A voyage puts several interests at risk at once, and ocean marine insurance has a coverage for each:
Hull: physical damage to the vessel and the property that is part of it.
Cargo: physical damage to the goods being carried, usually bought by the goods' owner.
Freight: the money earned for carrying goods, when a covered loss prevents the shipowner from collecting it.
Protection and indemnity (P&I): the liability side, covering bodily injury and property damage to the public and to the master and crew, plus legal liability for others' cargo.
Example: a storm sinks a ship carrying furniture. Hull pays the shipowner for the ship, cargo pays the furniture's owner, and freight replaces the transport charge the shipowner can no longer collect. Damage to the owner's own ship is never a P&I loss.
Two federal laws generate much of P&I's crew and worker claims. Under the Jones Act (46 U.S.C. §30104), a seaman injured in the course of employment may bring a civil action at law against the employer, with the right of trial by jury. When the employer is the vessel owner, that claim falls under P&I.
The Longshore and Harbor Workers' Compensation Act covers dock workers such as longshore workers, and its definition of employee leaves out a master or member of a crew of any vessel. The worker's employer pays compensation, and that liability is exclusive as to the employer. Under 33 U.S.C. §905(b), a covered worker injured by a vessel's negligence may also sue the vessel as a third party; that suit is the shipowner's P&I exposure. The vessel's liability cannot rest on the warranty of seaworthiness.