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VPIRB

At present there is only one VPIRB model available, the Mobilarm V100 VPIRB.

The Mobilarm V100 VPIRB is a portable, pocket-sized unit, which is designed to be worn by the user. It is constructed of high visibility, impact resistant material which is waterproof and unaffected by prolonged exposure to sunlight and oil.

The unit will float and is water resistant to 10m (33ft). Weight is approximately 180g (6.35oz).

The device will operate over a temperature range of -20 to +55o C (-4o to 131oF), and can be stored in locations with a temperature range of -30 to +70o C (-22o to 158oF).

The Mobilarm V100 VPIRB is also designed to ATEX standards (approvals pending as at April 2008) - so it can be used in hazardous environments (gas/fuel vapours, etc).

A concept diagram of the unit is shown here.

MOBILARM V100 VPIRB FEATURES

The Mobilarm V100 VPIRB is fitted with an integrated, 24 channel parallel GPS receiver, which offers a time-to-first-fix of 30 seconds after power up.

The device is equipped with a strobe light to assist in location. The strobe, which flashes once per second, provides 180 degree coverage at 7 candela. It automatically starts flashing as soon as the device is activated and remains on until it is switched off or the batteries expire.

OPERATING THE MOBILARM V100

The Mobilarm V100 VPIRB is armed by sliding a switch on the front of the unit, which allows the beacon to automatically activate when immersed in water for 5 seconds. A piezo sounds to alert the user to manually release the antenna and fully activate the beacon, since this increases the effective range of the distress call and GPS coordinates.

The antenna can be manually released and the beacon fully activated via a dual-action process of sliding a sleeve while pressing two buttons on both sides of the unit. This process also activates the beacon from the off position, i.e. even if it has not been armed beforehand as described above.

There is a period of 20 seconds before any distress call transmission is made (with visual and audible notification during this time that the beacon has been activated) to allow the device to be switched off, thereby catering for inadvertent operation of the switch (i.e. false alerts).

The Mobilarm V100 VPIRB is fitted with a piezo sounder to indicate when the transmitter is actually sending distress messages - this feature can also assist in location of inadvertently activated beacons.

A multi-coloured, high intensity Light Emitting Diode (LED) indicates various system states, such as activated, GPS position received, transmitting, etc.

The device's inbuilt battery will support transmission for a minimum of 18 hours and has a shelf life of 10 years.

There are no operator qualification requirements for EPIRBs. As the Mobilarm V100 VPIRB operates in an identical fashion to an EPIRB - i.e. it can be either turned on or off - operator qualifications are not required.

VPIRB 'MAYDAY - MAN OVERBOARD' DISTRESS SIGNAL

DSC message composition

The DSC message from the beacon is formatted as a distress alert. As discussed on the DSC pages of this website, DSC distress messages contain a 'nature of distress' field. This is set as 'man overboard' in the Mobilarm V100 VPIRB.

Given that time is of the essence in most man-overboard situations, it is vital that the beacon transmit an alert as soon as it is activated. Accordingly, the initial DSC alert from the Mobilarm V100 VPIRB will have the position and time fields set to the default 'no position/time available'.

The beacon's inbuilt GPS receiver will lock and provide an accurate position typically in less than 30 seconds, so the subsequent DSC message will include the GPS derived position/time and be transmitted immediately it is available.

Unique Identity Number

Each device is programmed with a unique identification number of a distinctive format, to identify transmissions from the beacon as a MSLD. User/owner details for each unit will be registered with SAR authorities, so that point of contact information is available if a distress call is detected by another ship or shore station.

Voice alerting

Although some recreational craft have fitted DSC equipment, there are many who have only a basic radiotelephone VHF radio. For this reason, the Mobilarm V100 VPIRB will also broadcast a synthesised voice MAYDAY message once activated.

The MAYDAY message will be transmitted on VHF channel 16 but only once a valid GPS position and time are available, as the international radio regulations require that voice distress messages contain position and time information.

The message will be transmitted in the following format.

MAYDAY MAYDAY MAYDAY
THIS IS (UNIQUE IDENTIFICATION NUMBER)
MAN OVERBOARD
POSITION xx.xxS/N xxx.xxE/W
TIME XXXX UTC
REPEAT*
POSITION xx.xxS/N xxx.xxE/W
TIME XXXX UTC

* repeating the position/time allows receiving vessels time to write it down

Message repetition

Once the initial DSC distress alert has been sent, a second DSC distress alert with position will be transmitted immediately the internal GPS is able to provide an accurate position - generally within 30 seconds.

