Feedback on recent two-tank and dive limits

[Blackcrusader]

No. The GF low setting only comes into play if you go into decompression.

@old frogman This is why GF's need to be understood. Even with my dive log on posted on the previous page you can see I did a 10 minute deco part of the dive. The deco obligation was cleared and NDL was returned and I could then continue on this multilevel dive. I did not end the dive after clearing the deco obligation. A dive table would not be able to calculate this. Yes we learned tables but I rarely look at tables anymore as it's very rare I could do a square profile dive.

As for the OP he just needs to spend some time learning what his Peregrine functions are and what settings he is using. I dive my Perdix in OC Tec mode so there is no safety stop countdown. If I want to do an NDL dive I decide wether or not and for how long and at what depth. My last stop is set at 3m depth

After I bought my Perdix in 2018 there have been several firmware upgrades and new features I have had to learn about. This is the nature of owning a dive computer. It is my obligation to know what it is telling me and not just assume it is a baby sitter. It's not. For me deco diving is recreational diving not technical diving. Thing is for NDL diving no one does dive planning anyway. It's enjoy your dive and either there is a time limit or come back with 30 -50 bar and remember not to exceed NDL.

 

[Jake 10]

Hi all,

I’d appreciate feedback on my recent two-tank dive (see images). My Shearwater Peregrine was giving warnings about NDL=1 at end of second dive and put me into a 5 minute safety stop for the first time. Dive guide assured me we were within safe limits, but looking back I’m not so sure.

Dive 1: 45 minutes, max depth of 68.8’, and avg dept of 52’.

Dive 2: 53 minutes, max depth of 69.7, and avg depth 45.

Admittedly I was distracted by bad viz and shifting currents, as well as keeping close tabs on my teenage son/buddy, and not as focused on depth and time as usual. I did not clock until later that our SI was only 34-35 minutes. I know the Shearwaters skew conservative and initially dismissed the buzzing computer for that, but have been kicking myself ever since. Dive guide was with only my buddy and me and appeared (and self-described) as laser focused on safety, but in retrospect this feels dodgy.

Would appreciate input from those in the know so that I can have a clearer assessment of how risky this was. Thank you!

without reading the entire thread,
- a 32 min surface interval is not a good approach when multi-dives
- you fail to mention if you dive Air or EANx
- check your system setup and check if your computer MODE is set to the type of gas you are diving
- verify the PP02 MOD is in range to your dive profile
- check conservatism is set to LOW/MED/HIGH before you dive
- check your OC MOD PP02 and OC Deco PP02

 

[lizzzzz]

Well that is a violation of the depth limits for a DSD for sure.

I was pretty shocked at the end of our dive when they told me they weren’t certified but were thinking about it.

 

[lizzzzz]

i have such a headache after reading all this. Iam close to 300 dives and used the following computer mares m1, suunto zoop, mares quad air, sherwater peregrine TX.

That's should not be rocket science to go dive with them. I don't play much with the factory setting and never encountered a problem whatsoever.


Let's just go diving.

Be safe

OP here. Honestly, I’ve done 50+ dives with this computer, including 100’+ ones, and have never had it buzzing alarms at me like on the dive in my first post and that’s a big part of my I was concerned.

I’ll take the initiative to re-read the settings, since I’ve had it a couple years, but will likely just defer to whatever it tells me next time - even if the divemaster says things are fine, if only for my peace of mind.

 

[lizzzzz]

What i do is that first of all i have a good understanding of the good old dive table and know the do and don't of ndl, surface interval and so on.

By mastering the concept of dive table you have a better understanding of computer, most diver don't have a clue of the dive table and don't use them. I've done my OW in 2005 and it was with dive table. I don't know how they do it now but i tend to believe newer diver stay away of them when training is complete

Diver where diving for years without dive computer and before they didn't had all those technical data on their wrist and everything was fine. You add data you add complexity of understanding what they mean.

