Tank Selection

[IndigoBlue]

Choosing a tank is often a bargain hunting proposition. That is why most divers first buy aluminum tanks. They cost less than steel, in the short term.

Divers who normally do not buy an aluminum tank, often buy a used steel 72 tank, because they seem to last forever, and they are also inexpensive as well. In the very long term, these are the best bargains out there.

SeaJay's analysis is technically correct. However not all dives are technical.

If you always dive shallower than 50 ft, and there is a 50 ft bottom under you, then any failure scenario should be able to be resolved by you ditching your weights and EBA back to the surface. Its not like you are diving to 330 ft on deco.

With a steel tank, you have less weight on your weightbelt. So my first suggestion would be to look for any bargain sales in your area for steel 72s.

If you are diving warm water as well, then an aluminum tank also becomes more feasible, since warm water does not require a lot of lead weighting to begin with. Adding 6 more pounds of lead to offset the tank is not a problem in warm water.

If you dive deeper than 50 ft, then everything SeaJay said is right on. But there are different ways to prepare for the failure contingencies as well. Buddy diving with each of you having a wing/bladder large enough to lift you both is one option. That is why instructors often wear larger capacity B/Cs, to catch and hold that run-away AOW student on the deep dive activity.

As long as you have sufficient ditchable weight, you can EBA in the event of a major B/C failure. With a thick wetsuit, you simply need more ditchable weight than with a drysuit. A lot more.

So your answer is going to depend on your exposure suit as well as your B/C. Generally speaking, an aluminum 80 will be your best bet, with a steel 72 possibly a good choice instead.

 

[LUBOLD8431]

For single tank diving in NE, I use either the PST E7-100's or a Faber HP-80. I like the PST 100's because I can use less lead than with an Aluminum 80, and yes, I still use a significant amount of lead (I either wear a two piece 5 mm wetsuit, or a drysuit). I dont dive AL 80's. For doubles, I have OMS/Faber 112's. I like steel cylinders much more than al 80's. With AL's I would have to dive with ALOT more lead. FOr me, its ridiculous to dive with AL 80's. I would hate to have that much lead on me. Even with doubles, I would need alot of lead. So, its steel for me. I only use aluminum cylinders for deco bottles, and drysuit inflation bottle.

 

[Curly]

...message truncated big-time...

...Of course, none of this is really that big of a deal - I'm just pointing out why I'd recommend that you buy AL80's as your first tanks and go steel when/if you begin diving dry.

Excellent info. Thanks. In short, yes, the negative buoyancy was a positive thing in my eyes. It would be nice lose some lead. Typically takes me a good 24 lbs. with the 7mm FJ and a single AL80. And I just don't want that much lead. Haven't written off the AL80. Thanks again for the thoughtful analysis. gfe

 

[SeaJay]

Glad to help. :biggrin:

Don't forget that in a wetsuit (especially a 7 mil FJ), that at depth you will lose a lot of buoyancy due to compression. Most estimate that their suits lose about 85% of it's inherent buoyancy at 85 feet... With as much as 70% lost in the first 30 feet of depth.

So... If your suit is 12 pounds buoyant at the surface, it'll be only about a pound and a half buoyant at 100 feet. It can vary considerably from suit to suit - I'm just using this as an example.

So... To compensate, you'll need to put 10.5 pounds of gas in your wing/BC at depth in order to be neutral. This increases to about 17 or 18 pounds if you've got a tank (HP100) full of air or nitrox.

Now, if at that point you have a catastrophic BC or wing failure, then you'll need to be able to "swim up" the missing 17 or 18 pounds. Since most can't swim up 17 or 18 pounds, you'll need to be able to ditch some weight.

Of course, this isn't a problem if you've got enough weight to ditch... If you've got at least 10 to ditch, you should be able to swim up the rest.

So... Back on land here... If you take your normal 24 puonds and subtract the weight that you'll save by going with a steel tank - say it saves you four pounds - will you have enough weight to be able to ditch?

The answer is yes... You'd still have 20 pounds of weight to ditch. So, the way I see it, just from what you've described here, you could probably do a single steel tank (especially if it was one of the E7's or E8's, or something with similar buoyancy characteristics) and still safely be able to get to the surface, even with a catastrophic bladder failure.

...Add doubles or more nonditchable weight somewhere else, and that might not be true. But for your case, it sounds like you should be okay.

There's a huge assumption that we're making in the first place here, though... And that's that you're correctly weighted at 24 pounds to begin with. For the sake of argument, I have assumed that that number is correct... But if it's not, then all of these calculations are going to be off. Just a word of warning.

Lastly, everything I've just reiterated concerns buoyancy only... Trim is a completely different issue. In short, you're taking the weight off of your hips and placing it on your back instead... What that does for your trim could be good, and it could be bad.

Anyway, you know my recommendation... Good luck with your decision. We'd really like to hear about your choice and how it affects your diving. Please let us know.

 

[Curly]

...

There's a huge assumption that we're making in the first place here, though... And that's that you're correctly weighted at 24 pounds to begin with. For the sake of argument, I have assumed that that number is correct... But if it's not, then all of these calculations are going to be off. Just a word of warning.
QUOTE]

Yep -- 24 pounds was perfect/proper weight for me this year -- wearing that particular suit, diving in fresh water, and with my current girth & body fat. I trying to lose some girth this winter (tougher as I get older...). 208 and hopefully heading to 185.

