Safely practicing dive computer violations

[shawnhar]

My wife and I are planning a dive tomorrow, with the goal of practicing basic skills such as buoyancy and finning technique. I'd also like to experiment with how our dive computers respond to safety violations, but am unsure how to do that in a safe way. (we are using Mares Smart, but I suspect the answer will not be model specific).

At our beginner stage of diving, I am most interested in seeing how our computers respond to excessive ascent speeds. The manual says they will beep and flash, but I have not found any way to simulate this behavior outside of an actual fast ascent. It seems to me that it would be good to learn what the alarm sounds like, while underwater and actually ascending, before I might need to recognize this during an emergency situation.

I guess I could ascend quickly just long enough to set the alarm off, but it doesn't strike me as the greatest idea to do even a little bit of something dangerous as part of a practice intended to increase safety! Also, at my current level of buoyancy skill I think I could start and then successfully arrest such an ascent, but am not absolutely sure of that, and would prefer not to find out by trying and failing

Are there better ways to practice this?

Looking to the future, the same question applies to NDL violations and decompression stops. To be clear, I have zero interest in ever intentionally going into required decompression, but before going deep would like to learn how my computer responds in case something were to go wrong.

I've read about people diving on Nitrox with a computer set to air (so the computer will exceed NDL while they are actually still inside it), or using two computers with one set to a more conservative algorithm (so they can exceed NDL on one while actually still being fine according to the other). Neither of these approaches sounds great to me, because:

1. They require additional training (Nitrox) or equipment (two computers) that I don't expect to have any time soon.
2. Even using these tricks, pushing a computer outside NDL requires a long and deep dive. But I want to practice using my computer on a shallow, easy dive, as preparation for perhaps later diving deep. It seems needlessly risky to have to push almost to the limit in order to practice what happens if you ever accidentally went past that limit.

Am I missing something obvious?

I'd love something like a 2x multiplier setting, so I could tell the computer to treat my 50 foot dive as 100 feet, and a 25'/min ascent rate as if it were 50. But that appears not to exist...

 

[Kimela]

As you dive, you will hear the warning dings of yours, and other folks' computers. I wouldn't attempt to try to set them off to know what they sound like. It's a little frustrating that our computers are generally on our wrists or around waist level, making it hard to hear the warnings. My advice to you is to keep an eye on your computer to watch your depth. You will, no doubt, ascend too quickly and learn what that sounds like, and slow your ascent when you see your computer telling you what to do! For now, just keep an eye on your computer. Just my 2 cents.

I was diving once with a Cobra (Suunto) and my Oceanic HUD and I "bent" the Cobra (I'm not sure if it said I had pushed my NDL limits or what - just that it locked me out for being bad) but my Oceanic was fine. I had gotten NO warnings on my Oceanic. I was told that the algorithm that Suunto uses is more conservative than what Oceanic was using. I hadn't changed anything to push limits - it's just the way they're programmed. I was glad my Cobra was my backup and it didn't effect my ability to continue diving.

Btw, my Cobra died an ugly death a year or so ago and is now an expensive paper weight. Maybe this episode was the beginning of its end anyway.

 

[dmaziuk]

I've read about people diving on Nitrox with a computer set to air (so the computer will exceed NDL while they are actually still inside it)

... as the guy who invented computers said back in 1864

On two occasions I have been asked, — "Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?" In one case a member of the Upper, and in the other a member of the Lower, House put this question. I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.

You shouldn't have a problem triggering the ascent rate alarm: move your arm up as you go up. The deeper the better: it's safer and you'll have easier time stopping. For NDL and deco: read the fine manual. Realistically, if your going into deco catches you entirely by surprise, you have other problems. If you're aware of your NDL going down to 0, and then hear an alarm, you should be able to make a good guess as to what it is about.

 

[divinh]

Would a safe way to have a more controlled ascent be to dump all of the air in your BC at depth and then use only fin power to go toward the surface? That way, your ascent rate will be completely dependent on your finning rate and you can slow down or stop at any moment without having your BC expand and lift you up further than you anticipate. I would guess you could fin fast enough to set off the computer.

As for mandatory decompression stops, your computer will have a symbol that indicates such and give you a timer that counts up as you exceed your limit. On a dive I had, the DM told all of us to get her attention when one of us hit five minutes on that timer. At that point, we gradually proceeded to the safety stop depth and waited out the mandatory decompression stop, then waited again for the usual safety stop. It totaled about 9 minutes for me. Had I failed the mandatory stop, the computer would have locked me out for 24 hours.

Definitely read up on the manual about mandatory decompression stops. I'm a recreational diver and avoid going into mandatory decompression but at some point, some recreational dives (or successive dives with short surface intervals) will put you there.

 

[shawnhar]

You shouldn't have a problem triggering the ascent rate alarm: move your arm up as you go up.

Doh! Simple, and obvious once pointed out

Realistically, if your going into deco catches you entirely by surprise, you have other problems

To be clear, I have absolutely no intention of going anywhere near deco! But I also don't plan on ever running out of air - yet all divers are trained what to do if this happens. I intend to keep practicing air sharing as my diving progresses, because I want to keep that skill sharp even though I hope to never need it.

I'm surprised that dive computer deco seems to be different. Sure I can read the manual, but that's not the same as experiencing it "for real" underwater (where "real" means the computer doing the same thing it would for an actual deco obligation, but without having to go deep or stay down long in order to practice it).

 

[Steve_C]

That way, your ascent rate will be completely dependent on your finning rate and you can slow down or stop at any moment without having your BC expand and lift you up further than you anticipate.

If you have a wetsuit on it will decompress as you go up so you will get some extra lift.

 

[JohnnyC]

Bth are pretty easy to do. Dive to a certain depth, send your computer up on an SMB. It will trigger. You’ll hear it,

For deco, also easy, do tie it to a line and drop it deep, let it sit there for long enough to go into deco, pull it up.

Do this on a dive devoted to these tasks specifically. Keep it shallow, short, and stick with your buddy so you can follow their computer during your short dive.

 

[uncfnp]

Dive Nav has training similation apps for many popular recreational computers.

Virtual Diving - Explore your Ocean

 

[TheCoolBeans]

if you want to see how your computer behaves in deco then tell it you're on air but dive on nitrox. Set it really conservative but do a typical dive.
Want to test the ascent alarm? Send it up on a dSMB.
Want to see what happened beyond MOD? Send it down on a weighted line.

Why you'd want to do these things kinda escapes me though. Is there not a YouTube video of someone already doing these things?

 

[Diver0001]

There are simulators you can download onto your smartphone.