Overview
(Typical Marine Radar Screen)
A popular OOW orals question is to tests a candidates ability to properly set up a marine radar. Questions regarding the IMO (International Maritime Organisation) radar performance standards are also not uncommon. All Deck Officers should have a sound understanding regarding both of these areas. Remember every time you change your range or pulse length you must go through the initial setup described below again.
Initial Setup
The first step is to switch on the radar. Before doing this you must check that the radar antenna is not obstructed and there is no persons within its vicinity. Once the radar is switched on and warmed up select an appropriate range and pulse length. You must now complete the initial settings adjustment. The order of adjusting settings on your radar can be easily be remembered as BGT Rain and Sea. This stands for Brilliance, Gain, Tuning, Rain and Sea. Each of these is described in more detail below.
Brilliance
This relates to the brightness of your radar screen. Think of trying to read this article on your computer in a dark environment. If the screen was very bright you would struggle to view this page properly. Likewise in a bright room you would wouldn’t be able to easily see this page if the screen brightness is turned down low. Your radars brilliance should be adjusted until the rotating tracing is barely visible and the screen can be easily viewed. The examples below show too much, too little and just the right amount of brilliance.
Too much brilliance Not enough Brilliance Correct amount
Gain
To an untrained person gain and brilliance could easily be confused as having the same effect. These are very different settings and you must understand the difference. Gain increased the amplification of the returned signals. It can make a weaker echo appear much stronger. Care must be taken when setting gain. If set too low you will not see some targets on the radar screen such as small fishing vessels. This clearly has serious implications for keeping a lookout and collision avoidance. Conversely setting the gain to high can result in significant clutter which results in the screen becoming unreadable and targets becoming lost within the clutter.
Gain should be set until a lightly speckled background is observed on the radar screen.
Tuning
Just like a normal car radio a marine radar must be tuned so that the receivers frequency matches the returned signal otherwise you may receive an incomplete picture or no picture at all. Each radars tuning controls will vary you must refer to the radars manual in order to determine the correct method of adjusting this setting. Modern marine radars are often fitted with an automatic tuning feature.
Rain clutter
The rain clutter control can also be known as the Differentiator or the Fast Time Constant (F.T.C). A heavy rainstorm can complete block out radar targets. The rain clutter setting solves this issue by ‘thinning out’ the returned targets on the screen. In effect it only shows the targets with a signal strength above a threshold limit which is adjusted by altering the rain clutter control. The rain echo will be much weaker than those returned from a solid object such as another vessel so you can easily remove the interfering echoes from your radar screen. Be careful when adjusting this clutter control. If set to high you can also thin out real targets such as other small vessels. A good use of this control is to reduce the rain clutter just enough to observe vessels in the area of rain.
Sea Clutter
This is also known as swept gain clutter. Like rain the returned echoes from the sea are much weaker than those returned by solid objects or vessels. Sea clutter works by reducing the gain applied to returned echoes. This reduction is applied from the centre of the screen outwards. As the sea clutter control is turned up the amount of gain is reduced gradually outwards from the centre of the screen. Care should be taken when adjusting sea clutter that you don’t obscure small targets.
IMO Performance Standards
Radar minimum performance standards are set by the International Maritime Organisation. The full list of requirements and standards is contained within IMO Resolution msc.192(79) Annex 34 ‘Adoption of The Revised Performance Standards for Radar Equipment’. A copy of this resolutions annex is available to download below. The main performance standards that you should be aware of for your oral examination are:
Range Discrimination
The radar system should be capable of displaying two targets on the same bearing, separated by 40 m in range, as two distinct objects.
Range Accuracy
The accuracy of ranges should be within 1% of the range of the range scale in use or 30 m, whichever is the greater distance.
Bearing Accuracy
The system accuracy of bearings should be within 1%.
Bearing Discrimination
The radar system should be capable of displaying two targets at the same range, separated by 2.5° in bearing, as two distinct objects.
Roll and Pitch
The target detection performance of the radar equipment should not be substantially impaired when own ship is rolling or pitching up to +/-10°.
IMO – Radar Performance Standards
