Massachusetts General Laws Part III. Courts, Judicial Officers and Proceedings in Civil Cases (Ch. 211-262) Ch. 223, § 44

No ship or vessel shall be attached in a civil action unless the plaintiff or a person on his behalf makes affidavit and proves to the satisfaction of a justice of a court that he has a good claim and reasonable expectation of recovering an amount, exclusive of all costs, equal at least to one-third of the amount of damages claimed, which affidavit shall be annexed to the writ of attachment, and the certificate of the justice that he is satisfied that the same is true shall be annexed to the writ of attachment or endorsed thereon.