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  Two MMSI Numbers, One Boat

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Author Topic:   Two MMSI Numbers, One Boat
6992WHALER posted 03-20-2012 12:15 PM ET (US)   Profile for 6992WHALER   Send Email to 6992WHALER  
I am considering installing a Standard Horizon GX1700 as a redundant DSC/GPS system on my boat. Besides the redundancy there are times when I would like to be able to monitor one radio channel while talking on a second. I find the scan modes to be distracting. At night I would like to turn off my main GPS network but I would still like the radio to be receiving GPS information for emergency use. The GX1700 would allow me to leave only one piece of electronics turned on.

All the radios on a boat are suppose to have the same MMSI number. It makes sense that I do not register my one boat with the FCC as two boats. If both radios have the same MMSI number they will both change from the working channel to the DSC channel if a DCS call is received. In my case more of a nuisance than a danger but I could see how on a big ship with several VHF radios it might be dangerous to have all the radios change channel automatically. I am considering getting a new MMSI number from the FCC for the new radio and leaving the old MMSI number in the old radio.

jimh posted 03-20-2012 12:34 PM ET (US)     Profile for jimh  Send Email to jimh     
I am in the same boat, so to speak, in that I have two MMSI numbers assigned to me. One is from the FCC and the other from the BoatUS database. I plan to get a new VHF Marine Band radio for my boat--only one boat here, too--and I plan to put the new FCC-issued MMSI into that radio.

The radio currently on the boat has the BoatUS-issued MMSI. In order to change it, I would have to sent the radio back to the manufacturer for re-programming. I think I will just leave it as-is. In that way, I can make test calls to myself!

David Pendleton posted 03-20-2012 02:04 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
As I understand it, best practice is to use the same MMSI for all fixed-mount radios on the boat. A separate MMSI can (and should) be used for a hand-held radio.

The scenario you describe (both radios responding to a DSC call) will only occur if you have both radios configured to automatically switch channels when a DSC call is received.

6992WHALER posted 03-20-2012 02:12 PM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
Handhelds are suppose to have the MMSI number of the mother ship.

So in my case it would have the same MMSI number as my fixed mount radios.

All emergency DCS calls would change the radios. I will have to check on non-emergency DSC calls. I know I can control position requests and such but I am not sure I can set the radio to ignore an actual DSC call.

David Pendleton posted 03-20-2012 02:41 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
My radio has a feature where automatic channel switching can be controlled; this includes distress calls. You are still alerted, but the radio does not automatically change channels.

Boat U.S. recommended to me that a handheld be assigned it's own MMSI because in general, they cannot be reprogrammed easily, are not typically sold with a boat and may be used on any vessel.

6992WHALER posted 03-20-2012 02:48 PM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
That is the problem with a handheld
When you hit the DSC button you want the coast guard to be looking for your boat. How did you fill out the form? What will the coat guard be looking for when you hit the button?

I will have to pull the radio's owners manual and check that out.

David Pendleton posted 03-20-2012 02:59 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
I would imagine they'd be looking for whatever I told them when they answer my verbal mayday.

The DSC distress call is only part of the equation.

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