46 CFR § 171.112 - Watertight door openings.
(a) The opening for a watertight door must be located as high in the bulkhead and as far inboard as practicable.
(b) No more than one door, other than a door to a bunker or shaft alley, may be fitted in a main transverse watertight bulkhead within spaces containing the following:
(1) Main and auxiliary propulsion machinery.
(2) Propulsion boilers.
(3) Permanent bunkers.