A heave compensator for a drill ship with a derrick and hoist system with a dead line provides a line reservoir on the dead line. The dead line is reciprocated to move the hook load relative to the vessel to control it relative to the sea bed. The line reservoir is expanded or contracted by changes in ballast pressure to counterbalance the hook load. To compensate for heave and friction in the hoist system a pressure source is provided to augment the ballast pressure for hook load and position control. Sensors and controls are provided to anticipate and compensate for oncoming heave excursions. The dead line being flexible permits latitude in selecting and orienting the compensator machinery. As an option, the vertical movement sensor is placed on the hook related structure for more responsiveness to hook load movements.