46 CFR §174.335

1. (a)Each hopper dredge must have sliding watertight doors (Class 3) approved under § 170.270 of this chapter if the sill for the door is—
   1. (1)Installed below the bulkhead deck; and
   2. (2)Less than 24 inches above the final waterline as shown by the calculations required by § 174.310 in each damage condition up to and including the maximum amount of assumed damage.
2. (b)Each hopper dredge must have sliding watertight doors (Class 3) approved under § 170.270 of this chapter, or quick acting hinged watertight doors (Class 1) approved under the same subpart if the sill of the watertight door is—
   1. (1)Installed below the bulkhead deck; and
   2. (2)Greater than 24 inches above the final waterline as shown by the calculations required by § 174.310 in each damage condition up to and including the maximum amount of assumed damage.