Not sure Bob is answering the question you asked there.. have you built the boat yet, or are you GOING to build it?
If it is built, then this will be more tricky to motorise, as you will have to cut holes in the hull, and on the centreline, for the prop tube and rudder, and then there may be a (lack of) access problem.
IF starting to build, then you have more of a chance. The superstructure can be arranged to lift off in one and some sort of hatch to get at the rudder can be arranged, the prop tube can be built in and you are almost there.
I see this is a static model (if I have googled the right version) and so weight, specifically up the top, MAY POSSIBLY need keeping down. AND I am assuming that the hull is reasonably hollow, or you would have to put cut-outs in the frames alternatively.
To get you going you will need a motor,coupling, propshaft and rudder (or use the rudder supplied), battery, electronic speed control (ESC) for the motor and a servo for the rudder. You woud have to supply a few details such as fitted prop size and length of hull for us to argue as to what sort of motor is best..but a low power 540 type is bound to be suitable (so you can allow for size).
Propshaft length, using a 4mm diameter shaft type, will depend on where the motor sits, you would need to position the motor, stick the coupling on and then measure from the end of the coupling to within about 5mm of the front face of the propellor. You can get shafts made, I would look at Marks model bits..he can supply shafts to size.
You will have to put the battery somewhere, low down, and allow for somewhere to put ballast (assuming you will need some). I would have a good surf and see if anyone else has motorised a Sanson tug, first..
Ashley
Edited By ashley needham on 02/12/2012 18:01:43