Oh well, I have been on several rough ferries crossings, mostly in the Clyde area where I'm based.
The most recent one was on Caledonian MacBrayne's ferry, MV
Coruisk, which happened on Hogmanay 2006. She is the winter relief ferry for the Rothesay to Wemyss Bay route, but because of bad weather that day, she had to be diverted to Gourock pier, which is used as a safe haven in event of bad weather. This added another 30 mins to the journey (total 1 hour).
On her return leg to Rothesay, the Southerly winds started to pick up really bad, from gale force 6 to 9 (a nearby weather station reported 80+ knots winds that night) and it was one of the most roughest crossing I've ever been on.
The whole vessel shuddered every time she hit waves and the spray would go up as far as the wheelhouse (see accompanying picture, so you can imagine how big the sprays were) and she took almost 3 hours to reach Rothesay. (when it would normally have taken just over 1 hour).
When she finally arrived at Rothesay, the problems didn't stop there. The passenger gangway were deemed too unsafe to use because of very high tide (surged by the storms) and also because it was too windy. It was decided that passengers would disembark via the car deck instead, but a strong gust almost blew a Cal-Mac crew off the car deck, so they asked every car owner on the ferry if they could take in a couple of foot passengers and give them a lift in their car. As I had my car with me, I agreed to give two passengers a lift to the pierhead.
In my 25 years of travelling with Caledonian MacBrayne, nothing like this has ever happened, so it was a pretty unique event. Full kudos
to the crew of MV
Coruisk who got us from A to Z safely in one of the worst storms ever to hit the West of Scotland in the final day of 2006.
Kev