RE: Shelly Foss Tug Build 76 inch
I have the astro flights in my 48 inch shelly foss but not sure if they would be good for a 4.5 inch prop. You want a motor that has sufficient windings and armitures so that the electronic speed control does not get figity at lower speeds. Creates a lot of heat when an electic motor is pushing a big prop at slow speeds and the electricity is arcing across the armitures as it spins around.
I am not an electrician nor do I know motors that well. I do know that the Pittman motors that I have do the best job at slow speeds and they are so quite. These motors were made for a particular navy project and were surplused many years ago. You can actually still get them as brand new but you pay over $200 or more for them. Probably not worth it. I found mine from other model builders that had them. The one in my harbor tug is brand new old stock.
I am not sure if the gearing in the Astros will be good for swinging the big prop either. I like the belt drive reduction over the gear. I have toyed with using various motors out of transfer pumps like they have at harbor freight for $25. Just take apart the impellor and pump on the front and you have a motor. Then order the belt, pulleys, bearings and shafts from some place in Europe over the internet and built the gear reduction unit. The trick is to find a motor with good windings and lots of armitures to reduce the arcing of the magnets when you are running slow to avoid the heat build up. Again I am probably not explaining this right but it does matter in terms of the quality of the motor to run at both slow and fast speeds efficiently. The 800 or 850 motor that was in one the previous pictures with the gear drive mounted on it really got hot with the 5 inch prop at all speeds. I replace that motor with the Pittman motor and it was just fine.
One guy I met at a rc meeting actually took at motor from a radar on a boat and used that for his belt driven drive motor. As I recall it was surplus and it was about 4 inches round by 6 inchs long. He was turning a 6 inch prop.
I am not sure when and if I will be getting around to finishing the 6 foot foss tug. I guess I would need maybe three more weekends to finish it but with the number of hobbies I have, I do not have that time right now.
Hope that helps
Dallas