Dive Computer for Recreational Use

[b1gcountry]

As I said in a recent post, I just Read Jarrod Jablonski's DIR Fundamentals book, and I had some questions about some of the decisions he came to. My biggest on was probably the section on Computer Diving. He quotes:

"All Divers should learn the proper use of decompression tables in order to learn the actual process of decompression diving. Divers who choose to use computers should do so after becoming well-versed in diving limits..."

He then presents a list of problems with Decompression Computer diving. This is pretty much along the lines of my own thinking, but most people I have heard on this board make it appear than the use of a computer for Recreational use is prohibited for DIR diving.

So are computers okay recreationally? If not, what are the reasons for recommending against them?

I also had a broader question of whether GUE actually had any recreational classes? I know Fundies is usually taught more as an introduction to tech than a real rec class. The book seemed to pay decent lip service to how uncertified divers should be trained, is there a plan for a GUE OW class?

Thanks,
Tom

 

[rjack321]

There is now an OW class, contact GUE headquarters to set one up. Its long and undoubtably expensive.

Computers are ok recreationally, but most DIR divers transition out of them after awhile. You're just hearing internet zealots here. Computers are fine up to a point (which is less than recreational limits IMO), beyond that they hinder awareness and team communication.

 

[lamont]

So are computers okay recreationally? If not, what are the reasons for recommending against them?

for recreational diving its not a huge deal. it adds the NDL countdown number to the display which isn't a huge UI problem. as long as you're not diving with your brain switched completely off its not that bad.

at some point down the road you'll probably get tired of the computer resetting to air when you're always diving 32% and you'll start ignoring it... which is when it is time to switch to gauge mode...

 

[jeckyll]

We had the computer discussion in fundies. But it was really a part of the repetitive dives discussion (which my instructor really wasn't fond of).

He mentioned that he'd rather do a single good & long dive, vs 4 or 5 dives a day. His exact words were: "Repetitive dives scare me".

However, as part of this he mentioned that if he was on a liveaboard / warm water 'look at the pretty fishes' dive vacation, he could see using a computer due to the number of repetitive dives involved.

YMMV.

Bjorn

 

[limeyx]

We had the computer discussion in fundies. But it was really a part of the repetitive dives discussion (which my instructor really wasn't fond of).

He mentioned that he'd rather do a single good & long dive, vs 4 or 5 dives a day. His exact words were: "Repetitive dives scare me".

However, as part of this he mentioned that if he was on a liveaboard / warm water 'look at the pretty fishes' dive vacation, he could see using a computer due to the number of repetitive dives involved.

YMMV.

Bjorn

which instructor?

As your dives get more aggressive (esp with deco dives) it's probably better to favor a larger number of shorter dives for a number of reasons:

1) In general, decompression is not linear with bottom time, so doing one 60 min dive at 100 feet will require a lot more deco than two 30 min dives.
2) You need more gas for longer dives -- gas that you have to carry around on the dive, and more gas needed for ascent
3) If you dive in open water (esp. ocean) conditions can change rapidly. It's relatively easy to can a 3rd or 4th dive, but less easy to signal divers on a long dive to come up
4) some areas such as here in southern california, most boats offer 3-4 dives per day. The boat is (generally) moved between dives, so the option of 1 long dive is just not there.

 

[PerroneFord]

I use my Vyper recreationally as a dive computer. But if I am going to do a longer dive, or a "technical dive" like a cave dive, I'll cut tables. But then I only do one or two of those in a day. I am not deco'ing with oxygen at this point, so I tend to err on the side of caution and limit my longer dives.

If I was jumping in 60ft of warm water for 45-60 minutes, I wouldn't worry too much about diving it with the NDL info turned on.

 

[TSandM]

I think a lot of people who are starting with DIR use computers -- I did. For my usual diving now, within my normal depth and time limits, and no more than 2 dives a day (and not that on sequential days) I'm happy with my ability to depth average and track my loading and follow the MDLs. But when we went to Cozumel, where we were doing more aggressive dives on a regular basis, and multiple dives per day for multiple days, I put my computer into computer mode as a reality check.

