Hello Peter,
I was pretty sure that was what it was. Doing a quick search for 'Falmouth work boat' throws up all sorts of sail plans and pictures, including a sail plan by Kingston Mouldings, as that gent produced the hulls (I think) for the Falmouth Maritime Museum working models which you can sail on an indoor pond with fans. He might be prepared to let you have a copy – better be quick though as Robin Whitmarsh is winding down Kingston Mouldings.
**LINK**
There's also quite a nice poster with a sail plan and constructional details. It's about the first thing that comes up.
Ian