Refusal of District Court to issue a warrant in rem for arrest of the vessel can be independently appealed.
Operation of the vessel in navigating the waters was sufficient maritime activity to give the court statutory in rem jurisdiction.
The lien against the vessel was perfected by the harm of the tort.
http://media.ca11.uscourts.gov/opinions/pub/files/201810374.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.