If they have replaced every part of the boat and the old boat no longer exists, then of course it's not the same boat as before.

Now it could be the SAME boat in the sense that it's identical in every way to the first boat, only made with newer materials.

kinda of like if you have two 2005 Honda Accords that are the same color with the same options etc. You have the SAME car but they are not one they are different.