Pressure Groups

[ibnygator]

AaronBBrown once bubbled...
Even though I dive with a computer, I still do the tables at the end of the day just to keep my chops up with them.

I do the table calcs after each dive not only to stay in practice, but to have the information as backup in case of a computer failure. I often go on multi-dive / multiple day trips and I'll be damned if I'll miss any dives due to a computer problem.

I do like the idea of calculating backward off of the average depth though to get yourself a starting point on the tables. Once I start diving per the tables though, I'd use them as I was taught. I did that for years before I got a computer and only "slightely" exceeded the tables a couple of times...

 

[Walter]

If your computer dies in the middle of a trip and you have no back up computer, you go back through your log and figure the tables. Use the tables as designed. WAGs can get you into trouble. If you have not exceeded the limits of your tables, you can find your repetitive group and continue diving. If you have exceeded the limits of the tables, take a 24 hour break from diving and then start diving again.

"Tables are meant to handle square profiles. By definition, a multi-level dive will generate less N2 retention than what the table provides at the max depth."

If you were diving a multilevel profile (very likely) this is true. The question is a matter of degree. How much less N2? There is no way to know. You can use tables as designed or you can make a WAG and greatly increase your chances of getting bent.

If you are keeping very close tabs on your depths and times during (I mean you record you were at 100 ft for 5 minutes, then moved to 80 feet for 10 minutes, then 60 feet for 5 minutes then up to 30 feet for 20 minutes - not a guess) the dive, it is possible to use tables for multilevel diving. I know of no one (except Pug) who currently recommends this practice. I used it when diving BC. I even used to teach it, but it has been forbidden for many years now. If you can locate it, Dennis Graver wrote an article explaining the process about 20 years ago.

I try to carry a back up computer on all dives.

 

[Uncle Pug]

awap once bubbled...
Bottom is pretty flat so profiles are fairly square.

A flat bottom doesn't mandate a square profile.

Square profiles are not a good idea IMO.

I agree that tables are meant to be used with square profiles... that is why I don't use tables.

I don't think I would want to do 4~5 90' dives over a period of 15hrs. either.

I would rather do 2~3 dives... any 4th dive would be <2ATA if included at all.

 

[redacted]

Uncle Pug once bubbled...

Snipped

I don't think I would want to do 4~5 90' dives over a period of 15hrs. either.

I would rather do 2~3 dives... any 4th dive would be <2ATA if included at all.

Your right, they are not really square. While one bank may give you 65 to 75 ft dives as you navigate through coral ridges and valleys, the other bank is more in the 80 to 90 ft range. And the 3rd feature (Stetson bank) is mostly 85 to 100 ft. But there are no walls or similar features that allow you to continue the dive as you ascend and off-gas. Just an anchor rope that gets a bit crowded but may get you a visit from some of the open water species. Only exception is the rig dives (if done) where there is interesting stuff everywhere.

And 5 dives on the first day is the norm with 4 per day on subsequent days. With nitrox it's not too bad doing them all but it was a real butt whipping on air. While the safety record is far from spotless, the problems seem to be divers who were not up to the challenges rather than simply pushing N2 loading too far. All diving is done within no-deco limits but many divers will still spend 10 minutes or more getting back to the boat on the anchor line.

Gulf Divers who run the 2 larger boats have depth limits of 130 ft for 1st dive and 100 ft for subsequent dives each day.

 

[radagalf]

you can afford to cancel that dive and buy a new bottom timer, whether it be a Vytec (most expensive option) or a $20 uw watch (least expensive option).