Sjoerd • Link
This yacht also appears as "Jamie", "Jenny" and "Jamaie" in sources.
The list of Navy vessels for December 1695 (House of Commons Journal) contains the Jemmy (still) in use
having a crew of 4 and with 4 guns of some sort.
In a list at http://www2.friend.ly.net/~dadadata/kemp/dictWXYZ…
Charles himself gets credit as a designer of the Jemmy.
The name could be short for "James", but as most of the kings other yachts were named after women (Catharine and Fubbs being a famous examples).
Annotator Dirk has put forward Jane Roberts, one of the kings's mistresses.