Seaman sign on/off in China

Hi, I am working at sea and lives in China with my Chinese wife and Swedish son. I hold a L visa with multiple entries and 90 days each stay. Am I allowed to sign on my ship in a Chinese port and am I allowed to sign off in Chinese port and stay in China with the L? Reason for asking is that I am not allowed to work on the L and if I sign on in a Chinese port with my L, is it considered as work?