Can someone please tell me if ferry boats rock very much?

I have done this crossing loads of times , having a cabin is a very good idea as often there is nowhere to sit comfortably in the main part of the ship. There is also loads to do and see on the ship and even a cinema if you are inclined . Take sturgeron and eat regularly (small amounts) . I only had one crossing which was a little rocky but that was in winter , mostly after the first 15 mins or so you don`t feel any movement just a gentle buzzing under your feet . It is quite enjoyable so try not to worry .

Unfortunately the ferry from Plymouth to Roscoff can be a little bit rocky depending upon the weather. We crossed last April and it was literally all over the place. My suggestion would be to either book a cabin prior to travel or failing that to get onboard and see what it's like. If the weather isn't great book a cabin once you board. They will be a lot cheaper and to be honest being in a cabin gives you the chance to lay down (and to have your own bathroom to be ill in)
Hope this helps

Plymouth to Roscoff

Old thread.
OP has presumably been and come back again by now Or not, as the case may be.