Bob,
Bad weather is something of a norm up there. Many years ago I travelled on P&O's old St Clair from Aberdeen to Lerwick and it was one of the roughest trips I have ever experienced.
However the English Channel has its moments, a couple of years back we were clinging to the sides of our bunks on a Brittany Ferries overnighter to St Malo but that is quite unusual on the route. With advancing age we now always book a four berth cabin to St Malo as accessing an upper bunk in a 'blow' can be, shall we say, interesting.
Colin