What makes us think we can trust any of them

[WarmWaterDiver]

With regard to ascent rate, Dive Rite's dive computers have had a variable ascent rate alarm, which alarms at lower ascent speeds in shallower waters and higher ascent speeds in deeper waters, at least since the NiTek3 generation. Their NiTek Duo has a bar graph as well now - as does the TUSA IQ-700 I also use. There are three depth ranges with different ascent speed alarm settings.

Personally, I find the bar graph and alarm to be helpful information in smoothing my ascent profile. The earlier NiTek3 only alarmed after the speed was exceeded and didn't provide any indicator for the user to see how close the speed was approaching the alarm speed. Others may not find such tools helpful due to individual differences.

This is an example of using a dive computer in concert with executing a smoothed variable rate ascent profile.

I will still do a safety stop for 3 to 5 minutes between 20 fsw and 10 fsw, as a choice. I am not 'penalized' by the dive computer if this is not performed with these models. I will often now also choose to spend 1 to 2 minutes at a depth about half my max depth. It doesn't hurt to do so as I'm ascending anyway, so there are usually a couple of 'flat spots' in my ascent profile.

 

[Uncle Pug]

Slightly off topic but since the issue was raised... ascent indicators introduce unnecessary hysteresis. Beyond that and IMO even more important to consider:

Using an ascent indicator and/or alarm to assist in controlling ascent will, for the majority of divers keep them from ever developing the skill to do so without it.

For those who have developed the ability to control their ascent going back to computer assisted ascent indicator/alarm will most likely prove to be skill-degrading.

This will probably be of no consequence until something goes sideways in a dive and the diver's attention is diverted from the indicator and the alarm only adds to the confusion (if heard at all.)

Being able to sense your position in the water column and automatically control it while your attention is demanded by other matters is not a trivial skill.

Shallow water practice of neutral bouyancy with your eyes closed greatly facilitates learning to sense small changes in depth. Practice managing multiple tasks under pressure while maintaining position and depth takes it to the next level. Multitasking under pressure with your eyes closed takes it a step beyond that.

 

[lamont]

I finally bent the snot out of my computer today. I did two dives on EAN30 while it was diving air. On the last one it was pissed and giving me 24 mins of deco at one point, and it still had around 14 left by the time we left our 8 minute stop at 10' (diving with jimmy, had to hit 60 mins, and we did push it pretty hard).

Time to convert to gauge mode only...

 

[Snowbear]

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.

I agree. All the Suunto (or any computer AFAIK) gives you is a "cieling" and sometimes a "floor."

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.

Yep is is When I was first learning to run my own profiles, rather than following the diving-with-a-computer SOP taught to and used by most recreational divers, I kept my Vyper in guage mode and put a Favor in my pocket. I wouldn't look at the Favor until I got to 20' (it kicks over to the 3min "safety stop" countdown at 19'). In air mode while I was diving EAN32, even after the aggressive 110' profiles possible with a 120cf tank and a good SAC rate, the Favor was more than "happy" with my "on the fly" dive profiling and ever slowing as I got shallower ascent, even after multiple dives. Using the Favor as a backup to verify what I had been taught by a former mentor as well as how much better I was "feeling" (subjective yes, but hey.... what works, works ) gave me the confidence to rely on what's left of my own brain to run these profiles.

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.

I disagree here. I am not saying that the improved profiles I use are incompatible with computers. My point has been that how most divers are taught to use dive computers is, in fact, to have the computer determine the dive profile (while using the other "rules of thumb" such as recreational depth limits and ascent rates). The NDL, especially for multi-level profiles, is determined by the computer. The ascent rates people use to get to their "safety stop" when they're "done" with their dive are determined by whatever sets off the ascent alarm (In the case of the Suunto, it's something like 33fpm IIRC). The depth and time of the deco.... um.... I mean "safety" stop is determinged by the computer.... when it "clears" it's OK to surface, at whatever rate the computer "allows" without sounding an alarm. I see this over and over and over with divers I dive with as well as reading posts here on ScubaBoard about "what computer should I get that "allows" the longest dives or is the "most conservative" based on what is "allowed" for NDL's. Even tech divers ask about which computer to use that will "give" them the "safest" profiles for deco dives and allows for gas switches so ir will run their deco schedule based on their dive. Some actually say they plan the dives based on a PC-based deco program, but want the submersible computer "as a backup" in case something happens to change the planned dive.

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'.

Even in guage mode the Suunto (at least my Vyper does anyhow) counts down the 3 minutes starting at 19' to 10'. My profiles tend to leave me wanting to spend more than 3 minutes in that range anyhow, so it doesn't really matter to me.

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

Again, no they don't. But most recreational divers trust their computers to determine their dive profiles more than they trust their own brains. Part of this trust means they trust that as long as they stay withing their computers' profiles, they are less likely yo get bent.

