1.   Ancient mariners believed that the vernal and autumnal equinoxes were accompanied by severe storms.

2.   Ancient mariners believed that the vernal and autumnal equinoxes were likely to be accompanied by severe storms.

3.   Ancient mariners believed that big storms formed on the equinoxes.

4.   Ancient mariners believed that the times of the autumn and spring equinoxes were more likely to be accompanied by severe storms.