Deepest Dive First, no exceptions?

[Lorenzoid]

Apologies. My search had multiple of hits in the "lies" thread and I got distracted from it. Thank you!

Kudos for at least giving it a search. And just to be clear, it's perfectly acceptable to start a new thread about something that's been discussed many times before.

I kind of enjoyed doing a Google of "reverse profiles," just to see what came up. Thanks to your reviving the topic, I ended up reading some of those old threads. At least one of the threads links to some actual studies or meta-studies. If I understand what I am reading, "deepest dive first"--at least at rec depths--has been debunked as a myth with origins in the use of tables.

 

[KeithG]

In our training we have been taught that a diver should always do their deepest dive first with subsequent dives shallower. How critical is this in shallower depths?

Context: My family will all be newly certified by the end of the weekend. As of Sunday evening we will have each dove to a max of about 30'. We are planning a family dive trip Monday to a local dive park. We're taught "deepest dive first." Which implies as newbies we can only make progress on successive trips if we don't want our first dive to possibly stretch our comfort levels.

Main question: At these depths is it going to wreck us to do a couple of 32' dives (to several training platforms) to verify everyone's comfort levels and then a final 40/45' dive? By the charts we'd still be within the limits for our dive times (that was a good practice exercise, but then I am a data geek). We'll have i300 computers in our gear as well to watch deco limits.

While I understand best practices, I can't imagine we're pushing the envelope. Nomex suit acquired.

Maybe it would be a good idea to have your instructor explain "why" they are teaching this rule?

you have successfully leanred the rule, but have no rationale to base it upon.

The rule is fine if it is being applied to a pair (or even a set) of dives to different depths where you will encounter NDL depending upon the order of the dives.

Blindly applying it in other situations is silly and can lead to irrational behaviour.

 

[txgoose]

Kudos for at least giving it a search. And just to be clear, it's perfectly acceptable to start a new thread about something that's been discussed many times before.

I didn't take it as a rebuke, but on other forums, for topics I know better, I understand why it is a bit of a faux pas to at least not try to search. Your added threads have been way cool reads.

 

[txgoose]

Maybe it would be a good idea to have your instructor explain "why" they are teaching this rule?

you have successfully leanred the rule, but have no rationale to base it upon.

He explain the "why." It was based on the, as I learn more, older thinking that it was just bad, bad, bad. Because he is an accomplished diver, I also suspect that he is telling us that why that he is required to teach us based on the SSI instructor manuals?

The rule is fine if it is being applied to a pair (or even a set) of dives to different depths where you will encounter NDL depending upon the order of the dives.

Blindly applying it in other situations is silly and can lead to irrational behaviour.

I don't complete disagree, but for a newbie it would strike me as patently more irrational/irresponsible to not at least stick to time tested "rules" until I know better or have read a lot more and verified the reading to my best ability. I am reading and I am learning.

 

[tursiops]

This is very old news now, but not all instructors/agencies/shops/boats have caught up yet.

 

[The Chairman]

If I understand what I am reading, "deepest dive first"--at least at rec depths--has been debunked as a myth with origins in the use of tables.

This is the best answer so far. The long taught "Deepest Dive first" does not make your dives any safer. It will give you more bottom time, but at those shallow depths, you're likely to run out of air before you run out of your NDL. Have fun and let us know how the family dive turns out!

 

[KeithG]

This is very old news now, but not all instructors/agencies/shops/boats have caught up yet.

And it promotes some less safe behavior. We encountered a DM who became concerned for our safety when he discovered that we only went to 40 feet on our morning dive before the 60 foot afternoon dive. He advised us that in the future we should do a quick bounce down to 70 feet in the morning so that we would be safe to go to 60 in the afternoon.

 

[tursiops]

And it promotes some less safe behavior. We encountered a DM who became concerned for our safety when he discovered that we only went to 40 feet on our morning dive before the 60 foot afternoon dive. He advised us that in the future we should do a quick bounce down to 70 feet in the morning so that we would be safe to go to 60 in the afternoon.

Well meaning, but stupid.

 

[KeithG]

Well meaning, but stupid.

It is situations like this that reinforce the need to know WHY and not just WHAT.

 

[HantsDiver]

This is the best answer so far. The long taught "Deepest Dive first" does not make your dives any safer. It will give you more bottom time, but at those shallow depths, you're likely to run out of air before you run out of your NDL. Have fun and let us know how the family dive turns out!

I (for once) agree with Chairman.

There is no benefit and some loss from following this "rule" - I have an article from a well respected tech instructor on this if anyone is interested (somewhere). It revolves around increased stress to "have" to do a certain dive first. Fundamentally it makes people feel like they are doing something wrong or have to do something that can potentially cause problems down the line.