Why do I sink when I turn upside-down?

[1isNone]

Another mystery of the life aquatic solved by the Scubaboard gurus. Thanks, guys.

With no fighting or bickering either! A strange time in a strange land, for certain...

 

[Storker]

I always surface horizontal, then roll over on my back to lounge, stare at the sky, look at the birds, rest etc., and I always have to add air to the wing/drysuit.

When I surface, the first thing I do is what they taught me in OW class: make sure I'm positively buoyant. That means filling up my wing completely, closing my shoulder valve and putting enough gas in my suit to take off any squeeze.

There's no way I'll sink after that. Even if I lie back.

 

[divad]

When I surface, the first thing I do is what they taught me in OW class: make sure I'm positively buoyant. That means filling up my wing completely, closing my shoulder valve and putting enough gas in my suit to take off any squeeze.

There's no way I'll sink after that. Even if I lie back.

Sounds hysterically drastic.

 

[Storker]

Sounds hysterically drastic.

"Hysterically drastic"? Filling up my wing and relaxing from the slight suit squeeze I always have if I've breathed down my tank?

OK...

 

[Subcooled]

Lost buoyancy also happens when launching an SMB or while taking photographs, or while doing anything that requires focus.
Swim upside down for ten hours and then your buoyancy starts to stabilize itself
The reasons for sinking have been listed above, but with experience you can avoid those.

 

[wetb4igetinthewater]

When you roll upside down, your lungs are now quite far below the second stage. That means the work of breathing increases, so you have to pull harder to inflate your lungs. This will feel like you are holding your lungs more full, and so you will tend to keep a smaller lung volume resulting in sinking.

I'm going to go inverted with a reference point to see what the difference is in what I feel.

 

[Subcooled]

And do pay attention to where your LEGS are after you roll upside down.
Do they point up as they did earlier? Hardly. The knees only bend to one side. So, maybe the legs are dropping and pulling you down.

 

[g1138]

You're probably rolling not on a perfect axis and your tank is swinging wide and taking some inertia pulling your down.

In addition, if you bring your legs up slightly in a seated or lean back against a wall stance, you're pushing your back/tank lower into depth. Essentially you're probably making a downward force when your roll.