Re: North Sea experience
I also have been in numerous hurricanes. A gale force 9 is frankly nothing and quite par for the course.
Actually it is the sea swell, not the wind speed that makes the difference.
I've been in force 12 conditions a couple of times and it's quite unpleasant and quite dangerous. On a cruise ship people are always injured. The ship handles it of course, it's designed to, but all the fittings, chairs, bottles, glasses, everything not nailed down just goes crashing about. People equally, thrown all over the place if they are not sat down. Many older people can't cope with that movement and will be knocked over.
If you booked a cabin at the front or back of the ship you're in hell for the duration. The extremities of the ship will constantly rise and fall by a huge amount. Could be 10-30 feet. Imagine standing in a block of flats with 5 floors and you're on floor 3. Every 10 seconds the floor you are standing on drops down to the first floor, then rises up to the 5th floor repeatedly over and over. Just horrible really.
These conditions don't happen often but when they do it's very unpleasant. Hence I always book a cabin mid-ships and always a balcony.