I have been fortunate to see the GF about a dozen times. Many sailors I have met have no idea what it is. However, being on the water gives you ample opportunity to see it. Here is a great explanation of the phenomenon: "The green flash is a type of mirage that occurs at sunrise or sunset only. And the best circumstances to view it are as you described: on the water or flat horizon, no fog, no clouds, no pollutants. The first ray of sunrise or last ray of sunset can be a brilliant green band. This is caused by refraction or bending of the rays of sunlight. At the horizon, sunlight - which is comprised of all colors - has to pass through a thicker atmosphere than if it were high in the sky. The sun is actually already below the horizon, but the refracted rays make it appear the sun has not yet set. The atmosphere prism bends blue wavelengths of sunlight the most, but since our atmosphere scatters blue light, the green appears visible in the sky. Close to the equator, the green flash is quick, lasting only a second or so. Near the poles, it can last longer."
So get out there and keep your eyes open!