Now it's time to choose a wrist computer.

[SaltyCracker]

I think you are looking at it backwards.

I think I've been looking at it backwards, forwards and inside out.

Liberal verses conservative isn’t really about experience, it’s about risk tolerance.

That's what I had in mind. I was considering the experience needed to make informed calculated risk decisions. Since I don't have that experience and I will also be responsible for my son tagging along with me, I'm mainly interested in how conservative I can be within practical reason.

Others may simply think because they haven’t been hit in the past, they won’t be hit in the future. That is risk normalization.

Yeah... I'm also prone to complacency so I'm interested in building in an extra dash of conservatism to cover that as well.

 

[Gandalf-the-Diver]

his was changed with firmware version 65. Now, both Tec and Rec mode allow fully customizable GFs. The three presets are there, but the user can also select custom. The Peregrine was initially shipped with a later firmware, so I believe the same is true for the Peregrine.

My Peregrine has three settings for conservatism, low, med , and high. It also has the option to customize the setting, however one wants. I have had my Peregrine since Sept, 2020, and it has always had that option.

 

[Gareth J]

Hi @Gareth J



Some of my dives have general run time limits, some operators prohibit deco diving. I take those aspects into consideration in planning my dives. Some of my dives, most of those in the Red Sea, Cocos, Galapagos, Revillagigedos, and Malpelo, were with small groups that descended and ascended together. NDL and gas were never really a consideration in those situations.

We have strict runtime limits on our dives. Before getting in the water, you put your surface to surface time on the log, and you are expected to stay within it, that's basic dive planning.

I can't remember there ever being a restriction on deco' dives on any of the Red Sea trips I have done. But that may well relate to the fact that the boat's have been catering for European divers.
I haven't done the Galapagos, my late partner really wanted to do that. I do have a few friends who have been, they where doing extra deco on the backend of the dives for an additional safety buffer.

Despite wanting to dive when I have been in the States, I have had very limited opportunity. I have done a few single days off Catalina, last minute making up the numbers, but novice stuff really.

 

[Belzelbub]

My Peregrine has three settings for conservatism, low, med , and high. It also has the option to customize the setting, however one wants. I have had my Peregrine since Sept, 2020, and it has always had that option.

Thanks, I figured that was the case as the non-Teric Shearwaters mostly share the same firmware. Since the Peregrine, which only has the Rec modes, was introduced after SW added custom GFs to the Rec modes, I figured the Peregrine would have that option. But, it’s good to have confirmation.

 

[scubadada]

We have strict runtime limits on our dives. Before getting in the water, you put your surface to surface time on the log, and you are expected to stay within it, that's basic dive planning.

No, by run time limits I mean everyone dives for +/- an hour. This is often needed to make an AM/PM 2 tank dive schedule. I realize your diving is different. Of course, we get in 4 dives/day and about 4 1/2 hours of dive time.

 

[dmaziuk]

And you're comparing the most liberal of the scale to DSAT?
And DSAT is considered "the only model actually designed and tested for recreational diving"?
It seems to me that an algorithm designed primarily for the rec diver community would be more on the conservative liberal side. I'm trying not to be dense or split hairs. But something seems backward to me.

Not really because a "technical" dive with multiple gases and/or rebreather can load your tissues with nitrogen way more than an hour on a single Al80. DSAT has a very long track record in addition to being designed and tested for this kind of diving, so it's reasonable to use it as the "gold standard".

Buhlmann's model, OTOH, was designed to be more general "one size fits all" and does not have 3 decades of real-life use for recreational diving, so... make of that what you will.

And when you say "bare" ZH-L16C, does that mean what my manual is calling ZH-L16C "unmodified"?

Yesno, the manual is full of it. There is the set formulae to calculate this stuff, and a set of "maximum allowed supersaturation" values to plug into it. According to Craig, SEAC's lowest conservatism level is GF High = 85. What that means is the formulae are unmodified ZH-L16, but the M-values are 85% of those of "bare" ZH-L16C.

 

[dmaziuk]

Funny.

I thought that at Cocos they pull you out of the water that fast so that the tiger shark doesn't chew your *ss off

I guess if you're diving with tigers at Cocos you better not go into deco, eh?

 

[SaltyCracker]

Hi @SaltyCracker

It is encouraging that you are attempting to learn more about your dive computer. Many divers never understand how their computer works.

You will not be one of the befuddled divers asking me why their computer is not working when they are in violation gauge mode. Enjoy your diving, there is nothing I enjoy more than diving with my family.

Thank you. Sometimes, being an anal retentive stickler for details pays off. I just can't imagine how I could deal with myself bringing my young son into this environment and encountering an avoidable, reckless injury. It's also important to me to instill a healthy respect and caution for what he's about to get himself into.

So, @SaltyCracker only you will be able to decide how you and your son dive your computers. I hope this thread and future endeavors help you make an informed decision.

You're right, ultimately, it'll be my decision. I want to begin on the conservative end of the spectrum without going overboard. I'm starting to think L4 is overboard.

Yes, this thread and those that offered patient, unbiased knowledge has been just what I was hoping for. Now I feel more comfortable that we can safety rely on our dive computers.

I did read the owners manual. Quite thoroughly I thought. But I did miss the stipulation you pointed out that setting 5 was the most conservative. That's what I guessed but was looking for back-up. Now I know.

