Answer
A. - It is the angle at which the ship’s Deck just begins to immerse or touch the sea surface
-At this angle, the curve transition from being concave to convex means GZ may continue to increase beyond this point, the rate at which it increases begins to decrease.
-Rate of increase of GZ (righting lever) w.r.t. the angle of heel stops accelerating & begins to slow down.
-Significance
a. Deck immersion indicator
b. Change in stability & operational awareness. Beyond this, heeling may cause rapid changes in the vessel’s stability behaviour