In order to supplment the control design for ship course keeping system with the unknown control direction and external nonzero time-varying disturbances, a robust adaptive control scheme is developed in this note, using the popular Backstepping, theNussbaum technique and the system transformation method. By employing the interent structural characters of marine ships, the novel integral form is derived by employing the invariance property of the Nussbaum function, which is to attenuate the defect of the time-varying multiplicative function. Compared with the existing results, the proposed algorithm is with more rigorous theory analysis. Numerical simulation results illustrate the effectiveness of the proposed scheme.