Diving Steel

[Bigg_Budd]

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]

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]

Originally Posted by Bigg_Budd

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.

Originally Posted by Bigg_Budd

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.

Originally Posted by Bigg_Budd

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]

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]

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]

Great stuff guys, just what I needed. Thanks for quick response, and the great advice.

Cheers!

[Scubastud16]

I like the 500 psi idea...I need to try that one! (I'm used the PADI pre-dive buoyancy check).

[Splitlip]

Originally Posted by Bigg_Budd

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]

Jason....I am guessing you will do fine with no additional weights.

[danielh03]

I am looking at a HP 135... any experiences out there?