Trusting a computer

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It's an interesting question. How much do we rely on technology for our safety underwater?
Do you carry a completely redundant gas source on every dive? Do you have a redundant flotation device? Do you carry spare mask? If the answer to any of these is no, I'd say you have pretty good faith in your technology. If yes, I'd say you're a cave diver or otherwise Hogarthian trained.
 
If you want a sanity check against your computer, the 130 rule (for 32%) or 120 for air are easy to use. They are incredably conservative shallow, and run table time at depth. (Up to 100 feet). However I don't feel confident trying to describe these in a post here.

And yes, the boat will normally tell you when they want you back on board, if they don't seem to ask them.
 
You are relying on a computer either way. Generally I see more mistakes from human brains than well designed software. And as software and algorithms go dive computers are not all that complicated.
 
So...I get a computer. Pretty cool! Here is my question....I'm having trouble wrapping my head around relying on this computer. I still pull out the table, and I can't believe my dive times.

What are your profiles? I bet if you go on a perfectly square profile dive, like a wreck, your time will be within a couple of minutes of the tables.
 
So now that everyone makes there own dive time on charter trips...how are people figuring dive times. For ex: if its a 40 foot dive and someone on the boat is diving nitrox, they could stay under greater than 2 hours probably. Is there an unwritten rule on how long people stay under as a courtesy?

All the charter boats I've been on the DM just tells you what the maximum time limit is. But it doesn't have anything to do with your NDL, it just has to do with the boats schedule, what time they have to be back at the dock, etc.
 
Most dive boats will allow 60 minutes under the water.

ALL liveboards, that I have been on, are MAKING IT MANDATORY to have a PERSONNAL dive computor while diving.

In these cases, the question about computor or table becomes a bit irrelevant :)
 
Couple things, DM shouldn't plan your dive. You should be doing that yourself. They may give you information, but you should be taking all of that in and doing the work yourself. A DM pointing at one of those comically oversized tables to a bunch of people with a mediocre understanding is as worthless as skipping it entirely. Some DM's give great briefings and you really don't do much. Most give pretty poor briefings and you should be doing much more planning.

It's been mentioned before, your computer is doing real time tracking of your tissue loading whereas a table will only do your deepest, or if you've got a Wheel, a couple levels. It will (assuming it's functioning properly) always have a more accurate representation of your tissue loading and thus your decompression status. The displayed NDL info, while different based on which algorithm it runs, will always be based on the information you feed it, when settings such as mix, altitude, etc, or information gathered from previous dives. A table won't give you all of this, especially once the first dive has you full of gas. Remember you always get deepest/longest with a table and that's all you get, no credit for shallower time, etc. Theoretically, more conservative, but people have still been bent on tables, even recreational ones.

As for algorithms being conservative or liberal, it's all a fallacy. People think a liberal setting "gives" you something, when in all actuality, it does nothing of the sort. Since tissue loadings are entirely theoretical, computers and tables give their best approximation. Your body may be entirely different. If tables drove your decompression status everyone diving the IANTD air table would be getting bent while the guys diving the USN table for the same depth would be fine since it "gives" you more time. Well obviously that's not the case. An extra minute over your NDL does not automatically mean you're going to get bent, leaving 5 minutes early does not mean you're going to get back on the boat free and clear. Bent is bent regardless of how many NDL minutes your computer was happily displaying as you were turned into a pretzel.

You hear about "undeserved hits," well really they're few and far between. Most often it comes out that there is some other factor that plays into it. Undiagnosed PFO's is a big one, people doing stuff like freediving during their SIT proclaiming, "I was just snorkeling!" Point is, whether it's a table or a computer, it's an approximation built on theoretical models that may or may not correlate to your body on any given dive. Again all you can do is have the most accurate information available and use it to mitigate the risk of decompression stress as much as possible. I hear lots of, "well this one gives me more time!" Ok, well be sure to tell that to your computer as you're sitting in a pressurized tube for 6 hours.

As for your computer specifically, the Suunto's are fine computers. They will modify the algorithm used to calculate an NDL based on several factors. Rapid ascents (unfortunately that could be moving your arm too fast too), SIT's shorter than 1 hour, reverse profiles, sawtooth profiles all reduce the amount of displayed NDL and increased STOP time once it goes into deco. If you follow what your computer tells you, theoretically you should be fine.

Bottom line, trust your computer, but realize no matter how conservative you dive, there's always the chance to get bent regardless of what you're using.
 
Rapid ascents (unfortunately that could be moving your arm too fast too), SIT's shorter than 1 hour, reverse profiles, sawtooth profiles all reduce the amount of displayed NDL and increased STOP time once it goes into deco. If you follow what your computer tells you, theoretically you should be fine.

I don't have a suunto, I've cressi leonardo that runs another variant of the dreaded proprietory "RGBM". As a side note, the leonrado doesn't seem to mind reverse or sawtooth profiles so much, as long as you don't trigger its "rapid ascent" logic. If your "ups" are too far too fast it may penalize you on the next dive. The more time you spend above ~7m at the end of the dive, the happier it is.
 
On my first trip to Coz. I rented all the equipment. The dive OP didn't require a computer. The DM's instructed anyone without to go no deeper than they do. The next year was the same rules but this time I took all my own gear including a DC.
Last year a computer was mandatory and rentals were a available.
To clarify, the first year I was on the same nitrox mix as the DM every dive.
I didn't know what I didn't know so I guess these were "trust me" dives.
I fear that ignorance is bliss for far too many holiday divers.
Now I take my safety in my own hands...
 
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