It is important for the mariners to be able to judge the critical wind velocity for the present layout of the mooring lines and the effect of the addition of the lines. In the present paper, the estimation procedure to find the critical wind velocity for the given mooring condition was shown and the representation of the diagrams were proposed to simplify the calculation procedures. The value which can be obtain from the Table 2 using a combination of α (dip angle of the line) and β (horizontal angle of the line) gives the square number of the critical wind velocity for the present layout of the mooring lines. Table 3 is the correction table for the different number and the different strength of the mooring lines from the standard condition, and Table 4 is for the correction to the different windage area of the vessel.