Thinking about buying a tank

[TxAgDiver]

Howdy,
I recently got open water certified and am going to do nitrox/AOW next month when we return from vacation. I just bought all of my gear except a tank (zeagle stiletto, hog D1 regs, cressi wrist comp, etc etc). During my open water certification dives i dove with a 3-4-5mil wetsuit, AL80, and about 9 lbs of weight. This wasnt a perfect amount of weight, i think I was still a little light when that tank got close to empty (500 psi) but it was hard to tell how i was floating with 3' visibility. Now i am researching and trying to decide which tank is best for me. And like everything else with scuba... there are wayyy to many options.

I think i have narrowed it down to 3 sizes: AL80, HP100, and LP85. I really like the steel tanks for their compact size and larger air volume. I am an air hog right now (new diver) and can tear through that al80 in no time. I am afraid the steel tanks would put me too close to not carrying any ditchable weight, since i will probably only need 10 lbs at most. I am a fairly strong swimmer so I am almost positive I could swim up either HP100 or LP85 but id rather not have to, i like the safety cushion of dropping weight and being positively buoyant in the case i become injured for whatever reason (this opinion may change with more experience, but it is what it is right now). The 3-4-5 mil wet suit i wore for open water was also a rental, the one i purchased is a 3/2 since i will be diving mostly in the Caribbean/Gulf, and thus providing less buoyancy than the suit i had for my open water class and lowering my overall needed weight even more.

So what do yall think? Will the steel tanks make me drop too much weight? I know with either steel or aluminum it will take some time to work out peak buoyancy, but is achieving perfect buoyancy with an aluminum tank really that much harder?

The hp100 is -10 full and -2.5 empty which is a swing of 7.5lbs.
The hp85 is -7.1 full and -0.7 empty which is a swing of 6.4 lbs
The aluminum 80 is -1.4 full and 3.4 empty which is a swing of 4.8lbs. (all weight values taken from scuba.com)
I know having the weight remain negative is better, but there it seems like with less variation in the AL80, it would be better of buoyancy? What am i missing here?
I also like the idea of getting used to an AL80 tank so that when I rent tanks, everything will be the same.

So basically what it boils down to, what suggestions would you have for a new diver in regards to tank selection with the above information? If i left anything out or yall need some more info just let me know. I am 5' 11" 180 lbs.
Thanks in advance, ive already got a ton of useful information off of this site!

 

[Scared Silly]

HP100 ... the steel std. cylinder.

 

[elan]

What manufacturer are you considering? Depending upon the mfg the buoyancy is different. The swing will be the same for the same volume regardless of the tank. So you have to take into account the buoyance whe closr to empty.

If you worry about being to negative you can go with a faber lp85 which IIRC is slightly positive when empty.

If you are a strong swimmer your lung capacity should be big so you can probably shift at least 5 lb from you average lung volume. And that helps a lot if you need to swim up

 

[RickyF]

Where and what depth will most of your local diving happen? Some of my local diving is 50-60' and I use an aluminum 80 which gives me ample air supply. Other wreck dives I do are 100-110' and I use a Steel 120 with nitrox which gives me plenty of air and I carry a 15 cf backup.

 

[halocline]

Sounds like you're thinking about it pretty well. I would not worry about ditchable weight with only a light wetsuit and single tank. You'd never want to ditch weight at depth anyway (another topic, I guess) and so you're really talking about being able to stay positive on the surface in the event your air is off or your BC isn't working. That only takes a couple of pounds, and you'll still have that with the steel tanks.

You really do need to specify where you're diving and what depth you're talking about. I live in TX too, and I use LP72s or AL63s in shallow local dives like aquarena, and a HP100 in the gulf, usually at the flower gardens. I have one AL80 which I don't use very much; it lacks the advantages of the other tanks. For shallow dives, it's great to have small tanks that are really easy to walk around in and close to neutral empty. For the deeper gulf dives, it's nice to have the extra air.

If I could keep only one tank for local TX diving, it would probably be a LP72 (which you can probably find for under $50 if you look around) and for the gulf (offshore) the HP100 is tough to beat. I'd consider one of the faber blue steel 100s; they're a bit lighter, I think 1lb negative empty.

 

[TxAgDiver]

Thanks for all the responses, sorry it has taken me so long to get back. As far as what depths and where I will be diving, that is a great questions. Since I am newly certified I will dive anywhere I can! haha. But really i guess the most visited places around here would be the flower gardens (shalowest reef is 60ish) and the Clipper (60-100 i think). These dives wont be done for a while until i have more experience, but they are on my list of what i want to do. Also diving the rigs offshore, depth varies out there so i dont really know. I am leaning heavily toward the HP100.

