Accidents are hard to avoid on board, with the deck continually moving up and down, and back and forth, at different rates and degrees.

Zhang said sometimes the rice he makes is too dry, because a sudden big lurch or sway of the boat causes the water to spill from the pot.

"Upturning whole meals is a common thing at sea and you just have to go and make something new," he smiled. Nothing seems difficult for him.

His spare time on board is filled doing keep-fit exercises, drawing pictures and singing.

This year, Zhang will spend three-and-a-half months at sea. He said his wife and daughter have got used to it and they can take good care of themselves.

However, 31-year-old Wei Yi, a law enforcement worker in China Marine Surveillance No 66, said his 2-year-old son is always on his mind.

Although he recorded videos and left hundreds of photos at home to enable his son to remain familiar with his father, the time spent apart still worries Wei.

When his son was sick shortly after his birth, he had to leave the infant and board ship.

"It was agony to leave my son, but I had to, because if I didn't, other colleagues would. The time spent at home is so precious for us all," Wei said, admitting this was the first time in his six years at sea that he could not focus on his work.

Wei is mainly in charge of coordination in offshore law enforcement in the East China Sea.

China has carried out routine patrols in the Yellow Sea, East China Sea and South China Sea since 2006.

During a recent routine patrol in East China Sea, the ship, along with China Marine Surveillance No 49, expelled a pair of Japanese Coast Guard survey vessels.

From June to August 2010, China Marine Surveillance had 19 ships and four planes conduct a special patrol in the South China Sea. During that mission, 228 foreign ships were intercepted and expelled from Chinese waters, according to the statistics from the agency, compared with 110 expulsions in 2007.

Next year, China plans to build another 36 patrol vessels to protect national marine rights and sovereignty, according to an official with the agency.

The ship's singing cook, Zhang Chunhui, prepares a meal for the crew in the galley aboard China Marine Surveillance No 66. Wang Qian / China Daily