Section 13.505 - Proof of service for tankerman-engineer endorsement(a) Service must be proved by a letter on company letterhead from the owner, operator, master, or chief engineer of a tankship or self-propelled tank vessel. The letter 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).CGD 79-116, 60 FR 17142, Apr. 4, 1995, as amended by CGD 79-116, 62 FR 25135, May 8, 1997; USCG-2006-24371, 74 FR 11260, Mar. 16, 2009