No deco and dive computers

[lowviz]

...//... I figure the DM can take care of himself.

You go, girl!

 

[chrpai]

It's the buddy that can get you everytime....

I did a wall dive "recently" in Lake Travis with a new buddy. He might be a member here so hopefully I'm not giving too much details. He said he had 1000+ dives but was new to dry suits. I usually ask more questions of a new buddy but he seemed ok and I didn't. He was using an AL80 and I was using an LP95.

We dropped down to about 60 for awhile and then up to 40. About 30 minutes into the dive I was getting close to my (non-discussed) turn pressure. The thought then occurred to me that he hadn't called the turn yet. A few seconds after we turned I signaled an ascent to 30' and then asked him for his pressure. Not good. I then called for 20'. We made it about 15 minutes when he then called low pressure. I still had 1200psi left and thought about passing him the long hose or calling for 10' and just stretch the gas out down to about 300psi. But before I could he thumbed the dive and I followed him up.

I don't really like doing long surface swims but oh well...

---------- Post added June 9th, 2013 at 09:36 PM ----------

My "buddy" will not do these dives with me so our agreement is that I hire a DM for at least the first day. I figure the DM can take care of himself.

Is the DM carrying a AAS him/herself?

If so, I'd calculate your bailout requirements and reserve that much in your backgas and your pony. Anything left over is yours to play with.

If not, it doesn't matter how many c-cards the DM has. You are carrying his/her backup gas.

 

[lowviz]

...//... it doesn't matter how many c-cards the DM has. You are carrying his/her backup gas.

Indeed, but that is not part of the "contract" of a guided dive.

 

[chrpai]

Indeed, but that is not part of the "contract" of a guided dive.

And people wonder why I don't want to be a DM.

Then again, I solo dive all the time....

 

[supergaijin]

I am diving a sunnto cobra 2. I understand all that, I was just makin sure I could go down to 120 for the deepest part of the dive and run my ndl time down to a few minutes left, for example, and then ascend to 100 ft for a few more minutes until time to ascend the line.

In my experience with Suunto, you will not be able to ride the computer to the NDL and then ascend a bit and get a few more minutes. IME it takes at least 1 ata of pressure change to get a significant increase in NDL time. On a wreck (often) you're basically doing a 'U' shape profile similar to what you'd calculate on tables. Computers don't add a great deal of extra dive time as they would on a typical reef dive.

last weekend i was diving nitrox with an air suunto computer. I was at the bottom with 1 min left of ndl time, i started to ascend and the computer jumped to 3 min, then 5 min, then 10 min, time increasing as i went up.

When you go from 90 feet to 60 feet your ndl time will about double..as you raise your ndl will increase much faster than your ascent rate, so you will not go into deco.

IME this will not happen if one is only ascending a 'little bit'. I have found that when I ride the computer to NDL, it will prompt me to ascend to the ceiling at 10'. However once above 30', the computer often gives me a new NDL as opposed to deco. This has so many factors- recreational computers are difficult to predict for deco/ close to deco dives.

Personally I'd question the nitrox and consider not using it.

Please check out your dive computer's manual and learn how it will be functioning and displaying your deco information.

You basically have it right though. As your NDL time counts down you will eventually be going into Deco. Depending on factors such as depth and time spent at it, you might easily just eliminate your deco obligations by ascending to a shallower depth... or you might not and have a deco obligation at your safety stop... there are many factors and many what ifs, but your basic premise is correct.

However, like I said, I'd probably dump the nitrox as the nitrox introduces other problems in regard to your depths and the benefits especially on your first deco dives are going to be out weighed by the issue of what happens if compounding all of this there comes a depth issue on top of things? What if your buddy F's up and gets narc'd and goes deeper than he should? You now are in deco and on top of it are faced with violating your maximum depth due to nitrox?

Be real careful and dive with a really good buddy. Adding further tasks will make things more dangerous through task loading.. I'd leave the camera on the boat if you were planning on bringing one... and do not do this dive without a complete understanding of your dive computer.

I agree that leaving the camera on the boat for this dive is a good idea. Even though the OP says that he has his bases covered, it really doesn't sound like he does.

