prop selection for heavy 37 foot sail

[Kudos]

Michigan wheel has a good prop calculator too. I contacted them when I needed to get a propeller for my boat. And their guess was spot on. I have a Hans Christian 38T, 33 ft waterline length and weighs 32,000 lb. The engine is a Perkins M50 with a 2.18 to one gear. The boat came with an 18x17, and I could only get 1,700 RPM out of the engine at full throttle. Michigan guessed a 20x10 and nailed it. I get 3000 RPM which is the engine's red line, at full throttle, and will do 7.6 knots on flatwater with a clean bottom. At 2,250 RPM I get about six and a half knots and it burns .71 gallons per hour. The final goal you want to reach is hitting your Max RPM at full throttle. With that you will get the best fuel economy speed and power available for your combination over the entire RPM range

[Bowdrie]

Within reason one needn't get too excited if the engine won't quite come up against the governor.
Say for instance that the engine should go to 3,000 revs but you only get 2,800 revs.
It's Ok, if you look at the HP curves for most engines you'll see that at the upper end the curve tends to get flatter somewhat.
That last few revs in reality just adds more fuel consumption and noise than it does useable/discernable power.
Just tossing numbers, but the boat, (or you,) will never know the difference between 52Hp and 50Hp.
A little bit of "over prop" is fine, it'll give you better fuel consumption for just "cruising along", (screwing around?,) in the lower RPM range you'll spend the vast majority of time using.