 

[NAM001]

I USE FABER STEEL LP95'S. sorry about the caps. i got them because i do not want to fool with the hassel of shops undr filling or not filling an aluminum tank. i had heard that some places will not fill with out an eddie test ect. not a problem with the steel. its lp so the any compressors can do it. i can over fill them for more capacity to 20% over with out feeling that i am close to pushing the limits 3000 psi 108 cf. whole different thread though. although negative the suit will counter that. weight swing is moot as it is .078 lb per cf no matter what the tank is made of. i use a 3/2 shortie and use 6-10 lead. 6' 230#. with a full suit you would need more. big difference from an al80 for me by about 6 lbs. i have 2 and am very happy with them. the tank comes with a combo yolk/din valve. i bellieve the inside is coated to prevent rusting. (again another thread) working is 2400, 2640 with 10% but many fill to 3500. never have to worry about cutting someone elses dive short from higher SAR, cant loose a bright white tank amongst the pink green and what ever colors ( for faber if its steel its white)

drawbacks. get trimmed and then use a rental al80 (on a tripp) and you are going to need more weight. cost 250 each, it does need a boot on it (round botomed) sometimes have had problems with dive boats not having a hole large enough to put the tank in when underway. ). it is 8" in diameter however so it will take an additional 3 " of strap to hold it in the bc.

good luck


KWS

 

[scubafanatic]

This year, I am seriously considering taking the plunge and buying my one piece of missing equipment -- a tank. Since I do not do much dive travel that doesn't require my truck, it's not a travel issue. It's more a peace of mind issue -- in that I know the tank's history, status, and can fix maintain the valve. Also -- since I'm looking at a LP steel 80/85/98 cf, there's the potential for greater single tank capacity. 90% of my dives are single-tankers, but the greater volume of the 85 & 98 would afford me more time (assuming buddy ain't an air hog).

Anyone have any recommendations? Ideally, I'd just go out and get a nice new OMS LP 98...but that's a little steep for a dude with four young kids.

Cheers,

g

Hi Curly,

Among my tank 'collection' I've got 3 OMS/Faber LP 85's (a single and a twinset)....I think you'd enjoy that tank..... @ 3000 psi it's a 97 cu. ft. tank and even at 3000 psi (overfilled a bit) it only weighs 38 lbs......not too long ( my 2 Faber LP 120's are a bit taller than I prefer and weigh 56 lbs full ) and not too short ( I've dove --but don't own---both LP 95 singles , in Cozumel, and twin LP 95's in Santa Rosa NM.....they did fine as singles, but I had 'issues' with them as doubles, as they're too short to easily reach back and do valve-shut-down-drills....otherwise fine in the water, but as doubles rather heavy on land.)

Also own a PST E7-120, a PST E8-130, an OMS/Faber LP 112 and a Scubapro LP 76 twinset......but I won't talk about them as none of them are on your 'list' as candidates.

I understand about your finite budget...... my OMS tanks, bought new, have run in the $350--$400 range (with boot,valve) .....maybe you can check out your local dive shops to see if they have what you want in a used tank? Unlike E-Bay, at the LDS you can verify condition prior to purchase.

(don't get me wrong, I'm a huge fan of E-bay, have bought a ton of gear there, and been happy with almost all of it....however, the only used tanks I've bought were my LP 76 twinset, which I've been very happy with.....otherwise it seems used tank deals on E-bay don't seem like bargains too often, not after you add in shipping/hydros/visuals/valve overhauls/repainting/tumbles/O2 cleaning that are often needed.)

Karl

 

[NAM001]

Hi Curly,

Among my tank 'collection' I've got 3 OMS/Faber LP 85's (a single and a twinset)....I think you'd enjoy that tank..... @ 3000 psi it's a 97 cu. ft. tank and even at 3000 psi (overfilled a bit) it only weighs 38 lbs......not too long ( my 2 Faber LP 120's are a bit taller than I prefer and weigh 56 lbs full ) and not too short ( I've dove --but don't own---both LP 95 singles , in Cozumel, and twin LP 95's in Santa Rosa NM.....they did fine as singles, but I had 'issues' with them as doubles, as they're too short to easily reach back and do valve-shut-down-drills....otherwise fine in the water, but as doubles rather heavy on land.)

Also own a PST E7-120, a PST E8-130, an OMS/Faber LP 112 and a Scubapro LP 76 twinset......but I won't talk about them as none of them are on your 'list' as candidates.

I understand about your finite budget...... my OMS tanks, bought new, have run in the $350--$400 range (with boot,valve) .....maybe you can check out your local dive shops to see if they have what you want in a used tank? Unlike E-Bay, at the LDS you can verify condition prior to purchase.

(don't get me wrong, I'm a huge fan of E-bay, have bought a ton of gear there, and been happy with almost all of it....however, the only used tanks I've bought were my LP 76 twinset, which I've been very happy with.....otherwise it seems used tank deals on E-bay don't seem like bargains too often, not after you add in shipping/hydros/visuals/valve overhauls/repainting/tumbles/O2 cleaning that are often needed.)

Karl

YOU ARE RIGHT ON WITH THE FABER LP 85 COMMENT. oops htere are the caps again. had i knows about the overfill capacities and the wilingness to over fill i probably would have bought the 85's instead of the 95's . by the time others have to surface i havve aometimes 15-1800 let in my lp95. i get my benefit with going in groups where i can find a match for me to maximize my dwn time. if i got a good deal on a pair of 85's i would probably buy some.

KWS