Dive Computer Failure -- Ending the Dive

[ratchet04]

Until recently I have always been a BT and Tables diver and always planned my own dive even when diving with a group charter. In fact I have turned down computers on rental equipment dives and thumbed more than one dive when my time was up based on the profile planned and actual dive executed regardless of what the DM or guides computer said the 'groups' NDL was because that was how I planned the dive (side note: I recommend trying this, the look from a new diver after giving the 'instructor finger waggle' to a DM is worth the cost in bottom time alone).

I'm not out to set a bottom time records and enjoy conservatively planned dives even at the loss of bottom time or depth. I'm not looking to enter a discussion about the merits of comp vs. BT; I just dive tame profiles and BT/Table is how I was trained (read: what I am comfortable with).

I finally purchased my first DC (Suunto Zoop). My choice to dive a computer is more one of redundancy than expediency. I will still dive my full SPG console with depth gauge and carry a bottom timer. I will still monitor both in the fashion I always have during a dive along with the added computer check. In reading the Zoop manual the procedure for correcting a computer failure is as follows: Ascend to 60ft, slow ascent to 30ft per minute, hold at 10-20ft for as long as air will allow, surface and discontinue diving for 24hrs minimum.

My question is why? The Zoop's failure outline makes sense if you have no redundancy, no idea what your bottom time is, no idea what you depth is and no plan other than 'trust the comp'. But, if I maintain contingency plan based on where the RDP places my PG, know the elapsed BT and maximum depth, why could I not just transfer the dive back to a BT/Table dive and proceed as planned. Once topside any subsequent dives that day (and probably trip) would be planned off of the RDP. I have to believe the RDP is more conservative than even the most conservative DC algorithm particularly when diving a square max depth profile and not using a eRDPML. Ignore any scenarios where the RDP puts me past an NDL, these are leisure dives that should remain well inside of any deco obligation.

I'll provide two examples:

1. Dive 1 of a day. Planned profile is 60ft for 35 minutes. Computer fails 10 minutes in. I don't know exactly when the comp failed but I know I am 10 minutes into a 35 minute dive via my BT. Why do I need to ascend? Why can't I continue the dive based on the planned profile and exit the water in PG 'N' per the RDP; conduct a surface interval and proceed to dive 2?
2. Dive 2 of a day (different day not related to example 1). Post SI, RDP says I would be an 'E' if you calculate a square profile using the table. Planned profile is 50ft for 45minutes. Comp fails 40 minutes in, thumb the dive and proceed to boat. Why could I not use the RDP to figure out I am a PG 'T' then proceed as planned later that day to dive using data from log and RDP for both of the previous two dives?

Curious how the SB community views this. I don't need to know that I am doing redundant math if I plan dives in this fashion, I know that and I'm happy to self identify as a math nerd. Besides, the point of redundancy is to be able to safely mitigate any critical equipment failure. Thanks!

 

[flots am]

I finally purchased my first DC (Suunto Zoop).

. . .
In reading the Zoop manual the procedure for correcting a computer failure is as follows: Ascend to 60ft, slow ascent to 30ft per minute, hold at 10-20ft for as long as air will allow, surface and discontinue diving for 24hrs minimum.

My question is why?

They assume you're only using their computer.

A failed computer means they assume that you have no idea where you have been or for how long.

The ascent procedure listed is the safest possible procedure given the available gas. If you have another way of calculating nitrogen loading and planning and ending your dive, you're free to use it. There are no guarantees of a completely safe dive with either tables or computers.

Also, if you're diving the computer on a multi level dive, it's entirely likely that you have exceeded the NDL listed in the square table profile, so switching back to tables isn't a lot of help.

flots.

 

[ratchet04]

They assume you're only using their computer.

A failed computer means they assume that you have no idea where you have been or for how long.

The ascent procedure listed is the safest possible procedure given the available gas. If you have another way of calculating nitrogen loading and planning and ending your dive, you're free to use it. There are no guarantees of a completely safe dive with either tables or computers.

Also, if you're diving the computer on a multi level dive, it's entirely likely that you have exceeded the NDL listed in the square table profile, so switching back to tables isn't a lot of help.

flots.

Just what I was looking for.

Thanks!

 

[beanojones]

My question is why? The Zoop's failure outline makes sense if you have no redundancy, no idea what your bottom time is, no idea what you depth is and no plan other than 'trust the comp'. But, if I maintain contingency plan based on where the RDP places my PG, know the elapsed BT and maximum depth, why could I not just transfer the dive back to a BT/Table dive and proceed as planned.

