Steel vs Al tanks buoyancy weight

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Diesel_Diver

Contributor
Messages
162
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Location
Bay of Fundy region
# of dives
100 - 199
Has anyone ever done a chart up on the various tanks compositions and sizes with a +/- system as to you buoyancy? As in add 2lbs lead for #$&*()’
Subtract 6 lbs lead for @;7,$£¥

Just kinda curious, my LDS has various tanks in their rental program and it’s a bitch at times to get it right .
 
Faber LP 85: -2.08 lbs
Faber LP 95: -2.71 lbs
Faber LP 108: -1.42 lbs
Luxfer 80 AL: +0 lbs
Faber HP 80: -6.14 lbs
Faber HP 100: -4.99 lbs
Faber HP 117: -4.24 lbs
Faber HP 120: -3.75 lbs
 
Faber LP 85: -2.08 lbs
Faber LP 95: -2.71 lbs
Faber LP 108: -1.42 lbs
Luxfer 80 AL: +0 lbs
Faber HP 80: -6.14 lbs
Faber HP 100: -4.99 lbs
Faber HP 117: -4.24 lbs
Faber HP 120: -3.75 lbs
I always though AL 80 were positive when empty
 
I always though AL 80 were positive when empty

Yes, the Al80 is about 4.4 lbs positively bouyant, but the OP was asking how much lead you would add or subtract by changing tanks.

I assumed that they are already carrying enough weight to be perfectly balanced with an AL80.
 
Yes, the Al80 is about 4.4 lbs positively bouyant, but the OP was asking how much lead you would add or subtract by changing tanks.

I assumed that they are already carrying enough weight to be perfectly balanced with an AL80.
Lol I was the OP , but yes that was my original intention and question. Gets all screwed up switching back and forth
 
I use a system I call the "Magic Number".
It works for any given exposure suit once you have determined your neutral buoyancy, and allows you to change tanks or BCDs and maintain proper weighting.

Add up all the pieces:
Tank at 500 psi
First stage negative buoyancy
BCD buoyancy
Fin buoyancy
Trim weights
Integrated weight
Extras

Once you have a total, and you know your weight requirement, the Magic Number stays the same.

For example, with my 5mil wetsuit, boots and hood, my Magic Number is -12:
+3.4 Al Tank at 500 psi
-1 lb. first stage
0 BCD buoyancy
-1 old Jet Fin buoyancy
-4 Trim weights
-8 Integrated weight
-1 Light Canister Extra
Add 'em up? -12

With the same wetsuit configuration, if I switch tanks, the Magic Number stays the same:
-2.7 Steel Tank at 500 psi
-1 first stage
0 BCD buoyancy
-1 old Jet Fin buoyancy
0 Trim weights
-6 Integrated weight
-1 Light Canister Extra
Add 'em up? -11.7

If I switch to a steel backplate and wing, and say, switch my Jet Fins for floaty Nova fins:
-2.7 Steel Tank at 500 psi
-1 # first stage
-5 BP/W buoyancy
+1 new Nova Fin buoyancy
0 Trim weights
-4 Integrated weight
0 No Extras
Add 'em up? -11.7

It stays constant for the same exposure suit configuration. I have a short list of M.N.'s for each of my suits from rash guard to drysuit with various liners. But don't forget that at the beginning of a dive you'll also be carrying 5 or more pounds of air that you'll breathe off. So at the beginning of the dive you'll always be heavy, even if you're neutral at the end.
Why is the AL80 only +3.4 lb instead of +4.4 lb? Because the weights in the various tables are at 0 psi with valve. But you'll be carrying 500 psi (~1 lb) in your tank when you do your neutral buoyancy check.
 

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