since the introduction of kerosene and cryostations, tankers have become pretty much useless. a way to remedy that is if there was a workshop update that allows them to retain the harbour boost of the ships used, partially at least. a 1/5 ratio seems reasonable since craft effectiveness past that would (or at least should) be a given by the point space age is reached. ships would still serve a purpose as a means to improve trading if this was implemented. otherwise it would probably be best to just remove tankers from the game and instead make a (fairly expensive) workshop upgrade called "tankers" that allows them to improve the oil max a bit, like compendiums do with science. just a thought