Well... I went out this afternoon and this is what I found.

A DVM on the battery posts measures about 13.8v when it's running. Took the
motor cover off and measured at the battery cable terminals inside and it
measures the same.

All the while the boat voltmeter reads pretty much pegged full scale... 18v.
The voltmeter has obviously gone south. That should be a lot cheaper than a
voltage regulator. :-)

Jack