Stupid questions as well as greetings

[Spyker]

Hi guys

Diving came easy to me and I really took to it naturally.:cool2: As a new diver with 35 dives that included a advanced qualification ,I'm starting to realize for the first time that there might be some danger to this diving thing. So now I need to know more.

I have been reading posts on Scubaboard since I started diving 6 months ago and feel you lot will be a big help in this quest for information. So please help me with question one of a many.

According to my modern day "instant training " we should know all about dive tables,but not concern ourselves with it to much,as THE COMPUTER will sort it all out. This has gotten me into a bit of a argument with my slightly more experienced buddy on holiday dives in Thailand.
We started with a wreck dive to 30m with 37 min. of bottom time, 50 min. surface time and then a 13m reef dive with 55 min. bottom time.

The difference of opinion came on the 3rd dive planned for 30 min. later. My buddy informed me that he did not think it was worth our while to dive, as the site was up to 16m deep and we will have to hang above the reef on 12m as we could not exceed our depth from the previous dive.Visibility was not great so this would really have been a wast of time.When I planned on my COMPUTER I had ample no deco time at 16m and felt he was over cautious. That is when the fight started.

I know it is rule that you dive shallower during a day of multiple dives but would like to clarify if this would have been a acceptable dive to do. And if yes, to what extend can you go deeper than a previous dive. My trusty computer reasoned that although for only 3min. I could happily dive to 30m !!??

Please clear this up for me.

 

[Steve_C]

People generally do the deeper dives first. That is the most common practice. I recently saw a study that suggested that doing in the reverse order and staying within NDL is not a significant risk. There is no magic number that says this is ok and that is not ok. But dive 3 was only 3 meters deeper than dive 2. That does not seem major to me. Personally forgetting dive 1, I would be willing to do dive 3 after dive 2.

30 min is a pretty short SI for a third dive given dive 1 was a deep dive.

Did your buddy have a computer or was he diving tables? Was it the same computer?

Different folks have different comfort margins.

Basic rule is that a buddy pair has to do dives that both divers are comfortable with. If buddy wants to thumb dive you are supposed to just say yes. Having a buddy who thinks they should not be there is not what you want on a dive. You can debate dive theory later over a beer.

Side question: When you say bottom time was that the total dive time or the actual bottom time?

 

[Spyker]

Hi Steve

We both dived the Suunto Zoop.
I buddied with the DM and did the dive. My friend abstained.Still had a few beers after. Happy ending.
Total dive time. Sorry not yet fluent with all the jargon.

The thing that keep me thinking about it is the fact that my computer was happy for me to plan a deeper dive while other divers are uncomfortable with it. As seen elsewhere on scubaboard, I now start to wonder how much I should trust it. As I'm lazy with paperwork it seemed a great invention to make my life easier while diving, but obviously it does not know everything.

Do I understand you correctly, that a deeper dive ( within limits) later in the day is not a unsafe thing to do?

 

[tursiops]

Since you are still outgassing for 12-14h after a dive, doing a deeper dive later (a "reverse profile") means poor nitrogen management, but according to the studies is not unsafe so long as you follow your computer. You can get more bottom-time in for the day by doing your deepest dive first, then successively shallower dives. However, many divers and operators still base their opinions and actions on whatever they learned "back when", and "back when" you never went more than 10 feet (3m) deeper on a later dive, because the models/tables had not been tested and approved for this. Today, with more knowledge, just dive, and follow the computer. See Divers Alert Network.

 

[miketsp]

Deeper dive as 2nd dive is common practice on the 1st day of diving at many locations I've visited, the reason being that the 1st dive of the trip is an easy shallow dive to check everyone's equipment and weighting. Once it's confirmed that everyone is ok then off to do a deeper more complicated dive. The rest of the trip they follow the recommendation of deeper dive first, but it's certainly not obligatory.

 

[Steve_C]

One of my two computers is a zoop. It is known as a conservative computer for what that is worth.

 

[KeithG]

"deeper dives first" is a common rule of thumb that is based upon giving you the longest NDLs on subsequent dives. It is factually correct and makes sense.

Unfortunately this rule of thumb is often reversed to "you cannot dive deeper than your previous dive". Which is totally incorrect. You can, your NDLs will just be shorter than if you did the dives in the opposite order.

Take a sample of 3 dives and run them through your tables both ways: deepest first and deepest last. You will find that your bottom time is more limited with deepest last.

I remember an operator that enforced this rule and even asked you to do a quick deep dip on every dive so that your depth would not be limited on the next dive. Stupid idea!

As long as you stay within your NDLs (by table or computer) you can do your dives in any order you choose. You may just have shorter bottom times.

 

[Spyker]

Thanks Guys

Makes a lot more sense to me now.

No wonder the computer allowed me to plan dives deeper than the one before. There is nothing wrong with it, it just makes sene to plan for deep dives first so that you have the longest total dive times for each dive. Better management like Tursiops call it.

That was a question, not a statement.