Introduction to Radar

introduction to radar

This is a very brief and concise overview of Radar in the hope that it will give you an overview but also show you the benefits of radar. If you have radar onboard your boat or intend to use it on another please consider taking an RYA Radar Course (1 day) and allow plenty of time to familiarise yourself with the set you will be using. 

What does RADAR stand for?

RAdio Detection and Ranging

What's the point of Radar?

The ability to see land masses and objects, other vessels (with radar reflectors) therefore aiding you in safe navigation. 

How does a Radar work?

  • In a basic sense it simply sends out a radio wave which bounces off an object (target) and reflects back. Similar to using a torch in the dark, when the light reflects off something it would show you where it is. The stronger the torch beam the more it will see.

What affects radar?

  • Transmitter Power Output - The higher the power output level the more chance that your radar will receive signals bouncing off objects and showing them as targets on your display. 
  • Beam Angle - Beam angle is determined by the length of your antenna. The longer the antenna is, the narrower the beam angle. This narrow beam angle increases the radars bearing resolution allowing you to discriminate easily between two objects that are close together. It also shows land mass contours with much greater resolution.

Main uses of radar:

  • Collision Avoidance i.e. look out, plotting, finding course & speed, finding closest point of approach, determining risk of collision
  • Navigation i.e. range, bearings & mixed fixes
  • Pilotage i.e. clearing lines

IRPCS & the use of radar:

  • Rule 5 - Lookout
  • Rule 6 - Safe Speed
  • Rule 7 - Risk of collision
  • Rule 7B - Proper use shall be made of radar equipment if fitted and operational, including long range scanning to obtain early warning of risk of collision and radar plotting or equivalent systematic observation of detected objects
  • Rule 7C - Assumptions shall not be made on the basis of scanty information, especially scanty radar information
  • Rule 19 - Conduct in restricted visibility 

SOLAS V Regulations:

Regulation 19

  • 2.1 All ships irrespective of size shall have:
  • 2.1.7 if less than 150 gross tonnage and if practicable, a radar reflector or other means, to enable detection by ships navigating by radar at both 9 and 3 GHz; 

RYA Note:  'If practicable' means if it is possible to use a radar reflector on your boat then you should use one (i.e. if you have an A-Frame or similar). You should fit the largest radar reflector in terms of Radar Cross Section (RCS) that you can.  Whatever size your boat is, you should fit the reflector according to the manufacturer's instructions and as high as possible for maximum detection range.


See MGN 599 for more information at: https://www.gov.uk/government/publications/mgn-599-m-pleasure-vessels-regulations-and-exemptions-guidance-and-best-practice-advice

Collision Avoidance:

  • Collision avoidance: Alter course as follows in collision situations depending on what sector the other craft appears.
  • This method of collision avoidance matches Rule 19 for radar users (conduct in restricted visability)

Head up Mode:


  • Head-up modes that the picture corresponds to the view from the helm.


  • When you alter course, the picture rotates. This can make it difficult to spot weak contacts.

North Up Mode:


  • Picture corresponds to the chart.

Course Up Mode:


  • Similar look to Head Up Mode
  • Good for collision avoidance but needs to be reset whenever you alter your course

Range & Bearings:

  • Depends on height of scanner & target.
  • Affected by the horizon

You can adjust the diameter of the VRM and position of the EBL which will move the intersection point between them. 

  • Variable Range Marker (VRM): An electronic mark or ring that can be placed over any target on your radar screen. This will let you know the range (nautical miles) between them and you. 
  • Electronic Bearing Line (EBL): Appears as a line that begins at your current location and intersects the VRM. 


  • Signal depends on size, material, aspect, texture, shape i.e. a port marker will show up better than a starboard marker

Risk of Collision:

Determining risk of collision using radar can be done via: 

  • Use the EBL (Electronic Bearing Line) and VRM (Variable Range Marker) to figure out the bearing and range of the other vessel
  • Use the bearing & range data (plotting sheet likely to be required)
  • Use long range scanning to gain early warning of other vessels on your intended route


  • Beware of: False echos
  • Beware of: Side echos – i.e. when a boat goes past you there can be a repeated appearance on screen
  • Beware of: Shadows – i.e. blind spots
  • Beware of: Interference – i.e. from another radar
  • Remember it can only see what's around it, not whats hidden behind that.. 
  • Remember it can't see everything.. if for example you have a small GRP powerboat with no radar reflector it would not beable to see this.. 
  • **ATTEND AN RYA RADAR COURSE PRIOR TO USE !** - See here for more information 

Using Radar not only takes learning, practice, but also being familiar with the Radar set you're using..

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