(Exclude tech dives from this discussion, because a majority of tech divers exquisitely plan and execute their dives, including full table usage.)

Let me say this first If you are a non-tech diver actually planning and executing your dives on a table then I have longed to meet you for a long time.

Outside of class, I have never seen anyone plan and then dive using tables. As a full time instrcutor/guide, I have seen just about every other use of a table. As a nitrogen narcosis test for AOW (old school AOW), etc.

The usual way divers 'use' tables is to take the in and out times and make up **** when writing their log books. They shave off the extra feet and time necessary to make some PG up, etc. Basically as a magic wand they wave at their dive times to make them fit spaces in their log books.

Here's a typical question I have heard from an American diver (IE not my diver) when filling out his log at the end of the day: "I did my first dive to 140' and we dove for 60 minutes. How do I figure out my pressure group?" He had a computer. When I told him he was not using tables to plan the dive, so he cannot use the tables to fill out his log book, he said "But I like backing up my computer with the tables." OMG WTF LOL!!!

This is not at all atypical. In fact as mentioned, I have never seen anyone pull out the tables before the first dive, and plan and write anything down indicating any dive planning. I have also seen lost of divers pull out a table after a 50 minute dive with a max of 70 feet, and then started looking on their computer for their average depth to do the tables. When they ask the same question about how to figure out their pressure group, and I tell them they were not using tables to plan the dive, so they cannot use the tables to fill out their log book, they also said "But I like backing up my computer with the tables." OMG WTF LOL!!! pt 2

Most dive boats have a table on the boat that they figure it it important to have, and I have seen captains run through that same post dive table fudging when waiting for help for a bent diver.

Working guides have learned to basically ignore anyone claiming to use a table, and even to an extent, trust people claiming to use a computer (the number of people who show a digital watch when asked what kind of computer they are using is also pretty large.)

Here's the question I have for you, possibly the last table using diver. Have you never accidentally hit 61 feet and actually still used the 60 foot table? Because all it takes is for you to drop one foot below 60 feet for a second and your conservative dive becomes one requiring a safety stop, and one where you are diving basically to a limit. Or you use a computer, and be freed from that.

This is not meant just to challenge what you do, rather to help you understand where the DM's are coming from. The joy of finger-waggling aside, the look on the other divers faces might be more disappointment that you are cutting their dive short than anything else. They spent the money on computers before they spent the money on dives, and you doing it the other way around costs them.

 

[DogDiver]

Personally I use my Citizen Aquamaster Pro as my primary gauge until I turn my cave dive. Then I start referring to my Aladin Tec2G for planned profile dependent intermediate stop and end of dive deco obligation. I carry a 2 gas Dive Rite computer as a backup using a similar algorithm. Third, I carry a USN set of tables in my pocket. No batteries in tables to fail. Again, this is a cave dive with known depth and planned bottom time. Even diving Roatan, I keep a set of tables in my BCD pocket.


Sent from my iPhone using Tapatalk

 

[ratchet04]

(Exclude tech dives from this discussion, because a majority of tech divers exquisitely plan and execute their dives, including full table usage.)

Let me say this first If you are a non-tech diver actually planning and executing your dives on a table then I have longed to meet you for a long time.

Outside of class, I have never seen anyone plan and then dive using tables. As a full time instrcutor/guide, I have seen just about every other use of a table. As a nitrogen narcosis test for AOW (old school AOW), etc.

The usual way divers 'use' tables is to take the in and out times and make up **** when writing their log books. They shave off the extra feet and time necessary to make some PG up, etc. Basically as a magic wand they wave at their dive times to make them fit spaces in their log books.

Here's a typical question I have heard from an American diver (IE not my diver) when filling out his log at the end of the day: "I did my first dive to 140' and we dove for 60 minutes. How do I figure out my pressure group?" He had a computer. When I told him he was not using tables to plan the dive, so he cannot use the tables to fill out his log book, he said "But I like backing up my computer with the tables." OMG WTF LOL!!!

This is not at all atypical. In fact as mentioned, I have never seen anyone pull out the tables before the first dive, and plan and write anything down indicating any dive planning. I have also seen lost of divers pull out a table after a 50 minute dive with a max of 70 feet, and then started looking on their computer for their average depth to do the tables. When they ask the same question about how to figure out their pressure group, and I tell them they were not using tables to plan the dive, so they cannot use the tables to fill out their log book, they also said "But I like backing up my computer with the tables." OMG WTF LOL!!! pt 2

Most dive boats have a table on the boat that they figure it it important to have, and I have seen captains run through that same post dive table fudging when waiting for help for a bent diver.

