First Dive Computer

[KenGordon]

Please share with me the data that any conservative deco algorithm is safer than any more liberal algorithm when used for recreational diving.

This is one of those bogus rhetorical techniques that boulderjohn is always warning about.

Show me the data that supports them being equally safe.

On the other hand we use tissue supersaturation as a proxy for risk. More supersaturation means more chance of injury. Staying down longer means more supersaturation, hence more risk.

 

[doctormike]

A Shearwater is not like a BWM. I own both. A nice car is really much nicer than a nasty car, or even an average utilitarian car. My Perdix is not much better than my Helo2. The screen is nicer (but not as nice as an Eon) but the two button interface sucks in comparison to the four button one. Imagine a web browser with no back button... However, most of all the computer is a very small part of diving enjoyment, whereas the car is actually pretty important in driving enjoyment. Of course if you can’t afford the fuel a BMW isn’t as much fun as a Kia. Choices have to depend on circumstances too.

OK. It's an analogy, not the identical issue!

I'm not saying that Shearwater is the best computer out there, or that it changes the experience of diving, or that there are no possible objections to it's design. I'm simply responding the the most frequent objection being raised in these threads (best computer for a new diver).

I'm on ScubaBoard a lot, and I read lots of these threads. Of all the DCs out there, Shearwaters are the one that gets almost universal rave reviews. And the most common objections to them in this context is not that a two button interface sucks (which I am hearing for the first time, but I totally accept from you as a legitimate concern). It's that they are (1) too expensive for a beginner trying to save money, and (2) for tech divers only.

All I'm saying is that those two common objections are similar to the objections that one might make comparing a mid-priced, superbly engineered car from a company with great customer support to a low priced mass market vehicle. And to be honest, I don't know jack about cars! Maybe BMW has terrible customer support, I don't know. I take the subway. But I think you get my point.

If a new diver can afford a Shearewater and has good enough eyes so that they aren't set on a watch sized unit, it's a darn nice computer and worth the investment.

 

[Lorenzoid]

Diving with a Suunto is like driving a car in a 40 mph zone that has a speedometer that only goes up to 35.

Terrible analogy. But I chuckled anyway.

Now, imagine a car that, if you exceed 35 mph in a 40 mph zone, locks up on you for the next 48 hours.

 

[scubadada]

This is one of those bogus rhetorical techniques that boulderjohn is always warning about.

Show me the data that supports them being equally safe.

On the other hand we use tissue supersaturation as a proxy for risk. More supersaturation means more chance of injury. Staying down longer means more supersaturation, hence more risk.

Hi @KenGordon

You assert that a conservative computer is "safer" than liberal computer without any evidence this is true. You invoke that it is intuitively obvous that longer underwater carries more risk. It may be that all the available deco algorithms are very, very safe and that no differences are practically detectable.

Again, we are discussing no stop, rec diving and not deco, tec diving. I have seen supersaturation used to an analyze various deco profiles, but have not seen it used to compare NDL exposures, do you have examples?

Good diving, Craig

 

[Lorenzoid]

It may be that all the available deco algorithms are very, very safe and that no differences are practically detectable.

I used to think along the lines that "if low risk is good, then even lower risk is better," regardless of the absolute level of risk we're talking about. That's probably why I chose a Suunto as my first computer. I figured it was the Volvo (back when Volvo's big selling point was safety features) of dive computers. But I have since warmed to the idea that, as a practical matter, i.e., given the level of risk we're talking about, there is no difference. If I recall correctly, it has been said that the average incidence of DCS among all divers--good divers, ignorant divers, divers with PFOs, etc.--is roughly one in 10,000 or 15,000 dives. So, if it were found that, say, one in 100,000 statistical dives properly following DSAT computers resulted in DCS, but "only" say, one in 200,000 statistical dives properly following Suunto computers resulted in DCS, is that really significant? I just made these numbers up, but I would guess the odds of a good diver who follows his computer and has no predisposing factors really are on the order of being struck by lightning despite taking reasonable precautions. As a practical matter, the data needed to make such calculations couldn't be gathered anyway.

