascents = yes, really a lot while photographing. Ascent rate violations = yes, according to the D4. Not as I'am and the Petrel were aware off, but it may have happened. Maybe my diving behavior triggered the Suunto to do this, you could be right about that. Anyway, I trust(ed) my Petrel then and was only using my D4i as backup. Don't even do that anymore.
BTW, this happened over a year ago. At the time my skills were not that good, a bit rough so to say. I have become much more carefull and in contol (GUE training) on ascends these days. Maybe the Suunto would not lock me out anymore, but I like the Petrel so much I have no more use for the D4i anymore.
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