Thanks for the prompt reply! John & Hannah Matthews were my maternal GGG grandparents. My GG grandfather was William Matthews , who is 17 on the 1851 census and the boatmen, alongside his Dad. And our William and your Fanny were brother & sister.
The funny thing is that our William married a Fanny and your Fanny married a William! Quite a co-incidence and must have been confusing.
My maternal grandmother was also called Fanny ( presumably named after HER grandmother , who died a year before she was born).
I've just got into all this and find it quite obsessive! But I haven't really worked out how to use this website (normally I use Ancestry.co.uk). I came across your message because I asked a friend, who has a canal boat, how to find out more about boats. By the 1861 census, our William & Fanny are Master & Wife on a boat called Tiger in Yeading near Uxbridge ( presumably on the Grand Union Canal). Anyway my friend's husband went onto Rootschat and his search pulled up your message!!
Good hunting!