MMSI Confusion: Handheld VHF/DSC?

by Tim on June 25, 2008

Here at Navagear, we’ve got a time-honored tradition of being confused about MMSI numbers. Let’s continue, shall we?

For those just joining, MMSI stands for Maritime Mobile Service Identity, and it’s a unique number assigned to your vessel for identification purposes within digital communication  protocols such as DSC (Digital Selective Calling, a feature included on virtually all new VHF and SSB radios) and AIS (Automated Identification System, in use by large commercial vessels and some recreational craft).

Oh wait…did I just say that MMSI numbers were assigned to vessels? That’s NOT entirely accurate. There are MMSI numbers assigned to ground stations, and groups of vessels, for instance.

And in the United Kingdom, apparently, there are MMSI numbers assigned to the new DSC-equipped handheld VHF radios. In fact, the UK Radiocommunications Agency has been quite clear about this:

“Under no circumstance should a vessel MMSI number be programmed into these portable radios.”

This notice appeared in the autumn of 2001, so things might have changed since then. But it got me thinking…what are we supposed to do here in the United States? What’s the FCC’s policy on MMSI numbers for handheld VHF radios?

The consensus among US boaters (see discussions here, for example) seems to be that we should use our vessel’s MMSI number, and without any other information, that’s certainly what I would have done. BoatUS, which is authorized to issue MMSI numbers for use on domestic waters only, seems to agree:

“The MMSI number is assigned to the vessel, not the radio. All radios, whether fixed installations or handheld and no matter how many, permanently associated with the same vessel should all use the same MMSI number.”

But boater consensus, and even instructions from BoatUS, do not FCC policy make! If anybody can help clarify what’s going on here, please do so in the comments.

{ 1 comment… read it below or add one }

Russ Irwin June 26, 2008 at 3:23 pm

If “all radios… associated with the same vessel” use the same MMSI, then which radio responds when there is a position request? For example an Icom 604 on board, and a Standard Horizon HX850S in the dinghy 3 miles away? Both?

And how about a VPIRB – same MMSI? Which responds? The VPIRB AND the on board VHF? Which one is the MOB?

Anybody know what the Icom 604 will do when you make a position request of it’s own MMSI?

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