Tanks and weighting

[NWA7265]

I’m tryin to figure out how different tanks effect weight needed.

I currently dive a steel 100 and I need 30# of lead when I dive my drysuit with 3 layers.

my instructor dive twin steel 100’s and doesn’t need any weight. But he said when he dives with just one steel 100 he needs 20# of lead

he told me if I go to two tanks I will probably not need any weigh either. So I’m looking at tank specs and trying to figure this out.

what exactly matters about the tank specs
HP100 is 34lbs empty and has a full buoyancy of -8.41lbs and an empty buoyancy of -.59lbs
Does the 34lb empty weight number matter? Or does the buoyancy numbers only mattter?

 

[Bowers]

34lbs only matters when carrying above water. The buoyancy of the tank plus valve, hardware and regulators is what you figure as weight towards your total ballast.
Im confused why your instructor would need 20lbs of lead when changing from double to single tank. The loss of a tank, bands and first stage reg shouldnt even come close to 20lbs.. does he also change out rigs from a heavy plate to a jacket or soft plate? That would be closer.

 

[NWA7265]

That’s why I’m confused. Only thing that would really change is he wouldn’t have a second reg first stage and then the tank bands. Everything else is the same.

reason I’m asking this is I’m trying to figure out how my weights will be changed when I go to 133’s. I’m looking to buy 133’s and Full bouy is -9.08lbs and empty bouy is 1.45lbs so when I’m in a single setup I would need more weight than my 100 now and for doubles I would need weight also? Bc it might become positive near the end of the dive depending how low it is.

 

[Marie13]

As an example, I need 29lbs with drysuit and steel HP80. With HP80 doubles and the same drysuit/undies, I need 23lbs.

I’m damned floaty on my own. I don’t need to tread water to stay afloat in a swimming pool in just a bathing suit. I float.

 

[Bowers]

If you keep about 500psi or more in your tank at the end of dive it will not get floaty, and will be pretty close to the same weight requirements as your 100. With 133 doubles you will most likely need in the ballpark of 6-8lbs lead if diving the same thermal protection (im making some assumptions about the weight of valves, bands and regs). As always a proper weight check is key when changing rigs.

*Edit i did that math based on 20lbs normal instead of 30. You would need closer to 18lbs with the doubles...

 

[Scuba Lawyer]

Not sure what the answer is to OP's question. Never really thought about it. For saltwater, all I know is that with a 5mm farmer john w/hooded jacket I need 26 lb with a single 2250 psi steel 72 tank or a steel 2400 psi LP 95 tank.

With twin steel 1880 psi 38's and twin 2190 psi steel 45's I need 20 lb.

With my twin 3450 psi steel HP 40's I need 16 lb.

I assume maybe density and thickness of tank steel is a factor?

 

[W W Meixner]

That’s why I’m confused. Only thing that would really change is he wouldn’t have a second reg first stage and then the tank bands. Everything else is the same.

reason I’m asking this is I’m trying to figure out how my weights will be changed when I go to 133’s. I’m looking to buy 133’s and Full bouy is -9.08lbs and empty bouy is 1.45lbs so when I’m in a single setup I would need more weight than my 100 now and for doubles I would need weight also? Bc it might become positive near the end of the dive depending how low it is.

NWA...

First of all...forget the calculations...far too many variables...

With your chosen kit/dry-suit system...with assistance...in the shallows or pool...establish neutral buoyancy...just as you were instructed during OW training...start with the smallest ballast pieces first...you should be dialed in within five minutes...

I'm 6' 3''...185 pounds...with dry-suit system...double HP steel 80's/100's...aluminium back-plate...no ballast

Same dry-suit system...single HP steel 117's...12 pounds ballast...double HP steel 117's...aluminium back-plate...no ballast...

With HP steel double 133's...unless your dry-suit does not fit properly and traps air...you will not need ballast...if you do...you are trapping air...which when evacuated at depth...will leave you plummeting to the bottom...plus if you can control your descent...with added ballast...you will be continually adding and evacuating ballast gas in order to maintain depth and profile...as you will be severely over-weighted...you'll exhaust yourself in no time...

