Our Cappy went for an 'accidental' swim when he tried to jump from our little dinghy onto the sail boat. He doesn't mind the sail boat, but HATES the little dinghy, so hubby decided to try to 'get him used to it' and took him for a ride. He stayed right at my husband's feet the whole time and tried to 'jump ship' onto any dock or other boat. And when he saw our boat in the distance, he tried to jump when he was too far away. He's quite a swimmer - but an angry one - meowing all the way to the back of the boat. Now, when we take him on the dinghy we make sure he's securely leashed.
When we leave him on the boat and go to town for any length of time, we leave a towel hanging over the back of the boat so he can make a beeline back there and claw his way back up should he fall.
And no, he doesn't have a life jacket. We researched this and found that they don't make life jackets for cats. When they have tried, it hasn't worked out - they really affect a cat's delicate balance. Using a small dog's life jacket isn't a good idea because those kind of jackets are made to keep a dog's head above water. Because cats bodies are different, they actually hold a cat's head underwater!
We talked to other cat owners who are boaters and most said that they don't put life jackets on them for this reason. Cappy wears a small harness with a piece of highly reflective tape on it, so we can see him at night, but the one time he got away from us at night, it was his big green eyes that we saw on the dock.
It's been a fun summer with him.
lin
Oh does he ever look proud of himself! Adorable! 
As long as he's safe cuz he's some kinda hunka-hunka kitty! 