Halocline, where do you like to dive? SA is only about 3 hours from me so if you have some good spots around there send me a PM, always looking for places to go and people to dive with. Our first trip will be to key largo in 2 weeks (probably not enough time to get me own tank, but thats no big deal). Cant wait!

Edit: I do plan on going nitrox later on as well if that makes a difference,

 

[halocline]

90% of my local diving is in aquarena springs, maximum depth 20 ft. Aquarena is closed while they're doing a major renovation to the site, and nobody seems to know when it will re-open. Hopefully sometime this summer. To dive there you need to take a course, then you volunteer dive and do maintenance work on the springs.

Other central tx spots are the comal river, lake travis, medina lake for the really desperate, and some others. Check out the tx swamp divers forum and you'll get all sorts of opinions about the local diving. I suspect lake amistad isn't too bad, but it's a bit of a drive.

 

[TxAgDiver]

Thanks again halocline.

I went in to my LDS today to pick up some stuff. I asked about tanks and they said that steel tanks need to have the air changed every so often (i think they said 4-5 months). Any one else heard of this? Its the first ive heard of anything like that. If that is the case, i may go with the aluminum. Keep in mind, a visual inspection comes with a year of free fills, so i dont think they were saying that just to get more money. If any thing it will be more work for them, even though it isnt too hard.

 

[TSandM]

I've never heard anyone say that about steel tanks, and there is no reason why a good, dry fill should need changing.

Going back to your original question: Swing weight on a tank is a function of its gas capacity. Air weighs approximately one pound for every 13 cubic feet, so an aluminum 80, which has 77 cubic feet of gas in it at working pressure, has about 5.5 pounds of air in it, so from full to completely empty would be a swing weight of 5.5 lbs. An HP 130 has ten pounds of air in it, so if it's 1 pound negative when empty, it will be 11 lbs negative when full. So you can see that swing weight has nothing to do with tank material, but only with tank capacity.

What the weight swings AROUND, though, is a function of material. Aluminum tanks cycle from slightly negative to several pounds positive. Steel tanks generally cycle from very negative to slightly negative. This is why you need less ballast with a steel tank. Given what you have said about your suit and your prior weighting, I suspect you would probably need little or no extra weight with an HP100 and a 3 mil suit -- maybe just a couple of pounds. And although a lot of us don't worry too much about ditchable weight, it's not an unreasonable concern for brand new diver. It's hard to come up with circumstances where you would ditch weight at depth, but if you have some kind of issue on a dive that leaves you on the surface pretty freaked out, it's nice for your buddy to be able to render you solidly buoyant.

As long as you are doing the dives which are recommended for a newly minted OW diver, above 60 feet in depth, an Al80 is probably a quite reasonable tank for you. They're cheap and readily available, and can be pretty easily resold, either to another new diver or to someone who wants a stage or deco tank. They are heavy on land for the amount of gas they hold, but if you don't have to carry much ballast, it isn't such a big deal.

For your future diving, the HP100 would be a better choice, because a single Al80 is a pretty marginal gas supply for dives in the 100 foot range (read NW Grateful Diver's gas management article on his website to find out why). But steel tanks are more expensive than aluminum, and HP steels are the worst. Steel tanks also corrode and have to be cared for a bit more carefully, and are susceptible to damage if you get boat fills that are wet.

Your concern about the dive shop's statement about changing out gas makes me think you're thinking you might have months on end where you don't dive -- in that case, you might consider buying the inexpensive tank and seeing how things go, before investing in the steels.

 

[redacted]

Don't think about one tank. Think about the tanks you will need.

An Al 80 is pretty much the workhorse for TX diving. That is probably the best place to start. And an HP 100, with nitrox, is about perfect for the Flower Gardens. I remember reading a thread about wet fills in steel tanks actually reducing the fraction of O2 in a steel tank. Ask you LDS what they are pumping that they need to make such a recommendation. Your gas consumption will get better with experience and you may want to think about smaller tanks for some of our diving, but that Al80 will work fine wherever that smaller tank may be appropriate.

I'd recommend starting out with an Al80 and add the HP 100 for your first FGB trip. That does mean changing weights a bit between a 2-tank dive but that should not be a problem. And keep a skeptical eye on your LDS.