weight change

[saying]

drysuit, Atlantic off the jersey coast, double AL 80s:
24 lbs (12 lbs plate, 8 lbs V-weight, and two 2s in my pockets)

change that over to some E7-120s.

AL80s are 4.something positive empty and the 120s are neutral. I'm guessing at just ditching the V-weight and rockin & rolling. Will bad things happen to me?

 

[ShakaZulu]

Considering:

Luxfer AL80

Weight = 31.4lbs
Bouyency = -1.4 to +3.4lbs, diff is 4.8lbs.

PST E7-120

Weight = 36.6lbs, thus you can subtract 5.2lbs per tank.
Bouyency = -1.3 to -10.3lbs, diff is 9.0lbs, thus at the beginning of the dive you will be 4lbs more negative than with the AL80's.

For doubles, I would remove 10lbs.

 

[DivesWithTurtles]

Considering:

Luxfer AL80

Weight = 31.4lbs
Bouyency = -1.4 to +3.4lbs, diff is 4.8lbs.

PST E7-120

Weight = 36.6lbs, thus you can subtract 5.2lbs per tank.
Bouyency = -1.3 to -10.3lbs, diff is 9.0lbs, thus at the beginning of the dive you will be 4lbs more negative than with the AL80's.

For doubles, I would remove 10lbs.

Shaka,

1. What would tank weight out of the water have to do with how much weight you wear?

2. What would buoyancy at the beginning of the dive have to do with how much weight you wear?

 

[ShakaZulu]

Shaka,

1. What would tank weight out of the water have to do with how much weight you wear?

Since the steel tanks are heavier than the aluminums, he can remove that amout of with from his belt.

2. What would buoyancy at the beginning of the dive have to do with how much weight you wear?

I'm not worried about the buoyancy at the beginning of the dive, I'm more concerned with the difference. He must realize that he will be 10lbs more negative at the beginning of the dive due to the extra weight of the air in his tanks.

The best way to do this, is to do a buyency test at the end of the dive with 500psi in each tank. Maybe he can do that too and let us know how much weight he dropped.

 

[DivesWithTurtles]

The best way to do this, is to do a buyency test at the end of the dive with 500psi in each tank. Maybe he can do that too and let us know how much weight he dropped.

Much better.

Or If he already knows what he currently needs accurately, compare the change in empty buoyancy.

EDIT -> Whoops, he also has to consider the change in mounting hardware.

 

[markfm]

http://www.huronscuba.com/equipment/scubaCylinderSpecification.html has a table with both AL and steel tanks, buoyancy characteristics with valves.
The table indicates you change from about +8 to +9 to neutral (for two tanks) if you're starting from a Catalina S80 or Luxfer 80, though perhaps not if starting from a Catalina C80 or a Luxfer S80.

Absolutely a pool test is great, for the misc HW weight changes.

 

[saying]

No hardware changes but for the bottles themselves.

Luxfer S080s to PST E7-120.

That's ~8.8 to ~0. Figuring I'm not getting on the boat ACTUALLY empty, let's say +8 vs -.5. I ditch the 8 lbs V-weight and I should be nearly copasetic, right? I mean closer to copasetic than either a block of granite or a Trident II.

 

[markfm]

According to the table (I have not seen the numbers elsewhere, cannot verify them), the Luxfer S80 is only +2.26 empty, so two of them would be +4.5lbs total, not +8. That would mean that you might want to only ditch the pair of 2 lb weights in your pockets, at least at first.

Purely theory, just what the table seems to be saying. That would seem the safer, if more "boring", approach. (sometimes boring is good