The Lilley & Gillie GS520 is a precision Off-Course Alarm system engineered by John Lilley & Gillie Ltd. in the United Kingdom. Designed to satisfy IMO and SOLAS requirements for vessel heading monitoring, the GS520 continuously compares the ship’s current heading against a preset target course. If the vessel veers beyond the allowable heading threshold—due to autopilot failure, steering gear malfunction, or heavy sea action—the system instantly triggers high-decibel audible and visual alerts to notify bridge watchkeeping officers.

Operating seamlessly with Transmit Magnetic Compass (TMC) sensor coils (such as the Lilley & Gillie GS820 pick-off) as well as master gyrocompass NMEA 0183 data feeds, the GS520 provides a critical safety layer for bridge navigation networks. It features a digital heading display, user-adjustable off-course limit thresholds, comprehensive self-test routines, and fail-safe relay outputs for integration into centralized Bridge Navigational Watch Alarm Systems (BNWAS) or main bridge alarm panels.

Key Features:
• IMO & SOLAS Compliant: Fulfills international carriage requirements for primary magnetic heading monitoring and off-course alarm functionality.
• Programmable Alarm Thresholds: Enables navigation officers to set custom off-course limits (typically 1° to 30°) suited to current sea conditions and maneuvering parameters.
• Multi-Source Heading Input: Accepts digital NMEA 0183 heading data ($HCHDG, $HCHDT, $HEHDT) from TMC pick-off units, fluxgate sensors, or gyrocompasses.
• Dual Audible & Visual Alerts: Features a high-intensity alarm LED, high-decibel internal buzzer, and front-panel alarm acknowledge button.
• Fail-Safe Alarm Relay Contacts: Equipped with potential-free relay outputs to trigger secondary bridge alarms, general alarm panels, or BNWAS units during heading drift or power loss.
• Compact Panel Design: Space-saving enclosure designed for flush mounting into helm consoles, steering stands, or overhead bridge panels.