Largest diameter prop. For 2004 Johnson175hp

[TheBrain]

Largest diameter prop. For 2004 Johnson175hp

I’m in the process of finding the perfect prop. For my 22’ aluminum crusier.

Engine Donor boat was a bass boat it’s prop 14.1/2 x 24 engine RPM at WOT was 4800

New aluminum prop. I recentely dinged up 14 ¼ x 21 has increased engine RPM at WOT to just under 5300.

Now concidering a larger diameter than 14 ½

Like will a 15” diameter be able to turn?
Thanks TB

 

[kevinj]

Diameter has very little effect on engine performance. The real driving factors are pitch, cupping, and # of blades. It sounds like the 21P got you just about right on the WOT RPM. Was that prop cupped? If it was you can probably use a 21P non-cupped prop and be right at 5500RPM WOT.

Really it sounds to me the 21P is probably just about right for your hull.

 

[faztbullet]

Diameter has very little effect on engine performance.

A prop's two dimensions each affect performance in different ways. For every inch of change in prop diameter the RPM varies by about 500 RPMs (up or down) and every inch of pitch changes the RPM by approximately 150 to 200 RPM. That why on heavy hulls and toons you use largest diameter possible. A 15 x 19 prop (like a Rebel) with what we call Mickey Mouse ears would work good as holds more water and will lift transom a tad bit underway..