is the line parallel to the slope of keel passing amidships
through:
-
(a) the top of the keel or line of intersection
of the inside of shell plating with the keel where a bar keel extends
above that line of a vessel with a metal shell; or
-
(b) the rabbet lower line of the keel of a vessel
with a shell of wood or a composite vessel; or
-
(c) the intersection of a fair extension of the
outside of the shell contour at the bottom with the centreline of
a vessel with a shell of material other than wood and metal.