DSAT and Buhlmann cannot really be directly compared because the two deco algorithms behave differently on 1st dives and then on repetitive dives.

I'm keeping this in mind as I ask any further questions.

Below you seem to agree that my setting of L4 is a reasonable conservative setting but the highlighted text is making me think I may be starting off more conservative than necessary if a setting L0 is = to GF high of 85/middle of the road and L2 is equal to GF high of 75 and considered "quite conservative". I'll have to start playing around in Dive Planner Mode I guess.

If your plan is a no stop dive, I believe you should follow the NDL plan on the computer you have chosen to use, with the conservatism setting you have selected. By remaining below the NDL, you will avoid ever having to deal with a potential missed deco stop.

Back in December, 2019, I corresponded with Seac. After some prodding, they supplied me with a table of the GFs they use. The most liberal setting (L0) uses a GF high of 85. This would be considered moderate or middle of the road along the spectrum. You can compare it to 40/85 in my previous post Now it's time to choose a wrist computer. Setting L2 uses a GF high of 75, this would be considered quite conservative. This corresponds to 35/75 in my previous post. L3-L5 are increasing, even more conservative.

I've been looking at theses graphs again trying to absorb the info offered.

However, this topic has been discussed on numerous previous occasions. All deco stops are not created equal. This is a 1st clean dive on air to 60 ft. NDLs come from my Shearwater Teric running Buhlmann ZH-L16C, and my Oceanic Geo 2, running both DSAT and PZ+. The NDLs vary widely, from 32 to 57 min. If you were to dive GF 35/75, 40/85, 45/95, or PZ+ to the DSAT NDL of 57 min, you would accrue deco time, somewhere between 17 and 3 min

View attachment 697745

So, all of these dive times on air at 60 feet are "safe". DSAT is the basis of the PADI Recreational Dive Planner, in use since the late 1980s. It is also the basis for the DSAT decompression algorithm used in Pelagic Pressure Systems computers almost as long.

It makes intuitive sense that a longer exposure should increase your risk for DCS. There is a probabilistic decompression model, SAUL, that has previously been discussed on SB. It allows one to estimate that risk Modern Decompression These are the same exposure times for a first, clean dive to 60 feet on air shown above. The dive times are ranked by probability of DCS, % and chance. SAUL includes a 3 min safety stop.

View attachment 697782

I started off assuming that the DSAT algorithm would be more conservative of the bunch because its association with the PADI Recreational Dive Planner. But if I'm looking at these graphs correctly, it seems that DSAT has the highest probability of DCS.
And DSAT looks much more liberal than GF 40/85 (which you describe as middle of the road)
Is this because of algorithms behaving differently on 1st dives and then on repetitive dives?

If I'm correct that DSAT resembles the PADI Recreational Dive Planner, and that the RDP is considered well suited for beginner rec divers, what would be a good target conservative setting on my SEAC Screen that runs ZHL-16C?

 

[dmaziuk]

If I'm correct that DSAT resembles the PADI Recreational Dive Planner, and that the RDP is considered well suited for beginner rec divers, what would be a good target conservative setting on my SEAC Screen that runs ZHL-16C?

Nobody in their right mind is going to answer that. The best you can hope is "I personally would set it to 0 but that's just me; what you do is up to you".

But if I'm looking at these graphs correctly, it seems that DSAT has the highest probability of DCS.

Which is better: the model that results in clinical DCS on every 1000th dive, every time, day in, day out, or the model that has 1 in 1100 chance of DCS but may have you do 2200 dives just fine and bend you back-to-back on your 2201st and 2202nd ones? This is covered in first chapters of the original DSAT report, their work was aimed at reliable and consistent. SAUL's predictions, OTOH, are just the numbers game and have never been tested or verified as far as I know.

 

[Belzelbub]

Below you seem to agree that my setting of L4 is a reasonable conservative setting but the highlighted text is making me think I may be starting off more conservative than necessary if a setting L0 is = to GF high of 85/middle of the road and L2 is equal to GF high of 75 and considered "quite conservative". I'll have to start playing around in Dive Planner Mode I guess.

Any of the Seac conservatism settings would seem to be conservative enough for most people. L2 or L3 would seem to be good starting points. I normally dive with my computer in 40/85, and that’s been good for me, so I wouldn’t be opposed to L0, but that is ultimately up to you. My daughters also dive, and use Oceanics. I set their computers to use PZ+ instead of DSAT as it’s a bit more conservative.

Running in Dive Planner mode is not a bad idea. Get an idea of what kind of NDL times you are looking at. Also, keep in mind that, regardless of the conservatism settings, you don’t need to hit the NDL on each dive. And, I’m betting that in most cases, you won’t be able to. Most new (adult) divers will be limited by gas supply more than NDL. Kids, on the other hand don’t tend to use nearly as much gas, so your son’s dives may be limited by your gas consumption.

I’d say pick one setting and try it out. Do some dives and see where you are. If you are gas limited, no reason to go for a more liberal setting. If you are hitting the NDL before using up the gas, then maybe bump it one step more liberal. Make notes of how you feel post dive, and make adjustments as appropriate.

Ultimately, that’s the beauty of GFs, you can adjust to where you are personally comfortable. While your computer doesn’t give the true flexibility of some, it’s more than most. 6 presets is not bad at all, most other computers only offer 2 or 3. And remember, even at the most liberal setting on your computer, you are still not at the theoretical max of the algorithm.