Computer Usage

[tombiowami]

I have a question for you tech guys here. I am admittedly a newbie to diving. I was trained (Naui Adv.) to use the tables and plan the dive for several possible bottom depths, then write these specs down on a slate. We then used the computer or bottom timer just to keep track of depth and time.

I am on the go slow approach, will be doing another 25 dives or so down in the easy caverns of Fla. and mabye Key Largo, then do the NC wrecks off the coast.

My question is that it seems most recreational divers (like myself at this point, no deco, one alum80, etc.) just use the computer for bottom times (no real planning) and ride the ndl limits as far as they can go. I am wondering if it will be hard to find people that are more conservative like me using the tables instead of relying on computers. It seems once in the official world of tech, that computers are obviously out since they don't handle the trimix for the most part.

When you guys are doing more rec oriented dives (or do you even make the distinction, I know underwater gas assimilitation is the same) do you plan them out the same as tech dives or just rely the computer?

I have a Suunto Mosquito that like I said, just use for logging purposes. Am I being too conservative? I have not been trained with Padi, and from what I have seen they have a multilevel dive chart, where Naui does not, so all of my profiles are sqare oriented.

I want to have at least 100 dives or so before investing in doubles if that is the way I end up going. I have 2 alum 80s with Yoke setups so would probably just invest in getting din valves, manifold, bands, wing, for them as I dive wet all the time up here.

Thanks for the help,

Tommy

 

[daylight]

Tommy,

Very thoughtful question.

FWIW, I plan my dives useing tables and use the computer. I take a conservative approach and expect the computer to crap out on any dive. The good thing about a computer is that it deals with multi-level but it is still only an aid.

Some advise I received a while ago has been very beneficial for me is to thoroughly plan every dive. This includes doing all the gas calculations manually for the dive. It has helped immeasureably as I progress to more advanced dives.

DSAO,

Larry

 

[Uncle Pug]

Originally posted by tombiowami

I have a Suunto Mosquito that like I said, just use for logging purposes. Am I being too conservative? I have not been trained with Padi, and from what I have seen they have a multilevel dive chart, where Naui does not, so all of my profiles are sqare oriented.

Tommy

Tommy,
Starting right now.....
On each dive.....
Keep track of your depth every 5 minutes.....
At the end of each dive guess what your average depth was....
Does your Mosquito give you an average depth logbook readout???
How close did you come in your guess as to your average depth???
If your mosquito doesn't give you this try to figure it out some other way.... down load the profile and average on paper....

This average depth is your *Dive Profile* .....
Figure your dive with this profile as your depth and you will be very close to what your computer is doing with multilevel averaging...

"But" you say, "This is only after the fact - what about planning - or even more important - during the dive!"

This is why I say start now....
You will become skilled at *knowing* what your profile is and adjusting your time accordingly.... on the fly....

The other day we did a 105 fsw dive for 56 minutes with the *computer* in gauge mode only....
And never exceeded NDL...

How? Profile was 58 fsw... (I know the new tables only allow 50 at 60 but the old 120 rule has always worked for me.)

 

[Rick Murchison]

Originally posted by tombiowami

I am on the go slow approach, will be doing another 25 dives or so down in the easy caverns of Fla. and mabye Key Largo, then do the NC wrecks off the coast.

Tommy

This statement lept off the page with big red flags all 'round it. Stay *out* of caverns until you've completed a formal cavern course. I'm sure you're "going slow" and being "conservative" but if you're going into caverns without the course you're playing with fire.
Get the proper training.
'Nuf said.
Rick

 

[tombiowami]

Rich, that brings up an interesting question I would like to address. When I said cavern I meant Ginnie springs, Blue Grotto, and Devil's which seem to enjoy a lot of activity in the OW community and are routinely labeled as "safe" for ow divers. But...

When I was there several things jumped out at me in terms of what exactly defines a cave. In other words..

At Blue Grotto, one easily gets more than 130' past the surface, which is technically a cave. (the water itself goes to 100 feet, and one is another hundred or so past the surface)

At Devil's Den, the "swim throughs" actually became restrictions where I was basically pulling myself through, and little visible light, which is technically a cave. In other words, no way could 2 people go 2 by 2, only one at a time. There was no warning of this ahead of time in the briefing, just "interesting swim throughs". They would start big and then get small.

At Ginnie they routinely advocate night diving by all, which caverns at night are defined as cave dives.

I will say that this trip was part of Naui Advanced training dives and the my instrutor/buddy (and good friend) is cave trained and I was learning a lot of the basics for cavern diving but this was not technically a cavern course. I was a bit overwhelmed at some of the stuff I ran into since I had never heard of anyone addressing the very real hazards of these "easy" caverns. I was pretty good at the frog kicks and bouancy to keep off the bottom. But, as a warning, while we were at Blue Grotto with 200' vis, some professional working divers came with their compressor and hose to the diver setup, which stirred up the whole place, if we had been back in the cavern it could have been bad since vis was reduced to 10 very quickly. It has the very fine black silt and very little flow so it hangs out a bit, and it is on the walls also.