Then I forgot to reset it to Nitrox and bent it and ignored it from that point onward, so I guess I did okay without it.

Anyway, the bottom line is that nobody is going to jump up and down and scream at you for using a computer for recreational dives. When you get to decompression, it becomes a bigger issue, because if one person is diving tables and another is trying to keep his computer happy, it splits the team up and makes everybody mad.

 

[DIR-Atlanta]

most people I have heard on this board make it appear than the use of a computer for Recreational use is prohibited for DIR diving.

It's not so much the "use" that is prohibited, as it is the "blind trust in a piece of technology". I often use the following simple analogy to illustrate the difference:

Suppose you are on a cross-country drive in your car, which consistently gets 500 miles from a tank of gas. You see a gas station with a sign out front that says "Next gas station - 100 miles". You notice that you have driven 450 miles since your last fill-up, but your gas gauge still shows a quarter of a tank. Do you blindly trust your gauge, which is telling you that you can make it to the next station with 25 miles to spare, or do you go more by what you know about your own car's gas mileage from driving it?

The "DIR approach" is not to trust the gauge completely, when you have better information available that has been built up through personal experience. The idea is that you should have developed a "feel" for what sorts of profiles you get with tables, before you start using a computer - kind of like learning to add by hand before starting to use a calculator.

A dive computer is just one source of information about decompression profiles, and if you have built up experience with tables beforehand, you will be better equipped to make intelligent decisions about what the computer is telling you (and whether you "believe it" or not).

So using a computer for most rec profiles is generally considered OK, and may in fact be necessary if you are planning to do multiple repetitive dives over the course of several days (and want to get some decent bottom time out of them). Multi-level profiles in particular are pretty hard to manage in any other way.

As several folks have mentioned, once you get into the longer decompression dives, you will want to start relying more on tables for your planning. This gives you the ability to determine a priori how much gas you need, what stops to do, etc. It also allows you to develop and discuss a cohesive dive plan with your team, rather than trying to "wing it" based on what the computer says (or worse, what several of them say).

 

[mstevens]

Here's a real-life example of how technology can get you in trouble if you're not careful. I was driving my wife's car, which has a great computer system. The fuel gauge was reading low, but the computer said I could easily make it back to home without running out. There aren't any stations in our town, but there are a couple in the town I'd have to go through to get home. I preferred to buy across the state line since prices tend to be lower. The gauge had dropped farther when I passed the last station before the state line, but the computer said I had 24 miles to empty and 10 miles to home and I wasn't certain how to interpret the gauge since I'm not that familiar with her car. That meant I'd still have 20 miles of fuel when I got to the station I wanted. A mile after the station, the computer still said 24 miles to empty, but the tank was dry. Talk about poor gas planning! I'd just crashed my motorbike and was on crutches so my wife had to come in my car to bail me out. Nobody got bent, otherwise hurt, or killed as a result. I don't dive DIR, but I've only had a computer for about a year and a half. It's a useful tool. It almost always tells me I have longer to go than my tables do, sometimes much longer. Maybe I do. Maybe it's wrong. The stakes are higher than with my car example. I prefer having the sanity check of always knowing what my tables say than simply relying upon the computer. At a minimum, when my tables say I should be wrapping up my dive I start watching the computer like a hawk. I'm usually ascending at the time. I mostly use it as a recording depth gauge, I suppose.

 

[b1gcountry]

Great! so I can keep my computer and my bright red split fins!


Just kidding, although I do have splits, and they are absolutely GREAT for frog kicking (for me). I can go backwards okay, but I do kick up whatever silt in the process...

Okay, back on topic!

Alright, I feel a lot better about the whole DIR computer thing now. I can't imagine doing a week diving on a dive charter/liveaboard without a computer. The first time I saw the list of "why computers are bad" it was quoted in relation to recreational computers. I can understand it a lot better now that I know it is mostly about deco computers.

One of the first places I ever heard about DIR was here:
http://www.njscuba.net/gear/eqpt_02_computers.html

It's kind of ironic that that kinda sparked my interest and made me look into it more...

Tom