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.

Collision Avoidance

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

Automatic Radar Plotting Aid (ARPA) will automatically predict intersecting courss

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 radar display.

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)