46 CFR §45.51

1. (a)For the purpose of this subpart, a type A vessel has—
   1. (1)No cargo ports or similar sideshell openings below the freeboard deck;
   2. (2)Only small freeboard deck openings fitted with watertight gasketed hatch covers of steel;
   3. (3)No dimension of a freeboard deck cargo opening greater than 6 feet and the total area not exceeding 18 ft 2; and
   4. (4)No more than two freeboard deck cargo openings to a single cargo space.
2. (b)For the purposes of this subpart a type B vessel is a vessel that does not meet the requirements in paragraph (a) of this section.