revisiting power calculations

When I first joined this forum I was a bit obsessed with power calculations. I have become much more learned since then. I have come across many different formula. I have come to an embarrassing conclusion. Wymans formula is probably the best but that hardly matters.
What matters is that you have enough horsepower and the props are not over or under powered. I believe the recommended horsepower for a Diesel Duck 32 is 50-80hp. I worked out 3 props for the Duck with 3 to 1 gear boxes.
1. 50hp @ 3000rpm Yanmar 22"D 18"P for 8.8kn
2. 75hp @ 2400rpm John Deere 27"D 22"P for 8.5kn
3. 22hp @ 3600rpm Yanmar 16"D 15"P.
I have estimated the Tc Value for the DD at 2,25ft. This means that the 22hp Yanmar is unsuitable as D. Gerr's formula for min size of prop gives 20.7".
Dave's formula for power recommends 65hp, and Wymans 78.6hp.
Starting with 65 or 78.6hp means the propellors will be different. Assuming the props are pitched to give the same speed, the bigger engine will accelerate much better. It will also deal better with bad weather.

 

What does George Buehler recommend?

 

Ike
I believe he recommends an Iveco 80hp. But I chose his boat as an example. It appears in "Voyaging under power" with an unspecified type of 80hp diesel, no mention of the prop.

 

Make sure the prop has sufficient blade area. My experience would indicate a 24" dia. minimum unless the boat is very light... which I doubt.