Using tables as backup to computer

[GrumpyOldGuy]

I would use my buddies computer for the time and depth. Then figure it out on the tables. The reason being that although my buddies depth may be slightly different (a few feet) using the tables gives me a huge buffer to cover the differences. Because a few feet can make a difference on computers, I would not use his NDR. Nor would I a trust a single computer for calculating NDR. (Its not just the s/w on a computer, but the depth sensors can be off also).

 

[String]

Assume a lot. Assumes buddy has exactly the same tissue loading as you from previous dives, isn't on a more aggressive algorithm or conservatism setting, wont get separated, didnt stay 3m or so shallower for a few mins and so on.
Sharing a computer is an exceedingly bad idea. There is no way you can guarantee its experienced conditions similar enough to you to get out safely.
Oh, also assumes your buddy HAS a computer

 

[RJP]

Treat the entire dive as a tables dive.

Remember, in many cases you can't just treat THAT dive as a tables dive. You may need to factor in repetitive dives.

Say for instance your computer dies on the second dive of the day. Of course on that dive you could probably determine your depth and time profile for that dive, but you can't accurately LOG that dive using tables/wheel without knowing what your ending pressure group from the FIRST dive of the day.

If you don't log EVERY dive with tables/wheel (or at least log depth, bottom time and surface interval so you can go back and calculate PG if needed) you're not really able to "use tables as a backup" all that easily.

 

[String]

Which is why i had the "NOTE" in there for that.

Its not that hard. Provided you have sane surface intervals and so on repeat tables will work even for computer dives although it does depend on your choice of tables.

BSAC tables id just assume a tissue code of G on leaving and factor in the SI. PADI you could do similar although with a lot more PGs its a bit more fiddly. Still only 2 minutes work.

 

[Dirkadiver]

Twiddles, maybe you need to go back through your OW course. You don't rely on your buddies computer in the event yours fails.

SNorman, there are several ways to calculate your pressure group. It really depends on how conservative you are or want to be. I agree with Blackwood on using the tables definition of bottom time, however I wouldn't try to calculate a multilevel dive based on memory. I'd use the deepest point of the dive to calculate Pressure group & RNT

 

[GrumpyOldGuy]

String,

I am not sure who you are addressing. I suggested using the dive buddies computer for time and max depth, then use the tables for all the dives. This only makes the assumption the buddy started and finished the dive with you and you hit the same max depth. These are not unreasonable for a buddy team . This is not the same as sharing a computed NDR which is bad since very small difference in profiles can change NDR.

 

[Thalassamania]

If you need to safely switch to tables you need a lot of information, to wit: the adjusted no-D limits for every depth your computer reports. You then need to take each and every one of those time depth pairs backwards into the table of your choice and determine the nitrogen designator that would have resulted from a dive to that depth for that length or time. You should then take as your working designator the "worst" case.

A detailed example of how to do this is provided by Mike Emmerman on PDF Page #197 (document page #189) of the Proceedings of Dive Computer Workshop.

 

[String]

This only makes the assumption the buddy started and finished the dive with you and you hit the same max depth. These are not unreasonable for a buddy team .

You'd be very surprised how much max depth varies even in a buddy pair. Also assume the buddy doesn't go AWOL.
Its a very poor excuse for not taking proper redundancy.

 

[GrumpyOldGuy]

You'd be very surprised how much max depth varies even in a buddy pair. Also assume the buddy doesn't go AWOL.
Its a very poor excuse for not taking proper redundancy.

I guess we have a difference of opinion then.

If my buddy go AWOL, the dive is done. Who care about a redundant timer, I have no backup gas.

If my buddy is not within 10-15ft, he is not my buddy, I am solo. This has a whole different set of rules.

FYI: I have very good dive buddy's, my 2 sons. We do compare our max depths and times after EVERY dive. All 3 of us are within 3-4 feet max depth and within 1 minute over the last 15 dives this year. Our NDR varies by up to 3 minutes. I am pretty comfortable with my opinion backed by this data.

 

[Blackwood]

I agree with Blackwood on using the tables definition of bottom time, however I wouldn't try to calculate a multilevel dive based on memory.

Yah, I don't recommend doing so as the result of equipment failure. Either plan to figure your own deco or don't do it at all. Mix-and-match is a recipe for disaster.