I am making a game folowing the development of civilizations on an alien planet, however as i am almost done with the geography of this planet, i have come to realize that my continents which are seperated by oceans are quite far apart and i am starting to worry that early intelligent life would not be able to spread to all continents of this planet (after all humans took a while to spread to the Americas).
My question is therefore: how large could oceans be that humans could (for simplicities sake I will let my aliens be very close to humans) realistically migrate across with only technology comparable to what humans on earth used to settle the islands of the pacific. Would it be easier or more difficult for humans to migrate across water in warmer regions of the planet than colder and how close would the islands in the oceans have to be? (Assuming that all conditions, including weather and climate, is the same as on earth.)
edit: to specify slightly, i did make some calculations on the distances between my continents at the specific places I imagine that migrations would follow and they mostly fall somewhere between 2700 km and 6750 km, which might not be that far from earth after all, but as one answer points out, I do not know what effect the ocean currents would have.