It really depends on the cat/cats. My ex girlfriends cats would never venture more that a few feet from her boat and were always on board in the morning whereas the late Mike Stevens would tell stories of having to wait a couple of days for his cats to return before he could set off!
Helps considerably if you have a lockable cat flap on the boat
Hve seen many cats happily living on narrowboats.
We only ever put the cats into life jackets when travelling on tidal waters, cats can quite happpily swim in canals, the main problem (for the cat) is getting out of the water once it has fallen in, especially on steel piled sections of canal.
Tim