Navigating by Radar
•Basic Methods, in Order of Preference
1. Range to two or more objects
–Measure objects directly ahead or astern first; measure objects closest to the beam last.
–Assuming proper operation of the fathometer, soundings give the navigator invaluable information on the reliability of his fixes.
•2. Range to known object
33.3. Bearings Only
Am I required to use Radar?
•Radar is not required on vessels under 1600 GT, but Navigation Rule 7 says
proper use shall be made of radar equipment if fitted and operational.
–In other words, whoever has one must use it.
•The Navigation Rules expect prudent mariners to avail themselves of all available means appropriate
...as to make full appraisal of the situation (Rule 5), e.g. the use of radar.
–Question for the Master: is radar use appropriate in the prevailing situation, as might be decided by an after-incident hearing?
–More importantly, Rule 7 specifies that assumptions shall not be made on the basis of scanty information, especially scanty radar information.
Radar is only one method
Manual: Plot all other vessels courses, plus location of fixed obstacles, and compute if they will intersect your current course
Experience may guide the master in realizing he will turn before reaching certain obstacles
May be cluttered unless software allows you to flag certain radar targets as non-threats
Radar Beacons (RACON)
In US, operated by US Coast Guard
May be supplemented or supplanted by Virtual AIS
Principles of Operation
Different than radar reflectors, which are passive. RACONs, also called radar beacons, radar responders, or radar transponder
beacons, are receiver/transmitter transponder devices used as a
navigation aid, identifying landmarks or buoys on a shipboard marine
When hit by a radar pulse, a RACON
transmits an identified (e.g., with an identifying code) that produces
a length line on the nautical chart
Inherent delay of the RACON system will make the echo appear behind the physical RACON
Permanent RACONs, in the US, should be on standard charts, and are used for things including:
identify aids to navigation, both seaborne (e.g. buoys) and land-based (e.g. lighthouses)
identify landfall or positions on inconspicuous coastlines
indicate navigable spans under bridges
identify offshore oil platforms and similar structures
identify and warn of environmentally-sensitive areas (such as coral reefs)