Backup Computer went into Deco

[dmaziuk]

I use a perdix for my primary and a more conservative aqualung i300(basically free) as a back up. I blow it up early in the dive trips but it then goes into guage mode which is all I need to get me back to the boat if and when my perdix ever goes belly up on a dive. Arguably I don't even "need" that. I won't be buying another perdix as a back up but if a cheap deal happens on a backup with the same algorithm and GFs available, I'll drop the cash. I am referring to OW diving. What should I be considering that I'm not?

Your next dive: your backup in gauge mode will get you back on the boat, but what are you going to do for the next dive?

I have a perma-buddy whose computer should be very close to mine, esp. early in the trip. So I'd go by her computer to get to the boat and either sit one out or stick to her for the next dive, depending on the circumstances. Then rent one once we're back to shore. Probably up the conservatism settings on that if it's later in the trip. With a perma-buddy and a shore where they have computers for rent and all that, I don't really see how having a locked-out backup is any better really.

 

[RayfromTX]

Your next dive: your backup in gauge mode will get you back on the boat, but what are you going to do for the next dive?

I have a perma-buddy whose computer should be very close to mine, esp. early in the trip. So I'd go by her computer to get to the boat and either sit one out or stick to her for the next dive, depending on the circumstances. Then rent one once we're back to shore. Probably up the conservatism settings on that if it's later in the trip. With a perma-buddy and a shore where they have computers for rent and all that, I don't really see how having a locked-out backup is any better really.

That's a great question. There are so many different scenarios that it would be hard to give a solid answer to your question.

It depends on the situation. The answer I give will be for me and it will be based on several variables. I assume that there will be some readers that will make a worst case condition assumption and my response will sound crazy. I am tempted therefore to not answer. I will anyway because sometimes good discussions come from differing POVs and even misunderstandings. First though, the i300 in vio still gives me depth, timer and rate of ascent. That's a lot more than nothing.

If I know where I'm at in regards to my NDL when my primary computer fails and I ascend upon primary pdc failure then I have to make a choice. If the failure is due to a low battery and the tissue saturation is stored then I'm replacing the battery and taking an easy second dive after the SI. What those numbers and conditions are is important. If it is a battery replacement and the saturation values are not stored and I'm essentially flying blind then I have to make a decision based on what I know about my tissue loading from monitoring the computer before the failure. Depending on the that knowledge and how sure I am of it then I will plan the second dive to either be moderately shallow or very shallow. If I've been near the edge or anywhere close then I will sit out the next dive or I'll go find some shallows and stay above 35 feet and finish with some time at 10 feet before surfacing.

If the perdix was toast and the i300 was in vio but functional, I would reset the i300 and dive the next day with it's more conservative limits.

That's what I would do. I would not advise others to do that. That's what I would do. I have limited experience and an analytical mind that thrives on numbers and systems and patterns. I do math and calculations in my head when I'm not occupied with something else. I would not say that I do that by choice. I acknowledge that most people don't think that way but I'm sure there are some that will read this and think, "yep, that's me".

I welcome input into my line of reasoning but attacking me for it will be like punching a ghost.

 

[dmaziuk]

No argument. If I ever get around to buying regs and upgrading to an AI computer, then I'll have my own backup, but for now: substitute my buddy's computer/rental computer for my own backup and it's pretty much my line of reasoning too.

 

[Centrals]

I used to dive with two Uwatec Aladin for many years until one of them died(large area of the screen turned black). So I bought a Oceanic Veo180 and compared it with my trusted workhorse Aladin on couple of dives. The Veo was a lot more liberal especially after ascending from the deepest part of the dive. So I am using the Aladin as my primary and the Veo as back up. Because I know I won't be able to bend or get the Veo into deco mode as long as I keep the Aladin within the ndl.
Many dives later, the Veo has never been to deco mode.

 

[TrimixToo]

Another thing to think about. I also use two computers (I have seen them fail in the water, though none of mine has ever failed). I have a VR3 and a Petrel. I used to set them to agree closely with each other, and they were always within a minute or so at every stop and within a couple of minutes run time.

A friend pointed out that having their conservatism set differently reduced the complexity of getting out of the water promptly were that to be an urgent necessity to do that. I find that argument compelling, though others might not. So now, I set the VR3 for zero conservatism. I dive the Petrel, and the VR3 is usually happy. Sometimes I need to add a minute to a stop here or there to keep the VR3 happy but not often. I don't particularly mind padding stops here and there.

If the Petrel ever dies in the water, I know the ratio for the mix and depth and how to distribute the time on the way up, so I can appropriately pad the stops the VR3 will suggest. If it's the VR3 that dies, I'll just use the Petrel to ascend.

John

 

[Stoo]

And "THIS" post is why a diver needs to "KNOW" tables in his/her head.. The simple 60/60=120/140 rule would have told him his computer was wrong... Just don't understand why people blindly follow computers ? I need to write a book called " DECO on the FLY" How to do simple deco in your head with navy tables and live....

Agreed... In my experience, when a computer is "wrong" it's normally really wrong. A 45 minute dive, resulting in a 45 minutes deco stop is clearly not correct. If one computer says you're clear and the other has a 5 minute stop, then that's just a reflection of different algorithms.

Computers are handy tools, but they shouldn't be used as a crutch.

 

[NCadiver]

The Cressida is downloadable. Stop in your local store and have them download it for you that way we won't have to guess at it.

 

[Dave Bevan]

Why not run the back up in Gauge mode?

If your other computer craps out (extremely highly unlikely) then just make a safe accent (9m/min) until your normal safety stop depth, carry out an extended safety stop and surface.

For normal recreational OW diving I don't even carry a back up depth gauge. In the first instance go with your buddy. Signal to end the dive hold hands and ascend using his/her computer. Worst case (Blue Water/Lost Buddy) I would shoot my DSMB and SLOWLY ascend using that. Its has a knots tied at 12m, 9m, 6m and 3m.

Don't let computers sucker you into thinking there is no other way to dive. With a bit of training you can safely dive with tables or ratio.

 

[dmaziuk]

Why not run the back up in Gauge mode?

Because in gauge mode it doesn't track your gas loading and you can't "just" switch from gauge to dive.

If you're already carrying a backup, why not run it in the dive mode? If you understand what you're doing, you won't bend it (what happened to OP notwithstanding), and if you don't, you have other problems.

 

[scubadada]

Why not run the back up in Gauge mode?

If your other computer craps out (extremely highly unlikely) then just make a safe accent (9m/min) until your normal safety stop depth, carry out an extended safety stop and surface.

For normal recreational OW diving I don't even carry a back up depth gauge. In the first instance go with your buddy. Signal to end the dive hold hands and ascend using his/her computer. Worst case (Blue Water/Lost Buddy) I would shoot my DSMB and SLOWLY ascend using that. Its has a knots tied at 12m, 9m, 6m and 3m.

Don't let computers sucker you into thinking there is no other way to dive. With a bit of training you can safely dive with tables or ratio.

I almost always do multiple dives per day over multiple days. I nearly always dive solo. I would just as soon have a backup that has tracked my exposure. To each their own.