Tank sizing???

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formernuke

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It is a matter of body style and comfort.

I like HP 100 personally but shorter people tend to 80's for example. I know others who like 120's.

See if you can borrow and try different ones and use what's most comfortable.
 

DAJ

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Just tossing out some averages to think about. First, you are just getting into buying gear so getting into diving and having a boat, you will most likely own several different tanks sooner or later so what you get first might not matter too much.

Second, you are getting into Nitrox and looking at doing 120 foot dives. If you ballpark a non-deco dive to 120 feet and you have an average consumption rate, you are looking at burning roughly 80cf of mix. If you are working or in rough conditions, that will be much higher.

Lastly, you need to really look at tank specs when you make these selections. Not all 100s or 130s are created equal. Some will be negative when almost empty while others can be positive. Some 130s can be the same length as another’s 100s. I prefer to dive with little to no weight on a weight belt so I go with cylinders that will work best for that purpose. Depending on location and what you want, the cylinder market (new and used) can be a bit rough right now.

Good luck with whatever you select and as I noted, if you are like many of us, you will own several anyway so your first cylinder might come down to the only size you can find that is available.
 

Wiznutaggie

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Wow, that was my first time posting here, and that was an amazing response. I've been on many forums before, but the amount of help you guys just threw out there is mind blowing! Really appreciate all the responses!!

Taking what everybody has been saying into account, I'm leaning towards the 117 or 133. Comparing the two to an AL80, the 117 is 2" shorter and the 133 is only 0.75" longer. Since an AL80 is pretty standard, I can't imagine a tank that's 0.75" longer being that much more unwieldy. I'm more inclined towards the 117 though as it is less buoyant than the 133 when empty (0.35# vs 1.45#), so less weight I'll have to add. They're both 8" tanks though, which I've not heard if there's any disadvantage to?
 

Marie13

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Given where you live, you want HP tanks. Easier to get filled to service pressure.
 

Marie13

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Just curious - why are hp easier to get filled?

If you’re not somewhere the shops will overfill LP tanks even a bit, HP tanks are better to get a full full on.
 

Rukkian

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If you’re not somewhere the shops will overfill LP tanks even a bit, HP tanks are better to get a full full on.
So you are saying there are shops that cannot fill to 2640, but can fill to 3400? That makes no sense, maybe I am missing something.
 

Marie13

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So you are saying there are shops that cannot fill to 2640, but can fill to 3400? That makes no sense, maybe I am missing something.

Probably not putting it correctly. If you can’t get overfills on LPs, better to have HPs.
 

Rukkian

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Probably not putting it correctly. If you can’t get overfills on LPs, better to have HPs.
That makes more sense. I get that non overfilled lp are bigger for the same volume, and may not be the best for bm tanks.
 

tbone1004

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probably not worded well regarding fills.
That said, there are only 3 reasons that you should ever choose a LP tank over a HP tank.

In order of importance

Reason 1-the tank that you need is not made in a HP version. The two obvious examples of this are the 4l steel tank used in the O2ptima, and LP50's that have never been made in a HP version
Reason 2-arguably reason 1.5, but the LP version of the tank offers very specific buoyancy characteristics that are advantageous to your specific application. This only really applies to sidemount cave diving where a LP85 or LP120 offer better buoyancy characteristics than the FX100 or FX149.
Reason 3-you are able to get cave fills on them and you find a screaming deal on a set of LP tanks.

If you can't get cave fills, then you should never get LP tanks because they are horrifically inefficient in terms of weight:gas volume.
 
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