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MOB1 type device Vs Portable VHF with panic button

Aug 21, 2019
108
Catalina 315 18 Grosse Pointe Park, MI
What is the advantage of carrying a MOB1 type device over a water proof, floating VHF, with a panic button such as a Standard Horizon HX890?
 
Jan 11, 2014
7,718
Sabre 362 113 Fair Haven, NY
The MOB1 is automatic, the life jacket inflates, the antenna pops up and the AIS and DSC signals are sent.

With a handheld the POB has to hold on to the radio and be able to push the panic button. If the POB is not conscious no signal is sent. The MOB1 is designed to be attached to an inflatable life jacket, so it can't be dropped while falling overboard.
 
Feb 21, 2013
3,581
Hunter 46 Point Richmond, CA
The MOB1, installed within or on the life-jacket, activates automatically on inflation to transmit an alert to all AIS receivers in the vicinity AND activate the DSC alarm on your vessel's VHF radio. Its your first line of defense for the man overboard to alert your crew, in addition to other boats. The MOB1 and a Standard Horizon HX890 VHF ratio with DSC/GPS/MOB feature work hand in hand.
 
Jan 4, 2010
972
Farr 30 San Francisco
But, it seems in automatic mode it does not send AIS signals as I read the manual. What I read is it makes a DSC call to your ship. I am bummed about this cause I bought one thinking it works entirely differently.
 
Aug 21, 2019
108
Catalina 315 18 Grosse Pointe Park, MI
When I am cruising, I am always with one other person. She will know if I fall off, I will know if she falls off. The one left on the boat can press the panic button on the VHF which has significant range with 25 Watts of power and an antenna on the mast.

The problem is that there is a fair chance that after one of us falls off (most likely me) the person over board will become separated from the boat. So, the person overboard is floating away alone. There is also a fair chance that the MOB1 device is out of range of any other boat. The PLB device will locate them. But with a significant time lag to communicate with authorities. A portable VHF has better range than the MOB1. The portable VHF will continue sending my GPS coordinates after the panic button is pressed every 4 minutes. This might possibly be confusing to authorities if the boat also pressed their panic button.

To sum up my thinking:

MOB1- Short range, does not alert authorities, may not be seen by anyone but the person that already knows you are overboard.
VHF-longer range, useful radio, may be confusing with the boat also pressing its distress button
PLB-long range, but slow response.

I am still trying to figure this one out. The discussion on this forum has been extremely helpful.
 
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Jan 11, 2014
7,718
Sabre 362 113 Fair Haven, NY
When I am cruising, I am always with one other person. She will know if I fall off, I will know if she falls off. The one left on the boat can press the panic button on the VHF which has significant range with 25 Watts of power and an antenna on the mast.

The problem is that there is a fair chance that after one of us falls off (most likely me) the person over board will become separated from the boat. So, the person overboard is floating away alone. There is also a fair chance that the MOB1 device is out of range of any other boat. The PLB device will locate them. But with a significant time lag to communicate with authorities. A portable VHF has better range than the MOB1. The portable VHF will continue sending my GPS coordinates after the panic button is pressed every 4 minutes. This might possibly be confusing to authorities if the boat also pressed their panic button.

To sum up my thinking:

MOB1- Short range, does not alert authorities, may not be seen by anyone but the person that already knows you are overboard.
VHF-longer range, useful radio, may be confusing with the boat also pressing its distress button
PLB-long range, but slow response.

I am still trying to figure this one out. The discussion on this forum has been extremely helpful.
Because VHF is line of sight and AIS uses frequencies near the VHF spectrum, it too is line of sight. Thus there is no distance advantage to a handheld VHF compared to an AIS.

If you are unconscious or otherwise incapacitated, the VHF is worthless.

Unless the VHF is firmly attached to you, there is a good chance you can or will be separated from the VHF.

Floating around Lake Michigan in cold water is not conducive to longevity. ;)
 
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Aug 21, 2019
108
Catalina 315 18 Grosse Pointe Park, MI
Because VHF is line of sight and AIS uses frequencies near the VHF spectrum, it too is line of sight. Thus there is no distance advantage to a handheld VHF compared to an AIS.

If you are unconscious or otherwise incapacitated, the VHF is worthless.

Unless the VHF is firmly attached to you, there is a good chance you can or will be separated from the VHF.

Floating around Lake Michigan in cold water is not conducive to longevity. ;)
Although it is true that both AIS and Marine VHF are line of sight. Line of sight is a limiting factor, not a guarantee of range. The VHF broadcasts at 6 Watts, whereas the MOB1 outputs 1 Watt. That will make a significant difference. I assume that any useful device will be tied to the person over-board since no device would help at all otherwise. Of course, an unconscious person cannot press the panic button. This is also an issue for the PLB as well.

It seems to me that there are significant tradeoffs no matter which device one chooses. I am also not too sure having 3 devices (MOB1, PLB, VHF) all tied to you is a particularly good thing either. Yes, absolutely, hypothermia is a huge issue for sure. The good thing is sailing season is a ways off still and we have time to figure this all out.
 
Jan 11, 2014
7,718
Sabre 362 113 Fair Haven, NY
Although it is true that both AIS and Marine VHF are line of sight. Line of sight is a limiting factor, not a guarantee of range. The VHF broadcasts at 6 Watts, whereas the MOB1 outputs 1 Watt. That will make a significant difference. I assume that any useful device will be tied to the person over-board since no device would help at all otherwise. Of course, an unconscious person cannot press the panic button. This is also an issue for the PLB as well.
Sending data requires less power than sending voice. Data packets require very little energy to send and are very short. Their range is not as limited by power as is voice transmission.
 
