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Acceptable Prop Slip

j-bone

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I have a 2005 Carrera 257 Party Effect with a 496HO. I'm wondering what is considered good prop slip at WOT (5000). It looks like I am at about 8%. Not sure if this is in the good range.

Also, does prop slip change based on load. In other words, does slip go up with more passengers and gear?
 

EBT531

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Are you using a GPS for your speed? 8% is excellent. Slip usually increases during cruise rpm's and is best at WOT
 

Crazyhippy

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Yes slip will increase with load. It also changes with trim angle.

Dont get too hung up on it, for all you know that 26" prop you are running is actually a 25.75" prop, or a 26.25".
 

Instigator

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If you get under 10% count your blessing in that boat, or most any boat for that matter.
RPM divided by gear ratio x prop pitch divided by 1056 equals theoretical speed. Then divide by actual GPS speed to determine actual slip.
Most people are either shocked or good story tellers. :D
 

Done-it-again

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If you get under 10% count your blessing in that boat, or most any boat for that matter.
RPM divided by gear ratio x prop pitch divided by 1056 equals theoretical speed. Then divide by actual GPS speed to determine actual slip.
Most people are either shocked or good story tellers. :D
Really? I’f so my shit is waaaay off.
 

Instigator

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Really? I’f so my shit is waaaay off.
Yuppers. The formula I posted is very accurate. Most so called performance boats will run 10%-15% or more slip. The smaller boats are easier to get to 10%. Larger say 25 or 26 foot and up boats are generally less efficent. That is why I said if you get to 10% slip, count your blessings.:D

Now if you have a Jet Bote you are allowed to Make Up your own efficiency formula.:D

Here is a link to check out.
You can fill in the boxes and leave one empty and calculate the empty box.
https://www.mercuryracing.com/prop-slip-calculator/
 

Instigator

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Really? I’f so my shit is waaaay off.
Post up your max rpm, drive gear ratio and prop pitch and I will wager I can tell you within 5mph or so how fast your boat actually goes, unless it is a Jet Bote of course.:D
 

j-bone

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Thanks for the input. Speed is GPS. If any of the variables is off, it could be the rpm, 4900-5100 rpm all looks the same what at WOT. I guess the prop could be off a little too.
 
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