Going into deco

[do it easy]

They look like AL80s to me?

 

[DandyDon]

Well, usually I'm in violent agreement with Grateful Diver. However, in this case I'd like to point out that a "reverse profile" generally refers to a single dive in which the latter part is deeper than the first. That is linked to higher probabilities of DCI.

In the case of a second dive being deeper than the first, recent evidence is that it has no impact on DCI incidents.

Reverse Profiles often refer to doing second dive deeper than first, and will always yield less NDL on any computer I think.

 

[SparticleBrane]

They look like AL80s to me?

Correct. Al80s tend to be long, and my tub isn't the largest in the world, so it tends to play tricks with your mind.
Now back to your regularly scheduled thread.

 

[nereas]

Correct. Al80s tend to be long, and my tub isn't the largest in the world, so it tends to play tricks with your mind.
Now back to your regularly scheduled thread.

So what is the coolest wreck in the NC area? And what is the best dive boat to get out there with? I need to check out NC somtime before I die and leave this world.

 

[Sharky1948]

Reverse Profiles often refer to doing second dive deeper than first, and will always yield less NDL on any computer I think.

I guess you're right on the definition of reverse profiles. The term is used multiple ways. Thanks!

Damn I hate being wrong!

 

[JeffG]

Nice twin tanks in your avatar, Sparticle. Are those twin 130s or twin 140s? They look really huge.

Good experienced eye for equipment there.

 

[DeepBound]

No, but I've done dives where one of my computers (the Genesis ReactPro) said I had about 20 minutes left, and my Nitek3 with its conservative modified Buhlmann algorithm said I had a short amount of deco. It was asking for 5 minutes at 10ft, what I did instead was 1 minute at 40, 2 minute at 30, wait at 20 until the computer was clear (about 5 minutes), then did 5 minutes at 10ft. I wasn't in a hurry, and better safe than sorry, and it gave me a chance to practice hovering while holding stops for when I start doing real deco dives.

Basically the computers made for tech divers dont try as hard to push the limits of your NDL time.. since you aren't required to stay within the NDL window, they might as well shorten it and give you more stops to increase your safety. But it was nice to have the recreational Genesis computer to show that it wasn't "really" a deco dive.

 

[MXGratefulDiver]

Well, usually I'm in violent agreement with Grateful Diver. However, in this case I'd like to point out that a "reverse profile" generally refers to a single dive in which the latter part is deeper than the first. That is linked to higher probabilities of DCI.

In the case of a second dive being deeper than the first, recent evidence is that it has no impact on DCI incidents.

In this case, it refers to violating one of the rules for using RGBM tables that Suunto computers are based on, which is that each successive dive must be shallower than the one before it. It's not based on empirical evidence, but rather on the mathematical model around which the algorithm is built. And it does penalize heavily for doing the deeper dive after the shallower one.

With respect to the OP, prior to deco training and doubles I did trust my computer for limited deco diving. The only time it "surprised" me was when I over compensated and came up too slowly, creating additional deco obligation.

Were you perhaps using a computer (like a Dive Rite) that uses a standard Buhlman algorithm? They won't give you credit for offgassing below 30 feet ... even though for most dive profiles you will be.

All of this points to the need to understand a little bit about how the numbers on the computer were derived ... because they'll vary wildly from one computer to another. I've worn my Suunto and Oceanic computers side-by-side on the same dive and watched them deviate from each other's NDL by as much as 28 minutes. That's pretty significant if you're one of those types who just watches the NDL and comes up when the computer tells you to. Computers will also ... in some cases ... allow you to ascend faster than you should. That's why occasionally someone will say they got an "undeserved" hit. In fact, the hit was deserved ... the diver just didn't understand the limitations of the information that was being displayed on the dive computer he was using ...

... Bob (Grateful Diver)

 

[Jason B]

Good experienced eye for equipment there.

I'll bet it was the flat bottom on the tanks that gave it away...

 

[halocline]

On a simulated reverse or "sawtooth" profile on the 2nd dive of the day, suunto computers went into deco (or close) while oceanic computers had close to an hour of NDL. This was on an old scubadiving mag chamber test of various computers.

It's also possible that something happened on the first dive to annoy the computer; my understanding is that if you have a too-quick ascent for any length of time on a 1st dive, the suunto software penalizes you on the 2nd dive. The amount of penalty is (supposedly, I don't have one of these computers) dependent on the surface interval time. So, with a momentary fast ascent and a shortened surface interval, even a relatively shallow 2nd dive can be problematic for the computer if it goes deep late in the dive or has multiple ups and downs.

Even though I bought an aeris computer, I avoid profiles like that specifically because I learned how much penalty the suunto adds for them. I'm not saying that your husband dove a profile like that, (how would I know?) but it would explain the computer complaining.