Bouyancy, breathing and SAC

[Jamdiver]

Quick query to Rick and or the more experienced divers.
I've noticed that at increased depths say in excess of 70ft that neutral buoyancy is much easier to attain. And that increased lung inhalations result in a smaller increase in depth as compared to those same inhalations at a shallower depth.

I assume that this is a direct result of the decreasing degree to which pressure changes with increased depth?
It's always nice to experience (in some ways) the physics of diving.

Eg. A change in depth from 20m to 10m resulting in a halving ofpressure exerted on the body (from water) as opposed to a change in depth from 30m to 20m resulting in a third less pressure (from water) being exerted on the body.

 

[scubafool]

It's funny you should ask that. Just a few days ago, a diver diving with Uncle Ricky demonstrated perfect bouyancy. Uncle Ricky was moved to the point of tears and granted the diver one wish. The diver thought about it a lot and decided that he wanted a bridge from the mainland to Hawaii because he was afraid to fly and got sick on boats, yet always wanted to dive in Hawaii.

Uncle Ricky frowned and pointed out how incredibily hard it would be to build a bridge that long and suggested he make an easier wish. The diver thought about it some more and said "Uncle Ricky, I want to understand women". Uncle Ricky responded, "Would you like two lanes on that bridge or four?"

ROTFL! So true!

After 6 months of marriage, I felt that I pretty much had The Dear One figured out. After 6 years of marriage, all I know is that I was wrong at 6 months. Looking forward to working on this mystery for the next 60 years, and hoping that I never quite solve it.

 

[Data]

very nice explanation rick,
a couple of things I like to add:
do this exercise at 30' where it is the most difficult to obtain (as explained by jamdiver)
also, before you even start to be buoyant you must be in trim (if you don't need to be vertical for whatever reason).
trim and buoyancy work hand in hand.
once you're in trim and at 30', get as close to buoyant as you can and to fine tune it take half a breath, that would be half a breath of your regular breath, not a very deep or very shallow breath unless that's how you breath.
now hold that half a breath for 10sec or so and make sure you're not moving up or down and you're ready to start the exercise.
all this is also made much easier by using backplates, harness and wing style setups, to simply place all your weight and buoyancy control devices above your lungs.

 

[Kevfin]

Another thread started in 2002 and resurrected???

As pertinent then as it is now…

 

[Rick Murchison]

Quick query to Rick and or the more experienced divers.
I've noticed that at increased depths say in excess of 70ft that neutral buoyancy is much easier to attain. And that increased lung inhalations result in a smaller increase in depth as compared to those same inhalations at a shallower depth.

I assume that this is a direct result of the decreasing degree to which pressure changes with increased depth?
It's always nice to experience (in some ways) the physics of diving.

Eg. A change in depth from 20m to 10m resulting in a halving ofpressure exerted on the body (from water) as opposed to a change in depth from 30m to 20m resulting in a third less pressure (from water) being exerted on the body.

Sounds like you already have a pretty good handle on the why & wherefore about easier control deeper. To put it in "physics" language, the change in buoyancy with vertical displacement is related to the change in pressure divided by the total pressure; that is, a 1 foot displacement at 100 feet (4 ATM) will have half the effect of a 1 foot displacement at 33 ft (2 ATM).
Rick

 

[Rick Murchison]

As pertinent then as it is now…

Or now as it was then, eh?
Rick

 

[beachbum70635]

With the explanation Uncle Ricky gave, this thread needs to come back once a month or so! Very nice Rick

 

[TSandM]

This is one of the fun things about Scubaboard . . . look up all threads or posts by somebody whose writing you like, you find all kinds of incredibly valuable information.