Tank Question - AL vs Steel

[I FA DAT]

Hello this question is a little green. I'm kind of new but I've learned a lot so far on this forum. I've been buying gear piece by piece. I'm looking to buy some tanks for diving offshore. So far I've only dove with AL 80's. What are the advantages of buying Steel 100s. How much more down time could I expect. The last 4 dives at 80 feet with Nitrox 32 I've averaged 25 minutes.

Obviously there is a big price difference with AL being $150 and Steel $350.
So is it worth the extra money?

Also on craigslist I bought a steel 120 for $50. I didn't realize what a beast it was until I set it next to a Al 80. Does anyone do regular diving with a tank that big?

Thanks, Trey

[N2Fixx]

My personal tanks are HP steel 100's and I love them. They are comparable in diameter to an AL80 but quite a bit shorter. Also, they are negatively buoyant throughout the dive, which I like. Your 120 that you picked up is likely a low pressure tank and I don't have enough experience with them to talk about them one way or another, so I will let someone else touch on that subject.
I have done some diving with HP steel 130's and I know I can turn into a bottom time animal with them...but, I try to stay out of deco as much as possible. The advantage that I could see with them is the ability to do multiple drops with one cylinder.

[stevemc1]

I have LP 120s and yes they are heavy, and if you put them up to 3000 or even 3300(they are 120 ft at 2400 psi) they will have 150-160 cu ft. They dont need any weight in the summer, and now with a wetsuit I need 6 to 10 lbs, depending on thge wetsuit. AL 80s hold 77 cu ft at 3000, and they need a lot of weight to get you down, and when they start to get empty, they float you up. real pain in the ass. That is why many people didnt want to get them when they came out, they were not right!

[IRONHEAD]

I am selling 2 newer al 80's to replace with one lp 108, my theory is I can double dive it yet I only pay for one fill instead of 2 and I only have to service one tank instead of 2 and I don't have to add 4 lbs of weight in my belt. if you dive shallow less than 80 foot dives aluminum is ok but if you dive 90 and deeper get into lp steels. hp steels are a waste for me because I can over jack a lp and get a ton of air in there at 3200 or 3400 psi. also run din connection if you want to jack your tanks up some.

[jfjf]

Originally Posted by stevemc1

I have LP 120s and yes they are heavy, and if you put them up to 3000 or even 3300(they are 120 ft at 2400 psi) they will have 150-160 cu ft. They dont need any weight in the summer, and now with a wetsuit I need 6 to 10 lbs, depending on thge wetsuit. AL 80s hold 77 cu ft at 3000, and they need a lot of weight to get you down, and when they start to get empty, they float you up. real pain in the ass. That is why many people didnt want to get them when they came out, they were not right!

The amount of bouyancy change depends on the volume of air consumed, not the tank. In other words, a 100 cu-ft aluminum tank will loose the same amount of weight as a steel 100 during a dive. An aluminum tank may become bouyant at the end of the dive, but the bouyancy change will be no more than a comparable steel tank.

Also the LP steels need to be filled to 2640 psi, not 2400 to meet the stated volumetric capacity of the tank.

I have both aluminum and steel tanks. I like being able to do multiple drops on the steel tanks, which is usually not practical with Al 80's for me. Large steel tanks (filled with nitrox) allow me to do longer dives than I could with an aluminum 80. If I fill the 80 tank with nitrox, I often run out of gas before I reach my no-deco limit for 60-100 ft depths.

[FredT]

Buoyancy on single aluminums sucks sludge diving wet or dry

Buoyancy on a good steel (PST or Worthington and a few other "off" brands) is generally a lot better diving wet or dry. As a rule you want to check empty buoyancy on the bottle before buying it. The old DOT 3AA "steel 72" is about the best tank out there for buoyancy distribution, but they aren't made any more.

Buoyancy on most double steels is right dangerous diving wet, but good diving dry.

Doubled aluminums shoud be used if diving wet.

As a general rule stages (deco or travel gas, and/or ponies) should be aluminum.

Doubled aluminums can have permanent ballast added to the bolt set to offset their bad buoyancy trim when they are doubled up.

The primary problem with AL tank buoyancy is that they tend to float you ass up when empty. Most of the negative in the tank is at the top, and it takes about 4 pounds in a boot weight to hold trim empty, which causes increased corrosion and a much shorter tank life.

[FredT]

BTW one of the boats I dive on has a limit of 3 tanks on board per diver due to deck space and payload limits. 3 120s fit just as well as 3 72s. Considering we normally do 3 to 5 drops per tank the 120s make much better sense logistically.

