Abstract: In this paper, definition and three principal conceptions of free-ballast ship in the world are described, including through flow system hull, non-ballast water ships(NOBS) hull (V-shaped hull) and monomaran hull. Then the developmental history and the current prospects of the free-ballast ship type employed in fishing vessels are discussed by referring to the features of fishing ships, and several opinions.The suggestions for future development of open sea fishing ships are provided in views of saving energy and reducing environmental pollution.