Thorough, stubborn, meticulous are all words to describe Guillermo del Toro at this point. The ship is not such a major part of the film, so, a detail most directors would leave to VFX and let go, but not the world's most hands-on director.
He believed that doing so would affect al the principles he held going into filming as the ship is a character in the film and all his characters have to be created by humans!
Frankenstein is therefore fully made by humans. A true masterpiece of taditional film making, something we just don't get to see anymore in modern cinema.
