Downflooding angle

The downflooding angle is the heel at which the first non-weathertight opening (an air pipe, vent, or unprotected door) immerses and admits water, capping the usable part of the $GZ$ curve. The IS Code 2008 truncates stability criteria at this angle when it falls below the second criterion angle. Designers raise it by siting openings high and inboard and by fitting weathertight closures, since flooding below the bulkhead deck collapses reserve buoyancy fast.