46 CFR §171.113

1. (a)For the purpose of this section, “trunk” means a large enclosed passageway through any deck or bulkhead of a vessel.
2. (b)Each trunk, other than those specified in paragraph (c) of this section, must have a watertight door at each end except that a trunk may have a watertight door at one end if—
   1. (1)The trunk does not pass through more than one main compartment;
   2. (2)The sides of the trunk are not nearer to the shell than is permitted by § 171.067(c) for the sides of a recess in a bulkhead; and
   3. (3)The vessel complies with the subdivision requirements in this part when the volume of the trunk is included with the volume of the compartment into which it opens.
3. (c)Each trunk that provides access from a crew accommodation space and that passes through a main transverse watertight bulkhead must comply with the following:
   1. (1)The trunk must be watertight.
   2. (2)The trunk, if used for passage at sea, must have at least one end above the margin line and access to the other end of the trunk must be through a watertight door.
   3. (3)The trunk must not pass through the first main transverse watertight bulkhead aft of the collision bulkhead.