# Slip numbers?



## Preston904 (Sep 9, 2016)

What kind of slip numbers do you guys usually see on a flat bottom skiff? 
I tested out my skimmer 14 this weekend with a yamaha 25 and its running 30mph by GPS with the stock 11 1/4 pitch prop.
I couldnt get the RPM since the tach I bought decided it didnt want to work so I have to order a new one.
I did plug the numbers into a calc and assuming 5% slip and 30mph its turning 6200. So either the prop slip is extremely low or my motor is turning even more RPM's.
Just wanted to see what kind of slip numbers other people get and see if im in the ball park.
Will be ordering another tach here soon.


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## Hardluk81 (Jan 3, 2016)

I don't have an answer to your question, but what kind of tach was it?


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## Preston904 (Sep 9, 2016)

got it off amazon, from a company called motor meters. just gonna go with a tiny tach i guess. Just wanted something that looked a little nicer


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## Vertigo (Jun 3, 2012)

Realistic slip is around 10%. The problem with trying to make any sense out of slip is that the pitch stamped on most props is not necessarily very accurate. If you don't know the pitch, whatever slip calculated is meaningless. BTW, 11 1/4 is the prop diameter, not the pitch. The stock Yamaha 11 1/4 prop is a 14 pitch. If you plug in your numbers with 14 pitch and 10% slip, you'll probably get an RPM of a little over 5000.


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## Preston904 (Sep 9, 2016)

Vertigo said:


> Realistic slip is around 10%. The problem with trying to make any sense out of slip is that the pitch stamped on most props is not necessarily very accurate. If you don't know the pitch, whatever slip calculated is meaningless. BTW, 11 1/4 is the prop diameter, not the pitch. The stock Yamaha 11 1/4 prop is a 14 pitch. If you plug in your numbers with 14 pitch and 10% slip, you'll probably get an RPM of a little over 5000.


I'm 100% sure it is not the diameter. It's the stock Yamaha 25hp prop. You couldn't even put that large of a prop on it... diameter was 9 7/8 I believe. Boats not here to verify at the moment.


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## Vertigo (Jun 3, 2012)

There is no such thing as an 11 1/4 pitch prop from Yamaha. The 11 1/4 diameter prop comes in 11, 12, 13, 14 pitch.


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## Preston904 (Sep 9, 2016)

Why don't you check out this list from Yamaha and scroll down and see for yourself that there is a 9 7/8 by 11 1/4 pitch. 
http://yamahaoutboards.com/sites/default/files/pdfs/Four-Stroke-F20-F2_5.pdf


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## Vertigo (Jun 3, 2012)

Well I'll be! I guess to answer you're question you'll need a tach.


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## No Bait / Lures Only (Apr 10, 2011)

Stock Yamaha prop, stainless or aluminum? I have the same motor with 12" and 13" pitch stainless steel propellers, the 12" power tec turns [email protected] gps mph, the 12" turbo hot shot turns [email protected] gps mph, the 13" solias turns [email protected] 30 gps mph. I run the Power Tec 12", my motor is modified, but is running on a 17'-6" x 6' Glades X skiff @ 350#. With the stock motor on a 14' boat should run about the same vs my 17'6....
30 gps for a stock motor is very good, but you still need to view the rpm on a tach for proper setup. My motor is 19" high on a 16" transom with a jack plate.


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## Preston904 (Sep 9, 2016)

Finally got a tach installed and did some testing today out in the St. John's. 
Boat was loaded with me and my wife, trolling motor, battery and cooler full of ice.
Stock 11 1/4 Yamaha aluminum prop.
Speed was 30.1mph at 5980 RPM.
Plugged these numbers into the merc prop calc with the 2.08 ratio from the lower unit and I'm getting 2% slip.


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## No Bait / Lures Only (Apr 10, 2011)

Preston904 said:


> Finally got a tach installed and did some testing today out in the St. John's.
> Boat was loaded with me and my wife, trolling motor, battery and cooler full of ice.
> Stock 11 1/4 Yamaha aluminum prop.
> Speed was 30.1mph at 5980 RPM.
> Plugged these numbers into the merc prop calc with the 2.08 ratio from the lower unit and I'm getting 2% slip.


Numbers sound good and you will still be able to carry a load with that prop, perfect.....


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