Debts amounting to at least fifty dollars ($50), contracted for the benefit of vessels, are liens in the cases provided in Section 491.
Actions for any of the causes specified in Section 491 shall be brought against the owners by name, if known, but if not known, that fact shall be stated in the complaint, and the defendants shall be designated as unknown owners. Other persons having a lien upon the vessel may be made defendants to the action, the nature and amount of such lien being stated in the complaint.