Scuppers and gravity deck drains from spaces above the freeboard deck that penetrate the shell below a line 24″ or .05B above the summer loadline, whichever is greater, must have an automatic nonreturn valve. This valve may be omitted if the piping is of thickness not less than extra heavy pipe.
source: CGD 73-49R, 38 FR 12290, May 10, 1973, unless otherwise noted.
cite as: 46 CFR 45.157