Aug 21, 2019
108
Catalina 315 18 Grosse Pointe Park, MI
Sending data requires less power than sending voice. Data packets require very little energy to send and are very short. Their range is not as limited by power as is voice transmission.
True, but still, given what the user's manual for the MOB1 says, I find it hard to be confident that the range will be sufficient.
 
Jan 11, 2014
7,718
Sabre 362 113 Fair Haven, NY
The MOB1 is intended for relatively short range, 5 to maybe 10 miles. The boat would have to be sailing quite fast to sail out of range of MOB1. It is primarily intended to notify the mother ship of the POB. It would take 45 to 60 minutes to sail out of range of the device. That should be plenty of time for the crew to mark the POB on the chart plotter, hit the DCS panic button on the fixed mount VHF, and turn the boat around to sail back.

Anyway, I went through this decision making process last year in preparation for an extended cruise to the Canadian Maritimes and down the east coast. We have MOB1s on our primary inflatable life jackets, an EPIRB, and a Spot Messenger. Each serves a specific purpose. Maybe this year we'll get to go.
 
Aug 21, 2019
108
Catalina 315 18 Grosse Pointe Park, MI
Well that seems logical, the manual for the MOB1 is much less clear on that point and implies that it only calls the mothership.
What I understood from the MOB1 manual is that it sends an AIS signal. Anyone listening will hear the AIS signal. But, since it is low power, it is only assumed to be picked up by the mothership. Too a DSC call is to a specific MMSI number and that number would be the mothership's. In any case, where I cruise, most boaters do not have AIS receive capability and the Coast Guard can be far away. So, it would seem that the MOB1 would only communicate with the mothership no matter.
 
Jan 11, 2014
7,718
Sabre 362 113 Fair Haven, NY
Anyone listening will hear the AIS signal. But, since it is low power, it is only assumed to be picked up by the mothership.
Correct, except any AIS receiver within range, about 5 miles, will here. The big issue is line of sight propagation. At water level line of sight is very short, most of the coverage is due to the height of the receiving antenna. An antenna at the top of a 50' mast will receive the signal much further away than a power boat with an antenna just a few feet above water.

A Class B AIS transmits at 2 watts, the MOB1 transmits AIS at 1 watt. So there will be some loss of distance due to reduced power, but is not as much a factor as antenna height.
 
Aug 21, 2019
108
Catalina 315 18 Grosse Pointe Park, MI
I am sorry to beat a dead horse here, but honestly I am just trying to figure this all out and do the right thing. It is true that my boat's antenna is 50' off the water. But, most of the boats in the region will be power boats with much lower antennas. Anyway, I honestly doubt if most of them even know what AIS even is, no less have it implemented and working on their boat. No one will hear a signal of any sort of they are not listening for it. Depending on other boaters hearing your distress signal is, well...distressing.
 
Jan 11, 2014
7,718
Sabre 362 113 Fair Haven, NY
I am sorry to beat a dead horse here, but honestly I am just trying to figure this all out and do the right thing. It is true that my boat's antenna is 50' off the water. But, most of the boats in the region will be power boats with much lower antennas. Anyway, I honestly doubt if most of them even know what AIS even is, no less have it implemented and working on their boat. No one will hear a signal of any sort of they are not listening for it. Depending on other boaters hearing your distress signal is, well...distressing.
The right thing for you to do may not be the same for me. Having the right information on which to make a decision is critical, and that's all I'm trying provide.

The primary purpose of the MOB1 is to immediately notify the crew that one of their crew members has gone overboard. If you look at the time line on one of the links I posted, this happens within a minute or so. It does this 2 ways, by sending a AIS distress signal within 15 seconds of activation and repeats that distress signal adding location information as the gps locks in. It also send a DSC signal to the MMSI number it is programed with (presumably the mothership). Both the AIS and DSC alerts tells the crew someone is overboard. That other boats may hear the AIS alert is a bonus. Of course, if the mothership doesn't have AIS or it is turned off. The system won't work.

No one will hear a PLB, not the mother ship, not any nearby boats. Only a satellite many miles away. Even after the CG gets the call and makes an all call only those boats with the ability to receive an EPIRB locater beacon will get the COB's location.

In my judgement, for the kind of sailing I do, it is a no brainer. The AIS wins hands down. Typically it is only my wife and I on the boat and like your situation there are not many other boats yet with AIS. Even the nearest CG Helicopter is hundreds of miles away in Detroit. The nearest CG station is 12 miles away and when I'm crossing the lake the CG will be 20 to 30 miles distant. I'll be in the water a long time if I wait for the CG to come get me.

Your mileage may vary.
 
May 17, 2004
3,420
Beneteau Oceanis 37 LE Havre de Grace
One note on the CG response - in addition to deploying their own boats they’ll likely also put out a Pan Pan with the coordinates of the PLB. So any other commercial or pleasure boats in the area are likely to be alerted to the distress. I’ve often heard those kinds of calls on the Chesapeake, sometimes followed up with someone checking out the area. They wouldn’t have the exact coordinates in real-time if you’re drifting, but it’s something anyway.