No attachment against any ship, boat, or other vessel of more than twenty tons, shall issue unless the plaintiff or someone in his behalf, shall first establish, to the satisfaction of the court in which he files his petition for attachment that he has a reasonable expectation of recovering an amount exclusive of all costs, equal to at least one-half the damages demanded in the petition for attachment. Reasonable notice of appearance before the court shall be given the owner, agent or master of said vessel, and at the time of the appearance the court shall determine the amount of such reasonable expectation of recovery and the amount of bond necessary to secure the release of the vessel if and when a writ be levied in accordance with this section. No attachment issued in violation of the provisions of this section shall create a valid lien upon the property sought to be attached, and no levy made under authority thereof shall be of any effect.