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Bigg_Budd
10-12-2007, 09:48
Just picked up my first steel tank (x7-120) after diving nothing but steel and AL 80s. I've got a couple of questions for you experts...

The tank is -11 full, -2 empty. So, seeing as how there is a +9 lbs swing in buoyancy during the dive, will this mean I will always feel heavier at the beginning of the dive?

I'm diving fresh water, and normally use 6-8 lbs in my shorty, 8-10 in my full 3 mill. Given the tank stats, I'm hoping to remove ~6-8 lbs of lead. My plan is to dial this in by strapping the tank on with 500 PSI, and figuring what weight is needed when empty. Is that good plan?

Since the tank will always be negative during the dive, I guess ditching my weights (or what's left of them) is kinda useless. Is that true? :)

What questions did I not ask? What else do I need to know about diving steel?

Thanks for the help!

BobArnold8265
10-12-2007, 09:57
I switched to steel tanks a number of years ago. If I remember correctly, I was able to take off between 6 and 8 pounds of lead when I went from a AL80 to S100 tank. I also bought a couple of steel 80s for my wife. They actually weigh slightly less than the AL80s and she got to shed 2 to 4 pounds of lead.

As far as ditching weights go, even with your steel tank, you will probably still be positive and likely will require a fw pounds of lead. Even though it's not much, in an emergency, you would still need to ditch your weights.

MSilvia
10-12-2007, 10:45
So, seeing as how there is a +9 lbs swing in buoyancy during the dive, will this mean I will always feel heavier at the beginning of the dive?

Yeah, and if you think that's a big swing, you should try my Asahi HP100 doubles! I'm like a freakin' stone at the beginning of a dive.


My plan is to dial this in by strapping the tank on with 500 PSI, and figuring what weight is needed when empty. Is that good plan?

That's a great plan... exactly what I'd recommend.


Since the tank will always be negative during the dive, I guess ditching my weights (or what's left of them) is kinda useless. Is that true? :)

The tank will always be negative, but assuming you have a wetsuit, etc, you should still be a little positive if you ditch. If not, you need a redundant buoyancy source, like a drysuit or double bladder wing. You could use a lift bag or SMB for extra buoyancy in a pinch, but that shouldn't be your "plan B".

subsur
10-12-2007, 10:52
ditching weights is not necessarily pointless. imagine you are at the end of the dive, almost no air in the tank. your tank is -2 lbs, no air in BC and XXX lbs on your belt. Your 3mm wetsuit is very bouyant, definitely more buoyant than +2 lbs, so the positive buoyancy of wetsuit will overcome -2 lbs of your tank if you drop your weights.
you will always be heavier in the beginning of a dive because you use the air that adds weight. as you said 9 lbs difference in your case.
you did not say what you used to dive with (you said your dived with both steel and Al but no further info). so hard to answer.

skdvr
10-12-2007, 11:00
The only numbers that matter are the empty weights. An AL 80 is a little over 4 lbs positive and your steel is -2 so you should be able to take off 6 lbs. That is exactly how much I add when I switch from my HP 130 to an AL 80, and I have just enough weight at the end of the dive with an empty tank. Yes you will be pretty heavy at the begining of the dive but you will get use to that. The good thing is that the extra weight is all centered on your back. Just remember that when you are using the 120 to just let enough air out of your BC to start your descent. If you just open the valve and dump everything like you probably do with your AL 80 you will rocket to the bottom. If I am descending to a deep spot I just start my descent and then add little bursts of air to keep me from stiking myself into the mud bottom like a dart.

Phil

Bigg_Budd
10-12-2007, 11:03
Great stuff guys, just what I needed. Thanks for quick response, and the great advice.

Cheers!

Scubastud16
10-12-2007, 17:26
I like the 500 psi idea...I need to try that one! (I'm used the PADI pre-dive buoyancy check).

Splitlip
10-12-2007, 20:19
Just picked up my first steel tank (x7-120) after diving nothing but steel and AL 80s. I've got a couple of questions for you experts...

The tank is -11 full, -2 empty. So, seeing as how there is a +9 lbs swing in buoyancy during the dive, will this mean I will always feel heavier at the beginning of the dive?

I'm diving fresh water, and normally use 6-8 lbs in my shorty, 8-10 in my full 3 mill. Given the tank stats, I'm hoping to remove ~6-8 lbs of lead. My plan is to dial this in by strapping the tank on with 500 PSI, and figuring what weight is needed when empty. Is that good plan?

Since the tank will always be negative during the dive, I guess ditching my weights (or what's left of them) is kinda useless. Is that true? :)

What questions did I not ask? What else do I need to know about diving steel?

Thanks for the help!

No matter what cylinder you are using you will be more negative at the beginning of the dive than the end of the dive.

Doing the math, your new 120's are almost 10 # more negative than an Al 80 at the beginning of the dive. 7 # at the end. so if the weights you carry are based on an Al 80, you should be able to shed about 7 # from what you have been carrying.

..............................empty......full
Luxfer 80..................+4.4 ......-1.4
Worthington X7-120.....-2....... -11

texdiveguy
10-12-2007, 21:45
Jason....I am guessing you will do fine with no additional weights.

danielh03
10-13-2007, 04:27
I am looking at a HP 135... any experiences out there?

texdiveguy
10-13-2007, 08:37
I am looking at a HP 135... any experiences out there?

