Thanks Paul
The boat is a classic, built in 1969. The company went belly-up some years later and have recently started producing new designs. An email to them over a month ago has remained unanswered

Looks like I might have to somehow try to make plans or drawings from photos and measurements of the real thing. Not something I have done before, or something I’m particularly looking forward to.
I am very new to rc boats, although I have been flying rc planes (both ic and electric) for a number of years.
Currently putting together a Graupner Scimitar Speed kit I bought about 15 years ago, powered by a Speed 600 motor through a 3:1 gearbox and driving a 35X prop. Will use two 3-cell li-pos in parallel and see how it goes.
Many thanks once again.
Chris