SPG and Computer?

[herman]

I guess I should qualify some of my post. The 2 computers that died were old Oceanic ones that had a now know manuf issue, the cases cracked and leaked water into them. The battery was on another puck type and it pretty much went unanounced on a night dive...I think the light was more than it could stand. I have had no problems out of my Suunto.

As for manually calculating NDL, yes and no. Can I get the exact numbers, no but then again I don't really need them. What I need to know is the NDL for my deepest dive and since most of my dives are typically shallow- less than 35 ft- the NDLs are very long. Since I know my total dive times, as long as my total bottom time for all the dives is not longer than the NDL for my max depth, I am well within the table limits, esp when you consider the surface interval for changing tanks and the fact I am usually on nitrox but diving it on air tables. As long as my total bottom time does not exceed the NDL for my deepest dive I am good with plenty of margin for error. If we are discussing deeper dives then I totally agree with you. I usually dive with 2 computers and always when I am pushing the limits.

 

[muddiver]

Unfortunately, Trident had stopped making these.

Fine, than use this

 

[muddiver]

I agree, if you can't check the batteries, you should not be using a DC. Maybe you had some other issue that you have not disclosed why the batteries died. It is like running out of gas, in your car or on your dive... generally a lame excuse.

Seriously, on the third dive of the day and your computer dives midway through the dive, are you telling me you have the time and data handy to manually calculate your NDL's for all 3 dives while submerged? If you can and get the right answer, I am totally impressed. I could run the numbers for sure, not so sure the answer would be right (I know my limits, tables are top side only for me).

A question though. If you are using a DC, which will tend to give you a lot more bottom time on repetitive dives and then you do your table thing since the battery died and find predictably that the tables indicated you have deco time that you have blown past, what do you do?

I have always followed the ideal that if you are going to dive a DC, you dive the DC. If you need redundancy, then dive with a buddy or buy a 2nd one. If you want to dive tables (and there are good reasons for some divers and dive profiles), then dive tables. Both work, I am not advocating either one is bad, but mixing them is difficult and unproductive.

I typically cary a copy of the U.S. Navy table printed up by Trident. It has the air decompression table on the back so you can figure a rough deco schedule if you over run the No-D table on front. Typically for a single tank dive the longest stop is :03 to :05 at 10'. Not much different than a safety stop.

 

[lavachickie]

I wanted to thank both the OP and all those that responded to this thread, because I showed up today with the intent to start a thread just like this one! =-) I learned everything I wanted (and more) from this thread!

I'm gathering the final pieces for our first drive trip. I'm a "start slow and build on your successes" kind of person, and especially when it comes to gear I like to buy it once by buying it right. I'm okay to use basics until I feel I've learned and earned my way to the big prize. =-)

I've amassed my basics (wetsuit, fins, mask/snorkel, light, etc.). I had planned to rent a DC on site. At the LDS last night I was descended upon like a piece of fresh meat in the middle of the Sahara when I mentioned this; everyone wanted me to buy buy buy now now now.

No no no cuz I'm broke broke broke!

As I will be poking around in uncomplicated shallow depths for my first many dives, I can calculate and store the profile in my head or on a slate, and all I NEED is a depth gage and a timer. You'd think, from the discussion I had last night, that these are no longer made. The "least" I could get was a $3-400 DC.

Whatever.

Once again... thanks Scuba Board. I love you guys. =-)

(Tip for new divers: walk into your LDS often. Hang out. Shoot the breeze. Finger the gear. And after they get to know you, but you don't quite have a bead on the cast of characters there yet, wait until you have 4-5 people standing around, and then throw out a question such as, "As a new diver, which big piece of gear should I buy first?" Then stand back and see what happens... while you may learn a lot about gear, more importantly, you learn is who there is reasonable and willing to help educate newbies, and who is just a blow hard looking to push people around and shove everyone else out of the way so s/he can get another chance to spout off his/her self aggrandizing stories. That's really good information to know.)

 

[GrumpyOldGuy]

I guess I should qualify some of my post. The 2 computers that died were old Oceanic ones that had a now know manuf issue, the cases cracked and leaked water into them. The battery was on another puck type and it pretty much went unanounced on a night dive...I think the light was more than it could stand. I have had no problems out of my Suunto.

As for manually calculating NDL, yes and no. Can I get the exact numbers, no but then again I don't really need them. What I need to know is the NDL for my deepest dive and since most of my dives are typically shallow- less than 35 ft- the NDLs are very long. Since I know my total dive times, as long as my total bottom time for all the dives is not longer than the NDL for my max depth, I am well within the table limits, esp when you consider the surface interval for changing tanks and the fact I am usually on nitrox but diving it on air tables. As long as my total bottom time does not exceed the NDL for my deepest dive I am good with plenty of margin for error. If we are discussing deeper dives then I totally agree with you. I usually dive with 2 computers and always when I am pushing the limits.

That makes sense, thanks for the details. I also like long, shallow dives as I see more critters and have a longer dive time. What I was referring to was diving multiple moderate depth (50-90ft) dives on on-square profiles. This is where I find running tables and a computer difficult, after 3 dives the tables are saying I am done, the DC still dives me bottom time. Thanks

 

[GrumpyOldGuy]

I typically cary a copy of the U.S. Navy table printed up by Trident. It has the air decompression table on the back so you can figure a rough deco schedule if you over run the No-D table on front. Typically for a single tank dive the longest stop is :03 to :05 at 10'. Not much different than a safety stop.

I don't think I qualify to use the navy tables:depressed:. If I recall, they are based on young, healthy fit divers. I don't meet that criteria on any level. But, again for a single tank dive using more modern tables, I would have no problem. It is after 3+ dives on a non-square profile that I would really have a hard time going back to the tables.

Thanks

 

[Guy Alcala]

That makes sense, thanks for the details. I also like long, shallow dives as I see more critters and have a longer dive time. What I was referring to was diving multiple moderate depth (50-90ft) dives on on-square profiles. This is where I find running tables and a computer difficult, after 3 dives the tables are saying I am done, the DC still dives me bottom time. Thanks

I find that when I use the average depth (which my computer gives me after each dive) instead of the max. depth for a typical multi-level shore dive, my tables are a lot closer to my computer (a Suunto Favor; I think it uses an older, slightly less conservative algorithm than RGBM, although the first dive NDLs are almost identical); tables are still a bit more conservative. I often carry a table with me on repetitive dives (I have the first dive NDLs memorized), or check and write down the computer's reduced NDLs for a repetitive dive on my wrist slate. This tends to understate my NDL slightly, given the lapse of time between when I write the info down and when I descend.

It's generally not a big deal; I'm usually aware of about how much time I have left, and if my computer craps out in between checks I know if I need to ascend soon or if it can wait a while.

Guy

 

[GrumpyOldGuy]

I understand what you are doing, it is actually a rather constructive idea. My only concern would be if the computer dies on dive 2, should I trust the information if gave me an hour ago from dive 1 or assume it might have lied to me. I would be tempted to call the dive just in case, unless I have my spare or my regular buddy.

 

[muddiver]

I don't think I qualify to use the navy tables:depressed:. If I recall, they are based on young, healthy fit divers. I don't meet that criteria on any level. But, again for a single tank dive using more modern tables, I would have no problem. It is after 3+ dives on a non-square profile that I would really have a hard time going back to the tables.

Thanks

I only use this procedure to ascend safely to the surface because the dive is being aborted due to the failure of the dive computer. There will be no subsequent dives for 24 hours.