Tank Questions

[runsongas]

if your tanks are stamped DOT SP 13488 on the crown, use the fx80 numbers. if they say DOT 3AA 3180, use the hp80 numbers.

 

[JackD342]

3498 - 3442 = 6?
um... 56? (Still trivial...)

Whoops!

 

[HKGuns]

They are all DOT SP 13488. Thank-you.

 

[almostDIR]

No, I am using the Optimal Buoyancy spreadsheet and picking the right tank is essential to getting your estimated weighting correct.

FX80's are 1.74 pounds negatively buoyant @ 0 PSI
HP80's are 7.22 pounds negatively buoyant @ 0 PSI

Throws the proper weight calculations off by a considerable amount and I'm a newb.....Sinking to the bottom of the lake like a rock isn't something I would enjoy!

Meh.
The REAL weight of the tank can differentiate a lot from the spec numbers of the manufacturer and what is stamped on the tank. you need to actually weight the tank by yourself to know the exact weight it has.
It is due to the manufacturing process and cannot be helped.
I have seen tanks which are for example older tanks stamped 12.4kg and the real weight of the tank is closer to 14kg so the specs and tables cannot be fully trusted I think

your other gear also weights a lot and has varying buoyancy characteristics so the best is just to take it all into water to see.

you will need to do the buoyancy check in water to see how much weight is actually needed. you may not be able to figure it out any other way especially if using heavy exposure protection like a drysuit where even small looking changes will make a big difference and where it is partially even a matter of taste how much air you want to keep in the suit to be comfortable

 

[tbone1004]

@HKGuns the calculator is wrong. The "HP80's" are actually "MP80's" which is what you'll hear them referred to on here. Those are very rare, somewhat old, and VERY heavy. You'd know if you had one

 

[HKGuns]

Thanks Tbone and everyone for their assistance and input.

 

[rsingler]

@HKGuns the calculator is wrong. The "HP80's" are actually "MP80's" which is what you'll hear them referred to on here. Those are very rare, somewhat old, and VERY heavy. You'd know if you had one

Thanks to all for their comments.
I'll revise the spreadsheet! FX80's are so commonly marketed as HP 80s in the US, that my mistake has probably led to a lot of 5 pound buoyancy errors. I indeed had the MP80, trying to be complete, but obviously mislabeled it. I will now list the XS Scuba tank with both names, and make sure to relabel the MP80 specs.

Thanks again for the group think.

 

[Bob DBF]

faber used to have some weird 3180 psi 3AA tanks that were 3498 with the 10% +rating overfill. They aren't that common though

those mid pressure tanks are much more negatively buoyant than the newer exemption 3442 tanks

They were/are called Mid Pressure (MP) and also included a 72 at 3000# service pressure (3300# with +), as well as the 3180 tanks. For a small tank the 72 is sweet.


Bob