Position Polling
or
Position Request

What is position request or position polling

Also referred to as DSC polling, track your buddy, Position report & location polling. This feature of your VHF can be used to track your friends and buddies position on your chartplotter

Position Polling is a feature of many 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 use Position Polling you contact a friend using DSC ( you must know his/her MMSI number), and if you both have a GPS connected to your VHF you can exchange positions. If you have a chartplotter you can see this position on the chart as in the image below.

In an emergency, Position Polling is used with the DSC RED button, to send your location to emergency and any vessels in your VHF range.

C-Map chart showing "Position Request"
c-map chart position request

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:

Fishing
Cruising in company
Safety
Tracking tenders
Setting racing marks
Tracking Charter Boats

Equipment needed

Position Polling is an easy process once learnt and the equipment is the same as most vessels carry anyway. You need:

A VHF with DSC and with input/output GPS
A Chartplotter or GPS linked to VHF
MMSI (9 digit numbers) for each VHF pre programmed into the radio

DSC enabled VHF radios referred to as Class D.

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.

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, like the Standard Horizon CPV350.

GPS or Chartplotter

External GPS receiver and navigation equipment which accept NMEA 0183 format are required.

MMSI number

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.

These are places you can register for the MMSI number.

For use in US waters; Boat US or Sea Tow. If you travel outside the US you will need to get your MMSI number from the FCC.org

UK registration and MMSI number

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.

ICOM video demonstration showing position Request & DSC procedure

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.

Manufacturers

Class D VHF radios;

Cobra MR F80B Fixed Mount VHF

Garmin 76csx

& the Rino 120

which is not DSC but can track your buddy

ICOM IC-M603 & M505 VHF/DSC plus AIS

Lowrance LVR-880

Navman 7200 "Track-Your-Buddy" and position polling

Nexus NX2500 Class D DSC VHF Radio

Northstar Explorer 725 DSC radio with wireless remote

Raymarine ray 218E

Standard Horizon HX850S VHF/GPS DSC Floating Radio

& CPV 350 chartplotter

Silva S15 radio navtex and DSC in one.

Si-tex DSC-900

Uniden WHAMx4BK

& Mystic &

UM625C VHF

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.

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.

Channels 9, 68, 69, 71, 72, & 78 are working channels to switch to once you have contacted a vessel or marina on 16.

For a full list of channels Passagemaker magazine has a good list showing International, Canadian and US channels. Remember some channels are not used internationally but only in the US and Canada.