**** Prop Slip Calculator ****

DoktorC · **Posted:** February 3rd, 2013, 11:00 am

KAL Racing wrote:

SHIVERS wrote:

http://www.rbbi.com/folders/prop/propcalc.htm
I've been using this one, It does the job!

It does the job if you are running under 100mph :mrgreen:

The merc one does actually work the best...or you can use the calculator on your phone for instant results lol...

SHIVERS · **Joined:** April 21st, 2012, 1:57 am **Posts:** 411

I don't see any difference other than the merc one doesn't give the mph in tenths

rbbi-- 8200/1.62/34/20%/130.4
merc--8200/1.62/34/20%/130

not that I WILL EVER BE THERE!

SHIVERS · **Joined:** April 21st, 2012, 1:57 am **Posts:** 411

now I see the problem, if you put in unfucking attainable parameters the computer tells you to move to Northbay :lol:

phillnjack · **Posted:** September 18th, 2015, 7:23 pm

here is one I use a lot

http://continuouswave.com/cgi-bin/propcalc.pl/

also the merc one as that is nice and simple to use too.

mattmak · **Joined:** June 5th, 2015, 8:56 am **Posts:** 533

Made some improvements to one I had already been using:

More decimal places, and numeric fields so mobile devices automatically switch to numbers for input..

http://mattmak.com/boat/propslipcalc/

hec2buck · **Joined:** August 22nd, 2013, 4:13 pm **Posts:** 273

Very good Matt. A simple calculation is : (PITCH X RPM) divided by 1584. This give you the theoretical speed with a 1.5:1 gear ratio. Simply multiply the above by 1.5 and divide by your gear ratio, to get your theoretical speed. Then take your GPS speed and divide it by the theoretical speed, to get your efficiency. Of course the slip is (100 - the efficiency)

MarkStein · **Posted:** February 2nd, 2019, 11:25 pm

Newbie question here but what is an acceptable..or should I say target slip percentage in a drag race application ?

p man · **Posted:** February 3rd, 2019, 3:05 pm

Maybe some will disagree but....
Thinking about slip % is waaay over rated. It's not a simple thing as props have progressive pitch, are never accurate in their marked pitch and slip can change based on as little as which way you part your hair.

Best you can do is start with some good advise for a setup and test test test from there.
I'm often wrong though so.....

MarkStein · **Posted:** February 3rd, 2019, 6:45 pm

p man wrote:

Maybe some will disagree but....
Thinking about slip % is waaay over rated. It's not a simple thing as props have progressive pitch, are never accurate in their marked pitch and slip can change based on as little as which way you part your hair.

Best you can do is start with some good advise for a setup and test test test from there.
I'm often wrong though so.....

Thank you

DoktorC · **Posted:** February 9th, 2019, 12:41 am

p man wrote:

Maybe some will disagree but....
Thinking about slip % is waaay over rated. It's not a simple thing as props have progressive pitch, are never accurate in their marked pitch and slip can change based on as little as which way you part your hair.

Best you can do is start with some good advise for a setup and test test test from there.
I'm often wrong though so.....

I think it's mostly used to call out BS speeds posted on the old interwebs..

The only number that really matters is the gps...like Pat mentioned the props may or may not be accurately marked, your tach isn't likely 100% accurate...so it's hard to compare slip numbers from one boat to the next or even prop to prop.

Once you've texted your props and setup and found your fastest combo then calculate you slip so you can sound smart when you're drinking beer with your buddies lol.

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