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.

Me neither. It's actually pretty somple once you figure it out. The profiles I advocate end up much more conservative than even the most conservative dive computer by the time I exit the water.

 

[Snowbear]

Using an ascent indicator and/or alarm to assist in controlling ascent will, for the majority of divers keep them from ever developing the skill to do so without it.

But in the case of the gal I talked about early on, this was a way to get her to start actually thinking about her ascent rate beyond keeping her ascent alarm from sounding. In her case, an emailed link to a thread about using the "stuff" to maintain neutral buoyancy and tell if and how fast one is ascending or descending may well get her to stop relying on those little bars on her computer. Too bad she lives in AZ. If she was farther North and West, I would hook her and her hubby/buddy up with a certain camel who could teach them much

 

[TSandM]

Shallow water practice of neutral bouyancy with your eyes closed greatly facilitates learning to sense small changes in depth.

Okay. I'm going to make a confession here. If anybody remembers my post about my 50th dive, the one where so many things went wrong that I was beginning to think I shouldn't do it -- and the one that ended so well, with me holding my stop while admiring the jellyfish . . . the last thing that went wrong that made me think I should scrub the dive was forgetting my computer. I went down (yes, mea culpa) with no way to tell depth or time. It was a "trust me" dive, because I trusted Bob's computer to guide us. Of course, we were also doing a dive I knew, with parameters with which I was entirely familiar. But it doesn't excuse going down without gauges, I know that.

However, I learned something incredibly valuable from that dive. I had NO way to know if I was going up or going down . . . except the physical sensations that were associated therewith. I HAD to pay attention to how I felt, because I had no other data. That dive was the beginning of my ability to control my buoyancy.

Today, I did one minute stops at 30, 20 and 10 feet, and took three minutes or more to get from 10 feet to the surface. I was able to do that because I have learned how to FEEL what's going on with my buoyancy . . . and taking away my machine crutch was the first step in that.

I'm not recommending diving without instruments. But UP's suggestion of closing your eyes gives you the same experience without, perhaps, quite the same risk. You have to learn to FEEL yourself underwater to be really comfortable and competent. If you're like me, and like objective data, you may never spend the time to pay attention to your body and the water and all the non-instrument-related information that is available to you all the time while you are diving.

 

[jeckyll]

Great thread. I know I will have to re-read parts of it a few times.

As an aside: I still find it fascinating how much additional knowledge is out there, beyond 'traditional learing' i.e. LDS based courses. Or perhaps I haven't taken the 'right course'

Thanks to all those posters who put together long responses meant to teach those of us who are new more than we can get from our textbooks (or computer manuals). You know who you are

Bjorn

 

[grazie42]

As yet another sidenote "feeling" your dive and learning to control your bouyancy with it will be a great help if you ever find yourself forced to make an ascent without your mask and perhaps even alone...it may feel a bit scary but nothing like as scary as if you´re doing it for the first time...

 

[100days-a-year]

...use the force Luke....

I like to think using an ascent rate indicator actually will decrease task loading VS.using a timer/guage combination or even a timer and visual references such as an anchor/down line or if the vis is clear the surface or structure.Thus allowing more awareness to prevent or deal with any SNAFUs.An audible signal is useless to me at times(hood).A graphic works fine for me.

One other thing,in a panic situation people tend to refer back to repetitive training.
Giving someone something to focus on(computer) becomes almost a security blanket and will allow them to feel comfortable enough to think.Trying to fly by the seat of your pants in panic mode while u/w particularly while ascending could lead to embolism.Following a computer may bend you at some point but your odds of surviving that are greater than embolisation.Feeling your way through a dive sounds great but how many people are really capable or interested in spending the time/effort becoming so attuned u/w that the dive is intuitive.

 

[Charlie99]

.One other thing,in a panic situation people tend to refer back to repetitive training........Trying to fly by the seat of your pants in panic mode while u/w particularly while ascending could lead to embolism.

The point others are making is that routinely making an ascent without reliance upon an ascent rate indicator means that that is the method of repetitive training that you refer back to in a problem situation.

When I look every once in a while at my SPG, I know what pressure to expect. When I look at my computer every once in a while, I know what to expect (that applies to time, depth, and deco status). This holds true during ascents too.

For instantaneous feedback, nothing works better than the little bits of gunk that you find in even the clearest of water. Great for small changes in depth, and for controlling ascent rate over a short period of time. A downcurrent or upcurrent can make that unreliable, so occasional check of absolute depth with a computer or an eyeball of the surface if visible is needed as a crosscheck of what the gunk in the water is telling you.

Your ears sense absolute depth. If your ears are telling you that depth has changed when you didn't intend to, you'd better be figuring out what's going on.