Under no circumstances plan deep boat dives with double 133's until you have fully familiarized yourself with their balance/stability...and negativity...

W.W...

 

[Bowers]

NWA...

First of all...forget the calculations...far too many variables...

With your chosen kit/dry-suit system...with assistance...in the shallows or pool...establish neutral buoyancy...just as you were instructed during OW training...start with the smallest ballast pieces first...you should be dialed in within five minutes...

I'm 6' 3''...185 pounds...with dry-suit system...double HP steel 80's/100's...aluminium back-plate...no ballast

Same dry-suit system...single HP steel 117's...12 pounds ballast...double HP steel 117's...aluminium back-plate...no ballast...

With HP steel double 133's...unless your dry-suit does not fit properly and traps air...you will not need ballast...if you do...you are trapping air...which when evacuated at depth...will leave you plummeting to the bottom...plus if you can control your descent...with added ballast...you will be continually adding and evacuating ballast gas in order to maintain depth and profile...as you will be severely over-weighted...you'll exhaust yourself in no time...

Under no circumstances plan deep boat dives with double 133's until you have fully familiarized yourself with their balance/stability...and negativity...

W.W...

How much are you wearing in the way of undergarments. I use 14 lbs total ballast weight (tank, plate, lead, etc..) when in my moderate underwear that i wear in 40’s F water. Though the OP seems overweighted with 30lbs, he did state he was wearing 3 undergarments of undisclosed thickness for undisclosed temps. So doubles may not be enough ballast in his case.

 

[victorzamora]

I’m tryin to figure out how different tanks effect weight needed.

I currently dive a steel 100 and I need 30# of lead when I dive my drysuit with 3 layers.

Firstly, are you correctly weighted now? What matters is that your wing is essentially empty at 15ft during your safety stop with an empty tank. Once that's true, you're correctly weighted.

Now that you're correctly weighted with that tank, you can figure out what you need to do regarding your buoyancy with a new tank setup. Without changing anything else (exposure protection, BC, etc), you're adding another HP100 and another reg (plus manifold, bands, etc). To get yourself correctly weighted, you need your wing to be empty(ish) when you're doing your 15ft safety stop. So you add the buoyancy of your additions (tank, regs, manifold, bands) to your current lead requirements.

what exactly matters about the tank specs

The empty buoyancy. Technically it's the "near-empty" buoyancy.

HP100 is 34lbs empty and has a full buoyancy of -8.41lbs and an empty buoyancy of -.59lbs
Does the 34lb empty weight number matter? Or does the buoyancy numbers only mattter?

So the manifold weighs a couple of pounds and the reg weighs a pound or so and the tank is gonna be near a pound negative at 500psi. I think you'd be safe shaving off 3-4# of lead and reweighting yourself.

Ignore what your instructor does. Ignore what your buddy does. Ignore what your neighbor's dog's best friend's ex-girlfriend's cenote guide does. What matters is you.

If you're correctly weighted at 30# of lead, you'll be way too light with 20# another HP100 (spec'd as above). If you're changing out a fluffy jacket BCD to a stainless-backplate BPW or changing exposure protection, or anything else...then maybe. But you'll need to check yourself again.

 

[NWA7265]

I just went diving last Saturday and I had 28# of lead. I had on a fourth element j2 too and bottom, fourth element xerotherm tip and bottom and fourth element arctic top and bottom. Fourth element xerotherm socks and arctic socks and then the xerotherm glove liners. Drysuit is a 4x apeks kvr1 I’m 6’3 220lbs. And when my tank got to abut 1700 psi I could feel myself wanting to go up. My wing was empty the whole dive. The only air I added was to my drysuit. I had to keep adjusting my drysuit air the rest of the dive and near the end my drysuit was almost empty. In the beginning of the dive my tank was 2600 psi and I was perfect. Still no air in my wing just added air to my drysuit to remove the squeeze and that was enough. That was with a HP100 and steel back plate. Just for an idea.