I understood that Luxfer cylinders are preferred. But has anyone uses Catalina for their stage(s)? Luxfer AL40s are currently unavailable in my market.
Catalina for stage bottle?
- Thread starter wunat
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The difference is quite noticeable.
The weight distribution is different, the Catalina's being more tail-heavy.
This means that the stage bottle hangs down a lot more and I hear it's quite annoying.
The weight distribution is different, the Catalina's being more tail-heavy.
This means that the stage bottle hangs down a lot more and I hear it's quite annoying.
OP
wunat:
I read it many times on various sources that AL40 is a popular stage bottle size. Why is it so? How about AL30? AL50?
MonkSeal
Contributor
It's all about bouyancy characteristics and the amount of deco time that it can be done using it (filled with e.g. nitrox 50 or O2).wunat:
In Europe we usualy use 7 litres (bigger than AL40) for nitrox 50 and the same one or AL40 for O2. Sometimes AL80 is used for nitrox 50 and it's usualy used as bottom stage.
AL30 would be too small, I guess that AL50 would be Ok but again there's bouyancy issue (you should check if it's ok).
Regarding Catalina, I tried it once and it was definitely annoying.
limeyx
Guest
wunat:
It's about the amount of gas that makes sense for the dives you do.
For the tech1 range, the maximum deco you will usually do is 30-35 minutes. Any more deco and you really need to bring more than one deco gas.
Since we usually prefer the 50% bottle (rather than just 100% O2) for tech1 dives, and we switch to it at 70 feet, assume a SAC of around 0.5, then an AL40 (as long as you plan a good minimum gas level in your back gas) can give you 30 mins of deco.
Some people like to allocate 1.5X deco gas, which is where the 7L tanks come from.
The reasoning against taking an Al80 for a Tech1 dive is something like
1) not needed (a 40 is fine) and so it's extra drag
2) if you take it, you might be tempted to get into a larger deco obligation than trained for.
If you need more gas than will fit in a 7L or a 40, then it's better to take two smaller tanks than one larger because you always need enough back gas to deco with the loss of one deco bottle. If you have 2 deco bottles, then there's more chance of at least one of them working/not being lost.
For O2, probably a 30 is fine gas-wise as you only breathe it shallow, but i'd still take a 40 for uniformity's sake (dont want all kinds of different sized tanks hanging off you)
However, I think you have to take practicality into it too.
if i were in a place where there were only 80's for deco, I'd use one.
If I was forced to use a 30, i'd be very very careful to limit my deco considerably, and would probably just not do the dive.
Also, since (at least in the US) the 40 is relatively standard, it means the team has more gear that is the same (which is a good thing). These tanks also dont become too negative or positive when full/empty.
The Luxfers are supposed to ride better -- but I dont have a Catalina to compare against.
For bottom stages, AL80's are the preferred choice simply because you dont really get enough gas in a 40 to offer a benefit. Usually these bottles will have some Helium in them so they aren't so negative at the start of a dive (compared to air or nitrox)
I'd do a tech1 dive on a AL30, but it would be shakey. I would limit my deco time to 15 or 20 minutes max.
Vs. with a AL40 I feel ok about planning for up to 25 minutes and having ~5 minutes to fudge with.
It feels about the same because its the same diameter, so I'd rather have a bit extra deco gas.
I would also use an AL80 if it were the only thing available. But I would not accumulate more than 30 minutes of deco time with only one gas. Having to deco out for 60 minutes on backgas in case the 80 were lost is about the most I'm comfortable planning for.
The 50 is the same diameter as a 80. Fat but manageable. There's a bit more there for contingencies, but since its just one gas, it still doesn't allow you to plan for any more deco than a 40 would ~30 mins max.
Vs. with a AL40 I feel ok about planning for up to 25 minutes and having ~5 minutes to fudge with.
It feels about the same because its the same diameter, so I'd rather have a bit extra deco gas.
I would also use an AL80 if it were the only thing available. But I would not accumulate more than 30 minutes of deco time with only one gas. Having to deco out for 60 minutes on backgas in case the 80 were lost is about the most I'm comfortable planning for.
The 50 is the same diameter as a 80. Fat but manageable. There's a bit more there for contingencies, but since its just one gas, it still doesn't allow you to plan for any more deco than a 40 would ~30 mins max.
limeyx
Guest
rjack321:
Yeah, basically the same for me.
AG's point on the 80 was that "OH, there's just one more fish I want to see," or "Hey, we can go 5 mins longer, we have an 80 of deco gas ... oh crud, the reg on the tank isn't working on the 80 and I didnt plan 80 or 90 mins deco on backgas.."
(i.e. better to remove the possibility of temptation by just not taking the gas)
MonkSeal
Contributor
And 80 full of nitrox 50 would not ride so well.limeyx:
I'm curious why the UK folks carry an 80 and go up to 40+ mins deco on one gas. (on the other board). To much risk in case of deco gas loss IMO. But then again they are carrying enough in the 80 to swap back and forth and minimize the deco on backgas. But that seems beyond Tech1. Would certainly be a long and challenging ascent esp. in mid-water. Not worth it for a few extra mins of BT.
If I was shore diving and had to swim a ways in and out, I have considered using an 80 just to compensate for the extra consumption. A scooter would be better, but I have an 80 already.
If I was shore diving and had to swim a ways in and out, I have considered using an 80 just to compensate for the extra consumption. A scooter would be better, but I have an 80 already.
limeyx
Guest
rjack321:
The 80 I am not sure about (I think one instructor all but insists on it), but I know they like to plan +50% deco gas for contingencies, which you aren't going to get from a 40.
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