The term 'navigational system' refers to a system of navigation used to determine the position of a vessel or aircraft. Two examples of navigational systems are LORAN (Long Range Navigation) and OBOE (Operational Beacon Over-the-Horizon Entry). LORAN is a hyperbolic navigation system that uses radio signals from multiple transmitters to determine the position of a vessel or aircraft. OBOE is a navigational system that uses two ground-based radio transmitters to determine the position of an aircraft. Both systems are used to provide accurate navigational information for vessels and aircraft.