Man Over Board Systems The Technical Stuff Explained
There are all these different SAR safety system confused
? Oh Yes as the world leader in Maritime Survivor Locating Devices we are regularly asked the following questions so we thought wed put down some of this knowledge in a format which is useful to you.
As youve probably seen, there all different types of beacons and systems. The questions are:-
1. What are they?
2. What do they do?
3. Whats the difference between them all?
4. Which one is right for me?
Lets start with 406MHz
If youve seriously been looking for a system which will get you located by somebody, you will more than likely have had 406MHz thrust at you from some direction. 406MHz is a satellite alerting frequency which can be utilised via a PLB (Personal Locator Beacon) or the larger ships EPIRB (Emergency Position Indicating Radio Beacon). 406MHz is simply an alerting frequency. When a 406MHz beacon is set off it sends an alert through a dedicated satellite system to a ground station, which could be hundreds of miles away from your current location, they are then tasked with the responsibility of initiating a SAR operation from there. However there is a significant time delay inherent to 406MHz beacons, it can take up to 90 minutes for an alert to be registered, also the position of the of the signal is not precise. The resolution is only to approx 6 km square which is a large area where the oceans of the world are concerned. There are 406MHz units available which are fitted with GPS, the idea being that the GPS co-ordinates of the beacon are sent out through the satellite to the SARground station. These are a good idea but in reality they have been proven to fail to work correctly in over 90% of instances. Because of these limitations all 406MHz beacons are fitted with a lower power 121.5MHz homing transmitter. This homing signal is used by approaching SAR vehicles to precisely home into the beacon. Another however 406MHz beacon is required to be registered with the authorities, which means if you are using the small personal version you cannot swap them amongst crew or friends If you dont register the beacon then the authorities are less likely to respond to your signal. Also the smaller personal 406MHz beacons do not have an automatic water activated function.
IN SHORT 406 MHz beacons are primary alerting beacons, they are intended to provide an alert of an incident directly to the SAR authorities. It is worth noting that the smaller 406 beacons known as 406 PLBs do not have a water activated function which means they are no good for Man Overboard alert and locate.
So is 406MHz the right choice for me?
Yes If you want to alert the authorities that your vessel is sinking or in distress.
NO If you are looking to quickly alert other crewmembers that you have fallen in the water.
Lets move on to 121.5MHz and 121.5MHz Alerting Units/PLBs
121.5MHz - weve already acknowledged the role of 121.5MHz in providing homing on the 406MHz beacons. Typically a 121.5MHz beacon with a power output of 100mW can be tracked by an inbound SAR helicopter at 10,000ft from as much as 30 miles away. So what does 121.5MHz offer? Well, it allows precise tracking of the target to within a few square metres and can provide an immediate alert of an incident when used in conjunction with an onboard receiver/alarm or Locator Unit (DF); which makes it ideal at providing Man Over board system cover for vessels, Jetty workers, Divers etc. Youve probably come across the confusing reports about 121.5MHz no longer being a recognised SAR frequencywhat has happened is a global tidying up of the use of frequencies for SAR. The 121.5MHz satellite channel has now been switched off globally which means the duty of alerting the SAR authorities of an incident has now been passed over to 406MHz. The role of tracking and homing is now firmly in the domain of 121.5MHz. Moving on and the 121.5MHz lends itself perfectly to self managed Alert & Locating systems, why? Because it can provide an immediate alert of an incident, precise tracking of an individual in the water through onboard locator units and importantly it integrates with all SAR worldwide which means if you need the intervention of outside SAR then they can very quickly and precisely track and locate the 121.5MHz signal coming from a person (or multiple persons) plbs. To give you an example of how this has been adopted around the worldto date the Spanish fishing fleet utilises daily in excess of 34,000 121.5MHz PLBs for all their fishermen, several thousand 121.5 PLB units are in operation in the Oil & Gas industry worldwide on a daily basis, hundreds of Coastguards world wide use 121.5MHz plbs daily, thousands of sport and commercial divers rely on 121.5 MHz PLBs to keep them safe every day, the list goes on.
IN SHORT 121.5MHz beacons are primarily homing beacons, they have the advantage that when they are used as part of a self managed system they can provide an immediate alert of an incident (typically within 5 to 10 seconds), they also allow very quick locating of lost individuals.
Sois 121.5MHz the right choice for me?
Yes If you are looking to quickly alert other crewmembers that you have fallen in the water.
No - If you want to alert the authorities that your vessel is sinking.
Yes If your vessel is sinking and you want to be located by the SAR authorities.
Yes If you are sailing at night time or in bad weather conditions
Yes If you are sailing in areas with strong currents
Ok so weve now looked at the two main frequencies utilised for SAR and man over board systems. In that case why am I coming across other Alert and Locating systems which use obscure frequencies away from the SAR homing frequency 121.5MHz? Some companies have developed self managed systems which operate on other frequencies, although these systems provide alert and locating of lost persons they do not have the significant advantage of integrating with local SAR which means that if you go out range of the boats tracking unit then you are quite simply lost .
by: jennyhicks
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