Posted by R Bear on May 04, 2001 at 11:55:53:
In Reply to: Hey McKane posted by seahunt on May 04, 2001 at 10:02:20:
My first back inflation BC was a drowning nightmare at the surface. At the time I dove Al 80s exclusively and thought it was a limitation of the technology. When I put doubles on it, the problem went away. When I put a heavy steel single on it, the problem went away.
Why?
The problem is simple physics.
A jacket lifts the load (you) from the front AND the back. This is like picking up a box from both ends. Back inflation with a floaty Al80 floats up in back and you push down in front. This puts your face in the water unless you compensate somehow. It is like trying to lift a box from one end only. You will roll the box over but can't lift it. Back inflation with a heavy tank (like doubles or heavy steel) puts a load in front (you) AND in back (your tanks) with lift (your bladder) in between. This is like lifting a tool box fron the handle in the center of the lid.
Are you with me?
The solution is to be sure that there is weight in the back. This can be achieved like I did (by accident) by adding heavier tanks in back. It can also be achieved by shifting trim weights backwards like using the rear pockets on a zeagle ranger, or mounting a V weight to your backplate. Another way of doing it is to mount a tank weight to your AL 80.
At any rate, your instructor friend doesn't understand the basics of trim, weight, and balance. Hopefully you now do.
DSAO
Ron