From our preceding studies, we disclosed the characteristics of the under-development device, called salivary NO₃^- Ion-Sensitive Field-Effect Transistors (NO₃^--ISFETs). These transistors have evaluated the navigators' mental workload in maneuvering a ship through the ship simulator experiments which can arrange the uniform experimental circumstances at the different simulator's scenario. The NO₃^--ISFETs give the quantitative evaluation of the mental workload, using NO₃^- in onedrop saliva. The NO₃^--ISFETs are supposed to be used for the navigators working anywhere in a ship around the clock. Therefore, our goal is to complete the NO₃^--ISFETs, which have the durability for mucin in saliva when they measure the salivary NO₃^- long time for the purpose of the prevention of navigator's human factors in their duties. This time, we tried to carry out another ship-simulator experiment with new NO₃^--ISFETs changed the polymer which is used at the device's sensor part. We can confirm the instrumental difference between conventional NO₃^--ISFETs and new ones, while we evaluate the variability of navigators' mental workload.