46 CFR §171.117

1. (a)Except as provided in paragraph (b) of this section, each port light with the sill located below the margin line must have a hinged, inside dead cover.
2. (b)The dead cover on a port light located in an accommodation space for passengers other than steerage passengers may be portable if—
   1. (1)The apparatus for stowing the dead cover is adjacent to its respective port light;
   2. (2)The port light is located above the deck that is immediately above the deepest subdivision load line;
   3. (3)The port light is aft of a point one-eighth of the LBP of the vessel from the forward perpendicular; and
   4. (4)The port light is above a line that—
      1. (i)Is parallel to the line formed by the intersection of the bulkhead deck and the side of the vessel; and
      2. (ii)Has its lowest point at a height of 12 feet (3.66 meters) plus 2 1/2 percent of the beam of the vessel above the deepest subdivision load line.
3. (c)For the purpose of paragraph (b) of this section, the beam of the vessel is measured at or below the deepest subdivision load line.
4. (d)Each dead cover must be designed so that—
   1. (1)It can be secured watertight; and
   2. (2)It is not necessary to release any of the special nuts required in § 171.116(f)(4) in order to secure the dead cover.