Also known as: mainsea · high seas · open sea
Written by attorneys · grounded in primary & secondary sources — see below
The open ocean beyond the territorial jurisdiction of any nation. Under traditional international law the main sea begins at the three-mile limit from shore.
Mina Mehta's vessel was seized by federal authorities hundreds of miles from any coast while carrying untaxed cargo. Congress invoked its Article I power to regulate commerce and punish offenses on the main sea. The court upheld the seizure because the incident occurred beyond any state's territorial waters.
Miguel Mendoza sailed a British merchant ship into a U.S. port during the War of 1812. Federal officers seized the vessel as enemy property on the main sea. The Supreme Court held that the executive could authorize such captures under the law of nations without further congressional grant.
Select any source to read its text and confirm it supports the definition.
Michelle Murphy's turbine failed during a transatlantic voyage, damaging her ship on the main sea. She sued the manufacturer in tort. The Supreme Court held that admiralty law governed because the injury occurred beyond territorial waters and involved a traditional maritime activity.
Megan Moore was captured after attacking a merchant vessel on the main sea. Prosecutors charged her with piracy as defined by the law of nations. The Supreme Court confirmed that Congress could define and punish such offenses committed beyond any country's jurisdiction.
Malcolm McKinley sued in Louisiana after suffering injury on a vessel operating on the main sea. The defendant moved to dismiss on forum non conveniens grounds. The Supreme Court held that the location of the accident on the high seas did not automatically bar application of the doctrine.
Maya Malik's vessel was ordered seized by presidential directive during the Korean War while operating far from shore. The seizure occurred on the main sea and raised separation-of-powers questions. The Supreme Court ruled that the President lacked authority to take private property without congressional authorization even in wartime.
No. Admiralty jurisdiction requires both a locality on navigable waters and a connection to traditional maritime activity. A claim arising on the main sea may support admiralty jurisdiction when the underlying activity is maritime in nature, but the mere fact of location does not confer jurisdiction by itself.
Supporting sources
Yes. Article I, Section 8 grants Congress power to define and punish piracies and felonies committed on the high seas. This authority extends to offenses occurring beyond the territorial jurisdiction of any state.
Supporting sources
No. Classification of homicide turns on mens rea and mitigating circumstances such as heat of passion, not on the geographic setting. A killing on the high seas receives the same analysis as any other intentional killing under common law principles.
Supporting sources
…offices and post roads, cl. 7, or to grant patents and copyrights, cl. 8, or to "punish Piracies and Felonies committed on the high Seas," cl. 10. It might not even need the power to raise and support an Army and Navy, cls. 12 and 13, for fewer people would engage in commercial shipping if they thought that a foreign power…