Sjoerd • Link
"Charles' first racing yacht was called 'Jamie' after his illegitimate son, the Duke of Monmouth, and his last was called 'Fubbs', his nickname for his mistress, Louise de Kéroualle. Fubbs is an old English word for chubby."
(So it's not at all unlikely that the 'Jamie/Jemmy/Jenny' was also called after his other mistress Jane Roberts.)
A yacht Katherine was sunk during the raid on the Medway in 1667, and a royal Yacht Katherine was used to transport the Princess Mary of Orange to Gravesend in 1689.
I don't know if these are all the same, in case they are there is a picture here http://web.onetel.net.uk/~sunhouse/Published_Chap…