Wisdom of trusting one's dive computer?

[drrich2]

What is the better approach? Trusting the computer or doing pre-dive planning?

A lot depends on what kind of diving you will be doing. The impression I've gotten from training materials and some online posts in the past is that the 'model' for recreational diving is a buddy pair embarking on a rather detailed planned dive of a site with underwater topography known to them. One with a fairly squarish profile, perhaps?

In the 'real world,' it seems like a great deal of diving in the southern U.S./Caribbean region rather follows this model:
1.) You go out on a hired dive boat.
2.) A guide leads the group around. Some dive op.s allow buddy pairs to head off and do their own thing, but most customers don't opt to do that.
3.) The customers aren't that familiar with the underwater topography, which will likely entail a multi-level dive. The guide will set the pace of a roughly 45 to 50 minute no-deco. dive. In some cases divers with plenty of left-over gas can mess around under the boat before they go up.
4.) Deco. is to be avoided like the plague.
5.) Many of the divers are vacation divers, and even the more avid divers mostly aren't GUE-trained or diving at that level. Most aren't knowledgable about handling deco. (I'm not, either).
Yes, I know some op.s don't provide free guide service, and some buddy pairs strike out on their own. I'm saying what I described is the majority practice for the greater region. My belief, anyway.

The very large majority of the time, 'riding the computer' works fine for the kind of diving they do. If it works well with a good margin of safety, then your GUE buddy's approach doesn't have much to improve on...for that kind of diving. He may well do some diving his way is superior for.

Since he just runs in gauge mode, I wonder...how reliable is his brain/focus, potentially in the context of narcosis at depth, in keeping accurate assessment of NDL, etc...? Maybe just fine, I'm not trained or practiced at that level.

And do we really want people who aren't trained and seasoned to a GUE Fundamentals level (or similar) trying to dive your friend's way, if they're not ready for it?

 

[Divectionist]

In situations where I can plan (i.e., not on a boat with guide where I don't know which spot it is going to be etc.), I certainly plan, whether it is a solo dive or buddy dive.

The shallow shore dives and Nitrox make NDL a non-issue for the dives I usually need to plan, however, I usually go about it this way:

- Have an idea of dive objective
- Time the tide to catch the best visibility/current, determine when to arrive, when to hit the water
- Draw dive site map drawn on slate with N point, as much info as I have (above/below waterline). Mark entry/exit and path if knowable.
- Assume pretty deep average depth and slightly higher than usual SAC for conservatism, calculate gas use and determine turn pressure (thirds if diving solo). Also jot down estimated turn time, which is a good checkpoint to compare actual vs. calculated. I can then make a call to hang around a bit more or get moving. I will usually hang around the exit point/safety stop area until I reach my GTR limit (set to surface with my reserve pressure). This means the exploratory section of my dive is shorter than it could be with all the conservatism, but there are sometimes virtual overheads like boat traffic and other contingencies that I don't get too bold about.

In practice, this is a very different approach to just jumping in and snooping around until my computer readings start to worry me. But following the plan means I do not have to worry and can truly enjoy/explore within the limits I set myself.

 

[johndiver999]

I have a Shearwater Teric. I pay attention to the NDL reading and I ascend any time it gets too low. According to the computer I have never incurred a deco obligation and I also have never been bent over the course of 67 dives.

I recently dived with a buddy who is into the GUE approach, and he said that he only dives with his computer in gauge mode and always calculates his dive plan in advance to avoid deco or account for it or whatever.

What is the better approach? Trusting the computer or doing pre-dive planning?

The lame thing about the pre-planning is it doesn't really leave any freedom. With the computer, it feels like I am safe to dive without any plan whatsoever, other than making sure not to incur deco.

If I have my computer set to conservative settings and it is a trusted brand and algorithm, aren't I safe to trust what it says?

Maybe it feels that way but it probably isn't. You really shouldn't be diving without SOME type of plan. In some situations, it might need to be rigorous and detailed and precise and others, it might be extremely casual.. sorta like the difference between diving 120 feet versus 20 ft.

In any regard, you should have enough understanding of the rough time/depth/deco limits for the expected dive - at least enough to become suspicious that the computer has made an error. After that, you can pretty much follow the computer and the chance of it failing and giving misleading or dangerous guidance is probably very, very low.

