Terry:
ZZ56 is correct on the prop diameter ( I just checked it).
I worked in a local hobby shop for a while and I concur with you on the plane science. The scale boat people never got into it that much. Don't know why. I suspect its because its a far more critical thing with planes to have the correct blade pitch and speed for optimum flying. The same could be argued for boats too. I suspect the go fast boats will be using the same degree of science you refer too, but the rest of us are in the dark ages.
Also with the brush less motors, they tend to be ideally suited to aircraft (i.e. high speed, light weight and light weight LipPo batteries with higher output than gel cell batteries). In boats, and certainly tugs, we usually need all the weight we can get, hence the biggest gel cell we can pack into a hull with the highest amp hour rating. LiPo's wouldn't help us in that regard. We'd only have to add more dead weight. Too, in Canada, we don't do much in the way of tug competition where a higher efficiency prop/motor combination would be sought. The Barrie Model Yacht Club ran tug towing competitions for several years. I don't know if they're doing it this year or not. Burnaby , B.C. club does too. I don't know of many others, hence most built tugs merely cruise the lakes and ponds without doing any meaningful work. Not trying to be miserable, just an observation and an attempt to explain why model boating is so different from planes.
That said, I'm interested in hearing/seeing what you come up with. It may change my whole thinking on tug powering.
On of my other tugs is built with the motor from a car power seat. It direct drives a 3 3/4" 4 blade prop. The combination, running free in the water, can develop enough speed to exceed the hull's ability to keep the vessel afloat. On the other hand, with a load on there is enough torque in the motor to get down and haul. It will easily pull a 14' boat with a 300lb (not me) person in it. So something must be working in that set up.
John