I am not the greatest swimmer and what compounds the problem is that I'm also sensitive to cold water. I remember going to a scout camp when I was a teenager. On the first day they had a mandatory swim check before you could do anything else. I watched all my friends in front of my jump in the water and start swimming. When it was my turn I jumped in and may as well have been hit by a car. I didn't realize that it was a glacier fed lake and as soon as I hit the water all my muscles contracted and I couldn't breathe. I thrashed around making embarrassing noises like I had the wind knocked out of me. After about 2 minutes of making a fool of myself much to the amusement of every scout in the camp I was able to acclimatize to the cold water and finish the swim check.
I have been on a couple cruises and I enjoyed the food (gluttony) aspect of it but as you know I am a movie enthusiast and have seen too many scenarios from White Squall, Poseidon Adventure, Jaws, The Perfect Storm, The Day After Tomorrow, and Titanic. Luckily having a large movie repertoire to draw on also helped me when I got scared of the water. I would just recall scenes form Speed 2 which would snap me out of my fear as I broke into laughter. I did just fine as long as I was confined to the dining area but going out on the deck made me realize how much water was surrounding me.
Some people have accused me of being a little paranoid and neurotic when it comes to water, but there are lots of other people who wear life jackets to work too just in case a dam upstream happens to break.