RPMs

[tony201]

Hi
I would like to know what RPM's a normal atomic 4 in good shape D/D would turn up to. What is the best cruising RPM.

[Don Moyer]

In one of their latest owner's manuals (circa 1975), Universal recommended a continuous cruising power setting of approximately 2000 RPM, or 80% of maximum available power. Working through the math backwards, this recommendation would suggest that an ideal propeller selection would be one that allows for a maximum of 2500 RPM, and still retain enough efficiency to provide a good cruising speed at 2000 RPM. From the attached homemade power curve, you can see that 2500 RPM will provide approximately 20 HP (usually considered as emergency power only).

Don

[67c&ccorv]

That's a 'torquey' motor Don - looks like a curve you would see on a Skyraider!:D

[julian hood]

I just instaled a new tach today with Don's help over the phone. A little wiring mixup but now as it should be. I have D/D with a small 3 blade feathered prop. What should I expect for cruising rpm's based on this type of prop? I noticed initially that I'm not getting anymore than 1700 RPM's with it in gear. If I should be getting more power what do I need to adjust to get this? I have a 27 ft Oday and I'm not getting over 5 knots at the top end.

[windrider1]

I recently removed the original propeller and replaced it with thweIndigo 3 blade prop. What a difference!!
They say it allows the A4 to hit a higher rpm range and reduce stress on the motor. I instantly gained more speed, reserve power, and smoothness.
You can find it online. I have seen positive input all over this web site and thats why I bought one.

[rigspelt]

I recently removed the original propeller and replaced it with thweIndigo 3 blade prop. What a difference!!
Which boat?