Displacement hull

[capehorn3]

Having a problem finding the right prop for my mini houseboat. This boat is not designed to plane but Suzuki recommends 5300-6300 RPM for my DF20 ALT and with the stock 9.25 x 9.0 prop I'm seeing
1000-2.2 MPH
1500-3.4
2000-4.0
2500-5.1
3000-5.8
3500-6.7
4000-7.3 max RPM
I bought a High Thrust Prop 4x10x5 and although the splines fit the hub is shorter than the shaft by about 1/2" and the hub base is larger in diameter by 1/2". I could add washers to shaft for the length but concerned about hub diameter. This is the prop I have Suzuki High Thrust (4x10x5) 58100-94JA0-019
I'm normally running at the 4-5 MPH speed and higher speed is not a goal, however don't want to cause any problems. I see Suzuki makes a 7 pitch but my understanding is that will still not get my RPM up to the 5300 minimum. Thanks for your advice.

[ChrigelKarrer]

No, the 7'' propeller will not likely to bring your engine to more than 4500 rpm.
The four blade you bought may can help a bit, you may try it for a short time adding washers to equalize the length difference. Check well that nothing is rubbing!

I fear that you need a bigger engine or - if you are lucky - to get a 40HP ECU to raise HP up to 40HP,
but i don't know if that will work on your engine.
This is a common practice in Italy to raise a 40HP engines to 60HP as the motor is the same.

Chris