What tank: AL80 or steel?

[eelnoraa]

Thank you all for you advices and comments.

Here is some more info about my siutation. I am a very new diver, OW certidifed about 2 monthes ago, and had about 10 dives since class. To the question of what kind of dive I am looking to do, I don't know what to say besides recreational dives. I plan to take AOW class and maybe a few more advanced class after that, but cave, tech .. are NOT on my list as of now.

I home dive site is north CA, Monterey to be specific, so cold water. Occassinally I will go to south CA. I think it is still considered as cold water. Currently, I am using SS backplate, rental AL80. With 7mm wetsuit, I need 18lb total (4 on cam band, 14 on belt). I think I am over weighted by a pound or two, but I am not sure, need to test this weekend. I am a smaller person, 5'6", 140lb. Size wise, I don't think I want anything longer than AL80.

Someone mentioned used AL80 in current hydro should be $100 or less?? then I don't have a good deal. The seller asks for $80 for a 2004 AL80, but out of hydro. I think hydro costs about $50, so making the true cost for putting in service for $130.

 

[Gombessa]

I home dive site is north CA, Monterey to be specific, so cold water. Occassinally I will go to south CA. I think it is still considered as cold water. Currently, I am using SS backplate, rental AL80. With 7mm wetsuit, I need 18lb total (4 on cam band, 14 on belt). I think I am over weighted by a pound or two, but I am not sure, need to test this weekend. I am a smaller person, 5'6", 140lb. Size wise, I don't think I want anything longer than AL80.

We dive in the same waters. Steels are preferred over aluminum in Monterey because they allow you to remove some weight off your weight belt. 14lb on a belt is kind of a pain to deal with, wouldn't it be nicer on the surface to be able to shed 4-5lb or so?

As a rule of thumb, aluminums are 4lb positive at the end of the dive, while steels are neutral or 1-2lb negative. That means, to be properly weighted to hold your safety stop at the end of the dive, using a steel will let you eliminate from your weight belt the difference in buoyancy between the aluminum and the steel tank - roughly 5lb.

I would highly recommend getting steel for local diving, here or in LA. LP80/85s, HP80s and HP100s are all popular choices, hold a bit more gas than AL80s, and let you lighten up your weighting.

Someone mentioned used AL80 in current hydro should be $100 or less?? then I don't have a good deal. The seller asks for $80 for a 2004 AL80, but out of hydro. I think hydro costs about $50, so making the true cost for putting in service for $130.

80 is a good ballpark for used, in-hydro AL80. If you're set on an AL, here's a brief list of what you should look out for:

1. Ask what the manufacture date is (date of first hydro). If it's prior to 1990, some shops just won't fill it, so it's easier if you just avoid those altogether.

2. If it's out of hydro or viz, ask that the seller guarantee a full refund if the tank fails and needs to be condemned. It's rare, but it could happen, and this type of arrangement is standard for used tank transactions.

3. Confirm the type of valve that's on the tank. You're probably looking for yoke, and most are, but once in a while they have DIN valves and you'll need to either get a plug or swap out the valve ($30-50).

 

[DCBC]

Like anything, it's a matter of preference. A persons size and the dimensions of the cylinder are a consideration as is price. Buoyancy is another factor. As an example:

A Luxfer 80 is just over 1 lbs. negative when it's full and just over 4 lbs positive when empty.
A Faber 72 steel cylinder is just over 8 lbs negative when full and over 3.5 lbs negative when empty.

After neutral buoyancy is achieved, the Aluminum cylinder buoyancy change (full to empty) is approx 5 pounds positive and with the steel 4.5 lbs positive (assuming neutral buoyancy at the beginning of the dive). Although there are considerations for the type of BC you have and if you are diving in warm or cold water (amount of weight required), it really boils down to personal choice.

 

[Van Isle]

The kind of deal that you have found comes around ALL THE TIME! There is no need to rush a decision on this one at all. I picked up 4 alu 80's 2 weeks ago, in vis and hydro, for $85 a piece.

One thing to note: according to the DAN report, one of the major contributing factors to diver accidents, besides running OOA or diving beyond training, is failure to establish buoyancy at the surface. For a new, OW diver that means that you WANT ditchable weight on the belt (or in an integrated system.) Ponder that before you take ~6lbs off the belt for an HP100.

