Considering the lengthy period of time that the Hesperus had been sitting at the dock, and considering the attention given to the repair work below decks, it was unrealistic to see the boat sail away without any thought given to the embedded seaweed, algae and barnacles which were undoubtedly on the hull.
Semi-serious. We all know that a 1.5 to 2 hour movie has to skip some things. While I believe your comment is likely to be correct, we must recognize the possibililty that he (fictionally) could have had the hull cleaned and the filmmaker just decided not to include that scene because he might not have thought it advanced the plot, which related to the Young Mariner's dealing with his guilt and grief.
TxMike Make a choice, to take a chance, to make a difference.
Mike: Thanks very much for the explanation. It helped straighten my perspective. (I have to admit that I am a cynical old, retired cruising sailor who has scraped too many hulls.)