Change in buoyancy from 12l to 15l cylinder

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BlueTrin

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Is there a rule of thumb about how much weight less you need to use if you equip a 15l stew vs 12l steel ?

It is obviously heavier but it is slightly bigger as well and will have more air meaning that you have even less weight when empty.
 
Is there a rule of thumb about how much weight less you need to use if you equip a 15l stew vs 12l steel ?

Not really. For example a LP and HP tank that have the same water capacity will have different buoyancy characteristics. Likewise, different manufacturing processes can influence the buoyancy of a given sized tank. Your best bet is to dig around for charts that give this information. Even the charts are often just a starting point though. It's just something you have to work out for yourself.

Here's information for Faber

Blue Steel Scuba - Cylinder Specs
 
Simple,don’t dive a 15l!

They’re heavy, uncomfortable, and unbalanced
 
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Not sure about your tanks over there but with our Australian tanks the 15lt is only .25kg more negative than our 12.2lt.
 
According to the SCUBA Doctor website AU spec steel Fabers are as follows:

Faber Steel Tanks AU spec.PNG

So a 15L is 3.6kg heavier in tare weight than a standard 12.2L but 1kg more negative underwater when full.
Faber 232 bar Steel Cylinder Range and Specifications Faber Steel Cylinders - 232 bar - The Scuba Doctor Dive Shop
 
So a 15L is 3.6kg heavier in tare weight than a standard 12.2L but 1kg more negative underwater when full.
Sorry, I left out the empty part lol
Buoyancy difference empty is the figure you need to worry about when working out the difference in lead to carry, and that's .25kg
I carry the same for both tanks.
 
Folks, note that the specs of the tanks in the EU/UK where the OP is are usually different from those in the US.

I use less lead with my 12L short and heavier tanks than with my 15L tanks!! (both are 230 Bar).
 
The internal volume is 3L larger, so add 3kg to your belt. Then subtract the weight of the 12 from the weight if the 15 (it should be stamped on the shoulder of the tank), and divide by 7.8. What you get is the difference in steel volume. Take that number of kg off your belt.
 

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