Judges have long struggled to determine what contracts are maritime. However, once an agreement has been held to be a maritime contract, the courts have generally applied principles of maritime law to the contractual dispute, "protecting the uniformity of federal maritime law." Norfolk Southern Ry. v. James N. Kirby Pty. Ltd., 543 U.S. 14, 29 (2004). The primary exception to the uniformity rule for maritime contracts is marine insurance.