Prop Slip

[FreeBeeTony]

Using an online prop calculator, I calculated my prop slip at ~0.22 using 3600 RPM @ 30MPH with a 1.5:1 ratio.

Does this seem correct for my 24' Grady?

What exactly does this number indicate?

Is the lower the number better? If so, how can it be improved?

 

[walleyehed]

Re: Prop Slip

Gotta have the prop pitch if you want a second opinion.....

 

[FreeBeeTony]

Re: Prop Slip

Sorry about that............current prop is a 17".

 

[walleyehed]

Re: Prop Slip

I get 26% slip...
gps speed? or dash speedo?
Do we know the tach is accurate?
is the prop alum. or SS?

 

[FreeBeeTony]

Re: Prop Slip

I used this calculator http://www.rbbi.com/folders/prop/propcalc.htm.

The prop is aluminum. speed was measured by GPS and dash, within 1 MPH of eachother.

At this point I have to assume tach is accurate.

 

[walleyehed]

Re: Prop Slip

I know it's trivial, but your final ratio is 1.47:1
That changes it a tad.
What number are you plugging in for pitch?

 

[FreeBeeTony]

Re: Prop Slip

I'm using 17 for pitch.

 

[walleyehed]

Re: Prop Slip

If it is a flat-blade (No cup), 17 will work...if it HAS cup, for aluminum, non-hustler, you need to use 7.4 as the pitch number.

 

[FreeBeeTony]

Re: Prop Slip

No cup.............

So is 0.22 about right for this set-up?

 

[walleyehed]

Re: Prop Slip

I get 24% with a flat 17 and that's likely about right.
To get any considerable drop in slip, you're gonna need a good, cupped prop.