Hi Mike,
Thanks for your lead to the Science Museum - no I hadn't spotted it.
I've received three images of the model and the invoice describes the model as scale 1:64, though the description of the 10266183 image says "This is a replica of a contemporary model (scale 1:96) of the 'Monarch', built of wood for service as a tug on the river Thames."
Originally, I had e-mails from Jasmine Rodgers (Image Executive), who said the images were old undigitised black and white slides and it would take a fortnight to have them processed, also, if I wanted new photos it would cost £50+VAT and that also depended on the conservation department agreeing.
Then she e-mailed to say that we in luck that the model had recently been digitally photographed and three new images were available.
There were very trusting in that they sent me the image files and then the invoice. They are very inquisitive regarding the use of the images. Because of copyright, I'm limited to using them for research - display is limited to the "Model Engineer Exhibition" (i.e. Judges' Notes) and then I must give credit to the Science Museum!
The images are very clear and show a water-line model and in particular the peculiar steering method of a rail-mounted truck filled with old chains, which would be moved across the beam to lift one of the paddles out of the water to give a tighter turn. The truck is adjacent to the ship's wheel so perhaps there was some sort of rope pulley system - this will be an interesting part to radio control!
Mayhemer Boneash has done some research, which has lead me to the Bolton and Watt Collection at Birmingham Library. In the collection there is reference to a "table of timber" for a Monarch (1833). There was a Monarch ship of that period and Bolton and Watt tended to list ships that had their engines installed, so I suspect it is not our tug - I shall enquire though.
Regarding the engine, I'm still trying to determine whether it had cross-head slides or the more common parallel motion linkages of the period. Because of the twin side beams, I can't use the normal Watt's parallel motion, so I'm in the process of producing a spreadsheet to calculate the geometry of one based on a short radius arm.
In the book "The Coming of the Comet" by Nick Robins, the model of the Monarch in the Newcastle Museum is described as having a cover over the crosshead slides - this may be an assumption, since the engine may have not been part of the model.
I will be using the monotube system as on the Edwardian Steam Launch, I will just unplug the electronic controller and transfer it to the tug - perhaps just adjusting the control parameters.
When researching, I'm continually amazed at the engineering competence of the late 18th/19th century pioneers. You start off thinking that they were a bunch of enthusiastic amateurs, few in number, working by themselves in dimly lit workshops and then you discover that behind them were complex organisations with design offices and draughtsmen as well as the filthy foundries.
Anyway back to the spreadsheets!
Ian.