MikeFerrara once bubbled...
This isn't correct Pete. If your center of gravity is in the same place as your center of buoyancy there are no apposing forces so assuming the same body position you'll stay balanced even as overall buoyancy changes and your whole body will rise. If those centers are offset then it's as you describe but if that's the case you won't trimmed.
However it is still possible to do a fin pivot but you have to arch your back lika a son-of-a-gun to keep your feet on the bottom (like you would want to. When you do this you're essentially doing something similar to the DIRF COG drill but with your feet touching the bottom.
You know you are right to a point. if you were entirerly correct you would never have to worry about trim as you would always be trimmed. you can create a situation where the two points are the same by using trim. Here I will use a flying analagy, where the center of gravity is almost always different the center of lift and this is adjusted the trim on the plane.
since you can adjust your buoyency on your upper body only you are shifting your center of buoyency BUT your center of gravity stays consistant relativly as long as you are in the same orientation. If you could adjust your center of buoyency over your entire body evenly then your arguement would be correct.
your center of gravity will change with attituce from vertical to horizontal and this is very much independant from your center of buoyency.
I agree when you are perfectly trimmed the two points are the same but add air to your BC your center of buoyency shifts while momentarily your center of gravity remains constant and your upper body will lift and you will be orientated at an angle. I agree your center of gravity will shift as a result but you will already have shifted positions.
lets go diving and you can show me a short ascent (say 10 feet)in the horizontal position just by using your BC. (i.e not forward movement)
EXAMPLE:
I know you or anyone else is not going to take my word for this so try this next time you are in the pool or shallow water (10 - 15 feet): (just remember this will not be a controlled ascent so be careful to breath and not be at the end of a deep dive)
lay flat on the bottom with no movement. Make yourself neutral. Now try to ascend to the surface without moving by only putting air in your BC. Make sure you are perfectly trimmed before you start. Keep you body in line with no arching your back or anytihg like that.
If you can maintain a perfect horizontal attitude all the way to the surface then you will have prooved your point. IPlease post here and tell me how it goes.
Thanks,
Pete