Dive Computer No Deco Computations Question

[gordonscuba]

Thank you all for your responses. From what I gather collectively the Sunnto software and algorithm seems to have some limitations and flaws. However, you have to honor the most conservative of the two.

With that being said, a dive computer is an expensive and major purchase. Some of your nicer and higher recommended models (Shearwater Teric for example) run over $1,100. How many divers out there are really spending the money to buy another expensive second computer to use as a backup? I feel like if you buy a “cheap” computer as a backup then you pay the price like I am with my Suunto.

On OC: dual Perdix 2.

On CC: Petrel 3 and NERD 2. In any case it's always two trimix-capable Shearwaters.

Sometimes I use a Teric for backup if I want a smaller object on the wrist, but the Perdix is preferable because I can just carry a spare battery and switch on the boat if needed. The Teric, one must remember to keep charged.

 

[tursiops]

I am aware of the Apple Watch issue and what happens if you exceed the maximum depth. I also agree with you that no matter what it should still provide info to safely get you to the surface in the event that happens. I rarely dive beyond 100 feet so fortunately this is not an issue.

From what I gather all computers seem to have shortcomings of some sort then. Is there a particular brand or model that is known to not have any shortcomings?

You mean, like, what is the best car? You've got to allow for personal preferences and use cases, or "best" (i.e. no shortcomings) is meaningless.

 

[Belzelbub]

With that being said, a dive computer is an expensive and major purchase. Some of your nicer and higher recommended models (Shearwater Teric for example) run over $1,100. How many divers out there are really spending the money to buy another expensive second computer to use as a backup? I feel like if you buy a “cheap” computer as a backup then you pay the price like I am with my Suunto.

Yeah, you aren’t wrong. Dive computers are often quite expensive. Diving is expensive. I’d say most divers are perfectly happy diving with a single computer, and far more often than not, it’s sufficient. There are, plenty of less expensive options out there. It just depends on what you want. Air integration adds to the price. Color screens add to the price, etc.

The good news is that there seems to be a trend lately with a lot of brands. Many are offering computers now running Buhlmann instead of proprietary algorithms. That’s a good thing.

From what I gather all computers seem to have shortcomings of some sort then. Is there a particular brand or model that is known to not have any shortcomings?

A lot of us on here, myself included, are big fans of Shearwater. Not saying their computers are perfect, but they have great customer service, and actually listen to their customers. They aren’t inexpensive, though. That said, they aren’t ridiculously expensive when comparing features. All of their line are color, and most have air integration. As I mentioned, those add cost.

I also have a Garmin as a daily wear and backup computer. I like it a lot as well. They complement each other well. Both run the same algorithm, and I can set to the same conservatism settings, including custom. The Shearwater has a bigger screen, air integration, and more customization options. The Garmin has GPS and heart rate tracking during the dive. The Shearwater is easier to use out of the box. The Garmin just takes a little use, then it becomes second nature.

I would absolutely, without hesitation, buy both of them again.

 

[scubadada]

Hi @butterwm

Your AWUs are set on the most liberal preset, GFs 70/85. A GF high of 85 is generally considered moderate in the conservative to liberal spectrum. The AWUs can be made more liberal if you use the custom GF setting. Your Suunto Vyper is set at the most liberal setting. Make sure the altitude setting is sea level if it is a manual setting.

On a first, clean dive the 2 computers should match pretty closely, the Suunto may evern be even more liberal. On a repetitive dive, the Suunto may have a shorter NDL if the surface interval is short or perhaps some other factors such as a faster ascent... It doesn't seem like the NDL difference should be terribly great.

If you dive the 2 computers for an NDL dive, the more conservative will be controlling. If you allow one to go into deco, you will have to clear it or you will be locked out for a period in violation gauge mode.

I dive 2 computers with different, though similar decompression algorithms., a Shearwater Teric running 80/95 and an Oceanic VT3 running DSAT. I have absolutely no problem doing NDL or light deco dives.

Best of luck on your future dives, let us know how you do.

 

[therookie]

I gusss my biggest concern is since there is a 30 minute split on the NDL if we follow the Apple Watch are we still safe because the Suunto shows up exceeding the limit.

I don't think anyone else commented on this so I would like to. As a new, inexperienced diver I would feel perfectly safe following the default NDL calculations that you were using on your Apple Watch - even though the computer I currently use is an RGBM(ish) implementation.

I was curious about the conservatism settings on the Oceanic+ app for the Apple Watch - couldn't find a manual online to save my life but there is a tutorial on Oceanic's website that shows that 0 is indeed the least conservative preset setting - other two look like this:

So you could always use one of those instead to increase the conservatism if you wished. However, the fact that Apple was comfortable with Oceanic using the "least conservative" as the default is a good indicator that it isn't a high-risk setting.

 

[boulderjohn]

I don't think anyone else commented on this so I would like to. As a new, inexperienced diver I would feel perfectly safe following the default NDL calculations that you were using on your Apple Watch - even though the computer I currently use is an RGBM(ish) implementation.

I was curious about the conservatism settings on the Oceanic+ app for the Apple Watch - couldn't find a manual online to save my life but there is a tutorial on Oceanic's website that shows that 0 is indeed the least conservative preset setting - other two look like this:
View attachment 862794
So you could always use one of those instead to increase the conservatism if you wished. However, the fact that Apple was comfortable with Oceanic using the "least conservative" as the default is a good indicator that it isn't a high-risk setting.

