Multi-day repetitive dive planning: planning for liveaboard divng

[Diver0001]

No fan list, just the people I could think of who would have interesting things to say about this. No intent to slight anyone else.

Obviously, I get all the other suggestions, but why no sleeping during surface intervals?

In a word, circulation.

Your blood carries nitrogen from the tissues to your lungs where it can be eliminated. When you're sleeping your circulation slows down and so does off gassing. That means that when you get back in the water for you next dive your computer has calcuated the surface interval on an incorrect assumption and the adjusted NDL it's showing you may be a little on the long side.....

R..

 

[gj62]

In a word, circulation.

Your blood carries nitrogen from the tissues to your lungs where it can be eliminated. When you're sleeping your circulation slows down and so does off gassing. That means that when you get back in the water for you next dive your computer has calcuated the surface interval on an incorrect assumption and the adjusted NDL it's showing you may be a little on the long side.....

R..

Exactly.

Similarly, moderate to heavy exercise should also be avoided for the same reason - an increase in circulation, etc, which could cause you to offgas more quickly and thereby bring on DCS. Of course, this is never a problem for me

 

[zboss]

- Do put your computer on a more conservative mode. Alternatively (what I do) dive Ean32 and put your computer on air whenever you can.

While I agree with just about everything you mentioned I disgree on three:

1) taking a minimum of three hour SI... why? Maybe after a very deep first dive take a two hour interval

2) putting your computer on air and diving nitrox... you take away the ability of the computer to do it's job and that is to protect you from oxtox, in the case of nitrox

3) Switching gasses... should only be done if you have cut personalized tables based on your gas consumption, or your are using a gas-switching capable computer.

 

[Diver0001]

<snip>

1) taking a minimum of three hour SI... why? Maybe after a very deep first dive take a two hour interval

Why not? A longer surface interval gives you more time for off gassing (perhaps even eliminating subclinical bubbles) and also forces you to pace yourself. It's a personal decision and corresponds to applying the XYZ rule to every dive. Point is extra conservatism is never a bad thing. Not enough, on the other hand can be.

2) putting your computer on air and diving nitrox... you take away the ability of the computer to do it's job and that is to protect you from oxtox, in the case of nitrox

It's good to debate this one. I think the principle is sound enough but what it gets you in conservatism may not be worth the price in bottom time for some. CNS/OTU loading isn't a problem to track. There are tables for that. But you're right, the computer can't do it for you then...

3) Switching gasses... should only be done if you have cut personalized tables based on your gas consumption, or your are using a gas-switching capable computer.

This is along the lines of using 32 and calculating 21. You'd get extra conservatism and better offgassing when it counts, namely in the water at your safety stop. I'm not sure this is a good recommendation for every diver but I certainly wouldn't hesitate to use it.

R..

 

[MechDiver]

2) putting your computer on air and diving nitrox... you take away the ability of the computer to do it's job and that is to protect you from oxtox, in the case of nitrox

It would be difficult, using rec nitrox and rec profiles, to have oxtox be a problem.

MD

 

[rcain1]

RCain, are you advocating trusting the boat to safely plan your dive? Or are you simply saying you have faith that they aren't going to get you hurt?

I myself ask question and give my views. I try not to “advocate” anything! This was a question/assumption. I would never take anybodies word that something was safe unless I checked it myself or really trusted them.

BUT…

OK, lets say on a dive boat they anchor and say, “were diving here”. I make my plans and figure out my dive with my buddy. I am still assuming that the dive boat is going to have me diving at a safe location aren’t I?

Of course I am going to plan all of my dives. I was just asking/assuming because I have only done one dive boat charter.

 

[MikeFerrara]

Most of what I do isn't really live aboard but...

I'm kind of agree with Curt and most of what Diver0001 said on this.

I prefer fewer long dives to a greater number of shorter dives. Climbing in and out is hard work and ascending is where all the trouble is.

I match my ascents and surface intervals to the dives I'm doing. In other words if I know I'm planning more diving I'll take extra care to limit bubbling from the first dive. The best way to describe it is to say that I'm more conservative when planning multiple dives only I'm not always within no-stop limits so the conservatism is in the ascent and the surface interval rather than adjusting depth or bottom time.

I don't use a computer and my schedules are similar to what you'd get from vplanner and sometimes padded as I mentioned above.

I use something other than air when ever I can and for anything of any depth prefer to use a high FO2 gas for the ascent. I prefer to do so even if the dive is within no-stop limits because I don't believe in NDL's. On heavy teaching days where I've started out in the morning teaching an Advanced nitrox class, moved on to teaching an AOW class and finished with doing ESA's with OW students, I've been seen doing it breathing a slung bottle of 50%. LOL No those days probably aren't good for for you but I've had to do lots of work in my life that I'm sure took years off my body.

Some of our dives involve difficult entries and exits so I adjust ascents and surface intervals for that also (it's a guess but what in decompression isn't). I often rest on the surface (breathing my ascent gas if I have it) for awhile before climbing out with heavy equipment.

In a week of diving I'll usually stick one or two light days in there someplace.

If I feel off, I assume I am and treat myself accordingly.

Stay warm, eat, drink and do what you think best.

 

[glbirch]

Apologies for the hijack, but looking at two opposite recommendations has me curious.

In a word, circulation.

Your blood carries nitrogen from the tissues to your lungs where it can be eliminated. When you're sleeping your circulation slows down and so does off gassing. That means that when you get back in the water for you next dive your computer has calcuated the surface interval on an incorrect assumption and the adjusted NDL it's showing you may be a little on the long side.....

R..

Is this a personal theory, or is there research that backs it? How does my computer know my personal heart-rate? Combining that comment with:

Similarly, moderate to heavy exercise should also be avoided for the same reason - an increase in circulation, etc, which could cause you to offgas more quickly and thereby bring on DCS. Of course, this is never a problem for me.

brings a whole set of questions to mind. Does this imply an 'optimal' heart/breath rate for N2 elimination? What (if any) would be variables? Given that individual at-rest heart rates can vary from under 40 beats/minute to over 90 depending on age, fitness and genetics, it sounds a little simplistic to say that both cases are true.

 

[gj62]

Given that individual at-rest heart rates can vary from under 40 beats/minute to over 90 depending on age, fitness and genetics, it sounds a little simplistic to say that both cases are true.

Ah ha - now you know why the tables are not, nor can ever be, perfect. There are others on this board that know far more than I regarding this subject, but my take would be that your "at rest" (not exercising, not sleeping) rate is what the tables/computers are trying to work with during your SIs.

Perhaps one day there will be tables based upon respiration heart rates. I pity the divers that push the tables to such extremes as to make this necessary.

 

[glbirch]

Ah ha - now you know why the tables are not, nor can ever be, perfect. There are others on this board that know far more than I regarding this subject, but my take would be that your "at rest" (not exercising, not sleeping) rate is what the tables/computers are trying to work with during your SIs.

On the surface that would be logical, but many of us have poor breathing habits when we are awake. Sleeping, our respiration and heartbeat slow, but we tend to breath deeper (IIRC). So I personally would not assume that sleeping during my surface interval is bad. As well, on a multi-day repetitive-dive trip, the majority of your off-gasing surface interval is at night. I would also suspect that the blood stream flushes N2 fairly quickly and it's the slower tissue compartments that are more of a factor. Would breath rate make much of a difference to how fast those tissues give up N2?

Maybe I should ask to have this moved. I don't want to take over reubencahn's thread.