46 CFR §174.220

1. (a)Each hatch exposed to the weather must be watertight, except that the following hatches may be only weathertight:
   1. (1)Each hatch on a watertight trunk that extends at least 430 millimeters (17 inches) above the weather deck.
   2. (2)Each hatch in a cabin top.
2. (b)Each hatch cover must—
   1. (1)Have securing-devices; and
   2. (2)Be attached to the hatch frame or coaming by hinges, captive chains, or other devices to prevent its loss.
3. (c)Each hatch that provides access to quarters or to accommodation spaces for crew members or offshore workers must be capable of being opened and closed from either side.
4. (d)Except as provided by paragraph (e) of this section, a weathertight door with a permanent watertight coaming at least 380 millimeters (15 inches) high must be installed for each opening in a deckhouse or companionway that—
   1. (1)Gives access into the hull; and
   2. (2)Is in an exposed place.
5. (e)If an opening in a deckhouse or companionway has a Class-1 watertight door installed, the height of the watertight coaming need only accommodate the door.