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  • Writer's pictureSailing The Dream

EPIRB, PLB, MOB devices - what are they, how do they work and what do we have

Every time we get into the discussion of what are our safety procedures and pieces of equipment with other sailors the discussion is always quite an interesting one.

We all have different budgets, experience and types of equipment on board. But the most interesting thing is the different knowledge of available gadgets in the market and how they actually work.

We aren’t experts, and we have no experience in deploying any of these (knock on wood) but we do like to research a lot on this subject and discuss it, we are always looking for better ways to keep us safe and learning from others but we also like to share and discuss our knowledge.

One of the most interesting topics is equipment such as EPIRBs, PLBs and MOB devices.

As mandated by the Australian regulations The Dream being an Australian registered vessel needs to have an EPIRB for the kind of sailing we do.

Our EPIRB device lives on its mounting bracket on the port side of the companionway, within easy reach if needed.

The existence of EPIRBs on boats is becoming super popular if not a must-have item and we are very happy when we see them on friends boats, but there still seem to be some confusion on how they work, with some people thinking that some sort of signal or icon will show on the chart plotter of nearby or within range vessels when the EPIRB is activated.

So every time we talk to someone that is not familiar with these systems, we like to discuss how they operate and explain or discuss the situations where the EPIRB should be used and what happens when it’s triggered.

(when we have guests on board further details are provided on a safety briefing)

Sometimes these people are not sailors and don’t have any boat experience they are just curious regarding what we can do in case of an emergency at sea.

So how does an EPIRB work?

When deployed the EPIRB will send a signal to the worldwide dedicated search and rescue satellite network that will then connect with an MRCC (Maritime Rescue Coordination Center) who will activate/coordinate a rescue mission.

Many hours may pass before rescue comes. Finding the signal transmitter (the boat or life raft in danger) can be difficult because not all devices have the same characteristics and the sea state will affect the signal and search efforts.

Each EPIRB belongs to a specific boat and should be registered with the specific authorities so that when a SAR (Search and Rescue) mission is needed the authorities know what kind of boat they are looking for and ideally if a sailing plan was lodge a more specific area of search can be established. This is very important especially when the SAR mission takes time and the batteries of the device start fading (they usually have a 48h battery life after deployment) no longer permitting a good signal transmission to assist the SAR.

There are different models with different ranges of accuracy in terms of the detail of the coordinates but in principle, all devices will begin transmissions when wet, although they can be manually activated also.

A PLB (Personal Location Beacon) works very similarly to an EPIRB but they are for personal use (should be on the lifejacket for example), usually are only manually activated or at least not activated automatically by the presence of water, and have a shorter battery life, around 24h.

So, one might think that if they work similarly why have both, or why have an EPIRB if I have a PLB or the other way round?

Besides the activation methods, the big difference is the battery life after deployment of the device (the EPIRBs are usually around 48h and the PLBs 24h), an EPIRB floats but the PLB requires a floating pouch and needs to be kept on a certain position for operating purposes.

At The Dream beside the EPIRB mounted on its bracket on the port side of the companionway we also have a PLB.

Our PLB usually "lives" in the grab bag but on specific situations may be with the person that is on watch, that would probably happen in severe sea state condition but while in the Mediterranean Sea we believe we can avoid such situations because we tend not to do such long passages that go beyond the 2-3 days that forecasts are reliable.

Another reason for our PLB “living” usually on the grab bag and not in our life jackets is that we are strong believers that the best chance of rescue in case of a MOB (Man Over Board) situation is our own vessel or nearby vessels and not through the assistance of an MRCC in a process that can be quite prolonged. And since the PLB doesn’t display any signal or alarm on our own boat or nearby boats, and it doesn’t activate automatically when in contact with water (in case the MOB is unconscious or seriously injured the PLB will not be triggered so it is of no help) we believe that this equipment is not suited for the type of sailing we usually do.

We also believe that in case of a MOB where our own vessel cannot assist and there are no other vessels nearby that can assist, the now single-handed crew will be able to raise the necessary other emergency procedures via the MRCC.

And then there’s an important detail to keep in mind, if an EPIRB or PLB is activated by mistake or accidentally and goes unnoticed by the crew (and the emergency signal is not cancelled immediately and relevant authorities not contacted also immediately) and a SAR mission gets underway there will be serious costs involved that will not be covered by any insurance (contrary to a real situation when a SAR is needed).

If in the case of the EPIRB where such accidental activation is unlikely to occur (if installed in the correct place and with care as per the instructions ), the case of a PLB that is inside a pocket on the lifejacket or jacket that accidental activation could happen, not super easy or likely for the PLB to be triggered but is still possible for that to happen.

