Feedback on recent two-tank and dive limits

[tursiops]

So far no one has answered this simple scenario question which is designed to test my point of view. All I have seen so far is various persons kicking the can down the road, going off on different tangents extolling the virtue of the Peregrine or the value of GUE basic recreational dive course.

I agree the Peregrine and Buhlmann GF is a great unit. But should it be in the hands of the newly certified recreational diver, as per the scenario question.

From the lack of a decisive answer so far, my only conclusion is that you guys are unsure and have doubts about this computer and others with the Buhlmann GF algorithm. Absence of a clear decisive answer speaks very loudly.

For those that may be confused there are two possible answers:
a. Yes, with additional precautions to make him or her safe with the dive computer.
b. Yes, just give him or her the dive computer and just say read the user manual and figure it out.

My nephew just bought himself and his wife and his two teen-age sons Peregrines. The sons were certified a couple of years ago...they are indeed new divers. The wife is equally inexperienced, but was certified some years ago. Everybody is using their new computers happily and no one is confused.

 

[tursiops]

Many people today buy their dive computers online. No quick five-minute explanation from a salesperson available. Just the user manual.

Perhaps you have never read the Peregrine manual. It is a model of clarity compared to Oceanic or especially Suunto.

 

[tursiops]

Re safety stops: there have been a lot of assertions in this thread about how they are not required for NDL dives.
Actually, they ARE required in the PADI tables for the last four decades if you go deep or get near your NDL, and thus are part of the DSAT algorithm on Oceanic computers, and some dive operators demand them at the end of EVERY dive, no matter the depth or nearness to NDL.

Info Thread 'History of the Safety Stop'

Aug 14, 2020

There have a number of threads recently on ScubaBoard that refer to a Safety Stop, and some assertions as to how it came about and when.

Here is what I can find on this topic; it would be nice to flesh it out so myths and speculation can be minimized! And always remember the research has been about reducing bubbling, not reducing incidence of DCS. That is a different subject.

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Origin of the term Safety Stop in early 1970s.

Andrew A Pilimanis, a researcher for the US Air Force, worked on bubbles in the blood, after diving, under a contract from the Office of Naval...

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[boulderjohn]

The real world. Not all new recreational divers coming out of the basic course are going to have a father, uncle, older brother etc. who is an experienced recreational diver or tech diver and who is going to sit beside him and help him or her with understanding and setting up the computer.

Isn't this true of all computers?

My first computer was a Suunto. The manual was a nightmare to understand.

 

[grantmac]

I literally taught myself (as a new diver who had only used tables) how to use my perdix with a 10 minute youtube video.

Oldfrogman seems to think everyone is as slow to learn as he is.

 

[Fat old english bloke]

GFs are simple, if someone is struggling with them they shouldn't be considering tech diving.

If someone cannot understand GFs (for the hard of thinking; I wrote ‘cannot’, not ‘does not’), should they even be diving?

 

[boulderjohn]

I literally taught myself (as a new diver who had only used tables) how to use my perdix with a 10 minute youtube video.

Oldfrogman seems to think everyone is as slow to learn as he is.

Personal opinion follows

I don't think he really believes anything he is writing in the last few pages. What characterizes his most recent posts is that they are all personal opinion (difficulty of learning materials for new divers), and the only response to those personal opinions is personal opinion (not that hard). He cannot be defeated on those terms.

As I pointed out a few pages ago, the content of his current argument is completely different from what he was arguing incessantly at first (GFs create deep deco stops on NDL dives). On that topic, he was clearly confused and clearly wrong. He never admitted that. I believe he is now shifting the focus and pretending that the current topic (which is just personal opinion) was what he was saying all along.

 

[Rush@2112!!]

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!

Always pay attention to your NDL if you don't want to sit through an obligatory stop. Follow the directions it gives. Check on your Shearwaters gradient setting. I would tend to agree with your dive guide. But you can take control of your own dive. Id have signaled my guide and buddy and headed towards shallower water if my computer read 1NDL. I did 2 dives with my Shearwater yesterday. First dive was 87 few max. 2nd was 60 ft. max. My computer never squawked. Hope this helps.

 

[Subcooled]

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

Your dive guide said it is perfectly safe for him/her. So, maybe it is.

However...

Have you been drinking enough water during the week prior to diving?
Sun bathing? Drinking alcohol? Dehydrated for some other reason?

Are you fat, in bad physical shape, old, or with a PFO?

When did you last excercise? What did you do after the dive? Carried doubles? Went to gym? A hot shower, perhaps?

Did you feel cold during the dive?

Did you maintain a stable depth or did it change a lot? (doesn't seem to be the case here)

Many things affect the risk of DCI.

 

[old frogman]

Your dive guide said it is perfectly safe for him/her. So, maybe it is.

However...

Have you been drinking enough water during the week prior to diving?
Sun bathing? Drinking alcohol? Dehydrated for some other reason?

Are you fat, in bad physical shape, old, or with a PFO?

When did you last excercise? What did you do after the dive? Carried doubles? Went to gym? A hot shower, perhaps?

Did you feel cold during the dive?

Did you maintain a stable depth or did it change a lot? (doesn't seem to be the case here)

Many things affect the risk of DCI.

You make very good point about situational conditions. And on many occasions the dive you execute may turn out to be quite different to the dive you anticipated and planned.

This is how the frogman executes a NDL recreational dive. I use one of my dive computers which has a DSAT algorithm (no conservative settings). I complete the bottom time. Just before or during my ascent I decide which safety stop profile I adopt, based on the dive conditions I just experienced.

I may choose to do 3 min at 15 ft, or perhaps 5 min at 15 ft, or if it has been bit of a tough dive I may break up the safety stop into 2 x stages, that is, 2 min at 15 ft followed by 3 min at 10 ft. (just a few stop options in my bag of tricks). It's all about using the safety stop to keep the DCS risk value to about 3%.

If doing a stop at 10 ft, I may shoot a DSMB, go slightly negative buoyant and just hang relaxed on the SMB. Off gassing at 10 ft is enhanced.

No messing about trying to decide on what GF to select or changing the GF mid ascent because it is not adequate for the actually experienced dive conditions.

Simple, no expensive over the top dive computer required.

Less is more.