46 C.F.R. § 13.505

(a) Provide evidence in a method prescribed by the Coast Guard of proof of service from the owner, operator, Master, or Chief Engineer of a tankship or self-propelled tank vessel. The evidence must specify—

(1) The classification of cargo (DL, LG, or both) carried while the applicant accumulated the service; and

(2) The number of days of officer, rating, and cadet service in the engine department on tankships or self-propelled tank vessels; or

(b) Service must be proved by certificates of discharge from tankships or self-propelled tank vessels with the appropriate classification of cargo (DL, LG, or both).