46 CFR § 45.51
Types of ships
April 15, 2021
(a) For the purpose of this subpart, a type A vessel has—
(1) No cargo ports or similar sideshell openings below the freeboard deck;
(2) Only small freeboard deck openings fitted with watertight gasketed hatch covers of steel;
(3) No dimension of a freeboard deck cargo opening greater than 6 feet and the total area not exceeding 18 ft2; and
(4) No more than two freeboard deck cargo openings to a single cargo space.
(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.