why does a ferry going to france take 9 hours to get there ,but only 6 hours to get back?

Answer 1

Did you consider the difference in local time?

And there are currents in the canal too.

Sometimes when a ferry does an overnight run they do not let you go as soon as you arrive, but at a more normal hour, the Hook of Holland to Harwich ferry does that. So the trip during the night takes as long as the one during the day, but you will be along the cay for 3 hours before you can disembark.

Answer 2

My initial thought would be the currents, but again that is just a guess.