The Mamie was a case heard by the United States Supreme Court in 1881. The case involved a dispute between the owners of a steamboat, the Mamie, and the owners of a wharfboat, the John B. Maury. The Mamie had been moored to the wharfboat for several months, and the owners of the wharfboat sought to collect rent for the use of the wharfboat. The owners of the Mamie argued that they were not liable for the rent, as they had not used the wharfboat for any purpose other than mooring the Mamie. The Supreme Court held that the owners of the Mamie were liable for the rent, as they had used the wharfboat for their own benefit. The Court reasoned that the owners of the Mamie had received a benefit from the use of the wharfboat, as it provided a safe and secure place to moor the Mamie. The Court also noted that the owners of the Mamie had not offered to pay for the use of the wharfboat, and thus had not acted in good faith. The Court's decision established that the owners of a vessel are liable for the rent of a wharfboat when they use it for their own benefit. The Court also established that the owners of a vessel must act in good faith when using a wharfboat, and must offer to pay for the use of the wharfboat if they wish to avoid liability for the rent.

In The Mamie, the Supreme Court was tasked with determining whether a ship captain could be held liable for damages caused by his vessel. The majority opinion found that the captain was not liable because he had no knowledge of any negligence or fault on behalf of his crew and thus could not have prevented the damage from occurring. However, in dissent, Justice Field argued that captains should always be held responsible for their vessels regardless of their knowledge or lack thereof regarding any negligent behavior on part of their crew. He stated that it is impossible to know what goes on aboard a ship at all times and therefore captains must take responsibility for anything which occurs while they are in charge. Furthermore, Field argued that if captains were allowed to escape liability simply due to ignorance then there would be little incentive for them to properly supervise their crews and ensure safety regulations were being followed.