How to Fix Common Radar and GPS Signal Issues on Your Boat

Whether you're cruising along the coastline or making an offshore passage, reliable radar and GPS systems are essential for safe and efficient navigation. On medium to large recreational boats, these technologies provide critical situational awareness, from tracking nearby vessels to pinpointing your location with precision. But what happens when your marine radar drops out, or your GPS signal becomes erratic?

These issues are not only frustrating, but they can also compromise safety. Fortunately, many common radar and GPS signal problems can be resolved with a bit of troubleshooting and know-how. In this guide, we’ll walk through typical issues that affect systems from top brands like Garmin, and provide solutions you can implement before calling in a technician.

1. Understanding How Marine Radar and GPS Systems Work

Before diving into problem-solving, it’s useful to understand the basic operation of your onboard radar and GPS systems:

Radar:

Marine radar systems use high-frequency radio waves to detect objects around your boat. These waves bounce off solid objects and return to the radar antenna (typically mounted on the mast or radar arch), providing real-time data on the position, movement, and distance of nearby vessels, coastlines, or weather systems.

GPS (Global Positioning System):

Marine GPS relies on satellite signals to triangulate your exact position. Your GPS antenna receives signals from multiple satellites in orbit and transmits location data to your chartplotter, autopilot, AIS, and other connected systems.

2. Common Radar Signal Issues and Their Causes

Symptoms of Radar Signal Failure:

• Radar screen not displaying any targets

• Radar dome powers on but no signal

• Inconsistent or intermittent contact readings

• Radar works intermittently when turning or heeling

Troubleshooting Steps:

A. Check Power and Connections

• Inspect power cables for corrosion or loose terminals

• Check fuse panels or breakers at the helm and radar dome

• Use a multimeter to verify voltage at the radar unit

B. Inspect the Antenna Dome or Open Array

• Look for physical damage from weather, birds, or impact

• Clean the surface of the antenna to remove salt buildup

• Ensure there are no objects obstructing the antenna’s sweep path

C. Software & Firmware Updates

Modern systems like Garmin Fantom radar often require updates to improve performance or fix bugs.

• Use Garmin Express or the ActiveCaptain app to check for firmware updates

• Always back up your chartplotter settings before updating

Learn how to update Garmin radar software on the official Garmin Support Page.

D. Test in Open Water

Radar is often distorted by nearby structures, marinas, or high wave interference. Take your boat into open water and perform a test sweep to isolate environmental factors.

3. Common GPS Signal Issues and Their Causes

Symptoms of GPS Problems:

• Chartplotter shows "No Position"

• GPS location drifts or jumps erratically

• Inaccurate heading or speed over ground (SOG)

• Autopilot unable to track waypoint

Troubleshooting Steps:

A. Antenna Placement and View of the Sky

• GPS antennas need a clear, unobstructed view of the sky

• Avoid mounting near metal structures, antennas, or radar domes

• Ideal placement: high on the boat, centered, and away from interference sources

B. Check Cables and Connections

• GPS cables can degrade over time from moisture, vibration, or UV damage

• Replace any cracked or frayed coaxial cables

C. Update Software & GPS Almanac

• Outdated software can prevent the system from syncing with new satellite configurations

• Update firmware via SD card or USB using Garmin software

Garmin's step-by-step GPS update process is detailed here.

4. Addressing Interference from Other Electronics

EMI (Electromagnetic Interference) and Its Impact

Modern recreational boats are packed with electronics: VHF radios, LED lighting, inverters, sonar, autopilot systems, and more. Each of these can potentially interfere with your GPS or radar.

Signs of Interference:

• Radar screen flickers when other electronics are active

• GPS drops out when engine is running

• Distortion when LED lights are on

Solutions:

• Separate cable routing: Don’t run GPS or radar wiring alongside high-power DC or AC lines

• Ferrite core filters: Add EMI suppressors to cables

• Install GPS on a dedicated breaker: Prevent power fluctuations from other systems

Protect your electronics with proper power components from our Victron Energy collection.

5. Troubleshooting Network and Data Link Failures

If Your Radar or GPS Doesn't Communicate with Other Systems:

• Check NMEA 2000 backbone for termination resistors and voltage (~9-12V)

• Use a network tester to ensure proper communication

• Ensure device instance IDs are not conflicting

Garmin Network Tips:

• Garmin radar domes connect via Garmin Marine Network (not NMEA 2000)

• Use marine-grade Ethernet cables for radar/chartplotter communication

• Check for firmware compatibility between devices

Master Bus & NMEA 2000 Interoperability:

If you're integrating Victron Energy power monitoring or control systems, ensure that NMEA 2000 data is configured properly for use with GPS or navigation data.

6. When to Replace or Upgrade Your Radar or GPS System

If you’ve worked through the diagnostics and are still experiencing issues, it may be time for a system upgrade.

Indicators You Need a New System:

• Unit is more than 8-10 years old

• No longer receiving software updates

• Poor resolution or display visibility

• Not compatible with modern NMEA 2000 networks

Upgrade Options to Consider:

• Garmin Fantom series radars: Solid-state performance with MotionScope Doppler technology

• Garmin GPSMAP chartplotters: Touchscreen integration and advanced mapping

Explore our full range of Garmin marine electronics.

7. Maintenance Tips to Avoid Future Signal Issues

Every 3 Months:

• Wipe down radar domes and GPS antennas

• Visually inspect cables and connectors

• Update firmware if available

Every 6 Months:

• Test radar in different weather conditions

• Perform a full GPS acquisition cycle

• Check for firmware compatibility across devices

Annually:

• Re-bed and reseal antenna mounts to prevent corrosion

• Clean and treat connectors with dielectric grease

Keep Your Navigation Reliable with Help from S & S Dockside Marine Supply

Maintaining a reliable radar and GPS system is essential for safe boating. Fortunately, many signal and connectivity issues can be resolved with careful diagnostics and routine maintenance. From proper antenna placement to firmware updates and electrical isolation, there are many tools available to the boat owner willing to get hands-on.

When it’s time to upgrade your radar or GPS system or if you need help finding compatible components, S & S Dockside Marine Supply is here to support your journey. We offer a complete line of Garmin radar units, chartplotters, GPS antennas, and Victron power solutions to keep your electronics performing at their best.

Visit S & S Dockside Marine Supply to explore premium marine electronics and get expert guidance tailored to your vessel.