 

[KenGordon]

Sorry, I thought I had posted this this morning, I must have been in a tunnel.


Rather than arguing about computer choice perhaps it would be better to promote diving in a manner least likely to lead to injury.

Stay hydrated.
Shallower is safer than deeper. (Even within tables/computer)
Use a reasonable gas, eg Nitrox 32 for 20-30ish m, and respect the MOD
Have long surface intervals.
Avoid deep repetitive dives.
Take a day off, or at least back off a bit, when doing multiple dives per day over several days.
Don’t drink the boat dry (beer wise).
Avoid doing work at depth.
Do not be warm at depth and cold shallower.
Be reasonably fit.
Work up to deeper/longer/repetitive diving.

And, back to the arguement, if you can’t remember all that set your computer a bit more conservatively.

 

[stuartv]

Man, you guys like to argue!

It is all deco diving. Your DSAT computer will allow no stops on a dive that would have stops on a Suunto. What is the difference other than marketing?

The difference is whether the (recreational, OW-qualified) diver is following their training or not. To some of us, adhering to our training is very important!

This is a post about how you can get to your DSAT NDL using a cylinder 50% bigger than a typical holiday diver’s one.

Seems to me that you are confirming the assertion that other limiting factors need to be overcome before NDL is a serious issue.

If you comprehended the entire post, you would have gotten that it was about how I hit my NDL every time and never used more than 78 cu-ft of gas. So, even a 100 would have been plenty. 100s are readily available.

And that was all based on the diver (myself) being a somewhat big guy, not in particularly good shape, and brand new to diving. Meaning, really, just about any diver could have some reasonable hope of having their gas outlast their NDL.

No, I don’t ignore Suunto stops. I am saying that all dives involve deco and that the distinction between no stop,’recreational’ diving and stops on ‘technical’ diving is about marketing. .

More baloney. The distinction is about mandatory stops or not and following one's training. That is not marketing.

All dives involve deco. NOT all dives involve mandatory deco stops.

It usually kicks off when someone repeats the Scubaboard Lore that Suunto are rubbish because of RGBM following someone saying not to worry about the algorithm because it will not often be the limiting factor. Then DSAT fans with air consumption to boast about claim they are the limiting factor and follow up with assertions that staying down longer is just as safe as not staying down longer.

Can you quote a single post where anyone said that Suunto are rubbish? Are YOU equating "more conservative" with "rubbish"? I'm not. I equate "more conservative" with "less bottom time".

Can you quote a single post where anyone said that staying down longer is JUST as safe as not staying down longer? I think you are inferring an assertion that staying down longer is less safe, but the difference is insignificant and then translating that to "just as safe".

I'll stipulate to staying down longer is less safe. Now, FOR NDL DIVING, I assert that the difference is so small that it doesn't matter. Please share any data you have that supports the notion that my assertion is wrong.

 

[KenGordon]

Hi @KenGordon

You assert that a conservative computer is "safer" than liberal computer without any evidence this is true. You invoke that it is intuitively obvous that longer underwater carries more risk. It may be that all the available deco algorithms are very, very safe and that no differences are practically detectable.

Again, we are discussing no stop, rec diving and not deco, tec diving. I have seen supersaturation used to an analyze various deco profiles, but have not seen it used to compare NDL exposures, do you have examples?

Good diving, Craig

Did you never meet anyone who has been bent on a simple dive inside of NDL? What does very very safe mean? Sounds like no bends at all.

You understand that supersaturation (ie tissue pressures above ambient) exists for all dives where the diver returns to the surface. And limiting that supersaturation is how disolved gas algorithms work. The NDL is when the expected supersaturation will reach the limit. So a longer NDL implies a higher limit of supersaturation and hence risk.

 

[doctormike]

Did you never meet anyone who has been bent on a simple dive inside of NDL?

That could only happen to a very reckless and foolish diver!

 

[KenGordon]

Terrible analogy. But I chuckled anyway.

Now, imagine a car that, if you exceed 35 mph in a 40 mph zone, locks up on you for the next 48 hours.

This is what Tesla ought to do when the user hasn’t touched the steering wheel appropriately for a while. There would be at least two people still alive in that case.