RRS01,
the image of the square rigger that I posted was of our Team Chairman with our model of HMS VICTORY, build specifically for the Trafalgar 200 celebrations. I don't have a square rigger myself (I referred to HMS RODNEY remember) but I have driven the VICTORY model in a display.
In answer to your questions:
the shaft size of a blower motor varies, but 1/4" Imperial would be about average. No real danger of getting bent provided that the propeller shaft is kept as short as possible and that the rudder is manufactured in such a fashion as to provide some protection to the propeller.
We don't control the sails. The only control measures we use are to reef-in the sail area in adverse windy conditions. The square riggers need to be in control at all times during pyrotechnic displays in order to give the most impressive of battle conditions, so are therefore propelled principally by the motors. If these vessels are propelled at a realistic speed, it certainly can give the impression that they are powered by the elements alone.
Some masts are designed to collapse during battle and we even have vessels that partially sink too!
I hope that this has been of help to you and if you need further clarification, please visit our website at:
www.pmbdt.co.uk where you will find more details about the HMS VICTORY build.
Good luck on your project and happy sailing.
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Sandy.