prop size/pitch

[P69]

I never paid much attention to boat rpm vs. speed until tonight, which was different because I spent the last 2 weeks doing bottom work in the yard, so now it's clean!

What is the right rpm for boat speed relationship and how do I know if the prop is adequate?

I  know very little about props/pitch/rpv vs. speed. My ignorance is so deep, I don't even understand pitch!

I have a 367 with at 2-blade prop (18 RH 1?) "Michigan Sailer" I don't know what the number after RH is, but it starts with a 1.
Hurth ZF15, Walter RV-26
Motor: Universal 5444


Here are the few data points over about 10 miles of flat, no current water.

2000 rpm: 5.5 kts
2500 rpm: 7.3 kts ( the 1.34 hull speed)
2100 rpm: 7.0 kts

So, it looks like I can get hull speed at about 2200 rpm.

With this information, what can you say about my prop?