how many boats can we carry?

[water folks]

Hi we now have two kayaks and one canoe. Some time in the future we will be going to four kayaks. Is there a rack system which will carry all of that? Or do I have to get a trailer? The car we currently have is a Ford Windstar, but (if my wife's wish is granted ) we will be getting a Pacifica in the near future. Any advice is appreciated. Oh we live in PA and vacation in Maine, as often as we can, so what ever we get will have to withstand hours at highway speeds.