Position polling or position request is the gathering of another boats position data i.e. GPS location.
Also referred to as ‘DSC polling”, “buddy tracking” , “position report” & “location polling”. This feature of your VHF can be used to track your friends location on your chartplotter.
Position Polling is a feature of DSC enabled VHF radios. DSC radios transmit & receive on channel 70 emergency signals and other important data including MMSI identity and location if GPS is input into the radio.
To utilize “Position Polling” and contact a friend using your DSC enabled VHF, you will need to connected a GPS to your VHF. Once you have the equipment setup all you need is his or her MMSI number (see below). If you have a chartplotter you can see their position on the chart (seen in the image below). The box of information given with the position request includes; range and bearing from your position. With this feature you can track your friends and know exactly where they are at any time. This feature is very popular with the fishing community.
You can see in the diagram above the black circle with red center is you. You have the MMSI number of a friend within VHF range. Plug this into your VHF and you will get the black box showing the position of your friend. Notice the box shows date and time of the fix, plus distance and bearing from your position.
There are many uses for position polling and they include:
- Cruising in company
- Tracking tenders
- Setting racing marks
- Tracking Charter BoatsYou will need:
- DSC enabled VHF with input/output for GPS
- Chartplotter or GPS linked to VHF
- MMSI# (9 digit numbers) for each VHF programmed into the radio
DSC enabled VHF
Class D DSC enabled VHF is the minimum for recreational boaters and is cheaper than Class A. Class D VHF equipment can receive signals on channel 70 at the same time as transmitting voice messages on a working channel. Class A DSC radios are the commercial equipment required by maritime industry.
Chartplotter or GPS
External GPS receiver and navigation equipment will be connected to VHF. Not all Class D DSC radios are the same. You must check your radio to see if it accommodates “position Polling”, plus the ability to input and output GPS data, You can also get a VHF with its own GPS, such as the Standard Horizon CPV350. Position Polling is an easy process once learnt and the equipment is the same as most vessels carry anyway.
MMSI stands for Maritime Mobile Service Identities are formed of a series of nine digits which are transmitted over the radio path in order to uniquely identify ship stations, ship earth stations, coast stations, coast earth stations, and group calls.
How to send a “Position request”
The following is how you send a position Request with Standard Horizon equipment. To send a position request first program the other parties MMSI number into your VHF directory. Then using the DSC features click on “place a call to an individual”. Look up the individuals Name and MMSI number and choose that.
Next you will be asked which channel you wish to communicate on. Select a channel and then send the transmission. The message will be sent, and once the other party acknowledges the request the VHFs will change to the chosen channel.
The message is sent using DSC, and since its digital, the channel you requested is transmitted to the other VHF, and the position and time is sent back on that channel.
This video from ICOM demonstrates how to use Position request and the commands needed. Its a simple demonstration.
If you want to determine a friends position and know his MMSI number this is easy. You send a digital request from your radio to his radio using his MMSI number via channel 70. When his radio acknowledges your request, you will get a report on his location and time of that location.
This is all done digitally so no one can hear you. Fisherman use this to locate good fishing grounds without alerting the whole fleet.
You will notice the box which appears on the chartplotter screen shows the lat & Lon and also the time this fix was valid.
List of Important VHF channels
Channel 16 is International the distress safety and calling channel. All vessels should monitor this channel and be prepared to assist another boaters in case of emergency. If you need to contact the Coast Guard use 16.
Channels 9, 68, 69, 71, 72, & 78 are working channels to switch to once you have contacted a vessel or marina on 16.
Channel 22A is the working channel of the coast guard when they want to communicate with boaters.
Channel 13 is the navigation and piloting channel. Here you call bridges locks for openings.
Channel 6 Internship safety channel, communicate on this channel with other vessels when navigating in Navigable waters.
Channel 70; Digital Selective Calling channel, a digital channel only.
USCG Navigation Center; has full list of vhf radio frequencies showing International, Canadian and US channels. Remember some marine vhf frequencies are not used internationally but only in the US and Canada