So what gives? Like the computer question, am I being too conservative or just aware?

Tommy

 

[Rick Murchison]

Just think "catastrophic first stage failure" - not so far fetched when diving a yoke mounted reg with rock above.
I can't even touch on all the possibilities here - please, please take the cavern course, then all will be clear.
"Common practice" doesn't necessarily mean common sense.
Rick

 

[tombiowami]

Oh, very much in agreement on that one. I have looked into the Y and H valves for singles along that first stage issue but it seems to me it is more pheasible just to go to doubles at that point and commit to in depth learning.

I was just shocked at the massive over stepping of the "what is a cave" rules.

Tommy

 

[Lost Yooper]

Hey Tommy,

For recreational dives, I don't give them a whole lot of thought. I just go. I don't have a problem with using a computer for recreational dives either. Today's computers are generally very conservative anyway. Depending, I might add in some deep stops, and I always ascend slowly (less than 30fpm).

I would say that you are probably being too conservative, but there's no such thing, I guess. A square profile is fine, but if you ignore other things like slow ascents, hydration, and post dive stress, then everything else can go out the window. For recreational dives, I use a computer and add in the rest on my own for recreational dives.

For technical dives, I use square tables planned to the maximum depth attainable (only staying at that depth for a couple minutes). Then, of course, utilize deep stops, gas switches, etc.

Take care.

Mike

 

[Lost Yooper]

Tommy,

I'm not familiar with the cavern diving you talk about, but I have been in and out of shipwrecks virtually sense I first put on a tank. It all boils down to common sense, IMO. Formal training is fine and dandy as long as you're being trained "correctly". I have adopted the experience and informal training (combined with common sense) way of thinking rather than the formal training way of thinking. Some people just have to have the C-card in their wallet -- not me.

If I had lived in an area where there were huge, easily penetrable caverns and swim thoughs, when I had only a handful of dives, I would have gone in. That's just who I am, and that's what I did with my wrecks up here. I have always been very comfortable underwater and well disciplined. You have to measure your own level of commitment, discipline, and conditions when evaluating a dive. If anything tells your gut not to go -- DON'T GO. I have called more than one dive due to a strange gut feeling.

Good luck.

Mike

PS. If there was one single class that I would say is a truly worth while class, it would be GUE Cave I. I want that class more than any other barr none. I am not particulary interested in cave diving, but there's a lot to be learned from a good instructor with that class.

 

[monster]

Tommy,

I'm a recreational diving instructor (PADI), although I do like to dive tec once in a while.

When I started out diving, I learned on the tables, and this is still pretty much the way I teach -- I find that my students are more responsible divers moving forward if they understand the fundamentals of dive theory first. In this case, that means understanding nitrogen loading and decompression limits so that they know what those numbers their computers are spitting out are and mean.

I rarely plan rec dives using tables anymore, but only because I've become familiar over time with safe no-deco profiles (based on the PADI tables); in other words, I still plan, although I may use plans I already know by heart, and also use my computer to plan before getting wet.

However, when I do tec dives, I use my rec computer -- a Suunto Vyper -- in gauge mode. That means I have to do all my plans (primary and backups) on software first, write them down (on slates and duct tape), and then dive those plans. Pretty much what I was doing when I first started rec diving. One of the main reasons for this is just what you said -- very few dive computers can calculate decompression info on the fly, especially with multiple gases. Those that do, well, they're quite pricey, and I'm still paying for all the other regulators that I had to buy to complete my tec set.

That being said, bear in mind that tec diving is inherently more demanding, and the need to be precise is greater here, so the usual rec dive method of diving approximate times (e.g., sometimes extending at bottom if NDLs allow, if we find something interesting to look at), we don't do when tec diving. When plan says it's time to go, it's time to go.

Two final notes: first on your computer, the Suunto Mosquito. Note that it doesn't have a Gauge Mode, but instead a Free Dive mode. If you used your Mosquito on a tec dive as a bottom timer, it would think you were on an inhumanly long free dive and eventually give you an "Er" display. Other than that, though, I don't think it will lock out or anything (haven't tested it on several consecutive tec dives), and it will continue to give you bottom time and depth information.

As for multi-level diving: you can actually plan multi-level dives using the square profile tables (as opposed to PADI's Wheel, the multi-level planner), simply by calculating the next level as another dive with 0:00 SIT. This is a bit more cumbersome than using the Wheel, though, and also, it does not give you information such as allowable next level and multi-level limits as opposed to no-decompression limit per depth level (the Wheel has markers for what your next depth level should be, as well as multi-level decompression limits).

Learning to average your dive profile on the fly might also be helpful, although I do recommend that you still consult a multi-level planner, as an average could be misleading. For example, on PADI tables, the multi-level limit for 120 ft is 13 minutes. If you spent 20 minutes at 120 and 20 minutes at 20, you would get an average of 40 minutes at 70, which looks safe, based on the tables but actually already put you into decompression.

Hope this was helpful.