Once the DSC message with position has been sent, the beacon will broadcast the voice distress message (described previously) on channel 16. The DSC and voice messages will be repeated every five minutes for the first thirty minutes (i.e. 6 transmissions of position), unless the device is manually switched off.

After the thirty minute interval, the repetition period will change to ten minutes. This will continue until the device is switched off, or the batteries expire.

Alerting Range

The Mobilarm V100 VPIRB will provide alerting ranges in the order of 2 nautical miles from a typical small boat. Larger vessels and shore stations with higher antennas will receive the distress call over longer ranges.

Summary of Mobilarm V100 VPIRB timing/operation

Time	Action
0	Mobilarm V100 VPIRB activated. Strobe light turns on, LED flashes and piezo sounds.
20 seconds	GPS receiver starts. Initial DSC distress alert with 'man overboard' and 'no position/time available' sent on VHF marine channel 70.
Within 30 seconds	GPS lock acquired and provides a position/time. DSC distress alert with 'man overboard' and position/time sent on VHF marine channel 70. then Synthesized voice MAYDAY message sent on VHF marine channel 16 with position and time.
Every 5 minutes thereafter, for 30 minutes	DSC distress alert and voice MAYDAY message sent as per above.
Every 10 minutes thereafter until batteries expire or device turned off	DSC distress alert and voice MAYDAY message sent as per above.

HOW IT WORKS

A person wearing a Mobilarm V100 VPIRB in the 'armed' position falls overboard.

Upon 5 seconds contact with water, the beacon goes into a warning state. The strobe light and LED starts flashing, and the piezo sounds to warn the wearer that water detection has occurred. After a 20 second delay, the GPS receiver powers up, and the beacon transmits an initial DSC distress alert.

Five seconds later, the DSC alert is received on board the parent vessel - the VHF DSC radio immediately emits a loud distress alarm, which will continue until manually cancelled.

The Mobilarm V100's identification number is displayed on the boat's DSC radio display - this unique number alerts the crew to the loss of one of their shipmates.

VHF DSC radio display screen showing alert from the Mobilarm V100

They bring the boat about, and start the search. Meanwhile, the person in the water has manually released the antenna on the device to increase the effective range of the distress call.

By this time, the beacon's inbuilt GPS has acquired a lock, and the device transmits a new DSC call with this position included.

VHF DSC radio display screen, showing position from the Mobilarm V100

The device then switches to radiotelephone mode, and transmits a voice MAYDAY call.

Other vessels in the area have now also received the MOB victim's position via the DSC distress alert and the voice MAYDAY message - they alter course, and converge on the GPS position.

Some of these vessels have their DSC and electronic charting systems interfaced together - they are able to see the position of the person in the water graphically with respect to their own position, i.e. as a distance and bearing from their own boat/ship.

Typical position output on chart plotter screen

Chart plotter display screen, showing distance and bearing information

If visibility is good, and conditions favourable, the parent vessel has by now located the person in the water. If visibility is poor, and/or the seas are rough, the automatic broadcast of GPS position reduces the search area to a radius of approximately 10m around the MOB victim.

The strobe light on the device is used for final visual homing on the person in the water.

The illustration below depicts the Mobilarm V100 VPIRB operation.

The VPIRB directly alerts your boat and every other vessel or station in the immediate vicinity on channel 70 DSC and channel 16 radiotelephone

ADVANTAGES OF THE MOBILARM V100 VPIRB

• Directly alerts the parent vessel, who is in the best position to find and recover a person who has fallen overboard
• Also alerts all VHF DSC and radiotelephone stations in range - other ships and (possibly) shore authorities
• Broadcasts distress signal to standard VHF DSC or VHF radio, which as a multi-purpose base unit can be used for other tasks such as calling other ships/shore stations or sending a distress alert
• No requirement for costly dedicated receiving base station, direction finding equipment or satellite rental time
• Provides in-water tracking by GPS position - the MOB's position can be displayed graphically on an electronic chart program
• Two methods of location - electronic by GPS and visual by strobe light
• Automatic or manual activation, with 20 second transmission delay to reduce false alarms
• Audible and visual indication of operation states - GPS lock, transmitting, low battery, etc.
• Localised nature of distress call and manual activation delay reduces potential for false alerting

AVAILABLE DOWNLOADS:

Marine Radio Standards
Marine radio and MSLD standards
Mobilarm V100 VPIRB compliance with standards
Mobilarm V100 VPIRB Technical Specifications