Buoyancy Inverted

[Garrobo]

Personally, I prefer to descend inverted, head down. What's the problem?

 

[Herk_Man]

It's a head squeeze. Your head is lower than everything else so all the air in there gets compressed more than the rest of you, making your head denser and causing you to descend. And the more you descend, the worse it gets. It will eventually lead to tinihedinitis.





















Sorry, slow day at work. No offense intended. Just having a little fun. (I'm betting you're finning, despite the belief that you're not.)

 

[TSandM]

I hope he comes back to clarify . . . I was reading "inverted" as lying on one's back, which is where I have seen the buoyancy difference.

 

[Herk_Man]

Which would then rule out my theory of a head squeeze... never mind.

 

[eponym]

I hope he comes back to clarify . . . I was reading "inverted" as lying on one's back, which is where I have seen the buoyancy difference.

That's how I first read it too.

And I'm not sure I understand it either. I'm horizontal, face-down (prone), not finning, just hanging out. I roll over so I'm face-up (supine). And I start to drop.

I have two theories, either or both of which might be correct:

1. My roll is not around my central axis but around my frontal plane (ventral), so I end up a tad lower in the water column.

2. I'm more relaxed lying on my back.

-Bryan

 

[stakanak]

Thanks guys. So if I am neutrally buoyant I am so in any position i.e head down feet up, horizontal, or heads up feet down, on my back etc.
I shall work on my breathing and fin movement on my next dive.
Scuba people rock!
Good Diving

 

[stakanak]

I actually meant head down feet to the surface, but it happens when I am on my back as well. I think because I am new, I am not noticing the subtleties of my breathing and fining unless consciously working on it.
Thanks again people
Good Diving!

 

[Herk_Man]

Correct. The buoyancy of an object in water is not dependant on it's orientation to the center of the earth. So, all else being equal, if your tendancy to move in the water column changes based on that orientation, you are doing something to induce it.

Now, here's the rub. It is very possible that the opposite of what you are implying is true. You may indeed be slightly negatively buoyant when in a "normal" (i.e. heads up) orientation but staying at the same depth because you are finning subconscientiously. But then when you invert, you STOP finning because you no longer have the urge to keep yourself from sinking. So... you sink.

I bet I'm right.

 

[fnfalman]

1
I'd guessed that is was the reduction in the total surface area presented (relative to gravity)... but I really don't know if this is correct.

You guessed correct.

When you achieve neutral buoyancy in horizontal trim, you have a lot more surface area presented to the water column than when you go vertical; inverted or otherwise.

When you achieve neutral buoyancy in vertical trim and go horizontal, you will find yourself slightly positively buoyant.

 

[redacted]

You guessed correct.

When you achieve neutral buoyancy in horizontal trim, you have a lot more surface area presented to the water column than when you go vertical; inverted or otherwise.

When you achieve neutral buoyancy in vertical trim and go horizontal, you will find yourself slightly positively buoyant.

Interesting. As I recall, gravity is a function of mass and distance. Shape of the mass was not an element of the equasion..

BUT, if a body is close but not quite neutral (like divers which are breathing), then surface area and friction may come into play and effect acceleration.