Greetings all, I am looking for suggestions as to the most suitable steam engine to put in to the 42" model of the paddle tug Iona which I have just acquired from a friend. It is plank on frame construction, I suspect with extra depth as it needs lots of ballast and currently has electric power with a 30 to 1 reduction. I have three engines to choose from and will use the existing O ring drive without the gearbox and think I should use a ratio of about 3.5 or 4.0 to 1. The engines I have are a PM Research V twin, 3/4" by 1/2", a Graham TVR1A slide valve twin 5/8" x 5/8" and a Raven double acting  twin oscillator 7/16" x 7/16". Have plenty of space for the engine but will probably be limited to about a 6" x 3" horizontal boiler. My first preference is to use the Raven as that matches the boiler the best but I am just a little worried that it might not have enough grunt. Any and all suggestions or comments most wellcome. Cheers, Ian.

Hi Ian,
I would try the smaller engine first and if it does not provide enough power go to the next larger one.
Regards,
Gerald.