Quick Deco Question

[declan long]

Hi Everyone

Just wanted to check/clarify something. When we have deco to complete when you have a stop at say nine metres and you are at eighteen and you ascend slowly, does this stop clear before you get there because due to the slow ascent you have off gassed enough so you can ascend shallower without reaching the m value?

Also when you have a stop in an sw petrel at 6 m why if you stay at nine does it still clear at the same rate as if i was at 6 asin the count down still counts down? explain please.

Thanks

Declan Declan Long

 

[Michael Guerrero]

Declan,

You really should take a class, read a book, or talk to an instructor about these questions. From your questions it really seems like you're groping in the dark here and there are tons of books and lecture materials available that can explain all this stuff to you. If you want some suggestions you can PM me. If you're going to be doing deco diving you really should get a solid understanding of deco theory and the model you are running.

Mike

 

[TracyN]

If you need to ask these questions you need to take a decompression class or not do any deco diving at all.

 

[Tippytoes12]

Declan

How will you know how much deco time you need to do at nine mts when you are at 18 mts ...also what are you doing at 18mts in deco?

Recreational diving is meant to be all non deco... so you shouldnt be going into deco at all.

Sorry if this sounds harsh. I had an instabuddy on my last trip ...she did her best to make it her last dive and it was no fun at all for me , the guide and her new husband who was back on the boat.

 

[declan long]

Hi Evryone

sorry but i am a certed deco diver. please can someone clairfy my understanding. i am not iterested in theese kind of comments. please answer.

 

[bradells]

Hi Evryone

sorry but i am a certed deco diver. please can someone clairfy my understanding. i am not iterested in theese kind of comments. please answer.

It depends. Go back to your training materials. You should be able to figure it out from there.

If you can't, have a chat with your instructor about it.

BRad

 

[Michael Guerrero]

Declan, I'm not trying to discourage you from doing decompression diving if you're already certified, but you're asking very basic questions. And you're not providing enough information for us to really give you an answer. These are things that should have been covered in your class if you have in fact taken a deco procedures class, which is why I suggested reading a book or watching some of the free online lectures about deco theory.

This is also not the first time you've posted questions that seem to demonstrate a lack of knowledge about basic decompression theory. If you paid an instructor to teach you this stuff you should ask them these questions or reread your training materials as was already suggested.

I don't mind discussing deco stuff at all, and if you were asking a this vs. that kind of question I'd be fully engaged, but you haven't really asked complete questions here.

For your first question, if you have a deco stop at 9 meters, and you are ascending slowly from 18 meters, it completely depends on how slowly and how much time you have to do at 9 meters as to whether the stop will be cleared. How do you expect us to answer a question like this with no details about the length of stop and ascent rate? Again, this is basic tech diving, and your incomplete answer seems to indicate you need further instruction in basic deco theory.

As to your second question, this is again basic decompression theory based on the model you are using. Are you using a bubble model or a saturation mode in your Petrel? Ambient pressure affects supersaturation and bubble size. Increasing the gradient between tissue tension and ambient pressure increases supersaturation. Your tissues will continue to off-gas at 9 meters, but there's a reduced gradient compared to 6 meters.

You need to go back to your training materials Declan.

 

[Tippytoes12]

Ok Declan apologies for the tone of my answer and point taken.

However why ask complete strangers even on a site like this....why not check your training manual, whoever certified you , a trusted colleague ?

 

[kwinter]

Why not give straight answers? The answer to your first question is yes. If the stop clears before you get there, it is because the algorithm has calculated sufficient offgassing due to the slow ascent. It happens all the time to recreational non-deco divers who end up with a small deco obligation at 3m but it has cleared by the time they ascend that far.

The answer to your second question is it doesn't. Or at least it shouldn't, but there might not be a big difference. If you stay at 9m you will still be offgassing (based on the whole dive profile), so your 6m stop will eventually clear. It shouldn't be at the same rate that it would have cleared at 6m, but it might not be a big enough difference to notice. I'm not positive how the Petrel handles this, but with some computers (like the VR3) the deco time shows the same while the clock counts slower. In other words it might still show 3 minutes of deco, but it could take 5 minutes to count down those 3 minutes.

Rather than beating someone up who asks a question, I believe his questions are about the computer algorithm and how it reacts. This is not something that his training materials or instructor might know, and I certainly don't remember it being part of my training either. So lighten up on the flame throwing.

 

[Diver0001]

Hi Everyone

Just wanted to check/clarify something. When we have deco to complete when you have a stop at say nine metres and you are at eighteen and you ascend slowly, does this stop clear before you get there because due to the slow ascent you have off gassed enough so you can ascend shallower without reaching the m value?

I think the question you're asking is if a stop clears while you're ascending to it, have you off gassed enough to roll through that stop? According to your deco model you can always ascend to your ceiling so the answer is that if a stop has cleared before you get there that you have off gassed enough that the ceiling is now shallower than the previously displayed stop depth, and therefore you can theoretically ascend beyond that.

In practice you wouldn't just roll through a shallow stop, though. In the range of the dive from 18 to 9 metres you ascend with 3m/min but once you're at 9 metres (or 6 at the most shallow) you'll want to slow your ascent even more. Unless there is a compelling reason not to, then you would still want to make 2-3 minute stops at 9, 6 and 3 even if your deco model is telling you that your ceiling is on the surface. The reason is to slow (and control) your ascent in the last metres where you are not able to incur a further decompression obligation.

I'm curious. I've seen a few threads lately where you were asking pretty basic questions about ascent strategies even though you're certified. What course did you take? Is this stuff that they covered in the theory but you didn't understand at the time or things that were never covered?

Also when you have a stop in an sw petrel at 6 m why if you stay at nine does it still clear at the same rate as if i was at 6 asin the count down still counts down? explain please.

I can't answer this question, I don't have a petrel and I don't ascend according to my computer. Depending on settings, computers can give results that make sense and results that don't make sense. My guess just based on what you wrote is that it may be possible that it's using a bubble model and giving you some kind of credit for stopping deeper than your ceiling. But that's just a wild guess.

R..