Over-propped - Suggestions?

[Pearl Island]

In 2015 purchased a Hatteras 45C with 2007 QSM 11 660hp with 1100 hrs. I could reach max 2,200rpm and was to high on the fuel curve (1800 rpm 19.8kt 21gls/hr) WOT 2,200rpm.
The prop was 28X34 with 2" cup.

I took 2" of the pitch and reached 2,320rpm under optimal conditions and was still a little bit high on the fuel curve (1800 rpm 18kt 18gls/hr), most of the time I do trolling so it have not been a big issue.

The engines now have 2,100 hrs. and I have added a dinghy on the foredeck and I get 2,250 rpm with clean bottom, full on fuel and water. I plan to get the boat out of the water for the first time in 3 years and want get it right, I do not mind to be slightly under-propped.

The prop is now 28X30 with 2" cup. Any suggestion if I should reduce diameter, pitch, cup or a combination of any?

 

[dsharp]

What RPM is the engine rated at? You need to make sure the engines can reach that rpm with a full load of fuel and water. Something doesn't sound right if you are only getting 18 knts. with that much hp in a 45 foot boat. Does the boat have a tower on it?

 

[Pearl Island]

WOT rpm is 2,350. I will reach 2,250 under optimal conditions (clean bottom, half fuel, calm sea)

 

[dsharp]

The spec.from Cummins is 2300 rpm, so you’re only 50 rpm off. You could remove the cup to pick up the rpm. I haven’t noticed a big performance gain cupping a prop on a large inboardprop. Sometimes a cup is added when there is evidence of cavitation.