FT

[I FA DAT]

Thanks everyone for your replys. The steel 120 I bought is LP 2400psi and yes it's heavy empty. So the LP Steel 120 overfilled is the best choice for multiple dives with one tank. What are the advantages of HP steel 100 over AL 80 besides bouyancy? How much longer in general will a steel 100 last compared to a AL 80 in 80ft? Thanks, Trey

[chronos27]

I've done a lot of dives with steel 100s filled to 3300-3400 psi. I like the weight balance better and they increased my dive time. I'm going to rent 80s until I can afford the steel 120s. Worthington has a 119 and a 130 that weight and dimension wise seem perfect.

[WonderBoy]

No question, go with LP steel cylinders, especially if you can get them filled to 3,000+psi.
Just for an FYI, I am on the heavy side () and with a 120 filled to 3500 psi, a month or two ago I did 4 drops, each about 20 minutes at 90 feet shooting fish. That's one cylinder, and still had about 300 psi in the cylinder when I was done. The advantage is clear at that point to me...

[eward4]

Worthington 130's are what I use. I don't have to put on any weight even with a 3mm wetsuit and I run out of bottom time way before air at 100'. Diving Nitrox of course.

[Gary H]

Originally Posted by I FA DAT

... How much longer in general will a steel 100 last compared to a AL 80 in 80ft? Thanks, Trey

A full AL80 is 77.4 cubic feet. A full HP100 is 104 cubic feet. How much longer will the HP100 last? About 34%

[keezdiver]

i suggest waiting on the tank purchase. figure out how YOU dive, and how you use air.

everyone talks up the steels like they are touched by god. but i get similar usage out of my AL80s.

with a 3mm wetsuit i can dive with as little as 4lbs of weight total. only time i have trouble is when i get my tank well below 500psi and have to do a free-floating (no line) safety stop.
normally i dive 6lbs....and i'm perfectly balanced on the bottom...almost no air in the BC, which means nice and streamlined.

as for bottom time. i regularly dive 2x on one al80.
this summer i did many dives on the Tbolt in 125ft, shooting fish, and generally i would just barely blink into deco (air). usually i'd come up with 1500-1700psi of air.
i'd take the tank into the shallower reef and dive the 70-80ft ledges for another 30mins on the same tank. generally hitting the deck with 300-500psi after doing a 5min safety stop.

if you don't beleive me....ask Swimsuit Whore...she does it right next to me. or talk to Mobile Diver...steve hates my air consumption. he's even commented that i don't need bigger tanks, i can get into more than enough trouble (deco wise) on an AL80.

so for me....i don't see the need to add so much more weight to my back. both while diving, while loading gear and on the deck.
besides...in the keys they rape you on overfill charges for big tanks...especially for nitrox.

[matts1w]

The issue with LP tanks is not being able to get fills to 3000 at many places.

You might also want to look at the HP 119s from worthington. They are kind of short and fat, and I find they trim out very well. I am not all that tall, and find the 120s way too long. Plus, if you pump them up to 3600 it is a ton of gas. Even at the 3442 pressure it is plenty of gas for most divers. Wearing a five mil and hooded vest I am still very heavy with the 119s and need zero weight (Im 5'6 and 158 lbs.). Even at 400 psi I can hold 15 feet with no effort.

If you do go with high pressure tanks and huge fills, you might want to convert your regs to din. Not everyone does this, but it is a stronger connection and probably the best practice. Let's face it, most of us when spearfishing are diving solo whether we believe it or not. Minimizing an o-ring blow is a good idea.

[Grin]

I say, get HP120s if you get HP steel tanks. I finally did it. They are about 2 inches taller than an aluminum 80 is all. Andof course, the bouyancy is superior to aluminum. If your going steel don't screw around with 100s. 100s are nice, I'm just saying why screw around with a negligable difference, just go all the way and get a real difference. The difference is: Why add 5-10 minutes of possible extra time getting 100s. If you want HP 100s, it is worth taking a look at getting LP85s instead. The reason is HP100=3500PSI for 100 and LP85s=2600PSI for 85. If you can get routine fills in your 85s to 3000 you will have 100PSI in a tank that is much cheaper up front and the same size as a HP100. And it is possible you might get fills to 3500 in the LP85s, so now your at around 110+PSI. Good luck getting hot fills in your HP 100s, actually you might struggle to get correct fills to 3500 in them. LP85s are likely to get 3000+ without even asking. I have a couple LP85s and a couple HP120s. The LP8s are very nice if you cannot afford to go all the way and get 120HPs. If I were to do it all agian I'd just get a bunch of HP120s. Theya re not nearly s big as you might think. Basically a few inches taller than a Al80 or HP100. And they definatly remove the factors about coming up with less PSI than you should and allow multiple dives on one tanks etc... A HP 100 is just a little nicer than a AL 80 and mostly becasue of the bouyancy factor rather than more capacity. The capacity of a HP100 can be very close to the same as a AL80 if the fills are not correct.