 

[Gombessa]

For a new, OW diver that means that you WANT ditchable weight on the belt (or in an integrated system.) Ponder that before you take ~6lbs off the belt for an HP100.

Whether or not you WANT ditchable weight to maintain positive buoyancy at the surface depends on what your buoyancy is at the surface (right, duh ) The OP listed her current rig as:

Currently, I am using SS backplate, rental AL80. With 7mm wetsuit, I need 18lb total (4 on cam band, 14 on belt).

Assuming her weighting is proper, if she moved to a steel tank and kept her cam weights, she would still have 10lb on a belt, and dropping that belt would leave her positively buoyant at the surface even with a full tank. If the trim characteristics of the steel allowed her to lose the cam weights, she would still have 12lb on the belt and would be even more positively buoyant at top.

In Monterey, chances are in singles you'll be diving with a substantial weight belt no matter what you try to do. I dive a steel tank with SSBP and wSTA and still need 10-16lb on a belt.

 

[Van Isle]

Whether or not you WANT ditchable weight to maintain positive buoyancy at the surface depends on what your buoyancy is at the surface (right, duh )

However, if we want to be ABOVE the surface, where we can comfortably breath uncompressed gas and not have our faces in the waves, our parts of bodies and rigs that are IN the water have to be buoyant enough to support the parts that we want ABOVE the water. All I suggest is that the OP ponder which of, if any, 8, or 10, or 12 lbs of ditchable weight fit in her comfort level. When trying to get in to a dive boat. In a 2 foot chop, during or after some emergency.

VI

 

[Gombessa]

However, if we want to be ABOVE the surface, where we can comfortably breath uncompressed gas and not have our faces in the waves, our parts of bodies and rigs that are IN the water have to be buoyant enough to support the parts that we want ABOVE the water.

The back-of-the-envelope calcs I posted above are with a full tank and ZERO gas in the wing. If the OP switches to a steel tank and ditches their weight, they're going to be 4-8lb positive in the water before even touching their inflator. Once they fill up their 30-40lb wing, they're even more buoyant. As far as the margins go, whether or not you consider a catastrophic wing failure, that's pretty good.

 

[stargost]

Eelnoraa,
I'm close to your situation in # of dives, also dive cold water (SoCal), and faced same dilemna. So I started renting AL80, and had to carry 26lbs of weights to be sure to remain at bottom when reaching 500psi :-(
Then looking at other divers, and reading this forum, I took a big jump and got a HP100. Same size, same weight (~), but I dive with less than 20lbs, and can stay significantly longer (I'm not the newbbie running out of air, forcing the pro to come back earlier ;-) - Note: "They" dive HP72, but also have tons of different size, models, etc !!

So I really like the HP100. Of course, I paid twice more than an AL80. Also it is unlikely I'll bring it for dayboat and so on. But for regular shore dive, it is really good.

 

[Van Isle]

An object can only express buoyancy in the water if that object is displacing that water. Everything above the surface of the water is dead weight and must be supported by the buoyancy of everything below the water line.

For example: I can float on the surface of pool, in my shorts, when holding a breath. Despite the fact that I am thus "positively buoyant" I cannot walk on water. Even if I wear a wetsuit and an alu 80 that is 4lbs "positively buoyant" I still cannot walk on the surface of the water. That buoyancy MUST be displacing water or it is dead weight.

So to keep your head, upper torso, top half of a tank, valve, 1st stage, etc etc, above the water requires a lot more than a back of the envelope calc. Or little more than a proper weight check and some ditchable weights IAW sport diving best practices.

Archimedes: It's not just a good idea. It's the LAW.

 

[Gombessa]

So to keep your head, upper torso, top half of a tank, valve, 1st stage, etc etc, above the water requires a lot more than a back of the envelope calc. Or little more than a proper weight check and some ditchable weights IAW sport diving best practices.

The reality of the situation is that you need to keep your head (+/- 10lb) above water. Also, the vast majority of your buoyancy (consisting of your exposure protection from the neck down and the wing) will be beneath the water keeping your head up, since at the surface the top of the wing will not be at head level. I don't know anyone who figures their lift with the purpose of getting their entire "upper torso and top half of a tank" above the water, but if that's what you're aiming for, then by all means do what you need to do to get there.