Aiming at the safety hazards existing in the net hauling operation of double-trawler fishing vessels under harsh marine environment, this paper analyzes the structure and layout of double-trawler fishing vessels, the operation of net haulers and the current safety devices, based on which, a set of pure mechanically structured hauler protection device that requires no significant adjustment of the vessel body has been designed. Using the spindle speed function of CNC machine tools, the operating states of four different hauling line speeds (28, 45, 65 and 75 m/min) of the net hauler were simulated to test the safety device. The results showed that, when the simulated crew triggered the safety device due to encountering dangers, the distance that the net rope winding the crew continued to move to the friction drum was less than 1.5 m. Through the conversion relationship of the distance, speed, and time, it was gained that the time span for the safety to shut down the hauling machine was less than 1s, which could avoid the occurrence of safety accidents caused by the net hauler to a greater extent. The research shows that this safety device can play a protecting role in the net hauling process of trawler vessels.