The only type of BC that will reliably float an unconscious or incapacitated diver face up is the horse collar type. A BP/wing, will reliably plant an unconscious diver face down or nearly so. Some BC jacket types like the Stabilizer may or may not tend to float the diver face up. But none except the horse collar will reliably do so. A BC of any type is not a PFD and is not rated as such or Coast Guard approved and is not a life saving device or personal floatation device, it is a buoyancy compensating device.
A BP/wing on the other hand is reliably going to place a diver in the horizontal swimming position (with trim adjustments of course), a jacket type may or may not depending on particular design and trim, a horse collar, well, it is very good at putting you head up underwater as well as on the surface. To dive a horse collar BC and get horizontal it must be treated as if you have no BC at all.
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A BP/wing on the other hand is reliably going to place a diver in the horizontal swimming position (with trim adjustments of course), a jacket type may or may not depending on particular design and trim, a horse collar, well, it is very good at putting you head up underwater as well as on the surface. To dive a horse collar BC and get horizontal it must be treated as if you have no BC at all.
N