Working guides have learned to basically ignore anyone claiming to use a table, and even to an extent, trust people claiming to use a computer (the number of people who show a digital watch when asked what kind of computer they are using is also pretty large.)

Here's the question I have for you, possibly the last table using diver. Have you never accidentally hit 61 feet and actually still used the 60 foot table? Because all it takes is for you to drop one foot below 60 feet for a second and your conservative dive becomes one requiring a safety stop, and one where you are diving basically to a limit. Or you use a computer, and be freed from that.

This is not meant just to challenge what you do, rather to help you understand where the DM's are coming from. The joy of finger-waggling aside, the look on the other divers faces might be more disappointment that you are cutting their dive short than anything else. They spent the money on computers before they spent the money on dives, and you doing it the other way around costs them.

Tis true that is how I have dove my whole life, not that I have 1000 dives or anything but the 75 in my log book have always been planned and executed on a table. Interesting that you have never seen it. I am not a tech diver and do not pretend to preach that tables are the way to go, it is just the way I have dove. I am excited to dive on a computer and my post was more of a question as to the proper procedure. I know a computer will help me safely extend dives if desired but I will still dive conservatively.

As far as diving a 60 foot profile and hitting 61, it could happen but thats a 70 foot profile. If you are planning 60 at 35 you are still in safety stop territory and still below the NDL of 70ft so it only affects the outgoing pressure group. I carry a table in my BC for that purpose. Though, if planning a true by the book square profile near the NDL of the next depth I am not sure why I would be hovering at 60 when I have a 10 foot range to hold in safely. Call it OCD but I have always used tables to avoid just the type situation with confusion (or worse DCS) caused by not knowing the where the math says I'm at beyond what my computer told me.

I take pride in my personal responsibility while diving whether privately or on a boat. I have discussed my plan with the operator everytime and dive accordingly. I can't remember ever having caused a computer diver to surface prematurely because I chose to do so. Its no different than an LOA situation for a new diver. They surface according to the operators policy and briefing and the group goes on. My buddy and I ascend, perform safety stop and surface. Due to air consumption constraints of a group this is always near the end of the operators dive and near the boat anyway. If I hit the deck 5 minutes earlier than the group with 1200psi knowing what my PG is I'm happy with that. The finger waggle line was more of a joke than anything; hope it wasn't received poorly. I have nothing but respect DMs, Instructors and Guides, all of whom are more seasoned than I but their computer knows nothing about my nitrogen saturation.

 

[scubastingray]

Until recently I have always been a BT and Tables diver and always planned my own dive even when diving with a group charter. In fact I have turned down computers on rental equipment dives and thumbed more than one dive when my time was up based on the profile planned and actual dive executed regardless of what the DM or guides computer said the 'groups' NDL was because that was how I planned the dive (side note: I recommend trying this, the look from a new diver after giving the 'instructor finger waggle' to a DM is worth the cost in bottom time alone).

Are you saying you use a square profile on a group dive and hold everyone to non multi-level standards? Correct me if I'm wrong, but that's what I got from this.
Your bottom timer and dive profiles aren't nearly as precise.

 

[dfx]

If you're using your dive computer to keep track of your N2 exposure and you dive anything other than a square profile, chances are that when you check your dive profile against the tables, it's gonna put you way past the NDL. With that in mind, the recommendation to take a 24h break from diving isn't such a bad one.

 

[scubastingray]

If you're using your dive computer to keep track of your N2 exposure and you dive anything other than a square profile, chances are that when you check your dive profile against the tables, it's gonna put you way past the NDL. With that in mind, the recommendation to take a 24h break from diving isn't such a bad one.

Something is going over my head. Of course tables will be ultra conservative, especially if your max depth is a quick dip for perhaps 1/10 of the total dive time. I wouldn't take a 24hr break just because of the limitations of square profiles and tables.
Of course you could take a time and try to model the dive by calculating each part separately, but it sounds like OP is just taking a square profile.

 

[beaverdivers]

Yes, your solution would work in the two examples. If you are just doing a few shallow relatively short dives, then your method works.

However if you are doing multiple dives, deeper longer dives such as live-aboards offer, then your best redundancy is another dive computer. Just make sure you carry it on all your dives!