I don't even have the "Harbor" available on my buildings list, to even try to construct! Will it not even appear on the list until an available beach tile exists in range of the level 3 city? I've triple-checked, and the tech is on my "completed" list. But it's like I haven't even researched it.
We honestly need a detailed FAQ for building a harbor. Too many people have trouble building them (myself as well, this patch around, apparently). Things like exact tile/influence distances, etc.