The question does not ask about how far can the eye see on a curving surface. The asker stated 'a flat surface' Since when in mathematics do we mix up a flat surface with a curved surface. You have turned a very simple question in to a complicated question by introducing a curved plane.
As one would expect, the further you travel from the Equator, the colder the ocean waters generally become. Near the Equator, surface water temperatures can be as high as 80Â° Fahrenheit (27Â° Celsius). Near the poles, the temperature drops to a chilly 28Â° Fahrenheit (-2Â° Celsius). The western side of oceans are usually warmer than the eastern side. This is due to the way in which both the atmospheric and oceanic currents move water from the equator towards the poles on the western side of oceans, and from the poles towards the equator on the eastern side of oceans.
Winter temperatures in the Pacific Ocean along California's coast typically range from 60 degrees Fahrenheit (16.5 degrees Celsius) off Newport Beach on the southern coast to 51 degrees F (10.6 Â°C) at Crescent City and Trinidad near the state's northern end.