So here's what the numbers mean.

1. The Buhlmann algorithm originally had a calculation that determined when it was safe to go to the surface. Years later, another man figured out a system for adding conservatism to it. That's what the two numbers with the slash represent.
2. Pay no attention to the first number (as in the 70 in 70/85). It only matters if you go seriously into deco. It determines the first deco stop in that case.
3. The second number is essentially a percentage of how close you get to the Buhlmann surfacing limits. The lower the number, the farther you are from the limits. The farther down you go, the safer (but shorter) your dive will be in terms of DCS risk.

 

[Belzelbub]

So you could always use one of those instead to increase the conservatism if you wished. However, the fact that Apple was comfortable with Oceanic using the "least conservative" as the default is a good indicator that it isn't a high-risk setting.

Yep. For comparison, the 85 in the least conservative/default setting corresponds to the medium setting that several other brands use. So the 85 isn’t overly aggressive at all.

Pay no attention to the first number (as in the 70 in 70/85). It only matters if you go seriously into deco. It determines the first deco stop in that case.

At first, I thought it odd that the GFLo they chose was so high. But, it does make sense after thinking about it. The AWU is intended for recreational divers. Functionality exists for light or unintended decompression, but moving that first stop up higher in the water column is a good idea for a diver that is likely not carrying extra gas.

 

[Tassie_Rohan]

From what I gather all computers seem to have shortcomings of some sort then. Is there a particular brand or model that is known to not have any shortcomings?

I wouldn't say all computers have shortcomings. Just get a computer that used Bühlmann ZHL-16C, but make sure you can modify the gradient factors. More computers use Bühlmann than don't. That way your computer will match other Bühlmann computers with the same GF, as well as dive-planning software on you phone or computer.

Avoid computers that use some 'modified'/'based upon'/'resembles' Bühlmann where they have felt compelled to add some layer of opaque wankery to protect you from yourself.

Folks: feel free to expand or correct this list:

Computer brands using Bühlmann that assume you are an adult with modifiable GF:

Shearwater (SurGF feature is very useful)
Heinrichs Weikamp
Ratio
Garmin
Mares
Scubapro?


Computer brands using in-house mumbo-jumbo algorithms, 'conservatism factors' and/or lock you out if you've been a naughty child and did something their lawyers object to:

Suunto
Cressi
Oceanic


Cheers
Rohan

 

[scubadada]

...Computer brands using Bühlmann...

See this for AI wrist computers

Air Integrated Wrist Computers in the US

*See last spreadsheet posted for update* There have been a number of new AI wrist computers in the last year. I have been keeping a spreadsheet for myself, thought others may be interested. All errors are my own, easy to correct if you let me know. Edit, I'll start with the errors, Suunto...

scubaboard.com

 

[Jai Bar]

Thank you all for your responses. From what I gather collectively the Sunnto software and algorithm seems to have some limitations and flaws. However, you have to honor the most conservative of the two.

With that being said, a dive computer is an expensive and major purchase. Some of your nicer and higher recommended models (Shearwater Teric for example) run over $1,100. How many divers out there are really spending the money to buy another expensive second computer to use as a backup? I feel like if you buy a “cheap” computer as a backup then you pay the price like I am with my Suunto.

This whole thread could be more productive if you upload the dive profiles of two mentioned dives, for both computers.

Suunto Vyper, the default 0 is the less conservative. Not familiar with Apple watch. This is irrelevant to discussion, but you should really be familiar with both your computer settings and their meaning.

Lastly, to your conclusion that Suunto RFBM has limitations and flaws.. Unlike you, I am not a diving computer expert, but ALL diving computers including the fancy and most expensive ones have limitations: they are based on this or that algorithm that tries to simulate the behavior of your tissues. None of them knows YOU and your specific physiology, health, physical condition etc.

They say Apple uses the Buhlmann 16-xx algorithm. It is used by many manufacturers due to its simplicity: it assumes that all your body tissues can be represented by 16 compartments. Imagine you have a bath tub, and let's call it a compartment. You open the faucet and ot starts filling with water. That is you beginning a dive as your body starts filling with Nitrogen. You have a fancy computer that knows to calculate how many minutes before bath is full to the brim. That is your NDL. If you open the plug- you begin ascent- then the water level beging to go down. But alas, the faucet is still pouring water in (because even during ascent one still absorbs nitrogen), the computer now has to recalculate again how many minutes to get full until bath is full to the brim

Now, instead of one bath you have got 16, each with a different faucet and plug, so computer calculates all of them and gives you the time until any of them will be full.

Not the best analogy, but sort of.

RGBM is a different approach instead of compatments, it assumes that there are bubbles (in tissues, including blood) with different size, and their behavior with dissolved gas and pressure changes (gradient). Supposedly, a more realistic model of whst happens throughout the dive.

Again, none of them is better, both are just a model with limitations and perhaps one can say inherently flawed.

That is why they teach you always take precautions and be more conservative- regardless of diving with tables or computer, because each diver and dive have different conditions and you are not comprised of 16 bathtubs and bubbles in the blood are sneaky bustards quite difficult to simulate their behavior in real-life..

Be careful, dive safely. Do not over trust your computers and confident that as long as you do what they say then you'll be all right. It is you, after all, who gets into the recompression chamber, not the computer...