ABSTRACTPiloting large vessels in increasingly congested waterways is no simple task. As in many scenarios involving decision making under uncertainty, masters, mates, and pilots engaged in piloting are inundated with much information and must make crucial decisions in real time. Piloting is also an inherently judgmental activity. Pilots and ship's captains invariably develop heuristics for transiting particular waterways. As vessels become larger, cargoes more hazardous, and the waterways more congested, decision aid technology is being considered to improve piloting decision making.This paper describes one approach to providing improved on‐board decision support to masters, mates on watch, and pilots navigating in restricted waters. We discuss (1) the use of cognitive decision aids in piloting, (2) the design of such a decision aid developed for New York harbor, and (3) the transition of the system from an off‐line prototype to an operational shipboard expert system for tankers transiting the Gulf of Ala