I've moved the lower range of the SST legend down to 40 degrees and re-rendered a number of the blue images - looks like data has just been bad (cloud cover) as lowering the range didn't increase the amount of visible data. Lower end of the scale is again 50 deg F.

This page describes (among other things) how to designate a *group* MMSI for a collection of boats. http://www.navcen.uscg.gov/faq/gmdssfaq.htm#boat

It is very simple: select any MMSI from any of the boats in the group, it will end in a zero. Move the zero to the *beginning* of the number. The resulting number is the group ID that all boats should enter.

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