RADAR part one: The basics
Including carriage requirements, Electronic Plotting Aids, Automatic Tracking Aids and ARPA
Relevant document and M-notices: SOLAS Chapter V, MGN 379, MSC.192(79)
RADAR (RAdio Detection And Ranging) was patented in Germany in 1904. though the acronym RADAR was coined by the US signal corps as they worked on the technology in the 1930s; for ease of reading we’ll use ‘radar’ in this article. The rapid development of radar during World War II, including the development of the magnetron, allowed sub-metre resolution. The radar we use today arose from the work done on these systems.
Questions on radar are common at OOW level. To avoid repetition and to keep this article focussed, see the comments on the syllabus in this article and consult the linked MIN/MGN covering the syllabus.
From MGN 379 - Use of electronic navigational aids:
‘Radar is an important tool for the watchkeeper in all conditions of visibility…and the mariner should be fully aware of their function and associated limitations.’
Common areas of questioning are:
Limitations of radar
Carriage requirements under SOLAS
Tracking (and standards for ARPA)
Setup (collision avoidance or navigation)
Radar is mentioned both implicitly and explicitly in the collision regulations. A few of these references are important for our understanding of how radar is to be used:
Rule 5
‘Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision.’
This includes radar; it is one of the available means. It is, of course, especially important in reduced and restricted visibility.
Rule 6b
‘In determining a safe speed the following factors shall be among those taken into account:
Additionally, by vessels with operational radar:
(i) the characteristics, efficiency and limitations of the radar equipment;
(ii) any constraints imposed by the radar range scale in use;
(iii) the effect on radar detection of the sea state, weather and other sources of interference;
(iv) the possibility that small vessels, ice and other floating objects may not be detected by radar at an adequate range;
(v) the number, location and movement of vessels detected by radar;
(vi) the more exact assessment of the visibility that may be possible when radar is used to determine the range of vessels or other objects in the vicinity.
We will discuss these characteristics, limitations, constraints etc. in this article.
Rule 7b, c and d
When using ‘all available means appropriate to the prevailing circumstances and conditions to determine if risk of collision exists’:
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.
Assumptions shall not be made on the basis of scanty information, especially scanty radar information.
Rule 19
This is another important mention of radar in the COLREGs because the moment another vessel is visible Rule 19 ceases to apply.
(d) Every vessel which detects by radar alone the presence of another vessel…etc.
Components of the radar system
The radar system on a ship consists of:
The antenna unit. This consists of an antenna that emits and receives waves and a motor that turns the antennae unit. The antenna contains the transceiver unit and signal processing unit.
The processing unit. The signal is sent from the antenna to the processing unit, along with signals from other external electronic devices (gyro compass, speed log). These are processed and turned into visual data, which is sent as a digital signal to the display unit.
The display unit and control unit are on the bridge. These are often what we think of when we picture a ‘radar unit’; a screen, with various controls underneath it.
Types of radar
There are two types of radar:
X-band (3cm, 9GHz)
S-band (10cm, 3GHz)
To save always referring to these by their frequency (as they are referred to in SOLAS) we’ll use x-band and s-band; make sure you know the frequencies and wavelengths given above.