So short story long i like to Kept it simple.

Be safe

OP. I appreciate this. I learned dive tables when I got certified as a teen, then barely touched them when I got recertified 20 years later. I love my computer, but this gave me the nudge I needed to refresh my old knowledge of tables.

 

[old frogman]

If a recreational diver is doing a "no decompression limit" (NDL) dive, he has the perception/expectation that at any time during the dive he is able to go straight to the surface (for whatever reason). On a NDL dive, his computer at the start of the ascent phase should not be telling him that he has to do multiple stops to the surface.

A safety stop is appropriate (and optional) for NDL diving. Unexpected multiple stops to the surface, which to the inexperienced basic scuba diver may be interpreted as mandatory is not appropriate and may cause anxiety which is not good.

Buhlmann with GF is appropriate for decompression dives however when used for recreational NDL dives use with caution.

Erik Baker's intent when developing the GF concept in the 1990s was for technical diving, not for NDL recreational diving.

 

[Blackcrusader]

I’ll take the initiative to re-read the settings, since I’ve had it a couple years, but will likely just defer to whatever it tells me next time - even if the divemaster says things are fine, if only for my peace of mind.

One should always dive to their own DC and remember a divemaster is just a guide. You can ascend to increase NDL anytime you like. I bought my Perdix as it does not have any audio or vibration alarms. I ended up turning off the LOW NDL alert. Apart from re reading the settings also spend some time studying gradient factors, GF99 and Surf GF which are added safety factors for your diving.

If you have less than the 1 hour surface interval that's fine but you will get shorter NDL times. The longer the SI the better. I really find I enjoyed as a recreational diver learning and using the features of my Perdix.
There was a reason I bought it and it was for its large digital display and the fact I can put things where I want and use colours I like.

I am responsible for my own dives not my dive buddy or my guide.

 

[Blackcrusader]

Buhlmann with GF is appropriate for decompression dives however when used for recreational NDL dives use with caution.

It is appropriate for NDL dives as well. Use with caution? You can say that about any DC especially when people never learn how their DC operates.

I remember when doing my BSAC sports diving deco courses in 1986 that Nitrox was considered to be for commercial divers and not for recreational divers. 21% was all we planned on. Nitrox was the voodoo gas. Now it's a standard gas and course for recreational divers. Of course later on I got nitrox certified to extend my NDL times for recreation diving.

No need to live in the past assuming that gradient factors are not for recreational diving when they are.
Learning about GF's is easy enough.

 

[JMarc]

On a NDL dive, his computer at the start of the ascent phase should not be telling him that he has to do multiple stops to the surface.

You are writing as if it was the computer job to do so. Whatever the computer and its settings, it's the diver responsibility to have monitored their computer so to not have more mandatory stops than planned beforehand, to have monitored their remaining gas to have enough for the stops, and to have communicated with their buddies so that's the case for everybody.

You write as if the deco obligation was a surprise discovered at the end of the dive. Thats not true.

Yes conservatism settings may change a profile from no deco to with deco obligation, that's why you discuss with your buddy.

Yes some GFlow can't be interpreted in a "lower is more conservative" way. But GFlow is irrelevant to NDL dive.

Yes it is sad that some computer with GF propose as default values of GFlow which are too low for air and nitrox according to our current understanding (this is BTW similar to the deep stop setting ON by default on some other computers). Again that is irrelevant for NDL dives and with little practical effect for sligh violations of them.

Your physiology won't change if you decide to do a NDL dive or a deco dive.

 

[old frogman]

Guys, this is the Basic Scuba section of Forums. Basic level scuba divers are a long way from doing decompression dives. The philosophies for NDL dives and decompression dives are a universe apart. When you commit yourself to a proper decompression dive you cannot make a quick dash to the surface when things go wrong.

My position on computers using Bhulmann with GF (air, nitrox and oxygen capable) is as entry level technical diving computers. Yes, they can be used by recreational level divers, but with caution.