I partially agree, as obviously the ship is slightly different from what it was before the plank was swapped. I would have said, that the overall appearance of the ship, as well as it's function and all the other defining characteristics, stay the same. Because even one plank is swapped, it still functions the way it did before. That's also why I wouldn't say that this can be applied to humans or any other living thing. Yes, we are a different person each new day, but that's not due to a bacteria dying or a skin cell getting replaced. It's because of the things we learn and experience on that day and that's something a ship can't do.