Getting to the perfect buoyancy

[roakey]

Originally posted by Walter
As long as I keep my weights at or near my waist (my center) I achieve trim merely by moving my body.

Walter,

I think I disagree with you but I need some more details. What do you mean by “moving your body?” If you're not perfectly horizontal in a natural swimming position (but not moving or kicking), your trim is wrong and some of your thrust is being used to “fake” perfect trim.

“Perfect trim” is relatively easy to do while moving because it’s easy to use your thrust and other hydrodynamics to get into and keep a flat profile. But it’s inescapable that some of your energy is being used to maintain proper trim, not for thrust. The torture test is when you come to a complete stop. If you don’t remain flat with the same body position as if you were swimming, your trim is wrong. Trim is ONLY a function of your center of mass and center of buoyancy. If they coincide, you’re perfectly trimmed. If one is forward or rearward of the other, you’re improperly trimmed.

Yes you can “ball up” or assume some pretzel-like shape to modify the position of your center of mass and buoyancy, but that doesn’t count. If you’re not properly trimmed while in a natural swimming position, you’re not properly trimmed, and only the movement of mass or buoyancy can accomplish proper trim. Mass is easier to adjust.

Roak

 

[Uncle Pug]

Originally posted by roakey
Gosh durnit Uncle Pug, I haven’t had the time to reply to this note and you beat me to my points.
Roak

Get outta bed earlier.... :tease:

 

[Uncle Pug]

Originally posted by roakey

Walter,
I think I disagree with you but I need some more details. What do you mean by “moving your body?” If you're not perfectly horizontal in a natural swimming position (but not moving or kicking), your trim is wrong and some of your thrust is being used to “fake” perfect trim.
Roak

Walter you are probably unaware of the forces you are exerting against the water to accomplish your perceived buoyancy control.

You are probably also unaware of the forces that you must exert against the water to change your position (attitude) in the water.

A sure way to tell is to get into your *swim trim* and then.....
stop all movement (hands, arms, legs,feet, body, head) with out adding or subtracting air from your BC and see what happens.

Yes it is fair to breath.... see what happens when you do.

What happens to your buoyancy? Go up...stay where you are...Sink?

What happens to your attitude (position in the water)?
Head down...stay where you are....Feet down?

If it takes movement to stay where you are in depth and position then you are not controlling your buoyancy ... you are compensating for poor trim with extra movement.

 

[The Chairman]

Hmnnn... but it sounds like bona-fide cavers to me!!!

Fin-Pivots are a GREAT starting point. If you can't deal with fin pivots then learning how to hover has a far steeper learning curve. Take one step at a time, and become comfortable with your fins on something stationary FIRST!!!

Hovering is next. I like the picking the coins off the bottom of the pool. Think I will try that and then use glue on one (grin).

As for staying still being the "acid test" for trim I sincerely disagree! However, I would rather contend that being still WITH your eyes closed -IS- the acid test. Once you remove that reference, your body can not subconsciously react to maintain your attitude. Use the force Luke...

As for horizontal being "essential" for neutral buoyancy, you are all wet. Cavers need -THAT- degree of control. The average (and above average) OW diver does not! They are not worrying about silt outs and such. They don't want to hit the bottom and they don't want to float to the surface.

Don't get me wrong TRIM IS A GREAT THING TO HAVE ON YOUR SIDE. But asking an OW or AOW to deal with trim while learning the real basics is just plain masochistic. I also agree that backplates and steel tanks GREATLY improve trim without much thought. Still, for MOST OW and AOW divers, their diving attitude (physical not mental) plays a far greater role in how easily they stay at a certain depth. Given a neutral diver trimmed perfectly, a slight incline will make you rise and a slight decline will make you fall.

 

[The Chairman]

As Roakey and I are WWWWWWAAAAAAAAYYYYYYY off topic (my bad), I split this topic (In the middle of my post too!) and put the breathing physiology/physics part in the diving medicine group... you may find it here:

http://www.scubaboard.com/showthread.php?s=&threadid=4933

Hope this doesn't offend anyone!

 

[Walter]

Pete, I personally think you should put it back the way you found it. Threads frequently switch topics as discussion progresses. Moving part of a thread to another forum is not a good idea. I don't particularly like switching threads to follow a discussion that was moving along and getting interesting. Such a move merely breaks the flow.

DSSW,

WWW™

 

[Lost Yooper]

I agree with everything UP and Roakey have said regarding trim and buoyancy. I will say that buoyancy control and trim are among the most neglected skills (buddy skills being worse perhaps) in OW and especially AOW classes. I agree with Roakey that this should apply more to AOW students, but it should be addressed more in OW too.

Instructors/agencies would be doing their students a tremendous favor by requiring excellant trim and buoyancy while doing their skills. Not only would exertion and air consumption decrease resulting from less drag, but that would be one less bad habit students would have to unlearn.

Take care.

Mike

 

[TexasMike]

So I can make sure I'm understanding everyone correctly...

Trim is defined as moving weight/equipment/etc. around so that the diver acheives being horizontal without having to exert himself at all once (near) neutral buoyancy is achieved. Right?

 

[The Chairman]

I don't know how to do that, and I am not sure that it can be done. Let no man join what the mighty NetDoc has torn asunder... well something like that. Even if I could, I think the off-gassing controversy was confusing some, and I didn't want it to take away from the main topic, which is merely buoyancy control. Sorry for the inconvenience.

 

[roakey]

Originally posted by TexasMike
So I can make sure I'm understanding everyone correctly...

Trim is defined as moving weight/equipment/etc. around so that the diver acheives being horizontal without having to exert himself at all once (near) neutral buoyancy is achieved. Right?

That defines "Correct trim." Simply the word "trim" means your attitude in the water. Trim consists of yaw, pitch and roll. Yaw doesn't enter in the equation unless you only have one fin, then you have a yaw problem.

Diving with double steels means you have to watch your roll. Most divers have a pitch problem, which is what we're addressing when we talk about trim.

Roak