 

[tursiops]

Planning to follow your computer and stay away from NDL and come up with plenty of gas IS a plan, and planning to ascend immediately should your computer fail, that IS a plan, perfectly OK for recreational no-deco diving. I am technically trained (and experienced) for Adv Trimix and CCR, but I see no reason why the plan for those kinds of dives needs to be forced onto all kinds of dives.

 

[Dubious]

But how can you know what the plan is when you don't know how long it will take you to explore any particular area?

I think that is a valid question, but I was taught via PADI you should have basic information about the site (depth, hazards, points of interest, etc) and have a primary goal in mind. From this info, you plan the dive.

I was taught on a computer but also learned tables. At a minimum, we were taught to use the table or our computer plan mode to determine NDL for the depth of objective. Based on this you have a basic understanding of limits and can plan for secondary objectives and/or plan on multi level dive.

I am not sure if that made sense. The idea is to know what you are going to do before getting in the water. Your quote, "with the computer, it feels like I am safe to dive without any plan whatsoever, other than making sure not to incur deco." is the main concern and I think it is the big reason why some divers express concerns with new divers being too reliant on the computer or worst just trusting the divemaster to keep them within limits (I saw this in Jamaica last week).

I am a new diver, so I am still learning but for me, I won't get in the water without a basic plan.

 

[drrich2]

I think that is a valid question, but I was taught via PADI you should have basic information about the site (depth, hazards, points of interest, etc) and have a primary goal in mind.

True. Often on dive boats there's a pre-dive briefing, with a max. recommended depth (sometimes an order!) and often a discussion with an overall dive site graphic to aid understanding. If you can...

1.) Listen and retain verbal instruction you heard once over the background boat noise from wherever you're standing during the briefing.
2.) Keep that info. in your head in a useful, global understanding way during your dive such you recognize where/when you are in the dive.

Some people reading that will go 'Yeah, so?' That was undoable for me for a long time. I'm a reader, and a re-read to study and acquire knowledge. Listening to a one-time verbal presentation by someone I don't know to a group over boat noise en route to the site didn't work; I'd mentally stop to think over something he said and miss the next piece he said, get distracted, not make something out, etc... Also, I'm one of those people you cannot give verbal directions on how to go anywhere beyond very simple, short, crude depictions. I am desperately grateful for the GPS for road navigation.

Over the years I've gotten a bit better about absorbing and retaining some of what I'm told in dive briefings. I'm a bit more experienced, not wasting mental bandwidth worrying about what all I need to do next and whether I can get ready in time, what if I run low on gas before everybody else, what if I get lost, etc...

My point is, knowing the dive plan is a good thing and can come in handy. But people vary widely in the extent to which they're capable of sucking up the info. to do that in real world settings (especially newbies). The way one person does things may not work well for someone else. For some people, the plan has to be really simple.

 

[JohnN]

There is little good science about NDL algorithms, and even less than the GUE methodology. Personally I don't wish to recall my average depth every 5 minutes and add it times a factor to a running total. Overall a very Ludite view of the world

FWIW, There are very committed GUE divers I've seen using AI computers.

 

[hroark2112]

There’s plenty of ways to skin a cat. None of which the cat will enjoy. They all work.

dive safely, pay attention to your air, NDL, and your buddy. Don’t worry about how anyone else is doing it as long as you’re doing it safely.

and have fun.

 

[ChuckP]

Different dives, different plan

I'll only add that yes for rec diving, you can certainly trust your computer as I haven't heard of any modern computer that you couldn't. You need to understand your computer and it's setting though - don't blindly trust something without an understanding of what decisions it's making for you.

 

[Esprise Me]

GUE basically teaches people to do rec dives as if they're tec dives. This is useful if you eventually want to go tec, because you won't have to learn as many new skills. Some would argue those skills have an important place in rec diving anyway, even if they're not quite as essential.

If you're diving shallow, you'll probably run out of air long before you hit your NDLs. So if you're worried you'll miss out on bottom time by having to adhere to a rigid dive plan based on a square profile, maybe find a buddy who's more your style for when you go to deeper sites, and humor your GUE buddy when you're diving a reef that's only 40 feet deep. (You can of course plan a dive using tables, and follow that plan based on time and depth shown by your computer, without putting your computer in gauge mode.) I like playing things by ear sometimes, having a dive plan along the lines of "let's swim out that way toward the reef, turn when we hit X psi, and come up when we hit Y psi (or Z minutes of NDL remaining)," and there are many environments where that's a perfectly adequate plan. But it's good to be able to make and execute a more detailed plan, because sometimes it's necessary.