However Nitrox is only a good thing IME- depending on the mix of course. If I had the opportunity I'll use Nitrox every dive- it just isn't that difficult to keep above a MOD.

I'd like to say again that diving until the NDL and expectig a significant increase in NDL time by ascending less than 1ata is not realistic.... in my experience with Suunto.

 

[Lorenzoid]

Personally I'd question the nitrox and consider not using it.
. . .

Mike, I only dived once with Olympus, but at least on the days I was there they were filling most tanks from a banked EAN 30, which, surprise surprise, was exactly appropriate for the depth of the wreck. The OP will be fine if he listens to his instructor/DM on this trip.


OP: I don't recommend you let your Cobra 2 go into unplanned deco even for a few minutes, despite what some cowboys may suggest is "okay." The problem with doing that is it can become a slippery slope, where today you may let it slide a couple of minutes and escape unscathed but tomorrow you may let it slide more and run into a problem. There's a potential to get careless. Good diving habits say follow your computer. From your comments, I think you know that. As I said, I also dive a Suunto, and as soon it counts down to the single digits, I get on the ascent line and start moving up at a normal 30 fpm or so, then slow down later. Works for me.

Have fun.

 

[wmason11]

That's my plan. Im not deco diving, so ill be sure to not let that ndl time run down close to 0. Ill have to experiment the depths to see how much time it will let me have if I ascend up 20 ft to explore the wreck a little more. But if it doesn't give me much more, then on to the line I go.

 

[Colliam7]

I will be diving 130s tanks on a trip and will be diving at depths over 100 ft. . . . I know I will run out of no deco time before air time so when im at a certain depth and my no deco time runs out, I need to simply go shallower to have more no deco time right?

You have received quite a bit of good feedback. The simple answer to your question is yes, you need to go shallower to have more no deco time. In fact, I think yardpro and BDSC gave some very 'spot on' feedback. My additional thoughts: 1) it has been suggested that this won't work with a Suunto computer. My experience, though, has been that it does work just that way with a Suunto, but I definitely agree with several posters who pointed out that you will need to ascend more than just a few feet (and, probably, closer to an atmosphere pressure change) to see any appreciable change; 2) you are presumably diving on NC shipwrecks out of Morehead City, and most of these have very limited vertical relief - the U-352 being a good example. So, although Jim gave some good advice regarding a multi-level dive, you really aren't looking at true multi-level dives on NC shipwrecks, unless you like swimming around the ascent line for 5-10 minutes, simply to watch the barracudas who are hanging there watching you. Once you approach your NDL at whatever depth you are diving, and begin your ascent, even if you are at 0 NDL when you start up, you will probably surface with a reasonable amount of NDL; 3) as you might imagine, and as several have implied, the real challenge is not so much moving back into the 'available NDL' realm, it is dealing with what happens if you wait until you are at 1 minute (or no minute) NDL to begin your ascent, and are then delayed for some reason. I know you are not planning to do this, just making the point. Knowing how to handle that situation, and understanding the computer you are using, is important.

You should definitely start ascending slowly and start making your way up to the boat right?

Yes! Once you approach your planned turn pressure, or approach your NDL, time to begin your ascent to the boat. Hope you have a great time diving our coast!

 

[flots am]

it all depends on the computer
last weekend i was diving nitrox with an air suunto computer. I was at the bottom with 1 min left of ndl time, i started to ascend and the computer jumped to 3 min, then 5 min, then 10 min, time increasing as i went up.

When you go from 90 feet to 60 feet your ndl time will about double..as you raise your ndl will increase much faster than your ascent rate, so you will not go into deco.

Not exactly. Depending on the computer, the dive and your ascent rate, your no-deco time can go up or down or vanish as you ascend. You can't actually count on getting more no-deco time.

If you ascend too slowly, you can actually accumulate more deco time.

Also, if you're riding the computer, it's entirely possible for it to require more deco time than you have gas for. One of the most interesting things I've ever seen was watching my buddy hang on the line and reading her computer, where it required 20 minutes of deco when she had 5 minutes of gas left.

If you're going to do a deco dive, plan it before you ever get wet and make sure you know what to expect and how much gas you need.

flots.

 

[DaleC]

The Suunto will clear deco as you go up. It also adds more NDL.