8. Limited to Movable Things.—
These liens arise only upon movable things engaged in commerce and navigation. They cannot exist in anything which is fixed and immovable and not the subject of maritime commerce or navigation. Thus they will subsist in vessels, rafts and cargoes but not upon a bridge or a ship totally out of commission (Rock Island Bridge, 6 Wall. 213; Pulaski, 33 Fed. 383). The lien has been sustained against a dredge. (Atlantic, 53 Fed. 607).