For all the above reasons in our case and at the moment our PLB is like a backup for the EPIRB and viewed as a possible way to extend the time we can provide rescue authorities with a signal to be used during a SAR. In case we need to take on the life raft the PLB will probably be with one of us while the other will have the EPIRB.

Only in certain situations, the PLB is with the person that is on watch.

Of course, things are not exactly this simple and straightforward but this is our general idea.

So if we don’t use PLBs on our life jackets what other equipments do we use and believe are more suitable for us?

We use MOB specific devices installed in our life jackets, that have both manual and automatic activation features.

After much research and although we already had a Life Tag system installed in The Dream we settled with a device with AIS features that we believe suits us best.

But if we already had a system installed why did we get new devices?

The system that was already installed at The Dream is from Raymarine and it’s called Life Tag, it is integrated within the Sea Talk network from Raymarine that we have installed at The Dream to run the chart plotter and other navigation instruments, it has a very loud alarm (big bonus point), shows a MOB icon on our chart plotter and is activated by water immersion, if device becomes out of the range of the Sea Talk, or it can be easily manually triggered. And is reasonably easy to turn off in case of an accidental trigger, It seems it fits the bill in all the correct points, right?

The big issue for us was the fact that it only places a MOB icon on the chart plotter at the coordinates where the incident occurred, it doesn’t give updated coordinates of the incident. And because we are shorthand’s sailors and in case of a MOB event we became single-handed sailors on the spot, it’s very difficult to perform an entire rescue manoeuvre without losing sight of the person in the water without even considering the fact that the now single-handed crew may not have seen the incident.

It only places the MOB sign in OUR chart plotter and only sounds an alarm on OUR boat.

It uses normal batteries, it’s constantly on with a presence light and continuously issues a signal to the Sea Talk system even when this one is not on so the batteries die fast. Of course, we could turn the device off when not sailing but it seems that we tend to forget to turn them off and turning them back on in between sails.

Well, and after testing and experimenting the devices on Ellas life jacket we also noticed that it doesn’t always trigger immediately and may have a few minutes delay, this might be because of our installation, we don’t know.

After much research, we found a device that fitted our needs better.

The system we installed in our life jackets is a MOB AIS, it’s designed to fit our Spinlock life jackets specifically but fits any similar life jackets also.

If installed correctly in the Spinlock style vest they will activate automatically once the vest inflates (it is not water activated, the life jacket on the other hand is) or it can be triggered manually.

It sends an AIS signal to all nearby chart plotters (up to 5nm depending on sea state conditions) with AIS features showing the updated coordinates of the MOB, it has its own MMSI number but can also be programmed with the vessel MMSI and in that case it should also trigger a DSC message over the vessels VHF radio for the MOB event, and DSC VHF messages to vessels within range of the VHF radio, extending the range of potential help.

Those were the reasons for our choice.

This MOB system will not trigger an immediate response from an MRCC and even if it does due to close proximity to shore that allows the DSC message to be picked up by the MRCC antennas in theory it should be possible for the MRCC to contact via VHF the vessel to confirm the situation and therefore any accidental trigger could be cancelled with the MRCC easily, besides cancelling on the device itself.

So, in theory, a MOB device (ours as example with a 5-6 miles range depending on sea state) will self-deploy the moment the lifejacket inflates and will display a MOB alert on the chart plotter with updated coordinates of the MOB, an alarm will sound and in theory a DSC VHF message will be immediately issued.

On a sailing vessel that averages 7knots, that gives a short-handed crew (now single-handed) less than 1h to be alerted and to perform all needed tasks like start the engine, drop sails and redirect towards the MOB before the device is out of range!

It really isn’t much time if you think that in bad sea state the range diminishes but when doing manoeuvres single handed you will likely lose visual contact with the MOB, so I guess this just slightly improves the chances of a rescue...

The system we have is the exact one on the link below but there are other similar options in the market.

But the most important thing to keep in mind DO NOT FALL OVERBOARD and DO NOT SINK THE BOAT.

Clockwise: 406Mhz with GPS EPIRB, AIS MOB1, PLB, Raymarine Life Tags


AIS - Automatic Identification System

DSC - Distress Signal Call

EPIRB - Emergency Position Indicating Radio Beacon

PLB - Personal Location Beacon

MOB - Man Over Board

SAR - Search and Rescue

MRCC - Maritime Rescue Coordination Center, the institution/department that coordinates all SAR missions efforts such as Coast Guard, Air Force, Navy, Commercial and Private vessels

*** The above post is the sole opinion of the website owners based on their experience and research.

*** Sailing The Dream is not affiliated or endorsed by OceanSignal or Raymarine nor by any of their associated resellers. However we wouldn't mind to test their products on our 50ft yacht



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