Miller
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Im getting ready for live aboard trip. It was recommended using Nitrox for the trip. So which is the limiting factor NDL or O2? Also on most live aboard which is more common 32 or 36?
NDL or O2 limit
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Wookie
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32 is much more common than 36 on liveaboards. Using NTX32 5 times per day will more likely limit you on O2 rather than NDL by day 4. Diving air 5 times per day will have you NDL limited by dive 3 each day. Your computer's settings will vary by manufacturer, and by your preference.
ianr33
Contributor
For once I disagree with Wookie!
If you are diving 32%,using Al 80 tanks,not going beyond a pO2 of 1.4 (111feet) and staying out of deco it is pretty much impossible to be O2 limited. I tested this pretty extensively on V-planner and could not get O2 limited even doing 12 dives a day.
O2 limit at a pO2 of 1.4 is 180 minutes a day. Over 5 dives thats 36 minutes at 111 feet per dive ,thats WAY over NDL's. (The O2 contribution on the shallow part of the dive is negligible)
Diving 36% O2 limits MIGHT be a problem,but not on 32% within the above parameters.
Following NOAA guidelines O2 loading from a dive just disappears abruptly at 24 hours.Obviously that does not reflect reality but O2 loading over multiple days is only going to be a problem with technical dives and/or high O2 mixes.
If you are diving 32%,using Al 80 tanks,not going beyond a pO2 of 1.4 (111feet) and staying out of deco it is pretty much impossible to be O2 limited. I tested this pretty extensively on V-planner and could not get O2 limited even doing 12 dives a day.
O2 limit at a pO2 of 1.4 is 180 minutes a day. Over 5 dives thats 36 minutes at 111 feet per dive ,thats WAY over NDL's. (The O2 contribution on the shallow part of the dive is negligible)
Diving 36% O2 limits MIGHT be a problem,but not on 32% within the above parameters.
Following NOAA guidelines O2 loading from a dive just disappears abruptly at 24 hours.Obviously that does not reflect reality but O2 loading over multiple days is only going to be a problem with technical dives and/or high O2 mixes.
RonFrank
Contributor
The limiting factor could be the diver! (IOW's YOU!).
Your question is too broad, kinda like saying how far will my car go on one gallon of gas without telling us anything about the car?
For most experienced divers NDL is the limiting depth factor, but multi-level profiles fix that easily, and in the end you run low on air. This is generally not a problem as on a live aboard in August, we were diving 6 hours/six dives a day, never on the same site, and that was plenty of diving. We did AIR BTW!
So that is a question for the Boat. Will they be moving around (most do), and how long to they give you on a site. You may want to ask about average, and max depth on most of the sites also.
IF you are in 30 feet of water on a lot of the dives, this is a brainless discussion. If you are bottomless so to speak, more relevant. Most boats like to anchor at a site, so your captain can definitely provide the numbers.
Personally, I'd go with the Nitrox unless it's way expensive. However if your dive buddy is doing air (as mine was in Aug), there is less of an advantage.
Your question is too broad, kinda like saying how far will my car go on one gallon of gas without telling us anything about the car?
For most experienced divers NDL is the limiting depth factor, but multi-level profiles fix that easily, and in the end you run low on air. This is generally not a problem as on a live aboard in August, we were diving 6 hours/six dives a day, never on the same site, and that was plenty of diving. We did AIR BTW!
So that is a question for the Boat. Will they be moving around (most do), and how long to they give you on a site. You may want to ask about average, and max depth on most of the sites also.
IF you are in 30 feet of water on a lot of the dives, this is a brainless discussion. If you are bottomless so to speak, more relevant. Most boats like to anchor at a site, so your captain can definitely provide the numbers.
Personally, I'd go with the Nitrox unless it's way expensive. However if your dive buddy is doing air (as mine was in Aug), there is less of an advantage.
Your boat will be most likely equipped with a compressor system that creates the same mic for every fill
Go for nitrox, the boat crew will advise you if there are any deep dive where you need to switch to air and sometimes they even adjust the mix to allow your a greater maximum depth
O2 loading will most likely not be a problem and NDL won't be an issue either. Most likely your dives will be limited by your air consumption or by max dive time set by the dive crew
Go for nitrox, the boat crew will advise you if there are any deep dive where you need to switch to air and sometimes they even adjust the mix to allow your a greater maximum depth
O2 loading will most likely not be a problem and NDL won't be an issue either. Most likely your dives will be limited by your air consumption or by max dive time set by the dive crew
scubafanatic
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...I agree with Wookie......EVERY liveaboard I've ever done offers either AIR-only or AIR and EAN32...never heard of a boat offering EAN36...the only place I've EVER used EAN36 was a few times in Cozumel. Wookie's experience mirrors my own...on AIR you'll be bumping up against NDL limits daily, unless you're doing pretty shallow dives...and when I'm diving larger capacity tanks and 4-5 dives daily, I really had to watch my O2 limits/loading......moreover, I'm using Oceanic computers, which are said to be pretty liberal.....if you're using a Sunnto computer, you'll bump up against your NDL and O2 limits substantially sooner than I would using my Oceanics.
...listen to Wookie.....he's the owner/operator of SPREE (liveaboard) for many years...and often does 'tech' charters as well as his usual recreational ones...there's a pretty good chance he knows what he's talking about !
....it has been my experience that you don't want to be the AIR-only diver in a group of Nitrox divers.....you will just piss everyone off if you keep making the group surface when you hit your all-too-soon NDL and all the other divers still have half a tank's worth of bottom time left !
ianr33
Contributor
I'm guessing you are referring to my post above?
The way NOAA deals with O2 exposures,and the way my Aeris computer deals with it (and probably many other computers as well) is that after a dive the O2 exposure from that dive (calculated CNS %) stays at the same level for 24 hours then magically goes to zero. So if you surface from a dive at 10a.m one day your overall O2 exposure as measured by a computer will suddenly drop at 10 a.m the next day.
Because of this computers could not care less about O2 exposure over several days of diving (They do of course care about N2 over several days)
Obviously this doe not mirror reality. Deco programs and more sophisticated computers (e.g. Shearwater) assume the O2 exposure decays away with a certain half life (believe 3 hours is pretty common)
Recreational computers will be conservative in logging O2 exposures. If you did one big dive in a day and exited at 8pm in the evening with a 100% O2 exposure then at 7.59a.m the next day most computers will still have you at 100% . Following the half life model you would be at 6% O2 loading (4 half lives)
highlandfarmwv
Contributor
If you go by computer you 'll probably be able to do all. the ATAs depend on your depth and how long not number of dives.
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