Weighting for steel tanks: LP 72 vs HP 100

[anchochile]

I was trained on Steel 72s and that's all I've used so far for diving Monterey. I'm interested in trying out a larger capacity tank, probably a Steel HP100, so that I can do some longer dives like the Metridiums.

I've found lots of conflicting specs on the buoyancy of Steel 72s and HP 100s. It seems like most sources say that LP 72's are anywhere from -1 to +1lbs when empty, and for HP100s I've seen stats ranging from -3.5lbs to neutral.

If they're both neutral when empty, I guess my weighting would stay the same, but it's a bit hard to tell. It would be great to drop a lb or two from my belt to compensate for the heavier tank on my back if I could.

Can anyone with direct experience with both of these tanks share their experience on buoyancy & weighting?

Thanks!

 

[runsongas]

i use roughly 2 pounds less on the belt with a hp100 than a lp72 with a pst hp100 vs pst lp72. the faber hp100s and worthington hp100s are similar with the worthington being slightly more negative by a pound or so.

the outliers are the faber 3180 tanks and asahi/heiser hp100s which are significantly more negative.

 

[tbone1004]

@anchochile
Worthingtons are bricks and you can take 2-4lbs off
Fabers are going to be damn near identical
PST's are going to be a pound or two less.

PST or Faber wouldn't get me to change my weighting. Worthing I would take either 2 or 4lbs off. 4lbs may make you feel a smidgen light

 

[anchochile]

i use roughly 2 pounds less on the belt with a hp100 than a lp72 with a pst hp100 vs pst lp72. the faber hp100s and worthington hp100s are similar with the worthington being slightly more negative by a pound or so.

the outliers are the faber 3180 tanks and asahi/heiser hp100s which are significantly more negative.

Thanks! I don't own tanks - I rent from my LDS and am not sure who the manufacturers are for the tanks, but I'll keep an eye out next time and start with your suggestion of 2lbs less.

 

[rjack321]

I'd take off 3lb but 2 is in the ballpark too for all the tanks @tbone1004 listed. 4 is probably too much UNLESS its a 3AA 3180+ psi faber. In which case take off 8. Those suckers are seriously heavy.

 

[TrimixToo]

Take one of each to the dock, full or empty but the same for both. Bring a piece of rope and a luggage scale. Weigh each underwater, suspended from the rope. Subtract the weight of the gas in each tank (.0862 lbs/cubic foot, IIRC, but look it up!). Do the arithmetic. This accounts for all the variations so long as your LDS has one kind of steel 72 and one kind of HP100.

 

[Billy Northrup]

100's are perfect for California NDL diving. My rule of thumb is take off 6lbs what you dive with an AL80 and be neutral at 500lbs near shore.

 

[socaljohn]

I dive lp72 and Worthington up 100, I have a 5lb hard weight mounted on the 72 with a hose clamp. All other weight some. So I add 5 using the 72.

 

[2airishuman]

I dive both as well as other steels.

There is some variation in buoyancy among purportedly identical cylinders due to inherent variations in the manufacturing process, even for one manufacturer. I believe this is probably due to wear on the tooling over time. Also as noted upthread, PST cylinders are overall typically slightly lighter, Worthington typically slightly heavier, Faber somewhere in between. This affects both dry weight and buoyancy.

You also may find that you typically surface with a larger reserve, and you may choose to carry less lead as a result.

I primarily dive LP72s and HP120s when I dive single cylinders. My HP100s are all twinned. When I switch from an LP72 to an HP120, I take off 1 pound if going to a PST and 4 pounds if going to a Worthington HP120.

My advice would be to take off a pound or two at most, then adjust based on the amount of air in your BC at the safety stop.