Not P but Moby-Dick (49)

[Mike Jing]

>From Chapter 60:

It is worse; for you cannot sit motionless in the heart of these perils,
because the boat is rocking like a cradle, and you are pitched one way and
the other, without the slightest warning; and only by a certain
self-adjusting buoyancy and simultaneousness of volition and action, can
you escape being made a Mazeppa of, and run away with where the all-seeing
sun himself could never pierce you out.

What does "buoyancy" mean here?