Computer Usage

[Uncle Pug]

Originally posted by monster
For example, on PADI tables, the multi-level limit for 120 ft is 13 minutes. If you spent 20 minutes at 120 and 20 minutes at 20, you would get an average of 40 minutes at 70, which looks safe, based on the tables but actually already put you into decompression.

And brought you back out just fine... with a run time of 45 minutes to get all compartments below 85%

Where as a 40 @ 70 puts several compartments above 100% and requires a total run time of 55 minutes to get all compartments below 85%

The point being that ascending directly from 40@70 is not as safe as running a straight 20@120 then 20@20 and the directly ascending. So it not only looks safe... it is actually safer than the average would indicate!

However if the goal is to avoid even getting close to the NDL at any point during the dive... you're right Monster.

 

[monster]

Thanks, Uncle Pug.

To add to what Uncle Pug said -- the "example" profile I quoted in fact ended up being very safe, in that you would surface with all your compartments loaded below their M0 limits, as the 20 minutes at 20 acted as a deco stop for having exceeded the NDL at 120.

And that's just fine for those of us who understand decompression theory and required decompression. Uncle Pug has it on the mark -- my reply was given in the context of NEVER exceeding NDLs, which is what I teach to my students, while they do recreational diving.

 

[Uncle Pug]

Originally posted by monster
my reply was given in the context of NEVER exceeding NDLs, which is what I teach to my students, while they do recreational diving.

And this is as it should be....
Exceeding the NDL denies one immediate access to the surface without the possible penalty of DCS....

However:
Another thing to consider is that all diving is in reality decompression diving....

In the example given (40@70) a dive that is allowed by the tables as within NDL actually *requires* decompression. That is why current training has divers do a 15' *safety stop*. In reality this is a *decompression stop* but calling it that would get the lawyers excited....

I would advise against direct ascent from any NDL dive...

I add 1 minute stops (safety/deco - call them whatever you want) every ten feet starting at 80% of max depth in ATA....

 

[monster]

Do you add your 1-minute stops even on recreational dives (i.e., "no-deco")? Just wondering.

And yep, every dive IS a deco dive, strictly speaking.

PADI teaches doing "recommended safety stops" of 3 minutes@15 ft/5 m after every [recreational] dive, with 3 scenarios that make the "recommended" stop a "required" stop. Myself, I like to make it at least 5 minutes, and at the end of every [recreational] dive. Helps when there's a lot of shallow reef, but I also like hanging in the blue anyway, so makes no diff to me...

 

[Uncle Pug]

Originally posted by monster
Do you add your 1-minute stops even on recreational dives (i.e., "no-deco")? Just wondering.

Yes....
Most of the time....
Preferably all the time....
If it is a NDL dive we don't do 3 @ 15 .....
Just the nice slow ascent with 1 @ each 10 ....

 

[Lost Yooper]

Super slow ascents are key for NDL dives (most all dives actually). The deep stops simply ensures that you are ascending slowly (less than 30FPM average). If you want to feel dramtically better on your recreational dives, do as UP suggests and make the final 20' ascent a virtual crawl to the surface. Sub DCS symptoms will virtually be eliminated (as long as you are well hydrated and avoid post dive physical stress).

Take care.

Mike

PS. Regardless of what PADI says, the 60FPM continuous ascent rate they talk about is not good. Sure, you'll live through it, but you can do yourself a favor by ascending less than 30FPM with breaks every 10' starting at 80% of the profile (in ATA).

 

[monster]

While I haven't tried the stops every 10 ft starting from 80% max ATA, I do advocate an ascent rate of 30 ft/min, or sometimes even slower, if possible.

Thanks for the input.

 

[Uncle Pug]

Originally posted by monster
While I haven't tried the stops every 10 ft starting from 80% max ATA, I do advocate an ascent rate of 30 ft/min, or sometimes even slower, if possible.

Thanks for the input.

Now if you really want to feel good....
Take 3 minutes to do the last 20 feet....

 

[Ontario Diver]

After reading this thread about three times, I'm starting to get it.

First of all; I did my dives #5 & 6 in the cenotes in the Yucatan. It was one of those "OW Qualified is fine" tours. ....They were wrong. I managed to get out with the only two lessons learned - 1) My bouyancy was in no way good enough.
2) Don't immeadiatly assume that Mr. and Mrs. "I have two hundred dives under my belt and have dived all over the world" are telling the truth. - They had , may I say "issues?"

A cavern is no place for things to go wrong. ( Like inside wrecks, eh LY?)

A couple of points (if I may) about profiles. I am now the proud owner of a Suunto Viper. It will output to my PC a depth per 20 sec profile (or 10, or 30 sec) of my dive. Man...I could cut hardwood with those. (OK not that bad but could use some improvement) It demands a 30 fpm ascent rate as most other computers does and will increase the manditory 3 min stop at 20 ft if it feels that you ascended too quickly at any point in the dive. I like prolonging to 5 if possible because dang it I paid for that air and I'm going to use it!

So guys, what is the best way to learn about deco diving - other than hanging out and listening to you guys. (I feel like we should be in a bar with a paper tablecloth covered in diagrams and notes )

 

[tombiowami]

OD, I had similar views on some OW is fine caverns in Fla. You can see from an earilier post that all of them technically became cave dives at one time or the other. I think it is a big case of money over safety for the people who run them. It will probably change once someone drowns.

I will defer to some who have already taken courses but GUE looks like pretty well thought out stuff and they have some good track records on bringing people back alive.

There are a few rundowns on people takiing these classes on the web and they are pretty tough.


There is a tendency I have seen for OW divers to get the computer and turn into deco divers. Remember deco is the same as an overhead environment and needs property safety, training, etc.

Tommy