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Old 27-01-2011, 10:00 AM   #1
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Prop Slip

Can anyone help, and tell me what the prop slip percentage is for a 3 blade surface peircing prop as apposed to a standand 3 blade stainless prop.
Thanks
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Old 27-01-2011, 10:02 AM   #2
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If only it was that simple
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Old 27-01-2011, 02:53 PM   #3
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you can only figure that out by testing it on your boat.

stick it on and go ..lets say 60 mph, remember at what RPM you did 60.
then take the rpm X the prop pitch divided thru the gear ratio ,divided thru 1056 = XY
now you take the differents between the number you got and 60 and figure out how much % that is from 60. THAT IS THE SLIP # !!!!!

example... boat runs 5000 rpm and does 60 with a 23 pitch prop.with a 1:50 gear.

5000X23 = 115000/1,50 = 76666.666/1056 = 72.601009 ( theoretical speed )

72.60-17% = 60.25 MPH

so the slip would be 17% !

Hope that helps !
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Old 27-01-2011, 04:25 PM   #4
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Thanks for that, We have worked out our theoretical speed using the same calculation as you however we have not bought a prop yet. before we have one made we want to try and get as near to the size for the speed that we need.

If the theroretical speed is what we want is there a reverse calculation to give the percentage of slip to work out the actual prop size we need allowing for slip.

our theoretical speed is 58.14 mph at 6000 rpm with a 22 pitch prop and a gear ratio of 2.15.

What size pitch do we need allowing for slip to obtain this speed.

Am i getting in to deep here and should i just suck it and see.
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Old 27-01-2011, 04:46 PM   #5
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What's the boat?
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Old 27-01-2011, 04:49 PM   #6
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It's a circuit racing boat running in the gt 30 class. The hull is a winrace i belive.
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Old 27-01-2011, 08:02 PM   #7
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Let me know your email and Ill send you a prop slip calculator!

You can work out any of the variables with it..

Alan
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Old 27-01-2011, 09:00 PM   #8
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Prop slip calculator

This one works just fine.

http://www.go-fast.com/Prop_Slip_Calculator.htm

That boat should not have much slip. 5% maybe!?!
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