Navigation Aids


How do we know where we are?


Navigation Aids


Navigation aids refer to almost all of the electronic systems on board a modern boat.


VHF Radio, fixed at the navigation centre with an aerial as high as possible, usually at the top of the mast, giving a transmission range of about 30 miles. It is good practice to have repeater speakers in the cockpit so that deck crew may hear broadcasts.


Generally the radio will be tuned into channel 16, which is the international calling and safety channel. It may be dual watched with a port authority or coastguard listening channel.


Modern sets have a facility to input and hold the GPS position, thus enabling position to be broadcast when in an emergency and the distress alert button is pressed. They have also a facility to call another station by using their Mobile Maritime Service Identity number  (MMSI) a unique 9 digit number. Using this number will call, alert, the other station, radio, that you wish to communicate with. They accept the call and you are then connected. Although the call is directed once in conversation anyone happening upon the same channel will hear your conversation.  


Handheld VHF radio, is a small hand set with a limited range, if you can see it you can probably talk to it. It is limited by the height of the aerial and the power output. But is a very useful tool when operating in marinas, ports and estuaries where it is necessary to be on deck whilst still maintaining communications.


Global Positioning System (GPS) can be a unit displaying latitude and longitude or a powerful GPS chart plotter, giving latitude, longitude, Speed over the ground (SOG) and Course over the ground (COG), wind direction and tide whilst displaying it all on a digital chart.


The above systems are probably the most useful safety devices as they allow communication with the rest of the world and you can identify your position without any working knowledge of navigation.


However, GPS Plotters should be operated with caution as using the wrong scale can run you into danger. An understanding of simple navigation charts should be learned so as not to finish up in restricted areas or areas of insufficient depth of water for the vessel. 


Navigation Telex (Navtex) is an extremely useful bit of kit which produces navigation warnings, meteorological warnings and urgent marine safety messages every 4 hours automatically. It has a range of about 200 miles off shore and is transmitted on the medium frequency 518 kHZ for International  Navtex in English or 490 kHZ Regional Navtex in local language, not available in US.


The following table lists the Navtex messages and their code letter,


                            A         Navigation warnings

                            B          Meteorological warnings

                            C         Ice reports

                            D         Search and Rescue information includes Pirate warnings

                            E          Meteorological forcast

                            F          Pilot service messages

                            G         AIS messages

                            H         LORAN messages

                            I           Not used

                            J           Satnav messages

                            K         Other electronic navaid messages

                            L          Navigation warnings, additional to A

                            T          Test transmissions (UK only)

                            V         Notices to fishermen (US only)

                            W        Environmental (US only)

                            X         Special services

                            Y         Special services

                            Z          No messages on hand


Your navtex receiver may be tuned to delete non appropriate messages, items A, B and D cannot be deleted.



Radio detection and ranging (Radar) uses radio waves to determine the range, altitude, direction and speed of an object. A pulse of radio waves, microwave, is sent out from the radar, if this pulse hits a solid object, target, it returns a similar pulse to the antenna which presents it, the target as a direction and range on a plan view.


The modern radar plan view may be integrated into a chart plotter thereby presenting a more accurate picture of our actual surroundings and aiding navigation.


The radar whether integrated or not is a very useful aid to navigation more especially in restricted or poor visibility. It can also be used in determining if a risk of collision exists and the effect of avoiding action. 



Automatic Identification System (AIS)  is an automatic tracking system used on ships and by Vessel Traffic Services (VTS) for identifying and locating vessels electronically.


The AIS display can be a unique graphical display or integrated into Radar or GPS plotter displays and presents us with the following information,


            Vessels unique identification, MMSI and name

            Position, latitude and longitude

            Course over ground, COG

            Speed Over ground, SOG

            Closest Point of Approach, CPA

            Navigation status, at anchor, not under command etc

            Destination, port and arrival times



Charts of the appropriate area, there should be both planning, large scale, and local, small scale charts available. These charts should be corrected in line with the most recent chart corrections.


Chart corrections are available through the internet or Admiralty Notices to Mariners.


Nautical Almanac for the year. This publication is the yachtsman bible full of useful information regarding port entry i.e. traffic lights, radio reporting, tide flow, tidal heights, lights, buoys, special cautions or hazards to entering the port. Pilot notes for entering the port and useful telephones numbers for supermarkets, restaurants, harbour and marina facilities. 


Dividers, pencils, eraser, compasses and plotter speak for themselves but should be maintained and available around the navigation centre.


Pilot book not essential but adds to the plan process with more useful information regarding passage making and ports of call.


Log book is required for reporting your passage and should contain crew list, departing  port and destination, date and time of departure. The body of the log is taken up with time, position, course, speed, log (distance run and total), barometer, comments.


Its purpose is to register your position and time etc in case your electronic equipment decides to stop working or is accidentally switched off or batteries run down. based on the log information a position may be worked up, without the information it would be guess work. The log should also contain any happenings or occurrences whilst on the passage.
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                                                                                                                                                                                                                                                                                   GT Yachting October 2012