Marine Radar 101: An Essential Guide for Seafarers

For safe navigation and collision avoidance at sea, a solid understanding of marine radars is essential for every mariner, especially the Officers of the Watch (OOW).

This equipment is undoubtedly one of our best navigational tools, but it’s only as good as its user.

While over-reliance on ship radars may lead to confusion, doubt, and close-quarter situations, knowing its limitations can help you to make safer decisions.

Key Takeaways

• Marine radar utilizes radio waves to provide a 360-degree bird’s-eye view around a vessel for navigation and collision avoidance.
• There are two main types – X-band effective for short range, and S-band for longer range detection.
• Key radar capabilities include target detection, tracking, accuracy, resolution, clutter reduction, and display.

What is a Marine Radar and How Does it Work?

A marine radar, also called a ship’s radar, is a navigational tool used to detect and track objects, including other vessels, landmasses, and navigational aids, while providing a 360-degree overhead view of a ship’s surroundings.

This bird’s-eye perspective of nearby marine traffic and geography makes marine radar invaluable for navigation, collision avoidance, and situational awareness at sea.

It operates based on the principles of radio detection and ranging (hence the term RADAR), utilizing electromagnetic pulses or radio waves to determine the distance and bearing of objects within its range.

Basic Operation

The operation of every marine radar involves the following key components and processes:

1. Antenna Scanner

The radar system includes an antenna installed on the ship’s mast that continuously rotates and emits frequency beams, also called echoes, to detect objects.

2. Transmission and Reflection

The emitted frequency beams travel outward and reflect off objects in the surrounding environment.

The time taken for these reflections to return to the radar receiver provides information about the presence and location of objects.

3. Display

The reflections received by the radar are displayed on a screen, allowing the operator to visualize the location and distance of objects in the vicinity.

Types of Marine Radar: X-Band vs. S-Band

There are two main types of marine radar systems installed on merchant vessels – X-band (3 cm wavelength) and S-band (10 cm wavelength).

X-Band Radar

An X-Band Radar operates in the frequency range of 9.2-9.5 GHz using a wavelength of 3 centimeters.

This makes it more effective at detecting small objects at shorter ranges, such as buoys and small vessels.

X-Band also responds to the signal emitted by a  Search and Rescue Transponder (SART).

S-Band Radar

An S-Band Radar operates in the frequency range of 2.9-3.1 GHz using a wavelength of 10 centimeters.

This radar type is better suited for early detection because it effectively detects targets on a range of more than 20 miles!

On board, you can see both radars set on different ranges- one for early detection and the other for discovering small objects reflecting weak echoes.

Key Features of Marine Radar

While both radars have different operational characteristics, they also share similar features outlined in SOLAS and the IMO performance standards.

In essence, marine radars should have these features and capabilities:

1. Detection Performance – The ability to reliably detect targets at specified ranges

2. Tracking – Tracking multiple targets and vectors to determine the course, speed, and closest point of approach (CPA)

3. Range and Bearing Accuracy – Precise target distance and direction measurements within strict tolerances.

4. Resolution – Specifically, range and bearing resolution. It’s the ability to display separate echoes from two targets at the same range or bearing and close together

5. Anti-Clutter Functions – Reduction of unwanted echoes, including sea clutter, rain, and other forms of precipitation, clouds, sandstorms, and interference from other radars. 

6. Signal Processing – Enhanced target presentation on the display. The picture update period, with minimum latency, should be adequate to ensure the target detection requirements are met. 

7. Presentation and Display – The echoes must be displayed on the PPI to provide a visual representation of the surrounding environment and the location of objects.

8. Integration -The ability to interface and share data with other navigation systems and sensors like AIS, GPS, autopilot, ARPA, and ECDIS for enhanced functionality and simplified operation.

Practical Tips and Tricks

As mentioned before, your ship’s radar is only as good as the user. Here are some best practices for using marine radar effectively:

• Adjust gain/sea clutter/rain clutter settings without diluting small, genuine echoes from weak targets.
• Familiarize yourself with different radar modes such as Head-up, Course-up, North-up, and True Motion modes,
• Understand whether you are using speed over the ground (SOG) or through the water (STW) and when to use them
• Keep in mind the proper antenna mounting and alignment. A target could be dead ahead on your radar screen but is slightly off to starboard on the visual.
• Understand radar limitations in adverse weather.
• Make use of the electronic bearing line (EBL), variable range marker (VRM), and parallel indexing.
• Check the accuracy of your radar’s range and bearing by comparing it to the nautical charts.

Marine Radar FAQ

Q: What is a ship radar?

A: A ship radar is the same as marine radar, which utilizes radio waves to detect objects and measure distances of targets at sea.

Q: What type of radar is used in the ocean?

A: The types of radar widely used by merchant vessels in the ocean are the S-Band and X-Band types of radars

Q: What are the advantages of marine radar?

A: A marine radar provides a bird’s-eye view of your ship and its surroundings while measuring distance and range and tracking your targets.

Ship radars can also “see” in the dark and during restricted visibility and detect small targets that may be difficult to see with the human eye.

Q: Why do ships have 2 radars?

A: Ships have two radars so that if one system fails, the other one will act as backup. Besides, SOLAS also suggests that aside from a 3 GHz radar, ships must also have a second 9 GHz radar.

“All ships of 3,000 gross tonnage and upwards shall, in addition to meeting the requirements of 

paragraph 2.5, have: 

A 3 GHz radar or, where considered appropriate by the Administration, a second 9 GHz radar, or 

other means, to determine and display the range and bearing of other surface craft, obstructions, buoys, shorelines, and navigational marks to assist in navigation and collision avoidance…”

-SOLAS Chapter V Regulation 19 Paragraph 2.7.1

Q: How far can radar detect at sea?

A: While range scales of 0.25, 0.5, 0.75, 1.5, 3, 6, 12, and 24 NM are provided, ship radars may also have a range of up to 96 nautical miles set in the system.

The longer ranges are used for detecting radio beacons and SART.

Q: How can radar detect small objects like buoys?

A: Using shorter pulse lengths and reduced minimum range settings can help detect smaller targets reflecting weak echoes on the ship’s radar.

Q: What might limit radar performance at sea?

A: Environmental factors like heavy rain, high seas, strong winds, and extreme temperatures can degrade radar capabilities.

If you have more questions about the marine radar, feel free to comment below or message me in my email.

May the winds be in your favor.