For seafarers' job promotion, you can browse the website: People's Republic of China (PRC), China Maritime Bureau [Public Service] Notice Announcement, click on the order of the Ministry of Transport of People's Republic of China (PRC) and China, and download the "Related Attachment: People's Republic of China (PRC) and China Seafarers' Competency Examination and Certification Rules: doc". According to the rules, applying for three-to-three management requires the following conditions:

cultivate

Complete basic safety training, be proficient in survival craft and rescue boat training, advanced fire fighting training, be proficient in first aid training, safety awareness training and designated safety responsibility crew training. Ships with a gross tonnage of less than 500 tons or less than 750 kilowatts (except special types of ships) are exempted from skilled training in survival craft and rescue boats, advanced fire fighting training and first aid training; Complete the post competency training corresponding to the third mate and the tube wheel.

Maritime service qualification

Have worked as a sailor, mechanic or senior sailor or mechanic on duty for at least 18 months.

Trainee on board

Under the guidance of the captain or qualified officer, he shall be on duty on the bridge or engine room for not less than 6 months on the ship of the corresponding class in the corresponding navigation area, or on the ship of one navigation area or one class lower.

Ability test

Pass the competency examination of three pairs and three tubes.

Apply for grade c

I have only seen so much at present, so judging from this, you may not be qualified to go to sea for 18 months. However, you have to ask the training institutions exactly, they know this best, and your application is Class C, so it is not so strict.