Thunderbird aln80 (neutral buoyancy)?

[sea_ledford]

There is a small difference in buoyancy swing of a neutral 80 (Thunderbird or Catalina), as compared to a "standard" AL80. The "neutral" tanks have a working pressure of 3300psi vs 3000psi. This shaves ~.5 lb off the buoyancy swing.
This is quite evident on sidemount, as the cylinder tail doesn't get quite so light when empty. Evidently much of the extra aluminum in the neutral design is in the base of the tank.
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Those tables are pretty terrible for accuracy. I once added a calculated column to one of the compilation tables (Lake Huron Scuba version, I think) that calculated the weight of air based on the numbers provided. It was all over the place.

As far as trim goes, I'm sure there are significant differences between them, but the actual buoyancy shift weight will be the same.

 

[Scared Silly]

maybe i should added this is California diving at the moment 48f bottom temp on my last dive in Monterey... so 7mm wet suits + extras like vests and socks so at the moment I am diving with 36lb in lead... with a al80 and 32lb of lead with a steal tank.

For cold water and 7mm wetsuits you are far better off with HP steel cylinders. Or even MP steel cylinders which have rather negative buoyancy characteristics.

 

[rjack321]

For cold water and 7mm wetsuits you are far better off with HP steel cylinders. Or even MP steel cylinders which have rather negative buoyancy characteristics.

As long as it's salt. For freshwater lp85s pretty bomb with thick wetsuits. And Al80s are great in fresh too

 

[jengineer61]

The only time I dive Aluminum is when I rent on holiday. Boat dive tank of choice is steel 95. Other wise beach diving is steel 65 - with about 4 extra pounds for not diving the 95. Get a back plate if you aren't doing that and that will redistribute a few pounds.