if you replace every cell in your brain are you really still the same person?
the answer is yes, because the information regarding the spatial and biochemical relationships between those cells hasn't changed, or rather, the continuous function describing the changes occurring to that information over time hasn't significantly changed its course or developed discontinuities as a result of the replacement.
similarly: if you replace every material comprising a ship, is it still the same ship?
the answer is yes, because it has the same internal structure and similar fluid dynamics.

fuck nihilismfags. (you) would have us believe "oh hurr durr durr, but what is it that makes you you, you can't point it out, it's not quantifiable." of course it's quantifiable, just because there's no specific physical object that stores our identity doesn't mean there's no specific physical *property* that stores our identity, that property is simply *not* an object, it's the *shape* of an object. you can pack matter into a sphere, and sure it won't be a perfect sphere, but that doesn't change the fact that you can measure the proximity of its shape to that of a sphere and identify the difference as objectively small. you can identify the matter as closely aligned to the ideal of a sphere. saying something's not quantifiable because it's not physical matter in and of itself is like schoolchildren who haven't learned calculus and think a function's rate of change isn't quantifiable because there are no fundamental operators they've learned up to that point that can describe it.