I dive a PST HP130 when diving single.....it is really nice.

CompuDude
10-13-2007, 14:27
I am looking at a HP 135... any experiences out there?

Fricking huge water heater of a tank. Great for boat dives where you want big BT (assuming you're allowed more than 45-60 min), but I lugged one around on shore dives ONCE and decided I'd rather carry doubles if I need that much gas on a shore dive.

ScubaBoy
10-14-2007, 18:17
I have a steel 80, and with 500lbs of air and no wetsuit (in a swimming pool) I'm perfectly buoyant (floating at eye level).

My instructor said some divers prefer steel because of the buoyancy at the end of the dive -- not as drastic a change as alum.

Splitlip
10-14-2007, 18:25
I have a steel 80, and with 500lbs of air and no wetsuit (in a swimming pool) I'm perfectly buoyant (floating at eye level).

My instructor said some divers prefer steel because of the buoyancy at the end of the dive -- not as drastic a change as alum.

Actually the change is the same given the same volume of gas. Steel does not get so positive when empty at the end of the dive. Less additional balast required for a cylinder that weighs about the same or less on the surface.

CompuDude
10-15-2007, 02:13
I have a steel 80, and with 500lbs of air and no wetsuit (in a swimming pool) I'm perfectly buoyant (floating at eye level).

My instructor said some divers prefer steel because of the buoyancy at the end of the dive -- not as drastic a change as alum.

What splitlip said.

Also, a steel 80 is often only 1-2 pounds negative when empty. So it makes sense it would not affect your buoyancy much in that states.

Bigg_Budd
10-15-2007, 09:48
I dove the tank this weekend. It was friggin' awesome. I went in a little heavy on the first dive, but was able to dial it in once I hit 500 PSI. I was able to strip 6 lbs of lead!

The bottom time was kick ass. I still had 1200 PSI left after a 45 minute dive. My buddy was pissed. :)

Splitlip
10-15-2007, 11:32
I have a steel 80, and with 500lbs of air and no wetsuit (in a swimming pool) I'm perfectly buoyant (floating at eye level).

My instructor said some divers prefer steel because of the buoyancy at the end of the dive -- not as drastic a change as alum.

What splitlip said.

Also, a steel 80 is often only 1-2 pounds negative when empty. So it makes sense it would not affect your buoyancy much in that states.

Here are stats for an 80 AL and 80 steel. wt,bouyancy empty, buoyancy full


Luxfer 80 ..........................31.38 .............4.4 ...........-1.4
Faber FX-80 ......................28.6 ..............-1.74 ..........-8.05

BSea
10-15-2007, 11:46
I dove the tank this weekend. It was friggin' awesome. I went in a little heavy on the first dive, but was able to dial it in once I hit 500 PSI. I was able to strip 6 lbs of lead!

The bottom time was kick ass. I still had 1200 PSI left after a 45 minute dive. My buddy was pissed. :)

I have a 120, and many times I use it for 2 dives. Beats haulin another tank.

CompuDude
10-15-2007, 12:33
I have a steel 80, and with 500lbs of air and no wetsuit (in a swimming pool) I'm perfectly buoyant (floating at eye level).

My instructor said some divers prefer steel because of the buoyancy at the end of the dive -- not as drastic a change as alum.

What splitlip said.

Also, a steel 80 is often only 1-2 pounds negative when empty. So it makes sense it would not affect your buoyancy much in that states.

Here are stats for an 80 AL and 80 steel. wt,bouyancy empty, buoyancy full


Luxfer 80 ..........................31.38 .............4.4 ...........-1.4
Faber FX-80 ......................28.6 ..............-1.74 ..........-8.05

Are you agreeing with me or disagreeing? We're talking about steel 80s, so the Luxfer stats aren't relevant... the 500psi buoyancy is just what I said it was... 1-2 lbs negative. Big difference from alum tanks, which would be ~4 lbs positive in the same state.

Splitlip
10-15-2007, 15:04
I agree.
I probably should have put it up under my my response to scubaboy. But -1.74 IS pretty close to "1-2 lbs negative" :)

Looking at the stats we see the steel weighs less, the change in bouyancy is about the same (77cf v. 80) and the steel tank is 1-2 # negative at the end.
I prefer the steel.

RECDiver
10-15-2007, 15:52
Try diving the steel tank without weights. If I am using a full 3mm wetsuit and my small 80cuft steel or my 100cuft steel I don't need any weight. If I use my ScubaPro Profile .5mm I have to use an aluminum cylinder. I am just too heavy with the steel and it tends to want to roll to one side sometimes. The only suit I need weight for is my drysuit with my BP/W and steel 100.

DZorn00
10-19-2007, 13:49
I guess I need a steel tank, currently in my 6.5 ml shorty I need 48 lbs of weight with an AL80. Steel sounds so much easier.

fire diver
10-19-2007, 14:08
I guess I need a steel tank, currently in my 6.5 ml shorty I need 48 lbs of weight with an AL80. Steel sounds so much easier.

THis has got to be a joke right?

cummings66
10-19-2007, 18:07
It's certainly the largest amount of weight I've ever seen a diver use, especially with a shorty. I use 4 lbs of lead myself. 8 with a drysuit.