This study adopted a new formula fishing-boat fuel which is based on the existing fishing-boat-fuel A (FBFA) with the addition of viscous agents (RDS0.5, PFO0.5) in two different proportions. FBFA, RDS0.5 and PFO0.5, respectively are tested in three real-scale fishing boats. During the actual ship trial, the engine operating conditions, engine fuel oil consumption, horse power output and navigation speed were assessed and recorded. Furthermore, fuel emissions were sampled and analyzed, fishing-boat diesel engine performance was assessed and differences in exhaust composition were compared. The results showed that the three new viscous agents fules used lack abnormal vibration and noise, and have similar output status in terms of engine operational performance. At the same boat, the fuel oil consumption rates were similar between the new formula and FBFA. Moreover, analysis of contamination displayed that RDS0.5 particulate matter (PM) content was less than that of FBFA. Consequently, RDS0.5 appears to cause less engine wear. Additionally, the exhaust emission analysis results identified RDS0.5 as the best fuel for the engine. Futhermore, regarding pollutant emissions, including CO, CO2, NOx, PM, PAHs, only CO emissions are slightly higher than for FBFA. However, the CO emission value does not exceed exhaust emission standards of the U.S. Environmental Protection Agency (EPA). It is remains within the allowable value range. RDS0.5 should have practical value.