In determining admiralty jurisdiction, the court will inquire into the nature and subject matter of the contract, and whether it was:

• a maritime contract and the service a maritime service;
• to be performed upon the sea, or upon waters within the ebb and flow of the tide; and
• substantially performed upon the sea, or tidewaters, although it had commenced and had terminated beyond the reach of the tide.[i]

The admiralty jurisdiction of a case rests upon grounds other than that of the form of the remedy pursued.  In all cases of contracts coming within the jurisdiction, the remedy may be sought in personam.  When the case is one in which there exists a maritime lien, the remedy may be pursued in rem.  Although local or state liens form no part of the admiralty and maritime jurisdiction conferred on the government of the United States, they might nevertheless be enforced by the admiralty courts when the contract to which they appertain is within the admiralty jurisdiction as a discretionary power, which the court might exercise for the purposes of justice.[ii]

[i] Archawski v. Hanioti, 350 U.S. 532 (U.S. 1956)

[ii] Steamer Petrel v. Dumont, 28 Ohio St. 602 (Ohio 1876)